JP4364100B2 - Wireless communication device - Google Patents

Description

  The present invention belongs to MIMO-OFDM that performs communication using a plurality of antennas and a plurality of subcarriers, and further belongs to a high-speed wireless LAN technology.

  In a conventional wireless LAN, for example, IEEE 802.11a, a known symbol (short preamble and long preamble) is transmitted before a data signal to perform synchronization processing and transmission path estimation. By using these preambles, subsequent signal portions and data portions can be demodulated.

  On the other hand, establishment of a high-speed wireless LAN standard called IEEE 802.11n is underway. In IEEE 802.11n, in order to achieve a transmission rate of 100 Mbps in the MAC layer, MIMO (Multi-Input Multi-Output) using a plurality of antennas is assumed. In the MIMO technology, in order to demodulate the transmission signal sequence on the reception side, it is necessary to estimate the transmission path response to each reception antenna using the transmitted preamble signal, but additionally estimate the number of transmission antennas on the transmission side. There is a need to. If the estimation of the number of transmission antennas fails, the subsequent data portion cannot be demodulated, so that a considerable accuracy is required for the estimation.

  As a method of knowing the number of transmission antennas on the reception side, a method of transmitting a signal for reporting the number of transmission antennas on the transmission side is also conceivable. However, this method increases overhead and inevitably reduces the throughput of data transmission.

Although a method of estimating the number of transmission antennas using the received preamble signal is also conceivable, the preamble signal of Non-Patent Document 1 is not based on the assumption that the number of transmission antennas is estimated, and this preamble signal is used. It is difficult to estimate the number of transmission antennas.
Jan Boer and two others “Backwards compatibility”, [online], September 2003, IEEE LMSC (publisher), [searched September 15, 2003], Internet <URL: ftp: // ieee: wireless @ ftp.802wirelessworld.com/11/03/11-03-0714-00-000n-backwards-compatibility.ppt>

  As described above, in the MIMO system, if the estimation of the number of transmission antennas fails, the subsequent data portion cannot be demodulated, so that a considerable accuracy is required for the estimation. On the other hand, there is a problem that the overhead cannot be denied in the method of transmitting a signal notifying the number of transmission antennas on the transmission side. In addition, there is a problem that it is difficult to estimate the number of transmission antennas using the preamble signal of Non-Patent Document 1.

  Therefore, in view of the above problems, the present invention makes it possible to easily estimate the number of antennas used for transmission on the receiving side without adding a signal for notifying the number of transmitting antennas on the transmitting side, and to correctly demodulate data symbols. It is to make it possible.

  (1) A wireless communication apparatus (transmitter) of the present invention includes a plurality of antennas and a plurality of known symbols that are continuous in time, each having a different subcarrier arrangement for transmitting known information. Known symbol transmitting means for transmitting a plurality of known symbol sequences having subcarrier arrangements in which subcarriers transmitting known information are adjacent to each other between adjacent known symbols, and the known Data symbol transmission means for transmitting data symbols using the plurality of antennas after transmission of the symbol string.

  The plurality of known symbol sequences have subcarrier arrangements in which the positions of subcarriers for transmitting the known information are different between known symbols transmitted simultaneously from different antennas.

  (2) The wireless communication apparatus (receiver) of the present invention includes a plurality of known symbols that are transmitted by a plurality of antennas and that have different subcarrier arrangements for transmitting known information and that are continuous in time. Receiving means for receiving a plurality of known symbol sequences having subcarrier arrangements in which subcarriers transmitting known information are adjacent to each other between adjacent known symbols and data symbols after the known symbol sequence And means for obtaining a channel characteristic estimation value for each subcarrier from each known symbol of the received known symbol string, and for each known symbol of the received known symbol string, the channel characteristic estimation value obtained from the known symbol and 1 The correlation with the estimated channel characteristic value obtained from the second known symbol is obtained, and the correlation value is determined in advance. Means for estimating the number of antennas based on the number of known symbols received so far if it is equal to or greater than a threshold; and means for reproducing the data symbols using the estimated number of antennas and the channel estimation value; Have

  The number-of-antennas estimation means is configured to estimate each channel characteristic estimation value for each subcarrier of each known symbol in the received known symbol sequence, and channel characteristics of a subcarrier adjacent to the subcarrier of the first received known symbol. Find the correlation with the estimate.

  According to the present invention, the number of antennas used for transmission can be easily estimated on the receiving side.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows a configuration example of a transmitter according to the first embodiment. The configuration shown in FIG. 1 is a physical layer of a transmitter, and a data sequence (bit string) 10 to be transmitted from an upper layer is input for each transmission unit (for example, frame or packet).

  The input data series 10 is subjected to, for example, error correction coding by the encoder 11 to generate a coded bit series. The encoded bit sequence is serial-parallel converted by a serial-parallel converter (S / P) 12 to be divided into a plurality of streams. Each stream is mapped onto the complex plane by modulators 13-1 to 13M to generate modulated data symbols.

