WO2002075949A1 - Multiple phase cdma modulation and demodulation method and apparatus - Google Patents

Multiple phase cdma modulation and demodulation method and apparatus Download PDF

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Publication number
WO2002075949A1
WO2002075949A1 PCT/KR2001/001627 KR0101627W WO02075949A1 WO 2002075949 A1 WO2002075949 A1 WO 2002075949A1 KR 0101627 W KR0101627 W KR 0101627W WO 02075949 A1 WO02075949 A1 WO 02075949A1
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Prior art keywords
phase
phases
modulation
cdma
signal
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PCT/KR2001/001627
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French (fr)
Inventor
Seung Moon Ryu
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Casuh Corporation
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Publication of WO2002075949A1 publication Critical patent/WO2002075949A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7073—Synchronisation aspects
    • H04B1/7075—Synchronisation aspects with code phase acquisition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7073—Synchronisation aspects
    • H04B1/7075—Synchronisation aspects with code phase acquisition
    • H04B1/7077—Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
    • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
    • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
    • H04B2201/70706—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation with means for reducing the peak-to-average power ratio
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/0007—Code type
    • H04J13/004—Orthogonal

Definitions

  • CDMA Code Division Multiple Access
  • Multiplexing technology for wireless communication is classified into frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA).
  • FDMA frequency division multiple access
  • TDMA time division multiple access
  • CDMA code division multiple access
  • the CDMA is multiplexing technology based on spread-spectrum system technology and is referred to as spread-spectrum multiple access (SSMA).
  • SSMA spread-spectrum multiple access
  • the CDMA has been settled as an international standard in the IMT-2000 system, which is referred to as third generation mobile communications, beating the TDMA due to its superiority in general characteristics in spite of its complexity in realization.
  • the principle of spread-spectrum originated from the concept that interference can be minimized by spreading the spectrum of a signal and had been developed during the 1st World War and the 2nd World War.
  • Spread-spectrum system technology has become a subject of intense research since 1950s to be mainly used for military communications and satellite communications. With the evolution of semiconductor technology in integrity and operating speed as well as the development of microprocessor technology, the spread-spectrum system has been used in commercial mobile communications in addition to the military communications and the satellite communications.
  • Spread-spectrum systems are classified into direct-sequence (DS) spread-spectrum systems, frequency-hopped (FH) spread-spectrum systems, and time-hopped (TH) spread-spectrum systems depending on the methods of spreading the bandwidth of a signal.
  • DS direct-sequence
  • FH frequency-hopped
  • TH time-hopped
  • DS spread-spectrum systems referred to as DS/CDMA systems employ a manner of spreading the frequency bandwidth by directly modulating a carrier, onto which a data sequence is modulated, with a broadband spreading signal.
  • the spreading signal composed of +1 and -1 is referred to as a spreading sequence, spreading code, or code sequence.
  • the signal which has been modulated with a spreading signal and has been transmitted from a transmitter is received at a receiver in a distorted form due to noises, interferences, signal disturbances, or the like. Then, the receiver multiplies the received signal by the same spreading signal as used by the transmitter to recover the original spectrum.
  • This operation is referred to as de-spreading.
  • signals of multiple channels are linearly summed, and the result of summation is transmitted, so that the signals of multiple channels can be simultaneously transmitted.
  • an increase in the number of channels results in an increase of the number of output signal levels in DS/CDMA.
  • the amplitude of an output signal in DS/CDMA varies in time varies with the lapse of time like an analog signal. Therefore, as the number of input channels increases, spread-spectrum systems employing DS/CDMA become complicated. This characteristic of DC/CDMA will result in difficulties in designing and realizing systems when the transmission rate of wireless communications goes higher in the future. Disclosure of the Invention
  • CDMA code division multiple access
  • a multiple phase CDMA modulation method including a first step of setting the range of a output level of a modulated signal; a second step of dividing a phase into sub-phases to transmit an output signal of different levels within the set range at different phases and setting modulation phases using the divided phases; a third step of multiplying input data of multiple channels by orthogonal codes and calculating the sum of the data; a fourth step of truncating the sum of data calculated in the third to the range of the output level set in the first step; a fifth step of selecting a phase to be allocated each of the different levels of an output signal within the output level range from among the modulation phases set in the second step; and a sixth step of transmitting the output signal having the modulation phases allocated to the different levels.
