JP4902320B2 - Transmission method and apparatus - Google Patents

Description

  The present invention relates to a transmission technique, and more particularly to a transmission method and apparatus for performing MIMO eigenmode transmission.

One of the techniques for achieving high quality and large capacity wireless communication systems is MIMO (Multiple Input Multiple Output). In the MIMO system, each of the transmission device and the reception device includes a plurality of antennas, and sets a channel corresponding to each antenna. Therefore, the MIMO system realizes a large capacity by setting channels up to the maximum number of antennas for communication between the transmission device and the reception device. Among such MIMO systems, the MIMO eigenmode system can increase the communication capacity. In the MIMO eigenmode system, a channel matrix (hereinafter referred to as “H matrix”) generated from values of transmission path characteristics between a plurality of antennas provided in a transmitting apparatus and a receiving apparatus is derived, and the rank of the H matrix is determined. A corresponding number of orthogonal transmission lines are formed. At that time, eigenbeams corresponding to the respective orthogonal transmission paths are formed (for example, see Non-Patent Document 1).
Kei Sakaguchi, “Construction of MIMO Eigenmode Communication System and Measurement Experiment Results”, IEICE Journal B, September 2004, J87-B, 9, p. 1454-1466

  As the formed eigen beam continues to be fixed, the antenna directivity and side lobes also remain fixed. In such a case, even a wireless device that is not a communication target may be able to continuously receive eigenbeams with a certain level of signal strength. As a result, continuous interception is easily performed by the wireless device. In terms of security, it is desirable that interception by a wireless device that is not a communication target is not continuous.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a transmission technique that reduces the continuity of interception by wireless devices that are not communication targets in MIMO eigenmode transmission.

  In order to solve the above problems, a transmission apparatus according to an aspect of the present invention includes a plurality of transmission antennas that transmit signals formed by a plurality of sequences while weighting by weight vectors is performed, and a plurality of transmission antennas An acquisition unit for acquiring a steering matrix derived by singular value decomposition of a transmission line matrix having a transmission line characteristic between each of the antennas and each of a plurality of receiving antennas as an element value, and steering acquired in the acquisition part While associating multiple column vectors contained in the matrix with multiple sequences, deriving multiple weight vector candidates orthogonal to the column vector associated with a sequence other than one sequence, switching the multiple candidates By selecting, a time vector that varies with time is derived for the one series, and the other series Against respectively, and a deriving unit that derives a weight vector fluctuates temporally.

  According to this aspect, the weight vector candidates that are orthogonal to each other are selected while being switched. Therefore, in MIMO eigenmode transmission, the continuity of interception by a receiving apparatus that is not the communication target is suppressed while suppressing the deterioration of SINR in the communication target receiving apparatus. Can be reduced.

  Another embodiment of the present invention is also a transmission device. The apparatus includes a plurality of transmission antennas that transmit signals formed by two sequences while weighting by weight vectors is performed, and transmission between each of the plurality of transmission antennas and each of the plurality of reception antennas. An acquisition unit that acquires a steering matrix derived by performing singular value decomposition on a transmission path matrix whose element values are path characteristics, and two column vectors and two sequences of the steering matrix acquired in the acquisition unit. By deriving a weight vector for the one series based on the column vector associated with one series, and varying each component included in the column vector associated with the other series A deriving unit for deriving a weight vector that varies with time with respect to other sequences.

  According to this aspect, since the weight vector for other sequences is changed, the continuity of interception by a receiving apparatus that is not a communication target can be reduced in MIMO eigenmode transmission.

  The deriving unit may derive a temporally varying weight vector by changing the amplitude while fixing the phase of each component. In this case, since the amplitude is changed while the phase is fixed, the shape of the side lobe can be modified while enabling in-phase synthesis in the receiving apparatus to be communicated.

  The deriving unit may derive a weight vector that varies with time by causing the inner product of the column vector corresponding to one series and the weight vector to change so as to approach a predetermined value. In this case, since the constraint condition is defined so that the inner product of the column vector and the weight vector approaches a predetermined value, it is possible to suppress the deterioration of the reception characteristics in the receiving device to be communicated.

  Yet another embodiment of the present invention is a transmission method. This method is a transmission method for transmitting signals formed in a plurality of sequences while weighting by a weight vector is performed from a plurality of transmission antennas, and each of a plurality of transmission antennas and a plurality of reception antennas. A step of obtaining a steering matrix derived by singular value decomposition of a transmission line matrix having element values of transmission line characteristics between them, a plurality of column vectors included in the acquired steering matrix, and a plurality of By associating a sequence and deriving a plurality of weight vector candidates orthogonal to a column vector associated with a sequence other than a single sequence, by switching among the candidates, In addition to deriving a temporally varying weight vector, it also varies temporally for each of the other sequences Comprising deriving Eight vector, a.

  Yet another embodiment of the present invention is also a transmission method. This method is a transmission method for transmitting signals formed by two sequences while weighting by a weight vector is performed from a plurality of antennas, each of a plurality of transmission antennas and a plurality of reception antennas. Obtaining a steering matrix derived by singular value decomposition of a transmission line matrix whose element value is a transmission line characteristic between and two column vectors and two sequences of the obtained steering matrix, To derive a weight vector for the one sequence based on the column vector associated with one sequence, and to change each component included in the column vector associated with another sequence To derive a temporally varying weight vector for the other sequences.

  A time vector that varies with time may be derived by varying the amplitude while fixing the phase of each component. A time vector that varies with time may be derived by performing variation so that the inner product of the column vector corresponding to one series and the weight vector approaches a predetermined value.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, in MIMO eigenmode transmission, continuity of interception by a wireless device that is not a communication target can be reduced.

  Before describing the present invention in detail, an outline will be described. Embodiments of the present invention relate to a MIMO system composed of at least two wireless devices. The transmitting side (hereinafter referred to as “transmitting device”) of the wireless devices is compatible with MIMO eigenmode transmission and transmits a packet signal formed by one sequence. In order to perform the MIMO eigenmode transmission, the transmission apparatus acquires transmission path characteristics respectively corresponding to combinations of the plurality of antennas of the transmission apparatus and the plurality of antennas of the reception apparatus (hereinafter, as described above, (The “H matrix” is a summary of the transmission path characteristics corresponding to each in the form of a matrix, etc.). Here, since the MIMO system uses the OFDM modulation scheme, the H matrix is derived in units of carriers. The transmission device derives a steering matrix for each carrier by performing singular value decomposition on the H matrix.

  In normal MIMO eigenmode transmission, a transmission weight vector is derived based on one column vector in the steering matrix. If such a transmission weight vector is fixed, the antenna directivity formed by the transmission device is also fixed. Therefore, when a receiving device that is not a communication target can receive a packet signal from the transmitting device, the packet signal is likely to be continuously received by the receiving device. As a result, it is necessary to improve security for third parties. The transmission apparatus according to the present embodiment derives a transmission weight vector that varies with time by varying each component included in the column vector.

  FIG. 1 shows a spectrum of a multicarrier signal according to an embodiment of the present invention. In particular, FIG. 1 shows the spectrum of a signal in the OFDM modulation scheme. One of a plurality of carriers in the OFDM modulation scheme is generally called a subcarrier, but here, one subcarrier is designated by a “subcarrier number”. In the MIMO system, 56 subcarriers from subcarrier numbers “−28” to “28” are defined. The subcarrier number “0” is set to null in order to reduce the influence of the DC component in the baseband signal. On the other hand, in a system that does not support the MIMO system (hereinafter referred to as “conventional system”), 52 subcarriers from subcarrier numbers “−26” to “26” are defined. An example of a conventional system is a wireless LAN compliant with the IEEE802.11a standard. Further, one signal unit composed of a plurality of subcarriers and one signal unit in the time domain is referred to as an “OFDM symbol”.