  The modulated data symbols are serial-to-parallel converted by serial-to-parallel converters (S / P) 14-1 to 14M so as to be transmitted on OFDM (orthogonal frequency division multiplexing) subcarriers. Signals on the frequency axis are converted into time waveforms by Fourier transform (IFFT) units 18-1 to 18-M. Output signals from the IFFT units 18-1 to 18 -M converted into time waveforms are input to the transmission circuit 19.

  In the transmission circuit 19, the output signals of the IFFT units 18-1 to 18-M are converted into analog signals by a D / A converter after a guard interval (GI) is added. The output signal of the D / A converter is frequency-converted (up-converted) into an RF (high frequency) band by the frequency converter and supplied to the transmission antennas 20-1 to 20-M via the power amplifier, thereby transmitting the signal. An OFDM signal is transmitted from the antennas 20-1 to 20-M to the wireless communication device of the communication partner.

  In this way, the preamble is transmitted before the data symbol is transmitted as the OFDM signal. In the following, a transmission system of a known symbol for preamble estimation, in particular, for channel estimation will be described.

  The known symbol pattern generator 15 is a ROM, for example, and stores a plurality of known symbol patterns. Each known symbol is transmitted by carrying information on some of a plurality of pre-assigned subcarriers of OFDM. The known symbol pattern is a pattern indicating which subcarrier is loaded with information of the known symbol (known information). The known symbol pattern generator 15 stores a plurality of known symbol patterns having different subcarrier arrangements for transmitting known information. In the example of FIG. 1, a known symbol pattern on the frequency axis is stored in the ROM.

  At the time of transmission of known symbols, a plurality of known symbol patterns stored in the ROM of the known symbol pattern generator 15 are sequentially read at the timing at which the known symbols are to be transmitted according to the signal from the counter 16. The counter 16 is used for time measurement, outputs a count value that changes from time to time, and generates a timing signal indicating the timing at which a known symbol is to be transmitted. The read known symbol pattern is input to the IFFT units 18-1 to 18 -M via the selector 17, converted into a time waveform, and then guided to the transmission circuit 19. When the known pattern of the time waveform is stored in the ROM, the read known symbols are guided to the transmission circuit 19 bypassing the IFFT units 18-1 to 18-M.

  Known symbols are transmitted multiple times per antenna. The selector 17 performs an operation of distributing the known symbol pattern read from the ROM of the known symbol generator 15 so as to be transmitted from an appropriate transmission antenna in accordance with the transmission order of the known symbols transmitted a plurality of times. That is, the selector 17 distributes the known symbol pattern to each of the transmission antennas 20-1 to 20-M according to the count value indicating the time information from the counter 16.

  Note that when there are a plurality of types of known symbols such as a short preamble and a long preamble included in the preamble of the wireless LAN, the counter 16 and the selector 17 read the plurality of types of known symbol patterns by switching from the ROM.

  Next, a known symbol transmission method for channel estimation will be described in detail with reference to FIG. FIGS. 2A, 2B, and 2C show the structures of radio frames including preambles when the number of antennas that simultaneously transmit known symbols is “1”, “2”, and “3”. ing. In the first embodiment, a system is assumed that transmits a short preamble SP for synchronization and a long preamble LP for channel estimation prior to data DATA as in a wireless LAN.

  Here, the configuration of the short preamble SP is not particularly limited. For example, the same structure as that of IEEE802.11a may be transmitted from a plurality of transmission antennas. The known symbol is used for estimating the transmission path response during MIMO communication, and corresponds to the long preamble LP in FIGS. 2A, 2B, and 2C in the wireless LAN.

  2A, 2B, and 2C, the long preamble LP transmitted from each transmission antenna is frequency division multiplexed. Here, the number of transmission antennas is M, the number of OFDM subcarriers is N, and the number n of N subcarriers is defined as 0th to (N-1) th (n = 0 to N-1). In the case where N / M is divisible enough, there is known symbol information (known information) in the subcarriers of the number obtained by the following equation (1), and there is no known information in the subcarriers of other numbers. And

Mk + m + i-2 mod N (1)
Here, m = 1, 2,..., M are antenna numbers, i = 1, 2, 3,... Are numbers in the time direction of known symbols, and k = 0, 1,. 1).

  For example, in the examples of FIGS. 2A, 2B, and 2C, it is assumed that the number of subcarriers is “12” (N = 12).

  In the case of FIG. 2A (the number of antennas is “1” (M = 1)), the subcarriers in which known information exists in one known symbol transmitted from the antenna 1 (i = 1) according to the equation (1). The location is as follows.

Antenna 1: 1st known symbol: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11} th subcarrier;
When the number of antennas is “1”, the subcarrier arrangement is such that known information is transmitted on all subcarriers.

  In the case of FIG. 2B (the number of antennas is “2” (M = 2)), two known symbols respectively transmitted from the antennas 1 (i = 1) and 2 (i = 2) from the equation (1). The position of the subcarrier where the known information exists in is as follows.

