WO2007133651A2

WO2007133651A2 - High-efficiency transmission of information through narrowband channels based on ultra spectral modulation

Info

Publication number: WO2007133651A2
Application number: PCT/US2007/011333
Authority: WO
Inventors: Alvin Dale Kluesing; Sai C. Manapragada
Original assignee: Photron Technologies Ltd.
Priority date: 2006-05-09
Filing date: 2007-05-09
Publication date: 2007-11-22
Also published as: WO2007133651A9; WO2007133651A3; WO2007133651A8

Abstract

Systems and methods for transmitting information at very high data rates through narrowband communication channels are provided. The systems and methods involve modulating a message signal with a novel non-return-to-zero, abrupt phase modulation technique and filtering the modulated signal with a sophisticated digital filter. The digital filter is designed based on a multiresolution decomposition of the frequency spectrum of the modulated signal.

Description

COMMUNICATION SYSTEMS AND METHODS FOR THE HIGH-EFFICIENCY

TRANSMISSION OF INFORMATION THROUGH NARROWBAND CHANNELS

BASED ON ULTRA SPECTRAL MODULATION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to United States Patent

Application Serial nos. 60/799,424 filed on May 9, 2006 entitled: Communications Systems and Methods for the High-Efficiency Transmission of Information Through Narrowband Channels Based on Non-Return-To-Zero Ultra Spectral Modulation, and 60/799,444 filed on May 10, 2006 entitled: Communications Systems and Methods for the High-Efficiency

Transmission of Information Through Narrowband Channels Based on Multi-Symbol Ultra Spectral Modulation and 60/799,475 filed on May 10, 2006 entitled: Multi-Channel Digital to Analog Converter for the High-Efficiency Transmission of Information Through Narrowband Channels and attorney docket number 67536-5004US (serial number not yet assigned) filed May 8, 2007 entitled: Communication Systems and Methods for the High Efficiency

Transmission of Information Through Narrowband Channels Based on Non-Return-to-Zero Ultra Spectral Modulation, the entire disclosure of all of which are hereby incorporated by reference. This application is also related to United States Patent Application Serial No. 1 1/171,592, filed on June 26, 2005 entitled: Systems and Methods for Designing a High- Precision Narrowband Digital Filter for Use in a Communications System with High Spectral Efficiency, and United States Patent Application Serial No. 11/171,177, filed on June 29, 2005 entitled: Systems and Methods for High-Efficiency Transmission of Information Through Narrowband Channels, the entire disclosures of both of which are hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to the transmission of information through communication channels. More specifically, this invention provides systems and methods for transmitting information at very high data rates through narrowband communication channels using a novel digital modulation scheme and sophisticated high- precision digital filtering. BACKGROUND INFORMATION

[0003] Advances in communications technologies, combined with the widespread adoption of personal communication devices ("PCSs"), have revolutionized the way information is disseminated and shared. Information can now be delivered directly to computer desktops, laptops, personal digital assistants ("PDAs"), cellular telephones, digital music players, and other portable devices over wired or wireless connections, providing a virtually unlimited connection experience for all users. In particular, the rapid expansion of wireless technologies has fueled the demand for faster and more efficient wireless transmission of voice, data, and video on a global basis. [0004] Information is transmitted over a wireless channel from an information source to a destination by means of a wireless communication system, such as the conventional system shown in FIG. 1. At its simplest form, wireless communication system 100 includes: (1) modulator 105; (2) transmitter 110; (3) wireless channel 115; (4) receiver 120; and (5) demodulator 125. Modulator 105 processes the information into a form suitable for transmission over wireless channel 115. The information may be in the form of voice, data, audio, imagery, video, or any other type of content conveyed in an information signal, also referred to as a message signal. Modulator 105 essentially translates the message signal into a modulated signal suitable for transmission over wireless channel 115 by modifying one or more characteristics of a carrier signal. The modulated signal is passed on to wireless channel 1 15 by transmitter 1 10, which usually filters and amplifies the modulated signal prior to its transmission. The function of wireless channel 115 is to provide a wireless link or connection between the information source and destination. Once transmitted through wireless channel 115, the modulated signal is detected and amplified by receiver 120 to take into account any signal attenuations introduced during transmission by wireless channel 115. Finally, the transmitted signal is demodulated by demodulator 125 so as to produce a close estimate of the original message signal.

[0005] The performance of a wireless communication system such as wireless communication system 100 is, in part, dictated by the performance of its modulator, e.g., modulator 105. For it is the modulator that is responsible for converting the message signal into a signal suitable for transmission so as to maximize the use of the overall system resources. For example, a high performance modulator should generate a modulated signal having a frequency spectrum that, when filtered and transmitted by a transmitter such as transmitter 1 10, would utilize only a small fraction of the total channel bandwidth, thereby enabling many users to share the channel bandwidth simultaneously. A high performance modulator should also work in conjunction with a high performance filter in the transmitter to ensure optimal preservation of the frequency spectrum of the modulated signal. [0006J Current wireless communication systems use many different modulation techniques, including, but not limited to, amplitude shift keying ("ASK"), frequency shift keying ("FSK"), binary phase shift keying ("BPSK"), quadrature phase shift keying ("QPSK") and its variations, minimum shift keying ("MSK") and Gaussian minimum shift keying ("GMSK"), among others. These modulation techniques are digital techniques in which the message signal is represented by a sequence of binary symbols. Each symbol may have one or more bits, depending on the modulation technique used.

[0007] Typically, these modulation techniques switch or key the amplitude, frequency, and/or phase of a carrier signal according to the binary symbols in the message signal, e.g., according to binary symbols "0" and "1." For example, different amplitudes are used to represent both binary symbols in ASK, different frequencies are used to represent both binary symbols in FSK, and different phases are used to represent both binary symbols in BPSK. QPSK is a variation of BPSK in which two bits or more are used per symbol. The phase of the carrier takes on one of four equally spaced values, such as 0, p/2, p, and 3p/2, with each value corresponding to a unique symbol, e.g., 00, 10, 11, and 01. MSK and GMSK are variations of FSK in which the change in carrier frequency from one binary symbol to another is half the bit rate of the message signal.

[0008] The selection of a digital modulation technique for use in a wireless communication system depends on several factors. A desirable digital modulation technique provides low bit error rates at low signal-to-noise ratios, occupies a minimum bandwidth, performs well in the presence of multipath and fading conditions, and is cost-effective to implement. Depending on the physical characteristics of the channel, required levels of performance and target hardware trade-offs, some modulation techniques will prove to be a better fit than others. Consideration must be given to the required data rate, acceptable level of latency, available bandwidth, and target hardware cost, size, and power consumption. For example, in personal communication systems that serve a large subscriber community, the cost and complexity of the receivers must be minimized. In this case, a modulation technique that is simple to detect is most attractive. In cellular systems where intersymbol interference is a major issue, the performance of the modulation technique in an interference environment is extremely important. [0009] The performance of a modulation technique is often measured in terms of its power efficiency and bandwidth efficiency. Power efficiency describes the ability of a modulation technique to preserve the fidelity, i.e., an acceptable bit error probability, of the message signal at low power levels. In digital communication systems, higher fidelity requires higher signal power. The amount by which the signal power should be increased to obtain a certain level of fidelity depends on the type of modulation employed. The power efficiency of a digital modulation technique is a measure of how favorably this tradeoff between fidelity and signal power is made, and is often expressed as the ratio of the signal energy per bit to noise power spectral density required at the receiver input for a certain probability of error.

[0010] Bandwidth efficiency describes the ability of a modulation technique to accommodate data within a limited bandwidth. In general, increasing the data rate implies decreasing the pulse-width of a digital symbol, which increases the bandwidth of the signal. Bandwidth efficiency reflects how efficiently the allocated bandwidth is utilized. Bandwidth efficiency is defined as the ratio of the throughput data rate per Hertz in a given bandwidth.

The system capacity of a digital modulation technique is directly related to the bandwidth efficiency of the modulation technique, since a modulation technique having a greater bandwidth efficiency will transmit more data in a given spectrum allocation. [0011] In general, modulation techniques trade bandwidth efficiency for power efficiency. For example, FSK is power efficient but not as bandwidth efficient and QPSK and GMSK are bandwidth efficient but not as power efficient. Since most wireless systems are bandwidth limited due to frequency spectrum allocations, modulation techniques that concentrate their performance on bandwidth efficiency are generally preferable. In fact, most wireless communication standards available today use more bandwidth-efficient modulation techniques such as QPSK and its variations, in use by the PHS and PDC Japanese standards, and IS-54 and IS-95 American standards, and GMSK, in use by the GSM global standard. [0012] The bandwidth efficiencies achieved by the digital modulation techniques currently adopted by the wireless standards are, however, only in the order of 1-10 bps/Hz. Such bandwidth efficiencies are not able to satisfy the rapidly rising demand for faster and more efficient wireless services that are capable of serving a large number of users simultaneously.

[0013] To address these concerns, two new sets of modulation techniques have been developed: (1) spread spectrum modulation techniques; and (2) narrowband modulation techniques. Spread spectrum modulation is a technique in which the modulated signal bandwidth is significantly wider than the minimum required signal bandwidth. Bandwidth expansion is achieved by using a function that is independent of the message and known to the receiver. The function is a pseudo-noise ("PN") sequence or PN code, which is a binary sequence that appears random but can be reproduced in a deterministic manner by the receiver. Demodulation at the receiver is accomplished by cross-correlation of the received signal with a synchronously-generated replica of the wide-band PN carrier. [0014] Spread spectrum modulation has many features that make it particularly attractive for use in wireless systems, First and foremost, spread spectrum modulation enables many users to simultaneously use the same bandwidth without significantly interfering with one another. The use of PN codes allows the receiver to separate each user easily even though all users occupy the same spectrum. As a result, spread spectrum systems are very resistant to interference, which tends to affect only a small portion of the spectrum and can be easily removed through filtering without much loss of information. Additionally, spread spectrum systems perform well in the presence of multipath fading and Doppler spread.

[0015] The main disadvantage of spread spectrum systems is that they are very bandwidth inefficient for a single user or a single wireless cell, since the bandwidth utilized is much more than that necessary for transmission. In fact, bandwidth efficiency for a single user is so low that most spread spectrum systems report bandwidth efficiency for the whole channel, to emphasize their ability to simultaneously serve many users with the available channel bandwidth. In addition, spread spectrum systems are also much more complex than systems employing traditional modulation techniques, thereby increasing overall system design, deployment, and maintenance costs. [0016] Narrowband modulation techniques, such as those described in U.S. Patent

No. 5,930,303, U.S. Patent No. 6,748,022, and U.S. Patent No. 6,445,737, provide an entirely different approach. Instead of spreading the signal over a wide bandwidth range to optimize the number of users sharing the channel bandwidth simultaneously, narrowband modulation techniques attempt to squeeze the frequency spectrum into a as narrow of a band as possible in order to maximize both the bandwidth efficiency for an individual user and the overall channel utilization for a large number of users. In the narrowband modulation techniques described therein, phase reversals occurring before, in the middle, at the end, or after a bit period are used to generate a modulated signal having most of its energy concentrated in a very narrow peak centered at a carrier frequency. As most of the signal energy is concentrated at and around the carrier frequency, transmission of the modulated signal may be accomplished by transmission of the narrow peak, thereby significantly improving the bandwidth efficiency for an individual user. [0017] While achieving improved bandwidth efficiencies, these narrowband modulation techniques are not very practical because they require the use of a specialized analog crystal filter with a resonant frequency tuned by a shunt capacitor. Such a filter is very difficult to implement in practice due to tuning imperfections of the shunt capacitor, irregularities of the crystal material employed, and other challenges associated with designing high-precision analog crystal filters. Furthermore, these narrowband modulation techniques are very susceptible to intersymbol interference, may not perform well under high bit error rates, and require higher transmission power than traditional modulation techniques such as FSK and BPSK. [0018] Because currently-available modulation techniques have not been able to achieve high bandwidth and power efficiencies while performing well under various channel conditions, broadband wireless services that reach a large number of users simultaneously have not yet been fully deployed. Such services should be able to serve users with voice, data, audio, imagery, and video at high data rates and low infrastructure costs to service providers and consumers alike. Such services should also be able to optimize the number of users served by better utilization of the allocated frequency spectrum.

