JP2005354238A - Wireless communication system, decoder, and decoding method employed by them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decoder quickly reducing a searching radius and decreasing the number of processing steps by conventional methods by just that much. <P>SOLUTION: Upon the receipt of a received signal vector, a path gain matrix, and a received SIR from a path gain / noise power estimate section 41 as input data from a reception antenna section 3, a re-transmission decision and pre-processing section 42 of a decoding section 4 decides whether the received SIR exceeds an SIR threshold value. When the received SIR exceeds the SIR threshold value, the re-transmission decision and pre-processing section 42 makes a data re-transmission request on the basis of compared powers. Further, when the received SIR exceeds no SIR threshold value, the re-transmission decision and pre-processing section 42 calculates input data to a transmission data estimate section 43. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radio communication system, a decoding apparatus, and a decoding method used for them, and more particularly to a decoding method in a receiving apparatus in a MIMO (Multiple Input Multiple Output) communication system.

  The MIMO communication system is a system as shown in FIG. 1, in which a data sequence is input to the encoding unit 1 and encoded into M (M is a positive integer) parallel sequences by the encoding unit 1. Data is transmitted from M transmission antenna units 2 (# 1 to #M), and data is received by N reception antenna units 3 (# 1 to #N) on the reception side (N is a positive integer). A system that restores the original data series in the decoding unit 4.

  In the MIMO communication system, data transmitted from each of the M antennas of the transmission antenna unit 2 undergoes fading, and is received by each of the N antennas of the reception antenna unit 3 in a form in which a signal multiplied by the path gain is superimposed. Therefore, it is necessary to estimate the signal transmitted from each transmission antenna from the signal received by each reception antenna in the decoding unit 4.

Antenna #m of the transmitting antenna section 2 (m = 1, ···, M) receiving the data sent from s _m, the antenna #n of the receiving antenna section 3 (n = 1, ···, N) in Data and noise are x _n and z _n , from antenna #m (m = 1,..., M) of the transmitting antenna unit 2 to antenna #m (m = 1,..., M) of the receiving antenna unit 3. When the path gain and h _mn, transmission signal, received signal path gain from the transmit antenna to each receive antenna, noise relationship applied by each receiving antenna,
x = Hs + z (1)
It can be expressed by the formula. However, (1) the vectors and matrices in equation, s = M-dimensional column vector the m component is s _m, x = N-dimensional column vector the m component is x _m, the z = m th component N-dimensional column vector with z _m , H = N × M-dimensional column vector with m-th component h _mn .

  Usually, the pilot signal is also included in the data x received by the N antennas of the receiving antenna unit 3, and the data is input to the path gain / noise power estimating unit 40, and the transmitted pilot signal is used. Each component of the matrix H, that is, a path gain from each transmitting antenna to each receiving antenna and a received SIR (Signal-to-Interference power Ratio) σ is calculated, and using the path gain H, the noise power σ, and the received signal x, Estimate the transmitted signal.

To perform signal estimation with maximum likelihood estimation:
(Fy) ^H H ^H H (fy) (2)
The transmission symbol vector candidate f that minimizes the value calculated by the expression However, if this is attempted by exhaustive search, it is necessary to search the number of transmission alphabet set elements to the number of transmission antennas, and the number of searches increases exponentially as the number of transmission alphabet elements and the number of transmission antennas increases. There is a problem of doing.

  For example, when the transmission alphabet is QPSK (Quadrature Phase Shift Keying) (ie, the number of transmission alphabets = 4), the number of transmission antennas = 2, the total number of searches is the square of 4, and the transmission alphabet is QPSK (ie, the number of transmission alphabets) = 16) When the number of transmitting antennas = 4, it is necessary to search for the fourth power of the total number of searches = 16.

