JP2011004142A - Receiver and receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver and a receiving method, which have successful characteristics even when noise enhancement occurs in linear detection and efficiently calculate a bit LLR (Log Likelihood Ratio) in an MIMO (Multiple Input Multiple Output) transmission system.SOLUTION: A signal detection part 203 detects separation of spatially multiplexed signals using a received signal and a propagation path estimated value estimated by a propagation path estimation part 204, and obtains coded bits LLR by making an inversion bit sequence remain in transmission signal candidates. The coded bits LLR, which are obtained by the signal detection part 203, are input in decoding parts 206-1 to 206-T by returning rearrangement performed in interleaver parts 103-1 to 103-T on the transmitting side by deinterleaver parts 205-1 to 205-T. In the decoding parts 206-1 to 206-T, error correction decoding is performed on the input coded bits. Parallel/serial conversion is performed on the bit sequence after the error correction decoding by a parallel/serial conversion part 207, and a transmission bit sequence is output.

Description

  The present invention relates to a receiving apparatus and a receiving method for receiving a signal by a MIMO transmission method.

  In a wireless communication such as a cellular phone system, MIMO (Multiple Input Multiple Output) transmission that performs spatial multiplexing transmission using a plurality of transmission / reception antennas is known as a technique for increasing a transmission speed without expanding a frequency band.

Since MIMO transmission performs spatial multiplexing transmission, it is necessary to perform MIMO signal detection in the receiving apparatus. MLD (Maximum Likelihood Detection) is known as an optimum method among MIMO signal detection methods. However, MLD is a method for detecting the most suitable one among all transmission signal candidates, and the amount of calculation becomes large. For example, if the number of transmission antennas is T and the number of modulation constellations is M, the number of transmission signal candidates is M ^T , which increases exponentially as the number of antennas and the number of modulation multilevels increase. For this reason, it is important to efficiently reduce the amount of calculation, that is, the number of transmission signal candidates, without significantly degrading the characteristics from the MLD. Examples of the MLD in which the amount of calculation is reduced include sphere decoding (Sphere Decoding), M algorithm, QRM (QR decomposition and M algorithm) -MLD, and the like.

  In general, a communication system performs error correction coding to improve communication reliability. Soft decision error correction decoding is known as high-performance error correction decoding. Soft decision error correction decoding performs error correction decoding on a bit LLR (Log Likelihood Ratio). The bit LLR in the maximum likelihood sequence obtained by MLD is obtained from the metric in the maximum likelihood sequence and its inverted bit sequence. However, since the MLD with the reduced amount of computation as described above reduces the number of transmission signal candidates, there is a possibility that the inverted bit sequence does not remain in the transmission signal candidate, and there is a problem that the bit LLR cannot be calculated.

  Non-Patent Document 1, which will be described later, describes a computational complexity reduction type MLD that takes into account the calculation of the bit LLR. The method is a method of obtaining a transmission signal candidate by performing a one-dimensional search in a direction in which noise is emphasized from an MMSE reception point obtained by detecting the received signal by MMSE (Minimum Mean Square Error). In the following equation (1) showing the component (vector P) in which noise is emphasized at the MMSE reception point, the eigenvector direction of a large eigenvalue is set as the noise enhancement direction.

Here, H is a channel matrix, I is a unit matrix, and σ ² is variance.

  Also, by searching in the direction of a plurality of eigenvectors from the one with the larger eigenvalue, the inverted bit sequence remains in the candidate, and the bit LLR can be obtained with high accuracy while reducing the amount of MLD computation.

Tsuji, Fukawa and Suzuki, “Bitstream Log Likelihood Ratio Calculation Algorithm in Coded MIMO-OFDM Suboptimal Detection”, IEICE Technical Report, RCS2007-232, March 2008.

  However, since Non-Patent Document 1 is a one-dimensional search, for example, when noise enhancement occurs in a plurality of directions, there is a problem that reception performance deteriorates. In addition, in order to calculate the bit LLR, it is necessary to search in a plurality of directions instead of one direction, and there is a problem that the number of transmission signal candidates increases.