  Each subcarrier is modulated by a variably set modulation method. As the modulation method, any one of BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), 64QAM, and 256QAM is used.

  Also, convolutional coding is applied to these signals as an error correction method. The coding rate of convolutional coding is set to 1/2, 3/4, and the like. Furthermore, the number of data to be transmitted in parallel is set variably. As a result, the data rate is also variably set by variably setting the modulation scheme, coding rate, and number of sequences. The “data rate” may be determined by any combination of these, or may be determined by one of them. In the conventional system, when the modulation method is BPSK and the coding rate is 1/2, the data rate is 6 Mbps. On the other hand, when the modulation method is BPSK and the coding rate is 3/4, the data rate is 9 Mbps.

  FIG. 2 shows a configuration of the communication system 100 according to the embodiment of the present invention. The communication system 100 includes a first wireless device 10a and a second wireless device 10b collectively referred to as a wireless device 10. The first radio apparatus 10a includes a first antenna 12a, a second antenna 12b, a third antenna 12c, and a fourth antenna 12d, which are collectively referred to as an antenna 12, and the second radio apparatus 10b is collectively referred to as an antenna 14. A first antenna 14a, a second antenna 14b, a third antenna 14c, and a fourth antenna 14d are included. Here, the first radio apparatus 10a corresponds to a transmission apparatus, and the second radio apparatus 10b corresponds to a reception apparatus.

  As a configuration of the communication system 100, an outline of a MIMO system will be described. It is assumed that data is transmitted from the first radio apparatus 10a to the second radio apparatus 10b. The first radio apparatus 10a transmits a plurality of series of data from each of the first antenna 12a to the fourth antenna 12d. As a result, the data rate is increased. The second radio apparatus 10b receives a plurality of series of data by the first antenna 14a to the fourth antenna 14d. Furthermore, the second radio apparatus 10b separates the received data by adaptive array signal processing and independently demodulates a plurality of series of data.

  Here, since the number of antennas 12 is “4” and the number of antennas 14 is also “4”, the combination of transmission paths between the antennas 12 and 14 is “16”. A transmission path characteristic between the i-th antenna 12i and the j-th antenna 14j is denoted by hij. In the figure, the transmission path characteristic between the first antenna 12a and the first antenna 14a is h11, the transmission path characteristic between the first antenna 12a and the second antenna 14b is h12, the second antenna 12b and the first antenna. 14a, the transmission path characteristic between the second antenna 12b and the second antenna 14b is h22, and the transmission path characteristic between the fourth antenna 12d and the fourth antenna 14d is h44. Has been. Note that transmission lines other than these are omitted for clarity of illustration. In order to acquire each channel characteristic, a training signal is transmitted from the first radio apparatus 10a to the second radio apparatus 10b. Further, the first radio apparatus 10a and the second radio apparatus 10b may be reversed.

  FIG. 3 is a sequence diagram showing a procedure for deriving a transmission weight vector in the communication system 100. The first radio apparatus 10a transmits a training signal to the second radio apparatus 10b (S10). The configuration of the training signal will be described later. The second radio apparatus 10b estimates the H matrix based on the training signal (S12). The second radio apparatus 10b transmits the H matrix to the first radio apparatus 10a (S14). The first radio apparatus 10a derives a transmission weight vector after deriving a steering matrix based on the H matrix (S16). The first radio apparatus 10a transmits a data signal to the second radio apparatus 10b while using the transmission weight vector (S18). Following this, when a data signal is transmitted from the first radio apparatus 10a to the second radio apparatus 10b, the first radio apparatus 10a uses a transmission weight vector that varies with time.

  4A to 4D show packet formats in the communication system 100. FIG. 4A to 4D show a format of a normal packet signal, not a training signal. Here, FIG. 4A corresponds to the case where the number of series is “4”, FIG. 4B corresponds to the case where the number of series is “3”, and FIG. Corresponds to the case where the number of series is “2”, and FIG. 4D corresponds to the case where the number of series is “1”. As described above, in this embodiment, since the number of series is “1”, only FIG. 4D is used, but a packet format used in a later-described modification will be described here. In FIG. 4A, it is assumed that data included in the four sequences is to be transmitted, and packet formats corresponding to the first to fourth sequences are shown in order from the top to the bottom.

  In the packet signal corresponding to the first stream, “L-STF”, “HT-LTF”, and the like are arranged as preamble signals. “L-STF”, “L-LTF”, “L-SIG”, “HT-SIG” are known signals for AGC setting, known signals for transmission path estimation, control signals, MIMO systems corresponding to conventional systems Correspond to the control signals corresponding to. The control signal corresponding to the MIMO system includes, for example, information on the number of sequences and the destination of the data signal. “HT-STF” and “HT-LTF” correspond to a known signal for AGC setting and a known signal for channel estimation corresponding to the MIMO system. On the other hand, “data 1” is a data signal. Note that L-LTF and HT-LTF are used not only for AGC setting but also for timing estimation.

  Also, in the packet signal corresponding to the second stream, “L-STF (−50 ns)”, “HT-LTF (−400 ns)” and the like are arranged as preamble signals. Further, in the packet signal corresponding to the third stream, “L-STF (−100 ns)”, “HT-LTF (−200 ns)”, and the like are arranged as preamble signals. In the packet signal corresponding to the fourth stream, “L-STF (−150 ns)”, “HT-LTF (−600 ns)”, and the like are arranged as preamble signals.

  Here, “−400 ns” or the like indicates a timing shift amount in CDD (Cyclic Delay Diversity). CDD is a process in which a waveform in the time domain is shifted backward by a shift amount in a predetermined section, and a waveform pushed out from the last part of the predetermined section is cyclically arranged at the head portion of the predetermined section. That is, “L-STF (−50 ns)” is cyclically shifted with a delay amount of −50 ns with respect to “L-STF”. The L-STF and the HT-STF are configured by repeating a period of 800 ns, and the other HT-LTFs are configured by a repeating part of a period of 3.2 μs and a GI part of 0.8 μs. Here, “data 1” to “data 4” are also CDDed, and the timing shift amount is the same value as the timing shift amount in the HT-LTF arranged in the preceding stage.

  In the first stream, HT-LTFs are arranged in the order of “HT-LTF”, “−HT-LTF”, “HT-LFT”, and “−HT-LTF” from the top. Here, these are sequentially referred to as “first component”, “second component”, “third component”, and “fourth component” in all series. If the calculation of the first component-second component + third component-fourth component is performed on all series of received signals, the receiving apparatus extracts a desired signal for the first series. Further, if the calculation of the first component + second component + third component + fourth component is performed on all series of received signals, the receiving apparatus extracts a desired signal for the second series. Further, if the calculation of the first component-second component-third component + fourth component is performed on all series of received signals, the receiving apparatus extracts a desired signal for the third series. Also, if the calculation of the first component + second component−third component−fourth component is performed on the received signals of all sequences, the desired signal for the fourth sequence is extracted in the receiving apparatus. These correspond to the combination of codes of predetermined components having an orthogonal relationship between sequences. The addition / subtraction process is executed by vector calculation.

  In the part from “L-LTF” to “HT-SIG” and the like, “52” subcarriers are used as in the conventional system. Of the “52” subcarriers, “4” subcarriers correspond to pilot signals. On the other hand, “56” subcarriers are used in the subsequent parts such as “HT-LTF”.

  In FIG. 4A, the sign of “HT-LTF” is defined as follows. The codes are arranged in the order of “+”, “−”, “+”, “−” in order from the top of the first sequence, and the codes are “+”, “+”, “+” in order from the top of the second sequence. Arranged in the order of “+” and “+”, the codes are arranged in the order of “+”, “−”, “−” and “+” in order from the top of the third series, and from the top of the fourth series. In order, the codes are arranged in the order of “+”, “+”, “−”, and “−”. However, the code | symbol may be prescribed | regulated as follows. The codes are arranged in the order of “+”, “−”, “+”, “+” in order from the top of the first sequence, and the codes are “+”, “+”, “+” in order from the top of the second sequence. Arranged in the order of “−” and “+”, the codes are arranged in the order of “+”, “+”, “+”, “−” in order from the top of the third series, and from the top of the fourth series. In order, the symbols are arranged in the order of “−”, “+”, “+”, “+”. Even such a code corresponds to a combination of codes of predetermined components having an orthogonal relationship between sequences.

