WO2004070971A1

WO2004070971A1 - Polarization coding

Info

Publication number: WO2004070971A1
Application number: PCT/DK2004/000082
Authority: WO
Inventors: Jyoti Prasad; Dikshitulu Kalluri; Veronique Farserotu; Nunta Vanichsetakul
Original assignee: Jyoti Prasad; Dikshitulu Kalluri; Veronique Farserotu; Nunta Vanichsetakul
Priority date: 2003-02-04
Filing date: 2004-02-04
Publication date: 2004-08-19

Abstract

The invention relates to a method and a system for communication employing electromagnetic waves, said method of communication involving polarization coding, whereby said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication. Further, the invention relates to an error correcting code (ECC) employing polarization.

Description

POLARIZATION CODING

Field of the invention

The invention relates to a method of communication employing electromagnetic waves, said method of communication involving polarization coding. Further, the invention relates to a system for communication of electromagnetic waves, wherein a polarization coding of transmitted signals is involved. The invention also relates to a transmitter and a receiver for such a system and/or method, and finally the invention relates to uses hereof.

Background of the invention

In the prior art the use of different polarizations in wireless communication systems has been well known. However, the different polarizations have been employed simply for frequency reuse. The different or multiple polarizations have been used just "pipe", keeping two independent channels in the same frequency.

An example of such a prior art system is disclosed in WO 99/17467 Al. This document discloses a CDMA communication system, wherein a base station generates two orthogonally polarized signals with different polarizations. The signals contain the same information and only the polarization differs, e.g. right slant polarization for one signal and left slant polarization for the other signal. A receiver receives both signals and decodes these. The decoding of these signals is part of the CDMA-arrangement and is not related to the polarization of the signals. The two differently polarized signals according to this prior art are used in order to enhance the average signal quality.

A further example of such a prior art technique is disclosed in EP 0 715 478 A2 that describes a communication system comprising a plurality of nodal transmitters. Each transmitter is able to transmit with different polarizations, e.g. +45° and -45°, in different sectors. Thus, signals emitted in a certain sector will always have the same polarization.

Further, US 5,764,696 A describes a transmitter for transmitting signals with dual or chiral polarization.

US 5,898,362 A describes a system for transmitting and receiving polarized CDMA signals wherein a number of signal data streams TDi to TDN are encoded using separate CDMA codes. The coded signals are converted into frequency, and these signals TSi to TSN are polarized differently in a network before being transmitted. The network involves a phase shifter for each of the signals TSi to TSN, a summation for the phase shifted signals, a summation for the non-phase shifted signals and two differently polarized antennas for transmitting summed signals. However, this prior art system does not involve coding by means of polarization, but uses polarization to enhance separation between CDMA encoded data streams.

US 4,521,878 A describes a system for transmitting and receiving data, wherein a polarization technique is utilized for increasing the data transmission capacity. This is achieved by having a part of the transmitter for modulating data (Dl and D2) and transmitting these by means of a N-polarized wave, and similarly, by having a part of the transmitter for modulating other data (D3 and D4) and transmitting these by means of a H-polarized wave. The V-polarized wave and the H-polarized wave are combined and transmitted via a common antenna. Thus, the data Dl and D2 always correspond to a V-polarization and the data D3 and D4 always correspond to a H- polarization. A coding as such involving polarization is not used.

Thus, it is an objective of the present invention to present an improved method and an improved system for transmitting electromagnetic waves, e.g. electric communication and in particular digital data. Further, it is an objective of the invention to provide a wireless communication method and system that allow the capacity of the system to be enhanced and/or that allow a reduction in power of the signals.

It is in particular an objective of the invention to provide such a system without increasing the bandwidth and/or the necessary power.

Summary of the invention

The invention relates to a method of communication employing electromagnetic waves, said method of communication involving polarization coding, whereby said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication.

Hereby it is achieved that a new dimension due to utilization of multiple polarizations is provided that allows the user to improve and/or to enhance the performance. Hereby performance can be enhanced without increase of bandwidth. It should be emphasized that according to the invention polarization of electromagnetic wave may be incorporated into modulation or multiplex access directly in order to take advantage of getting one more new dimension with respect to the nature of signal in addition to the other three natures, amplitude, phase and frequency.

Further advantages that may be provided by the invention are increase of the channel capacity, reduction of signal transmission power, and expansion of reachable distance of communications.

Preferably, as characterized in claim 2, a polarization coding using at least two different polarization values, e.g. multiple orthogonal polarizations may be utilized.

According to a particular advantageous embodiment as stated in claim 3, an error correcting code (ECC) may be employed. Preferably, as stated in claim 4, said polarization coding may comprise an error correcting code (ECC) involving polarization.

Hereby it is achieved that due to the nature of the invention a new dimension of wireless communication systems by connecting internally and directly the baseband technology: Error Correcting Code (ECC) and RF technology: polarization switching.

According to a preferable embodiment as characterized in claim 5, said method may involve switching between at least two polarizations based on an encoding, e.g. driven by an encoder.

According to a further preferred embodiment as characterized in claim 6, said encoding may advantageously be based on a trellis.

According to a still further preferred embodiment as characterized in claim 7, a method for composition of a trellis for encoding may be involved, whereby the performance may be enhanced.

Advantageously, as characterized in claim 8, a trellis realizing a maximum code distance may be employed, whereby the performance may be further enhanced.

According to a further advantageous embodiment as characterized in claim 9, said method may comprise a decoding at a receiver side, e.g. employing a Niterbi decoder.

According to another advantageous embodiment as characterized in claim 10, said decoding may employ an absolute value of difference between the result of hard- decision and one before decision in both polarizations as the metric. In accordance with a still further advantageous embodiment as characterized in claim 11, said method may involve switching of a transmitted signal in conjunction with a modulation scheme.

Advantageously, as characterized in claim 12, said modulation scheme may be based on a spread-spectrum (SS) scheme.

Hereby improvements in the performance, e.g. improvement of BER performance are provided.

Further, as stated in claim 13, said modulation may employ a Walsh-modulation, e.g. a 2-ary or larger (M-ary) Walsh-modulation.

Still further, as stated in claim 14, said modulation scheme may be based on a multiple polarization shift keying (MPSK) scheme, e.g. a quadruple polarization shift keying (QPSK) scheme.

Also, as stated in claim 15, said modulation scheme may employ a multi-carrier code division multiple access (MC-CDMA)-scheme.

Hereby further applications of the invention are presented, e.g. in connection with mobile communication systems etc.

According to a further advantageous embodiment as characterized in claim 16, said modulation scheme may employ an orthogonal frequency division multiple access (OFDM)-scheme.

Hereby the invention may find utilization in numerous applications, e.g. in connection with WLAN-systems and -techniques etc. According to a particular advantageous embodiment as characterized in claim 17, said method may involve guard time insertion, e.g. insertion of a guard time interval between consecutive symbols.

Hereby the effect of multipath fading may be avoided, for example in connection with the APC technology. Guard time interval may be inserted between two symbols whereby Inter-Symbol Interference (ISI) caused by the fading environment can be absorbed by the guard time.

The invention also relates to a system for communication of electromagnetic waves, wherein a polarization coding of transmitted signals is involved and wherein said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication.

Hereby it is achieved that a new dimension due to utilization of multiple polarizations is provided that allows the user to improve and/or to enhance the performance in comparison with the prior art systems. Hereby performance can be enhanced without increase of bandwidth. It should be emphasized that according to the invention polarization of electromagnetic wave may be incorporated into modulation or multiplex access directly in order to take advantage of getting one more new dimension with respect to the nature of signal in addition to the other three natures, amplitude, phase and frequency.

Advantageously, as stated in claim 19, said system may be designed in accordance with one or more of claims 1 to 17.

Further, the invention relates to a transmitter for transmission of electromagnetic waves, wherein a polarization coding of transmitted signals is involved and wherein said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication.

Advantageously, as stated in claim 21, said transmitter may be designed in accordance with one or more of claims 1 to 17.

The invention also relates to a receiver for reception of electromagnetic waves, wherein a polarization coding of transmitted signals is involved and wherein said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication.

Advantageously, as stated in claim 23, said receiver may be designed in accordance with one or more of claims 1 to 17.

The invention also relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 for wireless communication.

Further, the invention relates to such a use for wireless and mobile communication.

Still further, the invention relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 in connection with cellular communication systems.

The invention also relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 in connection with secure communication systems. In addition to the enhanced efficiency of the invention in comparison with conventional methods and systems, the invention facilitates an enhanced security without requiring larger bandwidth and/or power, whereby the application for secure communication is advantageous.

Also, the invention relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 in connection with a wireless local area network (WLAN).

Hereby an application is provided that allows physical connection between e.g. terminals to be removed while still providing an efficient and secure communication.

Still further, the invention relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 in connection with a wireless local loop (WLL).

Hereby further advantageous applications are provided, e.g. high-speed data communications via radio link for example in connection with the expansion of networks that according to this embodiment of the invention may take place over e.g. several buildings and whereby a reduction in installation costs compared with conventional networks is provided.

Further, telephony networks may be installed and expanded economically in rural area where the infrastructure is poor, and high-speed data communication may be provided economically without replacement of conventional subscriber line where a conventional infrastructure is already present.

The invention also relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 in connection with multiple-input- multiple-output (MIMO) technology.

Further, the invention also relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 in connection with an Intelligent Transportation System (ITS).

Hereby, efficient high-speed data communications may be provided using the invention for road-vehicle communications and intervehicle communications.

Still further, the invention relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 in connection with a High Altitude Stratospheric Platform Station (HAPS).

Hereby the invention may find utilization in connection with such systems that for some considerations seem to be similar to satellite communications but realize robust communication systems, e.g. robust against natural disasters that can destroy terrestrial infrastructure completely. Other advantages are also present such easily obtainable LOS (Line of Sight)-path and negligible effect of multipath.

Finally, the invention relates to use of a method according to one or more of claims 1 - 17, a system according to claim 18 or 19, a transmitter according to claim 20 or 21 and/or a receiver according to claim 22 or 23 in connection a Wireless Home Area Network (WHAN).

Further objectives and advantages related to the present invention will be described in the following. The figures

The invention will be described in further detail below with reference to the drawings of which

Fig. 1 illustrates utilization of multiple polarizations in conventional systems and the polarization coding according to the invention,

Fig. 2 shows an overview of the relationship between embodiments of the invention, F Fiigg..3 3 illustrates the principle of a Spread Spectrum system,

Fig. 4 shows a transmitter structure based on TC-SSP (Trellis Coded-Spread

Spectrum based on multiple Polarizations),

Fig. 5 shows a receiver structure based on TC-SSP,

Fig. 6 illustrates the relationship between RHCP (Right Hand Circular Polarization) and LHCP (Left Hand Circular Polarization) in TC-SSP,

Fig. 7 illustrates the design of a trellis of an encoder in PDMA (Polarization

Division Multiplex Access),

Fig. 8 is a comparison of BER (Bit Error Rate) performance between TC-SSP and conventional DS-SS, F Fiigg..9 9 shows a trellis of K = 4 with the maximum code distance,

Fig. 10 shows an example of a WLAN (Wireless Local Area Network) system,

Fig. 11 shows a service image of Hot Spot, e.g. in an airport, a station etc.,

Fig. 12 shows an example of a WLL (Wireless Local Loop) system,

Fig. 13 illustrates a subscriber line by WLL, F Fiigg..1 144 shows an Intelligent Transportation System (ITS),

Fig. 15 illustrates a High Altitude Stratospheric Platform Station (HAPS),

Fig. 16 shows transmitter and receiver configurations of a realization on SS in accordance with the invention,

Fig. 17 shows BER versus E_b N₀ obtained by APC on SS, F Fiigg..1 188 shows transmitter and receiver configurations of a realization on MPSK

(Multiple Phase Shift Keying) in accordance with the invention, Fig. 19 shows signal points in QPSK (Quadruple Phase Shift Keying) modulation and the mapping of C₂ and C₃, Fig. 20 shows BER versus E_b/N₀ obtained by APC on QPSK,

Fig. 21 shows a transmitter configuration of APC (Antenna Polarization

Codulation), Fig. 22 illustrates guard time insertion between two symbols, Fig. 23 shows an example of implementation of APC with guard time insertion, and Fig. 24 illustrates an application of APC (Antenna Polarization Codulation) on

OFDM (Orthogonal Frequency Division Multiplexing).

Detailed description

In the following a number of technologies and examples will be described, all using the inventive concept of "polarization coding" in accordance with the present invention.

The polarization coding concept according to the invention employs polarizations of electromagnetic wave in error correcting coding to enhance performance of communication. This concept allows the user to enhance capacity of communication systems or to reduce the power of signals without any increase of bandwidth and power. Due to this nature of the concept, these technologies pioneers a new dimension of wireless communication systems by connecting internally and directly the baseband technology: Error Correcting Code (ECC) and RF technology: polarization switching.

It should be emphasized that this new method and system of coding by using a new dimension, polarization, is a method and system that has not been used yet. Therefore, it should also be emphasized that these new technologies in accordance with the invention are completely different from conventional frequency reuse by using multiple orthogonal polarizations.

Figure la and lb illustrate such difference of utilization of multiple polarizations between the simple frequency reuse and our technologies, respectively. Thus, Figure la illustrates frequency reuse by using two polarizations, where the two channels are independent, both polarization signals are always turned on, and where the two channels are just "pipe". Figure lb illustrates a method of polarization coding in accordance with the invention, wherein the polarization itself conveys information, wherein transition of polarizations mean information, and wherein the two polarization signals are intermittent.

Although usage of multiple polarizations in wireless communication systems has been well known conventionally, they have been employed simply for frequency reuse. The multiple polarizations have been just used as "pipe", keeping two independent channels in the same frequency. Here, it should be noted that these polarizations are never involved in modulation or ECC (Error Correcting Code) directly in such type of conventional usage of multiple polarizations.

On the other hand, the new technologies in accordance with the invention based on the polarization coding, are realized by involving polarizations into ECC directly so that transitions of the multiple polarizations themselves convey certain information in order to facilitate the communication. This utilization of multiple polarizations brings new dimension that allows the user to improve and/or to enhance the performance. Due to the fact that ECC is performed involving polarization, as the new dimension, these technologies enhance performance without any increase of bandwidth even though they are taking advantage of the coding merit of ECC .

In the following the invention will be exemplified in connection with a number of technologies and applications and in particular the polarization coding concept will be applied on the following communication systems as illustrated in fig.2: - Application 1 : Application on Code Division Multiple Access (CDMA)

- Application 2: Application on M-ary Phase Shift Keying (MPSK) and M- ary Spread Spectrum (SS)

Although there are a number of advantages brought by the new technologies, the description below focuses on the following advantages:

- Increase of the channel capacity - Reduction of signal transmission power: 3dB - 6dB

- Expansion of reachable distance of communications (coverage area in terms of mobile communications): approximately 2 times (only the free space loss is considered based on 6dB gain in 2 - 5 GHz band)

In the following an embodiment of the invention, which will be referred to as TC- SSP (Trellis Coded-Spread Spectrum based on multiple Polarizations), will be described. This new scheme can be recognized as an additional technology to Polarization Division Multiplex Access (PDMA) that is the subject of PCT/DK01/00050, published as WO 02/060076 Al on 1 August 2002.

Conventionally, various modulations and multiplex access schemes for radio communications have been studied pursuing spectral-efficient ones. Those conventional schemes have been in terms of amplitude, phase and frequency even though there are some combinations of those natures of signal (cf. J. G. Proakis. DIGITAL COMMUNICATIONS. McGraw-Hill Book Co., 1995). Based on such historical background, here, it is possible to say that the new technologies in accordance with the invention are the first pioneering approach for the invention of new efficient modulation and multiplex access scheme employing polarizations of electromagnetic wave. It should be emphasized that the new technologies incorporate polarization of electromagnetic wave into modulation or multiplex access directly in order to take advantage of getting one more new dimension with respect to the nature of signal in addition to the other three natures, amplitude, phase and frequency, as mentioned above.

This new technology can improve performance of digital radio communication systems such as:

- Channel capacity

- Security of communications - Robustness against low Signal-to-Noise power Ratio (SNR) environments

- Reachable distance of communications (coverage area in terms of mobile communications) This new technology can be characterized by:

- Switching of the two different polarizations is driven by the encoder.

- For enhancing performance, this new technology provides a method for composition of trellis for encoding. The trellis is composed so as to avoid assigning codes that are transmitted in different polarizations at transitions to one same node in the trellis.

- Niterbi decoder at the receiver side employs the absolute value of difference between the result of hard-decision and one before decision in both polarizations as the metric.

The in-depth description of the new TC-SSP-technology is given later on.

The relationship between this new technology and PDMA (cf. PCT DK01/00050) is explained as follows. PDMA improves performance of conventional spread- spectrum (SS) systems with simple configuration. However, by sacrificing its complexity, its performance can be improved more by employing the trellis encoder and Viterbi decoder. In addition, PDMA requires high speed RF switching in order to switch polarizations depending on the spreading code. Therefore, polarization switching in the chip rate is required. In the case of wide-band SS systems, this requirement becomes very tight. In TC-SSP, the RF switching is required in the symbol rate. Table 1 below summarizes those comparisons between the two technologies.

Table 1 : Comparison between PDMA (given by PCT/DK01/00050) and TC-SSP

PDMA TC-SSP

Simplicity + -

Performance - +

Feasibility of RF - + Switch Prior to the description of TC-SSP technology in accordance with the invention, the principle of DS-SS; Direct Sequence - Spread Spectrum system will be briefly introduced.

Figure 3 illustrates the principle of the spread spectrum system (cf. R. Prasad. CDMA for Wireless Personal Communications. Artech House Publishers, 1996.).

In the spread spectrum system, spectrum of data signal is spread by multiplying (at 4) Pseudo random Noise (PN) code whose speed is much faster than that of the data signal 2. Let T_s and T_c denote the symbol duration of the data sequence and chip duration of the PN code, respectively. Then, the processing gain γ is defined as:

r=- (i)

Although the system depicted in the figure employs γ = 5 for the simplicity, it is typically defined as more than 10. By the spreading achieved by the multiplication of PN code to data sequence, robustness against interferers, security of communication and so on are enhanced.

Figures 4 and 5 show the transmitter and receiver structures, respectively, implementing TC-SSP technology in accordance with an embodiment of the invention.

For example, Right Hand Circular Polarization (RHCP) and Left Hand Circular Polarization (LHCP) may be employed as a combination of two different polarizations. It should be noted that there are other types of combination including two different polarizations such as horizontal and vertical polarizations, for instance.

First, the data sequence 2 composed by binary symbols (0,1) is encoded by a half- rate (r = 1/2) convolutional encoder 8 whose constraint length is K. Note that this encoder 8 generates two bits Co and Ci in the same time corresponding to one bit of input. Second, only C\ is BPSK-modulated by a BPSK (Binary Phase Shift Keying)-modulator 9 and multiplied (at 10) by PN code whose length is bits so as to spread its bandwidth M times. Note that the BPSK-modulated C_\ is composed by (+1,-1). The spread Ci is transmitted by one of the two different polarization antennas 13 and 14 depending on another bit Co, such like, for example, the spread Co is transmitted in RHCP when Co = 1 while the spread signal is transmitted in LHCP when Co = 0. As illustrated the switching is facilitated by a polarization switch 12 controlled by the polarization selection signal, e.g. Co.

According to this structure, the two antennas corresponding to RHCP 13 and LHCP 14 transmit signal alternatively, not in the same time. Figure 6 illustrates such nature of transmitted signals over the time axis. It is obvious that there is no chance to send signal in the two polarizations simultaneously. Moreover, it follows that the sign (+ or -) of the transmitted signal corresponds to C\ while the polarization that send the signal corresponds to Co. Therefore, it is possible to say that the polarization itself conveys information in this system.

In order to maximize the performance of this system, the trellis of the encoder is designed as shown in Figure 7. Although this figure shows the design of 4-state trellis as an example due to its simplicity, the principle is applicable for larger scale trellis without any problem. In this trellis, two paths go to, as illustrated by the reference 28, or come from, as illustrated by the reference 26, the same node are always assigned code that should be transmitted in the same polarizations.

The receiver, which receives the transmitted signal by means of two antennas, e.g. LHCP-antenna 15 and RHCP-antenna 16, corresponding to the transmitter illustrated in Figure 5 achieves soft decision in conjunction with a Niterbi decoder 20. The decoder 20 employs the absolute value of difference between the result, of hard- decision and one before decision in both polarizations. Here, chip synchronization and symbol synchronization are assumed to be acquired already for the simplicity. Then, suppose that χ_p[&T_c] denotes the received signal where the subscript _p varies from 0 to 1 corresponding to the two polarizations, i.e., p = 0 means LHCP while/? = / means RHCP. k is an integer that indicates time so that it varies from -∞to ∞ . Then, the outputs of the two matched filter 18, e.g. Barker code matched filters, illustrated in Figure 5 are expressed as follows:

where £ is an integer that indicates time so that it varies from -∞to ∞ . wfmj is the m-th matched filter weight. It should be noted that the bit rate of the outputs y_p[£T_s] is down-sampled from l/T_c to 1/T_S.

From those two outputs, the metric is obtained (e.g. using the metric calculation 19) as:

p_p[£T_s]=\ \ - y_p[£T_s] \ (3)

where \a\ denotes the absolute value of the value a. Niterbi decoder 20 decodes the received signals based on the metric, and finally a S/P-conversion at 22 is performed giving the output data 24.

This new technology can be characterized by:

-Switching of the two different polarizations equipped with the apparatus are driven by the encoder.

-Niterbi decoder at the receiver side employs the absolute value of difference between the result; of hard-decision and one before decision in both polarizations as the metric.

Performance improvement by using TC-SSP may be examined through computer simulations, which are presented here. Figure 8 compares BER versus Eέ/Νo [dB] between conventional DS-SS system and TC-SSP as explained in-depth in the previous section. Here, Ei/N₀ is defined as signal power par 1 data bit to noise power at the unit bandwidth ratio. Furthermore, 31 -bit M-sequence is employed as a spreading code in both systems. Then, γ = 31.

For TC-SSP, three different constraint lengths of encoder K varied as 3, 7 and 8 are examined. It is observed that the performance of TC-SSP is enhanced as K increases. By comparing the performance of TC-SSP with K = 3 and conventional DS-SS system at 1 x 10^"4 BΕR, it is obviously shown that TC-SSP improves the performance by 3dB. It should be noted that the improvement is enhanced as E&/No and/or K increase.

The trellis used in those simulations are generated as follows. Here, a case in which K = 4 is explained for the simplicity. According to J. G. Proakis. DIGITAL COMMUNICATIONS. McGraw-Hill Book Co., 1995, the trellis which realizes the maximum code distance is as shown in Figure 9. In this figure, solid lines correspond to the encoder input 0 while dotted lines correspond to the encoder input 1. The numbers put on each line specifies encoder output corresponding to the state transition. Now, this trellis is expressed by the following two matrices, namely state matrix S₃ and output matrix O₃:

It should be noted that rows and columns of those two matrices correspond to the states (0,1,2,3) and input bit (0,1) of the encoder, respectively. In the matrix O3, the included numbers 0,1,2 and 3 corresponds to the following codes: Number Co c,

0 0 0

1 0 1

2 1 0

3 1 1

Suppose- that C₀ = 0 means LHCP while Co = 1 means LHCP. Then, The outputs '0' and T are assigned in LHCP while the outputs '2' and '3' are assigned in RHCP. In order to achieve the trellis as described in Figure 7, it is necessary to make a pair of output as (0,1) and (2,3) in the same row of O₃ so that O₃ is rewritten as:

This modification of O₃ is automatically performed by the regulation as

Original Modified 0 ^ 0

1 - 2

2 ^ 3

3 - 1

The modified O₃ and S₃ had been used in the simulation in which K = 3. For K = 7 and 8, state matrices and output matrices are given in the same way as: 1. State matrix and output matrix that achieve the maximum code distance are chosen. They are listed in literatures, for example J. G. Proakis. DIGITAL COMMUNICATIONS. McGraw-Hill Book Co., 1995. 2. Output matrix is modified as mentioned above.

3. Those state and output matrices are employed in PDMA configuration as mentioned above.

In the following descriptions concerning the application of TC-SSP technology in accordance with the invention on WLAN, WLL, mobile communications, ITS and HAPS are presented. Wireless Local Area Network (WLAN) system provides IP access via radio link so that it is possible to remove physical connection between terminals, e.g. computers 34 in an office environment 30, and a backbone 32 of the network. Figure 10 shows the image of a WLAN system using WLAN-transmitters 36 communicating with a PDMA-transmitter 38 in accordance with the invention.

In addition to the application, usage of WLAN technology for broadband wireless access including "Hot Spot" concept is an attractive application of PDMA where it can enhance its performance. Figure 11 illustrates service image of Hot Spot. In cafeteria, airports, stations and so on, a base station 40 is equipped to provide internet connection. It enables mobile terminals, e.g. 42 and 44, to access internet services via high-speed radio link. However, this service coverage is limited to a very small area. IEEE802.il in United States, Hyperlau2 in Europe and MMAC (cf. http://www.arib.or.jp/mmac/what.html) in Japan have been considered as standards that define specifications including air-interface.

Since this system aims at providing multimedia contents, high-speed data transmission system is required. Here, it is expected that PDMA can play a significant role in those two WLAN applications. Furthermore, large markets are expected due to the fact that this application includes not only professional/business use but also personal use.

The advantage of TC-SSP applied on WLAN system can be summarized as follows:

- Channel capacity: Channel capacity is enhanced by using TC-SSP by taking advantage of utilization of polarizations as a new dimension that conveys information. - Coverage area: By comparing TC-SSP to the conventional system, coverage area can be widened if it is possible to keep same power and performance requirement.

- Power reduction: Being relevant to the previous point, power can be reduced if the distance and performance requirement are identical comparing to the conventional system.

- Security of communications: Signals are transmitted over the two different polarization channels that are chosen randomly in TC-SSP. This nature enhances security of communication due to the fact that it is difficult to track the switching of the two channels.

Recently, Wireless Local Loop (WLL) has been paid attention due to its easy installation and high data rate. The image of WLL system is shown in Figure 12. Typically at office buildings 46, many computers 50, e.g. in different offices 48, and so on are connected to the backbone 52. Here, suppose one case in which the- network has to be expanded over different buildings 46 as shown. In such case, the extension of network via cables over different buildings is often not easy and not economical due to the installation of new cable including reconstruction of buildings. In contrary, WLL provides high-speed data communications via radio link 54 so that it allows us to expand network easily over several buildings and to reduce installation cost.

In addition to the professional use, WLL is expected to be used for subscriber lines instead of those via cables, such as illustrated in Figure 12, where a base station 59 is shown in conjunction with subscribers in e.g. a home 56 and apartments 58 in a condominium 57. The subscriber line application of WLL is currently aimed at following two objectives (cf. Wireless Access Systems (WAS) Study Group ITU-R (ITU: International Telecommunication Union). http://www.itu.int/ITU-R/studv-groups/was^').: - To install and expand telephony networks economically in rural area where infrastructure is poor.

- To provide high-speed data communication economically without replacement of conventional subscriber line where conventional infrastructure is ready.

Although the first one can be a target application of a product in accordance with the invention, the second one is more interesting. In the second application, mail target is to provide high-speed data communications link, mainly for internet access, via radio link so that data rate is a critical point. Therefore, it is forecasted that the technologies according to the present invention that enhance data rate and capacity will be highly competitive in the market. Furthermore, the market of this type of application of WLL will grow up rapidly due to the fact that this system includes personal use, not only professional use.

The advantage of TC-SSP applied on WLL system can be summarized as follows:

Channel capacity: Channel capacity is enhanced by using TC-SSP by enhancing the performance.

Coverage area: By comparing TC-SSP with the conventional system, coverage area can be widened if it is possible to keep same power and performance requirement.

Power reduction: Being relevant to the previous point, power can be reduced if the distance and performance requirement are identical comparing to the conventional system.

In the following, other applications of TC-SSP technologies are briefly mentioned.

Intelligent Transportation System (ITS), cf. e.g. O. Andrisano M. Nakagawa, R. Verdone. Intelligent transportation system: The role of third generation mobile radio network. IEEE Communications Magazine, 38(9):144-151, September 2002. and S. Ohmori N. Nakajima, Y. Yamao. The future generations of mobile Communications based on broadband access technologies. IEEE Communications Magazine, 38(12):134-142, December 2000

is a new technology that combines mobile communications and traffic systems to solve problems such as traffic accidents, congestion and so on. This system is composed mainly by road-vehicle communications and intervehicle communications. Figure 14 illustrates such a system. Particularly in the road- vehicle communications, high-speed data communications are required between a local base station 62 which is equipped along with the trunk road and vehicles 60 in order to enable downloading of large amounts of data such as navigation data, multimedia contents for entertainment including music, movies, games etc. For such application, TC-SSP can be an attractive, mean to provide efficient highspeed data communications. Since effect of multipath fading is basically not severe in ITS system because of the fact that millimeter-wave is employed, it is suitable application of our technologies. Moreover, capacity improvement by our technologies allows us to take advantage of efficient high-speed data link.

High Altitude Stratospheric Platform Station (HAPS) (cf. S. Ohmori N. Nakajima, Y. Yamao. The future generations of mobile Communications based on broadband access technologies. IEEE Communications Magazine, 38(12):134-142, December 2000) is also one of new systems that have been attracting much attentions. Although the system seems to be similar to satellite communications, airships 64 are employed instead of communication satellites for playing the same roll in satellite communication systems as shown in Figure 15. Such system realizes robust communication system against natural disasters that can destroy terrestrial infrastructure completely. Such a system may as illustrated comprise communication with content providers 65, homes 67, vehicles 68, emergency or rescue vehicles 70, broadcasting units 66, mobile receivers and/or transmitters 71, computers, e.g. mobile computers and communication units 69, PSTN/PSDN- arrangements 72 etc.

Moreover, it is also advantageous that airships can be launched much less expensive than satellites.

Such system is also suitable target application for TC-SSP due to the reason that it is always possible to obtain LOS path and the effect of multipath is negligible due to its high elevation angle. TC-SSP will provide efficient high-speed data communication in this system.

In the above, TC-SSP technology and its applications have been described including in-depth technical information for each applications and its performance examined through computer simulations and theoretical considerations.

Although there may be various types of applications in terms of this embodiment of the invention, the new technology, TC-SSP, this document has focused mainly on WLAN, WLL and mobile communications. In addition, their application for ITS and HAPS have been also briefly described.

As a result, following advantages were verified in each application.

- Channel capacity

- Reachable distance of communications (coverage area in terms of mobile communications) .

Thus, it is expected that TC-SSP will play an important role as key technologies in the near future. Further on, another embodiment of the invention will be described and exemplified with reference to two new realizations involving the Antenna Polarization Codulation (APC) concept, cf. PCT/DK01/00755 published on 22 May 2003 under publication No. WO 03/043235 Al.

The APC-method is a novel "codulation" scheme that involves polarizations of electro-magnetic wave. The concept is to switch the polarization of transmitted signal in conjunction with modulation.

In the following, two new realizations of this APC concept in accordance with the present invention are explained. One is based on spread-spectrum (SS) system while another is based on Multiple Phase Shift Keying (MPSK) modulation. It is verified that those two realizations achieve remarkable improvement of BER performance through computer simulations.

Figures 16a and 16b show configurations of a transmitter and receiver, respectively, based on SS. At the transmitter, first, data sequence is performed by Serial-to-parallel (S/P) conversion 76. Then, the two digits output of S/P conversion are fed into the trellis encoder 78 of which coding rate is r = 2/3. Suppose that the output three digits are denoted as Cj, C₂ and C₃ whose durations are T_s [second]. Among those three digits, C₂ and C₃ are modulated by 2-ary Walsh modulator 80. In the 2-ary Walsh modulator 80, one of the four orthogonal codes is chosen and transmitted depending on the combination of C₂ and C3 as shown in Table 2 below. Note that the duration of a digit of an orthogonal code is equal to T_c = T_s/4

Table 2: Walsh modulation

c₂ c₃ Corresponding orthogonal

0 0 1 1 1 1

0 1 1 1 -1 -1

1 0 -1 -1 1 1

1 1 -1 1 -1 1 After the Digital-to- Analog conversion (D/A) 82 with the rate 1/T_C, the modulated signal is transmitted via the polarization switch 12 in one of two polarized signals, Right Hand Circular Polarization (RHCP) 13 or Left Hand Circular Polarization (LHCP) 14. The output digit of the encoder Cj is used to switch the polarization, i.e., when C_/ = 0 RHCP is selected while Cj = 0 LHCP is selected, for example. Thus, the polarization of the transmitted signal is switched in each T_s [second].

On the other hand, at the receiver, each signal received by RHCP 16 and LHCP 15 antennas are sampled by Analog-to-Digital conversion (A/D) 84 with the rate T_c and are fed into four correlators 86 that output cross-correlations between the incoming signal and the four orthogonal codes given in Table 2. Here, it is assumed that symbol synchronization between the transmitter and receiver is already acquired. Then, the correlators 86 output the following signals.

where the subscript p varies from 0 to 1 indicating LHCP and RHCP when p = 0 and p = 1, respectively. The subscript c varies from 0 to 3 corresponding to the four orthogonal codes. L is the length of an orthogonal code. It follows that L = 4 in this example. W_Vfi[m] where m = 0, • • • ,3 are weights of the c-th correlator at the polarization p. It should be noted that the correlator outputs are downsampled to the rate \/T_s [Hz]. Ideally, a correlator 86 that received the signal outputs 1 while the others output 0. However, those outputs are disturbed by noise. The difference between 1 and the outputs of correlators 86 are used as metric (e.g. at 88) in this application. Therefore, the metric for Niterbi Decoder 90 here is obtained as follows. γ_p,c[kTΛ=\ l - y_p λ\kT_s] \ , (7). where \a\ denotes the absolute value of a value a.

By using the metric γ_P,_c[kTJ, Niterbi Decoder 90 decodes the received signal encoded in the transmitter based on the soft decision. Figure 17 compares BER performance between APC on SS and BPSK. It is clearly observed that the application of APC improves the performance remarkably.

In this example, an application with 2-ary Walsh modulation has been shown. However, it should be emphasized that this is just an example so that it is naturally possible to extend it to larger Walsh modulation. For this extension, at the transmitter, 1-to-M S/P is performed. Then, the M bits are fed into the trellis encoder of coding rate r = M/(M + 1). Then, the bits among the M + 1 bits output from the encoder will be modulated by M-ary Walsh modulation. The modulated signal is transmitted in one of the two polarizations depending on the one bit output from the encoder that was not fed into the Walsh modulation.

The APC concept can be applied not only on SS but also on Multiple Polarization Shift Keying (MPSK). Figures 18a and 18b show transmitter and receiver configurations, respectively.

In the transmitter, the main difference from APC on SS is the modulation part. Here, QPSK modulation 94 is employed instead of Walsh modulation. Then, the digits C and C₃ is mapped as shown in Figure 19.

The modulated symbols are transmitted with the rate \/T_s in the two polarizations depending on the bit Cj according to the same principle mentioned in the previous section.

At the receiver, after the detection 100 of the QPSK modulated signal in both polarizations, metrics Y^for Viterbi decoder are calculated at 88 from the received signals χ _p[kT_s] where the subscript o varies from 0 to 3 corresponding to the four signal points of QPSK modulation illustrated in Figure 19 while the subscript /? is the identical one that was explained in the previous section. r_o,0[kT_s] = \ e^J° - x₀[kT_s] \²

ro,_ilkT_s] = \ e^J^ -x₀[kT_s] \² r_0,2[kT_s] = \ e^J* - x_Q[kT_s] \²

_oik _s] = \ e^Jϋ - -* mf

₂[k _s) = \ e» - - x,[kT_s)\²

Then, Niterbi decoder 90 realizes decoding based on the metric.

Figure 20 compares BER performance between APC on QPSK and the theoretical curve of QPSK. It is clearly observed that the application of APC improves the performance remarkably.

In this example, an application with QPSK modulation has been shown. However, it should be emphasized that this is just an example so that it is naturally possible to extend it to larger MPSK modulation. For this extension, at the transmitter, 1 -to-M S/P is performed. Then, the M bits are fed into the trellis encoder of coding rate r ~ M/(M + 1). Then, the M bits among the M + I bits output from the encoder will be modulated by M-PSK modulation. The modulated signal is transmitted in one of the two polarizations depending on the one bit output from the encoder that was not fed into M-PSK modulation.

In the above, two new realizations of the APC concept in accordance with the present invention has been explained. Through computer simulations, their remarkable performance improvements have been verified.

Further examples of the implementation of the present invention in connection with APC technology (cf. WO 03/043235 Al) will be described in the following:

Guard time insertion technique for multipath fading environments: In practice, it is hard to avoid the effect of multipath fading. As the further additional technique, insertion of the guard time is proposed.

Possibility of application of APC on MC-CDMA (Multi-Carrier Code Division Multiple Access) and OFDM (Orthogonal Frequency Division Multiple Access):

The possibility has been illustrated with a few examples, although it shall be understood that numerous other applications will fall within the scope of the invention. Further, it shall be understood that further detailed considerations may be required for some of these applications.

In the following, each of the above-mentioned items will be described.

First, the guard time approach for combating with fading environments applicable to the APC technology is provided. The transmitter configuration according to an embodiment of the APC technology is shown in Figure 21. This figure shows APC on M-ary SS (Spread Spectrum) (= Walsh modulation). 2 bits of data sequence generate 3 digits code (C_o,^,^) by the trellis encoder 78 (r=2/3). Then, C_λ and

C₂ are fed into a Walsh modulator 80 and up-converted after the digital-to-analog (D/A) conversion 82 while C₀ is used to decide the polarization at 12. By using this configuration, the performance is improved significantly as previously described.

Guard time 106 in the time interval is inserted between the two symbols 104 and 105 as depicted in Figure 22. In this figure, T_s denotes the symbol duration [sec] while T_g denotes the guard time [sec]. If T_g is long enough comparing with the depth of the fading environment, Inter-Symbol Interference (ISI) caused by the fading environment can be absorbed by the guard time 106. This approach is often employed in OFDM systems (cf. R.Nan Νee, R. Prasad, "OFDM for Wireless Multimedia Communications", Artech House Publishers, 2000.).

Figure 23 shows an example of the implementation of APC with the guard time insertion. In this configuration, the guard time is inserted at 108 as the final stage of the digital signal processing part. Of course, it is theoretically possible to insert the guard time in the RF (Radio Frequency) or IF (Intermediate Frequency) stages. These implementations are included as examples of the possible implementations of APC in accordance with the present invention.

Secondly, there are several possibilities for the application of APC on OFDM. In this application, the simplest extension of APC towards OFDM application will be described.

Figure 24 shows an application of APC on OFDM. In this figure, the number of subcarriers employed in OFDM is 52 in accordance with IEEE802.1 la. First, in this configuration, 52 bits of the data sequence produced by feeding the input data 2 to the Serial-to Parallel S/P-conversion 76 is fed into the encoder 110 (r=52/53) so that 53 digits code is generated. Second, the first digit is used to decide the polarization while the rest of 52 digits are fed into IFFT (Inverse Fast Fourier Transform) 112 to implement OFDM. After the up-conversion, the signal is transmitted through the polarization switch 12 driven by the first digit of the code. The possibility of the application of APC on OFDM and MC-CDMA are included in this patent application as examples of the implementation. This aspect of the invention may find utilization in connection with WLAN-systems and -techniques, cf. e.g. IEEE 802.11a (OFDM) and in connection with mobile communication systems, cf. e.g. CDMA 2000 (MC- CDMA). Other applications will be possible, which shall be evident to a skilled person.

It shall be obvious to a skilled person within the art that such applications may be exemplified with numerous examples within the field and that the invention may be utilized in connection with a wide variety of detailed arrangements. Detailed considerations required for such applications will be obvious to a skilled person on the basis of this application and with knowledge of currently readily available techniques within the field. Glossary

APC Antenna Polarization Codulation: New technology of PCOM:I ApS. CDMA Code Division Multiple Access: A multiple access scheme.

D/A Digital-to-Analog conversion: Conversion from digital signal to continuous signal. D/C Down Converter: Conversion of frequency to lower frequency.

IF Intermediate Frequency: Frequency band between the radio frequency and baseband.

ISI Inter-Symbol Interference: Interference between the two different symbols caused by multipath fading. MC-CDMA Multi-Carrier CDMA: CDMA using several carriers employed in cdma2000 systems etc. OFDM Orthogonal Frequency Division Multiplexing: Multiplexing using orthogonal frequency carriers employed in the standard IEEE802.11a etc. PDMA Polarization Division Multiplex Access: New technology of PCOM:I³

ApS. RF Radio Frequency: Frequency used for transmission of signals.

SS Spread Spectrum: A modulation scheme.

U/C Up Converter: Conversion of frequency to higher frequency.

Claims

Patent Claims

1. A method of communication employing electromagnetic waves, said method of communication involving polarization coding, whereby said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication.

2. Method according to claim 1, characterized in that a polarization coding using at least two different polarization values, e.g. multiple orthogonal polarizations are utilized.

3. Method according to claim 1 or 2, characterized in that an error correcting code (ECC) is employed.

4. Method according to one or more of claims l to 3, characterized in that said polarization coding comprises an error correcting code (ECC) involving polarization.

5. Method according to one or more of claims 1 - 4, characterized in that said method involves switching between at least two polarizations based on an encoding, e.g. driven by an encoder.

6. Method according to claim 5, characterized in that said encoding is based on a trellis.

7. Method according to claim 5 or 6, characterized in tha-t a method for composition of a trellis for encoding is involved.

8. Method according to claim 5, 6 or 7, characterized in that a trellis realizing a maximum code distance is employed.

9. Method according to one or more of claims 1 -8, characterized in that said method comprises a decoding at a receiver side, e.g. employing a Niterbi decoder.

10. Method according to claim 9, characterized in that said decoding employs an absolute value of difference between the result of hard-decision and one before decision in both polarizations as the metric.

11. Method according to one or more of claims 1-10, characterized in that said method involves switching of a transmitted signal in conjunction with a modulation scheme.

12. Method according to claim 11, characterized in that said modulation scheme is based on a spread-spectrum (SS) scheme.

13. Method according to claim 11, characterized in that said modulation employs a Walsh-modulation, e.g. a 2-ary or larger (M-ary) Walsh- modulation.

14. Method according to claim 11, characterized in that said modulation scheme is based on a multiple polarization shift keying (MPSK) scheme, e.g. a quadruple polarization shift keying (QPSK) scheme.

15. Method according to claim 11, characterized in that said modulation scheme employs a multi-carrier code division multiple access (MC-

CDMA)-scheme.

16. Method according to claim 11, characterized in that said modulation scheme employs a orthogonal frequency division multiple access (OFDM)-scheme.

17. Method according to one or more of claims 1 - 16, c h a r a c t e r i z e d i n that said method involves guard time insertion, e.g. insertion of a guard time interval between consecutive symbols.

18. System for communication of electromagnetic waves, wherein a polarization coding of transmitted signals is involved and wherein said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication.

19. System according to claim 18 and in accordance with one or more of claims 1 to 17.

20. Transmitter for transmission of electromagnetic waves, wherein a polarization coding of transmitted signals is involved and wherein said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication.

21. Transmitter according to claim 20 and in accordance with one or more of claims 1 to 17.

22. Receiver for reception of electromagnetic waves, wherein a polarization coding of transmitted signals is involved and wherein said polarization coding involves transitions of polarizations, e.g. multiple polarizations, whereby said transitions convey information in order to facilitate said communication.

23. Receiver according to claim 22 and in accordance with one or more of claims 1 to 17.

24. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 for wireless communication.

25. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 for wireless and mobile communication.

26. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 in connection with cellular communication systems.

27. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 in connection with secure communication systems.

28 Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 in connection with a wireless local area network (WLAN).

29. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 in connection with a wireless local loop (WLL).

30. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 in connection with multiple-input-multiple-output (MIMO) technology.

31. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 in connection with an Intelligent Transportation System (ITS).

32. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 in connection with a High Altitude Stratospheric Platform Station (HAPS).

33. Use of method according to one or more of claims 1 - 17, system according to claim 18 or 19, transmitter according to claim 20 or 21 and/or receiver according to claim 22 or 23 in connection a Wireless Home Area Network (WHAN).