  The present invention has been made in view of such circumstances, and an object of the present invention is to obtain good characteristics even in the presence of a plurality of noise enhancement components in the MIMO transmission system, and to efficiently generate the bit LLR. It is an object of the present invention to provide a receiving device and a receiving method that can be calculated.

The present invention is a receiving device for receiving a transmission signal transmitted from a transmitting device in a MIMO transmission method,
A propagation path estimator that performs propagation path estimation using the received signal and obtains a propagation path estimated value; and a signal detection section that generates a bit log likelihood ratio by performing MIMO separation on the received signal based on the transmission path estimated value; A decoding unit that performs error correction decoding on the bit log likelihood ratio,
The signal detection unit multiplies the received signal by a weight calculated from the transmission path estimation value to generate an initial signal, and noise is amplified from the propagation path estimation value and the initial signal. An update value calculation unit that obtains an update value in consideration of a plurality of directions, an addition unit that adds the initial signal and the update value, and a signal that is added by the addition unit are hard-decided to generate a transmission signal candidate A hard decision unit, a metric generation unit that calculates a metric from the transmission signal candidate, and a likelihood calculation unit that generates a bit log likelihood ratio of a maximum likelihood sequence from the metric. is there.

  Here, the update value calculation unit obtains the update value so that an inverted bit sequence of the maximum likelihood sequence remains in the transmission signal candidate.

  Further, the update value calculation unit obtains a singular value from the propagation path estimated value, and obtains the update value from the singular value so that the initial signal becomes a different modulation symbol point.

  Further, the update value calculation unit obtains an eigenvalue and an eigenvector from the propagation path estimation value, and obtains the update value from the eigenvalue and the eigenvector so that the initial signal becomes a different modulation symbol point.

  In particular, the update value calculation unit obtains the update value from only eigenvalues greater than a certain threshold and eigenvectors of eigenvalues greater than or equal to the threshold among the eigenvalues. Here, the threshold value is noise power.

Further, the present invention is a receiving device that receives a transmission signal transmitted from a transmitting device in a MIMO transmission method,
A propagation path estimator that performs propagation path estimation using the received signal and obtains a propagation path estimated value; and a signal detection section that generates a bit log likelihood ratio by performing MIMO separation on the received signal based on the transmission path estimated value; A decoding unit that performs error correction decoding on the bit log likelihood ratio,
The signal detection unit multiplies the received signal by a weight calculated from the transmission path estimation value to generate an initial signal, and noise is amplified from the propagation path estimation value and the initial signal. An update value calculation unit for obtaining an update value in consideration of a plurality of directions, an addition unit for adding the initial signal and the update value, and a signal output from the addition unit are hard-decided to generate a transmission signal candidate A hard decision unit; a metric generation unit that calculates a metric from the transmission signal candidate; and a likelihood calculation unit that generates a bit log likelihood ratio of a maximum likelihood sequence from the bit log likelihood ratio output from the metric and the decoding unit These are provided.

  Here, the initial signal generation unit generates an initial signal from a bit log likelihood ratio output from the decoding unit.

  Further, the update value calculation unit obtains the update value so that an inverted bit sequence of the maximum likelihood sequence remains in the transmission signal candidate.

  Further, the update value calculation unit obtains an eigenvalue and an eigenvector from the propagation path estimation value, and obtains the update value from the eigenvalue and the eigenvector so that the initial signal becomes a different modulation symbol point.

  Further, the update value calculation unit obtains the update value from only eigenvalues greater than a certain threshold and eigenvectors of eigenvalues greater than or equal to the threshold among the eigenvalues.

Further, the present invention is a receiving method in a receiving apparatus that receives a transmission signal transmitted from a transmitting apparatus in a MIMO transmission method,
A propagation path estimation step for performing propagation path estimation using the received signal and obtaining a propagation path estimation value; and a signal detection step for generating a bit log likelihood ratio by MIMO separation of the reception signal based on the transmission path estimation value; Performing error correction decoding on the bit log likelihood ratio,
The signal detection step includes an initial signal generation step of generating an initial signal by multiplying the received signal by a weight calculated from the transmission path estimation value, and noise is amplified from the propagation path estimation value and the initial signal. An update value calculation step for obtaining an update value in consideration of a plurality of directions, an addition step for adding the initial signal and the update value, a hard decision on the signal added in the addition step, and a transmission signal candidate A hard decision step for generating, a metric generation step for calculating a metric from the transmission signal candidate, and a likelihood calculation step for generating a bit log likelihood ratio of a maximum likelihood sequence from the metric. It is.

