JP2007282120A - Ofdm signal receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain excellent reception characteristics by removing interfering signal components included in reception signals when there are interfering signals asynchronous with a desired signal. <P>SOLUTION: The OFDM signal receiving device includes: a transmission line estimating means of calculating transfer factors of the desired signal and interfering signals by using preamble signals of the desired signal and interfering signals included in reception signals received by two receiving antennas; an interference extracting means of extracting the interfering signal components by suppressing a desired signal component included in the reception signals based upon the transfer factors of the desired signal and interfering signals obtained by the transmission line estimating means; and an interference compensating means of outputting a desired signal component wherein interfering signal components included in the reception signals are suppressed by using the interfering signal components by controlling the interfering signal components extracted by the interference extracting means based upon the transfer factors of the interfering signals obtained by the transmission line estimating means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an OFDM signal receiving apparatus having an interference cancellation function for a received OFDM (Orthogonal Frequency Division Multiplexing) signal.

  As one of the techniques using an interference canceller, a MIMO (Multiple Input Multiple Output) channel is configured using a plurality of transmitting antennas and a plurality of receiving antennas, and each receiving antenna is configured using a transmission path estimation circuit and an interference canceller on the receiving side. There is a technique of increasing the frequency utilization efficiency by increasing the number of channels by the number of transmission antennas by separating and restoring the transmission signals from the transmission antennas from the received signals.

  Here, a configuration when applied to OFDM signal transmission in a 2 × 2 MIMO transmission system including two transmitting antennas and two receiving antennas will be described with reference to FIG.

In FIG. 18, an OFDM signal transmitting apparatus 100 inputs two systems of input data sequences S1 and S2 to mapping circuits 101-1 and 101-2, maps them to a complex signal of a designated modulation scheme, and then inserts a preamble. The circuit 102-1 and 102-2 generate transmission signal sequences D ₁ [i] and D ₂ [i] with a predetermined preamble signal added to the head of the transmission signal, and a fast inverse Fourier transform circuit (IFFT) 103-1. , 103-2 divides it into subcarrier groups to generate an OFDM signal for multi-carrier transmission, D / A converters 104-1 and 104-2 convert the OFDM signal to an analog signal, and a transmitter (Tx) 105-1 and 105-2 are converted to a predetermined transmission frequency and transmitted from two transmission antennas 106-1 and 106-2.

The OFDM signal receiving apparatus 110 receives signals received by the two receiving antennas 111-1 and 111-2 as receivers (Rx) 112-1 and 112-2 and A / D converters 113-1 and 113-2. Is converted to a digital signal, and the received signal sequences x ₁ [i], x ₂ [i] of each subcarrier are demodulated by fast Fourier transform circuits (FFT) 114-1, 114-2, and then a transmission path estimation circuit 115, the transfer coefficient matrix H [i] of each subcarrier component (h ₁₁ [i], h ₁₂ [i], h ₂₁ [i], h ₂₂ [i]) of the four transmission path paths is estimated, The interference canceller 116 multiplies the inverse matrix H [i] ⁻¹ by the received signal sequences x ₁ [i] and x ₂ [i] output from the FFTs 114-1 and 114-2 to reduce mutual interference between channels. Finally, the output of the interference canceller 116 is converted into a bit string by the identification circuits 117-1 and 117-2 and output. Output as data series Y1, Y2.

  In this configuration example, descriptions of error correction processing performed to improve transmission quality in OFDM signal transmission and guard intervals added to eliminate the influence of delayed waves due to multipath are omitted.

The reception signals of the reception antennas 111-1 and 111-2 include a mixture of the transmission signals radiated from the two transmission antennas 106-1 and 106-2. Hereinafter, an operation principle for separating and restoring each transmission signal sequence from the received signal will be described. FIG. 19 shows two transmission signal sequences of the i-th subcarrier in burst transmission. This corresponds to the transmission signal sequences D ₁ [i] and D ₂ [i] input to the IFFTs 103-1 and 103-2 of the OFDM signal transmission apparatus 100. The preamble signal for estimating the leading transfer coefficient is configured using known patterns P ₁ [i] and P ₂ [i]. Preamble signal (P ₁ [i], 0) transmitted from the transmission antenna 106-1, preamble signal (0, P ₂ [i]) transmitted from the transmission antenna 106-2, and reception preamble signals corresponding thereto _{^{(P r 11 [i],}} P r 12 [i], P r 21 [i], P r 22 [i]) the relationship between the transfer coefficient _{(h 11 [i], h} 12 [i], h ₂₁ [i], h ₂₂ [i]) is used as a component and expressed as follows using a 2-by-2 transfer coefficient matrix H [i].

Accordingly, the transfer coefficient inverse matrix H [i] ⁻¹ can be estimated as follows.

On the other hand, for the data signal sequence, the i-th transmission subcarriers D ₁ [i] (n) and D ₂ [i] (n) at time n and the FFTs 114-1 and 114-2 of the OFDM signal receiving apparatus 110 are used. The relationship between the output reception subcarriers x ₁ [i] (n) and x ₂ [i] (n) is expressed as follows.