  In order to solve this problem, a method has been proposed in which the search range is limited to a distance within “radius” from the “center” (see, for example, Non-Patent Document 1). The basic idea of this proposed method is that an exhaustive search is performed, that is, as shown in FIG. The idea is to reduce the number of processing steps by limiting to those included in the “radius” [see FIG. 8B].

・・・（３）
という式、つまり送信シンボルの条件なし最小二乗解によって定める。ここで、Ｈの上付添字である「＊−１」は一般化逆行列を表している。 Specifically, first, the coordinate y of “center” is

... (3)
That is, it is determined by an unconditional least squares solution of transmission symbols. Here, “* −1”, which is a superscript of H, represents a generalized inverse matrix.

Next, “radius” is defined by a certain rule (a specific method will be described later), and from among transmission symbol candidate vectors existing at a distance within “radius” from “center”,
(Fy) ^H Q ^H Q (fy) (4)
This is a method of searching for a transmission vector that minimizes the value calculated by the equation. However, the matrix Q in the equation (4) is an upper triangular matrix obtained by performing Cholesky decomposition on a Hermitian matrix obtained by subjecting the propagation path gain matrix H to Hermitian substitution of H from the left.

・・・（５）
という式を満たすようなαを求めた時、
半径Ｄ＝αＮσ
と設定する。但し、Ｎ：受信アンテナ数、σ：受信ＳＩＲである。 Hereinafter, conventional processing will be described. First, the center y defined by the equation (3) is calculated, and then the radius is set. As a normal method of determining the radius, a probability p including a true solution is set (for example, p = 0.99)

... (5)
When α that satisfies the equation
Radius D = αNσ
And set. However, N is the number of receiving antennas, and σ is a receiving SIR.

next,
| Q _MM (f _M −y _M ) | ² <D ² (6)
A section in which there is a transmission symbol candidate from the antenna #M that satisfies the following equation is derived, and one candidate is selected from among the sections.
further,
| QM-1M-1 (fM -1 -yM-1) + qM-1M (f M -y M) | 2
<D ² − | q _MM (f _M −y _M ) | ² (7)
A section in which there is a transmission symbol candidate from the antenna # M-1 that satisfies the following expression is derived, and one candidate is selected from the sections.

When the above operation is performed for all antennas in the order of the transmission antennas M, M-1,..., 1 and the obtained transmission candidate vector is f,
(Fy) ^H Q ^H Q (fy) <D ² (8)
If judged whether satisfy equation, satisfies that updates the search radius D ² (4) to the left side of the equation, is not satisfied, the search radius D ² is not updated. Then, the transmission candidate vectors are calculated in the same manner as described above within the updated radius (or not updated as it is).

Emanuel Viterbo, et, al. "A Universal Latin Code Decoder for Fading Channels" (IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 45, NO. 5, JULY 1999, pp. 1639-1642).

  In the conventional decoding method described above, the number of subsequent search processing steps is reduced as the radius is updated as small as possible in the initial stage. In order to be updated to a smaller radius, it is necessary to select a candidate whose distance is as close to the center as possible from the transmission antennas at the initial stage, and the distance from the center is a transmission symbol candidate from each transmission antenna. Becomes smaller as it goes to the middle of the section where there is (see FIG. 7).

  However, in the conventional method described above, after identifying a section where there are transmission symbol candidates from each transmission antenna, the end of the section, that is, searching from the lower limit to the upper limit in order, as a result, in the initial stage, There is a first problem that a large update of the radius cannot be expected and the processing steps increase accordingly.

  In the conventional decoding method, the “radius” is simply calculated from the received SIR, and the subsequent steps are executed. In this method, when the received SIR is very large, the radius increases accordingly. While the number of minute processing steps increases, there is a second problem that the reliability of the resulting solution is low.

  Accordingly, an object of the present invention is to solve the above-mentioned problems and to rapidly reduce the search radius, and to that extent, it is possible to realize a reduction in processing steps that should have been executed by the conventional method. A communication system, a decoding device, and a decoding method used for them are provided.

