Method of reducing cochannel interference

Abstract: The present invention relates to a communication method, and the invention enables it to avoid in advance mistaken restoration of a signal series which is sent in the other communication even when the same channel is used in the other communication. A orthogonal matrix which is different for each communication is multiplied to the signal series and sent, and the signal series before orthogonal conversion is restored by multiplying the inverse matrix of the orthogonal conversion which is used on the sending side of the communication partner to the received signal series so that the other communication is performed by using the same channel. Even when the other communication is received, the signal series which is sent in the other communication is not restored even by multiplying the inverse matrix because the orthogonal matrix which is used in the orthogonal conversion is different from the other communication.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to a communication method, a transmitter and a receiver, and more particularly, is applicable to radio communication system such as a portable telephone system or the like. DESCRIPTION OF THE RELATED ART In this kind of radio communication system, an area for providing communication service is divided into cells having a desired size and a base station is set as a fixed radio station in the cell. The portable telephone device as a mobile radio station is installed in the cell so that the portable telephone device as a fixed radio station is constituted to be engaged in communication with the base station in the cell in which the portable telephone device is present. At that time, in this kind of radio communication system, the interference problem of an electronic wave is avoided by using a channel of frequency which is different between cells (this is simply referred to as a channel). By the way, when a different channel is used between adjacent cells in this manner, the problem of interference can be avoided, but at the same time, there arises a disadvantage in that the usage efficiency of the frequency is reduced. As a consequence, in recent years, the interference problem is avoided by changing the channel which is used in each cell at random for each predetermined timing, and the usage efficiency of the frequency is improved. By the way, in such radio communication system, the channel is only changed at random so that it is not necessarily possible to avoid that the channel becomes the same between adjacent cells. Thus, it is feared that the timing becomes the same. In the case where the same channel is used, there might arise an interference problem in the same manner as the prior art. For example, as shown in Fig. 1, in the cell 1A, when the portable telephone device 2A uses the predetermined channel to be engaged in communication with the base station 3A, and the same channel as the cell 1A is used in the adjacent cell 1B so that the portable telephone device 2B is engaged in communication with the base station 3B, it sometimes happens that the sending signal CB which is sent by the portable telephone device 2B reaches the base station 3A. In this case, the sending signal CB which reaches the base station 3A becomes an interference wave (so-called hindrance wave) with respect to the sending signal CA which is sent to the base station 3A. In this manner, even when an interference wave I is generated to the sending signal CA in this manner, the signal level of the sending signal CA is larger than the interference wave I, and no considerable problem is generated in normal cases However, in the case where because, for example, the portable telephone device 2A is distant from the base station 3A and the signal level of the sending signal CA becomes smaller than the interference wave I, the base station 3A receives the interference wave I by mistake instead of the sending signal CA from the portable telephone device 2A. As a consequence, the signal series transmitted by the portable telephone device 2B is restored, and the communication content of the other person is leaked with the result that a situation which is not preferable as a radio communication system might arise. For reference, in such a situation, even when the received data is not obtained as the radio communication system, it is desirable that the interference wave I is not demodulated. In DE 25 23 828 B, a method for encrypting speech signals transmitted via a channel with limited bandwidth, especially a CCITT speech channel, is disclosed, wherein a part of a pulse-code modulated speech signal is divided into k sampling patterns and each part is divided into m subparts, each consisting of k / m sampling patterns. By applying an orthogonal transformation on these sampling patterns, k / m image patterns are obtained, and the image data obtained for the m subparts of the respective image pattern are serially transmitted to a receiver over an analog channel. A speech scrambling system using discrete prolate spheroidal sequence coefficients (PC) which solves the problem of providing high fidelity and security in a scrambling system while simultaneously limiting the bandwidth of the scrambled signal to the bandwidth of the original analog speech signal is described in US 4,379,205. The analog speech signal is thereby digitally sampled, converted to prolate spheroidal sequence coefficients, scrambled and converted to scrambled samples. These scrambled samples are transmitted using pulse amplitude modulation (PAM) in the same frequency range as the original signal. At the receiving end, the inverse steps are performed to recover the original speech signal. To improve security, the scrambling is periodically modified. The invention described in GB 2 291 314 A refers to a method for coding an Orthogonal Frequency-Division Multiplexed (OFDM) signal by dividing