The thermal noise component included in the received signal is omitted. By multiplying the reception subcarrier x ₁ [i] (n), x ₂ [i] (n) by the transfer coefficient inverse matrix H [i] ⁻¹ obtained by the equation (3), the following is obtained. Thus, transmission subcarriers D ₁ [i] (n) and D ₂ [i] (n) are obtained.

As described above, in the conventional MIMO transmission system, transmission is performed from two transmission antennas on the same frequency channel at the same time, and the transmission path estimation circuit and the interference canceller are used from the reception signals of the two reception antennas on the reception side. The transmission signal from each transmission antenna can be separated and restored.
JP 2002-374224 A

  In a conventional MIMO transmission system, a plurality of transmission antennas are installed in the same apparatus or close to each other, and transmission signals can be synchronized. For this reason, it is possible to transmit a preamble signal from each transmitting antenna at the same time, and the receiving side can receive the preamble signal at the same time and perform transmission path estimation without causing mutual interference between channels. As a result, the interference canceller was able to separate the transmission signal.

  However, in the case of inter-cell interference shown in FIG. 20, unlike this, the desired station and the interfering station do not always transmit a preamble signal at the same time in synchronization with each other. That is, when there is an asynchronous interfering station with respect to the desired station, the receiving station receives an unknown signal from the interfering station while receiving the preamble signal of the desired station. Estimation cannot be performed normally. For this reason, the interference cancellation technique used in the conventional MIMO transmission system cannot be applied in an environment where a desired station and an interference station exist.

  An object of the present invention is to provide an OFDM signal receiving apparatus capable of removing an interference signal component contained in a received signal and obtaining good reception characteristics when there is an asynchronous interference signal with respect to a desired signal. To do.

  The first invention receives a desired signal transmitted as an OFDM signal from a desired station and an interference signal transmitted as an OFDM signal from an interference station asynchronous to the desired station by two receiving antennas. In the OFDM signal receiving apparatus that demodulates the received signal of each subcarrier by performing Fourier transform on the received signal of the antenna, each preamble signal of the desired signal and the interference signal included in the received signals received by the two receiving antennas is used. And a transmission path estimation means for calculating each transmission coefficient of the desired signal and the interference signal, and a desired signal component included in the received signal based on each transmission coefficient of the desired signal and the interference signal obtained by the transmission path estimation means. Interference extraction means for extracting interference signal components by suppressing the interference and interference extracted by the interference extraction means based on the transmission coefficient of the interference signal obtained by the transmission path estimation means No. controls the components, and a interference compensation unit for outputting a desired signal component suppress interference signal component included in the received signal using the interference signal component.

  Here, a synthesizing unit that performs in-phase synthesis of the desired signal component output from the interference compensation unit based on the transmission coefficient of the desired signal obtained by the transmission path estimation unit may be provided.

  The second invention provides a desired signal transmitted as an OFDM (Orthogonal Frequency Division Multiplexing) signal from a desired station and a plurality of interferences transmitted as OFDM signals from a plurality of J interfering stations asynchronous to the desired station. In an OFDM signal receiving apparatus that receives signals with a plurality of M (M ≧ J + 1) receiving antennas and demodulates the received signals of each subcarrier by performing a Fourier transform on the received signals of each receiving antenna. The transmission path estimation means for calculating the transmission coefficients of the desired signal and the plurality of interference signals using the desired signal and the preamble signals of the plurality of interference signals included in the received signal obtained by the transmission path estimation means Based on the transfer coefficients of the desired signal and the plurality of interference signals, the desired signal component contained in the received signal is suppressed to extract the corresponding plurality of interference signal components. Based on the transmission coefficients of the plurality of interference signals obtained by the interference extraction means and the transmission path estimation means, the plurality of interference signal components extracted by the interference extraction means are controlled, and the interference signal components are used in the received signal. In-phase synthesis of multiple desired signal components output from the interference compensation unit based on the transmission coefficient of the desired signal obtained by the transmission path estimation unit and the interference compensation unit that outputs the desired signal component in which the included interference signal component is suppressed Synthesizing means.

  In the OFDM signal receiving apparatus according to the first and second inventions, the transmission path estimation means uses the training signal sequence arranged in the transmission signal sequence of the desired signal and the interference signal, separately from the preamble signal, and the desired signal and interference signal. It is good also as a structure which calculates each transmission coefficient of a signal.

  In the first invention, a transmission path is estimated using a preamble signal in the process of receiving an OFDM signal, an interference signal is extracted by suppressing a desired signal using the calculated transmission coefficient, and a received signal is extracted using the interference signal. Interference signal components contained therein can be removed for each subcarrier. For this reason, even when the interference signal receiving interference from another cell is asynchronous with the desired signal, the interference signal suppression effect can be realized.

  Also, good reception characteristics can be obtained by combining the received signal after interference compensation in phase with the combining means connected to the subsequent stage of the interference compensation means.