A wireless communication system according to the present invention encodes a data sequence into M (M is a positive integer) parallel sequences in a transmission side apparatus and transmits the data series from M transmission antennas, and N reception antennas in a reception side apparatus. A wireless communication system that restores the data received in the original data sequence,
Means for determining whether a received SIR (Signal-to-Interference power Ratio) exceeds a preset received SIR threshold, and a retransmission request is sent to the transmitting apparatus when the received SIR exceeds the received SIR threshold Means for receiving is provided in the receiving-side apparatus.

In the decoding apparatus according to the present invention, a data sequence is encoded into M (M is a positive integer) parallel sequences in a transmission side device and transmitted from M transmission antennas, and the reception side device uses N reception antennas. In a system for restoring received data to an original data sequence, a decoding device for restoring data received by the receiving antenna to an original data sequence,
Means for determining whether a received SIR (Signal-to-Interference power Ratio) exceeds a preset received SIR threshold, and a retransmission request is sent to the transmitting apparatus when the received SIR exceeds the received SIR threshold Means.

  In the decoding method according to the present invention, the data sequence is encoded into M (M is a positive integer) parallel sequence in the transmitting side device and transmitted from the M transmitting antennas, and the receiving side device uses the N receiving antennas. A decoding method used in a wireless communication system for restoring received data to an original data sequence, wherein a reception SIR (Signal-to-Interference power Ratio) exceeds a reception SIR threshold set in advance on the receiving side device side And a step of sending a retransmission request to the transmission side apparatus when the reception SIR exceeds the reception SIR threshold.

  That is, the wireless communication system of the present invention is characterized in that it reduces the amount of processing required for decoding in a receiving apparatus in a MIMO (Multiple Input Multiple Output) communication system.

  Further, the wireless communication system of the present invention improves the total throughput of the system by determining whether to proceed to the decoding step or to proceed to the notification step of the retransmission request based on the received SIR (Signal-to-Interference power Ratio). It is characterized by making it.

  Thus, in the wireless communication system of the present invention, in order to solve the first problem, as described above, candidates in a section where there are transmission symbol candidates from the respective transmission antennas are not centered in order from the lower limit. It can be seen that an algorithm for searching in order from the center, that is, in order from the closest to the center, may be applied (see FIG. 6). In order to improve this point, a reception SIR threshold value may be set in advance, and it may be determined whether the reception SIR exceeds the threshold value before calculating the radius.

  In the wireless communication system of the present invention, in order to solve the second problem, the radius is calculated when the threshold is not exceeded, the following steps are executed, and the following steps are executed when the threshold is exceeded. First, a retransmission request is sent to the transmission side. The received signal at this time may be discarded, and the characteristics can be improved by decoding together with the retransmitted received signal.

  Therefore, in the wireless communication system of the present invention, the power comparison unit determines whether the reception noise exceeds a predetermined threshold noise power, and includes a retransmission request unit that requests retransmission if it exceeds the threshold. Conventionally, when the noise power is very large, it is necessary to considerably increase the search radius determined in the initial stage, and as a result, it is possible to avoid the problem that the signal estimation unit requires many steps. Here, the data can be discarded, or can be estimated by the signal estimation unit by improving the quality in combination with data obtained by requesting retransmission.

  Further, in the wireless communication system of the present invention, not only the candidates are calculated to both the transmission symbol candidate calculation and transmission candidate search order determination unit and the search range update unit, but also the sorted candidates are sorted in the order closer to the center y. This makes it possible to rapidly reduce the search radius, and accordingly, it is possible to reduce the processing steps that would have been executed by the conventional method.

  By adopting the configuration and operation described below, the present invention can rapidly reduce the search radius, and accordingly, it is possible to realize a reduction in processing steps that should have been executed by the conventional method. The effect is obtained.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a wireless communication system according to an embodiment of the present invention. In FIG. 1, a wireless communication system according to an embodiment of the present invention includes a transmission device including an encoding unit 1 and a transmission antenna unit 2, and a reception device including a reception antenna unit 3 and a decoding unit 4. ing.