  • a multiple phase CDMA modulation apparatus including a modulator for multiplying input data of multiple channels by respective orthogonal codes and calculating the sum of the results of multiplication to generate a CDMA-modulated signal; a level truncator for truncating an output level of the modulator within a predetermined range; a phase converter for mapping the different levels of an output signal from the level truncator to predetermined modulation phases; a transmitter for transmitting the output signal of the different levels at the modulation phases allocated to the respective different levels; and a controller for controlling the modulator, the level truncator, the phase converter, and the transmitter under external control.
  • a multiple phase CDMA demodulation method including a first step of restoring phases of a received signal to levels based on phase information used during modulation; a second step of synchronizing the restored levels of the received signal according to a predetermined synchronous code; and a third step of restoring the synchronized signal to an original signal using orthogonal codes used during the modulation.
  • a multiple phase CDMA demodulation apparatus including a receiver for receiving a signal which has been modulated in the manner of multiple phase CDMA; a phase discriminator for restoring phases of the signal received through the receiver to levels; a synchronous and demodulating circuit for synchronizing the levels of the received signal restored by the phase discriminator and demodulating the received signal using orthogonal codes used during the modulation; and a code generator for generating the orthogonal codes used during the modulation and outputting them to the synchronous and demodulating circuit for demodulation.
  • FIG. 1 is a schematic block diagram of a multiple phase code division multiple access (CDMA) modulation apparatus according to an embodiment of the present invention.
  • FIG. 2 is a schematic block diagram of a multiple phase CDMA demodulation apparatus for demodulating a signal modulated according to an embodiment of the present invention.
  • CDMA code division multiple access
  • FIG. 3 is a flowchart of a multiple phase CDMA modulation method according to an embodiment of the present invention.
  • FIG. 3A is a waveform diagram for explaining a procedure of truncating an output level of a CDMA-modulated signal according to the embodiment of the present invention.
  • FIG. 3B is a diagram showing an example of an output signal of truncated levels and examples of modulation phases allocated for transmission of the output signal according to the embodiment of the present invention.
  • FIG. 4 is a flowchart of a CDMA demodulation method for demodulating a signal that has been modulated according to the embodiment of the present invention.
  • FIG. 5 is a graph of bit error rate (BER) characteristic curves of signals modulated in the manner of multiple phase CDMA according to the embodiment of the present invention.
  • BER bit error rate
  • CDMA multiple phase code division multiple access
  • FIG. 1 is a schematic, block diagram of a multiple phase CDMA modulation apparatus according to an embodiment of the present invention.
  • the multiple phase CDMA modulation apparatus includes a modulator 10, a level truncator 20, a phase converter 30, a transmitter 40, and a controller 50.
  • the modulator 10 multiplies the input data of each of multiple channels, d n , by one of orthogonal codes, c n , and outputs the sum of the results of multiplication.
  • the modulator 10 includes a code generator 12 for generating the orthogonal codes c n and a modulation circuit 11 for multiplying the orthogonal codes c n by the input data d n , respectively, and summing the results of multiplication.
  • the level truncator 20 truncates the level of a signal output from the modulator 10 within a predetermined range.
  • the predetermined range of an output level can be set to be variable according to system characteristics and may be set by the controller 50.
  • the phase converter 30 selects a phase to be allocated to each of different levels of a signal output from the level truncator 20 from among predetermined modulation phases. For this, the phase converter 30 divides a phase into sub-phases and sets divided phases as modulation phases under the control of the controller 50.
  • the transmitter 40 transmits a signal of different levels using the different modulation phases that are allocated to the respective different levels by the phase converter 30.
  • the controller 50 controls the operations of the modulator 10, the level truncator 20, the phase converter 30, and the transmitter 40.
  • the phase converter 30 sets a guard phase to prevent an error from occurring due to between phases having different signs and defines the divided phases except the guard phase as the modulation phases. For this, the phase converter 30 sets the guard phase to a predetermined range under the control of the controller 50.
  • a phase of near 180° or a previous modulation phase may be set as the guard phase.
  • the phase converter 30 divides a phase into a plurality of sub-phases more than the number of levels within the predetermined range of an output level by a predetermined number, and sets a predetermined number of guard phases having a predetermined magnitude near positions ( ⁇ 180°) where phases having different polarities intersect each other.
  • the entire range of the guard phases can be variable depending on the operating characteristics of a system. Generally, when it is intended to transmit a frequency of a broad band even through the transmission characteristic of the system drops slightly, the range of a guard phase is narrowed. When an excellent transmission characteristic is necessary even though a frequency band transmittable is narrowed in a system, the range of a guard phase is widened.