Further, the present invention is a receiving method in a receiving apparatus that receives a transmission signal transmitted from a transmitting apparatus in a MIMO transmission method,
A channel estimation step for performing channel estimation using a received signal and obtaining a channel estimation value, a signal detection step for generating a bit log likelihood ratio by MIMO separation of the received signal, and the bit log likelihood ratio A decoding step for performing error correction decoding on
The signal detection step includes an initial signal generation step of generating an initial signal by multiplying the received signal by a weight calculated from the transmission path estimation value, and noise is amplified from the propagation path estimation value and the initial signal. An update value calculation step for obtaining an update value in consideration of a plurality of directions, an addition step for adding the initial signal and the update value, and a signal output from the addition step are hard-decided to generate a transmission signal candidate A hard decision step, a metric generation step for calculating a metric from the transmission signal candidate, and a likelihood calculation step for generating a bit log likelihood ratio of the maximum likelihood sequence from the bit log likelihood ratio output by the metric and the decoding step And.
The signal detecting step and the decoding step are repeatedly performed.

  According to the present invention, an initial signal is generated by multiplying a received signal by a weight calculated from a transmission path estimation value, and a plurality of directions in which noise is amplified are considered from the propagation path estimation value and the initial signal. An update value is obtained, and the initial signal and the update value are added and a hard decision is made to generate a transmission signal candidate, and a metric is calculated from the transmission signal candidate to generate a bit log likelihood ratio of the maximum likelihood sequence Therefore, the total number of transmission signal candidates is reduced, and the maximum likelihood sequence can be obtained efficiently. In addition, by considering a plurality of noise enhancement components, a multidimensional search becomes possible, and the direction in which the reception performance is deteriorated is obtained more accurately, so that the accuracy of searching for transmission signal candidates is improved. In the present invention, the inverted bit sequence can remain in the transmission signal candidate in one search.

  Further, according to the present invention, the performance can be further improved by using the error correction decoding result by the decoding unit and repeatedly performing error correction decoding and MIMO separation.

  Further, according to the present invention, since the update value is obtained so that the inverted bit sequence of the maximum likelihood sequence remains in the transmission signal candidate, the inverted bit sequence always remains in the transmission signal candidate. It is possible to calculate the bit log likelihood ratio of the likelihood sequence.

It is a block diagram which shows the structure of the transmitter in 1st Embodiment. It is a block diagram which shows the structure of the receiver in 1st Embodiment. It is a block diagram which shows the structure of the signal detection part in 1st Embodiment. It is a flowchart of the reception process in 1st Embodiment. It is a block diagram which shows the structure of the receiver in 3rd Embodiment. It is a block diagram which shows the structure of the signal detection part in 3rd Embodiment. It is a flowchart of the reception process in 3rd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Unless otherwise specified, the following embodiment describes a MIMO scheme in which different data are transmitted from T transmission antennas and received by R reception antennas. However, T and R are integers of 2 or more.

(First embodiment)
The MIMO transmission apparatus and reception apparatus according to the first embodiment of the present invention will be described below.

  FIG. 1 is a block diagram illustrating a configuration of a transmission apparatus according to the first embodiment. Transmitting apparatus 100 includes serial-to-parallel converter 101, encoding units 102-1 to 102-T, interleavers 103-1 to 103-T, modulating units 104-1 to 104-T, and transmitting units 105-1 to 105. -T, comprising transmission antenna units 106-1 to 106-T. The transmission bits are serial-parallel converted by the serial-parallel converter 101 and divided into T bit sequences. The bit sequence is subjected to error correction coding such as a convolutional code or a turbo code by the coding units 102-1 to 102-T. The coded bits are interleaved by interleavers 103-1 to 103-T, mapped to modulated signals by modulators 104-1 to 104-T, converted to radio frequencies by transmitters 105-1 to 105-T, Each is transmitted from the corresponding transmitting antenna 106-1 to 106-T.