[0019] Thus, there is a need to provide a digital modulation technique that achieves very high bandwidth efficiency under various channel conditions

[0020] There is also a need to provide a high-precision narrowband digital filter for use in conjunction with a narrowband digital modulation technique in a communication system that achieves high bandwidth efficiency when transmitting information through narrowband communication channels.

[0021] There is yet a further need to provide a communication system that optimizes bandwidth utilization when providing wireless services to a large number of users simultaneously under various channel conditions.

SUMMARY OF THE INVENTION

[0022] In view of the foregoing, a general object of the present invention is to provide a digital modulation technique that achieves high bandwidth efficiency under various channel conditions.

[0023] In one aspect, the present invention provides a high-precision narrowband digital filter for use in conjunction with a narrowband digital modulation technique in a communication system that achieves high bandwidth efficiency when transmitting information through narrowband communication channels.

[0024] In another aspect, the present invention provides a multiresolution-based communication system that optimizes bandwidth utilization when providing wireless services to a large number of users simultaneously under various channel conditions. [0025] In some embodiments, the present invention provides multiresolution-based communication systems and methods that are characterized by their bandwidth efficiency, high data rates and enhanced data capacity. The multiresolution-based communication system and methods of the present invention employ a novel narrowband digital modulation technique in conjunction with a high-precision digital filter to achieve broadband-like services within a narrow frequency spectrum. [0026] Embodiments the present invention, hereinafter referred to as Ultra Spectral

Modulation ("USM") technique, comprise a non-return-to-zero modulation technique that uses abrupt phase changes to represent incoming binary symbols in a modulated signal, herein referred to as a "USM-modulated signal." In one embodiment, the abrupt phase changes occur mid-pulse, i.e., in the middle of a bit period, after an integer number of cycles of the carrier signal. In an exemplary embodiment, a binary symbol, e.g., "0" or "1", is represented with an integer number of cycles, e.g., n cycles, of a carrier signal, of which n/2 cycles are used at a given phase and the other n/2 cycles are used at a phase shift, with the abrupt phase shift occurring mid-pulse. A preamble may be used in the beginning of each bit transmission to avoid phase reference problems. In one embodiment, the USM-modulated signal has a double-sideband suppressed carrier ("DSSC") frequency spectrum with two wide spectrum sidebands and no carrier.

[0027] In some embodiments, the USM technique represents all the information in the message signal with the abrupt phase shifts occurring in the USM-modulated signal. That is, all the information conveyed in the message signal may be recovered by knowing where the phase shifts occur or by preserving the positions of the phase shifts during transmission. As a result, transmission may be accomplished by transmitting only a narrow band of frequencies required for identifying the phase shifts, i.e., by transmitting only a portion of one or both sidebands in the USM-modulated signal within a narrow band of frequencies. [0028] In other embodiments, the present invention also provides a high-Q, low- tolerance digital filter that is able to preserve the positions of the phase shifts in a narrow band of frequencies. Filtering the USM-modulated signal with the digital filter designed according to the principles and embodiments of the present invention and described hereinbelow produces a filtered signal with a time response that accurately identifies where the abrupt phase shifts in the USM-modulated signal occur.

[0029] In some embodiment, systems and methods of the present invention provide bandwidth efficiency of at least 50 bits per second per hertz (bps/Hz). In other embodiments, systems and methods of the present invention provide bandwidth efficiency in the range of more than approximately 60 bps/Hz. In other embodiments, systems and methods of the present invention provide bandwidth efficiency in the range of approximately 60 bps/Hz to 100 bps/Hz. In still further embodiments, systems and methods of the present invention provide bandwidth efficiency of at least 100 bps/Hz. [0030] In a preferred embodiment, the digital filter may be designed by selecting a center frequency and a bandwidth based on a unique multiresolution-based decomposition of the frequency spectrum of a USM-modulated signal. The multiresolution-based decomposition may involve the use of signal primitives that are bifurcated in different scales to represent the frequency spectrum of a USM-modulated signal. The primitives may be in the form of fractal bifurcation patterns, wavelets, or any other signal primitive used in multiresolution decompositions.

[0031] In a preferred embodiment, the signal primitives are selected so as only a narrow band of frequencies need be transmitted. As a result, narrowband transmission of information may be accomplished since only a narrow band of frequencies of the message signal may be transmitted at any desired data rate. In one exemplary embodiment, the multiresolution-based communication systems and methods of the present invention is configured to transmit 5 Mbps in a 100 KHz channel. In another exemplary embodiment, the multiresolution-based communication systems and methods of the present invention transmits 5 Mbps in a 50 KHz channel . [0032] In a preferred embodiment, the signal primitives are selected so as only a narrow band of frequencies need be transmitted. As a result, narrowband transmission of information may be accomplished since only a narrow band of frequencies of the message signal may be transmitted at any desired data rate. In one exemplary embodiment the communication systems and methods of the present invention provide transmission of 5 Mbps in a 100 KHz channel. In another exemplary embodiment, the communication systems and methods of the present invention provide transmission of 5 Mbps in a very narrow 50 KHz channel. Those skilled in the field will recognize that these values are provided for example only, and are not intended to limit the invention in any way. For example, other channel widths may be employed such as 30 KHz, 25KHz, and the like. Additionally, wider channel widths may be employed if desired, such as 200 KHz or 100 KHz, however it is expected that the narrower bandwidth channel will be preferred for most applications [00331 According to some embodiments, transmission of a USM-modulated signal may be accomplished by two unique transmitter approaches: (1) a multiresolution-based transmitter filtering approach; and (2) a multiresolution-based look-up table transmitter approach. In the multiresolution-based transmitter filtering approach, the high-Q, low- tolerance digital filter is designed based on the selection of a bifurcation index, and a given data rate desired for transmission. The digital filter is used to filter the USM-modulated signal prior to transmission through a communications channel [0034] Accordingly, in other embodiments two unique receiver approaches may be used in conjunction with either one of the two unique transmitter approaches to recover the transmitted signal: (1) a multiresolution-based receiver filtering approach; and (2) a multiresolution-based spectral estimator receiver approach. In the multiresolution-based receiver filtering approach, a receiver filter designed according to the bifurcation index and the desired transmission data rate is used to extract the transmitted signal. The clock is recovered and used to phase lock the receiver clock, which is then synchronized with the transmitted signal. A demodulator including a correlator, a phase detector, and a decision block is then used to recover the transmitted signal. [00351 Iⁿ the multiresolution-based spectral estimator receiver approach, a spectral estimator is used to recover the spectrum of the transmitted signal. A spectral selector is used to select the transmitted frequencies in the recovered spectrum. A demodulator including a correlator, a phase detector, and a decision block is then used to recover the transmitted signal. [0036] The present invention also provides a unique transmitter/receiver polarization approach suitable for satellite communications. The satellite communication system makes use of horizontally polarized and vertically polarized antennas to transmit and detect USM- modulated signals. The satellite transmitter includes a signal generator for adapting a USM- modulated signal for transmission through the polarized antennas. The satellite receiver detects the transmitted signal by means of a spectral estimator or a multiresolution-based receiver filter, a reference phase lock loop, a spectral selector, and other receiver circuitry. [0037] Accordingly, in one aspect a system for transmitting information through a communications channel is provided, the system comprising: a modulator for modulating a carrier signal with a message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; and a filter for filtering out a portion of at least one sideband, the filter centered at a transmitter center frequency and having a transmitter filter bandwidth, the transmitter center frequency and the transmitter filter bandwidth selected based on a multiresolution decomposition of the at least one sideband.

[0038] In another aspect, a system for transmitting a message signal through a communications channel is provided, the system comprising: a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with the message signal using non-return- to-zero modulation with abrupt phase changes in the carrier signal.

[0039] Further, a method for transmitting information through a communications channel is provided, the method comprising: modulating a carrier signal with a message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; filtering out a portion of at least one sideband with a filter, the filter centered at a center frequency and having a filter bandwidth, the center frequency and the filter bandwidth selected based on a multiresolution decomposition of the at least one sideband; and transmitting the portion of the at least one sideband.

[0040] In yet another aspect, a method for transmitting a message signal through a communications channel is provided, the method comprising: providing a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with the message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal ; and transmitting the message signal by converting the message signal into at least one of the first or second set of samples stored in the look-up table.

[0041] In further embodiments, the present invention provides a communications system configured to modulate a carrier signal with a message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband, characterized in that: a frequency spectrum of the modulated signal is represented by signal primitives that are bifurcated in different scales. In some embodiments the signal primitives comprise fractal bifurcation patterns, wavelets, or combinations thereof. [0042] Additionally, a satellite system for receiving a signal is provided, comprising: a polarized antenna operative to receive a modulated signal the modulated signal generated by modulating a carrier signal with a message signal with abrupt phase changes in the carrier signal; a receiver filter centered at a receiver center frequency and having a receiver filter bandwidth, the receiver center frequency and the receiver filter bandwidth selected based on the transmitter center frequency and the transmitter filter bandwidth; a clock detector for detecting a transmitter clock and generating a phase-locked receiver clock; a demodulator for recovering the message signal; and a satellite housing at least the receiver filter, clock detector, and demodulator. In some embodiments the modulator is configured to modulate a carrier signal with a message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal to generate a modulated signal. In other embodiments the modulator is configured to modulate a carrier signal with a message signal using multi- symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols to generate the modulated signal.

[0043] In other embodiments a communications system and method for receiving a modulated signal is provided. For example, a receiver for receiving a transmission comprised of a modulated signal generated by modulating a carrier signal with a message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal, transmitted at a carrier frequency is provided, comprising: a fractal-based receiver filter operative to filter the transmission to retrieve a transmission signal; a clock detector operative to retrieve a transmission clock from the transmission and operatively associated with the fractal-based receiver filter; and a demodulator operative to accept the transmission signal from the fractal- based receiver filter and further operative to retrieve at least one binary symbol from the transmission signal. In some embodiments, the fractal-based receiver filter comprises a linear-phase digital filter. In other embodiments, the fractal-based receiver filter comprises a narrowband digital filter. When the receiver is fractal-based, a filter centered at a filter frequency may be provided, the filter frequency selected as a function of the carrier frequency, a fractal bifurcation index and a desired data rate. The receiver may have an associated bandwidth; and the associated bandwidth may be selected as a function of a fractal bifurcation index and a desired data rate.

[0044] In other embodiments, the receiver may be multi-resolution based, and the filter frequency is selected as a function of the carrier frequency and by signal primitives that are bifurcated in different scales. In some embodiments, the signal primitives comprise fractal bifurcation patterns, wavelets, or combinations thereof. [0045] ^' In another aspect, a receiver for receiving a transmission comprised a modulated signal generated by modulating a carrier signal with a message signal using nonreturn-to-zero modulation with abrupt phase changes in the carrier signal, transmitted at a carrier frequency is provided, comprising: a spectral estimator operative to generate a frequency spectrum of the transmission; a spectral selector operative to extract a transmission signal from the transmission; a clock detector operative to retrieve a transmission clock from the transmission and operatively associated with a receiver filter; and a demodulator operative to accept the transmission signal from the receiver filter and further operative to retrieve at least one binary symbol from the transmission signal. [0046] In some embodiments the receiver filter has a filter frequency selected as a function of the carrier frequency and signal primitives that are bifurcated in different scales.