Antenna 1: 1st known symbol: {0, 2, 4, 6, 8, 10} th subcarrier;
Antenna 1: 2nd known symbol: {1, 3, 5, 7, 9, 11} th subcarrier;
Antenna 2: 1st known symbol: {1, 3, 5, 7, 9, 11} th subcarrier;
Antenna 2: Second known symbol: {0, 2, 4, 6, 8, 10} th subcarrier.

  When the number of antennas is “2”, in the two known symbols transmitted continuously from each antenna in time, each subcarrier transmitting the known information of the second known symbol is known to the first known symbol. A subcarrier having a higher frequency adjacent to a subcarrier for transmitting information, and between the first and second known symbols, each known symbol has a subcarrier for transmitting known information between the two known symbols. It has subcarrier arrangements adjacent to each other.

  In the case of FIG. 2 (c) (the number of antennas is “3” (M = 3)), each antenna 1 (i = 1), 2 (i = 2), 3 (i = 3) is obtained from the equation (1). The positions of subcarriers where known information exists in the three known symbols to be transmitted are as follows.

Antenna 1: 1st known symbol: {0, 3, 6, 9} th subcarrier;
Antenna 1: 2nd known symbol: {1, 4, 7, 10} th subcarrier;
Antenna 1: 3rd known symbol: {2, 5, 8, 11} th subcarrier;
Antenna 2: 1st known symbol: {1, 4, 7, 10} th subcarrier;
Antenna 2: second known symbol: {2, 5, 8, 11} th subcarrier;
Antenna 2: 3rd known symbol: {0, 3, 6, 9} th subcarrier;
Antenna 3: 1st known symbol: {2, 5, 8, 11} th subcarrier;
Antenna 3: second known symbol: {0, 3, 6, 9} th subcarrier;
Antenna 3: Third known symbol: {1, 4, 7, 10} th subcarrier.

  When the number of antennas is “3”, in the three known symbols transmitted continuously from each antenna in time, each subcarrier transmitting the known information of the second known symbol is known to the first known symbol. A subcarrier having a higher frequency adjacent to a subcarrier transmitting information, and each subcarrier transmitting known information of the third known symbol is adjacent to a subcarrier transmitting known information of the second known symbol The subcarrier with the higher frequency. In this way, between the first and second known symbols, each known symbol has a subcarrier arrangement in which the subcarriers transmitting known information between the two known symbols are adjacent to each other. Even between the third known symbols, each known symbol has a subcarrier arrangement in which subcarriers transmitting known information between the two known symbols are adjacent to each other.

  Even when the number of antennas is “4” or more, the position of the subcarrier where information exists in the known symbols transmitted from each antenna is clear from the above analogy.

  2A, 2B, and 2C, the preamble structure is temporally represented, but for convenience, the subcarrier in which information exists is represented by hatching for the long preamble LP.

  Next, the receiver according to the first embodiment will be described with reference to FIG. FIG. 3 shows a configuration example of the receiver.

  An RF (Radio Frequency) band OFDM signal transmitted from the transmitter of FIG. 1 is received by a plurality of receiving antennas 30-1 to 30-M. The OFDM reception signals from the reception antennas 30-1 to 30 -M are input to the reception circuit 31. In the receiving circuit 31, the OFDM signals input from the receiving antennas 30-1 to 30 -M are each amplified by a low noise amplifier (LNA), and then frequency-converted (down-converted) to a baseband by a frequency converter. Further, the signal is converted into a digital signal by an A / D converter, and the guard interval (GI) is further removed. An output signal from the receiving circuit 31 is input to fast Fourier transform (FFT) units 32-1 to 32-M, whereby a time waveform signal is converted into a frequency waveform signal, that is, a waveform for each subcarrier. .

  Of the output signals from the FFT units 32-1 to 32 -M, the signal in the data symbol section is input to the MIMO signal processor 41. On the other hand, among the output signals from the FFT units 32-1 to 32-M, the preamble, particularly the signal in the known symbol section, is input to the dividers 33-1 to 33-M.

  The known symbol pattern generator 34 stores a plurality of known symbol patterns identical to the plurality of known symbol patterns stored in the known symbol pattern generator 15 shown in FIG. The symbol pattern generator 34 sequentially reads the known symbol patterns corresponding to the received known symbols according to the signal from the counter 35 when receiving the known symbols. Here, the counter 35 measures the number of received known symbols, and each time a known symbol is received, the counter value is incremented by one.

  The read known symbol patterns are output to the dividers 33-1 to 33-M, respectively. Transmission for each subcarrier is performed by dividing the waveform for each subcarrier of the known symbol input to the dividers 33-1 to 33-M by the waveform of each known information of the known symbol pattern output from the symbol pattern generator. An estimated value of the channel characteristic (transmission channel characteristic value) is obtained, stored in the memories 39-1 to 39-M, and input to the correlators 38-1 to 38-M.

  When the known symbol input to the dividers 33-1 to 33-M is the first known symbol input first (that is, when the value of the counter 35 is “1”), the transmission path characteristic value is Further, it is input to the shift circuits 36-1 to 36 -M. The transmission path characteristic value for each subcarrier of the first known symbol input to the shift circuits 36-1 to 36 -M is the transmission corresponding to the subcarrier having the lower frequency among the subcarriers adjacent to the subcarrier. The frequency is shifted by −1 so as to be a road characteristic value and stored in the memories 37-1 to 37-M.