  FIG. 2 is a block diagram showing a configuration of the receiving apparatus according to the first embodiment. Receiving apparatus 200 includes receiving antennas 201-1 to 201-R, receiving units 202-1 to 202-R, signal detecting unit 203, propagation path estimating unit 204, deinterleaver units 205-1 to 205-T, and decoding unit. 206-1 to 206-T and the parallel-serial converter 207. The signals transmitted from the transmission apparatus 100 are received by the reception antennas 201-1 to 201-R, converted from radio frequencies to baseband signals by the corresponding reception units 202-1 to 202-R, and received signals. Is output as The signal detection unit 203 uses the received signal and the propagation path estimation value estimated by the propagation path estimation unit 204 to perform separation detection of the spatially multiplexed signal and obtain the encoded bit LLR. The encoded bit LLR obtained by the signal detection unit 203 returns the rearrangement performed by the deinterleaver units 103-1 to 103-T at the deinterleaver units 205-1 to 205-T, The data is input to the decoding units 206-1 to 206-T. Decoding sections 206-1 to 206-T perform error correction decoding on the input coded bits. The bit sequence after error correction decoding is parallel-serial converted by the parallel-serial conversion unit 207, and a transmission bit sequence is output.

  FIG. 3 is a block diagram illustrating a configuration of the signal detection unit 203. The signal detection unit 203 includes a transmission signal candidate generation unit 300, a metric generation unit 305, and a likelihood calculation unit 306. The transmission signal candidate generation unit 300 includes an initial signal generation unit 301, addition units 302-1 to 302-T, hard decision units 303-1 to 303-T, and an update value calculation unit 304. Transmission signal candidate generation section 300 generates a transmission signal candidate for calculating a metric from the reception signal input from reception sections 202-1 to 202-R and the propagation path estimation value input from propagation path estimation section 204. The transmission signal candidate generation unit 300 uses the initial signal generation unit 301 to generate an initial signal, which is the first MIMO separation signal, using weights such as a ZF (Zero forcing) criterion and an MMSE (Minimum Mean Square Error) criterion. The update value calculation unit 304 obtains an update value for the initial signal from the initial signal and the propagation path estimation value. Adders 302-1 to 302-T add the updated value to the initial signal. The updated initial signal is hard-decided to the closest modulation symbol by the hard-decision units 303-1 to 303-T, and a transmission signal candidate is generated. The processing of the transmission signal candidate generation unit 300 will be described in detail using mathematical expressions.

  A received signal at a certain time is expressed as follows.

  Here, y is an R-dimensional received signal vector, H is a R-row T-column propagation path matrix, s is a T-dimensional transmission signal vector, and n is an R-dimensional noise vector. First, in order to generate an initial signal from a received signal, for example, the following MMSE weight W can be used.

P is a noise enhancement component, σ ² is variance, and I is a unit matrix of T rows and T columns.

Expression (3) can be approximated as the following expression (6) when σ _n ² << 1.

Further, when the expressions PH, ^HH in X ^ when the expressions (2), (4), (5) are substituted into the expression (3) are approximated by an average value, they can be expressed as the following expression (7). it can.

Furthermore, given the following equation (8):

  Expression (3) can be approximated as the following expression (9).

  From the equations (6) and (9), the transmission signal s can be expressed as the following equation (10).

However, α = 1 or 1 + σ _n ² .

The initial signal generation unit 301 generates αX ^ as an initial signal. That is, the transmission signal s is at a position shifted by -αPH ^H n from the initial signal αX ^. Therefore, the update value calculation unit 304 obtains -αPH ^H n as the update value.

Details of how to determine -αPH ^H n will be described. The singular value decomposition of the propagation path matrix H can be expressed as the following equation.

Incidentally, each of the U and V _{N R} rows _{N R} column, a unitary matrix of _{N T} rows _{N T} columns, expressed by the following equation.

However, u _l (1 ≦ l ≦ N _R ) and v _k (1 ≦ k ≦ N _T ) are complex vectors of N _R dimension and N _T dimension, respectively. Σ is a matrix of N _R rows and N _T columns having singular values as diagonal elements, and can be expressed as the following equation when the rank of H is W (≦ min (N _R , N _T )).

However, 0 <λ ₁ ^1/2 <λ ₂ ^1/2 <... <Λ _W ^1/2 , and diag () represents a diagonal matrix.

Using formula (11), -PH ^H n can be transformed as follows.

It may be determined to _{a w} in order to determine the -αPH ^H n. The _aw candidate a ^ _w is obtained as follows. First, let S ^ be the result of a hard decision on αX ^. Let b (r) be a modulation symbol point different from the k-th element of S ^. When the k-th element of S is b (r), it can be expressed as follows.

In order to search for a point having a small distance from the initial signal, that is, a noise enhancement amount, A that satisfies Equation (20) and minimizes A ^H A is obtained. This can be obtained, for example, by using the Lagrange's undetermined multiplier method, as shown in the following equation (24).

After obtaining A as in Expression (24), an updated value is obtained from Expression (16) and α (processing of the updated value calculation unit 304), and is substituted into the right side of Expression (10) (adding unit 302). -1 to 302-T), hard decision can be made and new signal candidates can be obtained (processing of hard decision units 303-1 to 303-T). Note that the number of transmission signal candidates is determined by the number of b (r), and b (r) is a modulation symbol point different from the k-th element of S ^, so the number is (M-1) T. However, M represents the modulation multi-level number. For example, M = 4 in the case of QPSK, and M = 16 in the case of 16QAM. Further, 1 ≦ k ≦ T. The total number of the transmitted signal candidate hard decision value also include the initial signal becomes (M-1) T + 1 carbon atoms, can be greatly reduced is the number of candidates when compared with M ^T number of conventional MLD. Also, since b (r) is a modulation symbol point different from the k-th element of S ^, all modulation symbol points are present in the k-th element of the transmission signal candidate, so that the inverted bit sequence of the maximum likelihood sequence is always present. The bit LLR can be obtained with high accuracy remaining in the candidate.

When obtaining a candidate for a _w as in equation (24), eigenvalues λ ₁ , λ ₂ ,..., Λ _W obtained by eigenvalue decomposition of H ^H H, not singular value decomposition of H, and the eigenvectors _{v 1,} v 2 to the respective eigenvalue, · · ·, _{v W} may be determined using. Further, it is not always necessary to use all eigenvalues (or singular values), and only some eigenvalues (or singular values) can be used. For selection of some eigenvalues, eigenvalues equal to or higher than a threshold, such as noise power, may be selected.

  In addition, with regard to the accuracy for obtaining the maximum likelihood sequence, the conventional technique searches for a transmission signal candidate in the eigenvector direction of the maximum eigenvalue of a component that degrades reception performance, such as noise enhancement, but in the present invention, a plurality of eigenvalues and eigenvectors are considered. And searching for transmission signal candidates. For this reason, in the prior art, only a one-dimensional search can be performed. However, in the present invention, a multi-dimensional search is possible, and a direction in which reception performance is deteriorated is obtained more accurately. The search accuracy is improved. Also, when obtaining the bit LLR, in the conventional technique, the one-dimensional search is performed a plurality of times so that the inverted bit sequence remains in the transmission signal candidate. However, in the present invention, the inverted bit sequence is performed by one search. Can remain as transmission signal candidates.

  After the transmission signal candidate is generated by the transmission signal candidate generation unit 300, the metric generation unit 305 generates a metric from the transmission signal candidate as shown in Equation (15), and the likelihood calculation unit 306 as shown in Equation (26). Bit LLR is calculated.