  • the phase converter 30 sets a modulation phase of the previous phase as a guard phase for each current one of the divided sub-phases, sets a phase which is different from the guard phase by 180° as reference phase, and resets a phase different from the reference phase by the current sub-phase as a current modulation phase.
  • FIG. 2 is a schematic block diagram of a multiple phase CDMA demodulation apparatus for demodulating a signal modulated according to an embodiment of the present invention.
  • the multiple phase CDMA demodulation apparatus includes a receiver 60 for receiving data modulated through multiple phase CDMA, a phase discriminator 70 for recovering the phase of a signal received through the receiver 60 to a signal level, a synchronous and modulating circuit 80 for synchronizing the signal level and demodulating the signal using an orthogonal code used during modulation, and a code generator 90 for generating an orthogonal code for demodulation and transmitting it to the synchronous and modulating circuit 80.
  • the phase discriminator 70 recovers the phase of a received signal to the level of the signal.
  • FIG. 3 is a flowchart of a multiple phase CDMA modulation method according to an embodiment of the present invention.
  • a multiple phase CDMA modulation apparatus sets the range of an output level in order to limit the output level of modulated signals in step S110.
  • the multiple phase CDMA modulation apparatus divides a phase into sub-phases and sets modulation phases with respect to the divided phases in order to transmit output signals of different levels within the set range at different phases in step S120
  • the modulation phases may be set in different manners according to a method of setting guard phases.
  • the multiple phase CDMA modulation apparatus divides a phase into sub-phases more than the number of levels within the set range by a predetermined number, sets a predetermined number of guard phases having a predetermined magnitude near a location where phases of different polarities intersect, and sets the other phases but the guard phases as modulation phases.
  • the multiple phase CDMA modulation apparatus divides a phase into sub-phases based on the number of levels of output signals and sets the divided phases as modulation phases for the different levels.
  • the multiple phase CDMA modulation apparatus multiplies input data of multiple channels by the respective orthogonal codes to perform CDMA modulation with respect to the individual channels in step S130.
  • the sum of modulated signals of the individual channels is calculated in step S140.
  • step S150 the multiple phase CDMA modulation apparatus truncates the sum of the modulated signals within the range of an output level set in step S110. Different levels of the sum of the modulated signals within the set range are allocated to predefined modulation phases, respectively, in step S160.
  • the multiple phase CDMA modulation apparatus selects a sub-phase from a set of the modulation phases which are selected in step S120 excluding the guard phases.
  • FIG. 3A is a waveform diagram for explaining a procedure of truncating an output level of a CDMA modulated signal to a predetermined range according to the embodiment of the present invention.
  • waveforms (a) through (g) show input signals of seven channels to be modulated.
  • a waveform (h) shows the sum of the input signals (a) through (g).
  • a waveform (i) shows an example in which the waveform (h) is truncated to the range ⁇ 3 of a level.
  • FIG. 3B is a diagram showing an example of an output signal of truncated levels and examples of modulation phases allocated for transmission of the output signal according to the embodiment of the present invention.
  • a waveform (a) shows an output signal of truncated levels, that is, an output signal whose levels are truncated to ⁇ 3.
  • (b) and (c) show the examples of modulation phases allocated to the individual levels of the output signal (a) in FIG. 3B.
  • (b) shows modulation phases when a phase near 180° is set as a guard phase
  • (c) in FIG. 3B shows modulation phases when a previous modulation phase is set as a guard phase.
  • a guard phase is set to 180°
  • a modulation phase allocated to a level of -3 is set to -135°
  • a modulation phase allocated to a level of -2 is set to -90°
  • a modulation phase allocated to a level of -1 is set to -45°
  • a modulation phase allocated to a level of 0 is set to 0°
  • a modulation phase allocated to a level of 1 is set to 45°
  • a modulation phase allocated to a level of 2 is set to 90°
  • a modulation phase allocated to a level of 3 is set to 135°.
  • the multiple phase CDMA modulation apparatus calculates a current modulation phase according to Formula (1).
  • FIG. 4 is a flowchart of a CDMA demodulation method for demodulating a signal which has been modulated according to the embodiment of the present invention. Referring to FIG.
  • a multiple phase CDMA demodulation apparatus restores phases of a received signal to levels in step S210, synchronizes the levels of the received signal in step S220, and demodulates the received signal using orthogonal codes used during modulation in step S230.