  In the correlators 38-1 to 38-M, the transmission path characteristic values for the subcarriers of the known symbols estimated by the dividers 33-1 to 33-M and 1 stored in the memories 37-1 to 37-M. A correlation value with the result of shifting the channel characteristic value for each subcarrier estimated from the first known symbol by −1 frequency is calculated, and the correlation value is input to the determiner 40.

  When the input correlation value is smaller than a preset threshold value (or less than the threshold value), the determiner 40 increments the counter 35 by one and receives the next known symbol. On the other hand, if the input correlation value is greater than or equal to the threshold (or greater than the threshold), the current counter value is output to the MIMO signal processor 41 as the estimated value of the number of transmission antennas.

  A detailed description of the algorithm for estimating the number of transmission antennas will be given later.

  In the MIMO signal processor 41, transmission path characteristics for each subcarrier of each known symbol stored in the memories 39-1 to 39-M with respect to the signal in the data symbol period from the FFT units 32-1 to 32-M. By using the value and the counter value of the counter 35 as the estimated value of the number of transmitting antennas, for example, MIMO signal reception processing such as maximum likelihood estimation is performed. Channel decoding is performed on the signal after the MIMO signal reception process, and the transmitted data 42 is reproduced.

  Here, the influence of the transmission path is almost the same between adjacent subcarriers transmitted from the same antenna, that is, the transmission path characteristics of adjacent subcarriers transmitted from the same antenna have a high positive correlation value. . In addition, it is considered that the time variation of the transmission path is moderate, and the transmission path is substantially the same between symbols that are temporally adjacent. Furthermore, the transmission path characteristics between subcarriers transmitted from different antennas are considered to have a relatively low correlation. At this time, the channel characteristic value estimated by the n-th subcarrier signal of the i-th known symbol received by the divider (divider 33-j) of the j-th receiving antenna (the divider 33-j) If the output signal) is Hj (i, n), it is expected that the following transmission line characteristic Hj (i, n) is obtained.

<When the number of transmission antennas is "1">
Since all the subcarriers are transmitted from the same antenna, the channel characteristics value Hj (1, n) of the even-numbered (nth) subcarrier and the channel characteristics of the adjacent subcarrier of the next number The value Hj (1, n + 1) has a high positive correlation.

<When the number of transmission antennas is “2”>
In the first received known symbol (i = 1), the even-numbered (n-th) subcarrier and the next-numbered adjacent subcarrier (n + 1-th) are transmitted from different antennas. (1, n) and Hj (1, n + 1) are considered to have a relatively low correlation.

  In the second known symbol (i = 2), the even-numbered (nth) subcarrier and the adjacent subcarrier (n + 1) of the first received known symbol (i = 1) are from the same antenna. Hj (2, n) and Hj (1, n + 1) have a high positive correlation value because they are transmitted and are adjacent subcarriers.

<When the number of transmission antennas is “3”>
In the first received known symbol (i = 1), the even-numbered (n-th) subcarrier and the next-numbered adjacent subcarrier (n + 1-th) are transmitted from different antennas. (1, n) and Hj (1, n + 1) are considered to have a relatively low correlation.

  In the second known symbol (i = 2), the even-numbered (n-th) subcarrier and the adjacent subcarrier (n + 1) of the first received known symbol (i = 1) are different from each other. Hj (2, n) and Hj (1, n + 1) are considered to have a relatively low correlation.

  In the third known symbol (i = 3), the even-numbered (n-th) subcarrier and the adjacent subcarrier (n + 1) of the first received known symbol (i = 1) are from the same antenna. Hj (3, n) and Hj (1, n + 1) have a high positive correlation value because they are transmitted and are adjacent subcarriers.

  As can be seen from the above, if the number of transmitting antennas is M, the subcarrier transmission path characteristics estimated from the Mth received known symbol and the subcarrier transmission path characteristics estimated from the first received known symbol Therefore, the number of antennas can be estimated by detecting the high positive correlation value.

  Hereinafter, the algorithm of the transmission antenna number estimation procedure in the receiver of FIG. 3 will be described with reference to FIG. First, after setting “1” as an initial value in the counter 35 (step S101), the frequency waveform of a known symbol received by the j-th antenna is input to the divider 33-j (steps S102 to S103). The waveform for each subcarrier input to the divider 33-j is divided by a known symbol pattern to obtain a transmission line characteristic value.

  The transmission path characteristic value of each subcarrier (n = 0 to N−1) of the known symbol received i-th (i = 1, 2, 3,...) at the j-th receiving antenna, that is, the divider output is Hj ( i, n). Since the transmission line characteristic value of each subcarrier of the known symbol received first (i = 1) can be expressed as Hj (1, n), the characteristic shifted by −1 frequency is expressed as Hj (1, n + 1). be able to. A correlation value between the transmission path characteristic Hj (i, n) of each received known symbol and the characteristic Hj (1, n + 1) obtained from the first known symbol is obtained by the correlator 38-j (step S104). . This correlation calculation is defined as follows when the i-th known symbol is received.

