JP2003134084A - Radio receiver and radio receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reception quality by removing correlation between spreading codes in an OFDM-CDMA system. SOLUTION: A matrix A is prepared by convolution operation between a channel estimation value and a spreading code. In this embodiment, since a multipass does not straddle over a plurality of OFDM symbols, the convolution operation is multiplication operation. Correlative operation AHA (matrix) of the matrix A is calculated. The gain values of fading propagation lines of respective spreading codes appear in the diagonal components of the matrix AHA and the correlation values of respective spreading codes appear in components other than the diagonal components. A plurality of signals from which the correlation of spreading codes of a pass included in window width W' is removed are demodulated buy solving an equation AHAx=b of an inverse spread signal b, i.e., by multiplying the inverse spread signal b by the inverse matrix [AHA]<-1> .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM-CDMA radio receiving apparatus and radio receiving method used in a digital radio communication system.

[0002]

2. Description of the Related Art In recent years, in a digital radio communication system, it is possible to effectively use the advantage that transmission data obtained by the OFDM modulation system can be transmitted at high speed and the advantage that the CDMA modulation system is resistant to interference and noise. In this way, a method capable of transmitting high-quality transmission data to a large number of communication terminals at high speed, that is, a communication method combining an OFDM method and a CDMA method (hereinafter,
The FDM-CDMA system) has been developed.

FIG. 4 is a block diagram showing the structure of a conventional OFDM-CDMA radio receiving apparatus. The wireless signal is received by the wireless reception unit 402 via the antenna 401. The radio reception unit 402 performs a predetermined radio reception process (for example, down conversion or A / D conversion) on the received signal, and outputs the signal after the radio reception process to the guard interval removal unit 403.

The guard interval removing section 403 removes the guard interval inserted in the signal after the radio reception processing, and outputs the signal after the guard interval removal to the serial / parallel (S / P) converting section 404. S /
In the P conversion unit 404, the signal after the guard interval is removed is S / P converted, and the signal after the S / P conversion is FFT in parallel.
(Fast Fourier Transform) Output to the processing unit 405.

The FFT processing unit 405 performs FFT processing on the signal after S / P conversion to convert it into information for each subcarrier, and the signal after this FFT processing is fading compensation unit 40.
Output to 6. Note that pilot symbols, which are known signals in the signal after the FFT process, are output to channel estimation section 408 for each subcarrier.

The channel estimation section 408 for each subcarrier is
Channel estimation is performed for each subcarrier using pilot symbols for each subcarrier, and the obtained channel estimation value for each subcarrier is output to fading compensation section 406.

Fading compensation section 406 multiplies the signal for each subcarrier after FFT processing by the channel estimation value for each subcarrier, and performs fading compensation for the signal for each subcarrier after FFT processing. . The fading-compensated signal for each subcarrier is output to despreading section 407. The despreading unit 407 performs despreading processing on the signal for each subcarrier after fading compensation with the spreading code used on the transmission side to reproduce the received data.

[0008]

In the OFDM-CDMA system, since fading propagation paths are different for each subcarrier to which spread codes are assigned, orthogonality between spread codes cannot be maintained, and cross correlation between spread codes occurs. There is a problem in that it becomes difficult to maintain communication quality once it occurs.

The present invention has been made in view of the above circumstances, and provides a radio receiving apparatus and a radio receiving method capable of removing cross-correlation between spreading codes and improving reception quality in the OFDM-CDMA system. The purpose is to do.

[0010]

A radio receiving apparatus according to the present invention is an OFDM-CDMA radio receiving apparatus for receiving a reception signal including a spread-modulated OFDM symbol and a known signal, and the reception signal is known. Channel estimation means for performing channel estimation for each subcarrier using a signal,
Fading compensation means for performing fading compensation for each subcarrier using the channel estimation value obtained by the channel estimation means, and spread-modulated O after fading compensation.
A configuration is provided that includes despreading means for performing despreading processing on the FDM symbol, and interference removing means for performing interference canceling processing on the signal after the despreading processing and outputting received signals of all codes.

According to this configuration, since fading compensation is performed for each subcarrier and multipath interference cancellation is performed, that is, since the channel estimation value for each subcarrier is used,
It is possible to remove cross-correlation between spreading codes that occurs due to different fading propagation paths for each subcarrier to which spreading codes are assigned, and to improve reception performance.