  In the transmission apparatus, the data sequence is input to the encoding unit 1, and the data encoded by the encoding unit 1 into M (M is a positive integer) parallel sequence is M transmission antenna units 2 (# 1 to # 1). #M), and the receiving device receives the data with N (N is a positive integer) receiving antenna units 3 (# 1 to #N), and the decoding unit 4 restores the original data series. Yes.

  FIG. 2 is a block diagram showing a configuration of the decoding unit 4 of FIG. In FIG. 2, the decoding unit 4 includes a path gain / noise power estimation unit 41, a retransmission determination / preprocessing unit 42, and a transmission data estimation unit 43.

  FIG. 3 is a flowchart showing the operation of the retransmission determination and preprocessing unit 41 of FIG. The retransmission determination and operation of the preprocessing unit 41 will be described with reference to FIGS.

  First, when a received signal vector x, a path gain matrix H, and a received SIR (Signal-to-Interference power Ratio) σ are input (INPUT) to the retransmission determination and preprocessing unit 42 (Step S1 in FIG. 3), reception is performed. SIRσ is compared with a predetermined SIR threshold σ_th to determine whether received SIRσ exceeds SIR threshold σ_th (σ> σ_th) (step S2 in FIG. 3).

  If the reception SIRσ exceeds the SIR threshold σ_th, the retransmission determination and preprocessing unit 42 makes a data retransmission request based on the compared power (step S3 in FIG. 3).

In addition, if the received SIRσ does not exceed the SIR threshold σ_th, the retransmission determination and preprocessing unit 42 performs the following three calculations (step S4 in FIG. 3), and the calculated data (d, T _m , S _m , y, Q) is output (OUTPUT) (step S5 in FIG. 3), and these data are used as an input to the transmission data estimation unit 43.

The retransmission determination and preprocessing unit 42 first obtains the search radius D from the noise power σ as the calculation in step S4. As a normal method of determining the search radius D, when the probability p that a true solution is included is set and α satisfying the above equation (3) is obtained,
Radius D = αNσ
And set. Here, N is the number of reception antennas, and σ is the reception SIR.

Next, the retransmission determination and preprocessing unit 42 sets d, T _m , and y. in this case,
d ← D ² ,
T _mm ← D ² (m = 1,..., M),
y ← (generalized inverse matrix of H) x,
S _m ← y _m
It becomes.

Finally, the retransmission determination and preprocessing unit 42 performs Cholesky decomposition on H ^H H ((Hermitian transpose of H) × H), and sets the obtained upper triangular matrix to Q. Data (d, T _m , S _m , y, Q) calculated by these calculations is output to the transmission data estimation unit 43.

  4 and 5 are flowcharts showing the operation of the transmission data estimation unit 43 in FIG. The operation of the transmission data estimation unit 43 will be described with reference to FIG. 1, FIG. 2, FIG. 4, and FIG.

First, when the data (d, T _m , S _m , y, Q) calculated by the retransmission determination and preprocessing unit 42 is input to the transmission data estimation unit 43 (step S11 in FIG. 4), the order m is set. M is set (m ← M) (step S12 in FIG. 4). Here, the order m corresponds to the transmission antenna number (m = M, M−1,..., 1) from which the symbol to be estimated is transmitted. That is, the algorithm according to the present embodiment is an algorithm that narrows down candidates in order from the transmission antenna M and finally narrows down antenna candidates.