each OFDM symbol into a plurality of subsymbols. Thereby, subcarriers for each subsymbol are formed from different portions of a plurality of signal sets. The most important data are coded on a signal set which provides a substantially constant contribution to the corresponding subcarriers and are thus conveyed most ruggedly. Less important data are coded on signal sets which vary between corresponding subcarriers from subsymbol to subsymbol in dependence on predetermined functions and are thus conveyed less ruggedly. Contributions from these signal sets sum substantially to zero across an OFDM symbol. Alternatively, the signal sets coded with the most important data are assigned every r-th subcarrier forming an OFDM symbol and signal sets coded with less important data are assigned to intermediate subcarriers wherein each intermediate carrier is coded with data derived from a plurality of signal sets. In each of these systems the most important data serves as a phase and amplitude reference for the signal sets carrying less important data. In US 5,367,516 a method and apparatus for transmitting and receiving signals is described which includes an analyzer for decomposing an input signal into a plurality of signals with each one of these signals occupying one of a corresponding plurality of channels and a synthesizer comprising a plurality of channels with each channel being adapted to receive one of said analyzer signals for combining said plurality of signals to reconstruct the input signal. SUMMARY OF THE INVENTION In view of the foregoing, an object of this invention is to provide a communication method which is capable of avoiding restoring the signal series which is sent in other communication by mistake even when the same channel is used in the other communication, and is to provide a transmitter and receiver which use the communication method. The foregoing object and other objects of the invention have been achieved by the provision of a communication method. In the communication method, the orthogonal conversion is performed by multiplying an orthogonal matrix which is different for each communication to signal series which is sent, and the signal series to which the orthogonal conversion is performed is sent by using the predetermined channel. On the receiving side, the signal series before the orthogonal conversion is restored by multiplying the inverse matrix of the orthogonal matrix which is used on the sending side of the communication partner to the received signal series. With the above arrangement, the signal series is multiplied with the orthogonal matrix which is different for each communication and transmitted, and at a receiving side, the received signal series is multiplied with an inverse matrix of the orthogonal matrix used at a transmitting side of the communication partner, so that the signal series before orthogonal conversion is restored. Therefore, even when another communication is performed and received by using the same channel, since the orthogonal matrix used for the orthogonal conversion differs from one communication to another, inverse orthogonal conversion cannot be attained for one communication even if an inverse matrix for another communication is multiplied, thereby signal series sent in another communication being not restored. The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a system structure view explaining that the sending signal which is sent by the other communication becomes an interference wave; Fig. 2 is a system structural view explaining a principle of the present invention; Figs. 3A to 3C are signal transition views explaining an operation at the time of receiving a sending signal from the communication partner in a radio communication system to which the present invention is applied; Figs. 4A to 4C are signal transition views explaining an operation at the time of receiving an interference wave in the radio communication system; Fig. 5 is a block view showing a structure of a transmitter provided in the portable telephone set; Fig. 6 is a block view showing a structure of a receiver provided in the station; and Fig. 7 is a signal transition view explaining an orthogonal conversion at the time of using the first dimension orthogonal matrix. DETAILED DESCRIPTION OF THE EMBODIMENT Preferred embodiments of this invention will be described with reference to the accompanying drawings: In the beginning, the principle of the present invention will be explained by using Fig. 2. In Fig. 2, reference numerals 5A, 5B denote the portable telephone device respectively. Reference numeral 6A and 6B denote the base station to which the present invention is applied. As shown in Fig. 2, the portable telephone device 5A uses the predetermined channel to be engaged in radio communication with the base station 6A in the cell 1A. At the same time, the same channel is used in the adjacent cell 1B so that the portable telephone device 5B is engaged in radio communication with the base station 6B. At that time, for example, in the portable telephone devices 5A and 5B both QPSK modulation (Quadrature Phase Shift Keying; Four Phase Transition Modulation) is used as a modulation method of the sent data. The signal series of the modulated sending signal are defined as x (A) 1 , x (A) 2 , X (A) 3 , ... ... X (A) k-1 , X (A) k , X (A) k+1 , ... ... and X (B) 1 , X (B) 2 , X (B) 3 , ... ... X (B) k-1 , X (B) k , X (B) k+1 , ... .... The portable telephone device 2A to which the present invention is applied groups N (N is an integer which is 1 or more) sending signal series x (A) n (n=1, 2, 3, ... ...). The grouped sending signal series x (A) k , ... ... x (A) k+N and a predetermined Nth normal orthogonal matrix M A are multiplied in order as shown in the following equation. As a consequence, an orthogonal conversion is added to the sending signal series x (A) n (n=1, 2, 3, ... ...) and a