The radio receiving apparatus of the present invention adopts a configuration in which the multipath is within one OFDM symbol in the above configuration.

The radio receiving apparatus of the present invention adopts a configuration in which the multipath extends over a plurality of OFDM symbols in the above configuration.

According to this structure, the multipath has a plurality of O's.
It is possible to remove cross-correlation between spreading codes, which occurs due to different fading propagation paths of subcarriers to which spreading codes are assigned, even if it extends to FDM symbols or within one OFDM symbol, thereby improving reception performance. be able to.

In the radio receiving apparatus of the present invention having the above-mentioned structure, the OFDM-CDMA system is a two-dimensional spreading OFD in which chips are spread and arranged on the frequency axis and the time axis for transmission.
An M-CDMA system is adopted.

According to this configuration, even in the case of two-dimensional spreading, it is possible to remove the cross-correlation between spreading codes that occurs due to different fading propagation paths for each subcarrier to which spreading codes are assigned. The reception performance can be improved.

The radio receiving apparatus of the present invention has the above-mentioned configuration in which the interference removing means removes the cross-correlation for the maximum spreading factor.

With this configuration, it is possible to reduce the calculation load when the delayed wave does not extend over the symbols.

A radio base station apparatus of the present invention comprises the above radio receiving apparatus. A communication terminal device of the present invention is equipped with the above-mentioned wireless reception device. According to these configurations, in the OFDM-CDMA digital wireless communication system, it is possible to remove the cross-correlation between spreading codes that occurs due to different fading propagation paths for each subcarrier to which spreading codes are assigned. The performance can be improved.

A radio receiving method of the present invention is an OFDM-CDMA radio receiving method for receiving a received signal including a spread-modulated OFDM symbol and a known signal, wherein a known signal of the received signal is used for subcarriers. A channel estimation step for performing channel estimation for each subcarrier, a fading compensation step for performing fading compensation for each subcarrier using the channel estimation value obtained by the channel estimation means, and a spread modulation OFDM symbol after fading compensation The method includes a despreading step of performing a spreading process, and an interference removing step of performing an interference removing process on the signal after the despreading process and outputting received signals of all codes.

According to this method, fading compensation is performed for each subcarrier to perform multipath interference cancellation, that is, since the channel estimation value for each subcarrier is used,
It is possible to remove cross-correlation between spreading codes that occurs due to different fading propagation paths for each subcarrier to which spreading codes are assigned, and to improve reception performance.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION
Considering the techniques of the DMA system, attention is paid to the problems peculiar to the OFDM-CDMA system that cannot be solved by these respective techniques. That is, the OFDM method employs a technique of inserting a guard interval to absorb multipath. Further, in the CDMA system, a RAKE receiving technique is introduced in order to maintain orthogonality on the time axis.

However, in the OFDM-CDMA system in which spread modulation signals are arranged for each subcarrier for communication,
It is required to maintain orthogonality between subcarriers, which is not a problem with the FDM system alone or the CDMA system alone. Therefore, the present inventor has arrived at the present invention to solve this point.

That is, the essence of the present invention is that the fading compensation is performed for each subcarrier to perform multipath interference cancellation, and the fading propagation paths for the subcarriers to which the spreading codes are assigned are different from each other. The purpose is to remove the correlation and improve the reception performance.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. (Embodiment 1) In this embodiment, OFDM-CDM is used.
In the A system, a case will be described in which the cross-correlation between spreading codes is removed and the reception quality is improved when the multipath does not reach a plurality of symbols (within one OFDM symbol).

FIG. 1 is a block diagram showing the configuration of a radio receiving apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a configuration of a wireless transmission device that performs wireless communication with the wireless reception device according to the first embodiment.

The transmission data is digitally modulated by the modulator 201, and the signal after digital modulation is S / P converter 20.
2 is output. The S / P conversion unit 202 performs S / P conversion on the digitally modulated signal, and outputs the S / P converted signal to the plurality of spreading units 203.

Each spreading section 203 performs spread modulation processing on the signal after S / P conversion with each spreading code. The spread signal is output to the S / P conversion unit 204. S / P
The conversion unit 204 stores the number of chips for subcarriers. These chips are output to the IFFT processing unit 205.

The IFFT processing section 205 performs IFFT processing on the chip and outputs the signal (frequency information) for each subcarrier after the IFFT processing to the P / S conversion section 206. P / S conversion section 206 performs P / S conversion on the signal for each subcarrier after the IFFT processing, and outputs the signal after P / S conversion to guard interval insertion section 207.