(Correlation value) = Hj (i, 0) * Hj (1,1) + Hj (i, 1) * Hj (1,2) + Hj (i, 2) * Hj (1,3) +... + Hj (i, N-2) * Hj (1, N-1)
However, a * b is an operation of multiplying a by the complex conjugate of b.

  In the determiner 40, the correlation value calculated by the correlator 38-j is determined. If this value is greater than a predetermined threshold (or greater than or equal to the threshold) (step S105), the currently received symbol is the last known symbol ( The number of known symbol patterns received so far obtained by the counter 35 is estimated as the number of transmission antennas. Here, since the number of known symbols is equal to the number of transmission antennas, the value of the counter 35 becomes the estimated value of the transmission antenna (step S106).

  The MIMO signal processor 41 reproduces data symbols using the estimated number of transmission antennas. If the correlation value is equal to or smaller than the threshold value (or smaller than the threshold value) in step S105, the next known symbol is received (step S107), the counter 35 is incremented by 1 (step S108), and the process returns to step S103. Then, the transmission path characteristic value is estimated from the new known symbol in the same manner as above (step S103), and the characteristic H1 (n + 1) shifted by −1 frequency from the transmission path characteristic value estimated using the first received known symbol and Is calculated (step S104). Thereafter, the operation of steps S103 to S108 is repeated every time a known signal is received.

  When there are a plurality of receiving antennas, the following method is also conceivable.

  (A) Only when the correlation value is equal to or greater than the threshold value (or greater than the threshold value) for all reception antennas, the number of transmission antennas is determined by regarding the end of the known symbol.

  (B) The correlation values calculated from all the receiving antennas are averaged, and when the total correlation value is equal to or greater than the threshold value, the number of transmitting antennas is determined by regarding the end of the known symbol.

  Although the condition of (a) is more severe, the number of transmitting antennas can be reliably detected when the conditions match.

  As described above, according to the first embodiment, the number of transmission antennas is estimated by blind processing while performing transmission path estimation for each antenna using a known symbol without notifying the number of transmission antennas on the transmission side. Is possible.

(Second Embodiment)
The configuration of the transmitter according to the second embodiment is the same as that shown in FIG. What is different is the known symbol pattern. Hereinafter, the second embodiment will be described with a focus on differences from the first embodiment.

  First, a known symbol transmission method for channel estimation according to the second embodiment will be described in detail with reference to FIG. FIGS. 5A, 5B, and 5C show structures of radio frames including preambles when the number of antennas that simultaneously transmit known symbols is “1”, “2”, and “3”. The configuration is the same as that of FIG. 2 except for FIG. Here, if the number of transmission antennas is M, the number of OFDM subcarriers is N, and N / M is not divisible, subcarriers of Equation (2) (numbers of N subcarriers from 0th) It is assumed that there is known symbol information in the (N−1) th definition) and no known information is present in the other subcarriers.

Mk + m−i + N mod N (2)
For example, in the examples of FIGS. 5A, 5B, and 5C, it is assumed that the number of subcarriers is “12” (N = 12).

  In the case of FIG. 5A (the number of antennas is “1” (M = 1)), the position of the subcarrier where information is present in one known symbol transmitted from the antenna 1 is as follows from the equation (1). Become.

Antenna 1: 1st known symbol: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11} th subcarrier;
When the number of antennas is “1”, the subcarrier arrangement is such that known information is transmitted on all subcarriers.

  In the case of FIG. 5B (the number of antennas is “2” (M = 2)), the position of the subcarrier where the known information exists in the two known symbols respectively transmitted from the antennas 1 and 2 according to Equation (1). Is as follows.

Antenna 1: 1st known symbol: {0, 2, 4, 6, 8, 10} th subcarrier;
Antenna 1: 2nd known symbol: {1, 3, 5, 7, 9, 11} th subcarrier;
Antenna 2: 1st known symbol: {1, 3, 5, 7, 9, 11} th subcarrier;
Antenna 2: Second known symbol: {0, 2, 4, 6, 8, 10} th subcarrier.

  When the number of antennas is “2”, in the two known symbols transmitted continuously from each antenna in time, each subcarrier transmitting the known information of the second known symbol is known to the first known symbol. A subcarrier with a lower frequency adjacent to a subcarrier transmitting information, and between the first and second known symbols, each known symbol is a subcarrier transmitting known information between the two known symbols. Have subcarrier arrangements adjacent to each other.

  In the case of FIG. 5C (the number of antennas is “3” (M = 3)), subcarriers in which known information exists in three known symbols respectively transmitted from the antennas 1, 2, and 3 from Equation (1). The position of is as follows.