  FIG. 4B corresponds to the first to third sequences in FIG. FIG. 4C is similar to the first series and the second series in the packet format shown in FIG. Here, the arrangement of “HT-LTF” in FIG. 4C is different from the arrangement of “HT-LTF” in FIG. That is, the HT-LTF includes only the first component and the second component. In the first sequence, HT-LTFs are arranged in the order of “HT-LTF” and “HT-LTF” from the top, and in the second sequence, HT-LTFs are arranged from the top to “HT-LTF”, “− They are arranged in the order of “HT-LTF”. If the calculation of the first component + the second component is performed on the reception signals of all sequences, the reception device extracts the desired signal for the first sequence. Also, if the first component-second component calculation is performed on all series of received signals, the receiving apparatus extracts a desired signal for the second series. These can also be said to be orthogonal as described above. In FIG. 4D, only one “HT-LTF” is arranged. Here, the packet signals shown in FIGS. 4A to 4D, particularly FIG. 4D, are transmitted while being beam-formed by MIMO eigenmode transmission.

  FIGS. 5A to 5D show training signal packet formats in the communication system 100. FIG. Note that the training signal indicates that the number of sequences in which a known signal for channel estimation, that is, HT-LTF is arranged is larger than the number of sequences in which a data signal is arranged. In the following, for the sake of clarity, “L-STF” to “HT-SIG” included in the packet format are omitted. That is, the configuration after “HT-STF” is shown. FIG. 5A shows a case where the number of sequences (hereinafter referred to as “main sequences”) in which data signals are arranged is “3”, and FIG. 5B shows that the number of main sequences is “2”. FIGS. 5C to 5D show the case where the number of main sequences is “1”. That is, in FIG. 5A, data signals are arranged from the first series to the third series, and in FIG. 5B, data signals are arranged in the first series and the second series. In 5 (c)-(d), data signals are arranged in the first stream.

  Of the first to third sequences in FIG. 5A, the arrangement related to HT-LTF is the same as the arrangement in FIG. 4B. However, in the subsequent stage, blank periods are provided from the first series to the third series. On the other hand, in a blank period from the first series to the third series, HT-LTF is arranged in the fourth series. Further, following the HT-LTF arranged in the fourth series, data is arranged from the first series to the third series. In the fourth series, one HT-LTF is arranged.

  With such an arrangement, the number of sequences in which “HT-STF” is arranged becomes equal to the number of sequences in which data signals are arranged, and therefore included in the amplification factor set by “HT-STF” in the receiving apparatus. Error can be reduced, and deterioration of data signal reception characteristics can be prevented. In addition, since “HT-LTF” arranged in the fourth sequence is only arranged in one sequence, the “HT-LTF” arranged in the fourth sequence in the receiving apparatus is so distorted as to be caused by AGC. The situation where it is amplified can be reduced. Therefore, it is possible to prevent deterioration in accuracy of transmission path estimation.

  Of the first and second sequences in FIG. 5B, the arrangement related to HT-LTF is the same as the arrangement in FIG. 4C. However, in the subsequent stage, blank periods are provided in the first series and the second series. On the other hand, in the blank period in the first sequence and the second sequence, HT-LTF is arranged in the third sequence and the fourth sequence. Further, following the HT-LTF arranged in the third series and the fourth series, data is arranged in the first series and the second series. The arrangement of HT-LTFs in the third series and the fourth series is the same as the arrangement in FIG.

  Here, with respect to the timing shift amount, it is assumed that the priority is defined such that the priority decreases in the order of “0 ns”, “−400 ns”, “−200 ns”, and “−600 ns”. That is, it is defined that “0 ns” has the highest priority and “−600 ns” has the lowest priority. Therefore, in the first series and the second series, values of “0 ns” and “−400 ns” are used as timing shift amounts. On the other hand, values of “0 ns” and “−400 ns” are also used as timing shift amounts in the third and fourth series. As a result, the combination of “HT-LTF” and “HT-LTF” in the first sequence is also used in the third sequence, and “HT-LTF (−400 ns)” and “−HT in the second sequence are used. Since the combination of “−LTF (−400 ns)” is also used in the fourth stream, the processing becomes simple.

  The arrangement related to the HT-LTF in the first series in FIG. 5C is equivalent to the arrangement for the first series in FIG. Here, two “HT-LTF” are arranged. However, in the subsequent stage, a blank period is provided in the first series. On the other hand, in the blank period in the first sequence, HT-LTF is arranged in the second sequence to the fourth sequence. In addition, following the HT-LTF arranged from the second series to the fourth series, data is arranged in the first series. Here, the arrangement of HT-LTFs arranged from the second series to the third series is similar to the arrangement in FIG.

  FIG. 5D is configured in the same manner as FIG. 5C, but the combination of symbols “HT-LTF” in FIG. 5D is different from that in FIG. Here, the combination of codes “HT-LTF” is defined such that an orthogonal relationship is established between sequences. Further, in FIG. 5D, it is defined that the combination of “HT-LTF” codes is fixed for each of a plurality of sequences. Here, in FIG. 5D, as in FIG. 5C, “0 ns”, “−400 ns”, and “−200 ns” having high priorities even in the second to fourth series. Is used.

  One “HT-LTF” is arranged in the fourth series in FIG. 5A, that is, a series in which data is not arranged (hereinafter referred to as “sub-sequence”). Also, two “HT-LTFs” are arranged in the third series and the fourth series in FIG. Furthermore, four “HT-LTFs” are arranged from the second series to the fourth series in FIGS. When these are compared, the length of “HT-LTF” arranged in the subsequence in FIGS. 5C to 5D is the longest. That is, when the number of main sequences in the packet signal for which a training signal is to be generated increases, the length of the sub-sequence decreases and transmission efficiency improves. It is assumed that the training signal is not beam-formed by MIMO eigenmode transmission.

  6A to 6D show other packet formats for training signals in the communication system 100. FIG. FIGS. 6A to 6D correspond to FIGS. 5A to 5D, respectively. In FIGS. 6A to 6D, the timing shift amount is defined while being associated with each of the plurality of sequences. Here, a timing shift amount “0 ns” is defined for the first sequence, a timing shift amount “−400 ns” is defined for the second sequence, and a timing shift amount “−” is defined for the third sequence. 200 ns ”is defined, and the timing shift amount“ −600 ns ”is defined for the fourth stream.

  Therefore, in FIG. 6A, “−600 ns” is used instead of the timing shift amount “0 ns” in the fourth series in FIG. 5A. In FIG. 6B, instead of the timing shift amounts “0 ns” and “−400 ns” in the third sequence and the fourth sequence in FIG. 5B, “−200 ns” and “−600 ns”. Is used. On the other hand, in FIGS. 6C to 6D, timing shift amounts “0 ns”, “−400 ns”, and “−200 ns” from the second series to the fourth series in FIGS. 5C to 5D are used. Instead of “−400 ns”, “−200 ns”, “−600 ns” are used.

  FIG. 6D is configured in the same manner as FIG. 6C, but the combination of symbols “HT-LTF” in FIG. 6D is different from that in FIG. Priorities are provided in advance for combinations of signs of “HT-LTF”. That is, the code combination in the first sequence in FIG. 4A has the highest priority and the code combination in the fourth sequence has the lowest priority. In addition, a combination of codes is used in order from a combination of codes with higher priority for a sequence in which a data signal is arranged, and a code in order from a combination of codes with a higher priority is also used for a sequence in which no data signal is arranged. Use a combination of In this way, if the combination of codes is the same, calculation of transmission path characteristics for the “HT-LTF” portion of the sequence in which no data is arranged when the receiving apparatus performs the + − operation to extract each component. In addition, a common circuit can be used for the calculation of the transmission path characteristics for the “HT-LTF” portion of the sequence in which data is arranged.