Next, the transmission data estimation unit 43
| S _m −y _m | ≦ √T _m / q _mm
Singled out of the symbols transmitted from the transmitting antenna M satisfying the expression candidate (S _i), further y _M a distance vector is obtained by rearranging the order of increasing distance e _m, the dimension of the vector (i.e., transmission as a candidate (Number of symbols) is set to Num _m (sort e _m ← transmission candidate symbol vector after sorting, Num _m ← number of transmission candidate symbols, c _m ← 0) (step S13 in FIG. 4), and 1 is set to the transmission candidate symbol counter c _m Set (c _m ← c _m +1) (step S14 in FIG. 4). The transmission candidate symbol counter _cm is an integer in the range of 1,..., Num _m and represents the transmission symbol candidate number of the dimension currently being searched.

The transmission data estimation unit 43 determines whether or not the transmission symbol candidates in that order have been exhausted (c _m > Num _m ) (step S15 in FIG. 4), and determines that the processing has ended if it has been exhausted (m = M). (Step S22 in FIG. 5) If not exhausted, it is determined whether the order m exceeds 1 (m> 1) (Step S16 in FIG. 4).

If the order m exceeds 1, the transmission data estimation unit 43 prepares for determining a next order transmission symbol candidate (that is, a symbol transmitted by the antenna M-1).
T _i-1 ← T ₁ + | q ₁₁ (S ₁ −e _{1C i} ) | ²
S _i-1 <-r _i-1 -Σ (q _{i-1 j} / q _{i-1 i-1} ) (e _j -y _j )
i ← i-1
Such calculation is executed (step S17 in FIG. 4), and it is determined whether the remaining radius T _i-1 is a positive number (T _i-1 <0) (step S18 in FIG. 4). If the remaining radius T _i-1 is a positive number, the transmission data estimation unit 43 returns to the process of step S13 and estimates the transmission symbol of the transmission antenna M-1.

  On the other hand, the transmission data estimation unit 43 increments m by 1 (m ← m + 1) if m ≠ M in the above process end determination (step S24 in FIG. 5), and returns to step S13. If m = M, the transmission data estimation unit 43 outputs the vector f as an estimated value of the transmission symbol (OUTPUT) (step S23 in FIG. 5), and ends the process.

Further, if the order m does not exceed 1, the transmission data estimation unit 43 satisfies the vector d (with a superscript of d) ≧ d (that is, the currently calculated transmission symbol candidate is outside the current search radius). If there is (step S20 in FIG. 4), the process returns to step S14 to increment the transmission candidate symbol counter _cm .
Where the vector d is
_{d ← T M -T 1 + |} q 11 (S 1 -e 1Ci) | 2
(Step S19 in FIG. 4).

If the transmission data estimation unit 43 is vector d <d (that is, the currently calculated transmission symbol candidate is within the current search radius) (step S20 in FIG. 4),
d ← vector d,
T _M ← vector d
T _m-1 ← | q _mm S _k −e _{m, Cm} ) | ²
m = M, M−1,..., 2
f _k ← e _k ; k = 1,..., M
| S _i −y _i | ≦ √T _i / q _ii
S _i satisfying the condition is selected from the transmission alphabet, and sort e _ii <-sorted transmission candidate symbol vector and Num _i ← number of post-transmission candidate symbols are performed (step S21 in FIG. 4).

As described above, the transmission data estimation unit 43 updates the search radius based on the currently estimated candidate, determines the candidates of the respective orders based on the new radius, returns to step S14, and sets the transmission candidate symbol counter _cm . Increment.

  As described above, in this embodiment, the retransmission determination and preprocessing unit 42 determines whether or not the reception noise exceeds a predetermined threshold noise power, and if it exceeds, a retransmission request is made. When it is very large, it is necessary to considerably increase the search radius determined in the initial stage, and as a result, it is possible to avoid the problem that the transmission data estimation unit 43 requires many steps. Here, the data can be discarded, or can be estimated by the transmission data estimation unit 43 by improving the quality in combination with data obtained by requesting retransmission.