In the guard interval insertion unit 207, P
A guard interval that is a copy of a part of the signal after the IFFT process is inserted into the signal after the / S conversion. The signal after the insertion of the guard interval is output to radio transmitting section 208.

The radio transmission section 208 performs a predetermined radio transmission process (for example, on the signal after the insertion of the guard interval).
D / A conversion, up-conversion, etc.) is performed, and the signal after the wireless transmission processing is transmitted as a wireless signal via the antenna 209.

The radio signal is received by the radio receiving section 102 via the antenna 101. The wireless reception unit 102 performs a predetermined wireless reception process (for example, down conversion or A / D conversion) on the received signal, and outputs the signal after the wireless reception process to the guard interval removal unit 103.

The guard interval removing section 103 removes the guard interval inserted in the signal after the radio reception processing, and the signal after the guard interval removal is S / P.
Output to the conversion unit 104. The S / P conversion unit 104 performs S / P conversion on the signal after the guard interval is removed, and S / P conversion is performed.
The converted signals are output in parallel to the FFT processing unit 105.

In the FFT processing unit 105, the signal after S / P conversion is subjected to FFT processing and converted into information for each subcarrier, and the signal after this FFT processing is performed by the fading compensation unit 10.
Output to 6. It should be noted that pilot symbols, which are known signals in the signal after the FFT processing, are output to each subcarrier-based channel estimation section 108 for each subcarrier.

Each subcarrier channel estimation section 108
Channel estimation is performed for each subcarrier using pilot symbols for each subcarrier, and the obtained channel estimation value for each subcarrier is output to fading compensation section 106.

The fading compensation unit 106 multiplies the signal for each subcarrier after FFT processing by the channel estimation value for each subcarrier, and performs fading compensation for the signal for each subcarrier after FFT processing. . The fading-compensated signal for each subcarrier is output to despreading section 107.

The despreading section 107 performs despreading processing on the signal for each subcarrier after fading compensation with the spreading code used on the transmitting side to reproduce the symbol. This symbol is output to multicode interference canceller 109. The multi-code interference removing unit 109 performs multi-code interference removing processing on the reproduced symbol. By this multi-code interference removal processing, received data of all codes is output.

Next, the operation of the radio receiving apparatus having the above configuration will be described. As mentioned above, OFDM-CD
In the MA method, since the fading propagation path is different for each subcarrier to which the spreading code is assigned, orthogonality between the spreading codes cannot be maintained, cross-correlation of the spreading codes occurs, and it becomes difficult to maintain communication quality. In the present embodiment, fading compensation is performed for each subcarrier to remove cross-correlation between spreading codes.

Specifically, the fading compensation section 106 in the radio receiving apparatus shown in FIG. 1 performs fading compensation using the channel estimation value for each subcarrier, and after performing despreading processing using the output, The multi-code interference removing unit 109 removes multi-code interference from the despread signal (b). Hereinafter, the multi-code interference cancellation will be described in detail.

First, the matrix A is created by the convolution operation between the channel estimation value and the spreading code. In this embodiment, since the multipath does not extend over a plurality of OFDM symbols, multiplication is used instead of convolutional calculation.

The calculation amount of the matrix A is N, the number of transmitted symbols, Q is the spreading factor, W'is the delay time (window width) for canceling interference in the propagation path model shown in FIG. If the number of codes is K, (NQ + W'-1)
X (KN). The delay time W ′ is the number of OFDM symbols affected by multipath. In the present embodiment, since the multipath is within one OFDM symbol,
W '= 1. K is the number of multicodes being transmitted.

Next, the correlation operation A ^H A (matrix) of the matrix A
To calculate. The calculation amount of the matrix A ^H A is (KN) × (K
N). In the matrix A ^H A, the gain of the fading propagation path of each spreading code (subcarrier) appears in the diagonal component, and the cross-correlation of each spreading code (subcarrier) appears in addition to the diagonal component.

Then the expression A ^H for the transmitted symbol x
By solving Ax = b, i.e. by multiplying the inverse matrix of ^{A H A [A H A]} -1 relative despread signal b,
It is possible to demodulate a plurality of signals from which the cross-correlation of the spreading code for the path included in the window width W ′ has been removed. As a result, received data of all codes can be obtained.

Here, the multipath interference cancellation will be concretely described using the following equation. The definition of the variable is as follows.