  FIG. 7 shows a packet format of a training signal that is finally transmitted in the communication system 100. FIG. 7 corresponds to the case where the packet signals of FIG. 5B and FIG. 6B are modified. An operation using an orthogonal matrix described later is performed on “HT-STF” and “HT-LTF” arranged in the first sequence and the second sequence in FIG. 5B and FIG. 6B. As a result, “HT-STF4” is generated from “HT-STF1”. The same applies to “HT-LTF”. Further, CDD with timing shift amounts “0 ns”, “−50 ns”, “−100 ns”, and “−150 ns” is performed for each of the first to fourth streams. The absolute value of the timing shift amount at the second CDD is set to be smaller than the absolute value of the timing shift amount at the first CDD for HT-STF and HT-LTF. Similar processing is executed for “HT-LTF” arranged in the third series and the fourth series, “data 1” of the first series, and the like.

  FIG. 8 shows the configuration of the first radio apparatus 10a. The first radio apparatus 10a includes a first radio unit 20a, a second radio unit 20b, a fourth radio unit 20d, a baseband processing unit 22, a modem unit 24, an IF unit 26, and a control unit 30, which are collectively referred to as a radio unit 20. Including. The IF unit 26 includes a combining unit 90, a decoding unit 92, a separation unit 94, and an encoding unit 96. Also, as signals, a first time domain signal 200a, a second time domain signal 200b, a fourth time domain signal 200d, which are collectively referred to as a time domain signal 200, a first frequency domain signal 202a, which is generically referred to as a frequency domain signal 202, A frequency domain signal 202b and a fourth frequency domain signal 202d are included. The second radio apparatus 10b is configured in the same manner as the first radio apparatus 10a. The first radio apparatus 10a includes a plurality of antennas 12 and performs communication with a second radio apparatus 10b (not shown) and a plurality of antennas 14 (not shown). .

  As a reception operation, the radio unit 20 performs frequency conversion on a radio frequency signal received by the antenna 12 and derives a baseband signal. The radio unit 20 outputs the baseband signal to the baseband processing unit 22 as a time domain signal 200. In general, baseband signals are formed by in-phase and quadrature components, so they should be transmitted by two signal lines. Here, for clarity of illustration, only one signal line is used. Shall be shown. An AGC and A / D converter are also included. AGC sets the amplification factor based on “L-STF” and “HT-STF”.

  As a transmission operation, the radio unit 20 performs frequency conversion on the baseband signal from the baseband processing unit 22 and derives a radio frequency signal. Here, a baseband signal from the baseband processing unit 22 is also shown as a time domain signal 200. The radio unit 20 outputs a radio frequency signal to the antenna 12. That is, the radio unit 20 transmits a radio frequency packet signal from the antenna 12. Further, a PA (Power Amplifier) and a D / A converter are also included. The time domain signal 200 is a multicarrier signal converted into the time domain, and is a digital signal.

  As a reception operation, the baseband processing unit 22 converts each of the plurality of time domain signals 200 into the frequency domain, and performs adaptive array signal processing on the frequency domain signal. The baseband processing unit 22 outputs the result of adaptive array signal processing as the frequency domain signal 202. One frequency domain signal 202 corresponds to data included in each of a plurality of transmitted sequences. As a transmission operation, the baseband processing unit 22 receives the frequency domain signal 202 as a frequency domain signal from the modulation / demodulation unit 24, and executes dispersion processing using a weight vector. That is, the eigenbeam is formed in the MIMO eigenmode transmission. The description of MIMO eigenmode transmission will be described later.

  The baseband processing unit 22 converts the frequency domain signal into the time domain and outputs the time domain signal 200. It is assumed that the number of antennas 12 to be used in the transmission process is specified by the control unit 30. Here, the frequency domain signal 202, which is a frequency domain signal, includes a plurality of subcarrier components as shown in FIG. For the sake of clarity, it is assumed that the signals in the frequency domain are arranged in the order of subcarrier numbers to form a serial signal.

  FIG. 9 shows the structure of a signal in the frequency domain. Here, one combination of subcarrier numbers “−28” to “28” shown in FIG. 1 is referred to as an “OFDM symbol”. In the “i” th OFDM symbol, subcarrier components are arranged in the order of subcarrier numbers “1” to “28” and subcarrier numbers “−28” to “−1”. Also, the “i−1” th OFDM symbol is arranged before the “i” th OFDM symbol, and the “i + 1” th OFDM symbol is arranged after the “i” th OFDM symbol. And In addition, in the part such as “L-SIG” in FIG. 4A and the like, a combination of subcarrier numbers “−26” to “26” is used for one “OFDM symbol”.

  Returning to FIG. The modem unit 24 demodulates the frequency domain signal 202 from the baseband processing unit 22 as a reception process. Note that demodulation is performed in units of subcarriers. The modem unit 24 outputs the demodulated signal to the IF unit 26. Further, the modem unit 24 performs modulation as transmission processing. The modem unit 24 outputs the modulated signal to the baseband processing unit 22 as the frequency domain signal 202.

  As a reception process, the IF unit 26 combines signals from the plurality of modulation / demodulation units 24 in the combining unit 90 to form one data stream. Further, the decoding unit 92 performs decoding after executing deinterleaving on one data stream. The IF unit 26 outputs the decoded data stream. In addition, the IF unit 26 inputs one data stream as transmission processing, performs encoding and interleaving in the encoding unit 96, and then separates them in the separation unit 94. Further, the IF unit 26 outputs the separated data to the plurality of modulation / demodulation units 24.

  The control unit 30 controls the timing of the first radio apparatus 10a. Hereinafter, the processing content of the first radio apparatus 10a will be described in association with the operation in FIG. An outline of MIMO eigenmode transmission will be described as a premise of the processing. Therefore, hereinafter, (1) an outline of MIMO eigenmode transmission, (2) transmission of a training signal, and (3) derivation of a transmission weight vector will be described in this order.

(1) Outline of MIMO Eigenmode Transmission The H matrix has the number of elements determined from the number of a plurality of antennas 12 and the number of a plurality of antennas 14 (not shown) for each subcarrier. For example, as shown in FIG. 2, when the number of the plurality of antennas 12 is “4” and the number of the plurality of antennas 14 is also “4”, the H matrix has 4 rows and 4 for one subcarrier. It becomes a column. In addition, each component included in the H matrix has the above-described transmission path characteristics, and corresponds to hij in FIG.

  Such an H matrix is derived in the second radio apparatus 10b as described above. Hereinafter, processing for one subcarrier will be described for ease of explanation. The training signal received by the second radio apparatus 10b is shown as a received signal vector Y. Y represents the number of antennas 14 as the number of elements. The transmitted training signal is shown as a transmission signal vector X. X is the number of antennas 12 and the number of elements. If defined as above, the relationship between the Y, X, and H matrices is shown as follows.

ｎは、雑音ベクトルである。Ｈ行列は、アンテナ１４の数を行の数とし、アンテナ１２の数を列の数とする。また、図２の場合、Ｈ行列の各要素は、以下のように示される。

n is a noise vector. In the H matrix, the number of antennas 14 is the number of rows, and the number of antennas 12 is the number of columns. Moreover, in the case of FIG. 2, each element of H matrix is shown as follows.

Σは、以下のように示される対角行列であり、特異値行列に相当する。

The control unit 30 of the first radio apparatus 10a performs singular value decomposition on the H matrix. The singular value decomposition for the H matrix is shown as follows.