  • This demodulation procedure is similar to a typical phase shift keying (PSK) demodulation method. Thus, a detailed description thereof will be omitted.
  • FIG. 5 is a graph of bit error rate (BER) characteristic curves of signals modulated in the manner of multiple phase CDMA according to the embodiment of the present invention. More specifically, FIG.
  • FIG. 5 shows BER characteristics of a signal modulated in the manner of conventional DS/CDMA and signals modulated according to the embodiment of the present invention when 8, 16, 32, and 64 input channels are used for the signals, respectively, and an output level is truncated to "6".
  • all of the modulated signals except the signal having 64 input channels have similar BER characteristics to the signal modulated in the manner of conventional DS/CDMA.
  • the modulated signal having 64 input channels has a similar characteristic curve to the signal modulated in the manner of conventional DS/CDMA until a point where a BER is 10 "3 .
  • audio signal receivers demodulate audio signals using a signal having a BER of no greater than about 10 "3 Accordingly, there is no problem in applying a signal whose level is truncated according to the embodiment of the present invention to audio communications.
  • the present invention allows the output level of a transmitting circuit to be maintained constant in a spread spectrum system applying a DS/CDMA method, thereby increasing the power efficiency of the spread spectrum system and remarkably simplifying the structure of a receiving circuit.
  • the present invention enable multichannel CDMA signals to be easily employed by conventional M-ary PSK transmit-receive apparatus using a TDMA method. Therefore, the present invention can overcome the problems of difficulties in designing and realizing a system occurring when transmission speed increases in wireless communications. In other words, the present invention can cope with the future wireless communication environment where a transmission speed is faster than now.

Abstract

Multiple phase code division multiple access (CDMA) modulation and demodulation methods and apparatuses are provided. According to the methods and apparatuses, the range of an outlet level of a modulated signal and modulation phases for modulating a signal of different levels are set. A CDMA-modulated signal is truncated to the set output level range. Different levels of the modulated signal within the output level range are allocated to the modulation phases, respectively, the modulated signal is transmitted at the modulation phases, and the modulated signal is demodulated. Accordingly, the level of a transmitting signal is maintained constant so that power efficiency is increased and a receiving circuit is remarkably simplified. In addition, multichannel CDMA signals can be easily employed by an existing M-ary PSK transmit-receive apparatus using a TDMA method.

Description

MULTIPLE PHASE CDMA MODULATION AND DEMODULATION METHOD AND APPARATUS
Technical Field The present invention relates to a code division multiple access
(CDMA) modulation and demodulation method and apparatus, and more particularly, to a method and apparatus for truncating an output level to a predetermined range and modulating data using as many sub-phases as the number of levels within the truncated range, and a method and apparatus for demodulating the modulated data.
Multiplexing technology for wireless communication is classified into frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA).
Of those, the CDMA is multiplexing technology based on spread-spectrum system technology and is referred to as spread-spectrum multiple access (SSMA). The CDMA has been settled as an international standard in the IMT-2000 system, which is referred to as third generation mobile communications, beating the TDMA due to its superiority in general characteristics in spite of its complexity in realization.
From the historical perspective, the principle of spread-spectrum originated from the concept that interference can be minimized by spreading the spectrum of a signal and had been developed during the 1st World War and the 2nd World War. Spread-spectrum system technology has become a subject of intense research since 1950s to be mainly used for military communications and satellite communications. With the evolution of semiconductor technology in integrity and operating speed as well as the development of microprocessor technology, the spread-spectrum system has been used in commercial mobile communications in addition to the military communications and the satellite communications.
Background Art
Spread-spectrum systems are classified into direct-sequence (DS) spread-spectrum systems, frequency-hopped (FH) spread-spectrum systems, and time-hopped (TH) spread-spectrum systems depending on the methods of spreading the bandwidth of a signal.
DS spread-spectrum systems referred to as DS/CDMA systems employ a manner of spreading the frequency bandwidth by directly modulating a carrier, onto which a data sequence is modulated, with a broadband spreading signal. Here, the spreading signal composed of +1 and -1 is referred to as a spreading sequence, spreading code, or code sequence.