  In this embodiment, the transmission data estimation unit 43 not only calculates candidates for both transmission symbol candidate calculation, transmission candidate search order determination, and search range update, but also determines the determined candidates in order from the center y. By sorting [see FIG. 6], the search radius can be rapidly reduced, and accordingly, the processing steps that should have been executed in the conventional method can be reduced.

It is a block diagram which shows the structure of the radio | wireless communications system by one Example of this invention. It is a block diagram which shows the structure of the decoding part of FIG. It is a flowchart which shows the operation | movement of the resending determination and pre-processing part of FIG. It is a flowchart which shows operation | movement of the transmission data estimation part of FIG. It is a flowchart which shows operation | movement of the transmission data estimation part of FIG. It is a figure which shows the search order of the transmission symbol candidate by one Example of this invention. (A), (b) is a figure which shows the search order of a transmission symbol candidate. (A), (b) is a figure which shows the conventional search method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Encoding part 2 Transmission antenna part 3 Reception antenna part 4 Decoding part 41 Path gain and noise power estimation part 42 Retransmission determination and pre-processing part 43 Transmission data estimation part

Claims (12)

The transmission side apparatus encodes the data series into M (M is a positive integer) parallel series, transmits the data series from the M transmission antennas, and the reception side apparatus receives the data received by the N reception antennas as the original data. A wireless communication system for restoring a sequence,
Means for determining whether a received SIR (Signal-to-Interference power Ratio) exceeds a preset received SIR threshold, and a retransmission request is sent to the transmitting apparatus when the received SIR exceeds the received SIR threshold And means for receiving the radio communication system.   The radio communication system according to claim 1, wherein the receiving side device searches for candidates in a section where there are transmission symbol candidates from each of the transmission antennas in order of increasing distance from the center of the search radius.   The radio communication system according to claim 2, wherein when the reception SIR threshold is not exceeded, the search radius is calculated to search for a candidate in a section where the transmission symbol candidate exists.   4. The wireless communication system according to claim 1, wherein the wireless communication system is a MIMO (Multiple Input Multiple Output) communication system. The transmission side apparatus encodes the data series into M (M is a positive integer) parallel series, transmits the data series from the M transmission antennas, and the reception side apparatus receives the data received by the N reception antennas as the original data. A decoding device for restoring data received by the receiving antenna to an original data sequence in a system for restoring to a sequence,
Means for determining whether a received SIR (Signal-to-Interference power Ratio) exceeds a preset received SIR threshold, and a retransmission request is sent to the transmitting apparatus when the received SIR exceeds the received SIR threshold A decoding device.   6. The decoding apparatus according to claim 5, wherein candidates in a section in which there are transmission symbol candidates from each of the transmission antennas are searched in order of increasing distance from the center of the search radius.   The decoding apparatus according to claim 6, wherein when the reception SIR threshold is not exceeded, the search radius is calculated to search for a candidate in a section where the transmission symbol candidate exists.   8. The decoding apparatus according to claim 5, wherein the system is a MIMO (Multiple Input Multiple Output) communication system.   The transmission side apparatus encodes the data series into M (M is a positive integer) parallel series, transmits the data series from the M transmission antennas, and the reception side apparatus receives the data received by the N reception antennas as the original data. A method of decoding used in a wireless communication system for restoring to a sequence, comprising: determining whether a reception SIR (Signal-to-Interference power Ratio) exceeds a preset reception SIR threshold on the receiving side device; And a step of sending a retransmission request to the transmission side apparatus when the reception SIR exceeds the reception SIR threshold.   The decoding method according to claim 9, wherein the receiving side device searches for candidates in a section where there are transmission symbol candidates from each of the transmission antennas in order of increasing distance from the center of the search radius.   11. The decoding method according to claim 10, wherein when the reception SIR threshold is not exceeded, the search radius is calculated to search for a candidate in a section where the transmission symbol candidate exists. The decoding method according to claim 9, wherein the wireless communication system is a MIMO (Multiple Input Multiple Output) communication system.

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