resulting sending signal series y (A) n (n=1, 2, 3, ......) are sent in order. On the other hand, at the base station 6A which is a receiving side, when a sending signal CA is received from the portable telephone device 5A of the communication partner, N received signal series y (A) n (n=1, 2, 3, ... ...) are grouped, and the grouped received signal series y (A) k , ... ... y (A) k+N are successively multiplied with an inverse matrix M A -1 of the Nth normal orthogonal matrix M A used on the sending side as shown in the following equation. As a consequence, the signal series X (A) n (n=1, 2, 3, ... ...) is restored which is equal to the signal series x (A) n (n=1, 2, 3, ... ...) before orthogonal conversion. In the similar manner, at the time of sending data, the portable telephone device 5B groups the N sending signal series x (B) n (n=1, 2, 3, ... ...). The grouped sending signal series x (B) k , ... ... X (B) k+N and the predetermined Nth normal orthogonal matrix M B are multiplied in order for each group as shown in the following equation. As a consequence, the orthogonal conversion is added to the sending signal series x (B) n (n=1, 2, 3, ... ...), and the resulting sending signal series y (B) n (n=1, 2, 3, ... ...) are sent in order. For reference, the Nth normal orthogonal matrix M B which is used in the portable telephone device 5B and the Nth normal orthogonal matrix M A which is used in the portable telephone device 5A are matrixes which are completely different from each other. At the base station 6B which is a receiving side, when the sending signal CB from the portable telephone device 5B of the communication partner is received, the N received receiving signal series y (B) n (n=1, 2, 3, ... ...) are grouped, and the grouped y (B) k , ... ... y (B) k+N and the inverse matrix M B -1 of the Nth normal orthogonal matrix M B used at a sending side are multiplied in order for each group as shown in the following equation. Consequently, the signal series X (B) n (n=1, 2, 3, ... ...) which is equal to the signal series x (B) n (n=1, 2, 3, ... ...) before the orthogonal conversion is restored. By the way, at the base station 6A, only the sending signal CA sent by the portable telephone device 5A reaches, but the sending signal CB sent by the portable telephone device 5B also reaches depending on the situation. In that case, the sending signal CB from the portable telephone device 5B acts as an interference wave I. When the signal level of the sending signal CB is large as compared with the sending signal CA from the portable telephone device 5A, trouble is caused to communication with the portable telephone device 5A. In other words, as the base station 6A, it is not recognized that the signal is a sending signal from either of the portable telephone devices 5A or 5B so that it is feared that the sending signal CB from the portable telephone device 5B is received by mistake. In such a case, the base station 6A groups the N received signal series y (B) n (n=1, 2, 3, ... ...) received from the portable telephone device 5B so that the demodulation processing is performed by multiplying the inverse matrix M A -1 to the grouped signal series y (B) k , ... ... y (B) k+N as shown in the following equation as in the normal receiving processing. However, as seen from the equation (5), the receiving signal series y (B) n (n=1, 2, 3, ... ...) from the portable telephone device 5B is a result obtained from a multiplication of the orthogonal matrix M B which is different from the orthogonal matrix M A so that the diagonal reverse conversion is not obtained even when the inverse matrix M A -1 is multiplied with the result that the original signal series x (B) n (n=1, 2, 3, ... ...) is not restored. In this case, the received signal series becomes a signal series which is the original signal series x (B) n (n=1, 2, 3, ...) orthogonally converted with another orthogonal matrix consisting of M A -1 M B , so that the signal becomes ostensibly a noise signal, and even when the signal series is QPSK demodulated, the sending data of the portable telephone device 5B is not restored. In this manner, in the case of the radio communication system to which the present invention is applied, the orthogonal matrix which is different for each communication at the sending side is multiplied with the signal series. On the receiving side, the received signal series is multiplied with the inverse matrix of the orthogonal matrix which is used on the sending side (namely, the communication partner of its own station) so that the original signal series before the orthogonal conversion is restored. As a consequence, even when the same channel is used in the other communication, the restoration of the sent signal series by the other communication is avoided in advance with the result that the leakage of the data sent in the other communication can be avoided in advance. For reference, there is described here that the leakage problem is avoided when the sending signal CB of the portable telephone device 5B is received by the base station 6A. For the same reason, the leakage problem can be also avoided even when the base station 6B receives the sending signal CA of the portable telephone device 5A. Here, the orthogonal conversion using the orthogonal matrix and the inverse conversion thereof will be explained by using the signal transition view. In the beginning, the sending signal series x (A) n (n=1, 2, 3, ... ...) of the portable telephone device 5A is QPSK modulated so that the π/4, 3π/4, 5π/4 or 7π/4 phase states can be assumed. As a consequence as shown in Fig. 3A, on the complex surface (IQ surface), the phase state is present at a position where the phase state becomes π/4, 3π/4, 5π/4 or 7π/4. When such sending signal series x (A) n (n=1, 2, 3, ... ...) is multiplied to the Nth normal orthogonal matrix M A , the resulting signal series y (A) n (n=1, 