The signal which has been modulated with a spreading signal and has been transmitted from a transmitter is received at a receiver in a distorted form due to noises, interferences, signal disturbances, or the like. Then, the receiver multiplies the received signal by the same spreading signal as used by the transmitter to recover the original spectrum. This operation is referred to as de-spreading. According to DS/CDMA, signals of multiple channels are linearly summed, and the result of summation is transmitted, so that the signals of multiple channels can be simultaneously transmitted. Thus, an increase in the number of channels results in an increase of the number of output signal levels in DS/CDMA. In other words, the amplitude of an output signal in DS/CDMA varies in time varies with the lapse of time like an analog signal. Therefore, as the number of input channels increases, spread-spectrum systems employing DS/CDMA become complicated. This characteristic of DC/CDMA will result in difficulties in designing and realizing systems when the transmission rate of wireless communications goes higher in the future. Disclosure of the Invention
To solve the above problems, it is a first object of the present invention to provide a multiple phase code division multiple access (CDMA) modulation method and apparatus for truncating the sum of signals to the predetermined range of a level and transmitting data with as many divided phases as the number of levels within the truncated range.
It is a second object of the present invention to provide a multiple phase CDMA demodulation method and apparatus for demodulating the above modulated data .
To achieve the first object of the present invention, there is provided a multiple phase CDMA modulation method including a first step of setting the range of a output level of a modulated signal; a second step of dividing a phase into sub-phases to transmit an output signal of different levels within the set range at different phases and setting modulation phases using the divided phases; a third step of multiplying input data of multiple channels by orthogonal codes and calculating the sum of the data; a fourth step of truncating the sum of data calculated in the third to the range of the output level set in the first step; a fifth step of selecting a phase to be allocated each of the different levels of an output signal within the output level range from among the modulation phases set in the second step; and a sixth step of transmitting the output signal having the modulation phases allocated to the different levels.
There is also provided a multiple phase CDMA modulation apparatus including a modulator for multiplying input data of multiple channels by respective orthogonal codes and calculating the sum of the results of multiplication to generate a CDMA-modulated signal; a level truncator for truncating an output level of the modulator within a predetermined range; a phase converter for mapping the different levels of an output signal from the level truncator to predetermined modulation phases; a transmitter for transmitting the output signal of the different levels at the modulation phases allocated to the respective different levels; and a controller for controlling the modulator, the level truncator, the phase converter, and the transmitter under external control.
To achieve the second object of the present invention, there is provided a multiple phase CDMA demodulation method including a first step of restoring phases of a received signal to levels based on phase information used during modulation; a second step of synchronizing the restored levels of the received signal according to a predetermined synchronous code; and a third step of restoring the synchronized signal to an original signal using orthogonal codes used during the modulation. There is also provided a multiple phase CDMA demodulation apparatus including a receiver for receiving a signal which has been modulated in the manner of multiple phase CDMA; a phase discriminator for restoring phases of the signal received through the receiver to levels; a synchronous and demodulating circuit for synchronizing the levels of the received signal restored by the phase discriminator and demodulating the received signal using orthogonal codes used during the modulation; and a code generator for generating the orthogonal codes used during the modulation and outputting them to the synchronous and demodulating circuit for demodulation.
Brief Description of the Drawings
FIG. 1 is a schematic block diagram of a multiple phase code division multiple access (CDMA) modulation apparatus according to an embodiment of the present invention. FIG. 2 is a schematic block diagram of a multiple phase CDMA demodulation apparatus for demodulating a signal modulated according to an embodiment of the present invention.
FIG. 3 is a flowchart of a multiple phase CDMA modulation method according to an embodiment of the present invention. FIG. 3A is a waveform diagram for explaining a procedure of truncating an output level of a CDMA-modulated signal according to the embodiment of the present invention.
FIG. 3B is a diagram showing an example of an output signal of truncated levels and examples of modulation phases allocated for transmission of the output signal according to the embodiment of the present invention.
FIG. 4 is a flowchart of a CDMA demodulation method for demodulating a signal that has been modulated according to the embodiment of the present invention. FIG. 5 is a graph of bit error rate (BER) characteristic curves of signals modulated in the manner of multiple phase CDMA according to the embodiment of the present invention.
Best mode for carrying out the Invention Hereinafter, preferred embodiments of a multiple phase code division multiple access (CDMA) modulation apparatus and method according to the present invention will be described in detail with reference to the attached drawings.
FIG. 1 is a schematic, block diagram of a multiple phase CDMA modulation apparatus according to an embodiment of the present invention. Referring to FIG. 1 , the multiple phase CDMA modulation apparatus includes a modulator 10, a level truncator 20, a phase converter 30, a transmitter 40, and a controller 50.