Q _F : Spreading factor on frequency axis, Q _F = 2 Q _{T in} the example: Spreading factor on time axis, Q _T = 1 Q: Spreading factor, Q = Q _T × Q _F = 2 K in the example : Multi-code number, K = 2 in the example, k: spreading code number, k = 0, 1, ..., K-1 N: number of symbols, N = 1 in the example W ': window width of delay profile, that is, RAKE combining and Time window width for removing multipath interference, W'in the example
= 1 and the delay wave does not extend between symbols, so R
There is no need for AKE combining or multipath interference cancellation. w: Path number of delay profile (w = 0, 1, ..., W
-1) M: number of subcarriers, M = 2 in the example, m: subcarrier number (m = 0, 1, ..., M-1) α _{w, i} : path w, fading waveform of subcarrier m (w = 0, 1, ..., W−1) h _{k, f} : value of code of frequency axis f of code k (f = 0,
1, ... Q _F −1) _{bt, m} : time t, received signal of subcarrier m (m = 0,
1, ..., M−1) _{nt, m} : noise at time t, subcarrier m (m = 0,1,
, M-1) x _{k, t} : time t, transmission signal of spread code k (k = 0, k =
0, 1, ..., K-1)

(Time 0) The reception signal of subcarrier 0 is expressed by the following equation (1). α ₀₀ h ₀₀ x ₀₀ + α ₀₁ h ₁₀ x ₁₀ + n ₀₀ = b ₀₀ (Equation 1)

The reception signal of subcarrier 1 is expressed by the following equation (2).
As shown in. α ₀₁ h ₀₁ x ₀₀ + α ₀₁ h ₁₁ x ₁₀ + n ₀₁ = b ₀₁ ... Formula (2)

Therefore, the cross-correlation matrix of spreading codes is as shown in the following equation (3).

[Equation 1]

The transmission signal is expressed by the following equation (4).

[Equation 2]

The signal after the IFFT is expressed by the following equation (5).

[Equation 3]

Therefore, by solving the following equation (6) for x, it is possible to obtain a received signal in which the cross-correlation of spreading codes due to fading is compensated.

[Equation 4]

Here, the cross-correlation matrix is as shown in the following equation (7). ｜ α ₀₀ ｜ ² h ₀₀ ^* h ₁₀ + ｜ α ₀₁ ｜ ² h ₀₁ ^* h
₁₁ indicates the cross-correlation of the codes.

[Equation 5]

Note that the fading char for each subcarrier is
If the channels are the same, that is, α₀₀= Α ₀₁In case of
As shown in (8), the cross-correlation between spreading codes is
It becomes zero.   ｜ α₀₀｜²h₀₀ ^*h_Ten+ | Α₀₁｜²h₀₁ ^*h₁₁= 0                                                               ... Formula (8)

As described above, according to this embodiment,
Multipath interference elimination by fading compensation for each carrier
(3)
Α ₀₀, Α₀₁Channel estimation value for each subcarrier like
Is used for each subcarrier to which a spreading code is assigned
Between spreading codes generated due to different fading propagation paths
Cross-correlation can be removed and reception performance can be improved.
You can

(Embodiment 2) In this embodiment, OF
In the DM-CDMA system, a case will be described in which the cross-correlation between spreading codes is removed to improve the reception quality when the multipath extends over a plurality of symbols (outside one OFDM symbol).

Specifically, the multipath interference cancellation in this embodiment will be described using the following equation. The definition of the variable is as follows.

Q _F : Spreading factor on frequency axis, Q _F = 2 Q _T in example: Spreading factor on time axis, Q _T = 1 Q: Spreading factor, Q = Q _T × Q _F = 2 K in example : Multi-code number, K = 2 in the example, k: spreading code number, k = 0, 1, ..., K-1 N: number of symbols, N = 2 in the example, W ′: window width of delay profile, that is, RAKE combining and Time window width for removing multipath interference, in the example W =
2 and the delayed wave extends between symbols. w: Path number of delay profile (w = 0, 1, ..., W
-1) M: number of subcarriers, M = 2 in the example, m: subcarrier number (m = 0, 1, ..., M-1) α _{w, i} : path w, fading waveform of subcarrier m (w = 0, 1, ..., W−1) h _{k, f} : value of code of frequency axis f of code k (f = 0,
1, ... Q _F −1) _{bt, m} : time t, received signal of subcarrier m (m = 0,
1, ..., M−1) _{nt, m} : noise at time t, subcarrier m (m = 0,1,
, M-1) x _{k, t} : time t, transmission signal of spread code k (k = 0, k =
0, 1, ..., K-1)

(Time 0) At time 0, the 0th symbol is received. The received signal of each subcarrier can be expressed by the above equations (1) and (2). That is, the received signal of subcarrier 0 is represented by the above equation (1), and the received signal of subcarrier 1 is represented by the above equation (2).