2, 3, ... ...) becomes a random state as shown in Fig. 3B. On the other hand, at the base station 6A which is a receiving side, this signal series y (A) n (n=1, 2, 3, ... ...) is received. As described above, when the inverse matrix M A -1 the orthogonal matrix M A which is used on the sending side is multiplied with this signal series y (A) n (n=1, 2, 3, ... ...), the resulting signal series X (A) n (n=1, 2, 3, ... ...) becomes the same as the original signal series x (A) n (n=1, 2, 3, ... ...) as shown in Fig. 3C so that the resulting signal series is brought back to the position of the phase state comprising π/4, 3π/4, 5π/4 or 7π/4 on the complex surface. Consequently, when the signal series X (A) n (n=1, 2, 3, ... ...) is subjected to QPSK demodulation, the sending data from the portable telephone device 5A can be accurately restored. Furthermore, since the sending signal series x (B) n (n=1, 2, 3, ... ...) of the portable telephone device 5B is also QPSK modulated, π/4, 3π/4, 5π/4 or 7π/4 phase state is assumed with the result that the phase is present on the position comprising π/4, 3π/4, 5π/4 or 7π/4 on the complex surface as shown in Fig. 4A. When such sending signal series x (B) n (n=1, 2, 3, ... ...) is multiplied with Nth normal orthogonal matrix M B , the resulting signal series y (B) n (n=1, 2, 3, ... ...) is such that the phase state becomes random as shown in Fig. 4B. In the case where such signal series y (B) n (n=1, 2, 3, ... ...) is received with the base station 6A which is not the communication partner, the signal series y (B) n (n=1, 2, 3, ... ...) becomes an interference wave for the base station 6A. However, the base station 6A does not recognize that the signal series is either the sending signal from the communication partner or the interference wave, the demodulation processing is performed as in the normal receiving processing. However, even when the inverse matrix M A -1 of the orthogonal matrix M A is multiplied with this signal series y (B) n (n=1, 2, 3, ... ...), the inverse matrix M A -1 is not the inverse matrix of the orthogonal matrix M B which is used at the sending time. As shown in Fig. 4C, the phase state is not brought back to the original state so that the phase state becomes a random state. Consequently, even when the signal series shown in Fig. 4C is QPSK demodulated, the sending data from the portable telephone device 5B is not restored. Consequently, the leakage of the data sent by the other communication can be avoided, and the generation of the undesirable state as a radio communication system can be avoided. Here, a concrete structure of the portable telephone device 5A (or 5B) and the base station 6A (or 6B) to which such principle is applied will be explained hereinbelow. In the beginning, the portable telephone device 5A (or 5B) has the transmitter 10 shown in Fig. 5. This transmitter 10 roughly comprises a QPSK modulation circuit 11, an orthogonal conversion part 12, and a sending part 13 so that the sent data S1 supplied via the predetermined noise processing circuit or the like is input to the QPSK modulation circuit 11 in the beginning. The QPSK modulation circuit 11 converts the sent data S1 into a sending signal series S2 of the phase data by performing the QPSK modulation processing on the sent data S1 so that the sending signal series S2 is output to a serial/parallel conversion circuit (S/P) 14 of the orthogonal conversion part 12. For reference, this sending signal series S2 corresponds to the aforementioned signal series x (A) n (n=1, 2, 3, ... ...) (or x (B) n (n=1, 2, 3, ... ...)). The serial/parallel conversion circuit 14 is a circuit for grouping N groups of the sending signal series S2 so that the sent signal series which is input is N parallel signal by dividing the input signal series S2 into N signals and the resulting parallel signal series ST 1 through ST N is output to an orthogonal conversion circuit 15. The orthogonal conversion circuit 15 is a circuit for adding an orthogonal conversion to the sending signal series by using a predetermined Nth normal orthogonal matrix. The parallel signal series ST 1 through ST N are defined as one group and Nth normal orthogonal matrix is multiplied in order, and each group of signal series ST 1 through ST N are subjected to an orthogonal conversion. At that time, the orthogonal conversion circuit 15 searches for a matrix which is completely different from the Nth normal orthogonal matrix which is used in the other communication, and the matrix is not used for the orthogonal conversion, and a matrix which is selected at random from the Nth normal orthogonal matrixes which are present in plurality. This is because when an attempt is made to search for a matrix which is completely different from the Nth normal orthogonal matrix which is used in the other communication, it is necessary to inspect a matrix which is used in the other communication with the result that the selection processing of the orthogonal matrix for the processing becomes complicated. As a consequence, this orthogonal conversion circuit 15 obtains a matrix ostensibly different from the matrix which is used in the other communication by selecting at random a matrix out of the Nth normal orthogonal matrixes which are present in plurality so that the matrix selection processing is simplified. Here, a method for selecting the Nth normal orthogonal matrix will be concretely explained. In the orthogonal conversion circuit 15, for example N Nth Walsh vectors are prepared as the Nth diagonal vector whose vector components comprise two values. The orthogonal conversion circuit 15 gives a random phase rotation to this Nth Walsh vector respectively so that the Nth random normal orthogonal matrix is generated by combining the random phase rotation. In other words, as shown in the following equation, a random phase rotation is given to the Walsh vectors W 1 , W 2 , ... ... W N by multiplying random phase rotation components e jZ1 , e jZ2 , ... ... e jZN (here Z1 through ZN denote phase rotation angles) to Nth Walsh vectors W 1 , W 2 , ... ... W N . Then, 1/√N is multiplied so that a random Nth normal orthogonal matrix M is generated. However, in the equation (6), W 1 T , W 2 T , ... ... W N T is what is vector placed so as to have a vector component in a line direction of the Walsh vectors W 1 , W 2 , ... ... W N having vector component in the row direction. By using such selection method, the orthogonal conversion circuit 15 selects the Nth normal orthogonal matrix and multiplies it to the parallel signal series ST 1 through ST N so that the orthogonal conversion is added to the signal series ST 1 , through ST N . The resulting parallel signal series ST 1 ' through ST N ' are output to a parallel/serial conversion circuit (P/S) 16. The parallel/serial conversion circuit 16 is a circuit for collecting grouped sending signal series into one group by converting a parallel signal into a serial signal so that the parallel signal series ST 1 ' through ST N ' which are input are converted into a serial signal series S3, which is output to a reverse Fourier conversion circuit (IFFT) 17 at the sending part 13. For reference, this signal series S3 corresponds to the aforementioned signal series y (A) n (n=1, 2, 3, ... ...) or y (B) n (n=1, 2, 3, ... ...). The reverse Fourier conversion circuit 17 dissipates and overlaps the signal series S3 with a plurality of multiple carriers having a different frequencies by adding a reverse Fourier conversion to the signal series S3. Then the resulting sending signal S4 is output to a high frequency circuit 18. The high frequency circuit 18 converts this sending signal S4 into a predetermined channel of sending signal S5 in frequency. At the same time, after the sending signal S5 is amplified to a predetermined power, the sending signal is sent via an antenna 19. For reference, the high frequency circuit 18 changes at random the channel of the sending signal S5 for each of the predetermined timing (so-called frequency hopping is performed). As a consequence, the usage efficiency of the frequency is improved while avoiding the situation that the channel becomes the same as the other communication. In contrast, the base station 6A (or 6B) has a receiver 20 as shown in Fig. 6. This receiver 20 roughly comprises a receiving part 21, an orthogonal conversion part 22, and a QPSK demodulation circuit 29. The signal S10 received via the antenna 23 is input to a high frequency circuit 24 of the receiving part 21. The high frequency circuit 24 amplifies the sending signal S10 to a predetermined power, and at the same time, the received signal S10 is converted into a received signal S11 of a base band, and the received signal is output to the Fourier conversion circuit (FFT) 25. The Fourier conversion circuit 25 extracts a signal series S12 which is dissipated and overlapped with the a plurality of multiple carriers by adding the Fourier conversion to the receiving signal S11 and the extracted signal is output to a serial/parallel conversion circuit (S/P) 26 of the diagonal reverse conversion part 22. For reference, this signal series S12 corresponds to the aforementioned signal series y (A) n (n=1, 2, 3, ... ...) (or y (B) n (n=1, 2, 3, ... ...)). The serial/parallel conversion circuit 26 is a circuit for dividing the signal series S12 into groups comprising N signal series, and the circuit converts the signal series into N parallel data by dividing input signal series S12 into groups comprising N signal series and the resulting parallel signal series SR 1 through SR N are output to a diagonal reverse conversion circuit 27. The diagonal reverse conversion circuit 27 is a circuit for performing diagonal reverse conversion by using an inverse matrix of Nth normal orthogonal matrix which is used by the orthogonal conversion circuit 15 of the communication partner. The diagonal reverse conversion circuit adds the diagonal reverse conversion for each group with respect to the signal series SR 1 through SR N by multiplying the inverse matrix in order by defining the input parallel signal series SR 1 through SR N as one group. The resulting signal series SR 1 ' through SR N ' is output to a parallel/serial conversion circuit (P/S) 28. For reference, the diagonal reverse conversion circuit 27 recognizes Nth normal orthogonal matrix which is used on the sending side by receiving processing or the like of the control signal, for example, at the time of the start of the communication. The parallel/serial conversion circuit 28 is a circuit for collecting received signal series which is grouped into one group by converting the parallel signal into a serial signal. The input parallel signal series SR 1 ' through SR N ' are converted into a serial signal series S13. And this signal series S13 is output to a QPSK modulation circuit 29. For reference, this signal series S13 corresponds to the aforementioned signal series X (A) n (n=1, 2, 3, ... ...) (or X (B) n (n=1, 2, 3, ... ...)). The QPSK modulation circuit 29 restores the received data S14 from the signal series S13 which is phase data by performing a predetermined demodulation processing such as, for example, diagonal delay wave detection to the QPSK modulated signal series S13. In this manner, the received data S14 which is the same as the sent data S1 on the sending side is restored on the receiving side. For reference, bi-direction communication is performed between the portable telephone device 5A (or 5B) and the base station 6A (or 6B) so that the portable telephone device 5A (or 5B) is provided with a receiver which is approximately the same as the aforementioned receiver 20. In the similar manner, the base station 6A (or 6B) is provided with a transmitter which is approximately similar to the aforementioned transmitter 10. In the aforementioned structure, in the case of this radio communication system, the orthogonal conversion is applied to the signal series by multiplying the Nth normal orthogonal matrix which is different for each communication to the signal series which is QPSK modulated at the time of sending the signal, and the orthogonally converted signal series is sent. On the other hand, on the receiving side, the diagonal reverse conversion is applied to the signal series by multiplying the inverse matrix of the Nth normal orthogonal matrix which is used on the sending side of the communication partner to the signal series which has been received and the signal series which is subjected to the reverse conversion is subjected to QPSK demodulation. For example, in the portable telephone device 5A which is shown in Fig. 2, the signal series x (A) n (n=1, 2, 3, ... ...) is subjected to the orthogonal conversion by multiplying the Nth normal orthogonal matrix M A to the signal series x (A) n (n=1, 2, 3, ... ...) to be sent so that the signal series y (A) n (n=1, 2, 3, ... ...) which is subjected to the orthogonal conversion is sent. Furthermore, in the portable telephone device 5B, the signal series x (B) n (n=1, 2, 3, ... ...) is subjected to the orthogonal conversion by multiplying the Nth normal orthogonal matrix M B which is different from the orthogonal matrix M A to the signal series x (B) n (n=1, 2, 3, ... ...) to be sent with the result that the signal series y (B) n (n=1, 2, 3, ... ...) which is subjected to the orthogonal conversion is sent. By the way, in the case where the base station 6A receives the sending signal CA from the portable telephone device 5A which is a communication partner, the inverse matrix M A -1 of the orthogonal conversion M A is multiplied to the received signal series y (A) n (n=1, 2, 3, ... ...) with the result that the original signal series x (A) n (n=1, 2, 3, ... ...) can be accurately restored and the sent data sent by the portable telephone device 5A with QPSK demodulation can be accurately restored. On the other hand, in the case where the base station 6A receives the sending signal CB from the portable telephone device 5B, the original signal series x (B) n (n=1, 2, 3, ... ...) is not restored even when the inverse matrix M A -1 is multiplied to the received signal series y (B) n (n=1, 2, 3, ... ...), because the inverse matrix M A -1 is not an inverse matrix of the orthogonal matrix M B which is used on the sending side. In this case, when the inverse matrix M A -1 is multiplied, the matrix comprising M A -1 M B to the signal series x (B) n (n=1, 2, 3, ... ...) is multiplied so that the signal series becomes random and looks ostensibly like a noise signal with the result that the original sent data is not restored even when the QPSK demodulation is performed temporarily. In this manner, this radio communication system multiplies the orthogonal matrix which is different for each communication to the signal series on the sending side and sends it, while the system multiplies the inverse matrix of the orthogonal matrix which is used at the sending side of the communication partner to the received signal series on the receiving side and the original signal series is restored with the result that the same channel is used in the other communication. Even when the signal series is received, the orthogonal matrix which is used at the sending time is different from the other communication so that the diagonal reverse conversion is not realized by multiplying the inverse matrix, and the signal series which is sent in the other communication is not restored. As a consequence, the leakage of the sent data which is sent in the other communication can be avoided in advance. Furthermore, in the case of the radio communication system, a completely different Nth normal orthogonal matrix is not selected by examining the Nth normal orthogonal matrix which is used in the other communication at the time of selecting the Nth normal orthogonal matrix in the orthogonal conversion circuit 15. In actuality, the matrix which is different from the matrix which is used in the other communication is selected by selecting the orthogonal matrix at random out of the Nth normal orthogonal matrixes which are present in plurality. Consequently, a process of examining the matrix which is used in the other communication becomes unnecessary so that a selection processing of the orthogonal matrix can be simplified. Also, depending on the situation, an orthogonal matrix to be used is assigned to each base station in advance, and the terminal station may select the orthogonal matrix to be used in accordance with the base station with which the communication is performed. Furthermore, in the case of the radio communication system, a plurality of orthogonal matrixes are not prepared in advance at the time of selecting the orthogonal matrix. In actuality, N Nth Walsh vectors are prepared in advance, and random phase rotation is given to the Walsh vectors W 1 , W 2 , ... ... W N so that Nth normal orthogonal matrix is obtained by combining the Walsh vectors W 1 , W 2 , ... ... W N . Consequently, the calculation part for calculating the normal orthogonal matrix is constituted with addition and subtraction processing, and at the same time, a memory for memorizing a plurality of orthogonal matrixes becomes unnecessary and the normal orthogonal matrix can be calculated with a simple structure. For reference, Nth normal orthogonal matrix which is calculated by using the Walsh vector is shown here as a reference. For example, when N=1 is set, and random rotation angles which are selected by the portable telephone devices 5A and 5B are set to ZA and ZB, the Walsh vector becomes '1' at the time of N=1 with the result that the normal orthogonal matrixes M A and M B generated in the portable telephone device 5A and 5B are shown in the following equation. [Equation 7] M A = e jZA , M B = e JZB For reference, when the normal orthogonal matrixes M A and M B are used, it means that the signal series having a phase state which is set to π/4, 3π/4, 5π/4 or 7π/4 on the complex surface is rotated in a predetermined direction by phase rotation angles ZA and ZB. Incidentally, in this case, when the base station 6A receives the sending signal from the portable telephone device 5B which is the other communication, the matrix which is shown in the following equation is multiplied to the signal series x (B) n (n=1, 2, 3, ... ...). [Equation 8] M A -1 M B = e j(ZB-ZA) It can be seen that when the phase rotation angles ZA and ZB are different, the signal series x (B) n (n=1, 2, 3, ... ...) which is sent in the other communication is not restored. Furthermore, the N=2 is set, and random phase rotation angles which are selected by the portable telephone devices 5A and 5B are set to ZA1, ZA2, ZB1 and ZB2 respectively. A vector shown in the following equation is used as the line displacement vectors W 1 T and W 2 T of the second Walsh vectors W 1 and W 2 . [Equation 9] W 1 T = (1, 1), W 2 T = (1, - 1) Then, the normal orthogonal matrixes M A and M B which are generated in the portable telephone devices 5A and 5B are shown in the following equation. Incidentally, in this case, when the base station 6A receives the sending signal from the portable telephone device 5B which is the other communication, the state is obtained that the signal series x (B) n (n=1, 2, 3, ... ...) is multiplied with the matrix shown in the following equation. It can be seen that when the phase rotation angles ZA1 and ZB1 and the phase rotation angles ZA2 and ZB2 are different from each other, the signal series x (B) n (n=1, 2, 3, ... ...) which is sent in the other communication is not restored. Thus, in the aforementioned structure, the sending side multiplies and sends the orthogonal matrix which is different from each other for each communication to the signal matrix, and the receiving side restores the original signal series before the orthogonal conversion by multiplying the inverse matrix of the orthogonal matrix used by the sending side of the communication partner to the received signal series with the result that the same channel is used in the other communication. Even when the same channel is received, the mistaken restoration of the signal series which is sent in the other communication can be avoided in advance, and the leakage of the sent data which is sent in the other communication can be avoided in advance. Incidentally, in the aforementioned embodiment, there is described a case in which N Nth Walsh vectors are prepared at the time of selecting the orthogonal matrix, respective random phase rotation is given to the Walsh vector, and the Walsh vector to which the phase rotation is given is combined thereby generating more random orthogonal matrix. However, the present invention is not limited thereto. The same advantage as described above can be obtained by generating more random orthogonal matrix by arranging each vector component of the predetermined orthogonal matrix at random. Furthermore, in the aforementioned embodiment, there is described a case in which normalized orthogonal matrix is used as the orthogonal matrix. However, the present invention is not limited thereto. An arbitrary orthogonal matrix which is not normalized may be used. In summary, the same advantage as described above can be obtained by using any orthogonal matrix when the signal series is subjected to the orthogonal conversion by using the orthogonal matrix at the time of sending data. Furthermore, in the aforementioned embodiment, there is described a case in which QPSK modulation is used as the modulation method for the sent data. However, the present invention is not limited thereto. Other modulation method such as BPSK modulation (Binary Phase Shift Keying), 16 QAM modulation (16 Quadrature Amplitude Modulation) may be used. Furthermore, in the aforementioned embodiment, there is described a case in which the present invention is applied to a radio communication system of the communication method such that the signal series is dissipated to a plurality of multiple carriers and is overlapped to send the resulting sending signal to the predetermined channel by converting the frequency, and at the same time, the channel of the sending signal is changed at random for each predetermined timing. However, the present invention is not limited thereto. The present invention may be applied to the radio communication system of the other communication. In summary, when there is a possibility that the so-called same channel interference is generated in which the same channel is used to perform at least two or more communications so that two or more communication electronic waves interfere with each other. As described above, according to the present invention, the orthogonal matrix which is different for each communication is multiplied to the signal series and sent, and the receiving side restores the signal series before the orthogonal conversion by multiplying the inverse matrix of the orthogonal matrix which is used on the sending side of the communication partner to the received signal series. As a consequence, the other communication is performed by using the same channel so that even when the signal series is received the diagonal reverse conversion is not realized even by multiplying the inverse matrix to the signal series because the orthogonal matrix which is used in the orthogonal conversion is different from the other communication, and the signal series which is used in the other communication is not restored. By doing so, even when the same channel is used in the other communication, it is possible to avoid in advance mistaken the restoration of the signal series which is sent in the other communication.