  In the second invention, even when there are two or more interfering stations, at least one receiving antenna more than the number of interfering stations is used, and a transmission path is estimated and calculated using a desired signal and a preamble signal of each interfering signal. Each interference signal can be extracted by suppressing the desired signal using the transfer coefficient, and each interference signal component included in the received signal can be removed for each subcarrier using each interference signal. For this reason, even when the interference signal receiving interference from another cell is asynchronous with the desired signal, the interference signal suppression effect can be realized. Furthermore, a good reception characteristic can be obtained by performing in-phase synthesis of the received signal after interference compensation by the synthesis means connected to the subsequent stage of the interference compensation means.

  Also, in the first and second inventions, by using a training signal sequence arranged separately from the preamble signal for transmission path estimation, it is possible to perform transmission path estimation with high accuracy, and to suppress the interference signal suppression effect. Can be increased.

(First embodiment)
FIG. 1 shows a first embodiment of the OFDM signal receiving apparatus of the present invention. In the description of the prior art, the interference canceller in the 2 × 2 MIMO transmission system is shown, but in this embodiment, the desired signal from the desired station 1 and the interference from the other third interfering station 2 are transmitted to the two receiving antennas. An OFDM signal receiving apparatus that receives signals will be described.

In FIG. 1, the OFDM signal receiving apparatus receives signals received by two receiving antennas 11-1 and 11-2 as receivers (Rx) 12-1 and 12-2 and an A / D converter 13-1, In 13-2, each signal is converted into a digital received signal. The received signals R = (r ₁ , r ₂ ) output from the A / D converters 13-1 and 13-2 are branched, and one is input to the fast Fourier transform circuits (FFT) 14-1 and 14-2. Then, the received signal X [i] = (x ₁ [i], x ₂ [i]) of each subcarrier is demodulated, and the other is input to the transmission path estimation unit 15 to receive the received desired signal and the preamble of the interference signal. The transmission coefficient h ^d _1d [i], h ^d _2d [i] of each subcarrier of the desired signal using the signal and the transmission coefficient h ^u _1u [i], h ^u _2u [i] of each subcarrier of the interference signal Is calculated. The received signals X [i] = (x ₁ [i], x ₂ [i]) output from the FFTs 14-1 and 14-2 are branched, one being the interference extracting unit 16 and the other being the interference compensating unit 17. Is input.

In the interference extraction unit 16, the received signals X [i] = (x ₁ [i], x ₂ [i]) output from the FFTs 14-1 and 14-2 and the desired signal output from the transmission path estimation unit 15. Input the transfer coefficient h ^d _1d [i], h ^d _2d [i] of each subcarrier and the transfer coefficient h ^u _1u [i], h ^u _2u [i] of each subcarrier of the interference signal. The interference signal component Uex [i] in which the desired signal component is suppressed is extracted. In the interference compensation unit 17, the reception signal X [i] output from the FFTs 14-1 and 14-2, the interference signal component Uex [i] output from the interference extraction unit 16, and the transmission path estimation unit 15 output. The input signal h ^u _1u [i], h ^u _2u [i] of each subcarrier of the interference signal is input, and the desired signal Y [i] = (y ₁ [i], y ₂ [i]) is output. This desired signal Y [i] = (y ₁ [i], y ₂ [i]) is input to identification circuits (DET) 18-1 and 18-2, converted into a bit string, and output data series Z [i ] = (Z ₁ [i], z ₂ [i]).

FIG. 2 shows a format of a transmission signal sequence in the first embodiment. Here, the transmission signal sequence of the desired signal is shown, but the interference signal has the same format. A preamble signal having a known pattern used for timing synchronization, frequency synchronization, and transmission path estimation in normal OFDM burst transmission is arranged at the head of the transmission signal sequence. Here, the desired signal and the preamble signal of the interference signal are set as K data values. Desired signal: Pd (0), Pd (1),..., Pd (K-1)
Interference signal: Pu (0), Pu (1), ..., Pu (K-1)
It expresses. In order to distinguish between the desired signal and the interference signal, each preamble signal is different.

FIG. 3 shows a configuration example of the transmission path estimation unit 15 in the first embodiment. In FIG. 3, the transmission path estimation unit 15 branches an input received signal R = (r ₁ , r ₂ ), respectively, and inputs one to matched filters 21-1 and 21-2 that detect a desired signal. The other is input to matched filters 22-1 and 22-2 that detect interference signals. The matched filters 21-1 and 21-2 calculate impulse responses of desired signals included in the received signals, and input the impulse responses to fast Fourier transform circuits (FFT) 23-1 and 23-2 to perform Fourier transform. Then, transfer coefficients h ^d _1d [i] and h ^d _2d [i] of each subcarrier of the desired signal are calculated.

Here, the transfer coefficient h ^d _1d [i] calculated by the FFT 23-1 is a component corresponding to the i-th subcarrier of the transfer coefficient of the desired signal received by the receiving antenna 11-1. The transmission coefficient h ^d _2d [i] calculated in (1) is a component corresponding to the i-th subcarrier of the transmission coefficient of the desired signal received by the receiving antenna 11-2. Similarly, matched filters 22-1 and 22-2 calculate impulse responses of interference signals included in the received signals, and input the impulse responses to fast Fourier transform circuits (FFT) 24-1 and 24-2. Then, Fourier transform is performed to calculate transfer coefficients h ^u _1u [i] and h ^u _2u [i] of each subcarrier of the interference signal.

FIG. 4 shows a configuration example of the matched filter 21 in the first embodiment. In FIG. 4, the matched filter 21 for detecting a desired signal includes K-1 delay circuits 25-1 to 25- (K-1), K multiplier circuits 26-1 to 26-K, and a synthesis circuit. The delay amount T of each delay circuit is a sampling period. The received signals r ₁ (r ₂ ) sequentially delayed by the delay circuits 25-1 to 25- (K-1) are converted into complex conjugate Pd () of the preamble signal of the desired signal by the multiplier circuits 26-1 to 26-K. 0) ^* , Pd (1) ^* ,..., Pd (K-1) ^*, and the synthesis circuit 27 synthesizes and outputs the multiplication results. Thereby, the impulse response of the desired signal included in each received signal is calculated.

Similarly, in the matched filter 22 that detects an interference signal, the coefficients of the multiplication circuits 26-1 to 26-K are converted into complex conjugates Pu (0) ^* , Pu (1) ^* ,..., Pu (K -1) Calculate the impulse response of the interference signal by setting ^* .

  An example of the impulse response calculated by each matched filter is shown in FIG. A plurality of incoming waves (three waves in the example) exist in the impulse response of the signal received in the multipath environment. FIG. 6 shows transfer coefficients obtained by Fourier transforming 64 impulses of the impulse response from the leading wave. In FIG. 6, the horizontal axis corresponds to the frequency, and the value on the vertical axis represents the transfer coefficient of the corresponding subcarrier component. Although the impulse response and the transfer coefficient are complex numbers, FIG. 5 and FIG. 6 are each represented by an amplitude component.

On the other hand, where the number of the OFDM symbol is n, the i-th transmission subcarrier D [i] (n) of the desired signal, the i-th transmission subcarrier U [i] (n) of the interference signal, the FFT 14-1, The relationship between the received subcarriers x ₁ [i] (n) and x ₂ [i] (n) output from 14-2 is expressed as follows.
_{x 1 [i] (n)} = h d 1d [i] · D [i] (n) + h u 1u [i] · U [i] (n) ... (6-1)
_{x 2 [i] (n)} = h d 2d [i] · D [i] (n) + h u 2u [i] · U [i] (n) ... (6-2)
These outputs are input to the interference extraction unit 16, and a desired signal is removed for each subcarrier to extract an interference signal.

FIG. 7 shows a configuration example of the interference extraction unit 16 in the first embodiment. In FIG. 7, the interference extraction unit 16 includes a desired signal suppression circuit 31, an arithmetic circuit 32, and an interference signal separation circuit 33. The desired signal suppression circuit 31 outputs the received signals x ₁ [i], x ₂ [i] output from the FFTs 14-1 and 14-2 to the multiplication circuits 34-1 and 34-2 and the transmission path estimation unit 15. The transmission coefficients h ^d _2d [i] and h ^d _1d [i] of the respective subcarriers of the desired signal to be inputted are respectively multiplied, and the subtraction circuit 35 uses the output of the multiplication circuit 34-1 to output the multiplication circuit 34-2. The output is subtracted. The i-th subcarrier component of the signal after subtraction becomes only the interference signal component by removing the desired signal as follows.
h ^d _2d [i] · x ₁ [i] (n) − h ^d _1d [i] · x ₂ [i] (n)
_{^{= (H d 2d [i]}} · h u 1u [i] - h d 1d [i] · h u 2u [i]) · U [i] (n)
= Δ [i] ・ U [i] (n) (7)

The arithmetic circuit 32 transmits the transfer coefficient h ^d _1d [i], h ^d _2d [i] of each subcarrier of the desired signal output from the transmission path estimation unit 15 and the transfer coefficient h ^u _1u [of each subcarrier of the interference signal]. i], using a h ^u _2u [i], is a function of the transfer coefficient as shown below 1 / delta calculating a [i].
1 / Δ [i] = 1 / ( h ^d _2d [i] · h ^u _1u [i] −h ^d _1d [i] · h ^u _2u [i]) (8)
The interference signal separation circuit 33 is configured to multiply the output of the desired signal suppression circuit 31 and the output 1 / Δ [i] of the arithmetic circuit 32 by the multiplication circuit 36, and suppresses the desired signal component in the received signal. U [i] (n) is extracted and output as an interference signal component Uex [i] (n).

FIG. 8 shows a configuration example of the interference compensation unit 17 in the first embodiment. In FIG. 8, the interference compensation unit 17 includes an interference signal control circuit 41 and an interference subtraction circuit 42. The interference signal control circuit 41 outputs the interference signal component Uex [i] (n) output from the interference extraction unit 16 in the multiplication circuits 43-1 and 43-2 and the interference signal output from the transmission path estimation unit 15. The subcarrier transmission coefficients h ^u _1u [i] and h ^u _2u [i] are multiplied and given to the interference subtraction circuit 41. The interference subtraction circuit 41 subtracts the multiplication result of the multiplication circuit 43-1 from the reception signal x ₁ [i] output from the FFT 14-1 by the subtraction circuit 44-1, and outputs the result from the FFT 14-2 by the subtraction circuit 44-2. The multiplication result of the multiplication circuit 43-2 is subtracted from the received signal x ₂ [i]. The outputs y ₁ [i] and y ₂ [i] of the subtraction circuits 44-1 and 44-2 are as follows from the equations (6-1) and (6-2).
_{y 1 [i] = x 1} [i] (n) - h u 1u [i] · Uex [i] (n) → h d 1d [i] · D [i] (n) ... (9-1)
_{y 2 [i] = x 2} [i] (n) - h u 2u [i] · Uex [i] (n) → h d 2d [i] · D [i] (n) ... (9-2)
As a result, the outputs y ₁ [i] and y ₂ [i] of the interference compensator 17 are only desired signals from which the interference signals in the received signal are removed.

  As described above, it is possible to perform transmission path estimation using the desired preamble signal and the existing preamble signal of the interference signal, extract the interference signal using the calculated transmission coefficient, and perform interference compensation using this. In the configuration of the present embodiment, two receiving antennas are used to extract interference signals, and interference compensation processing is performed on each received signal.

(Second Embodiment)
In the first embodiment, the interference signal is extracted and removed by channel estimation using the characteristics of the interference signal. In the second embodiment, a training signal sequence arranged before the preamble signal is used. Transmission path estimation is performed.

FIG. 9 shows a format of a transmission signal sequence in the second embodiment. At the beginning of the transmission signal sequence, a training signal sequence is arranged before the preamble signal having a known pattern. This training signal sequence is added for the purpose of improving the transmission path estimation accuracy as compared with the case where an existing preamble signal is used. For example, a PN sequence consisting of ± 1 is used as a training signal sequence, which is transmitted using a single carrier of BPSK modulation. Here, the training signal sequence of the desired signal and the interference signal is set as K ′ data values. Desired signal: Cd (0), Cd (1),..., Cd (K′−1)
Interference signal: Cu (0), Cu (1), ..., Cu (K'-1)
It expresses. In order to distinguish between the desired signal and the interference signal, the preamble signals are different from each other and are highly orthogonal to each other.

FIG. 10 shows a configuration example of the matched filter 21 in the second embodiment. The difference from the matched filter 21 in the first embodiment shown in FIG. 4 is that the complex conjugates Cd (0) ^* , Cd (1) of the training signal sequence of the desired signal are used as the coefficients of the multiplication circuits 26-1 to 26-K. ^* , ..., Cd (K'-1) ^* is used. The same applies to the matched filter 22 that detects an interference signal. By using this training signal sequence, it is possible to improve the impulse response calculated by the matched filter and the estimation accuracy of the transfer coefficient obtained by Fourier transform. As a result, the interference extraction unit (FIG. 1, FIG. 7: 16) can extract the interference signal with higher accuracy, and the interference suppression characteristic in the interference compensation unit (FIG. 1, FIG. 8: 17) is improved. . The same applies to the embodiments described below.

(Third embodiment)
FIG. 11 shows a third embodiment of the OFDM signal receiving apparatus of the present invention. The feature of this embodiment is that an SD synthesis unit 19 is arranged at the output stage of the interference compensation unit 17 in the configuration of the first embodiment shown in FIG. 1, and the interference signal component is removed from the received signal by the interference compensation unit 17 The signal Y [i] = (y ₁ [i], y ₂ [i]) is synthesized in phase, and the synthesized output W [i] is identified by the discriminating circuit 18 and output as an output data series Z [i]. It is in. The SD combining unit 19 receives the transfer coefficients h ^d _1d [i] and h ^d _2d [i] of each subcarrier of the desired signal output from the transmission path estimation unit 15.

FIG. 12 shows a configuration example of the SD composition unit 19 in the third embodiment. In FIG. 12, the SD synthesis unit 19 inputs the transfer coefficients h ^d _1d [i] and h ^d _2d [i] of each subcarrier of the desired signal output from the transmission path estimation unit 15 to the complex conjugate calculation unit 51. The desired signals y ₁ [i], y ₂ [i] from which the interference signal components output from the interference compensation unit 17 have been removed and the complex conjugate calculation unit 51 output to the multiplication circuits 52-1 and 52-2. The complex conjugates h ^d _1d [i] ^* and h ^d _2d [i] ^* of the transfer coefficient of the desired signal are input and multiplied, and the adder circuit 53 combines the outputs of the multiplier circuits 52-1 and 52-2. . The i-th signal W [i] after synthesis is expressed as follows.
_{^{W [i] = h d 1d}} [i] * · y 1 [i] (n) + h d 2d [i] * · y 2 [i] (n)
= (| H ^d _1d [i] | ² + | h ^d _2d [i] | ² ) · D [i] (n) (10)