Σ is a diagonal matrix shown as follows and corresponds to a singular value matrix.

U and V are singular matrices, which are unitary matrices each constituted by the number of antennas 12 by 4 columns and the number of antennas 14 by 4 columns. V corresponds to the aforementioned steering matrix. Further, V ^H is composed of four column vectors, and each of the four column vectors is associated with each singular value included in the singular value matrix. For example, when a packet signal formed by four sequences is transmitted in MIMO eigenmode transmission, v1 to v4 are used as transmission weight vectors for each of the first sequence to the fourth sequence. In the second radio apparatus 10b, is received by the receiving weight vector represented by U ^H is made. Such a reception weight vector is derived by, for example, MMSE (Minimum Mean Square Error).

(2) Transmission of Training Signal The control unit 30 cooperates with the IF unit 26, the modulation / demodulation unit 24, and the baseband processing unit 22 in FIGS. 5 (a)-(d), 6 (a)-(d), A packet signal having a packet format as shown in FIG. 7 is generated, and control for transmitting the generated packet signal is executed. Here, the processing for generating the packet format shown in FIGS. 5B and 6B will be mainly described, but the same processing is executed for other packet formats.

  In the IF unit 26, data to be arranged in at least one of a plurality of series is input. Here, as shown in FIGS. 5B and 6B, data to be arranged in two series is input. The control unit 30 provides the baseband processing unit 22 with “HT-STF” and “HT-STF” sequences in which the input data is arranged, that is, the first sequence and the second sequence. An instruction is given to generate a packet signal from “HT-LTF” arranged in a plurality of series in the subsequent stage and data arranged in the first series and the second series. As shown in FIGS. 4A to 4D, the control unit 30 includes “L-STF”, “L-LTF”, “L-SIG”, and “HT-SIG” in the previous stage of the HT-STF. An instruction is output to the baseband processing unit 22 so as to be arranged.

  Here, as described in FIG. 5B and FIG. 6B, the case where two “HT-LTFs” are arranged for one series will be described. That is, the entire “HT-LTF” is formed by repeating “HT-LTF” in the time domain. Further, the combination of codes “HT-LTF” is defined so that an orthogonal relationship between main sequences or sub-sequences is established. As a result, as described above, if the first component and the second component are added in the main sequence, the HT-LTF for the first sequence is extracted. Further, if the second component is subtracted from the first component in the main sequence, the HT-LTF for the second sequence is extracted.

  Note that the number of “HT-LTFs” arranged in one sequence is determined by the number necessary to establish the orthogonal relationship. Therefore, if the number of sequences to establish the orthogonal relationship is “2”, the number of “HT-LTF” per sequence is “2”. On the other hand, if the number of sequences to establish the orthogonal relationship is “3” or “4”, the number of “HT-LTF” per sequence is “4”.

  The control unit 30 causes the baseband processing unit 22 to execute CDD on HT-LTF or the like. Note that CDD corresponds to causing the HT-LTF arranged in another series to perform a cyclic timing shift in the HT-LTF based on the HT-LTF arranged in one series. The control unit 30 provides a priority in advance for the timing shift amount. Here, as described above, the priority of the timing shift amount “0 ns” is set to be the highest, and subsequently, the priority is decreased in the order of “−400 ns”, “−200 ns”, and “−600 ns”. Set.

  Furthermore, the control unit 30 causes the baseband processing unit 22 to use the timing shift amount in order from the timing shift amount with the highest priority for the main sequence. For example, in the case of FIG. 5B, “0 ns” is used for the first sequence, and “−400 ns” is used for the second sequence. Also, the control unit 30 causes the timing shift amounts to be used in order from the timing shift amount with the highest priority for the subsequences. For example, in the case of FIG. 5B, “0 ns” is used for the third series, and “−400 ns” is used for the fourth series. Through the above processing, a packet signal having the packet format shown in FIG. 5B is generated.

  On the other hand, different timing shift amounts may be set for a plurality of sequences. For example, “0 ns” is set as the timing shift amount of the first sequence, “−400 ns” is set as the timing shift amount of the second sequence, and “−200 ns” is set as the timing shift amount of the third sequence. Is set, and “−600 ns” is set as the timing shift amount of the fourth stream. Through the above processing, a packet signal having the packet format shown in FIG. 6B is generated.

  After the packet signal of the packet format as shown in FIGS. 5A to 5D and FIGS. 6A to 6D is generated by the above processing, the control unit 30 transmits the packet signal to the baseband processing unit 22. These packet signals are deformed. That is, the control unit 30 changes the packet format shown in FIGS. 5B and 6B to the packet format shown in FIG. The baseband processing unit 22 performs CDD on the extended sequence after extending the number of sequences to the number of multiple sequences. Further, the control unit 30 causes the radio unit 20 to transmit the modified packet signal.

(3) Derivation of transmission weight vector The control unit 30 receives the H matrix from the second radio apparatus 10b via the radio unit 20, the baseband processing unit 22, and the like. The controller 30 derives the steering matrix by performing singular value decomposition as described above, and obtains a column vector, for example, v1 ^H (hereinafter referred to as “v1”) from the steering matrix. In the embodiment, without using v1 as a transmission weight vector as it is, the control unit 30 derives a transmission weight vector that varies with time by changing each component included in the acquired column vector v1. Here, in particular, a transmission weight vector that varies with time is derived by varying the amplitude while fixing the phase of each component. Note that the fluctuation is made on a packet signal basis.

  The above process will be specifically described. Here, for convenience of explanation, the column vector v1 has four components, and the four components are represented as v1 (1), v1 (2), v1 (3), and v1 (4). To do. One component is indicated by a complex number and has an in-phase component and a quadrature component. The control unit 30 stores a table in which variation patterns for each of v1 (1), v1 (2), and v1 (3) are shown. The table includes a plurality of amplifications such as “1.1 times”, “0.9 times”, and “1.15 times” for each of v1 (1), v1 (2), and v1 (3). The rates are lined up. Further, the control unit 30 acquires the amplification factor in order from the front of the table for each packet signal, and multiplies v1 (1) and the like. Here, the multiplication is performed on the in-phase component and the quadrature component such as v1 (1). As a result, the values of v1 (1), v1 (2), and v1 (3) vary in packet signal units. Here, the multiplication results are indicated as v1 '(1), v1' (2), and v1 '(3).

  Further, the changed column vector is denoted by v1 ', and the remaining component of the varied column vector is denoted by v1' (4). The control unit 30 determines the value of v1 ′ (4) so that the inner product value of v1 and v1 ′ becomes a predetermined value “α”. As a result, v1 'is specified, and the control unit 30 sets this as a transmission weight vector. The above processing is performed in units of packet signals. In other words, the control unit 30 causes the component other than one of the components to execute a variation according to a predetermined pattern, and the inner product of v1 and the transmission weight vector is a predetermined value for one component. By performing the adjustment so as to approach “α”, a transmission weight vector that varies with time is derived. As a result, even if the column vector value is the same over a plurality of packet signals, the transmission weight vector has a different value for each packet. Further, the baseband processing unit 22 transmits a signal that has been weighted by the weight vector.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it is realized by a program having a communication function loaded in the memory. Describes functional blocks realized by collaboration. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 10 shows the configuration of the baseband processing unit 22. The baseband processing unit 22 includes a reception processing unit 50 and a transmission processing unit 52. The reception processing unit 50 executes a part corresponding to the reception operation among the operations in the baseband processing unit 22. That is, the reception processing unit 50 performs adaptive array signal processing on the time domain signal 200, and for that purpose, derivation of the weight vector of the time domain signal 200 is performed. Further, the reception processing unit 50 outputs the result of array synthesis as the frequency domain signal 202. The reception processing unit 50 estimates the above-described H matrix based on the frequency domain signal 202 corresponding to the training signal.

  The transmission processing unit 52 executes a part corresponding to the transmission operation among the operations in the baseband processing unit 22. That is, the reception processing unit 50 generates the time domain signal 200 by converting the frequency domain signal 202. In addition, the transmission processing unit 52 associates a plurality of sequences with the plurality of antennas 12, respectively. Further, the transmission processing unit 52 executes the CDD as shown in FIGS. 5A to 6D, 6A to 6D, and FIG. On the other hand, MIMO eigenmode transmission is executed. The transmission processing unit 52 finally outputs the time domain signal 200.

  FIG. 11 shows the configuration of the reception processing unit 50. The reception processing unit 50 includes an FFT unit 74, a weight vector deriving unit 76, a first combining unit 80a, a second combining unit 80b, a third combining unit 80c, and a fourth combining unit 80d, which are collectively referred to as a combining unit 80.

  The FFT unit 74 converts the time domain signal 200 into a frequency domain value by performing FFT on the time domain signal 200. Therefore, it is assumed that the frequency domain values are configured as shown in FIG. That is, the frequency domain value for one time domain signal 200 is output on one signal line.

  The weight vector deriving unit 76 derives a reception weight vector for each subcarrier from the frequency domain value. The reception weight vector is derived so as to correspond to each of a plurality of sequences, and the reception weight vector for one sequence has elements corresponding to the number of antennas 12 in units of subcarriers. In addition, an adaptive algorithm may be used to derive a reception weight vector corresponding to each of a plurality of sequences, or transmission path characteristics may be used. However, a known technique is used for these processes. Therefore, the description is omitted here. The weight vector deriving unit 76 calculates the first component-second component + third component-fourth component or the first component + second component, etc., as described above, when deriving the received weight vector. To do. Finally, as described above, weights are derived in units of subcarriers, antennas 12 and sequences. The weight vector deriving unit 76 derives a reception weight vector and derives the above-described H matrix in units of subcarriers.

  The synthesizer 80 synthesizes the frequency domain value converted by the FFT unit 74 and the received weight vector from the weight vector derivation unit 76. For example, among the received weight vectors from the weight vector deriving unit 76, the weight corresponding to one subcarrier and the weight corresponding to the first stream are selected as one multiplication target. The selected weight has a value corresponding to each of the antennas 12.

  As another multiplication target, a value corresponding to one subcarrier is selected from the values in the frequency domain converted by the FFT unit 74. The selected value has a value corresponding to each of the antennas 12. Note that the selected weight and the selected value correspond to the same subcarrier. While being associated with each of the antennas 12, the selected weight and the selected value are respectively multiplied, and the multiplication result is added, whereby a value corresponding to one subcarrier in the first sequence is obtained. Derived. In the first synthesizing unit 80a, the above processing is also performed on other subcarriers, and data corresponding to the first stream is derived. Further, in the second synthesis unit 80b to the fourth synthesis unit 80d, data corresponding to the fourth series is derived from the second series by the same processing. The derived first to fourth sequences are output as the first frequency domain signal 202a to the fourth frequency domain signal 202d, respectively.

ここで、δは、シフト量を示し、ｌは、サブキャリア番号を示している。さらに、行列Ｃと系列との乗算は、サブキャリアを単位にして実行される。すなわち、分散部６６は、Ｌ−ＳＴＦ等内での循環的なタイミングシフトを系列単位に実行する。また、タイミングシフト量は、図５（ａ）−（ｄ）、図６（ａ）−（ｄ）のごとく設定される。 FIG. 12 shows the configuration of the transmission processing unit 52. The transmission processing unit 52 includes a distribution unit 66 and an IFFT unit 68. The dispersion unit 66 associates the frequency domain signal 202 with the antenna 12. First, processing when transmitting a training signal will be described. The distribution unit 66 performs CDD in order to generate a packet signal corresponding to the packet formats of FIGS. 5A to 5D and FIGS. 6A to 6D. CDD is performed as matrix C as follows.

Here, δ indicates a shift amount, and l indicates a subcarrier number. Further, the multiplication of the matrix C and the sequence is executed in units of subcarriers. That is, the distribution unit 66 performs a cyclic timing shift within the L-STF or the like on a sequence basis. Further, the timing shift amount is set as shown in FIGS. 5A to 5D and FIGS. 6A to 6D.

  The distribution unit 66 multiplies the training signal generated as shown in FIGS. 5A to 5D and FIGS. 6A to 6D by the steering matrix, thereby obtaining the number of training signal sequences. Is increased to the number of series. Here, the dispersion unit 66 extends the order of the input signal to the number of a plurality of sequences before performing multiplication. In the case of FIGS. 5B and 6B, since “HT-STF” or the like arranged in the first sequence and the second sequence is input, the number of input signals is “2”. Yes, represented here by “Nin”.

  Therefore, the input data is indicated by a vector “Nin × 1”. Further, the number of the plurality of series is “4”, and is represented by “Nout” here. The distribution unit 66 extends the order of the input data from Nin to Nout. That is, the vector “Nin × 1” is expanded to the vector “Nout × 1”. At that time, “0” is inserted into the components from the Nin + 1 line to the Nout line. On the other hand, with respect to “HT-LTF” arranged in the third series and the fourth series in FIGS. 5B and 6B, the components up to Nin are “0”, and the Nin + 1th row HT-LTF and the like are inserted in the components from to the Nout line.

ステアリング行列は、「Ｎｏｕｔ×Ｎｏｕｔ」の行列である。また、Ｗは、直交行列であり、「Ｎｏｕｔ×Ｎｏｕｔ」の行列である。直交行列の一例は、ウォルシュ行列である。ここで、ｌは、サブキャリア番号を示しており、ステアリング行列による乗算は、サブキャリアを単位にして実行される。さらに、Ｃは、前述のごとく、ＣＤＤを示す。ここで、ＣＤＤにおけるタイミングシフト量は、複数の系列のそれぞれに対して異なるように規定されている。すなわち、第１の系列に対して「０ｎｓ」、第２の系列に対して「−５０ｎｓ」、第３の系列に対して「−１００ｎｓ」、第４の系列に対して「−１５０ｎｓ」のようにタイミングシフト量が規定される。 The steering matrix S is shown as follows.

The steering matrix is a “Nout × Nout” matrix. W is an orthogonal matrix, which is a “Nout × Nout” matrix. An example of an orthogonal matrix is a Walsh matrix. Here, l indicates a subcarrier number, and multiplication by the steering matrix is executed in units of subcarriers. Further, C represents CDD as described above. Here, the timing shift amount in the CDD is defined to be different for each of the plurality of sequences. That is, “0 ns” for the first sequence, “−50 ns” for the second sequence, “−100 ns” for the third sequence, “−150 ns” for the fourth sequence, etc. The amount of timing shift is defined in FIG.

  When performing the MIMO eigenmode transmission, the dispersion unit 66 inputs the above-described transmission weight vector from the control unit 30 (not shown), and receives the packet signal of FIG. 4D from the modulation / demodulation unit 24 (not shown). The distribution unit 66 multiplies the packet signal by the transmission weight vector. The IFFT unit 68 performs IFFT on the signal from the dispersion unit 66 to generate a time domain signal 200.

  The operation of the communication system 100 configured as above will be described. The first radio apparatus 10a transmits a training signal to the second radio apparatus 10b. When receiving the training signal, the second radio apparatus 10b derives an H matrix, and transmits the derived H matrix to the first radio apparatus 10a. When receiving the H matrix, the first radio apparatus 10a acquires a column vector included in the steering matrix by performing singular value decomposition. When transmitting the packet signal, the first radio apparatus 10a derives a transmission weight vector by changing the component included in the column vector for each packet signal. The first radio apparatus 10a transmits the packet signal to the second radio apparatus 10b while performing weighting with the transmission weight vector.

  Below, a modification is demonstrated. As in the embodiment, the first modification relates to the first radio apparatus 10a that derives a temporally varying transmission weight vector by varying each component included in the column vector. The processing for changing the transmission weight vector in the modification is different from the processing in the embodiment. In the embodiment, the amplitude component is changed while fixing the phase component of each component. However, in the modification, the phase component of each component is changed. That is, the control unit 30 varies the phase of each component and derives a transmission weight vector that varies with time by adjusting the amplitude of each component so as to compensate for the power variation caused by the phase variation. . The communication system 100 according to the first modification is the same type as the communication system 100 shown in FIG. 2, and the first radio apparatus 10a is the same type as the first radio apparatus 10a shown in FIG. It is.

  This will be specifically described. The control unit 30 acquires the column vector v1 as in the embodiment. Further, the control unit 30 stores a table in which variation patterns for each of v1 (1), v1 (2), v1 (3), and v (4) are shown. The table shows “0.1 °”, “−0.1 °”, “0.15 °” for v1 (1), v1 (2), v1 (3), and v1 (4), respectively. A plurality of phase fluctuation amounts are arranged. Further, the control unit 30 acquires the fluctuation amount in order from the front of the table for each packet signal, and rotates the phase component such as v1 (1). Here, the rotation is performed by complex multiplication on v1 (1) and the like. As a result, the values of v1 (1), v1 (2), v1 (3) v1 (4) vary in packet signal units. Here, the rotation results are also indicated as v1 '(1), v1' (2), v1 '(3), and v1' (4), and the column vector including these components is also indicated as v1 '.

  The control unit 30 calculates the inner product of v1 and v1 '. If the inner product value is smaller than the threshold value, the control unit 30 extracts another fluctuation amount from the table, and repeats the above-described processing to re-derived the column vector v1 '. When the inner product value is equal to or greater than the threshold value, the control unit 30 derives the ratio of the inner product value to the predetermined value, and derives the amplification factor based on the ratio. For example, if the ratio is “0.9”, the amplification factor is derived as “1 / 0.9”. The predetermined value may be determined in advance, or may be a value of an inner product between v1. The control unit 30 increases each component of the column vector v1 'according to the amplification factor. For example, when the amplification factor is “1.1”, the control unit 30 multiplies “√1.1” by the in-phase component and the quadrature component of each component. The above processing is also performed in units of packet signals. As a result, even if the column vector value is the same over a plurality of packet signals, the transmission weight vector has a different value for each packet. Further, the baseband processing unit 22 transmits the packet signal while performing weighting with the transmission weight vector.

  The second modification also relates to the first radio apparatus 10a for deriving a transmission weight vector that varies with time, as in the past. Up to now, the case where a packet signal formed by one series is transmitted is targeted, but the second modification is intended for the case where packet signals formed by two or more series are transmitted. That is, FIGS. 4A to 4C are targeted for transmission. The communication system 100 according to the second modification is the same type as the communication system 100 shown in FIG. 2, and the first radio apparatus 10a is the same type as the first radio apparatus 10a shown in FIG. It is.

  The control unit 30 acquires the steering matrix V as before. Next, the control unit 30 extracts column vectors from the steering matrix V by the number of sequences. For example, when the number of series is two, the control unit 30 extracts v1 and v2 as column vectors. Here, v1 is associated with the first sequence, and v2 is associated with the second sequence. In addition, the control unit 30 derives a plurality of transmission weight vector candidates that are orthogonal to the column vector associated with a sequence other than one sequence. For example, a plurality of column vectors orthogonal to the column vector v2 are derived as transmission weight vector candidates w1 'to be used for the first stream. Therefore, there are a plurality of transmission weight vector candidates w1 '. Similarly, a plurality of transmission weight vector candidates w2 'are derived for the second stream.

  The control unit 30 derives a transmission weight vector that fluctuates in time by selecting a transmission weight vector candidate while switching. For example, the transmission weight vector w1 that varies with time is derived by selecting the transmission weight vector candidate w1 'while switching. Here, the combination pattern of the candidates w1 ′ and w2 ′ to be selected is stored in advance in the memory of the control unit 30, and in the pattern, the cycle for selecting the same combination is defined to be long. It is better to be.

  The above operation will be described more specifically. Here, for clarity of explanation, it is assumed that the number of sequences is two. The control unit 30 generates a plurality of vectors orthogonal to both v1 and v2 while using the Gram-Schmidt orthogonalization method. Since the Gram-Schmidt orthogonalization method is a well-known technique, the details are omitted, but since the two column vectors v1 and v2 are both four-dimensional, four orthogonal vectors are generated. These four orthogonal vectors correspond to the above-described transmission weight vector candidates w1 'and w2'. In the four orthogonal vectors, there is no clear distinction between the transmission weight vector candidates w1 ′ and w2 ′, and the four orthogonal vectors are also transmission weight vector candidates w1 ′ and w2 ′. is there.

  The control unit 30 selects two of the four orthogonal vectors and outputs them as transmission weight vectors w1 and w2. As described above, the selection pattern is stored in the memory of the control unit 30. In the pattern, it is desirable that the cycle for selecting the same combination is defined to be long. Further, the baseband processing unit 22 transmits packet signals formed in a plurality of sequences while performing weighting with a transmission weight vector.

  Similarly to the second modification, the third modification also relates to the first radio apparatus 10a that derives a temporally varying transmission weight vector when transmitting a packet signal formed by two or more sequences. . However, the method of deriving the transmission weight vector that varies with time is different from the second modification.

  The control unit 30 acquires the steering matrix V as before. Next, the control unit 30 extracts column vectors from the steering matrix V by the number of sequences. For example, when the number of series is two, the control unit 30 extracts v1 and v2 as column vectors. Here, v1 is associated with the first sequence, and v2 is associated with the second sequence. Further, the control unit 30 derives a transmission weight vector for the one series based on the column vector associated with one series, and each component included in the column vector associated with the other series , The transmission weight vector that varies with time is derived with respect to other sequences.

  For example, the control unit 30 determines the column vector v1 associated with the first sequence as the transmission weight vector w1 for the first sequence. Further, the control unit 30 derives a transmission weight vector w2 that temporally varies with respect to the second sequence by varying each component of v2 associated with the second sequence. Specifically, a transmission weight vector w2 that varies with time is derived by varying the amplitude while fixing the phase of each component. In particular, the control unit 30 varies the amplitude with respect to one of the four components included in the column vector v2. Here, the variation pattern, that is, the amplification factor pattern, is stored in advance in the memory of the control unit 30.

  Note that the control unit 30 causes fluctuation so that the inner product of the transmission weight vector w2 and the column vector v2 approaches a predetermined value. That is, if the inner product of the derived transmission weight vector w2 and column vector v2 is smaller than a predetermined value, the control unit 30 discards the transmission weight vector w2 and then extracts another amplified value from the memory. The transmission weight vector w2 is derived again based on the extracted amplification value. Further, the baseband processing unit 22 transmits packet signals formed in a plurality of sequences while performing weighting with a transmission weight vector.

  According to the embodiment of the present invention, a transmission weight vector that varies with time is derived while varying each component included in the column vector. Therefore, in MIMO eigenmode transmission, continuous interception by a wireless device that is not a communication target is derived. Can be reduced. Moreover, since the continuity of interception is reduced, security can be improved. In addition, since the amplitude is varied while the phase is fixed, the shape of the side lobe can be modified while enabling in-phase synthesis in the receiving apparatus to be communicated. Further, since the constraint condition is defined so that the inner product of the column vector and the weight vector approaches a predetermined value, it is possible to suppress the deterioration of the reception characteristics in the receiving device to be communicated. Also, since the components other than one of the column vector components are varied in a predetermined pattern, the processing can be simplified. Further, since the adjustment is executed for one component, the processing can be simplified. Further, since the amplitude is adjusted while changing the phase, it is possible to suppress the reduction in transmission power while changing the shape of the side lobe.

  In addition, since transmission weight vector candidates that are orthogonal to each other are selected while switching, it is possible to reduce the continuity of interception by wireless devices that are not communication targets while suppressing deterioration of SINR in the communication target wireless devices in MIMO eigenmode transmission . Further, the transmission weight vector candidates orthogonal to each other need only be derived first, and after that, only these are selected, so that the processing can be simplified. Moreover, since deterioration of SINR is suppressed, it is possible to suppress deterioration of reception characteristics. In addition, since the transmission weight vector for one sequence is changed, the continuity of interception by wireless devices that are not communication targets can be reduced in MIMO eigenmode transmission. Further, since the amplitude is varied while fixing the phase, the shape of the side lobe can be modified while enabling in-phase synthesis in the wireless device to be communicated. Further, since the constraint condition is defined so that the inner product of the column vector and the transmission weight vector approaches a predetermined value, it is possible to suppress the deterioration of the reception characteristics in the wireless reception device.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

  In the embodiment of the present invention, the second radio apparatus 10b derives the H matrix. However, the present invention is not limited to this, and the H matrix may be derived in the first radio apparatus 10a corresponding to the transmission side. That is, the H matrix in the uplink may be derived, and the H matrix may be used to derive the transmission weight vector in the downlink. At that time, a training signal is transmitted from the second radio apparatus 10b to the first radio apparatus 10a.

  Further, when the H matrix is derived in the first radio apparatus 10a, the number of antennas 14 when the second radio apparatus 10b transmits a training signal and the antennas when the second radio apparatus 10b receives a packet signal The number of 14 may be different. For example, the number of the former is “2” and the number of the latter is “4”. At that time, the first radio apparatus 10a derives a transmission weight vector after deriving an H matrix for “two” antennas 14. Further, the second radio apparatus 10b receives the packet signals transmitted from the first radio apparatus 10a and weighted by the transmission weight vector by the “four” antennas 14. According to this modification, the second radio apparatus 10b does not need to transmit the H matrix and can improve the transmission efficiency.

  In the embodiment of the present invention, the communication system 100 targets multicarrier signals. However, the present invention is not limited to this. For example, the communication system 100 may process a single carrier signal. According to this modification, the present invention can be applied to various communication systems.

The features of the invention described in the embodiments may be defined by the following items.
(Item 1)
A plurality of transmit antennas for transmitting signals weighted by weight vectors;
Of the steering matrix derived by singular value decomposition of the transmission path matrix having the transmission path characteristics between each of the plurality of transmitting antennas and each of the plurality of receiving antennas as element values, a predetermined column vector is An acquisition unit to acquire;
A derivation unit for deriving a temporally varying weight vector by varying each component included in the column vector acquired in the acquisition unit;
A transmission device comprising:

(Item 2)
The transmission device according to Item 1, wherein the deriving unit derives a temporally varying weight vector by varying the amplitude while fixing the phase of each component.
(Item 3)
3. The transmission device according to item 2, wherein the derivation unit derives a temporally varying weight vector by causing the inner product of the column vector and the weight vector to vary so as to approach a predetermined value. .

(Item 4)
The derivation unit causes a component other than one of the components to change according to a predetermined pattern, and the inner product of the column vector and the weight vector approaches a predetermined value for one component. 4. The transmission apparatus according to item 3, wherein a weight vector that varies with time is derived by performing the adjustment as described above.
(Item 5)
The deriving unit derives a temporally varying weight vector by changing the phase of each component and adjusting the amplitude of each component so as to compensate for the power fluctuation caused by the phase fluctuation. The transmission device according to Item 1.

(Item 6)
A transmission method for transmitting a signal weighted by a weight vector from a plurality of transmission antennas,
Obtains a predetermined column vector from the steering matrix derived by singular value decomposition of the transmission path matrix whose element value is the transmission path characteristics between each of the plurality of transmitting antennas and each of the plurality of receiving antennas. A transmission method characterized by deriving a temporally varying weight vector by varying each component included in the acquired column vector.

It is a figure which shows the spectrum of the multicarrier signal which concerns on the Example of this invention. It is a figure which shows the structure of the communication system which concerns on the Example of this invention. FIG. 3 is a sequence diagram showing a procedure for deriving a transmission weight vector in the communication system of FIG. 2. 4A to 4D are diagrams showing packet formats in the communication system of FIG. FIGS. 5A to 5D are diagrams showing a packet format for training signals in the communication system of FIG. FIGS. 6A to 6D are diagrams showing another training signal packet format in the communication system of FIG. FIG. 3 is a diagram illustrating a packet format of a training signal that is finally transmitted in the communication system of FIG. 2. It is a figure which shows the structure of the 1st radio | wireless apparatus of FIG. It is a figure which shows the structure of the signal of the frequency domain in FIG. It is a figure which shows the structure of the baseband process part of FIG. It is a figure which shows the structure of the process part for reception of FIG. It is a figure which shows the structure of the process part for transmission of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 radio | wireless apparatus, 12 antenna, 14 antenna, 20 radio | wireless part, 22 baseband process part, 24 modem part, 26 IF part, 30 control part, 100 communication system.

Claims (6)

A plurality of transmission antennas for transmitting signals formed in a plurality of sequences while weighting by weight vectors is performed;
An acquisition unit for acquiring a steering matrix derived by performing singular value decomposition on a transmission path matrix having element values of transmission path characteristics between each of the plurality of transmission antennas and each of the plurality of reception antennas;
After associating a plurality of column vectors and a plurality of sequences included in the steering matrix acquired in the acquisition unit, and deriving a plurality of weight vector candidates orthogonal to a column vector associated with a sequence other than one sequence By selecting a plurality of candidates, a time vector that varies with time is derived for the one sequence, and a time vector that varies with time for each of the other sequences. A derivation unit to derive,
A transmission device comprising: A plurality of transmission antennas for transmitting signals formed by two sequences while weighting by a weight vector is performed;
An acquisition unit for acquiring a steering matrix derived by performing singular value decomposition on a transmission path matrix having element values of transmission path characteristics between each of the plurality of transmission antennas and each of the plurality of reception antennas;
Associating two column vectors and two sequences in the steering matrix acquired in the acquisition unit, and deriving a weight vector for the one sequence based on the column vectors associated with one sequence, A derivation unit that derives a temporally varying weight vector for the other series by varying each component included in the column vector associated with the other series;
A transmission device comprising:   The transmission device according to claim 2, wherein the derivation unit derives a temporally varying weight vector by varying the amplitude while fixing the phase of each component.   The deriving unit derives a temporally varying weight vector by causing the inner product of a column vector corresponding to one series and a weight vector to change so as to approach a predetermined value. Item 4. The transmission device according to Item 3. A transmission method for transmitting signals formed in a plurality of sequences while performing weighting by weight vectors from a plurality of transmission antennas,
Obtaining a steering matrix derived by singular value decomposition of a transmission path matrix having transmission path characteristics between each of a plurality of transmission antennas and each of a plurality of reception antennas as element values;
A plurality of candidates are obtained by associating a plurality of column vectors included in the acquired steering matrix with a plurality of sequences, and deriving a plurality of weight vector candidates orthogonal to the column vector associated with a sequence other than one sequence. Deriving a temporally varying weight vector for the one sequence and deriving a temporally varying weight vector for each of the other sequences, ,
A transmission method comprising: A transmission method for transmitting signals formed by two sequences while weighting by a weight vector is executed from a plurality of antennas,
Obtaining a steering matrix derived by singular value decomposition of a transmission path matrix having transmission path characteristics between each of a plurality of transmission antennas and each of a plurality of reception antennas as element values;
Two column vectors and two sequences in the obtained steering matrix are associated with each other, a weight vector for the one sequence is derived based on the column vector associated with one sequence, and the other sequence Deriving a temporally varying weight vector for other sequences by varying each component contained in the associated column vector;
A transmission method comprising:

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