The modulator 10 multiplies the input data of each of multiple channels, dn, by one of orthogonal codes, cn, and outputs the sum of the results of multiplication. For this, the modulator 10 includes a code generator 12 for generating the orthogonal codes cn and a modulation circuit 11 for multiplying the orthogonal codes cn by the input data dn, respectively, and summing the results of multiplication. The level truncator 20 truncates the level of a signal output from the modulator 10 within a predetermined range. The predetermined range of an output level can be set to be variable according to system characteristics and may be set by the controller 50.
The phase converter 30 selects a phase to be allocated to each of different levels of a signal output from the level truncator 20 from among predetermined modulation phases. For this, the phase converter 30 divides a phase into sub-phases and sets divided phases as modulation phases under the control of the controller 50.
The transmitter 40 transmits a signal of different levels using the different modulation phases that are allocated to the respective different levels by the phase converter 30. The controller 50 controls the operations of the modulator 10, the level truncator 20, the phase converter 30, and the transmitter 40.
The phase converter 30 sets a guard phase to prevent an error from occurring due to between phases having different signs and defines the divided phases except the guard phase as the modulation phases. For this, the phase converter 30 sets the guard phase to a predetermined range under the control of the controller 50.
A phase of near 180° or a previous modulation phase may be set as the guard phase.
When a phase of near 180° is to be set as a guard phase, the phase converter 30 divides a phase into a plurality of sub-phases more than the number of levels within the predetermined range of an output level by a predetermined number, and sets a predetermined number of guard phases having a predetermined magnitude near positions (±180°) where phases having different polarities intersect each other. Here, the entire range of the guard phases can be variable depending on the operating characteristics of a system. Generally, when it is intended to transmit a frequency of a broad band even through the transmission characteristic of the system drops slightly, the range of a guard phase is narrowed. When an excellent transmission characteristic is necessary even though a frequency band transmittable is narrowed in a system, the range of a guard phase is widened.
Alternatively, when a previous modulation phase is to be set as a guard phase, the phase converter 30 sets a modulation phase of the previous phase as a guard phase for each current one of the divided sub-phases, sets a phase which is different from the guard phase by 180° as reference phase, and resets a phase different from the reference phase by the current sub-phase as a current modulation phase.
FIG. 2 is a schematic block diagram of a multiple phase CDMA demodulation apparatus for demodulating a signal modulated according to an embodiment of the present invention. Referring to FIG. 2, the multiple phase CDMA demodulation apparatus includes a receiver 60 for receiving data modulated through multiple phase CDMA, a phase discriminator 70 for recovering the phase of a signal received through the receiver 60 to a signal level, a synchronous and modulating circuit 80 for synchronizing the signal level and demodulating the signal using an orthogonal code used during modulation, and a code generator 90 for generating an orthogonal code for demodulation and transmitting it to the synchronous and modulating circuit 80. The phase discriminator 70 recovers the phase of a received signal to the level of the signal.
FIG. 3 is a flowchart of a multiple phase CDMA modulation method according to an embodiment of the present invention. Referring to FIG. 3, a multiple phase CDMA modulation apparatus sets the range of an output level in order to limit the output level of modulated signals in step S110. Next, the multiple phase CDMA modulation apparatus divides a phase into sub-phases and sets modulation phases with respect to the divided phases in order to transmit output signals of different levels within the set range at different phases in step S120
The modulation phases may be set in different manners according to a method of setting guard phases. In other words, when guard phases are set near 180°, the multiple phase CDMA modulation apparatus divides a phase into sub-phases more than the number of levels within the set range by a predetermined number, sets a predetermined number of guard phases having a predetermined magnitude near a location where phases of different polarities intersect, and sets the other phases but the guard phases as modulation phases. Alternatively, when previous modulation phases are set as guard phases, the multiple phase CDMA modulation apparatus divides a phase into sub-phases based on the number of levels of output signals and sets the divided phases as modulation phases for the different levels. Then, the multiple phase CDMA modulation apparatus_sets a modulation phase of the previous phase as a guard phase for each current one of the divided phases (sub-phases), sets a phase which is different from the guard phase by 180° as a reference phase, and resets a phase different from the reference phase by the current sub-phase as a current modulation phase.