(Time 1) At time 1, the delayed waves of the first symbol and the 0th symbol are combined and received. The received signals of the respective subcarriers are the following equations (9) and (10)
Can be shown as That is, the received signal of subcarrier 0 is represented by the following equation (9), and the received signal of subcarrier 1 is represented by the following equation (10).

Α ₀₀ h ₀₀ x ₀₁ + α ₀₀ h ₁₀ x ₁₁ + α ₁₀ h ₀₀ x ₀₀ + α ₁₀ h ₁₀ x ₁₀ + n ₀₀ = b ₁₀ ... Formula (9) α ₀₁ h ₀₁ x ₀₁ + α ₀₁ h ₁₁ x ₁₁ + α ₁₁ h ₀₁ x ₀₀ + α ₀₁ h ₁₁ x ₁₀ + n ₁₁ = b ₁₁ ... Formula (10)

(Time 2) At time 2, the delayed wave of the first symbol is received. The received signal of each subcarrier can be expressed by the following equations (11) and (12). That is, the received signal of subcarrier 0 is represented by the following equation (11), and the received signal of subcarrier 1 is represented by the following equation (12). α ₁₀ h ₀₀ x ₀₁ + α ₁₀ h ₁₀ x ₁₁ + n ₂₀ = b ₂₀ ... Formula (11) α ₁₁ h ₀₁ x ₀₁ + α ₁₁ h ₁₁ x ₁₁ + n ₂₁ = b ₂₁ ... Formula (12)

Here, the cross-correlation matrix is as shown in the following equation (13).

[Equation 6]

Therefore, by solving the above equation (6) for x, it is possible to obtain a received signal in which the cross-correlation of spreading codes due to fading is compensated.

As described above, according to this embodiment,
Multipath interference elimination by fading compensation for each carrier
(3)
Α ₀₀, Α₀₁, Α_Ten, Α₁₁Check each subcarrier like
Since the channel estimation value is used, the multipath has multiple OFDs.
Even if it extends to M symbols, the sub-cap
Diffusion caused by different fading propagation paths for each rear
Cross-correlation between codes can be removed, improving reception performance.
You can go up.

(Third Embodiment) In the present embodiment, OF
In the DM-CDMA system, a case where two-dimensional spreading is performed in which chips are spread and arranged on the frequency axis and the time axis for transmission will be described.

Specifically, the multipath interference cancellation according to this embodiment will be described using the following equation. The definition of the variable is as follows.

Q _F : Spreading factor on frequency axis, Q _F = 2 Q _{T in} the example: Spreading factor on time axis, Q _T = 2 Q: Spreading factor, Q = Q _T × Q _F = 4 K in the example : Multi-code number, K = 2 in the example, k: spreading code number, k = 0, 1, ..., K-1 N: number of symbols, N = 2 in the example, W ′: window width of delay profile, that is, RAKE combining and Time window width for removing multipath interference, W'in the example
= 1 and the delayed wave does not extend between symbols. w: Path number of delay profile (w = 0, 1, ..., W
-1) M: number of subcarriers, M = 2 in the example, m: subcarrier number (m = 0, 1, ..., M-1) α _{w, i} : path w, fading waveform of subcarrier m (w = 0, 1, ..., W-1) h _{k, f, t} : frequency value f of code k, code value of time axis t (f = 0, 1, ..., Q _F -1, t = 0, 1) ,…, Q _T −
1) b _{t, m} : time t, received signal of subcarrier m (m = 0,
1, ..., M−1) _{nt, m} : noise at time t, subcarrier m (m = 0,1,
, M-1) x _{k, t} : time t, transmission signal of spread code k (k = 0, k =
0, 1, ..., K-1)