(Fourth embodiment)
FIG. 13 shows a fourth embodiment of the OFDM signal receiving apparatus of the present invention. The feature of this embodiment is that the first embodiment shown in FIG. 1 and the third embodiment shown in FIG. 11 use two receiving antennas 11-1 and 11-2 to interfere with one interfering station 2. While the configuration is such that the signal is canceled, it is generally extended to cancel a plurality of interference signals using a plurality of receiving antennas. Here, when J is the number of interfering stations and M is the number of receiving antennas to be used, M ≧ J + 1. The transfer coefficient from the desired station 1 to the receiving antenna 11-m is represented by h ^d _md [i], and the transfer coefficient from the interference station 2-j to the receiving antenna 11-m is represented by h ^u _mj [i] (m = 1, 2, ..., M, j = 1, 2, ..., J).

  The feature of this embodiment is that there are M reception systems compared to the configuration of the third embodiment shown in FIG. 11, a transmission path estimation unit 15 ', an interference extraction unit 16', an interference compensation unit 17 ', and SD synthesis. It is in the structure of the part 19 '.

Channel estimation unit 15 ', the received signal _{R = (r 1, ...,} r M) of the receiving antennas 11-1 to 11-M determine the transfer coefficient of each subcarrier of the desired signal and the interference signal from the. Details will be described with reference to FIG. The interference extraction unit 16 ′ receives received signals X [i] (n) = (x ₁ [i] (n),..., X after Fourier transform of the received signals R output from the FFTs 14-1 to 14-M. _M [i] (n)) is input, and interference signal components Uex [i] (n) = (u ₁ [i] (n),..., U from J interference stations included in each received signal _J [i] (n)) is extracted. Details will be described with reference to FIG. The interference compensator 17 ′ subtracts the interference signal component Uex [i] (n) from the received signal X [i] (n) after the Fourier transform, and removes each interference signal component in the received signal. Details will be described with reference to FIG. The SD synthesizing unit 19 ′ performs in-phase synthesis of the desired signal Y [i] (n) = (y ₁ [i] (n),..., Y _M [i] (n)) after interference compensation, and the synthesized output W Output as [i] (n). Details will be described with reference to FIG.

FIG. 14 shows a configuration example of the transmission path estimation unit 15 ′ in the fourth embodiment. In FIG. 14, the transmission path estimation unit 15 ′ branches the received signals R = (r ₁ ,..., R _M ) of the receiving antennas 11-1 to 11 -M, respectively, and a desired signal detection circuit 28 and an interference signal detection circuit 29. It is the structure which inputs to -1-29-J.

The desired signal detection circuit 28 includes M matched filters 21-1 to 21-M and fast Fourier transform circuits (FFT) 23-1 to 23-M. Matched filters 21-1 to 21 -M that receive received signals R = (r ₁ ,..., R _M ) calculate impulse responses of desired signals included in the received signals, and convert the impulse responses to FFT 23-1. ˜23-M and Fourier-transformed to calculate the transfer coefficients h ^d _1d [i],..., H ^d _Md [i] of each subcarrier of the desired signal.

The interference signal detection circuit 29-j includes M matched filters 22-j-1 to 22-j-M and a fast Fourier transform circuit (FFT) 24-j-1 to 24-j-M. Matched filters 22-j-1 to 22-j-M to which received signals R = (r ₁ ,..., R _M ) are input, calculate impulse responses of interference signals included in the received signals, and each impulse response. Are input to FFT24-j-1 to 24-j-M and Fourier-transformed to calculate transmission coefficients h ^u _1j [i],..., H ^u _Mj [i] of each subcarrier of the interference signal.

  The desired signal detection circuit 28 and the interference signal detection circuit 29-j have the same configuration, but in the matched filters 21-1 to 21-M of the desired signal detection circuit 28, the preamble signal or training of the desired signal is used as the coefficient of each multiplier circuit. The transmission path is estimated using the signal, and the matched filter 22-j-1 to 22-j-M of the interference signal detection circuit 29-j transmits using the preamble signal or training signal of the interference signal as the coefficient of each multiplier circuit. Estimate the road.

これらの出力を干渉抽出部１６′に入力し、サブキャリアごとに希望信号を除去して干渉信号を抽出する。 On the other hand, in FIG. 13, the OFDM symbol number is n, and the i-th transmission subcarrier D [i] (n) of the desired signal and the i-th transmission subcarrier U _j [ The relationship between i] (n) and the received signal x _m [i] (n) Fourier-transformed by FFT 14-m is expressed as follows.

These outputs are input to the interference extraction unit 16 ′, and the desired signal is removed for each subcarrier to extract the interference signal.

FIG. 15 shows a configuration example of the interference extraction unit 16 ′ in the fourth embodiment. In FIG. 15, the interference extraction unit 16 ′ includes desired signal suppression circuits 31-1 to 31 -J, an arithmetic circuit 32, and an interference signal separation circuit 33. The desired signal suppression circuit 31-j receives the received signals x _M [i] (n) and x _m [i] output from the FFTs 14-M and 14-m to the multiplication circuits 34-j-1 and 31-j-2. (n) and the transfer coefficients h ^d _md [i] and h ^d _Md [i] of each subcarrier of the desired signal output from the transmission path estimation unit 15 ′ are input and multiplied, respectively, and the subtraction circuit 35-j Then, the output of the multiplier circuit 31-j-2 is subtracted from the output of the multiplier circuit 31-j-1. Here, j = m is set, and the received signals x ₁ [i] (n) to x _J [i] (n) output from the FFTs 14-1 to 14 -J to the desired signal suppression circuits 31-1 to 31 -J. ) And the reception signal x _M [i] (n) output from the FFT 14-M are input in common, but they are M reception signals x ₁ [i] (n) to x _M. Any combination of [i] (n) and one may be used. That is, the desired signal suppression circuits 31-1 to 31-J multiply the M + 1 received signals among the M received signals and the corresponding transfer coefficients of the desired signals, and each suppress the desired signal. Output the signal component.

The i-th signal v _m [i] (n) output from the desired signal suppression circuit 31-j is expressed as follows.

As a result, the output v _m [i] (n) of the desired signal suppression circuit 31-j is removed from the desired signal and becomes only the interference signal component. Here, V [i] to the J output of the desired signal suppression circuit 31-1~31-J (n) = ( v 1 [i] (n), ..., v J [i] (n)) as _Assuming that S [i] is a matrix of J rows and J columns that represents s _mj [i] in equation (12) in vector display, equation (12) is expressed as follows.
V [i] (n) = S [i] · U [i] (n) (13)

Each element s _mj [i] of S [i] represents the transmission coefficients h ^d _1d [i],..., H ^d _Md [i] of the subcarriers calculated by the transmission path estimator 15 ′ and the interference signals. subcarrier transfer coefficient _{^{h u 1j [i], ...}} , can be calculated from h ^u _Mj [i]. The arithmetic circuit 32 calculates an inverse matrix S ^-1 [i] of this S [i], and multiplies it by V [i] (n) by the interference signal separation circuit 33, thereby obtaining a desired signal in the received signal. The interference signal component Uex [i] (n) = (u ₁ [i] (n),..., U _J [i] (n)) with suppressed components is obtained as follows. Input to ′.
Uex [i] (n) = S ⁻¹ [i] · V [i] (n) (14)

この結果、干渉補償部１７′の出力Ｙ[i](n)は、受信信号中の干渉信号を除去した希望信号のみとなる。 FIG. 16 shows a configuration example of the interference compensation unit 17 ′ in the fourth embodiment. In FIG. 16, the interference compensation unit 17 ′ includes an interference signal control circuit 41 and an interference subtraction circuit 42. In the interference signal control circuit 41, each element is composed of a transfer coefficient h ^u _mj [i] of each subcarrier of the interference signal with respect to the interference signal component Uex [i] (n) output from the interference extraction unit 16 ′. The interference transfer coefficient matrix H ^u [i] of M rows and J columns is multiplied, and the subtraction circuits 44-1 to 44-M of the interference subtraction circuit 42 subtract the output of the interference signal control circuit 41 from X [i] (n). To do. The output Y [i] (n) = (y ₁ [i] (n),..., Y _M [i] (n)) of the interference subtraction circuit 42 is as follows from the equation (11).

As a result, the output Y [i] (n) of the interference compensation unit 17 ′ is only the desired signal from which the interference signal in the received signal has been removed.

FIG. 17 shows a configuration example of the SD synthesis unit 19 ′ in the fourth embodiment. In FIG. 17, the SD synthesizing unit 19 ′ _converts the transmission coefficients h ^d _1d [i] to h ^d _Md [i] of each subcarrier of the desired signal output from the transmission path estimation unit 15 ′ into the complex conjugate calculation unit 51 ′. The desired signal Y [i] from which the interference signal component output from the interference compensation unit 17 'is removed to the multiplication circuits 52-1 to 52-M and the desired signal output from the complex conjugate calculation unit 51'. The complex conjugates of the transfer coefficients h ^d _1d [i] ^* to h ^d _Md [i] ^* are inputted and multiplied, and the synthesis circuit 53 ′ synthesizes the outputs of the multiplication circuits 52-1 to 52-M. The i-th signal W [i] after synthesis is expressed as follows.

  In this way, the interference compensation unit 17 ′ can perform in-phase synthesis of a plurality of reception signals from which interference signals have been removed, and obtain better reception characteristics.

The figure which shows 1st Embodiment of the OFDM signal receiver of this invention. The figure which shows the format of the transmission signal series in 1st Embodiment. The figure which shows the structural example of the transmission path estimation part 15 in 1st Embodiment. The figure which shows the structural example of the matched filter 21 in 1st Embodiment. The figure which shows the example of an impulse response. The figure which shows the example of a transmission coefficient. The figure which shows the structural example of the interference extraction part 16 in 1st Embodiment. The figure which shows the structural example of the interference compensation part 17 in 1st Embodiment. The figure which shows the format of the transmission signal series in 2nd Embodiment. The figure which shows the structural example of the matched filter 21 in 2nd Embodiment. The figure which shows 3rd Embodiment of the OFDM signal receiver of this invention. The figure which shows the structural example of the SD synthetic | combination part 19 in 3rd Embodiment. The figure which shows 4th Embodiment of the OFDM signal receiver of this invention. The figure which shows the structural example of transmission-line estimation part 15 'in 4th Embodiment. The figure which shows the structural example of interference extraction part 16 'in 4th Embodiment. The figure which shows the structural example of interference compensation part 17 'in 4th Embodiment. The figure which shows the structural example of SD synthetic | combination part 19 'in 4th Embodiment. The figure which shows the structural example of a MIMO transmission system. The figure which shows the format of the transmission signal series in a prior art. The figure which shows the example of interference between other cells.

Explanation of symbols

1 desired station 2 interfering station 11 receiving antenna 12 receiver (Rx)
13 A / D converter 14 Fast Fourier transform (FFT)
DESCRIPTION OF SYMBOLS 15 Transmission path estimation part 16 Interference extraction part 17 Interference compensation part 18 Identification circuit (DET)
19 SD synthesis unit 21, 22 Matched filter 23, 24 Fast Fourier transform (FFT)
25 Delay circuit (T)
26 Multiplication Circuit 27 Synthesis Circuit 31 Desired Signal Suppression Circuit 32 Arithmetic Circuit 33 Interference Signal Separation Circuit 34, 36 Multiplication Circuit 35 Subtraction Circuit 41 Interference Signal Control Circuit 42 Interference Subtraction Circuit 43 Multiplication Circuit 44 Subtraction Circuit 51 Phase Conjugate Operation Unit 52 Multiplication Circuit 53 Synthesis Circuit

Claims (4)

A receiving signal is received by two receiving antennas from a desired station as an OFDM (orthogonal frequency division multiplexing) signal and an interference signal transmitted as an OFDM signal from an asynchronous station asynchronous to the desired station. In the OFDM signal receiving apparatus that demodulates the received signal of each subcarrier by Fourier transforming the received signal of the antenna,
Transmission path estimation means for calculating each transfer coefficient of the desired signal and the interference signal using each preamble signal of the desired signal and the interference signal included in the received signals received by the two receiving antennas;
Interference extraction means for suppressing the desired signal component contained in the received signal and extracting the interference signal component based on the transmission coefficients of the desired signal and the interference signal obtained by the transmission path estimation means;
The interference signal component extracted by the interference extraction means is controlled based on the transmission coefficient of the interference signal obtained by the transmission path estimation means, and the interference signal component contained in the received signal is used using this interference signal component An OFDM signal receiving apparatus comprising: interference compensation means for outputting a desired signal component with suppressed signal. The OFDM signal receiving apparatus according to claim 1, wherein
An OFDM signal receiving apparatus, comprising: a synthesizing unit that performs in-phase synthesis of a desired signal component output from the interference compensation unit based on a transmission coefficient of the desired signal obtained by the transmission path estimation unit. A desired signal transmitted as an OFDM (Orthogonal Frequency Division Multiplexing) signal from a desired station and a plurality of M interference signals transmitted as OFDM signals from a plurality of J interfering stations asynchronous to the desired station. In an OFDM signal receiving apparatus that receives a reception antenna of M ≧ J + 1) and demodulates a reception signal of each subcarrier by performing Fourier transform on the reception signal of each reception antenna,
Transmission path estimation means for calculating each transmission coefficient of the desired signal and the plurality of interference signals using the preamble signal of the desired signal and the plurality of interference signals included in the reception signals received by the plurality of reception antennas;
Based on the desired signal and the transfer coefficients of the plurality of interference signals obtained by the transmission path estimation means, the desired signal component contained in the received signal is suppressed to extract the corresponding plurality of interference signal components. Interference extraction means;
A plurality of interference signal components extracted by the interference extraction means are controlled based on transmission coefficients of the plurality of interference signals obtained by the transmission path estimation means, and are included in the received signal using the interference signal components. Interference compensation means for outputting a desired signal component with suppressed interference signal components,
An OFDM signal receiving apparatus comprising: combining means for combining a plurality of desired signal components output from the interference compensation means in phase based on a transmission coefficient of the desired signal obtained by the transmission path estimation means . In the OFDM signal receiving device according to claim 1 or 3,
The transmission path estimation means is configured to calculate each transfer coefficient of the desired signal and the interference signal using a training signal sequence arranged in the transmission signal sequence of the desired signal and the interference signal separately from the preamble signal. An OFDM signal receiving apparatus.

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