The signal primitives may be comprised fractal bifurcation patterns, wavelets, or combinations thereof. In some embodiments the spectral selector extracts the transmitted signal within a narrowband corresponding to a transmission filter bandwidth. [0047] Additionally, the receiver may further comprise: a receiver clock operatively associated with the clock detector and operative to synchronize the receiver with the transmission signal; wherein the clock detector is further operative to phase-lock the receiver clock with the transmission clock. In this exemplary embodiment the demodulator may be comprised of a correlator operative to accept the transmission signal from the fractal-based receiver filter and further operative to correlate the transmission signal with the receiver clock, thereby generating a correlated transmission signal; a phase detector operatively connected to the correlator and operative to determine a phase of the correlated transmission signal; and a data bit decider operatively connected to the correlator and operative to employ the phase of the correlated transmission signal with the correlated transmission signal to retrieve the at least one binary symbol. Additionally, the data bit decider may be comprised of a Costas decision loop.

[0048] In another aspect of the present invention a modulated signal is provided. In some embodiments, a modulated signal in a frequency spectrum of a carrier is provided, the modulated signal being formed by modulating the carrier with a message signal with abrupt phase changes in the carrier signal and comprising: a first sideband occupying a first portion of the frequency spectrum; and a carrier frequency, the carrier frequency transmitting no data. In other embodiments, a second sideband occupying a second portion of the frequency spectrum is provided wherein the first and second sidebands are symmetric. In some embodiments the second sideband is suppressed, and suppression of the second sideband may yield a single-sideband suppressed-carrier signal. In some embodiments the modulated signal is transmitted through a frequency channel and the modulated signal is operative to transmit data at a rate of at least 5 megabits per second when the frequency channel is 50 kilohertz wide. In some embodiments the modulated signal comprises a carrier signal with a message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal to generate the modulated signal. In other embodiments the modulated signal comprises a carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols to generate the modulated signal. [00491 I^{n a} further aspect, additional embodiments of a signal are provided. For example, a modulated signal transported via a propagation medium is provided, where the modulated signal is formed by modulating the carrier with a message signal using non-return- to-zero modulation with abrupt phase changes in the carrier signal or multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols; comprising: a first data bit pattern representing a first binary digit; and a first datum bit pattern associated with the first data bit pattern; wherein the first data bit pattern is 180 degrees out of phase from the first datum bit pattern. The modulated signal may further comprise a second data bit pattern representing a second binary digit; and a second datum bit pattern representing a second binary digit; wherein the first data bit pattern is 180 degrees out of phase from the second data bit pattern. In some embodiments, each of the data bit patterns and datum bit patterns are sinusoidal. In another embodiment, the first data bit pattern and first datum bit pattern comprise a first bit; and the second data bit pattern and second datum bit pattern comprise a second bit. Additionally, in some embodiments the first data bit pattern persists for a first half of a pulse width; and the first datum bit pattern persists for a second half of a pulse width.

[0050] In another aspect of the present invention a method for decoding data from a modulated signal generated by modulating a carrier signal with a message signal using non- return-to-zero modulation with abrupt phase changes in the carrier signal or multi-symbol modulation having abrupt' phase changes in the carrier signal to represent incoming binary symbols, is provided, comprising: receiving at least a portion of a frequency sideband of the modulated signal, the frequency sideband corresponding to a bit of the data; determining the location of at least one phase shift within the modulated signal, the at least one phase shift occurring within the bit; and ignoring a carrier frequency of the modulated signal. In some embodiments the operation of determining the location of a phase shift within the modulated signal comprises receiving the location of the at least one phase shift. In some embodiments, the location of the at least one phase shift is received from a transmitter transmitting the frequency sideband. [0051] ' Additionally, the method of decoding data may further comprise the steps of preserving the location of the at least one phase shift during transmission of the modulated signal; wherein the operation of determining the location of a phase shift comprises retrieving the location of the at least one phase shift from the modulated signal. In some embodiments, only the portion of the frequency sideband of the modulated signal is received. [0052] In other aspects a system for transmitting information through a communications channel is provided, the system comprising: a modulator for modulating a carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; and a filter for filtering out a portion of at least one sideband, the filter centered at a transmitter center frequency and having a transmitter filter bandwidth, the transmitter center frequency and the transmitter filter bandwidth selected based on a multiresolution decomposition of the at least one sideband [0053] In another aspect, a system for transmitting a message signal through a communications channel is provided, the system comprising: a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband .generated by modulating a carrier signal with the message signal using multi- symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols.

[0054] Further, a method for transmitting information through a communications channel is provided, the method comprising: modulating a carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; filtering out a portion of at least one sideband with a filter, the filter centered at a center frequency and having a filter bandwidth, the center frequency and the filter bandwidth selected based on a multiresolutϊon decomposition of the at least one sideband; and transmitting the portion of the at least one sideband.

[0055] In yet another aspect, a method for transmitting a message signal through a communications channel is provided, the method comprising: providing a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols; and transmitting the message signal by converting the message signal into at least one of the first or second set of samples stored in the look-up table. [0056] In further embodiments, the present invention provides a communications system configured to modulate a carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband, characterized in that: a frequency spectrum of the modulated signal is represented by signal primitives that are bifurcated in different scales. In some embodiments the signal primitives comprise fractal bifurcation patterns, wavelets, or combinations thereof. [0057] Additionally, a satellite system for receiving a signal is provided, comprising: a polarized antenna operative to receive a modulated signal the modulated signal generated by modulating a carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols, the modulated signal at a carrier frequency and having at least one sideband; a receiver filter centered at a receiver center frequency and having a receiver filter bandwidth, the receiver center frequency and the receiver filter bandwidth selected based on the transmitter center frequency and the transmitter filter bandwidth; a clock detector for detecting a transmitter clock and generating a phase-locked receiver clock; a demodulator for recovering the message signal; and a satellite housing at least the receiver filter, clock detector, and demodulator.

[0058] In other embodiments a communications system and method for receiving a modulated signal is provided. For example, a receiver for receiving a transmission comprised of a modulated signal generated by modulating a carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols, transmitted at a carrier frequency, is provided, comprising: a fractal-based receiver filter operative to filter the transmission to retrieve a transmission signal; a clock detector operative to retrieve a transmission clock from the transmission and operatively associated with the fractal-based receiver filter; and a demodulator operative to accept the transmission signal from the fractal-based receiver filter and further operative to retrieve at least one binary symbol from the transmission signal. In some embodiments, the fractal-based receiver filter comprises a linear-phase digital filter. In other embodiments, the fractal-based receiver filter comprises a narrowband digital filter. When the receiver is fractal-based, a filter centered at a filter frequency may be provided, the filter frequency selected as a function of the carrier frequency, a fractal bifurcation index and a desired data rate. The receiver may have an associated bandwidth; and the associated bandwidth may be selected as a function of a fractal bifurcation index and a desired data rate. [0059] In other embodiments, the receiver may be multi-resolution based, and the filter frequency is selected as a function of the carrier frequency and by signal primitives that are bifurcated in different scales. In some embodiments, the signal primitives comprise fractal bifurcation patterns, wavelets, or combinations thereof.

[0060] In another aspect, a receiver for receiving a transmission comprised of a modulated signal generated by modulating a carrier signal with a message signal using multi- symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols, transmitted at a carrier frequency, is provided, comprising: a spectral estimator operative to generate a frequency spectrum of the transmission; a spectral selector operative to extract a transmission signal from the transmission; a clock detector operative to retrieve a transmission clock from the transmission and operatively associated with a receiver filter; and a demodulator operative to accept the transmission signal from the receiver filter and further operative to retrieve at least one binary symbol from the transmission signal. In some embodiments, the receiver filter has a filter frequency selected as a function of the carrier frequency and signal primitives that are bifurcated in different scales. The signal primitives may comprise fractal bifurcation patterns, wavelets, or combinations thereof. Further, the spectral selector may extract the transmitted signal within a narrowband corresponding to a transmission filter bandwidth. [0061] In another embodiment, the receiver may further comprise a receiver clock operatively associated with the clock detector and operative to synchronize the receiver with the transmission signal; wherein the clock detector is further operative to phase-lock the receiver clock with the transmission clock. Additionally, the demodulator may be comprised of a correlator operative to accept the transmission signal from the fractal-based receiver filter and further operative to correlate the transmission signal with the receiver clock, thereby generating a correlated transmission signal; a phase detector operatively connected to the correlator and operative to determine a phase of the correlated transmission signal; and a data bit decider operatively connected to the correlator and operative to employ the phase of the correlated transmission signal with the correlated transmission signal to retrieve the at least one binary symbol. In some embodiments the data bit decider may be a Costas decision loop.

[0062] In a further aspect, additional embodiments of a signal are provided. For example, a modulated signal transported via a propagation medium is provided, where the modulated signal is formed by modulating the carrier with a message signal using multi- symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols, a first data bit pattern representing a first binary digit; and a first datum bit pattern associated with the first data bit pattern; wherein the first data bit pattern is 180 degrees out of phase from the first datum bit pattern. The modulated signal may further comprise a second data bit pattern representing a second binary digit; and a second datum bit pattern representing a second binary digit; wherein the first data bit pattern is 180 degrees out of phase from the second data bit pattern. In some embodiments, each of the data bit patterns and datum bit patterns are sinusoidal. In another embodiment, the first data bit pattern and first datum bit pattern comprise a first bit; and the second data bit pattern and second datum bit pattern comprise a second bit. Additionally, in some embodiments the first data bit pattern persists for a first half of a pulse width; and the first datum bit pattern persists for a second half of a pulse width.

[0063] In another aspect, the present invention provides a method for decoding data from a modulated signal, the modulated signal formed by modulating the carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols, comprising the steps of: receiving at least a portion of a frequency sideband of the modulated signal, the frequency sideband corresponding to a bit of the data; determining the location of at least one phase shift within the modulated signal, the at least one phase shift occurring within the bit; and ignoring a carrier frequency of the modulated signal. In some embodiments the operation of determining the location of a phase shift within the modulated signal comprises receiving the location of the at least one phase shift. Further in some embodiments, the location of the at least one phase shift is received from a transmitter transmitting the frequency sideband. In another embodiment only the portion of the frequency sideband of the modulated signal is received. Additionally, the method may further comprise the step of preserving the location of the at least one phase shift during transmission of the modulated signal; wherein the operation of determining the location of a phase shift comprises retrieving the location of the at least one phase shift from the modulated signal. [0064] In another aspect, the present invention provides a multi-channel digital to analog converter capable of achieving the high sampling rate required by the modulation technique. The multi-channel digital to analog converter may be composed of a number of off-the-shelf digital to analog converters at high sampling rates that are slided in time to achieve the sampling rate suited for the digital modulation technique. In one exemplary embodiment, four off-the-shelf digital to analog converters running at 500 MSPS may be used for a carrier frequency of 2 GHz.

[0065] For example in some embodiments, systems for transmitting information through a communications channel are provided comprising: a modulator for modulating a carrier signal with a message signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; and a multi-channel digital to analog converter comprised of a plurality of digital to analog converters and delay elements arranged in a sliding time scale to operate at high sampling rates. In some embodiments the modulator is configured to modulate a carrier signal with a message signal using non-return- to-zero modulation with abrupt phase changes in the carrier signal to generate the modulated signal. In an alternative embodiment the modulator is configured to modulate a carrier signal with a message signal using multi-symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols to generate the modulated signal. [0066] In another embodiments, systems for transmitting a message signal through a communications channel are provided comprising: a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with the message signal; and a multi-channel digital to analog converter formed of a plurality of digital to analog converters and delay elements arranged in a sliding time scale to operate at high sampling rates.

[0067] Additionally, in other aspects methods for transmitting a message signal through a communications channel are provided comprising: providing a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with the message signal; transmitting the message signal by converting the message signal into at least one of the first or second set of samples stored in the look-up table; and passing the samples through a multi- channel digital to analog converter formed of a plurality of digital to analog converters and delay elements arranged in a sliding time scale to operate at very high sampling rates. [0068] In further embodiments, a system for transmitting information through a communications channel is provided comprising: a modulator for modulating a carrier signal with a message signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; a filter for filtering out a portion of at least one sideband, the filter centered at a transmitter center frequency and having a transmitter filter bandwidth, the transmitter center frequency and the transmitter filter bandwidth selected based on fractal bifurcations; and a multi-channel digital to analog converter comprises of a plurality of digital to analog converters and delay elements arranged in a sliding time scale to operate at high sampling rates. In some embodiments the fractal bifurcations may be comprised of a set of fractal bifurcations at a fractal bifurcation index for modeling the frequency spectrum of the modulated signal. Additionally in some embodiments, the transmitter center frequency is selected based on the carrier frequency, a desired transmission data rate, and the fractal bifurcation index. In another embodiment the transmitter filter bandwidth is selected based on a desired transmission rate and a fractal bifurcation index. [0069] Advantageously, the communication systems and methods of the present invention enable high data rates to be delivered through narrowband frequency channels under a variety of channel conditions. The communication systems and methods of the present invention may operate as a standalone network or be integrated into existing wireless systems at very low overhead costs. In addition, the communication systems and methods of the present invention enable wireless service providers to provide broadband wireless services to a large number of users simultaneously by accessing a fully-utilized frequency spectrum that may be divided into various channels of very narrow bandwidths.

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The foregoing and other objects of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

[0071] FIG. 1 is an exemplary schematic diagram of a conventional wireless communication system;

[0072] FIG. 2 is an exemplary diagram of the frequency spectrum of a USM- modulated signal according to the principles and embodiments of the present invention;

[0073] FIG. 3 is an exemplary diagram of a magnified frequency spectrum of a USM- modulated signal according to the principles and embodiments of the present invention;

[0074] FIGS. 4A-B are exemplary diagrams of two sets of signal primitives for modeling the frequency spectrum of a USM-modulated signal according to the principles and embodiments of the present invention;

[0075] FIG. 5 is an exemplary bifurcation tree generated according to the principles and embodiments of the present invention;

[0076] FIG. 6 is an exemplary modeled frequency spectrum generated by adding a set of signal primitives according to the principles and embodiments of the present invention; [0077] FIG. 7 is an exemplary schematic diagram showing the selection of a filter bandwidth and center frequency according to a bifurcation tree;

[0078] FIG. 8 is an exemplary graph of a filter bandwidth selected according to the principles and embodiments of the present invention versus a bifurcation index for a given desired data rate;

(0079) FIG. 9 is an exemplary graph showing the capacity of a communication system designed according to the principles and embodiments of the present invention versus a bifurcation index; [0080] FIG. 10 is an exemplary plot showing the frequency response of a high-Q, low tolerance, linear-phase digital filter designed according to the principles and embodiments of the present invention;

[0081] FIG. 11 is an exemplary schematic diagram of a transmitter system using the multiresolution-based transmitter filtering approach to transmit message signals through a communications channel according to the principles and embodiments of the present invention;

[0082] FIG. 12 is an exemplary schematic diagram of a transmitter system using the multiresolution-based look-up table transmitter approach to transmit message signals through a communications channel according to the principles and embodiments of the present invention;

[0083] FIG. 13 is an exemplary schematic diagram of a receiver system using the multiresolution-based receiver filtering approach to recover message signals transmitted through a communications channel according to the principles and embodiments of the present invention; [0084] FIG. 14 is an exemplary plot showing the frequency response of a high-Q, low tolerance, linear-phase digital receiver filter superimposed with the frequency response of a high-Q, low tolerance, linear-phase digital transmitter filter designed according to the principles and embodiments of the present invention; [0085] FIG. 15 is an exemplary schematic diagram of a demodulator for use with the communications receiver system shown in FIG. 13;

[0086] FIG. 16 is an exemplary plot showing a reference signal to be used in a matched filter according to the principles and embodiments of the present invention; [0087] FIG. 17 are exemplary plots of signals generated by a second order Costas decision loop for use in a receiver system according to the principles and embodiments of the present invention;

[0088] FIG. 18 is an exemplary schematic diagram of a receiver system using the multiresolution-based spectral estimator receiver approach to recover message signals transmitted through a communications channel according to the principles and embodiments of the present invention;

[0089] FIG. 19 is an exemplary embodiment of a communication system designed according to the principles of the present invention;

[0090] FIG. 20 is another exemplary embodiment of a communication system designed according to the principles of the present invention;

[0091] FIG. 21 is another exemplary embodiment of a communication system designed according to the principles of the present invention;

[0092] FIG. 22 is yet another exemplary embodiment of a communication system designed according to the principles of the present invention; [0093] FIG. 23 is an exemplary embodiment of a satellite communication system designed according to the principles of the present invention;

[0094] FIG. 24 is yet another exemplary embodiment of a satellite communication system designed according to the principles of the present invention;

[0095] FIG. 25 is an exemplary schematic diagram showing digital samples from a USM modulated signal being fed into a digital to analog converter; and

[0096] FIG. 26 is an exemplary schematic diagram showing a multi-channel digital to analog converter designed according to the principles and embodiments of the present invention..

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0097] Generally, in accordance with exemplary embodiments of the present invention, systems and methods are provided for transmitting information through narrowband communication channels. Information, as used herein, may be in the form of voice, data, audio, imagery, video, or any other type of content conveyed in an information signal, also referred to as a message signal. The message signal represents information by means of binary symbols, with each symbol having one or more bits.

[0098] Message signals according to the present invention are modulated prior to transmission through a communications channel. A channel, as used herein, may be any communications channel, including a wired channel, e.g., cable, or a wireless channel. In general, modulation refers to the process by which information conveyed in the message signal is encoded in a carrier signal to generate a modulated signal. Typically, the encoding involves modifying one or more characteristics of the carrier signal according to the binary symbols in the message signal. A carrier signal may be any analog signal of a given frequency, for example, a sinusoidal wave at 100 KHz. A modulated signal, as used herein, refers to the carrier signal that has been modified according to the message signal. [0099] The modulated signal has a frequency spectrum representation comprising its frequency components. Modulated signals according to the ultra spectrum modulation ("USM") technique of the present invention have frequency spectrums comprising no carrier and two bands or "sidebands" of frequencies, one above (the "upper sideband" or "USB") and one below (the "lower sideband" or "LSB") the carrier frequency. Transmission of one of the sidebands is referred to as single-sideband suppressed-carrier ("SSSC") transmission and transmission of both sidebands is referred to as double-sideband suppressed carrier ("DSSC") transmission.

[00100] Transmission of the modulated signal through a communications channel may first be accomplished by filtering the modulated signal to extract the necessary frequencies. Accordingly, the modulated signal may be filtered by an analog or digital filter. In one embodiment, the modulated signal is filtered by a linear-phase digital filter as described hereinbelow. A filter, as used herein, is any device, process, or algorithm for limiting the spectrum of a signal to a given band of frequencies. The band of frequencies is generally referred to as the bandwidth of the filter.

[00101] The bandwidth of the channel refers to the band of frequencies allocated for transmission of one or more modulated signals. For example, a channel having a bandwidth of 100 MHz supports the transmission of one or more modulated signals within a frequency spectrum of 100 MHz. If, for example, each modulated signal is filtered down to a bandwidth of 10 KHz, then the channel is able to support the transmission of 10,000 such signals. The amount of data that can be transferred in a channel having a given bandwidth is referred to as the channel's data rate and expressed in bits per second. The maximum data rate supported by a channel for a given bandwidth, noise level, and other channel assumptions is referred to as the channel capacity and given by the Shannon-Hatley theorem. [00102] Aspects of the invention further provide for a multiresolution-based decomposition of the sidebands using signal primitives. The signal primitives may be bifurcated a number of times to generate smaller, self-similar primitives at different scales or levels of detail. The number of bifurcations is given by a bifurcation index.

[00103] The present invention further provides for the design of a digital filter, transmitter and receiver based on the multiresolution-based decomposition of the sidebands. A digital filter may be designed based on a bifurcation index and a desired data rate as described hereinbelow to transmit a modulated signal modulated with the USM technique. The USM-modulated signal may also be transmitted by using a multiresolution-based lookup table, with entries generated according to the multiresolution-based decomposition of the sidebands of a USM-modulated signal. Different alternative embodiments of receivers for demodulating the transmitted modulated signal and recovering the original message signal are also described hereinbelow. It will further be appreciated that as new and different modulation techniques, filter design approaches, and transmitter and receiver circuitry are developed such modulation techniques, filter design approaches, and transmitter and receiver circuitry may also be accommodated by the present invention.

ULTRA SPECTRAL MODULATION |00104] Non-Return-to-Zero Modulation

[00105] Embodiments of the invention comprise non-return-to-zero modulation techniques that uses abrupt phase changes in a carrier signal to represent incoming binary symbols. The abrupt phase changes occur mid-pulse, i.e., in the middle of a bit period, after an integer number of cycles of the carrier signal, or at a bit boundary. In an exemplary embodiment, a binary symbol, e.g., "0" or "1", is represented with an integer number of cycles, e.g., n cycles, of a carrier signal, of which n/2 cycles are used at a given phase and the other n/2 cycles are used at a phase shift, with the abrupt phase shift occurring mid-pulse. A preamble may be used in the beginning of each bit transmission to avoid phase reference problems common in non-return-to-zero modulation techniques. The modulated carrier signal is referred to herein as the "USM-modulated signal."

[00106] A message signal may be modulated using the USM technique of the present invention by using a sinusoidal carrier having a given carrier frequency. The modulated signal may be a sinusoidal wave having abrupt phase shifts every mid-pulse. Each bit is represented with two sinusoidal patterns, a "data bit" pattern lasting for the first half of the pulse-width, e.g., for the first two cycles of the carrier frequency, and a "datum bit" pattern lasting for the second half of the pulse-width, e.g., for the last two cycles of the carrier frequency. In addition, a preamble may be used in the beginning of each bit period to avoid phase reference problems common in non-return-to-zero modulation techniques.

[00107] A data bit pattern for a given binary digit, e.g., "0" or "1," has a phase that may be 180° degrees away from the phase of the datum bit pattern. Additionally, a data bit pattern for a given binary digit has a phase that may be 180° degrees away from the phase of the data bit pattern of the other binary digit. For example, a data bit pattern for a "0" bit may have a phase of θ while the datum bit pattern for the "0" bit may have a phase of θ - π. Conversely, a data bit pattern for a "1" bit may have a phase of θ - π while the datum bit pattern for the "1" bit may have a phase of θ. [00108] The main characteristic of the USM technique lies in the abrupt phase shifts occurring mid-pulse. The abrupt phase shifts may be viewed as another layer of phase reversals occurring on top of traditional BPSK modulation techniques, in which phase shifts occur only at the bit transitions, i.e., at the edge of each pulse. Having the datum bit pattern inserted in each pulse provides a non-return-to-zero modulation technique with a DSSC frequency spectrum.

[00109] It should be understood by one skilled in the art that the carrier signal, carrier frequency, and phase values used to modulate a signal according to the USM technique may all be selected as desired. Further, it should be understood by one skilled in the art that the abrupt phase shifts may be of π +/- φ degrees, where φ may be any phase value between 0 and 180 degrees. It should also be understood by one skilled in the art that the phase of the data bit pattern for the "0" bit may be selected as desired, with the corresponding data bit pattern for the "1" bit being a phase shift away. Additionally, it should be understood by one skilled in the art that the USM technique may be used on a larger alphabet, e.g., the USM technique may be used to transmit an alphabet of symbols such as "00," "01," "10," and "11," without deviating from the principles and embodiments of the present invention.

[00110] The use of the USM technique results in a DSSC modulated signal having a frequency spectrum containing two wide spectrum sidebands and no carrier. Referring now to FIG. 2, an exemplary schematic diagram of the frequency spectrum of a USM-modulated signal according to the principles and embodiments of the present invention is described. Frequency spectrum 200 has two main symmetric sidebands, upper sideband 205 and lower sideband 210, which are respectively above and below carrier frequency 215 at 20 MHz. As shown in FIG. 2, upper sideband 205 extends to about 30 MHz, while lower sideband 210 extends to about 10 MHz, thereby resulting in a USM-modulated signal bandwidth of around 20 MHz. [00111] Since the sidebands are symmetric, transmission of both sidebands is not required. A message signal may be USM-modulated and transmitted in a SSSC system, that is, transmitted with a single sideband. However, since the USM technique represents all the information in the message signal with the abrupt phase shifts occurring in the USM- modulated signal, all the information conveyed in the message signal may be recovered by knowing where the phase shifts occur or by preserving the positions of the phase shifts during transmission. That is, if the phase shifts are known, the original message signal can be recovered. For example, knowing that the initial phase of the USM-modulated signal corresponds to a "O₃" the positions of the phase shifts every mid-pulse, and the occurrence of a phase shift at the beginning of a pulse when there is continuity in the bit pattern conveys enough information for a receiver to be able to recover the original message signal. [00112] As a result, transmission may be accomplished by transmitting only a narrow band of frequencies required for identifying the phase shifts, i.e., by transmitting only a portion of one or both sidebands in the USM-modulated signal within a narrow band of frequencies - the portion representing the abrupt phase shifts. The USM-modulated signal may therefore be filtered with a very sharp narrowband filter as described hereinbelow that preserves the abrupt phase shifts in the USM-modulated signal and attenuates the other frequency components. Because the phase shifts are abrupt, i.e., occurring at once with an immediate change in phase, the sudden shift in phase is reflected in the wide spectrum sidebands that may be filtered out by a narrowband filter as described hereinbelow to produce a filtered USM-modulated signal that ramps up and down according to the phase shifts. The ramping up and down in the filtered USM-modulated signal is a result of the return-to-zero USM technique. [00113] The narrowband filter used to generate a filtered USM-modulated signal may have a given center frequency and a given bandwidth selected by simulation to produce the desired result of accurately preserving the abrupt phase shifts in the USM-modulated signal within a band as narrow as possible. As described hereinbelow, the center frequency and bandwidth of the narrowband filter may be selected according to a multiresolution-based decomposition of the frequency spectrum of a USM-modulated signal. Doing so ensures an even more accurate filtering process, that is, an even more accurate positioning of the abrupt phase shifts occurring in a USM-modulated signal. As such, abrupt phase shifts occurring in a USM-modulated signal may determine peaks or valleys in the filtered USM-modulated signal, which may ramp up and down according to the abrupt phase shifts. [00114] It should be understood by one skilled in the art that the narrowband filter must be carefully chosen in order to accurately capture the position of the phase shifts in the USM-modulated signal. As described hereinbelow, it will be appreciated that in the exemplary embodiment the narrowband filter is a high-Q, low tolerance, linear-phase filter with a sharp passband, sharp transition bands, and sharp stopbands. In one embodiment, the filter may be designed to have a passband ripple of no more than 0.1 dB and a uniform stopband attenuation of at least 60 dB. Such a filter may be designed based on a multiresolution-decomposition of the frequency spectrum of a USM-modulated signal. [00115] Modulating a signal with the USM technique of the present invention may produce a USM-modulated signal having a unique DSSC frequency spectrum. The unique feature of the frequency spectrum is that the abrupt phase shifts occurring mid-pulse result in sidebands that have repeating self-similar spectral lines that may be modeled using signal primitives such as wavelets or fractals. Referring now to FIG. 3, an exemplary schematic diagram of a magnified frequency spectrum of a USM-modulated signal according to the principles and embodiments of the present invention is described.

[00116] Frequency spectrum 300 has two main sidebands that are symmetric around the carrier frequency. The symmetry of the sidebands is reflected in the self-similar patterns A1-A2, B1-B2, and C1-C2. These self-similar patterns may be modeled with signal primitives, as described hereinbelow, and aid in the selection of a center frequency and a filter bandwidth for the narrowband filter of the present invention.

Multi -Symbol Modulation [00117] In an alternative embodiment the Ultra Spectral Modulation ("USM") comprises a multi-symbol modulation technique that uses abrupt phase changes in a carrier signal to represent incoming binary symbols. The abrupt phase changes occur mid-pulse, i.e., in the middle of a symbol period, after an integer number of cycles of the carrier signal, or at a symbol boundary. In an exemplary embodiment, two bits are used per symbol and four symbols are represented in the carrier signal, e.g., "00," "01," "10," and "11." Each is represented with an integer number of cycles, e.g., n cycles, of a carrier signal, of which n/2 cycles are used at a given phase and the other n/2 cycles are used at a phase shift, with the abrupt phase shift occurring mid-pulse. The modulated carrier signal is referred to herein as the "USM-modulated signal." [00118] A message signal may be modulated using the USM- technique of the present invention by using a sinusoidal carrier having a given carrier frequency. The modulated signal may be a sinusoidal wave having abrupt phase shifts every mid-pulse. Each symbol is represented with two sinusoidal patterns, a "data bit" pattern lasting for the first half of the pulse-width, e.g., for the first two cycles of the carrier frequency, and a "datum bit" pattern lasting for the second half of the pulse-width, e.g., for the last two cycles of the carrier frequency.

[00119] A data bit pattern for a given symbol, e.g., "0O₅" "01," "10," or "11," has a phase that may be 180° degrees away from the phase of the datum bit pattern. Additionally, a data bit pattern for a given binary digit has a phase that may be θ° degrees away from the phase of the data bit pattern of the other binary digit. For example, a data bit pattern for a "" bit may have a phase of θ while the datum bit pattern for the "" symbol may have a phase of θ - π/4. Conversely, a data bit pattern for a "" symbol may have a phase of θ - π while the datum bit pattern for the "" symbol may have a phase of θ. The phase shifts for the other two symbols may be, for example, π/2 for the '"' symbol and 3/4 π for the "" symbol.

[00120] One characteristic of the USM technique lies in the abrupt phase shifts occurring mid-pulse. T he abrupt phase shifts may be viewed as another layer of phase reversals occurring on top of traditional BPSK modulation techniques, in which phase shifts occur only at the bit transitions, i.e., at the edge of each pulse. Having the datum bit pattern inserted in each pulse ensures a modulation technique with a DSSC frequency spectrum.

[00121] It should be understood by one skilled in the art that the carrier signal, carrier frequency, and phase values used to modulate a signal according to the USM technique may all be selected as desired. Further, it should be understood by one skilled in the art that the abrupt phase shifts may be of π +/- φ degrees, where φ may be any phase value between 0 and 180 degrees. It should also be understood by one skilled in the art that the USM technique may be used with a multi-symbol alphabet with any desired number of bits per symbol without deviating from the principles and scope of the present invention. [00122] The use of the USM technique may result in a DSSC modulated signal having a frequency spectrum containing two wide spectrum sidebands and no carrier. Referring again to FIG. 2, an exemplary schematic diagram of the frequency spectrum of a USM- modulated signal shows frequency spectrum 200 having two main symmetric sidebands, upper sideband 205 and lower sideband 210, which are respectively above and below carrier frequency 215 at 20 MHz. As shown in FIG. 2, upper sideband 205 extends to about 30 MHz, while lower sideband 210 extends to about 10 MHz, thereby resulting in a USM- modulated signal bandwidth of around 20 MHz.

[00123] Since the sidebands are symmetric, transmission of both sidebands is not required. A message signal may be USM-modulated and transmitted in a SSSC system, that is, transmitted with a single sideband. However, since the USM technique represents all the information in the message signal with the abrupt phase shifts occurring in the USM- modulated signal, all the information conveyed in the message signal may be recovered by knowing where the phase shifts occur or by preserving the positions of the phase shifts during transmission. That is, if the phase shifts are known, the original message signal can be recovered. For example, knowing that the initial phase of the USM-modulated signal corresponds to a "00," the positions of the phase shifts every mid-pulse, and the occurrence of a phase shift at the beginning of a pulse when there is continuity in the bit pattern conveys enough information for a receiver to be able to recover the original message signal. [00124] As a result, transmission may be accomplished by transmitting only a narrow band of frequencies required for identifying the phase shifts, i.e., by transmitting only a portion of one or both sidebands in the USM-modulated signal within a narrow band of frequencies — the portion representing the abrupt phase shifts. The USM-modulated signal may therefore be filtered with a very sharp narrowband filter as described hereinbelow that preserves the abrupt phase shifts in the USM-modulated signal and attenuates the other frequency components. Because the phase shifts are abrupt, i.e., occurring at once with an immediate change in phase, the sudden shift in phase is reflected in the wide spectrum sidebands that may be filtered out by a narrowband filter as described hereinbelow to produce a filtered USM-modulated signal that ramps up and down according to the phase shifts. [00125] The narrowband filter used to generate a filtered USM-modulated signal may have a given center frequency and a given bandwidth selected by simulation to produce the desired result of accurately preserving the abrupt phase shifts in the USM-modulated signal within a band as narrow as possible. As described hereinbelow, the center frequency and bandwidth of the narrowband filter may be selected according to a multiresolution-based decomposition of the frequency spectrum of a USM-modulated signal. Doing so ensures an even more accurate filtering process, that is, an even more accurate positioning of the abrupt phase shifts occurring in a USM-modulated signal. As such, abrupt phase shifts occurring in a USM-modulated signal may determine peaks or valleys in the filtered USM-modulated signal, which may ramp up and down according to the abrupt phase shifts.

MULTIRESOLUTION-BASED DECOMPOSITION OF USM SIDEBANDS [00126] The self-similar patterns present in frequency spectrum 300 shown in FIG. 3 may be modeled using a set of signal primitives. Referring now to FIGS. 4A-B, exemplary diagrams of two sets of signal primitives for modeling the frequency spectrum of a USM- modulated signal according to the principles and embodiments of the present invention are described. Signal primitive 400 in FIG. 4A is a bifurcating signal primitive with a trapezoidal shape. Signal primitive 414 in FIG. 4B is a bifurcating signal primitive with an arch-like shape. Signal primitives 400 and 414 may be generated, for example, by any fractal pattern generator capable of generating fractals, such as various fractal pattern generators implemented as software routines. For example, a Moire or Mandelbrot fractal pattern generator as implemented in the art with Java or Matlab may be used to generate fractal primitives. Other programs may also be used to generate other signal primitives, such as wavelet primitives.

[00127] Both signal primitives 400 and 414 have two symmetric bifurcations, an inner bifurcation and an outer bifurcation, that may be further bifurcated to generate additional bifurcations at different scales, resolutions, or levels of detail. The bifurcation process can be thought of in terms of a "bifurcation tree," with each level of the tree representing a different scale, resolution, or level of detail. The root of the tree corresponds to the original signal primitive, e.g., signal primitive 400 in FIG. 4A or signal primitive 414 in FIG. 4B. [00128] At each subsequent level in the bifurcation tree, each bifurcation may generate an additional signal primitive that has the exact same structure as its originating signal primitive, except that it is at a lower scale or higher resolution. Each outer bifurcation in the new signal primitive may be centered at the outer edges of its previous bifurcation. For example, bifurcating signal primitive 400 results in signal primitives 402 and 404, with the same structure as signal primitive 400 and with the outer bifurcations of signal primitives 402 and 404 centered at the outer edges of signal primitive 400. Similarly, bifurcating signal primitive 414 results in signal primitives 416 and 418, with the same structure as signal primitive 414 and with the outer bifurcations of signal primitives 416 and 418 centered at the outer edges of signal primitive 414.

[00129] Each bifurcation step may be indexed with an integer, referred to herein as the

"bifurcation index." The bifurcation index indicates the scale, level of detail, or depth within the bifurcation tree. At each scale or level in the bifurcation tree, there are 2N signal primitives, where N is the bifurcation index. For example, N = O denotes the root or start of the bifurcation tree with original signal primitives 400 (FIG. 4A) and 414 (FIG. 4B). At N = 1, there are two signal primitives, 402-404 at FIG. 4A and 416-418 at FIG. 4B. At N = 2, there are four signal primitives, 406-412 at FIG. 4A and 420-426 at FIG. 4B. [00130] Referring now to FIG. 5, an exemplary bifurcation tree generated according to the principles and embodiments of the present invention is described. Bifurcation tree 500 is shown at a depth or bifurcation index of 5, i.e., at 5 different scales or levels of detail. Each vertical line beyond the tree root corresponds to one signal primitive generated off signal primitive 505. At each level of the tree, twice the signal primitives in the previous level, i.e., 2N signal primitives, are generated. For example, at N = 1, there are two signal primitives, i.e., signal primitives 510-515. At N = 2, there are four signal primitives, i.e., signal primitives 520-535. [00131] It will be appreciated that each signal primitive can be thought of as two sidebands around a particular frequency. For example, signal primitive 505 can be thought of as a very rough modeled representation of the sidebands of a USM-modulated signal. A modeled frequency spectrum that more closely resembles or approximates the sidebands of a USM-modulated signal may therefore be generated by using a set of signal primitives at different levels of detail. [00132] Signal primitives, such as signal primitives 400 (FIG. 4A) and 414 (FIG. 4B), can be used to represent the frequency spectrum of a USM-modulated signal by first selecting a desired modeling accuracy, i.e., by selecting how close the modeled frequency spectrum should be to the original frequency spectrum, and determining a corresponding bifurcation index required to achieve the desired accuracy. The modeled frequency spectrum may then be generated by adding all signal primitives at all levels of the bifurcation tree.

[00133] Referring now to FIG. 6, an exemplary modeled frequency spectrum generated by adding a set of signal primitives according to the principles and embodiments of the present invention is described. Modeled frequency spectrum 600 was generated by adding, at each frequency, a set of signal bifurcations at a bifurcation index of N = 6. As it can be seen from the figure, the higher the bifurcation index used to generate a modeled frequency spectrum, the higher the resolution and the closer to the spectrum of the USM-modulated signal the modeled frequency spectrum would be.

MULTIRESOLUTION-BASED DIGITAL FILTER DESIGN [00134] It will be appreciated that using a bifurcation tree to model the frequency spectrum of a USM-modulated signal may be thought of as dividing the bandwidth of the USM-modulated signal into 2N bifurcations. The USM-modulated signal having modeled frequency spectrum 600 shown in FIG. 6 and magnified frequency spectrum 300 shown in FIG. 3 was filtered with a digital filter having a given center frequency and a given bandwidth that were selected by simulation to produce the desired result of accurately preserving the abrupt phase shifts in the USM-modulated signal within a band of frequencies as narrow as possible. [00135] Referring now to FIG. 7, an exemplary schematic diagram showing the selection of a filter bandwidth and center frequency according to a bifurcation tree is described. Designing a high-Q, low tolerance narrowband digital filter to preserve the abrupt phase shifts in a USM-modulated signal starts with the realization that the filter bandwidth may be selected as the narrow bandwidth needed to model the frequency spectrum of the USM-modulated signal with the signal primitives, as illustrated in diagram 700.

[00136] This narrow bandwidth is a fraction of the total bandwidth of the USM- modulated signal. The fraction of the total bandwidth is given by the division of the frequency spectrum of the USM-modulated signal into 2N signal primitives. That is, the bandwidth of the filter, denoted herein by BWF, may be selected as:

BWF * ^- (1) where BW is the total bandwidth of the USM-modulated signal and N is the bifurcation index.

[00137] The total bandwidth of the USM-modulated signal may be given, in turn, by a desired data rate for transmission. For example, with the carrier signal used to generate a USM-modulated signal having 4 cycles per pulse-width, the bandwidth of the total modulated signal may be given by four times the desired data rate, that is:

[00138] The bandwidth of the high-Q, low tolerance narrowband digital filter that may

B „„W.F„ « Λx D ^ataRate = _ D_ataR_a_te ( .2_.) be used to preserve the abrupt phase shifts in a USM-modulated signal may therefore be given as a function of a desired data rate and a bifurcation index. Similarly, the center frequency of the digital filter, denoted herein as FF, may be given as a function of the desired data rate, bifurcation index and the carrier frequency FC, according to: VK = 2M - 1, where M = 1 :(2^N-1), and N ≠ 0.

F^ F_C ±(2" -K) ≤ ₍₃₎

[00139] Accordingly, the capacity of a communication system (given in bits/sec/Hz) that uses the USM-modulation technique of the present invention and a high-Q, low

C = 2^N-² (4) tolerance, linear-phase narrowband digital filter designed with a bandwidth and center frequency as above to transmit a fraction of a sideband of a USM-modulated signal may be given by:

[00140] It should be understood by one skilled in the art that Equation (3) described hereinabove gives the values of the center frequency FF within the range of the frequency spectrum from (F_c - BWF) to (F_c + BWF).

[00141] It should also be understood by one skilled in the art that other values of F_F may exist outside the hereinabove mentioned range based on a given bifurcation index. For example, if it is desired to select a center frequency outside the range from (F_c — BWF) to (F₀ ^•+^■ BWF), the value of F₀ in equation (3) described hereinabove may be set to a value offset by

BWF.

[00142] Referring now to FIG. 8, an exemplary graph of a filter bandwidth selected according to the principles and embodiments of the present invention versus a bifurcation index for a given desired data rate is described. Graph 800 shows that the communication system of the present invention may enable data rates exceeding 5 Mbps to be delivered through frequency channels as narrow as 50 KHz under a variety of channel conditions. [00143] Referring now to FIG. 9, an exemplary graph showing the capacity of a communication system designed according to the principles and embodiments of the present invention versus a bifurcation index is described. Graph 900 shows that broadband-like wireless services may be achieved with the communication system of the present invention within a very narrow frequency spectrum. Transmission of a fraction of one or two sidebands may result in a capacity exceeding 100 bits/second/Hz for a bifurcation index of 9 and above, far superior than any currently-available wireless communication system. [00144] It should be understood by one skilled in the art that selecting a given bifurcation index is a function of the system design for a particular application. For example, if it is desired to transmit 100 channels in a total bandwidth of 36 MHz, the bifurcation index may be chosen to optimize the filter design for a given desired data rate, carrier signal, number of users accessing the channels, and so forth. [00145] It should also be understood by one skilled in the art that the high-Q, low tolerance, linear-phase digital filter designed according to the principles and embodiments of the present invention may have additional design parameters other than the filter bandwidth and center frequency selected as above. For example, to achieve a very sharp stopband, the digital filter may be designed with a uniform stopband attenuation of, for example, at least 60 dB. And to minimize the passband ripple, the filter may be designed with a passband ripple of no more than 0.1 dB. These stringent filter design conditions may generate digital filters having a large number of filter taps. Those filters may be implemented in hardware using specially configured circuit boards. With decreasing hardware costs, such filters may be easily implemented in a cost-effective manner.

[00146] Referring now to FIG. 10, an exemplary plot showing the frequency response of a high-Q, low tolerance, linear-phase digital filter designed according to the principles and embodiments of the present invention is now described. Frequency response 1000 of a higher low tolerance, liner-phase digital filter designed according to the principles and embodiments of the present invention is shown with very sharp passbands, transition bands, and stopbands. The passband ripple of the digital filter having frequency response 1000 is very small to insignificant, while the stopband attenuation is very high. The bandwidth of the digital filter having frequency response 1000 was designed to be around 58.6 KHz and the center frequency was designed at approximately 47.6 KHz away from the carrier frequency used. Using such a filter provides the transmission of 5 Mbps within the very narrow bandwidth of the digital filter. Of course, other data rates are also achieved, and these values are provided for illustration only and are not intended to limit the teaching of the invention.

MULTIRESOLUTION-BASED TRANSMITTER FILTERING APPROACH [00147] Referring now to FIG. 1 1, an exemplary schematic diagram of a transmitter system using the multiresolution-based transmitter filtering approach to transmit message signals through a communications channel according to the principles and embodiments of the present invention is described. Transmitter system 1100 may be used to transmit a message signal according to the principles and embodiments of the present invention by using USM modulator 1105 to modulate the message signal into a carrier signal and high-Q, low tolerance, linear-phase digital filter 1110 designed as above, such as the digital filter having frequency spectrum 1000 shown in FIG. 10, to filter the USM-modulated signal. [00148] It should be understood by one skilled in the art that additional functional blocks may be present in transmitter system 1 100, such as a channel encoder to introduce redundancy in the message signal prior to modulation by USM modulator 1105 and a transmitter circuit having an amplifier to amplify the message signal prior to transmission through a communications channel. MULTIRESOLUTION-BASED LOOK-UP TABLE TRANSMITTER APPROACH

[00149] Referring now to FIG. 12, an exemplary schematic diagram of a transmitter system using the multiresolution-based look-up table transmitter approach to transmit message signals through a communications channel according to the principles and embodiments of the present invention is described. Transmitter system 1200 may be used to transmit a message signal according to the principles and embodiments of the present invention via a simple look-up table operation. Multiresolution-based look-up table 1205 may be generated by sampling a modeled USM-modulated signal, such as modeled USM- modulated signal with modeled frequency spectrum 600 shown in FIG. 6. [00150] Since the frequency spectrum of a USM-modulated signal may be modeled with signal primitives as described hereinabove, an alternative embodiment to transmission of a message signal involves sampling the modeled USM-modulated signal as above and transmitting the samples through the communications channel. Sampling the modeled USM- modulated signal is an approximation to sampling a USM-modulated signal filtered with a narrowband digital filter, as performed in communication system 1100 shown in FIG. 11.

[00151] Multiresolution-based look-up table 1205 therefore stores samples extracted from the time response counterpart of a modeled frequency spectrum of a USM-modulated signal. The samples may be independent of the USM-modulated signal, that is, they may be extracted from the time response counterpart of a modeled frequency spectrum of any USM- modulated signal and used in the transmission of any USM-modulated signal.

[00152] In one embodiment, multiresolution-based look-up table 1205 may contain two rows of samples, with each row corresponding to a different binary symbol, e.g., "0" or "1." The samples for each binary symbol may be extracted by observing the modeled frequency spectrum of a USM-modulated signal and noting which patterns arise as a result of an abrupt phase shift corresponding to a "0" or a "1." Transmission of a binary symbol in a message signal may be accomplished by simply encoding the symbol into its corresponding samples stored in look-up table 1205.

[00153] In another embodiment, multiresolution-based look-up table 1205 may contain

T rows of samples, with each row corresponding to a different binary symbol, e.g., "00," "01," "10," or "11." The samples for each binary symbol may be extracted by observing the modeled frequency spectrum of a USM-modulated signal and noting which patterns arise as a result of an abrupt phase shift corresponding to a "00," "01 ," "10," or a "11." Transmission of a binary symbol in a message signal may be accomplished by simply encoding the symbol into its corresponding samples stored in look-up table 1205.

[00154] It should be understood by one skilled in the art that this multiresolution-based look-up table transmission approach is very simple and cost-effective to implement, in addition to achieving high data rates within a very narrow frequency spectrum. It should also be understood by one skilled in 'the art that such a system employs high oversampling to reduce the noise in the system and achieve the desired data rates without being significantly affected by channel distortions.

MULTIRESOLUTION-BASED RECEIVER FILTERING APPROACH [00155] Referring now to FIG. 13, an exemplary schematic diagram of a receiver system using the multiresolution-based receiver filtering approach to recover message signals transmitted through a communications channel according to the principles and embodiments of the present invention is described. Receiver system 1300 may be used to recover a message signal transmitted according to the principles and embodiments of the present invention by first filtering the transmitted signal with high-Q, low tolerance, linear-phase digital filter 1305. Digital filter 1305 may be a filter designed based on high-Q, low

_DW/Z7 ^{4 x} BataRate DataRate

BWF « Tj ± o = TT^ — ± δ (5) tolerance, linear-phase digital filter 1110 shown in FIG. 11. The center frequency of digital filter 1310 is selected as a function of a carrier frequency, a bifurcation index and a desired data rate as given in equation (3) described hereinabove. The bandwidth of digital filter 1305 may be selected as a function of a bifurcation index and a desired data rate with the addition of a small band of frequencies to take into account channel distortions such as fading and inter-symbol interference, as follows: where δ is the small band of frequencies related to a guard band, DataRate is the desired data rate and N is the bifurcation index. [00156] It should be understood by one skilled in the art that equation (5) is derived from equation (2) above giving the bandwidth of a digital transmitter filter, with the addition of the small band of frequencies δ.

[00157] Referring now to FIG. 14, an exemplary plot showing the frequency response of a high-Q, low tolerance, linear-phase digital receiver filter superimposed with the frequency response of a high-Q, low tolerance, linear-phase digital transmitter filter designed according to the principles and embodiments of the present invention is described. As illustrated in plot 1400, the frequency response of receiver filter 1405 is slightly wider than the frequency response of a transmitter filter designed as described hereinabove, such as transmitter filter 1110 shown in FIG. 11. The frequency response of receiver filter 1305 also shows that receiver filter 1305 has slightly smaller passband ripple and an even sharper stopband than its corresponding transmitter filter, such as transmitter filter 1110 shown in

FIG. 11.

[00158] Referring back to FIG. 13, once the transmitted signal is filtered by receiver filter 1305, the transmitter clock is recovered and used to phase-lock the receiver clock by clock detection circuitry 1310. The phase-locked receiver clock is then used to synchronize communications receiver 1300 with the transmitted signal in order to extract the binary symbols in the message signal encoded into the abrupt phase shifts in the transmitted signal. The message signal is recovered by demodulator 1315.

[00159] Referring now to FIG. 15, an exemplary schematic diagram of a demodulator for use with the communications receiver system shown in FIG. 13 is described. Demodulator 1500 recovers a message signal transmitted by communications transmitter system 1100 shown in FIG. 11 or communications transmitter system 1200 shown in FIG. 12. The first step towards recovering the message signal is performed by correlator 1505, which correlates the phase-locked receiver clock with the filtered transmitted signal, i.e., with the transmitted signal filtered by receiver filter 1305 shown in FIG. 13, in order to extract the transmitted signal at the desired frequencies. Correlator 1505 may be implemented with any correlator circuitry known to one skilled in the art, including matched filter circuitry. [00160] Referring now to FIG. 16, an exemplary plot showing a reference signal to be used in a matched filter according to the principles and embodiments of the present invention is described. Reference signal 1600 is a zero-phase four-cycle sinusoidal wave generated at the center frequency selected for the transmitter filter used to transmit a message signal for recovery by demodulator 1505, such as transmitter filter 1110 shown in FIG. 11 and designed based on the multiresolution-based decomposition as described hereinabove. Reference signal 1600 may be used in correlation with the filtered transmitted signal in blocks of four cycles to generate a noiseless output signal with the same phase as the transmitted signal. [00161] The matched filter employs four-cycle reference signal 1600 in a receiver system for which the corresponding transmitter employs a USM technique using four cycles per pulse-width to modulate a binary symbol into a sinusoidal carrier signal. It should be understood by one skilled in the art that the number of cycles chosen for the sinusoidal reference signal used by the matched filter may be selected as any number of cycles that match the number of cycles used by a ultra spectral modulator when encoding each binary symbol in a message signal within a given pulse-width.

[00162] Referring back to FIG. 15, the phase of the output signal generated by correlator 1505 is detected by phase detector 1510, and the detected phase is then used with the output signal generated by correlator 1505 in data bit decision block 1515 to recover the binary symbols encoded in the transmitted signal, i.e., to recover the message signal. Data bit decision block 1515 may be implemented with any well-known data bit decision circuitry to one skilled in the art, including with a Costas decision loop. [00163] Referring now to FIG. 17, exemplary plots of signals generated by a second order Costas decision loop for use in a communications receiver system according to the principles and embodiments of the present invention is described. Plot 1700 shows the message signal transmitted with a communications transmitter system of the present invention, such as communications transmitter system 1100 shown in FIG. 11 and communications transmitter system 1200 shown in FIG. 12. Plot 1705 shows the frequency response of a Hubert transform filter used in the Costas loop, and plot 1710 shows the output signal generated by the Costas loop superimposed with the message signal recovered by the Costas loop. [00164] As illustrated, the binary symbols of the message signal plotted in plot 1700 were correctly recovered by the Costas loop in the output signal plotted in plot 1710. The exemplary Costas loop used to recover the binary symbols was designed with the following Costas loop parameters: Kl = 0.1, A = 0.16665/4; B = 0.01389/16; and F = center frequency of the transmit filter selected according to equation (3) above. It should be understood by one skilled in the art that other parameters may be used in a Costas loop for recovering message signals transmitted and received according to the principles and embodiments of the present invention.

MULTIRESOLUTION-BASED SPECTRAL ESTIMATOR RECEIVER APPROACH

[00165] Referring now to FIG. 18, an exemplary schematic diagram of a communications receiver system using the multiresolution-based spectral estimator receiver approach to recover message signals transmitted through a communications channel according to the principles and embodiments of the present invention is described. Receiver system 1800 may be used to recover a message signal transmitted according to the principles and embodiments of the present invention by using spectral estimator 1805 to estimate the frequency spectrum of the transmitted signal.

[00166] Once the frequency spectrum of the transmitted signal is generated by spectral estimator 1805, spectral selector 1810 is used to extract the transmitted signal at the desired frequencies, i.e., at the transmitted frequencies within the narrowband selected for the transmission filter bandwidth according to equation (2) above. The message signal is then recovered by demodulator 1820 taking as inputs a phase-locked receiver clock generated by clock detection circuitry 1815 and the transmitted signals recovered by spectral selector 1810. [00167] It should be understood by one skilled in the art that traditional spectral estimation, spectral selection, and demodulation circuitry may be used by communications receiver system 1800. For example, demodulator 1820 may be implemented with the correlator, phase detector, and data bit decision circuitry of demodulator 1315 shown in FIG. 13 and described above with reference to FIG. 15.

COMMUNICATION SYSTEMS

[00168] It should also be understood by one skilled in the art that communication systems designed according to the principles and embodiments of the present invention may be implemented using any combination of the transmitter and receiver systems shown in FIGS. 1 1-12, 13, and 18. [00169] Referring now to FIG. 19, an exemplary embodiment of a communication system designed according to the principles of the present invention is described. Communication system 1900 may be implemented with transmitter system 1905 and communications receiver system 1920. Transmitter system 1905 may be a transmitter system designed using the multiresolution-based transmitter filtering approach as described hereinabove with reference to FIG. 11. Receiver system 1920 may be a receiver system designed using the multiresolution-based receiver filtering approach as described hereinabove with reference to FIG. 13.

[00170] Referring now to FIG. 20, another exemplary embodiment of a communication system designed according to the principles of the present invention is described. Communication system 2000 may be implemented with transmitter system 2005 and communications receiver system 2015. Transmitter system 2005 may be a transmitter system designed using the multiresolution-based look-up table transmitter approach as described hereinabove with reference to FIG. 12. Receiver system 2015 may be a receiver system designed using the multiresolution-based receiver filtering approach as described hereinabove with reference to FIG. 13.

[00171] Referring now to FIG. 21, another exemplary embodiment of a communication system designed according to the principles of the present invention is described. Communication system 2100 may be implemented with communications transmitter system 2105 and communications receiver system 2120. Communications transmitter system 2105 may be a transmitter system designed using the multiresolution- based transmitter filtering approach as described hereinabove with reference to FIG. 1 1. Communications receiver system 2120 may be a receiver system designed using the multiresolution-based spectral estimator receiver approach as described hereinabove with reference to FIG. 18.

[00172] Referring now to FIG. 22, yet another exemplary embodiment of a communication system designed according to the principles of the present invention is described. Communication system 2200 may be implemented with communications transmitter system 2205 and communications receiver system 2215. Communications transmitter system 2205 may be a transmitter system designed using the multiresolution- based look-up table transmitter approach as described hereinabove with reference to FIG. 12. Communications receiver system 2205 may be a receiver system designed using the multiresolution-based spectral estimator receiver approach as described hereinabove with reference to FIG. 18.

[00173] It should be understood by one skilled in the art that the communication systems of FIGS. 19-22 may operate in a standalone wireless network or be integrated into existing wireless standards and systems at very low overhead costs. In addition, the communication systems of FIGS. 19-22 may be used in a variety of communications applications, including in satellite systems with polarized transmitter and receiver antennas.

[00174] Further, it should be understood by one skilled in the art that although the systems and methods of the present invention were described with reference to wireless communications, they may also be used in wired communications to achieve broadband-like wired services within a very narrow frequency spectrum.

SATELLITE COMMUNICATION SYSTEM

[00175] Referring now to FIG. 23, an exemplary embodiment of a satellite communications system designed according to the principles of the present invention is described. Satellite communications system 2300 may be used in the transmission of signals modulated with the USM technique of the present invention. A message signal may be first modulated by USM modulator 2305, using either the fractal-based transmitter filtering approach or the fractal-based look-up table transmitter approach, and adapted for transmission over horizontally polarized antenna 2315 and vertically polarized antenna 2325 by signal generator block 2310.

[00176] The transmitted signal may be received at horizontally polarized antenna 2320 and vertically polarized antenna 2330. The message signal may be recovered by spectral estimator 2335, reference phase lock loop 2340, time synchronization block 2345, clock detection 2350, spectral selector 2355, information decoder 2360, and data bit decision block

2365.

[00177) Referring now to FIG. 24, yet another exemplary embodiment of a satellite communications system designed according to the principles of the present invention is described. Satellite communications system 2400 may be used in the transmission of signals modulated with the USM technique of the present invention. A message signal is first modulated by USM modulator 2405, using either the fractal-based transmitter filtering approach or the fractal-based look-up table transmitter approach, and adapted for transmission over horizontally polarized antenna 2415 and vertically polarized antenna 2425 by signal generator block 2410. [00178] The transmitted signal may be received at horizontally polarized antenna 2420 and vertically polarized antenna 2430. Communications receiver system 2435 may be a receiver system designed using the fractal-based receiver filtering approach as described hereinabove with reference to FIG. 13.

MULTI-CHANNEL DIGITAL TO ANALOG CONVERTER

[00179] Referring now to FIG. 25, an exemplary schematic diagram showing digital samples from a USM modulated signal being fed into a digital to analog converter is described. In the exemplary embodiment eight samples 2500a — 2500 h are shown and are feed in serial or in parallel to digital to analog converter 2510. Feeding eight samples 400a — 40Oh into the digital to analog converter 2510 may require the use of buffers 2512a - 2512h for each sample. The data rate and carrier frequency that may be used in such a system is dependent on the sampling rate and speed of the digital to analog converter used. [00180] Referring now to FIG. 26, an exemplary schematic diagram showing a multi- channel digital to analog converter 2600 designed according to the principles and embodiments of the present invention is described. The multi-channel digital to analog converter 500 may receive the samples from an ASIC 2610 implementing the USM technique described above. Multi-channel digital to analog converter 2600 is comprised of a plurality of channels. In one embodiment as shown in the figure, four channels 2612a — 2612d are used. Each channel has a 500 MSPS digital to analog converter 2614a - 2614d , such as an AD9959 digital to analog converter (D/ A) sold by Analog Devices, Inc.. A delay is introduced at three of the channels to compose a time scale for transmitting the samples. In the exemplary embodiment a ¹A time delay is introduced at D/A 2614b, a Vi time delay is introduced at D/A 514c and a % time delay is introduced at D/A 2614d. With the four digital to analog converters operating at 500 MSPS, a carrier frequency of 2 GHz may be achievable. While four channels are shown with three time delays, other arrangements are possible and within the scope and spirit of the present invention. [00181] While the specific embodiments illustrated herein employ a USM modulated signal, it should be understood by those of skill in the art that the multi-channel digital to analog converter of the present invention may be employed with other types of modulation schemes and signals.

[00182] The foregoing descriptions of specific embodiments and best mode of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Specific features of the invention are shown in some drawings and not in others, for purposes of convenience only, and any feature may be combined with other features in accordance with the invention. Steps of the described processes may be reordered or combined, and other steps may be included. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. Further variations of the invention will be apparent to one skilled in the art in light of this disclosure and such variations are intended to fall within the scope of the appended claims and their equivalents. The publications referenced above are incorporated herein by reference in their entireties.

Claims

WHAT IS CLAIMED IS:

1. A satellite-based system for receiving a signal, comprising: a polarized antenna operative to receive a modulated signal, the modulated signal generated by modulating a carrier signal with a message signal with abrupt phase changes in the carrier signal; a receiver filter centered at a receiver center frequency and having a receiver filter bandwidth, the receiver center frequency and the receiver filter bandwidth selected based on the transmitter center frequency and the transmitter filter bandwidth; a clock detector for detecting a transmitter clock and generating a phase- locked receiver clock; a demodulator for recovering the message signal; and a satellite housing at least the receiver filter, clock detector, and demodulator.

2. A system for transmitting a message signal through a communications channel, the system comprising: a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with the message signal.

3. A method for transmitting information through a communications channel, the method comprising: modulating a carrier signal with a message signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; filtering out a portion of at least one sideband with a filter, the filter centered at a center frequency and having a filter bandwidth, the center frequency and the filter bandwidth selected based on a multiresolution decomposition of the at least one sideband; and transmitting the portion of the at least one sideband.

4. A method for transmitting a message signal through a communications channel, the method comprising: providing a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with the message signal; and transmitting the message signal by converting the message signal into at least one of the first or second set of samples stored in the look-up table.

5. A communications system, said system configured to modulate a carrier signal with a message signal using abrupt phase changes in the carrier signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband, characterized in that: a frequency spectrum of the modulated signal is represented by signal primitives that are bifurcated in different scales.

6. A system for transmitting information through a communications channel, the system comprising: a modulator for modulating a carrier signal with a message signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; and a filter for filtering out a portion of at least one sideband, the filter centered at a transmitter center frequency and having a transmitter filter bandwidth, the transmitter center frequency and the transmitter filter bandwidth selected based on a multiresolution decomposition of the at least one sideband.

7. The communications system of claim 5 wherein the signal primitives comprise fractal bifurcation patterns, wavelets, or combinations thereof.

8. The communications system of claim 5 wherein the modulated signal is transmitted at a bandwidth efficiency of at least 50 bps/Hz.

9. The communication system of any of claims 1, 2 and 5 - 8 wherein the modulator is configured a carrier signal with a message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal to generate a modulated signal.

10. The communication system of any of claims 1, 2 and 5 - 8 wherein the modulator is configured to modulate a carrier signal with a message signal using multi- symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols to generate the modulated signal.

1 1. A modulated signal in a frequency spectrum of a carrier comprising, the modulated signal formed by modulating the carrier with a message signal using abrupt phase changes in the carrier signal; a first sideband occupying a first portion of the frequency spectrum; and a carrier frequency, the carrier frequency transmitting no data.

12. The modulated signal of claim 11 further comprising: a first data bit pattern representing a first binary digit; and a first datum bit pattern associated with the first data bit pattern; wherein the first data bit pattern is 180 degrees out of phase from the first datum bit pattern.

13. The modulated signal of claim 11, further comprising: a second data bit pattern representing a second binary digit; and a second datum bit pattern representing a second binary digit; wherein the first data bit pattern is 180 degrees out of phase from the second data bit pattern.

14. The modulated signal of claim 1 1, wherein each of the data bit patterns and datum bit patterns are sinusoidal.

15. The modulated signal of claim 12, wherein: the first data bit pattern and first datum bit pattern comprise a first bit; and the second data bit pattern and second datum bit pattern comprise a second bit.

16. The modulated signal of claim 11, wherein: the first data bit pattern persists for a first half of a pulse width; and the first datum bit pattern persists for a second half of a pulse width.

17. The modulated signal of claim 11 , further comprising: a second sideband occupying a second portion of the frequency spectrum; wherein the first and second sidebands are symmetric,

18. The modulated signal of claim 17, wherein the second sideband is suppressed.

19. The modulated signal of claim 18, wherein suppression of the second sideband yields a single-sideband suppressed-carrier signal.

20. The modulated signal of claim 10, wherein: the modulated signal is transmitted through a frequency channel; and the modulated signal is operative to transmit data at a rate of at least 5 megabits per second when the frequency channel is 50 kilohertz wide.

21. The modulated signal of claim 11 , wherein: the modulated signal is transmitted through a frequency channel; and the modulated signal is operative to transmit at least 100,000 bits per second per kilohertz of frequency of the frequency channel.

22. A receiver for receiving a transmission comprised of a modulated signal generated by modulating a carrier signal with a message signal with abrupt phase changes in the carrier signal, transmitted at a carrier frequency, comprising: a fractal-based receiver filter operative to filter the transmission to retrieve a transmission signal; a clock detector operative to retrieve a transmission clock from the transmission and operatively associated with the fractal-based receiver filter; and a demodulator operative to accept the transmission signal from the fractal- based receiver filter and further operative to retrieve at least one binary symbol from the transmission signal.

23. The receiver of claim 22, wherein the fractal-based receiver filter comprises a linear-phase digital filter.

24. The receiver of claim 22, wherein the fractal-based receiver filter comprises a narrowband digital filter.

25. The receiver of claim 22, wherein the fractal-based receiver comprises: a filter centered at a filter frequency, the filter frequency selected as a function of the carrier frequency, a fractal bifurcation index and a desired data rate.

26. The receiver of claim 25, wherein: the fractal-based receiver filter has an associated bandwidth; and the associated bandwidth is selected as a function of a fractal bifurcation index and a desired data rate.

27. The receiver of claim 22, further comprising: a receiver clock operatively associated with the clock detector and operative to synchronize the receiver with the transmission signal; wherein the clock detector is further operative to phase-lock the receiver clock with the transmission clock.

28. The receiver of any of claims 22 — 27 wherein modulation is performed by modulating a carrier signal with a message signal using non-return-to-zero modulation with abrupt phase changes in the carrier signal to generate a the modulated signal.

29. The communication system of any of claims 1, 2 and 5 — 7 wherein modulation is performed by modulating a carrier signal with a message signal using multi- symbol modulation having abrupt phase changes in the carrier signal to represent incoming binary symbols to generate the modulated signal.

30. A method for receiving a transmission comprised of a modulated signal generated by modulating a carrier signal with a message signal with abrupt phase changes in the carrier signal, transmitted at a carrier frequency, comprising: filtering, with a fractal-based receiver filter, the transmission to retrieve a transmission signal; retrieving a transmission clock from the transmission and operatively associated with the fractal-based receiver filter; retrieving at least one binary symbol from the transmission signal.

31. The method of claim 30, wherein the transmission occurs entirely in a sideband.

32. The method of claim 30, wherein transmission is transmitted through a frequency channel; and the transmission transmits at least 100,000 bits per second per kilohertz of frequency of the frequency channel.

33. A system for transmitting information through a communications channel, the system comprising: a modulator for modulating a carrier signal with a message signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; and a multi-channel digital to analog converter comprised of a plurality of digital to analog converters and delay elements arranged in a sliding time scale to operate at high sampling rates.

34. A system for transmitting a message signal through a communications channel, the system comprising: a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with the message signal; and a multi-channel digital to analog converter comprised of a plurality of digital to analog converters and delay elements arranged in a sliding time scale to operate at very high sampling rates.

35. A method for transmitting a message signal through a communications channel, the method comprising: providing a look-up table for storing a first set of samples corresponding to a first data bit and a second set of samples corresponding to a second data bit, wherein the first set of samples and the second set of samples are generated based on a multiresolution decomposition of at least one sideband, the at least one sideband generated by modulating a carrier signal with the message signal; transmitting the message signal by converting the message signal into at least one of the first or second set of samples stored in the look-up table; and passing the samples through a multi-channel digital to analog converter comprised of a plurality of digital to analog converters and delay elements arranged in a sliding time scale to operate at very high sampling rates.

36. The system of claims 33 and 34 wherein the plurality of digital to analog converters comprises at least four.

37. The system of claims 33 and 34 wherein the plurality of digital to analog converters comprises four and delay elements are introduced at three of the four converters.

38. A system for transmitting information through a communications channel, the system comprising: a modulator for modulating a carrier signal with a message signal to generate a modulated signal, the modulated signal at a carrier frequency and having at least one sideband; a filter for filtering out a portion of at least one sideband, the filter centered at a transmitter center frequency and having a transmitter filter bandwidth, the transmitter center frequency and the transmitter filter bandwidth selected based on fractal bifurcations; and a multi-channel digital to analog converter formed of a plurality of digital to analog converters and delay elements arranged in a sliding time scale to operate at high sampling rates.

39. The system of claim 38, wherein the fractal bifurcations comprise a set of fractal bifurcations at a fractal bifurcation index for modeling the frequency spectrum of the modulated signal.

40. The system of claim 38, wherein the transmitter center frequency is selected based on the carrier frequency, a desired transmission data rate, and the fractal bifurcation index.

41. The system of and of claims 34 - 40, wherein the transmitter filter bandwidth is selected based on a desired transmission rate and a fractal bifurcation index.