(Time 0) At time 0, the 0th spread signal on the time axis of the 0th symbol is received. The received signal of each subcarrier can be expressed by the following equations (14) and (15). That is, the received signal of subcarrier 0 is represented by the following equation (14), and the received signal of subcarrier 1 is represented by the following equation (15). α ₀₀ h ₀₀₀ x ₀₀ + α ₀₀ h ₁₀₀ x ₁₀ + n ₀₀ = b ₀₀ … Equation (14) α ₀₁ h ₀₀₁ x ₀₀ + α ₀₁ h ₁₀₁ x ₁₀ + n ₀₁ = b ₀₁ … Equation (15)

(Time 1) At time 1, the delayed waves of the first spread signal on the time axis of the 0th symbol and the 0th spread signal on the time axis of the 0th symbol are combined and received. The received signal of each subcarrier is shown by the following equations (16) and (17). That is, the received signal of subcarrier 0 is represented by the following equation (16), and the received signal of subcarrier 1 is represented by the following equation (17). α ₀₀ h ₀₁₀ x ₀₀ + α ₀₀ h ₁₁₀ x ₁₀ α ₁₀ h ₀₀₀ x ₀₀ + α ₁₀ h ₁₀₀ x ₁₀ + n ₁₀ = b ₁₀ ... Formula (16) α ₀₁ h ₀₁₁ x ₀₀ + α ₁₀ h ₁₁₁ x ₁₀ α ₁₁ h ₀₀₁ x ₀₀ + α ₁₀ h ₁₀₁ x ₁₀ + n ₁₁ = b ₁₁ (Equation (17))

(Time 2) At time 2, the delayed waves of the 0th spread signal on the time axis of the first symbol and the first spread signal on the time axis of the 0th symbol are combined and received. The received signal of each subcarrier is expressed by the following equation (18) and the following equation (19).
Indicated by. That is, the received signal of subcarrier 0 is represented by the following equation (18), and the received signal of subcarrier 1 is represented by the following equation (19). α ₀₀ h ₀₀₀ x ₀₁ + α ₀₀ h ₁₀₀ x ₁₁ α ₁₀ h ₀₁₀ x ₀₀ + α ₁₀ h ₁₁₀ x ₁₀ + n ₂₀ = b ₂₀ ... Formula (18) α ₀₁ h ₀₀₁ x ₀₁ + α ₀₁ h ₁₀₁ x ₁₁ α ₁₁ h ₀₁₁ x ₀₀ + α ₁₁ h ₁₁₁ x ₁₀ + n ₂₁ = b ₂₁ (Equation 19)

(Time 3) At time 3, the delayed waves of the first spread signal on the time axis of the first symbol and the 0th spread signal on the time axis of the first symbol are combined and received. The received signal of each subcarrier is expressed by the following equation (20) and the following equation (21).
Indicated by. That is, the reception signal of subcarrier 0 is represented by the following equation (20), and the reception signal of subcarrier 1 is represented by the following equation (21). α ₀₀ h ₀₁₀ x ₀₁ + α ₀₀ h ₁₁₀ x ₁₁ α ₁₀ h ₀₀₀ x ₀₁ + α ₁₀ h ₁₀₀ x ₁₁ + n ₃₀ = b ₃₀ ... Formula (20) α ₀₁ h ₀₁₁ x ₀₁ + α ₀₁ h ₁₁₁ x ₁₁ α ₁₁ h ₀₀₁ x ₀₁ + α ₁₁ h ₁₀₁ x ₁₁ + n ₃₁ = b ₃₁ Equation (21)

(Time 4) At time 4, the delayed wave of the first spread signal on the time axis of the first symbol is received. The received signal of each subcarrier is expressed by the following equation (22) and the following equation (2)
3). That is, the received signal of subcarrier 0 is expressed by the following equation (22), and the received signal of subcarrier 1 is expressed by the following equation (23). α ₁₀ h ₀₁₀ x ₀₁ + α ₁₀ h ₁₁₀ x ₁₁ + n ₄₀ = b ₄₀ ... Formula (22) α ₁₁ h ₀₁₁ x ₀₁ + α ₁₁ h ₁₁₁ x ₁₁ + n ₄₁ = b ₄₁ ... Formula (23)

Here, the cross-correlation matrix is as shown in the following equation (24).

[Equation 7]

Therefore, by solving the above equation (6) for x, it is possible to obtain a received signal in which the cross-correlation of spreading codes due to fading is compensated.