Antenna 1: 1st known symbol: {0, 3, 6, 9} th subcarrier;
Antenna 1: 2nd known symbol: {2, 5, 8, 11} th subcarrier;
Antenna 1: 3rd known symbol: {1, 4, 7, 10} th subcarrier;
Antenna 2: 1st known symbol: {1, 4, 7, 10} th subcarrier;
Antenna 2: Second known symbol: {0, 3, 6, 9} th subcarrier;
Antenna 2: 3rd known symbol: {2, 5, 8, 11} th subcarrier;
Antenna 3: 1st known symbol: {2, 5, 8, 11} th subcarrier;
Antenna 3: Second known symbol: {1, 4, 7, 10} th subcarrier;
Antenna 3: Third known symbol: {0, 3, 6, 9} th subcarrier.

  When the number of antennas is “3”, in the three known symbols transmitted continuously from each antenna in time, each subcarrier transmitting the known information of the second known symbol is known to the first known symbol. A subcarrier having a lower frequency and adjacent to a subcarrier transmitting information, and each subcarrier transmitting known information of the third known symbol is assigned to a subcarrier transmitting known information of the second known symbol. Adjacent, lower frequency subcarrier. In this way, between the first and second known symbols, each known symbol has a subcarrier arrangement in which the subcarriers transmitting known information between the two known symbols are adjacent to each other. Even between the third known symbols, each known symbol has a subcarrier arrangement in which subcarriers transmitting known information between the two known symbols are adjacent to each other.

  Even when the number of antennas is “4” or more, the position of the subcarrier where information exists in the known symbols transmitted from each antenna is clear from the above analogy.

  The configuration of the receiver according to the second embodiment is the same as that of FIG. 3, but the processing operation is different from that of the first embodiment. Here, the processing operation of the receiver according to the second embodiment will be described with a focus on differences from the first embodiment.

  As in the first embodiment, the OFDM signal received by the antennas 30-1 to 30-M passes through the reception circuit 31 and the fast Fourier transform (FFT) units 32-1 to 32-M, and then the waveform for each subcarrier. Is converted to Of the output signals from the FFT units 32-1 to 32 -M, the signal in the data symbol section is input to the MIMO signal processor 41, and the preamble, particularly the signal in the known symbol section, is divided by the dividers 33-1 to 33-33. M is input. The dividers 33-1 to 33-M obtain the transmission line characteristic value by dividing the waveform of each input sub-carrier of the known symbol by the known symbol pattern output from the symbol pattern generator 34, and the transmission line The characteristic values are stored in the memories 39-1 to 39-M and input to the correlators 38-1 to 38-M.

  When the known symbol input to the dividers 33-1 to 33-M is the first known symbol input (that is, when the value of the counter 35 is “1”), the transmission path characteristic value is Input to the shift circuits 36-1 to 36 -M. The transmission path characteristic value for each subcarrier of the first known symbol input to the shift circuits 36-1 to 36 -M is the transmission corresponding to the subcarrier having the higher frequency among the subcarriers adjacent to the subcarrier. The frequency is shifted by +1 so as to be a road characteristic value, and stored in the memories 37-1 to 37-M.

  In the correlators 38-1 to 38-M, the transmission path characteristic value for each subcarrier of the known symbol estimated by the dividers 33-1 to 33-M and the first stored in the memories 37-1 to 37-M. A correlation value with a result obtained by shifting the channel characteristic value for each subcarrier estimated from the known symbol by +1 frequency is calculated, and the correlation value is input to the determiner 40.

  When the input correlation value is smaller than a preset threshold value (or less than the threshold value), the determiner 40 increments the counter 35 by one and receives the next known symbol. On the other hand, if the input correlation value is greater than or equal to the threshold (or greater than the threshold), the current counter value is output to the MIMO signal processor 41 as the estimated value of the number of transmission antennas.

  A detailed description of the algorithm for estimating the number of transmission antennas will be given later.

  In the MIMO signal processor 41, as in the first embodiment, each known symbol stored in the memories 39-1 to 39-M with respect to the signal in the data symbol section from the FFT units 32-1 to 32-M. By using the channel estimation value for each subcarrier and the counter value of the counter 35 as the estimation value of the number of transmission antennas, for example, MIMO signal reception processing such as maximum likelihood estimation is performed. Channel decoding is performed on the signal after the MIMO signal reception process, and the transmitted data 42 is reproduced.

Here, the influence of the transmission path is almost the same between adjacent subcarriers transmitted from the same antenna, that is, the transmission path characteristics of adjacent subcarriers transmitted from the same antenna have a high positive correlation value. . In addition, it is considered that the time variation of the transmission path is moderate, and the transmission path is substantially the same between symbols that are temporally adjacent. Furthermore, the transmission path characteristics between subcarriers transmitted from different antennas are considered to have a relatively low correlation. At this time, the channel characteristic value estimated by the n-th subcarrier signal of the i-th known symbol received by the divider (divider 33-j) of the j-th receiving antenna (the divider 33-j) Output signal) H
If j (i, n) is assumed, the following transmission path characteristics Hj (i, n) are expected to be obtained for all receiving antennas.

<When the number of transmission antennas is "1">
Since all subcarriers are transmitted from the same antenna, propagation value estimation value Hj (1, n) of the even-numbered (nth) subcarrier and propagation of adjacent subcarriers of the preceding number The estimated value Hj (1, n-1) of the road characteristic has a high positive correlation.

<When the number of transmission antennas is “2”>
In the first known symbol (i = 1) received, the even-numbered (n-th) subcarrier and the adjacent subcarrier (n−1) of the preceding number are transmitted from different antennas. , Hj (1, n) and Hj (1, n-1) are considered to have a relatively low correlation.

  In the second known symbol (i = 2), the even-numbered (n-th) subcarrier and the adjacent subcarrier (n−1) of the first received known symbol (i = 1) are the same. Since it is transmitted from the antenna and is an adjacent subcarrier, Hj (2, n) and Hj (1, n-1) have a high positive correlation value.

<When the number of transmission antennas is “3”>
In the first known symbol (i = 1) received, the even-numbered (n-th) subcarrier and the adjacent subcarrier (n−1) of the preceding number are transmitted from different antennas. , Hj (1, n) and Hj (1, n-1) are considered to have a relatively low correlation.

  In the second received known symbol (i = 2), the even-numbered (nth) subcarrier and the first received known symbol (i = 1) adjacent subcarrier (n−1) are respectively Since the signals are transmitted from different antennas, Hj (2, n) and Hj (1, n-1) are considered to have a relatively low correlation.

  In the third known symbol (i = 3), the even-numbered (n-th) subcarrier and the adjacent subcarrier (n−1) of the first received known symbol (i = 1) are the same. Since it is transmitted from the antenna and is an adjacent subcarrier, Hj (3, n) and Hj (1, n-1) have a high positive correlation value.

  As can be seen from the above, if the number of transmitting antennas is M, the subcarrier transmission path characteristics estimated from the Mth received known symbol and the subcarrier transmission path characteristics estimated from the first received known symbol Therefore, the number of antennas can be estimated by detecting the high positive correlation value.

  Hereinafter, with reference to the flowchart shown in FIG. 6, the algorithm of the transmission antenna number estimation procedure of the receiver of FIG. 3 according to the second embodiment will be described. In FIG. 6, the same parts as those in FIG. In FIG. 6, step S104 of FIG. 4 is replaced with step S104 ′.

  First, after setting “1” as an initial value in the counter 35 (step S101), the frequency waveform of the known symbol received by the j-th antenna is input to the divider 33-j (steps S102 to S103). The waveform for each subcarrier input to the divider 33-j is converted into a transmission line characteristic value by dividing by a known symbol pattern.

  The transmission path characteristic value of each subcarrier (n = 0 to N−1) of the i-th known symbol received at the j-th receiving antenna (i = 1, 2, 3,...), that is, the divider output is Hj ( i, n). Since the transmission path characteristic value of each subcarrier of the known symbol received first (i = 1) can be expressed as Hj (1, n), the characteristic shifted by +1 frequency is Hj (i, n-1). Can be represented. A correlation value between the transmission path characteristic Hj (i, n) of each received known symbol and the characteristic Hj (1, n-1) obtained from the first known symbol is obtained by a correlator 38-j (step S104). This correlation calculation is defined as follows when the i-th known symbol is received.

(Correlation value) = Hj (i, 1) * Hj (1,0) + Hj (i, 2) * Hj (1,1) + Hj (i, 3) * Hj (1,2) +... + Hj (i, N-1) * Hj (1, N-2)
However, a * b is an operation of multiplying a by the complex conjugate of b.

  In the determiner 40, the correlation value calculated by the correlator 38-j is determined. If this value is greater than a predetermined threshold (or greater than or equal to the threshold) (step S105), the currently received symbol is the last of the known symbols. The number of transmitting antennas is estimated based on the number of known symbol patterns received so far, which is determined by the counter 35. Here, since the number of known symbols is equal to the number of transmission antennas, the value of the counter 35 becomes the estimated value of the transmission antenna (step S106).

  The MIMO signal processor 41 reproduces data symbols using the estimated number of transmission antennas. In step S105, if the correlation value is less than or equal to the threshold value (or less than the threshold value), the next known symbol is received (step S107), the counter 35 is incremented by one (step S108), the process returns to step S103, and a new In the same manner as above, the channel characteristic value is estimated from the known symbol (step S103), and the correlation with the characteristic H1 (n-1) shifted by +1 frequency of the channel characteristic estimated using the first received received symbol is calculated. (Step S104 ′). Thereafter, the operation of steps S103 to S108 is repeated every time a known signal is received.

  Also in the second embodiment, when there are a plurality of receiving antennas, the following method is also conceivable.

  (A) Only when the correlation value is equal to or greater than the threshold value (or greater than the threshold value) for all reception antennas, the number of transmission antennas is determined by regarding the end of the known symbol.

  (B) The correlation values calculated from all the receiving antennas are averaged, and when the total correlation value is larger than the threshold value, the number of transmitting antennas is determined by regarding the end of the known symbol.

  Although the condition of (a) is more severe, the number of transmitting antennas can be reliably detected when the conditions match.

  As described above, according to the second embodiment, as in the first embodiment, while performing transmission path estimation for each antenna using a known symbol without notifying the number of transmission antennas on the transmission side, The number of transmission antennas can be estimated by blind processing.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The figure which showed the structural example of the transmitter which concerns on the 1st thru | or 2nd embodiment of this invention. The figure explaining the transmission method of the known symbol by 1st Embodiment. The figure which showed the structural example of the receiver which concerns on 1st thru | or 2nd embodiment. The flowchart for demonstrating the transmission antenna number estimation algorithm in 1st Embodiment. The figure explaining the transmission method of the known symbol by 2nd Embodiment. The flowchart for demonstrating the transmission antenna number estimation algorithm in 2nd Embodiment.

Explanation of symbols

10: Transmission data;
11 ... Encoder;
12 ... Series-parallel converter;
13-1 to 13-M: modulator;
14-1 to 14-M ... serial-parallel converter;
15 ... Known symbol pattern generator;
16 ... counter;
17 ... selector;
18-1 to 18-M ... IFFT unit;
19 ... transmission circuit;
20-1 to 20-M: transmitting antenna;
30-1 to 30-M ... receiving antenna;
31 ... receiving circuit;
32-1 to 32-M ... FFT unit;
33-1 to 33-M: divider;
34. Known symbol pattern generator;
35 ... Counter;
36-1 to 36-M: shift circuit;
37-1 to 37-M ... memory;
38-1 to 38-M ... correlator;
39-1 to 39-M ... memory;
40: Judgment device;
41 ... MIMO receiver;

Claims (2)

A known symbol sequence including a plurality of known symbols that are transmitted in time and having a plurality of subcarriers for transmitting known information and having a plurality of subcarriers in time, wherein (a) the known information of each known symbol is The subcarriers to be transmitted are arranged on the frequency axis every "number of known symbols included in the known symbol sequence minus 1" subcarriers, and the known information of the known symbols is transmitted between the plurality of antennas. (B) between two known symbols that are adjacent in the time direction with the same antenna, the subcarriers that transmit the known information of the later known symbols of the two known symbols are The frequency adjacent to the subcarrier transmitting the known information of the previous known symbol of the two known symbols on the frequency axis And receiving means and the known symbol sequence, and for receiving the data symbols after said known symbol sequence is higher subcarrier,
Means for obtaining a channel characteristic estimation value for each antenna and each subcarrier from each known symbol of the received known symbol sequence;
Of the plurality of known symbols in the received known symbol string, the subcarrier position of the transmission path specific estimation value for each antenna and each subcarrier of the first known symbol that is the head on the time axis is represented by the subcarrier. Storage means for storing a channel characteristic estimation value at each subcarrier position for each antenna of the first known symbol after being shifted to a subcarrier position having a lower frequency adjacent to the frequency axis;
For each known symbol subsequent to the first known symbol in the received known symbol string, the channel characteristic estimation value for each antenna and subcarrier of the known symbol, and for each antenna stored in the storage means The number of antennas is estimated from the number of known symbols received so far if the correlation value is equal to or greater than a predetermined threshold value. Means for estimating the number of antennas,
Means for reconstructing the data symbol using the estimated number of antennas and the channel characteristic estimate;
And the number of the known symbols included in the known symbol sequence is equal to the number of the antennas used for transmission of the known symbol sequence . A known symbol sequence including a plurality of known symbols that are transmitted in time and having a plurality of subcarriers for transmitting known information and having a plurality of subcarriers in time, wherein (a) the known information of each known symbol is The subcarriers to be transmitted are arranged on the frequency axis every "number of known symbols included in the known symbol sequence minus 1" subcarriers, and the known information of the known symbols is transmitted between the plurality of antennas. (B) between two known symbols that are adjacent in the time direction with the same antenna, the subcarriers that transmit the known information of the later known symbols of the two known symbols are The frequency adjacent to the subcarrier transmitting the known information of the previous known symbol of the two known symbols on the frequency axis And receiving means and the known symbol sequence, and for receiving the data symbols after said known symbol sequence is lower subcarriers,
Means for obtaining a channel characteristic estimation value for each antenna and each subcarrier from each known symbol of the received known symbol sequence;
Of the plurality of known symbols in the received known symbol string, the subcarrier position of the transmission path specific estimation value for each antenna and each subcarrier of the first known symbol that is the head on the time axis is represented by the subcarrier. Storage means for storing a channel characteristic estimation value at each subcarrier position for each antenna of the first known symbol after shifting to a higher frequency subcarrier position adjacent on the frequency axis;
For each known symbol subsequent to the first known symbol in the received known symbol string, the channel characteristic estimation value for each antenna and subcarrier of the known symbol, and for each antenna stored in the storage means The number of antennas is estimated from the number of known symbols received so far if the correlation value is equal to or greater than a predetermined threshold value. Means for estimating the number of antennas,
Means for reconstructing the data symbol using the estimated number of antennas and the channel characteristic estimate;
And the number of the known symbols included in the known symbol sequence is equal to the number of the antennas used for transmission of the known symbol sequence .

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