Claims: A transmission method for reducing cochannel interference in a cellular wireless communication network, wherein modulated RF signal data ( x ( A ) / n , x ( B ) / n ) to be transmitted are grouped as vectors ( x ( A ) , x ( B ) ), the vectors ( x ( A ) , x ( B ) ) are multiplied with orthogonal matrices ( M A , M B ) to generate transformed vectors ( y ( A ) , y ( B ) ), and the transformed vectors ( y ( A ) , y ( B ) ) are serialized ( y ( A ) / n , y ( B ) / n ) and transmitted over an air interface, characterized by the steps of multiplying preset orthogonal vectors ( w 1 , w 2 ) by random phase rotations ( R A or R B ) which are different for each communication to obtain phase rotated vectors, generating said orthogonal matrices ( M A , M B ) by arranging said phase rotated vectors in matrix form. A transmitting method according to claim 1, characterized in that said preset vectors ( w 1 , w 2 ) are Walsh vectors. A reception method for reducing cochannel interference in a cellular wireless communication network, wherein received orthogonally transformed and modulated RF signal data ( y ( A ) / n , y ( B ) / n ) are grouped as vectors ( y ( A ) , y ( B ) ), the vectors ( y ( A ) , y ( B ) ) are multiplied with the inverse matrices ( M -1 / A, M -1 / B) of orthogonal matrices ( M A , M B ) to generate transformed vectors ( X ( A ) , X ( B ) , and the transformed vectors ( X ( A ) / n , X ( B ) / n are serialized ( X ( A ) / n , X ( B ) / n ) and demodulated, characterized in that said orthogonal matrices ( M A , M B ) have been generated by multiplying preset orthogonal vectors ( w 1 , w 2 ) by random phase rotations ( R A or R B ) which are different for each communication to obtain phase rotated vectors, and arranging said phase rotated vectors in matrix form. A reception method according to claim 3, characterized in that said preset vectors ( w 1 , w 2 ) are Walsh vectors. A transmitter (10) for a cellular wireless communication network, comprising means (15) for performing an orthogonal transformation on modulated RF signal data ( x ( A ) / n , x ( B ) / n to be transmitted which are grouped as vectors ( x ( A ) , x ( B ) ) said means (15) performing the orthogonal transformation by multiplexing said vectors ( x (A) , x (B) ) with an orthogonal matrix ( M A , M B ) and transmitting means (13, 19) for transmitting the output ( y ( A ) , y ( B ) ) of said orthogonal transformation means, characterized in that said means for performing said orthogonal transformation are adapted to multiply preset orthogonal vectors ( w 1 , w 2 ) by random phase rotations ( R A or R B ) which are different for each communication to obtain phase rotated vectors, and adapted to generate said orthogonal matrix ( M A , M B ) by arranging said phase rotated vectors in matrix form. A transmitter according to claim 5, characterized in that said preset vectors ( w 1 , w 2 ) are Walsh vectors. A receiver (20) for a cellular wireless communication network, comprising receiving means (21, 23) for receiving orthogonally transformed modulated RF signal data ( y ( A ) / n , y ( B ) / n ) grouped as vectors ( y ( A ) , y ( B ) ) and means (27) for performing an inverse orthogonal transformation on the received RF signal data ( y ( A ) , y ( B ) ) said means (27) performing said inverse orthogonal transformation by multiplexing said vectors with the inverse matrix ( M -1 / A, M -1 / B) of an orthogonal matrix ( M A , M B ). characterized in that said orthogonal matrix ( M A , M B ) has been generated by multiplying preset orthogonal vectors ( w 1 , w 2 ) by random phase rotations ( R A -1 or R B -1 ) which are different for each communication to obtain phase rotated vectors, and by arranging said phase rotated vectors in matrix form. A receiver according to claim 7, characterized in that said preset vectors ( w 1 , w 2 ) are Walsh vectors.

Inventors: SAKODA KAZUYUKI, SUZUKI MITSUHIRO, SAKODA, KAZUYUKI, SUZUKI, MITSUHIRO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1998
Main classification: H04K1
IPC codes: H04L23, H04J11