As described above, according to this embodiment, the
Multipath interference elimination by fading compensation for each carrier
(3)
Α ₀₀, Α₀₁, Α_Ten, Α₁₁Check each subcarrier like
Since the channel estimation value is used,
Also, the phasing for each subcarrier to which the spreading code is assigned
Cross-correlation between spreading codes caused by different propagation paths
Can be removed, can improve the reception performance
It

(Embodiment 4) In the present invention, cross-correlation may be removed not for all subcarriers but for the maximum spreading factor in multicode. Specifically, in the matrix calculation in the multipath interference canceller, the maximum spreading factor is calculated, and the cross-correlation for the maximum spreading factor is removed. When the spread code is interleaved, it is deinterleaved and then demodulated. By doing so, when the delayed wave does not span symbols, N = 1 in KN × KN which is the size of the matrix A can be set. This gives the matrix A
The maximum value of the size of Q can be set to Q × Q, and the calculation load can be reduced.

The present invention is not limited to Embodiments 1 to 4 above, but can be implemented with various modifications. For example,
The number of paths, the number of subcarriers, and the number of received signals in Embodiments 1 to 4 above are not limited and can be variously changed and implemented. Further, as the OFDM-CDMA system, even in the time domain spreading system in which each spread data spread in chip units by spread codes is arranged in the same subcarrier in the time direction, each spread data spread in chip units A frequency domain spreading method of allocating and allocating to different subcarriers may be used.

The radio receiving apparatus of the present invention can be applied to a communication terminal apparatus such as a radio base station apparatus or a mobile station in a digital radio communication system. This makes O
In the FDM-CDMA digital wireless communication system, it is possible to remove cross-correlation between spreading codes that occurs due to different fading propagation paths for each subcarrier to which spreading codes are assigned, and improve reception performance. .

[0079]

As described above, in the radio receiving apparatus and radio receiving method of the present invention, fading compensation is performed for each subcarrier and multipath interference cancellation is performed. Therefore, a fading propagation path for each subcarrier to which a spreading code is assigned is used. It is possible to remove the cross-correlation between spreading codes due to the difference between the two, and to improve the reception performance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a wireless reception device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a wireless transmission device that performs wireless communication with the wireless reception device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a propagation path model.

FIG. 4 is a block diagram showing the configuration of a conventional OFDM-CDMA wireless receiver.

[Explanation of symbols]

101,209 antenna 102 wireless receiver 103 Guard interval removal unit 104, 202, 204 S / P converter 105 FFT processing unit 106 Fading compensation section 107 despreading unit 108 Channel estimation unit for each subcarrier 109 Multi-code interference canceller 201 Modulator 203 diffusion unit 205 IFFT processing unit 206 P / S converter 207 Guard interval insertion section 208 wireless transmitter

Claims (8)

[Claims] 1. An OFDM-CDMA wireless receiving apparatus for receiving a reception signal including a spread-modulated OFDM symbol and a known signal, wherein channel estimation is performed for each subcarrier using the known signal of the reception signal. Channel estimation means, fading compensation means for performing fading compensation for each subcarrier using the channel estimation value obtained by the channel estimation means, and despreading for performing despreading processing on the spread-modulated OFDM symbol after fading compensation Means, and interference canceling means for performing interference canceling processing on the signal after the despreading processing and outputting received signals of all codes,
A wireless reception device comprising: 2. The radio receiving apparatus according to claim 1, wherein the multipath is within one OFDM symbol. 3. The radio receiver according to claim 1, wherein the multipath extends over a plurality of OFDM symbols. 4. The OFDM-CDMA system is a two-dimensional spreading OFDM-CDMA system in which chips are spread and arranged on a frequency axis and a time axis to perform transmission. The wireless reception device according to any one of claims. 5. The radio receiving apparatus according to claim 1, wherein the interference removing unit removes the cross correlation for the maximum spreading factor. 6. A radio base station apparatus comprising the radio receiving apparatus according to claim 1. Description: 7. A communication terminal device comprising the wireless reception device according to claim 1. Description: 8. A wireless receiving method of an OFDM-CDMA system for receiving a received signal including a spread-modulated OFDM symbol and a known signal, wherein channel estimation is performed for each subcarrier using the known signal of the received signal. Channel estimation step, fading compensation step for performing fading compensation for each subcarrier using the channel estimation value obtained by the channel estimation means, and despreading for performing despreading processing on the spread-modulated OFDM symbol after fading compensation An interference removing step of performing interference removing processing on the signal after the despreading processing and outputting received signals of all codes;
A wireless reception method comprising: