JP4327684B2 - OFDM signal transmitting method and OFDM signal transmitting apparatus - Google Patents

Description

  The present invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) signal transmission method and an OFDM signal transmission apparatus using a plurality of transmission antennas.

  Among OFDM signal transmission schemes, especially the scheme of simultaneously transmitting different data using a plurality of transmission antennas has the advantage of being able to transmit a large amount of data at high speed, but the error rate characteristics of the data are likely to deteriorate. Therefore, a pilot subcarrier is formed by superimposing a known signal called a pilot symbol on one or a plurality of specific subcarriers on the transmission side, and propagation path compensation of each subcarrier is performed based on the pilot subcarriers on the reception side. There is known a method of obtaining a received signal with good error rate characteristics by performing frequency offset compensation.

  In this way, when the same known signal is transmitted using a plurality of transmission antennas using pilot subcarriers of the same frequency, the transmission signals of the pilot subcarriers interfere with each other to form a directional beam. When the carrier frequency (5 GHz band) is higher than the pilot subcarrier interval (about 4.4 MHz) as in the OFDM signal based on the IEEE 802.11a standard, the directional beam corresponding to each pilot subcarrier is almost equal. Face in the same direction. In this case, the null point at which the electric field of each directional beam suddenly falls also points in the same direction, so it is almost impossible to receive pilot subcarriers in the null point direction, and the reception characteristics deteriorate rapidly. To do.

In order to cope with such a problem, Patent Document 1 discloses a technique in which a pilot subcarrier is transmitted using only one transmission antenna, and a null signal is transmitted in the frequency band of the pilot subcarrier using the other transmission antennas. Yes. According to this method, the problem of mutual interference between pilot subcarriers due to transmission of pilot subcarriers from a plurality of transmission antennas can be avoided, so that deterioration of reception characteristics due to formation of a directional beam can be prevented.
Japanese Patent Laid-Open No. 2003-304216

  In the method of transmitting pilot subcarriers from only a single transmission antenna as in Patent Document 1, the total transmission power of pilot subcarriers is reduced as compared to the case of transmitting pilot subcarriers from a plurality of transmission antennas. This deteriorates the reception performance of the receiver.

  If the transmission power of pilot subcarriers from a single transmission antenna is made larger than the transmission power of data subcarriers from each transmission antenna, the total transmission power of pilot subcarriers can be increased and reception performance is improved. . On the other hand, increasing the transmission power of pilot subcarriers from a single transmission antenna will cause uneven transmission power within the frequency band of the OFDM signal. This increases the dynamic range of the D / A converter of the receiver (especially the input dynamic range).

  An object of the present invention is to provide an OFDM signal transmission method that reduces the composite third-order distortion without reducing the transmission power of pilot subcarriers. A further object of the present invention is to increase the area where high-quality reception is possible.

  According to a first aspect of the present invention, in an OFDM signal transmission method for transmitting an OFDM (Orthogonal Frequency Division Multiplexing) signal having a plurality of subcarriers orthogonal to each other using a plurality of transmission antennas, A pilot for transmitting a pilot signal, wherein the pilot signals are orthogonal to each other within a plurality of unit times and have a frequency that is an integer multiple of the unit time. Generating subcarriers, and generating the OFDM signal from the data subcarriers and pilot subcarriers.

  Here, the pilot subcarriers may be orthogonal on the frequency axis. In addition, the pilot subcarrier includes, for example, a product of a PN (pseudorandom noise) sequence orthogonal to each other within a plurality of unit times between the plurality of transmission antennas and data indicating the polarity of the pilot subcarrier.

  According to the second aspect of the present invention, in an OFDM signal transmission apparatus that transmits an OFDM (Orthogonal Frequency Division Multiplexing) signal having a plurality of subcarriers orthogonal to each other using a plurality of transmission antennas, And a pilot for transmitting a pilot signal, wherein the pilot signals are orthogonal to each other within a plurality of unit times and have a frequency that is an integer multiple of the unit time. Means for generating subcarriers, and means for generating the OFDM signal from the data subcarriers and pilot subcarriers.

  According to the present invention, even if the received power of one pilot subcarrier is small, the possibility that the received power of other pilot subcarriers is increased is increased. Therefore, a so-called dead zone in which the reception power of all pilot subcarriers simultaneously drops can be reduced, and the area where high-quality reception is possible increases. Further, since the transmission power of pilot subcarriers from each transmission antenna can be made uniform, there is no occurrence of complex third-order distortion, and there is no need to particularly increase the input dynamic range of the D / A converter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
As shown in FIG. 1, in the OFDM system according to the first embodiment of the present invention, an OFDM signal is transmitted from an OFDM signal transmission apparatus 100 having a plurality of transmission antennas 101a and 101b, respectively. The transmitted OFDM signal is received by an OFDM signal receiving apparatus 200 having a plurality of receiving antennas 201a and 201b. Here, a case where the OFDM signal transmission apparatus 100 has two transmission antennas 101a and 101b and the OFDM signal reception apparatus 200 has two reception antennas 201a and 201b will be described, but the present invention is not limited to this. The present invention is also effective when an antenna and a receiving antenna are provided.

  As schematically shown in FIGS. 2A and 2B, in the present embodiment, the OFDM signal transmission apparatus 100 forms two OFDM signals from two different transmission data, and transmits these from different transmission antennas 101a and 101b. To do. The first OFDM signal shown in FIG. 2 (a) is superimposed with transmission data DATA_a (N, K), and the second OFDM signal shown in FIG. 2 (b) is superimposed with transmission data DATA_b (N, K). Yes. Here, DATA_a (N, K) represents data transmitted from the transmission antenna 101a and transmitted on the Kth subcarrier of the Nth symbol. DATA_b (N, K) represents a signal transmitted from the Nth symbol K subcarrier in the data transmitted from the transmission antenna 101b. The pilot subcarrier will be described later.

  Now, the transfer function of the propagation path from the transmission antenna 101a to the reception antenna 201a (hereinafter, the transfer function of the propagation path is referred to as a propagation path response value) is Haa, and the propagation path response value from the transmission antenna 101a to the reception antenna 202b is Hab, Assuming that the propagation path response value from the transmission antenna 101b to the reception antenna 201a is Hba and the propagation path response value from the transmission antenna 101b to the reception antenna 202b is Hbb, the reception signal RXa of the reception antenna 201a and the reception signal RXb of the reception antenna 201b Can be written as:

TXa and TXb indicate transmission signals from the transmission antennas 101a and 101b, respectively. The transmission signals TXa and TXb can be demodulated by multiplying the reception signals RXa and RXb by the inverse matrix of the matrix formed by the propagation path response values Haa, Hab, Hba, and Hbb.
In the first embodiment, apart from a data subcarrier for transmitting data, a pilot subcarrier for transmitting a known signal used for compensating a residual phase error of a frequency offset or a clock offset is used. That is, at the time of reception, a residual phase error is detected and compensated using a known signal transmitted by a pilot subcarrier.

  Here, for comparison, in Patent Document 1, the OFDM signal shown in FIG. 30 (a) is transmitted from the first transmission antenna, and the OFDM signal shown in FIG. 30 (b) is transmitted from the second transmission antenna. Is sent. That is, as shown in FIG. 30A, pilot subcarriers indicated by diagonal lines are transmitted only from the first antenna. From the second antenna, pilot subcarriers are not transmitted as shown in FIG. 30 (b), and a null signal is transmitted at a frequency corresponding to the pilot subcarriers as indicated by a blank. Therefore, since the pilot subcarriers are transmitted without interfering with each other, the reception characteristics are not deteriorated by the directional beam, but the total transmission power of the pilot subcarriers is reduced.

  On the other hand, according to the first embodiment, good reception characteristics can be obtained while transmitting pilot subcarriers from the two transmission antennas 101a and 101b and sufficiently securing the total transmission power of the pilot subcarriers.

  Next, the OFDM signal transmission apparatus 100 shown in FIG. 1 will be described with reference to FIG. The OFDM signal transmitting apparatus 100 includes an encoder 102, a serial / parallel converter 103, modulators 104a and 104b, a serial / parallel converter 105, a pilot subcarrier insertion unit 106, and an IFFT (Inverse Fast Fourier Transform) unit 107a and 107b. Have.

  The input transmission data is a wireless packet having a structure as described later, and is encoded by the encoder 102. The encoded data is subjected to serial / parallel conversion by the serial / parallel converter 103, so that the encoded data is distributed into first transmission data corresponding to the transmission antenna 101a and second transmission data corresponding to the transmission antenna 101b. The first transmission data and the second transmission data are subcarrier modulated by modulators 104a and 104b, respectively. For example, BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), or 64QAM is used as a modulation method of the modulators 104a and 104b.

  The modulated data output from the modulator 104a is distributed to a plurality of first data subcarriers by the serial / parallel converter 105a. Similarly, the modulation data output from the modulator 103b is distributed to a plurality of second data subcarriers by the serial / parallel converter 105b.

  Modulated data allocated to the first data subcarrier and the second data subcarrier (hereinafter referred to as the first data subcarrier and the second data subcarrier) are input to pilot subcarrier insertion section 106. In pilot subcarrier insertion section 106, some subcarriers of the OFDM signal are allocated to pilot subcarriers for transmitting pilot signals, and the remaining subcarriers are allocated to data subcarriers for transmitting data signals.

  Specifically, pilot subcarrier insertion section 106 transmits a pilot signal transmitted on at least one first pilot subcarrier between first data subcarriers (hereinafter referred to as a first pilot subcarrier in this specification). And pilot signals (hereinafter referred to as second pilot subcarriers) transmitted on at least one second pilot subcarrier are inserted between the second data subcarriers, respectively. . A set of first data subcarriers and first pilot subcarriers is called a first subcarrier signal, and a set of second data subcarriers and second pilot subcarriers is called a second subcarrier signal.

  The IFFT units 107a and 107b perform inverse fast Fourier transform on the first subcarrier signal and the second subcarrier signal output from pilot subcarrier insertion section 106, respectively. As a result of the inverse fast Fourier transform, the first subcarrier signal and the second subcarrier signal are multiplexed by converting the signal on the frequency axis into the signal on the time axis, as shown in FIGS. 2 (a) and 2 (b). The first OFDM signal a and the second OFDM signal b are generated. The OFDM signals a and b are sent to the transmission antennas 101a and 101b via a wireless transmission unit (not shown), and transmitted from these antennas 101a and 101b.

Next, pilot subcarrier insertion section 106 will be described using FIG.
In pilot subcarrier insertion section 106, the first data subcarrier from serial / parallel converter 105a and the second data subcarrier from serial / parallel converter 105b are output as they are to IFFT units 107a and 107b. At this time, at least one first pilot subcarrier and second pilot subcarrier are inserted between the first data subcarriers and between the second data subcarriers, respectively. In the present embodiment, there are four first pilot subcarriers and four second pilot subcarriers.

  The PN sequence generator 110 generates a PN (pseudorandom noise) sequence. The first pilot subcarrier is generated by obtaining the product of the PN sequence PN (i) and the polarity data Sa (j) of the first pilot subcarrier stored in the ROM 121a by the multiplication units 111a to 111d. Similarly, the second pilot subcarrier is generated by obtaining the product of the PN sequence PN (i) and the polarity data Sb (j) of the second pilot subcarrier stored in the ROM 121b by the multiplication units 112a to 112d. Assuming that the baseband signal of the first pilot subcarrier transmitted from the transmitting antenna 101a is Pa (i, j), Pa (i, j) is expressed as PN (i) and Sa (j) as follows. Expressed as a product.

  However, i is a symbol number and is arranged in the time direction. j is the number of the pilot subcarrier, and is arranged in the frequency direction. Similarly, the pilot subcarrier baseband signal Pb (i, j) from the transmitting antenna 101b is represented by the product of PN (i) and Sb (j) as follows.

  In the first embodiment, the number of pilot subcarriers transmitted from the transmitting antennas 101a and 101b is four (j = 1 to 4), and the first and second transmitted from the transmitting antennas 101a and 101b, respectively. The pilot subcarrier polarity data Sa (j) and Sb (j) (j = 1, 2, 3, 4) are set as follows.

  That is, the polarity data Sa (j) and Sb (j) multiplied by the PN sequence are different between the first pilot subcarrier transmitted from the transmission antenna 101a and the second pilot subcarrier transmitted from the transmission antenna 101b. Thus, the polarity pattern of the first pilot subcarrier and the polarity pattern of the second pilot subcarrier are different. Here, the polarity pattern of the first pilot subcarrier is a pattern of combinations of the polarities of the first pilot subcarriers. Similarly, the polarity pattern of the second pilot subcarrier is a pattern of combinations of the polarities of the second pilot subcarriers. The effect obtained by making the polarity patterns of the first pilot subcarrier and the second pilot subcarrier different from each other will be described in detail later. Here, the polarity data and the PN sequence of the pilot subcarrier are expressed using rational numbers, but it is also possible to use complex polarity data or complex PN sequences.

  Next, the OFDM signal receiving apparatus 200 in FIG. 1 will be described with reference to FIG. The OFDM signal receiving apparatus 200 includes FFT (Fast Fourier Transform) units 202a and 202b, an interference cancellation circuit 203, a residual phase error detector 204, phase compensation units 205a and 205b, a serial / parallel converter 206, and a decoder 207.

  An OFDM signal received by the receiving antenna 201a is input to the FFT unit 202a through a radio receiving unit (not shown), and is divided into signals of each subcarrier by being subjected to Fourier transform. Similarly, the OFDM signal received by the receiving antenna 201b is also divided into subcarrier signals by being subjected to Fourier transform by the FFT unit 202b.

  As shown in FIG. 1, the signal received by the receiving antenna 201a is superimposed with the OFDM signal transmitted from the transmitting antennas 101a and 101b, and the signal received by the receiving antenna 201b is also transmitted from the transmitting antennas 101a and 101b. OFDM signals to be superimposed are superimposed. The interference cancellation circuit 203 performs interference cancellation in order to separate and receive the OFDM signals from the transmission antennas 101a and 101b. The interference cancellation method for this purpose is a known technique, but here, a method of multiplying the reception signal by the inverse matrix of the matrix formed by the propagation path response of Equation (1) will be described. The inverse matrix of the matrix created by the propagation path response of Equation (1) can be written as follows:

  The OFDM signal from the transmitting antennas 101a and 101b is separated by multiplying the inverse matrix of Equation (6) by the received signal vector generated from the received signals output from the receiving antennas 201a and 201b, respectively. In the multipath environment, since the channel response value differs for each subcarrier, there are as many channel response values as the number of subcarriers, and the derivation of the inverse matrix coefficient and the multiplication of the inverse matrix are performed for each subcarrier. The signal thus separated by the interference cancellation circuit 203 is sent to the residual phase error detector 204.

  The residual phase error detector 204 detects residual components such as a frequency offset and a clock offset compensated by using a radio packet preamble (not shown). The residual phase error detector 204 further detects the residual phase error of the two received signals RXa and RXb using the known signal transmitted by the pilot subcarrier, and sends this to the phase compensation units 205a and 205b.

FIG. 6 shows the detection principle of the residual phase error detector 204. Here, the detection of the residual phase error will be described by taking as an example a case where it is applied to a signal that is not subjected to interference removal. That is, with respect to pilot subcarriers, the matrix expressed by Equation (6) (the right side of Equation (6)) is represented by a unit matrix, or weighted and combined with the outputs of FFT units 202a and 202b, This is a case where a matrix that maximizes the power-to-noise power ratio, that is, a matrix or a vector that performs reception diversity can be used. When transmitting binary pilot subcarriers generated from a binary PN sequence using two transmitting antennas 101a and 102b, the OFDM signal receiving apparatus before interference cancellation uses 2 ² = There are four received signal point (1, 1), (1, -1), (-1, 1), (-1, -1) candidates. Here, for example, (1, −1) represents that a modulated signal “1” is transmitted from the transmitting antenna 101a and a modulated signal “−1” is transmitted from the transmitting antenna 101b.

  When transmitting the first pilot subcarrier and the second pilot subcarrier generated from the common PN sequence in the transmission antennas 101a and 101b from the transmission antennas 101a and 101b as in the first embodiment, the reception signal point is (1 , 1) and (-1, -1), or (1, -1) and (-1, 1). This combination does not change during radio packet reception. For example, when the combination of received signal points is (1, −1) and (−1, 1), it looks to the OFDM signal receiving device as if a BPSK signal was transmitted from a single transmitting antenna.

  Next, a case where residual phase error is detected using pilot subcarriers Pa (1) and Pb (1) transmitted on the (−k + 1) th subcarrier will be described. Now, only the FFT 202a connected to the receiving antenna 201a is considered, and the pilot subcarrier propagation path response value from the transmitting antenna 101a to the receiving antenna 201a in the (−k + 1) th subcarrier is assumed to be Haa. Similarly, the propagation path response value from the transmitting antenna 101b to the receiving antenna 201a is assumed to be Hba. When the polarities of the pilot subcarriers are expressed by equations (4) and (5), the polarities corresponding to the (−k + 1) th pilot subcarrier are Sa (1) = 1 and Sb (1) = 1. . Therefore, since the pilot signal in which signals from the two transmitting antennas are multiplexed is multiplied by the propagation path response value of Haa + Hba, two points (1, 1) and (-1, -1) are received. Therefore, the residual phase error detector calculates the propagation path response value Haa + Hba using the propagation path response values Haa and Hba, and creates the reference signal points (1, 1) and (−1, −1).

  Now, assume that (1, 1) is transmitted in the next OFDM symbol, and the received signal point at this time is the “next symbol” shown in FIG. At this time, the residual phase error detector 204 can detect the phase difference θ between the current received signal point (1, 1) and the next symbol as a residual phase error. The residual phase error detection value can be obtained from both the output of the system of the receiving antenna 201a, the output of the system of the receiving antenna 201b, and a plurality of outputs. In this case, it is possible to output both average values and weighted average values to the phase compensators 205a and 205b.

  In the first embodiment, residual phase error detection using pilot subcarriers is performed without using interference cancellation. However, residual phase error can also be detected after interference cancellation is performed. In this case, the reception signal points of the pilot subcarriers appear as many as the transmission signal points from the transmission antennas 101a and 101b. In addition, when applying the detection of residual phase error using pilot subcarriers after performing interference cancellation, the signal power-to-noise power ratio of pilot subcarriers deteriorates, and the estimation accuracy deteriorates.

  The phase compensation units 205a and 205b perform phase compensation by performing phase rotation on the received signal by the residual phase error. The two received signals after phase compensation are converted into serial signals by the parallel / serial converter 206 and decoded by the subsequent decoder 207 to obtain a received signal corresponding to the transmitted signal.

  As described above, pilot subcarriers are used to detect residual phase errors. Since the reception power of the pilot subcarrier is low, for example, when the pilot subcarrier is received in a state where it is buried in noise, the residual phase error may be erroneously detected. In that case, since the phase compensation units 205a and 205b perform phase compensation according to an erroneous residual phase error detection result, there is a high possibility that all data subcarriers will be received in error. Therefore, it is no exaggeration to say that the reception power of the pilot subcarrier determines the reception characteristics of the OFDM signal receiving apparatus. In order to solve this problem, in the present embodiment, as described above, the polarities of the first pilot subcarrier transmitted from the transmission antenna 101a and the second pilot subcarrier transmitted from the transmission antenna 101b are different.

  FIG. 7 schematically shows transmission directivity images of the antennas 101a and 101b when transmitting pilot subcarriers of the same polarity pattern from the two transmission antennas 101a and 101b, and a transmission combined beam pattern by the antennas 101a and 101b. Yes. The polarity data Sa (1), Sa (2), Sa (3), Sa (4) of the first pilot subcarrier transmitted from the transmission antenna 101a is expressed by Equation (4), and the second data transmitted from the transmission antenna 101b. The pilot subcarrier polarity data Sb (1), Sb (2), Sb (3), and Sb (4) are expressed by the following equation (7).

  The transmission antennas 101a and 101b are assumed to be omnidirectional antennas as shown on the upper side of FIG. For this reason, when pilot subcarriers having the same polarity are transmitted simultaneously from the antennas 101a and 101b, the transmission signals interfere with each other, and the combined beam pattern forms a directional beam. Further, taking the case of the IEEE802.11a standard as an example, the center frequency (carrier frequency) of the OFDM signal is 5 GHz, whereas the interval between pilot subcarriers is as small as about 4.4 MHz. The directional beams of the two pilot subcarriers are directed in substantially the same direction as shown in the lower side of FIG. As a result, there is a possibility that a dead zone where the reception power of the four pilot subcarriers greatly decreases, that is, a dead band where the reception characteristics of the OFDM signal receiving apparatus are significantly deteriorated may occur.

  On the other hand, FIG. 8 shows the antenna 101a when the polarity pattern of the first pilot subcarrier transmitted from the transmission antenna 101a is different from the polarity pattern of the second pilot subcarrier transmitted from the transmission antenna 101b according to the first embodiment. , 101b and the transmission combined beam pattern by the antennas 101a and 101b. The polarity data Sa (1), Sa (2), Sa (3), Sa (4) of the first pilot subcarrier transmitted from the transmission antenna 101a is expressed by Equation (4), and the second data transmitted from the transmission antenna 101b. The pilot subcarrier polarity data Sb (1), Sb (2), Sb (3), and Sb (4) are expressed by equation (5).

  According to Equations (4) and (5), for example, the phase difference between the first pilot subcarrier controlled according to polarity data Sa (1) and the second pilot subcarrier controlled according to polarity data Sb (1) is zero. In contrast, the phase difference between the first pilot subcarrier controlled according to the polarity data Sa (2) and the second pilot subcarrier controlled according to the polarity data Sb (2) is 180 °. As a result, for example, as shown in the lower side of FIG. 8, the direction of the directional beam formed by the pilot subcarriers of polarity Sa (1) and Sb (1) and the polarity Sa (2) and Sb (2) The direction of the directional beam formed by the pilot subcarriers of the pilot subcarriers differs by 180 °.

  FIG. 9 shows an average normalized reception level of pilot subcarriers at the receiver when pilot subcarriers are transmitted using the embodiment of the present invention. There are two transmitting antennas, and Pa (1), Pa (2), Pa (3), Pa (4) and Pb (1), Pb (2), Pb using equations (4) and (5). (3) Four pilot subcarriers Pb (4) are used. Note that the pilot subcarrier polarity is 5 GHz at the center frequency of the OFDM signal, the signal bandwidth is about 20 MHz, the antenna element spacing is a half wavelength, and each element is omnidirectional. The propagation channel model uses “Channel model D (NLOS)” shown in IEEE802.11-03-940 / r1 “TGn Channel model”. The X axis in FIG. 9 shows the angle seen from the transmission antenna, and the received power of four pilot subcarriers corresponding to a certain transmission angle is shown on the Y axis.

  As can be seen from FIG. 9, at some angles, the pilot subcarrier power may drop compared to other angles. However, since the reception power of other pilot subcarriers increases at that location, the receiver can compensate for the residual phase error using a pilot subcarrier having a high level.

  On the other hand, FIG. 10 shows received power when pilot subcarriers are transmitted using Equations (4) and (7). That is, the characteristics are obtained when pilot signals having the same polarity are used. As can be seen from FIG. 10, at one angle, the power of the pilot subcarrier may drop compared to the other angles. The tendency is the same for other pilot subcarriers, and the power of all pilot subcarriers drops simultaneously. Therefore, in a receiver that exists at such an angle, it is difficult to compensate for the residual phase error even if other pilot subcarriers are used.

  Therefore, even if the reception power of one pilot subcarrier is small on the reception side, there is a high possibility that the reception power of other pilot subcarriers will increase. For this reason, it is possible to reduce the dead zone in which the reception power of all pilot subcarriers falls simultaneously, and the area where high quality reception is possible is expanded.

  Further, in the first embodiment, it is not necessary to particularly increase the transmission power of subcarriers for all antenna transmission antennas 101a and 101b, so that the composite third-order distortion does not increase, and the D / A converter does not increase. There is no need to increase the input dynamic range.

  In the above description, an example in which the OFDM signal transmission apparatus 100 includes two transmission antennas 101a and 101b has been described. FIGS. 11A and 11B show examples of two types of polarity patterns of the first to fourth pilot subcarriers transmitted from each transmission antenna when four transmission antennas 101a to 101d are used as an example. Indicates. FIGS. 11C and 11D show examples of two types of polarity patterns of the first to fourth pilot subcarriers transmitted from each transmission antenna when three transmission antennas 101a to 101c are similarly used. Indicates. Here, two types of pilot subcarrier polarities 1 and 2 are prepared for the first to fourth pilot subcarriers. The pilot subcarrier polarity 1 is a polarity pattern when a real number is used, and the pilot subcarrier polarity 2 is a polarity pattern when an imaginary number is used. The pilot subcarrier polarity 2 is generated using a Fourier matrix coefficient.

  In pilot subcarrier polarity 1 in the case of the four transmitting antennas shown in FIG. 11A, the polarity of the first pilot subcarrier is Sa (1) = 1, Sa (2) = 1, Sa (3) = 1, Sa (4) = − 1, the polarity of the second pilot subcarrier is Sb (1) = 1, Sb (2) = − 1, Sb (3) = 1, Sb (4) = 1, and the third pilot subcarrier The carrier polarity is Sc (1) = 1, Sc (2) = − 1, Sc (3) = − 1, Sc (4) = − 1, and the polarity of the fourth pilot subcarrier is Sd (1) = 1. , Sd (2) = 1, Sd (3) = − 1, and Sd (4) = 1. Here, consider a vector having each polarity as an element for pilot subcarriers transmitted from a certain frequency. Since four pilot subcarriers are transmitted from each antenna and there are four transmission antennas, the following four vectors having four elements can be defined.

  s (1) to s (4) are vectors different from each other. For example, no matter how many times the vector of s (1) is multiplied, it does not become another vector. In this way, because the pilot subcarrier vector transmitted from a certain frequency is different from the pilot subcarrier vector transmitted from another frequency, the directional beam of each pilot subcarrier points in a different direction. It is possible to reduce the dead zone. Although s (1) to s (4) are orthogonal to each other, the directional beams can be directed in different directions even if they are not necessarily orthogonal.

  In the pilot subcarrier polarity 2 in the case of the four transmitting antennas shown in FIG. 11B, the polarity of the first pilot subcarrier is Sa (1) = 1, Sa (2) = 1, Sa (3) = 1, Sa (4) = − 1, and the polarity of the second pilot subcarrier is Sb (1) = 1, Sb (2) = − j, Sb (3) = − 1, Sb (4) = − j, The pilot subcarrier polarity is Sc (1) = 1, Sc (2) = − 1, Sc (3) = 1, Sc (4) = 1, and the fourth pilot subcarrier polarity is Sd (1) = 1. , Sd (2) = j, Sd (3) = − 1, and Sd (4) = j. Here, j is an imaginary unit. In this case as well, as described above, regarding pilot subcarriers transmitted from a certain frequency, when considering vectors having respective polarities as elements, the respective vectors are different from each other in the complex domain, and are orthogonal in the complex domain. Although there is a relationship, the relationship is not necessarily orthogonal.

  On the other hand, in the pilot subcarrier polarity 1 in the case of the three transmitting antennas shown in FIG. 11C, the polarity of the first pilot subcarrier is Sa (1) = 1, Sa (2) = 1, Sa (3) = 1. , Sa (4) = − 1, and the polarity of the second pilot subcarrier is Sb (1) = 1, Sb (2) = − 1, Sb (3) = 1, Sb (4) = 1, The polarities of the pilot subcarriers are Sc (1) = 1, Sc (2) = − 1, Sc (3) = − 1, and Sc (4) = − 1. Also in this case, as described above, when considering vectors having respective polarities as elements for pilot subcarriers transmitted from a certain frequency, the respective vectors are different from each other.

  Next, in the pilot subcarrier polarity 2 in the case of the three transmitting antennas shown in FIG. 11D, the polarity of the first pilot subcarrier is Sa (1) = 1, Sa (2) = 1, Sa (3) = 1, Sa (4) =-1, and the polarity of the second pilot subcarrier is Sb (1) = 1, Sb (2) =-j, Sb (3) =-1, Sb (4) =-j The polarities of the third pilot subcarriers are Sc (1) = 1, Sc (2) = − 1, Sc (3) = 1, and Sc (4) = 1. In this case as well, as described above, regarding the pilot subcarriers transmitted from a certain frequency, considering the vectors having the respective polarities as elements, the respective vectors are different from each other, and each vector is multiplied by a number in the complex domain. But it won't be another vector.

  By determining the arrangement of the pilot subcarriers in this way, the directional beams of the pilot subcarriers are directed in different directions, and thus it is possible to reduce the dead zone.

  By the way, the pilot subcarrier polarities shown in FIGS. 11A, 11B, 11C, and 11D can be expressed by the following formula (9) in the complex domain.

Where s _k (i) is the polarity of the pilot subcarrier, j is an imaginary unit, i is the number of the pilot subcarrier, k is the antenna number of the transmission antenna, and the first element of k is transmitted from the transmission antenna 101a, for example. The second element of k indicates a signal transmitted from the transmission antenna 101b.

  According to Equation (9), the phase difference between the subcarriers of the first to fourth pilots transmitted from the antenna 101b with k = 2 is −90 °. The phase difference between pilot subcarriers transmitted from the antenna 101c with k = 3 is −180 °, and the phase difference between pilot subcarriers transmitted from the antenna 101d with k = 4 is −270 °. Thus, when the transmission antennas are different, the phase difference between pilot subcarriers is different. Accordingly, since the directional beams corresponding to the pilot subcarriers are directed in different directions as before, the dead zone can be reduced.

  The phase difference −90 ° and the phase difference 270 ° are the same, and the phase difference −270 ° and the phase difference 90 ° are also the same. Therefore, in order to faithfully represent FIGS. 11 (a), (b), (c), and (d), the exponent term in Equation (9) requires a minus sign, but there is no minus sign from the above discussion. Since the same applies to the case, the symbol is omitted in Equation (9).

  Further, according to FIGS. 11A and 11B, the polarity of the fourth pilot subcarrier among the pilot subcarriers transmitted from the first transmitting antenna 101a is first to first as shown in the following formula (10). Inverted with respect to the third pilot subcarrier.

  In other words, the polarities of the first to fourth pilot subcarriers are expressed by the following formula (11).

  Furthermore, when generalized, the polarity of the pilot subcarrier is expressed by Equation (12) or (13) depending on the pilot subcarrier number i.

  In the above description, i is the number of the pilot subcarrier, but i can be replaced with the frequency of the pilot subcarrier. Specifically, for example, -21, -7, +7, 21 is used as the value of i. At this time, in consideration of the periodicity of the Fourier transform function, it is also possible to express the pilot subcarrier polarity as in the following formula (14).

Here, s _k (i) is the polarity of the pilot subcarrier, j is an imaginary unit, i is the frequency of the pilot subcarrier, k is the antenna number of the transmitting antenna, and N is the number of input points in the inverse Fourier transform.

  Even using Equation (14), if the transmission antenna is different, the phase difference between the pilot subcarriers is different, so that the dead zone can be reduced. In consideration of the Fourier transform pair, expression (14) is equivalent to shifting the transmission signal by one sample for each transmission antenna on the time axis.

  Next, another embodiment of the present invention will be described. In other embodiments described below, the pilot subcarrier insertion unit 106 in the OFDM signal transmitting apparatus 100 is different from that in the first embodiment.

(Second Embodiment)
As shown in FIG. 12, the pilot subcarrier insertion unit 106 according to the second embodiment includes ROMs 121a and 121b storing polarity data for the first pilot subcarrier and the second pilot subcarrier, and subcarrier pattern control. A device 122 is added. In the ROMs 121a and 121b, as illustrated in FIG. 13, the polarity data representing the polarities Sa (1) to Sa (4) of the first pilot subcarrier and the polarities Sb (1) to Sb ( Polarity data representing 4) is stored for each of three patterns (pattern A, pattern B, and pattern C). Which polarity data of pattern A, pattern B, and pattern C is read from the ROMs 121a and 121b is determined by address data given to the ROMs 121a and 121b.

  In the second embodiment, the polarities of the first pilot subcarrier and the second pilot subcarrier transmitted from each of the transmission antennas 101a and 101b are not fixed but change for each radio packet. That is, polarity data of a different pattern for each wireless packet is read from the ROMs 121a and 121b, and multiplied by the PN sequence generated by the PN sequence generator 110 by the multipliers 111a to 111d and 112a to 112d.

  Radio packet counter 123 provided outside pilot subcarrier insertion section 106 shown in FIG. 12 counts the number of radio packets in transmission data input to encoder 102 in FIG. It passes to the carrier pattern controller 122. The subcarrier pattern controller 122 changes the address data given to the ROMs 121a and 121b each time the count value of the wireless packet counter 123 is incremented by one. Thereby, the subcarrier pattern controller 122 changes the patterns of the polarity data of the first and second pilot subcarriers read from the ROMs 121a and 121b, respectively.

  For example, pattern A polarity data is read when a certain wireless packet is transmitted, pattern B polarity data is read when the next wireless packet is transmitted, and pattern C polarity data is read when the next wireless packet is transmitted. As a result, the pilot subcarrier polarity pattern is changed for each radio packet. The change of the polarity data pattern by the subcarrier pattern controller 122 is performed at random for each radio packet, for example.

  The polarity data read from the ROMs 121a and 121b in this way is input to the multipliers 111a to 111d and multiplied by the PN sequence generated by the PN sequence generator 110 in the same manner as in the first embodiment, whereby the first pilot subcarrier is obtained. And second pilot subcarriers are generated. The generated first pilot subcarrier and second pilot subcarrier are inserted between the first data subcarrier and the second data subcarrier, respectively, thereby generating the first subcarrier and the second subcarrier. Is done.

  The first subcarrier and the second subcarrier are input to IFFT units 107a and 107b shown in FIG. 3 to generate a first OFDM signal and a second OFDM signal. The first OFDM signal and the second OFDM signal are respectively sent to the transmission antennas 101a and 101b via a wireless transmission unit (not shown) and transmitted from these antennas 101a and 101b.

  According to the second embodiment, for example, when transmitting pilot subcarriers controlled by pattern A polarity data and when transmitting pilot subcarriers controlled by pattern B polarity data, antennas 101a and 101b are used. The pattern of the directional beam formed is different.

  Here, for example, in the OFDM signal receiving apparatus located at a place where the received power is lower than that of the pattern A pilot subcarrier, when a pilot subcarrier of a pattern B different from the pattern A is transmitted, There is a high possibility that the received power of the carrier will recover. Therefore, by changing the pilot subcarrier pattern for each radio packet, it is possible to reduce places where reception is not possible at all because the reception power of the pilot subcarrier is low.

  When changing the pattern of the polarity data of the pilot subcarrier for each radio packet, it is not always necessary to make the change random. For example, among the various patterns of the polarity data of the pilot subcarrier, a pattern in which the reception characteristic is improved for each OFDM signal receiving device is stored, and stored in correspondence with the OFDM signal receiving device of the transmission destination It is also possible to transmit pilot subcarriers using a certain pattern.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the third embodiment, an error occurs in the previously transmitted radio packet, and the polarity pattern of the pilot subcarrier is changed only when a retransmission packet is transmitted. As shown in FIG. 14, in the pilot subcarrier insertion unit 106 according to the third embodiment, except that the radio packet counter 123 in FIG. 12 is replaced with the retransmission detector 124, the pilot subcarrier shown in FIG. The same as the carrier insertion unit 106.

  As illustrated in FIG. 15, the wireless packet includes a unique word used for synchronization by the OFDM signal receiving apparatus, a transmission source field for specifying a transmission source (OFDM signal transmission apparatus), and a transmission destination (OFDM signal reception apparatus). ), A retransmission field indicating whether the wireless packet is a retransmission packet or not, and an error detection field for determining whether an error has occurred in each field, followed by a plurality of data symbols Followed.

  The transmission signal input to the encoder 102 in FIG. 3 is also input to the retransmission detector 124. The retransmission detector 124 analyzes the retransmission field in the wireless packet that is the transmission signal, and if the wireless packet is a retransmission packet, notifies the subcarrier pattern controller 122 to that effect. Upon receiving notification that the radio packet is a retransmission packet, the subcarrier pattern controller 122 changes the address data given to the ROMs 121a and 121b, and reads the first and second pilot subcarriers read from the ROMs 121a and 121b, respectively. Controls the pattern of polarity data. As a result, a radio packet including a pilot subcarrier having a polarity pattern different from that of the previously transmitted radio packet is transmitted to the same transmission partner.

  In the third embodiment, it is determined by analyzing the retransmission field that the wireless packet is a retransmission. However, an upper layer that performs wireless access control (for example, Medium Access Control (MAC layer) in the IEEE802.11a standard) directly It is also possible to notify the carrier pattern control device that the wireless packet is a retransmission packet.

  As described above, in the third embodiment, retransmission packets are transmitted to the same transmission partner according to a polarity pattern different from the pilot subcarrier of the wireless packet transmitted by the OFDM signal transmission apparatus 100 last time. As a result, the pattern of the directional beam formed by the plurality of transmission antennas changes at the time of retransmission, and the probability that the OFDM signal receiving apparatus can correctly receive the retransmission packet increases.

(Fourth embodiment)
In pilot subcarrier insertion section 106 according to the fourth embodiment of the present invention, two PN sequence generators 110a and 110b are provided as shown in FIG. The first PN sequence generator 110a generates a first PN sequence PNa that modulates the first pilot subcarrier transmitted from the transmission antenna 101a. Second PN sequence generator 110b generates a second PN sequence PNb that modulates the second pilot subcarrier transmitted from transmitting antenna 101b.

  The polarity patterns of the first pilot subcarrier and the second pilot subcarrier may all be the same or different. Here, a case where the same polarity data S is used will be described. The first pilot subcarrier is modulated as follows according to the PN sequence PNa and the pilot subcarrier polarity data S.

  Similarly, the second pilot subcarrier is modulated as follows according to the PN sequence PNb and the pilot subcarrier polarity data S.

  FIG. 17 shows the first OFDM signal and the second OFDM signal including data subcarriers and pilot subcarriers thus modulated. The first OFDM signal and the second OFDM signal are transmitted to IFFT units 107a and 107b, respectively, and transmitted from transmission antennas 101a and 101b.

FIG. 18 shows the detection principle of the residual phase error detector 204 shown in FIG. 5 according to the fourth embodiment. Here, a case where the residual phase error is estimated before performing interference cancellation will be described. When a binary PN sequence and a binary pilot subcarrier are transmitted by the two transmission antennas 101a and 101b, as in FIG. 6 in the first embodiment, 2 ² = 4 received signal points (1 , 1), (1, -1), (-1, 1), (-1, -1) candidates exist. In the first embodiment, the received signal point has a combination of (1, 1) and (-1, -1), or a combination of (1, -1) and (-1, 1). On the other hand, in the fourth embodiment, pilot subcarriers transmitted from the transmission antennas 101a and 101b are modulated by different PN sequences, so that all four reception signal points may appear for each OFDM symbol. There is.

  For example, in the fourth embodiment, a combination of (1, -1) and (-1, 1) is transmitted, and a combination of (1, 1) and (-1, -1) is transmitted. There are two possible ways. In the former combination, the phase difference between the signals from the transmitting antenna 101a and the transmitting antenna 101b is 180 °, while the latter combination is 0 °. Therefore, when the combination of the former is transmitted and when the combination of the latter is transmitted, the directional beam for transmission is different, so that the received power changes. Note that the four received signal point candidates (1, -1), (-1, 1), (1, 1), and (-1, -1) are as described in the first embodiment. It can be obtained by combining the channel coefficient to each transmitting antenna and receiving antenna with the signal transmitted by the pilot subcarrier.

  Next, a method for measuring the residual phase error will be described. Assume that the received symbol of the pilot subcarrier is (1, 1). In this case, in the first embodiment, (1, 1) is also transmitted as the next symbol or (-1, -1) is transmitted, so that the receiving side receives a BPSK signal from a single antenna. The received power does not change.

  On the other hand, in the fourth embodiment, (−1, 1) may be transmitted as the next symbol. Therefore, the received symbols including the phase error are “next symbol 1” and “next symbol 2” shown in FIG. There are two possible ways. When the reception signal point of the next symbol is (1, 1) or (-1, -1), the residual phase error detector 204 detects the phase difference θ1 as a residual phase error. On the other hand, when the reception signal point of the next symbol is (-1, 1) or (1, -1), the residual phase error detector 204 determines the reception signal of (-1, 1) from the current propagation path response value. And a phase difference θ2 between (−1, 1) and “next symbol 2” is detected as a residual phase error detector 204.

  The phase compensation units 205a and 205b perform phase compensation by performing phase rotation on the received signal by the residual phase error. The two received signals after phase compensation are converted into serial signals by the parallel / serial converter 206 and decoded by the subsequent decoder 207, whereby a received signal corresponding to the transmitted signal is obtained. In the fourth embodiment, the method for measuring the residual phase error before performing the interference removal has been described. However, it is also possible to detect the residual phase error after performing the interference removal. When interference cancellation is performed, pilot subcarriers transmitted from a single antenna appear in the output after interference cancellation, so that only two received signal points appear.

As described above, according to the fourth embodiment, a combination of (1, 1) and (-1, -1) is transmitted in the OFDM symbol as shown in FIG. -1,1) may be transmitted. Therefore, the received power changes for each OFDM symbol. Therefore, even if the received power of the pilot subcarrier decreases in a certain OFDM symbol and the residual phase error cannot be detected, the received power may be recovered in the next symbol. As a result, it is possible to eliminate a dead zone due to a decrease in all received power of pilot subcarriers.
(Fifth embodiment)
The pilot subcarrier insertion unit 106 according to the fifth embodiment of the present invention includes, as shown in FIG. 19, the second embodiment shown in FIG. 12 or the third embodiment shown in FIG. The fourth embodiment shown is combined. That is, in the fifth embodiment, the polarity of pilot subcarriers is different for each transmission antenna, and the PN sequence for modulating pilot subcarriers is different for each transmission antenna. Therefore, the baseband signal of the pilot subcarrier can be written as follows for the transmitting antennas 101a and 101b.

  In this case, the pilot subcarriers are as shown in FIG. 20, and the directional beams formed by the transmitting antennas 101a and 101b for the pilot subcarriers are directed in different directions for each frequency and in the symbol time direction. Therefore, even if the reception level of the pilot subcarrier is low at a certain frequency or a certain time, the pilot subcarrier can be received at another frequency or another symbol, and the dead zone can be reduced.

(Sixth embodiment)
In the pilot subcarrier insertion unit 106 according to the sixth embodiment of the present invention, the PN sequence from the PN sequence generators 110a and 110b is input to the transmission diversity circuits 125a and 125b as shown in FIG. The subcarrier is transmitted as follows.

  However, “*” indicates a complex conjugate. As shown in equations (19)-(22), the PN sequence is transmitted using transmission diversity using two transmission antennas 101a and 101b and two symbols. The transmission diversity method expressed by the equations (19) to (22) is the same as the transmission diversity method disclosed in US Pat. No. 6,185,258B1.

  The specific pilot subcarrier signals shown in Equations (19)-(22) are applied to the -k + 1th subcarrier and the k-4th subcarrier in FIG. Equations (19)-(22) are shown for the j-th pilot subcarrier, and the transmission method can be changed for other subcarriers. Specifically, it can be described as follows.

  The specific pilot subcarriers shown in Expressions (23) to (26) are applied to the −k + 4th subcarrier and the k−1th subcarrier in FIG. The residual phase error detector 204 in the OFDM signal receiving apparatus shown in FIG. 5 performs decoding corresponding to transmission diversity using, for example, a decoding method disclosed in US Pat. No. 6,185,258B1. It is possible to maximize the signal-to-noise power ratio of the pilot subcarrier.

  As can be seen from the equations (16)-(19), diversity transmission is performed using two symbol times here, so that diversity gain cannot be obtained by receiving only one symbol. FIG. 23 shows a signal when the −k + 4th subcarrier is modulated using Expressions (16) − (19). As shown in FIG. 23, the residual phase error is detected with the signal that received only one symbol in symbol 1, but since the symbol received last time can be used from the second symbol, the received signals of symbol 1 and symbol 2 are By using this, it is possible to detect the residual phase error of symbol 2. Similarly, the residual phase error of symbol 3 can be detected using the received signals of symbol 2 and symbol 3. That is, it is possible to detect a phase error by overlapping two symbols. It is also possible to perform all residual phase error detection using only the currently received single symbol.

  As described above, according to the sixth embodiment, by transmitting pilot subcarriers using transmission diversity, it is possible to detect an accurate residual phase error and improve reception performance.

(Seventh embodiment)
In pilot subcarrier insertion section 106 according to the seventh embodiment of the present invention, as shown in FIG. 24, subcarrier arrangement apparatus 126a for changing the positions of pilot subcarriers and data subcarriers between transmission antennas 101a and 101b and 126b is provided. In the subcarrier arrangement devices 126a and 126b, the locations of pilot subcarriers and data subcarriers are different at the transmission antennas. Next, the pilot subcarrier insertion unit 607 will be specifically described with reference to FIG.

  Modulated signals obtained by multiplying the PN sequence and the polarity Sa (1) -Sa (4) for the transmitting antenna 101a are respectively input to the subcarrier arrangement device 126a as pilot subcarriers Pa (1) -Pa (4). In subcarrier arrangement apparatus 126a, data subcarriers and pilot subcarriers are rearranged and input to IFFT unit 107a. Since the transmission antenna 101b is the same, description thereof is omitted.

  In FIG. 25, as shown in the subcarrier arrangement in the seventh embodiment, pilot subcarriers of the subcarriers are transmitted only from a single transmission antenna. For example, a pilot subcarrier PN (1) modulated with a PN sequence is transmitted from the transmission antenna 101a as a −k-th subcarrier, and a data subcarrier (DATA) is transmitted from the transmission antenna 101b. Similarly, for the −k + 2nd subcarrier, a pilot subcarrier is transmitted from the transmission antenna 101a, and a data subcarrier (DATA) is transmitted from the transmission antenna 101b.

  Since the data signal is a random signal, the correlation between the first data subcarrier transmitted from the transmission antenna 101a and the second data subcarrier transmitted from the transmission antenna 101b is generally low. For this reason, the phase difference between the subcarriers transmitted from the transmission antenna 101a and the subcarriers transmitted from the transmission antenna 101b is different between the −kth subcarrier and the −k + 2nd subcarrier. There is a high possibility that the directional beams of the pilot subcarrier transmitted on the carrier and the pilot subcarrier transmitted on the −k + 2nd subcarrier are different.

  Therefore, according to the seventh embodiment, since the probability that the received power of all pilot subcarriers simultaneously falls due to the influence of null is very small, there is no dead zone. Also, even if the pilot subcarrier power happens to fall in one symbol period, there is a high possibility that the data signal is different between the current symbol and the next symbol. . As described above, according to the seventh embodiment, it is possible to increase the probability of receiving pilot subcarriers and reduce the dead zone.

  The change of the arrangement of pilot subcarriers can also be performed in a radio packet.

For example, in the IEEE 802.11a standard, a pilot signal for estimating the transfer function of all subcarriers is inserted in the unique word shown in FIG. It is possible to ask for a response. However, since a pilot signal is transmitted using only pilot subcarriers in a data symbol, it is difficult to follow the propagation path response when the temporal variation of the propagation path is fast. However, by changing the arrangement of pilot subcarriers between radio packets and transmitting pilot signals from other subcarriers, it becomes possible to follow the propagation path responses of other subcarriers. Therefore, accurate reception can be performed by using this method. In addition, although all the polarities of the pilot subcarriers are the same in the seventh embodiment, it can be the same as in the first to sixth embodiments.

(Eighth embodiment)
According to the present invention, even when receiving a wireless packet in which a part for transmitting data from a single antenna and a part for transmitting data from a plurality of antennas are received in one wireless packet, the residual phase error is compensated. It can be done accurately. According to the radio communication preamble signal proposal proposed by Jan Boer et al. In “Backwards compatibility,” IEEE 802.11-03 / 714r0, as shown in FIG. 26, first, from one transmission antenna 101a, time synchronization, frequency synchronization and AGC A short preamble sequence x01 used for transmission, a long preamble sequence x02 for channel response estimation, and a first signal field x03 including a field indicating a modulation scheme and length of a radio packet, and a second signal field used subsequently in IEEE 802.11n Send x04. The second signal field describes the number of transmission antennas to be multiplexed, the multiplexing method, and the like. Next, a long preamble sequence x05 for propagation path response estimation is sequentially transmitted from the transmission antenna 101b. After transmission of the preamble signal is thus completed, transmission data x08 and x09 are simultaneously transmitted from the plurality of transmission antennas 101a and 101b.

  The wireless communication preamble signal shown in FIG. 26 is the same as the IEEE 802.11a standard wireless communication preamble signal shown in FIG. 27 based on transmission from the transmission antenna 101a from the short preamble x01 to the first signal field x03. is there. Accordingly, the wireless reception device based on the IEEE 802.11a standard that has received the preamble signal shown in FIG. 26 can recognize the received packet as a wireless packet based on the IEEE 802.11a standard. Therefore, the preamble signal shown in FIG. 26 enables IEEE 802.11n that transmits different data from a plurality of antennas simultaneously on one radio to coexist with the IEEE 802.11a standard that transmits data from a single antenna. To do.

  In the wireless packet of IEEE 802.11a shown in FIG. 27, pilot subcarriers are inserted after the SIGNAL field, and it is possible to compensate for the residual phase error based on this. On the other hand, when the present invention is applied to the radio packet shown in FIG. 26, a configuration is considered in which pilot subcarriers are inserted in the SIGNAL field and SIGNAL2 field, and thereafter pilot subcarriers are also arranged in the DATA portion of X08 to X09. In the subsequent X08 to X09 and later, a configuration in which the pilot subcarriers described in the first to seventh embodiments of the present invention are arranged can be considered. In the eighth embodiment, a case where pilot subcarriers using the first embodiment are transmitted will be described.

  Therefore, specific control when the wireless packet shown in FIG. 26 is received will be described with reference to FIG. FIG. 28 shows a receiving apparatus when receiving the wireless packet shown in FIG. 28 differs from FIG. 5 in that the output of the decoder 207 is input to the SIGNAL analysis unit 208, and the residual phase error detection unit 204 is controlled based on the result of the SIGNAL analysis unit 208.

  The receiver that has received the short preamble x01 detects the beginning of the long preamble sequence x02 using AGC and time synchronization means (not shown) and detects the FFT window. At the same time, the frequency offset is estimated and compensated. The receiver that has received the long preamble sequence x02 measures the propagation path responses of all subcarriers using known pilot subcarriers. In particular, the propagation path response of the pilot subcarrier is passed to the residual phase error detector 204. Since the above processing can be realized by a known technique, description thereof is omitted.

  Next, the wireless receiver receives the SIGNAL field x03. The SIGNAL field is subjected to FFT in FFT 202a and FFT 2b. The FFT output is input to the interference cancellation circuit, but since the SIGNAL field is transmitted from a single antenna, it is not necessary to perform interference cancellation. Therefore, the process performed by the interference cancellation circuit is a process of multiplying the unit matrix, or a process of improving the signal power to noise power ratio by weighted synthesis of the outputs of the FFTs 202a and 202b. Next, the output of the interference cancellation circuit is input to the residual phase error detector 204.

  FIG. 29 is a conceptual diagram of processing performed by the residual phase error detector according to the eighth embodiment. Now, assume that the propagation path response when receiving the long preamble transmitted from the transmitting antenna 101a and received by the receiving antenna 201a is Haa shown in FIG. When the pilot subcarrier is transmitted by BPSK, the values that can be taken by the pilot subcarrier received by the data part are the points (1) or (-1) shown in FIG. Detect phase error.

  Next, when the reception point of the pilot subcarrier of the SIGNAL part is the “next symbol at the time of single antenna transmission” shown in FIG. 29, the residual phase error detector indicates the point (1) and “at the time of single antenna transmission. The phase difference θ1 from the point of “next symbol” is measured as a residual phase error, and this is corrected by the phase compensator. Similarly, when the SIGNAL 2 part is received, it is possible to detect the residual phase error.

  Note that the demodulator 207 that has demodulated the SIGNAL2 unit passes the decoding result to the SIGNAL analysis unit 208. The SIGNAL analysis unit 208 analyzes the second signal field, analyzes the number of multiplexed transmission antennas and the multiplexing method, and passes them to the residual phase error detection unit 204.

  Next, the receiver receives the long preamble from the transmission antenna 101b and measures the propagation path response from the transmission antenna 101b. Next, a case where the DATA parts X08 to X09 are received will be described. Here, the case where the DATA section is multiplexed with signals from the two transmission antennas 101a and 101b and the multiplexed pilot subcarriers have the polarities of equations (4) and (5) will be described. As described above, the number of multiplexed transmission antennas can be recognized from the signal from the SIGNAL analysis unit 208.

  Here, attention is paid to pilot subcarriers having polarities of Sa (1) and Sb (1) described in the leftmost of the equations (4) and (5) among the four pilot subcarriers. The polarities of pilot subcarriers transmitted at this frequency are Sa (1) = 1 and Sb (1) = 1. Therefore, when the propagation path response from the transmission antenna 101a to the reception antenna 201a is Haa and the propagation path response from the transmission antenna 101b to the reception antenna 201a is Hba, the propagation path response of the pilot subcarrier received by the DATA unit is The value is Haa + Hba shown in FIG. Therefore, the residual phase error detector obtains a reference point using the synthesized channel response value Haa + Hba based on the measured channel response values Haa and Hba and the multiplexing information from the SIGNAL analysis unit 208, and this A deviation from the reference point is detected.

  Specifically, since the pilot subcarriers are transmitted as BPSK signals modulated by PN sequences, the points (1, 1) and (-1, -1) shown in FIG. 29 are received. That is, when a single antenna is received, the residual phase error can be detected with reference to points (1) and (-1) in FIG. 29, but the transmission is switched to transmission from a plurality of antennas. In this case, it is necessary to detect the residual phase error with reference to the points (1, 1) and (-1, -1).

  Thus, since it is necessary to switch the operation of the residual phase error detector in the case of single antenna transmission and in the case of multiple antenna transmission, in the eighth embodiment, the second signal field X04 (SIGNAL2 shown in FIG. ) Is analyzed. In the second signal field, the number of signals multiplexed on the transmission side or the multiplexing method is described. By analyzing this, the reference point of the propagation path response value can be obtained, and a single signal field can be obtained. It is possible to switch between a reference point when receiving a transmission signal from an antenna and a reference point when receiving a signal transmitted from a plurality of antennas. Therefore, even when receiving a signal from a single antenna or receiving signals from multiple antennas, it is possible to switch the reference signal point appropriately in either case. Appropriate residual phase error can be detected and guaranteed.

(Ninth embodiment)
In the embodiments described so far, the OFDM signal transmitting apparatus that transmits a different signal for each transmission antenna has been described. However, the present invention is also applicable to an OFDM signal transmitting apparatus that uses a transmission method that transmits a different signal for each of a plurality of transmission beams. Is possible.

  FIG. 31 shows an OFDM transmission apparatus that transmits different signals for each of a plurality of transmission beams according to the ninth embodiment of the present invention. In FIG. 31, an encoder 102, a serial / parallel converter 103, modulators 104a and 104b, serial / parallel converters 105a and 105b, and a pilot subcarrier insertion unit 106 are the same as those in the first to eighth embodiments. Therefore, the description is omitted.

  According to the ninth embodiment, the subcarrier in which the pilot subcarrier is inserted between the data subcarriers by the pilot subcarrier insertion unit 106 is input to the beamformer 108. The beamformer 108 weights and synthesizes the output from the serial / parallel converter 105a and the output from the serial / parallel converter 105b, and outputs them to the IFFT units 107a and 107b. The output after IFFT is output from the transmission antennas 101a and 101b.

  The beamformer 108 is a device that performs processing for forming a plurality of transmission beams, and a known technique can be used as a method for realizing the processing. The transmission beam may be formed independently for each subcarrier, or the same beam may be formed for all subcarriers. In FIG. 31, the beam former 108 is inserted before the IFFT units 117a and 107b, but may be inserted after the IFFT units 117a and 107b.

  As described above, even when the OFDM signal is generated for each transmission beam instead of generating the OFDM signal for each antenna as in the first to eighth embodiments, the first to eighth polarities of the pilot subcarriers are used. The same setting as in the embodiment can be performed.

  In the present embodiment, the pilot subcarrier polarity pattern is described as being fixed in a radio packet for the sake of simplicity. However, even if it is changed in a radio packet, that is, for each OFDM symbol, it is obtained by the present invention. It does not impair the effect. As shown in FIG. 12, the radio transmitter has a plurality of polarity patterns in the ROM, and a counter for counting the number of OFDM symbols is provided instead of the radio packet counter, and each antenna is selected from the plurality of polarity patterns according to the counter. The polarity pattern of the pilot subcarriers may be changed by selecting one of them.

(Tenth embodiment)
Next, a tenth embodiment of the present invention will be described. This embodiment is different from the first to ninth embodiments in that the polarity of the pilot subcarrier changes for each OFDM symbol, and the frequency of the pilot subcarrier, that is, the position of the pilot subcarrier changes periodically. It is. As described above, when the positions of the pilot subcarriers are periodically changed, it is possible to estimate the propagation paths of all the subcarriers.

  32 to 35 show the pilot subcarrier arrangement of the present embodiment when the number of transmission antennas is four. That is, FIG. 32 shows the pilot subcarrier arrangement of the OFDM signal transmitted from the first transmitting antenna, and similarly, FIGS. 33, 34, and 35 are OFDM transmitted from the second, third, and fourth transmitting antennas, respectively. The pilot subcarrier arrangement of the signal is shown. 32 to 35, the horizontal axis represents the subcarrier number (-26 to 26 in this example), that is, the frequency (position) of the subcarrier, and the vertical axis represents the OFDM symbol number (DATA1 to DATA12 in this example). In FIG. 32 to FIG. 35, pilot subcarriers are arranged in cells other than blanks, and the symbols written in the cells indicate the polarity of the pilot subcarriers. 32 to 35, the PN sequence is not described, and the description about the data subcarrier is also omitted.

  In this embodiment, pilot subcarriers are orthogonal to each other in a plurality of unit times between transmission antennas. In the example of FIGS. 32 to 35, the pilot subcarriers are orthogonal to each other among the four transmission antennas in the 4 OFDM symbol period, with one OFDM symbol time as a unit time. Further, the frequency (position) of the pilot subcarrier changes in a period that is an integral multiple of a plurality of unit times, for example, 4 OFDM symbol periods.

  The polarities of the pilot subcarriers shown in FIGS. 32 to 35 can be described as follows using a description method similar to Equation (9).

Where S _{Ppos (i, t), k, t} indicates that the P _pos (i, t) th subcarrier is used as a pilot subcarrier, k is a transmission antenna number, and t is an OFDM symbol. Indicates the number. In Expression (27), the right side of Expression (9) is multiplied by polarity data P _rot (i, t) expressed by the following Expression (28).

Here, P _pos (i, t) is a conversion function for converting the subcarrier number from the pilot subcarrier number i and the OFDM symbol number t, and can be described specifically as follows, for example.

FIG. 36 shows the value of the polarity data P _rot (i, t) obtained by substituting the number k of the transmitting antenna and the number t of the OFDM symbol in Equation (28). As can be seen from FIG. 36, Equation (28) has periodicity with respect to the number t of the OFDM symbol, and in this embodiment, the cycle is 4 OFDM symbol intervals. Specifically, the value of the polarity data P _rot (i, t) is the same when t = 1 and when t = 5.

  Further, as can be seen from Equation (29), the position (frequency) of the pilot subcarrier changes according to the period of Equation (28). For example, in the subcarriers transmitted from the first to fourth transmission antennas, first, subcarrier numbers −20, −7, +7 are included in the first 4 OFDM symbol sections (DATA1 to DATA4 sections) where t = 1 to 4. , +20, pilot subcarriers are arranged.

Here, for example, focusing on the pilot subcarrier arranged at subcarrier number −20, the polarity of the pilot subcarrier transmitted from the first transmission antenna is “1, 1, 1, 1”, and transmission is performed from the second transmission antenna. The pilot subcarriers to be transmitted have a polarity of “1, j, −1, −j”, the pilot subcarriers transmitted from the third transmission antenna have a polarity of “1, −1, 1, −1”, and the fourth transmission antenna. The pilot subcarriers transmitted from 1 are “1, -j, −1, j”, and the pilot subcarriers transmitted from the first to fourth transmission antennas are orthogonal to each other within 4 OFDM symbol intervals. The same applies to the pilot subcarriers arranged at the other subcarrier numbers -7, +7, and +20, and the first to fourth transmission antennas are orthogonal to each other within 4 OFDM symbol intervals.

  Next, pilot subcarriers of subcarrier numbers -17, -4, +10, and +23 are transmitted in the next 4 OFDM symbol periods (DATA5 to DATA8 periods) in which t = 5 to 8, and at this time, The polarities of the pilot subcarriers transmitted from the first to fourth transmission antennas are the same as those of the first 4 OFDM symbol periods of t = 1 to 4, and are orthogonal to each other.

  Further, as shown in FIGS. 32 to 35 and Expression (27), the pilot subcarriers are orthogonal on the frequency axis. For example, paying attention to the pilot subcarriers shown in FIG. 33 transmitted from the second transmission antenna, in the first 4 OFDM symbol intervals (DATA1 to DATA4 intervals) where t = 1 to 4, the subcarrier number is set to −20. The polarity of pilot subcarriers arranged is “1, j, −1, −j”, and the polarity of pilot subcarriers arranged at the position of subcarrier number −7 is “−j, 1, j, −1”, The polarity of the pilot subcarrier arranged at the position of the subcarrier number +7 is “−1, −j, 1, j”, and the polarity of the pilot subcarrier arranged at the position of the subcarrier number +20 is “−j, 1, j, -1 ", which are found to be orthogonal to each other.

It should be noted that the period of the formula (28) and the pilot subcarrier position change period shown by the formula (29) are not necessarily the same, and the period of the formula (29) is an integral multiple of the period of the formula (28). good. Moreover, although Formula (29) is produced | generated from the Fourier coefficient, what is necessary is just a series orthogonal about the time-axis t. FIG. 37 shows another example of the polarity data P _pos (k) when a real number is used.

  Next, pilot subcarrier insertion section 106 according to the present embodiment will be described using FIG. The overall configuration of the OFDM signal transmission apparatus including pilot subcarrier insertion section 106 is the same as that in FIG. In pilot subcarrier insertion section 106 shown in FIG. 38, transmission data from serial / parallel converters 105a and 105b in FIG. 3 are input to subcarrier allocation apparatuses 126a and 126b, respectively.

On the other hand, the first pilot generated by calculating the product of the PN sequence from the PN sequence generator 110 and the polarity data Sa (j) of the first pilot subcarrier stored in the ROM 121a by the multiplication units 111a to 111d. The subcarrier is input to the subcarrier arrangement apparatus 126a. Similarly, the second unit generated by calculating the product of the PN sequence from the PN sequence generator 110 and the polarity data Sb (j) of the second pilot subcarrier stored in the ROM 121b by the multiplication units 112a to 112d. The pilot subcarrier is input to the subcarrier arrangement apparatus 126b. Here, in the ROMs 121a and 121b, P _rot (i, t) represented by the equations (27) to (29) is stored as the polarity data Sa (j) and Sb (j), respectively.

  The process of changing the polarity of the pilot subcarrier or changing the position of the pilot subcarrier for each OFDM symbol is performed as follows. First, when transmitting DATA1, the counter 131 recognizes that it is time to transmit DATA1 by counting the clock signal 130 of the OFDM symbol period, and sends it to the subcarrier arrangement controller 132 and the pilot pattern controller 133 with respect to DATA1. Command to control subcarrier arrangement and pilot pattern is issued. On the other hand, when transmitting DATA2, similarly, the counter 131 recognizes that it is time to transmit DATA2 by the clock signal 130, and sends the subcarrier arrangement for DATA2 to the subcarrier arrangement controller 132 and the pilot pattern controller 133. A command to control the pilot pattern is issued. Specifically, the pilot pattern controller 133 reads the values according to the equations (27) and (28) from the ROMs 121a and 121b, and the subcarrier arrangement controller 132 inserts the pilot subcarrier at the position according to the equation (29). To do. In this way, the pilot subcarriers as shown in FIGS. 32 to 35 are configured.

Next, an OFDM signal receiving apparatus having a function of detecting a residual phase error by receiving pilot subcarriers represented by Expression (27) will be described using FIG.
An OFDM signal received by the receiving antenna 201a is input to the FFT unit 202a through a radio receiving unit (not shown), and is divided into signals of each subcarrier by being subjected to Fourier transform. Similarly, the OFDM signal received by the receiving antenna 201b is also divided into subcarrier signals by being subjected to Fourier transform by the FFT unit 202b.

  Of the subcarriers output from the FFT units 202a and 202b, the data subcarrier is input to the interference cancellation circuit 203, and the pilot subcarrier is input to the residual phase error detector 204 and the propagation path fluctuation detector 210. The residual phase difference detected by the residual phase error detector 204 is compensated by the phase compensators 205a and 205b. On the other hand, the propagation path fluctuation detected by the propagation path fluctuation detector 210 is compensated by the propagation path fluctuation compensators 211a and 211b. Since elements other than the residual phase error detector 204, the propagation path fluctuation detector 210, and the propagation path fluctuation compensators 211a and 211b are the same as those of the OFDM receiver in FIG.

  In this embodiment, the phase compensator 204 and the propagation path compensators 211a and 211b are individually provided. However, since both can be regarded as compensating for the propagation path response, the phase compensator 204 and the propagation path It is also possible to implement the compensators 211a and 211b with a single compensator. Further, in the present embodiment, the phase compensator 204 and the propagation path compensators 211a and 211b are arranged at the subsequent stage of the interference cancellation circuit 203, but may be arranged at the preceding stage.

  The residual phase error detector 204 detects the residual phase error using the pilot subcarrier. The pilot subcarrier polarity data in each OFDM symbol and the PN sequence multiplied by the polarity data are known in the OFDM signal receiving apparatus. Therefore, the residual phase error detector 204 corresponds to the detection principle shown in FIG. 6 explained in the first embodiment, the detection principle shown in FIG. 18 explained in the fourth embodiment, and FIG. 23 explained in the sixth embodiment. The residual phase error can be detected using either the detection principle shown in FIG. 29 or the detection principle shown in FIG. 29 described in the eighth embodiment.

  Next, propagation path estimation using pilot subcarriers will be described. Now, the -20th pilot subcarrier will be described as an example. The propagation path response value from the transmission antenna 101a to the reception antenna 201a is Haa, the propagation path response value from the transmission antenna 101b to the reception antenna 201a is Hba, and the propagation path response value from the transmission antenna 101c to the reception antenna 201a (not shown). Is a propagation path response value from a transmitting antenna 101d to a receiving antenna 201a (not shown) as Hda.

  In this case, the signals received in the sections DATA1, DATA2, DATA3, and DATA4 can be written as follows if the noise component is omitted.

  Here, the signal before the residual phase error is removed is described, and exp (jnθ) (n = 1, 2, 3) represents the residual phase error component. Next, when it is desired to know the value of the propagation path estimated value Haa, the estimated value of Haa is obtained by performing the following processing.

  Here, since it can be assumed that the phase difference between several symbols indicated by the residual phase error component exp (jnθ) (n = 1, 2, 3) is sufficiently close to 1, the estimated value of Haa can be calculated using Equation (34). It becomes possible to ask. This is because the pilot subcarriers are transmitted every period (four OFDM periods in the present embodiment) in which the pilot subcarriers are orthogonal as shown in FIGS.

  Similarly, the estimated value of Hba can be obtained by the following equation.

  In general, it is possible to obtain a channel response value corresponding to each transmission antenna by performing calculation using the complex conjugate of the series shown in FIGS. 32 to 35 as a coefficient. For example, as described in the eighth embodiment, when the wireless packet configuration as shown in FIG. 26 is used, it is possible to estimate the propagation path response values of all subcarriers at the long preamble portion at the head of the packet. Become. However, since the propagation path response may vary within the packet due to surrounding fluctuations, especially when the length of the wireless packet is longer than the propagation path fluctuation, the propagation path estimation value estimated by the long preamble portion Further, there is a possibility that the propagation path estimation value estimated in the DATA1 to DATA4 sections is different. Even in such a case, by making the pilot subcarriers orthogonal to each other within a plurality of unit times between a plurality of transmission antennas, and changing the frequency (position) of the pilot subcarriers at a cycle that is an integral multiple of the unit time. The fluctuation can be compensated in the propagation path fluctuation compensators 211a and 211b.

  In the above description, the propagation path fluctuation value is estimated using the signal before the residual phase error compensation, but the propagation path fluctuation estimation can be performed using the signal after the residual phase compensation. In this case, since the residual phase error component in Expressions (30) to (33) can be ignored, the propagation path fluctuation value can be obtained with high accuracy.

  FIG. 40 shows the configuration of an OFDM receiver that performs propagation path fluctuation estimation using a signal after residual phase compensation. In FIG. 40, the outputs of the FFT units 202a and 202b are transferred to the residual phase error detector 204 and the phase compensators 205a and 205b, and the propagation path fluctuation detection is performed using the signals subjected to the phase compensation by the phase compensators 205a and 205b. The detector 210 detects the fluctuation of the propagation path response.

  Thus, in this embodiment, the position of the pilot subcarrier is changed for each orthogonal section of the pilot subcarrier. Here, the orthogonal section is a section in which the pilot subcarriers are orthogonal to each other between the transmission antennas, and is a 4 OFDM symbol section in the example shown in FIGS. Therefore, it is possible to obtain a propagation path estimation value from each transmitting antenna by performing processing such as Expression (34) using the received signal in the orthogonal section. In addition, after transmitting pilot subcarriers in one orthogonal section, it is possible to estimate channel estimation values corresponding to all subcarriers by using another subcarrier as a pilot subcarrier.

  In the above description, since there are four transmission antennas, a series (for example, FIGS. 32 to 35) in which the orthogonal period of pilot subcarriers is 4 OFDM sections is used. However, when there are three or two transmission antennas, It is also possible to use a sequence with a short orthogonal period. Also, in this embodiment, orthogonalization is realized by changing the polarity of the pilot subcarrier. However, orthogonalization can be realized by changing the type of PN sequence for each transmission antenna to perform channel estimation. Is possible. That is, as shown in the fourth embodiment, a PN sequence is provided for each transmission antenna, and pilot subcarriers are orthogonalized on the time axis to perform propagation path estimation as shown in the tenth embodiment. It becomes possible.

  FIG. 41 shows the configuration of pilot subcarrier insertion section 106 when the PN sequence is changed and pilot subcarriers are orthogonalized on the time axis. The difference from the pilot subcarrier insertion unit shown in FIG. 38 is that the pilot subcarrier polarity is changed for each OFDM symbol, that is, for each DATA in FIG. 38, whereas in FIG. The generator 11a, 110b is provided.

  As described above, according to the tenth embodiment, pilot subcarriers are made orthogonal to each other within a plurality of unit times between a plurality of transmission antennas, and the frequency (position) of the pilot subcarriers is a period that is an integral multiple of the unit time. Further, by making the pilot subcarriers orthogonal on the frequency axis, the directivity patterns formed by the transmitting antennas during pilot subcarrier transmission can be varied.

  Therefore, as in the first to ninth embodiments, it is possible to reduce the dead zone in which the reception power of all pilot subcarriers decreases simultaneously, to increase the area where high-quality reception is possible, and to combine 3 Generation of secondary distortion can be prevented. Further, it is possible to easily obtain a propagation path estimated value corresponding to each transmission antenna on the receiving side.

  In addition, in this embodiment, since the subcarriers to which the pilot signal is transmitted change with time, the subcarriers to which the pilot signal is transmitted are dropped due to fading, making it difficult to measure the residual phase error. Even in the case of a failure, a pilot signal is transmitted from another subcarrier after a unit time. Therefore, there is also an effect that the probability that the pilot signal can be accurately received is increased.

Equation Chapter 1 Section 1 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.

1 is a block diagram of an OFDM communication system according to an embodiment of the present invention. The figure which shows the subcarrier arrangement | positioning of the OFDM signal transmitted from two transmission antennas according to the 1st Embodiment of this invention. Block diagram of the OFDM signal transmission apparatus in FIG. Block diagram of pilot subcarrier insertion unit according to the first embodiment of the present invention Block diagram of the OFDM signal receiver in FIG. The figure explaining the residual phase error detection principle corresponding to the 1st Embodiment of this invention The figure which shows typically the transmission directivity image and transmission synthetic beam pattern of each transmission antenna which transmits the pilot subcarrier of the same polarity pattern from two transmission antennas The figure which shows typically the transmission directivity image and transmission synthetic | combination beam pattern of each transmission antenna which transmits the pilot subcarrier of a different polarity pattern from two transmission antennas according to 1st Embodiment. The figure which shows the average normalized reception level of the pilot subcarrier in a receiver at the time of transmitting a pilot subcarrier using embodiment of this invention The figure which shows the received power when transmitting the 1st and 2nd pilot subcarrier using a certain polarity data The figure which shows the polar pattern of the pilot subcarrier transmitted from each transmitting antenna when extending the 1st Embodiment of this invention to the OFDM apparatus which has four transmitting antennas Block diagram of pilot subcarrier insertion unit according to second embodiment of the present invention The figure which shows the various polarity patterns of the pilot subcarrier transmitted from each transmission antenna in the 2nd Embodiment of this invention Block diagram of pilot subcarrier insertion section according to third embodiment of the present invention The figure which shows an example of the structure of the radio | wireless packet of an OFDM signal Block diagram of pilot subcarrier insertion unit according to the fourth embodiment of the present invention The figure which shows the subcarrier arrangement | positioning of the OFDM signal transmitted from two transmission antennas according to the 4th Embodiment of this invention. The figure explaining the residual phase error detection principle corresponding to the 4th Embodiment of this invention Block diagram of pilot subcarrier insertion unit according to the fifth embodiment of the present invention The figure which shows the subcarrier arrangement | positioning of the OFDM signal transmitted from two transmission antennas according to the 5th Embodiment of this invention. Block diagram of pilot subcarrier insertion unit according to sixth embodiment of the present invention The figure which shows the subcarrier arrangement | positioning of the OFDM signal transmitted from two transmission antennas according to the 6th Embodiment of this invention. The figure explaining the residual phase error detection principle corresponding to the 6th Embodiment of this invention Block diagram of pilot subcarrier insertion unit according to seventh embodiment of the present invention The figure which shows the subcarrier arrangement | positioning of the OFDM signal transmitted from two transmission antennas according to the 7th Embodiment of this invention. The figure which shows an example of the preamble signal for radio | wireless communication The figure which shows the preamble signal for the wireless communication of IEEE 802.11a standard FIG. 26 is a block diagram of an OFDM signal receiving apparatus when receiving the wireless packet shown in FIG. The figure explaining the process performed with the residual phase error detector in the 8th Embodiment of this invention. The figure which shows the subcarrier arrangement | positioning of the OFDM signal transmitted from two transmission antennas based on a prior art The block diagram of the OFDM signal transmitter according to the ninth embodiment of the present invention The figure which shows the pilot subcarrier arrangement | positioning of the OFDM signal transmitted from a 1st transmitting antenna according to the 10th Embodiment of this invention. The figure which shows the pilot subcarrier arrangement | positioning of the OFDM signal transmitted from a 2nd transmission antenna according to the 10th Embodiment of this invention. The figure which shows the pilot subcarrier arrangement | positioning of the OFDM signal transmitted from a 3rd transmission antenna according to the 10th Embodiment of this invention. The figure which shows the pilot subcarrier arrangement | positioning of the OFDM signal transmitted from a 4th transmission antenna according to the 10th Embodiment of this invention. The figure which shows the example of the polarity data of the pilot subcarrier in the 10th Embodiment of this invention The figure which shows the other example of the polarity data of the pilot subcarrier in the 10th Embodiment of this invention Block diagram of pilot subcarrier insertion unit according to the tenth embodiment of the present invention Block diagram of an OFDM signal receiving apparatus according to a tenth embodiment of the present invention Block diagram of a modification of the OFDM signal receiving device according to the tenth embodiment of the present invention Block diagram of a modification of pilot subcarrier insertion unit according to the tenth embodiment of the present invention

Explanation of symbols

100: OFDM signal transmitting apparatus;
101a, 101b ... transmitting antennas;
102 ... Encoder;
103 ... serial-parallel converter;
104a, 104b ... modulators;
105a, 105b ... serial-parallel converter;
106 ... pilot subcarrier insertion part;
107a, 107b ... IFFT unit;
108 ... beam former;
126a, 126b ... Subcarrier placement device;
131 ... Counter;
132 ... subcarrier arrangement controller;
133 ... Pilot pattern controller;
201a, 201b ... receiving antennas;
202a, 202b ... FFT unit;
203 ... interference canceling circuit;
204 ... residual phase error detector;
205a, 205b ... phase compensation units;
206 ... parallel-serial converter;
207 ... Decoder;
210 ... propagation path fluctuation detector;
211a, 211b ... propagation path fluctuation compensator;

Claims (4)

In an OFDM signal transmission method for transmitting an OFDM (Orthogonal Frequency Division Multiplexing) signal having a plurality of subcarriers orthogonal to each other using a plurality of transmission antennas,
Generating data subcarriers for transmission of data signals;
(A) A first vector having as an element the polarity of each pilot subcarrier transmitted from a first antenna over a plurality of OFDM symbols, and a second antenna transmitted over a plurality of OFDM symbols. A second vector having each of the polarities of the pilot subcarriers as an element, and (b) the polarity of each of the pilot subcarriers of the first frequency transmitted from the plurality of transmitting antennas. The third vector having elements and the fourth vector having elements of the polarities of the pilot subcarriers of the second frequency transmitted from the plurality of transmission antennas are arranged to be orthogonal to each other, and (c ) changes the frequency by an integer multiple of the period of unit time, and generates a pilot subcarrier for the transmission of the pilot signal scan And-up,
Generating the OFDM signal from the data subcarriers and pilot subcarriers.   The pilot subcarrier comprises a product of a PN (pseudorandom noise) sequence orthogonal to each other in a plurality of unit times between the plurality of transmission antennas and data indicating the polarity of the pilot subcarrier. The described OFDM signal transmission method. In an OFDM signal transmitting apparatus for transmitting an OFDM (Orthogonal Frequency Division Multiplexing) signal having a plurality of subcarriers orthogonal to each other using a plurality of transmission antennas,
Means for generating data subcarriers for transmission of data signals;
(A) A first vector having as an element the polarity of each pilot subcarrier transmitted from the first antenna over a plurality of OFDM symbols, and a second antenna transmitted over a plurality of OFDM symbols. A second vector having each of the polarities of the pilot subcarriers as an element, and (b) the polarity of each of the pilot subcarriers of the first frequency transmitted from the plurality of transmitting antennas. The third vector having elements and the fourth vector having elements of the polarities of the pilot subcarriers of the second frequency transmitted from the plurality of transmission antennas are arranged to be orthogonal to each other, and (c ) changes the frequency by an integer multiple of the period of unit time, and generates a pilot subcarrier for the transmission of the pilot signal hands And,
Means for generating the OFDM signal from the data subcarriers and pilot subcarriers. The pilot subcarrier comprises a product of a PN (pseudorandom noise) sequence orthogonal to each other in a plurality of unit times between the plurality of transmission antennas and data indicating the polarity of the pilot subcarrier. The OFDM signal transmitting apparatus according to the description.

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