After completing the setting of modulation phases, the multiple phase CDMA modulation apparatus multiplies input data of multiple channels by the respective orthogonal codes to perform CDMA modulation with respect to the individual channels in step S130. The sum of modulated signals of the individual channels is calculated in step S140. Next, in step S150, the multiple phase CDMA modulation apparatus truncates the sum of the modulated signals within the range of an output level set in step S110. Different levels of the sum of the modulated signals within the set range are allocated to predefined modulation phases, respectively, in step S160. Here, the multiple phase CDMA modulation apparatus selects a sub-phase from a set of the modulation phases which are selected in step S120 excluding the guard phases.
Thereafter, the multiple phase CDMA modulation apparatus transmits a signal of different levels, which are allocated to the different modulation phases, using the different modulation phases in step S170. FIG. 3A is a waveform diagram for explaining a procedure of truncating an output level of a CDMA modulated signal to a predetermined range according to the embodiment of the present invention. In FIG. 3A, waveforms (a) through (g) show input signals of seven channels to be modulated. A waveform (h) shows the sum of the input signals (a) through (g). • A waveform (i) shows an example in which the waveform (h) is truncated to the range ±3 of a level.
FIG. 3B is a diagram showing an example of an output signal of truncated levels and examples of modulation phases allocated for transmission of the output signal according to the embodiment of the present invention.
In FIG. 3B, a waveform (a) shows an output signal of truncated levels, that is, an output signal whose levels are truncated to ±3. In FIG. 3B, (b) and (c) show the examples of modulation phases allocated to the individual levels of the output signal (a) in FIG. 3B. In FIG. 3B, (b) shows modulation phases when a phase near 180° is set as a guard phase, and (c) in FIG. 3B shows modulation phases when a previous modulation phase is set as a guard phase.
Referring to (a) and (b) in FIG. 3B, a guard phase is set to 180°, a modulation phase allocated to a level of -3 is set to -135°, a modulation phase allocated to a level of -2 is set to -90°, a modulation phase allocated to a level of -1 is set to -45°, a modulation phase allocated to a level of 0 is set to 0°, a modulation phase allocated to a level of 1 is set to 45°, a modulation phase allocated to a level of 2 is set to 90°, and a modulation phase allocated to a level of 3 is set to 135°. Meanwhile, when a previous modulation phase is set as a guard phase, the multiple phase CDMA modulation apparatus calculates a current modulation phase according to Formula (1).
Current modulation phase = Previous modulation phase + 180° + Current absolute phase • • (1)
In the case where the initial modulation phases of the output signal (a) of FIG. 3B are set as shown in (b) of FIG. 3B, when the multiple phase CDMA modulation apparatus is to set a previous modulation phase as a guard phase, a modulation phase allocated to a second level, "-2", of the output signal is set to -45° according to Formula (1). The results of applying Formula (1) with respect to the individual levels of the output signal (a) shown in FIG. 3B are shown in FIG. 3B(c). FIG. 4 is a flowchart of a CDMA demodulation method for demodulating a signal which has been modulated according to the embodiment of the present invention. Referring to FIG. 4, a multiple phase CDMA demodulation apparatus restores phases of a received signal to levels in step S210, synchronizes the levels of the received signal in step S220, and demodulates the received signal using orthogonal codes used during modulation in step S230. This demodulation procedure is similar to a typical phase shift keying (PSK) demodulation method. Thus, a detailed description thereof will be omitted. FIG. 5 is a graph of bit error rate (BER) characteristic curves of signals modulated in the manner of multiple phase CDMA according to the embodiment of the present invention. More specifically, FIG. 5 shows BER characteristics of a signal modulated in the manner of conventional DS/CDMA and signals modulated according to the embodiment of the present invention when 8, 16, 32, and 64 input channels are used for the signals, respectively, and an output level is truncated to "6".
Referring to FIG. 5, for the signals modulated according to embodiment of the present invention, all of the modulated signals except the signal having 64 input channels have similar BER characteristics to the signal modulated in the manner of conventional DS/CDMA. In addition, the modulated signal having 64 input channels has a similar characteristic curve to the signal modulated in the manner of conventional DS/CDMA until a point where a BER is 10"3. Generally, audio signal receivers demodulate audio signals using a signal having a BER of no greater than about 10"3 Accordingly, there is no problem in applying a signal whose level is truncated according to the embodiment of the present invention to audio communications.
The above description just concerns embodiments of the present invention. The present invention is not restricted to the above embodiments, and various modifications can be made thereto within the scope defined by the attached claims. For example, the shape and structure of each member specified in the embodiments can be changed.
Industrial Applicability
The present invention allows the output level of a transmitting circuit to be maintained constant in a spread spectrum system applying a DS/CDMA method, thereby increasing the power efficiency of the spread spectrum system and remarkably simplifying the structure of a receiving circuit. In addition, the present invention enable multichannel CDMA signals to be easily employed by conventional M-ary PSK transmit-receive apparatus using a TDMA method. Therefore, the present invention can overcome the problems of difficulties in designing and realizing a system occurring when transmission speed increases in wireless communications. In other words, the present invention can cope with the future wireless communication environment where a transmission speed is faster than now.

Claims

What is claimed is:
1. A multiple phase code division multiple access (CDMA) modulation method comprising: a first step of setting the range of a output level of a modulated signal; a second step of dividing a phase into sub-phases to transmit an output signal of different levels within the set range at different phases and setting modulation phases using the divided phases; a third step of multiplying input data of multiple channels by orthogonal codes and calculating the sum of the data; a fourth step of truncating the sum of data calculated in the third step within the range of the output level set in the first step; a fifth step of selecting a phase to be allocated each of the different levels of an output signal within the output level range from among the modulation phases set in the second step; and a sixth step of transmitting the output signal of the different levels at the modulation phases allocated to the different levels.
2. The multiple phase CDMA modulation method of claim 1 , wherein the second step comprises dividing a phase into sub-phases more than the number of the different levels within the output level range by a predetermined number and setting a predetermined number of guard phases having a predetermined magnitude near a position where phases having different polarities intersect each other.
3. The multiple phase CDMA modulation method of claim 1 or 2, wherein the fifth step comprises allocating the different levels of the output signal to the phases, respectively, other than the guard phases.
4. The multiple phase CDMA modulation method of claim 1 , wherein the second step further comprises a step of (2-1) setting a modulation phase of a previous phase as a guard phase for each current one of the divided sub-phases, setting a phase which is different from the guard phase by 180° as a reference phase, and resetting a phase different from the reference phase by the current sub-phase as a current modulation phase.
5. A multiple phase code division multiple access (CDMA) modulation apparatus comprising: a modulator for multiplying multiple pieces of input data of multiple channels by orthogonal codes and calculating the sum of the multiple pieces of data to generate a CDMA-modulated signal; a level truncator for truncating an output level of the modulator within a predetermined range; a phase converter for allocating different levels of an output signal from the level truncator to predetermined modulation phases; a transmitter for transmitting the output signal of the different levels at the modulation phases allocated to the respective different levels; and a controller for controlling the modulator, the level truncator, the phase converter, and the transmitter under external control.
6. The multiple phase CDMA modulation apparatus of claim 5, wherein the phase converter divides a phase into sub-phases more than the number of the different levels within the output level range by a predetermined number, sets a predetermined number of guard phases having a predetermined magnitude near a position where phases having different polarities intersect each other, and allocates the different levels of the output signal to the phases, respectively, other than the guard phases, under the control of the controller.
7. The multiple phase CDMA modulation apparatus of claim 5,
wherein the phase converter sets a modulation phase of a previous
phase as a guard phase for each current one of the sub-phases, sets a
phase which is different from the guard phase by 180° as a reference
phase, and resets a phase different from the reference phase by the
current sub-phase as a current modulation phase, under the control of the controller.
8. A multiple phase code division multiple access (CDMA) demodulation method comprising: a first step of restoring phases of a received signal to levels based on phase information used during modulation; a second step of synchronizing the restored levels of the received signal according to a predetermined synchronous code; and a third step of restoring the synchronized signal to an original signal using orthogonal codes used during the modulation.
9. A multiple phase code division multiple access (CDMA) demodulation apparatus comprising: a receiver for receiving a signal which has been modulated in the manner of multiple phase CDMA; a phase discriminator for restoring phases of the signal received through the receiver to levels; a synchronous and demodulating circuit for synchronizing the levels of the received signal restored by the phase discriminator and demodulating the received signal using orthogonal codes used during the modulation; and a code generator for generating the orthogonal codes used during the modulation and outputting them to the synchronous and demodulating circuit for demodulation.
10. The multiple phase CDMA demodulation apparatus of claim 9, wherein the phase discriminator restores the phases of the received signal to the levels based on phase information used during the modulation.
PCT/KR2001/001627 2001-02-17 2001-09-27 Multiple phase cdma modulation and demodulation method and apparatus WO2002075949A1 (en)

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