Here, λ _{k, n} represents the n-th bit LLR of the modulation symbol transmitted from the k-th transmission antenna. S _b represents a transmission signal candidate defined by b = [b _1,1 ,..., B _{k, n} ,..., B _{T, N} ]. b ⁺ represents a set of b _where b _{k, n} = 1, and b ⁺ = [b _1,1 ,..., b _{k, n} = 1,..., b _{T, N} ]. b ⁻ represents a set of b b _{, n} = 0 in b, and b ⁻ = [b _1,1 ,..., b _{k, n} = 0,..., b _{T, N} ]. Thus, lambda _{k, n} is obtained by the difference between the minimum metric is generated using the minimum metric and b ^over generated using the b ^+.

  FIG. 4 is a flowchart of the reception process in the first embodiment. In step s401, the signal transmitted from the transmission apparatus 100 is received by the reception antennas 201-1 to 201-R, and the initial signal generation unit 301 of the signal detection unit 203 uses the received signal as an initial signal, for example, MIMO by MMSE. A separated signal is generated. In step s402, the update value calculation unit 304 generates an update value from the initial signal in a direction in which reception performance such as noise enhancement deteriorates. In step s403, the addition units 302-1 to 302-T add the updated value to the initial signal, and the hard decision units 303-1 to 303-T make a hard decision to generate transmission signal candidates. In step s404, the metric generation unit 305 calculates the metric of the transmission signal candidate. In step s405, the likelihood calculating unit 306 obtains the bit LLR of the maximum likelihood sequence from the metric obtained in step s404. In step s406, the bit LLR output from the signal detection unit 203 is subjected to the rearrangement performed by the deinterleaver units 205-1 to 205-T in the transmission side interleaver units 103-1 to 103-T. The error correction decoding is performed on the encoded bits input by the decoding units 206-1 to 206-T. Then, the parallel / serial conversion unit 207 performs parallel / serial conversion on the bit sequence after error correction decoding, and outputs a transmission bit sequence.

  As described above, in the first embodiment, it is possible to calculate the bit LLR with high accuracy while realizing the MLD with a low calculation amount.

(Second Embodiment)
The present embodiment searches for transmission signal candidates by a method different from the first embodiment. The receiving apparatus according to this embodiment can be described with reference to FIGS. 2 and 3 as in the first embodiment. Since the difference from the first embodiment is the processing content of the update value calculation unit 304 in FIG. 3, only the update value calculation unit 304 will be described in this embodiment.

Expression (3) can be expanded as the following expression.

  Using the fact that P is a Hermitian matrix, the equation (27) becomes the following equation (28).

  Therefore, s can be expressed as the following equation (29).

However, n is a T-dimensional vector, and each element is a Gaussian variable having an average of 0 and a variance σ _n ² . Therefore, in order to obtain s, it is only necessary to know P ^1/2 n ^˜ , and the update value calculation unit 304 of the present embodiment obtains P ^1/2 n ^˜ .

  Substituting equation (11) into P yields the following equation (30).

Therefore, P1 ^{/ 2} is obtained as in the following equation (31).

Here ^{D ~} is the following formula (32).

Additionally, it expressed as ^{D ~} again following formula (33).

Here, ν _k is the following equation (34).

Using equation ^{(31), P} 1/2 ^{n ~} can be expressed by the following equation (35).

  Here, a is the following equation (36).

a is a T-dimensional vector. Average n Each element of ^~ is 0, because it is a Gaussian variable of variance sigma _n ^{2, n ~} of the probability density function p ^{(n ~)} is given by the following equation (37).

  Since V is a unitary matrix, the probability density function p (a) of a is as shown in the following equation (38).

If a _k is the k-th element of a, P ^1/2 n ^˜ can be expressed as the following equation (39).

  Therefore, s becomes the following equation (40).

  Let s ^ be the result of hard decision on X ^. Let b (r) be a modulation symbol point different from the k-th element of s ^. When the k-th element of s is b (r), it can be expressed as the following equation (41).

Expression (41) can be expressed as a following expression (42) in a vector format.

Here, C ^H is the following equation (43).

  Since p (a) is given by equation (38), the likelihood estimation of a can be solved by the Lagrange multiplier undetermined multiplier method. Therefore, a that minimizes f (a) in the following equation (44) may be obtained.

  Where λ is a complex Lagrange multiplier. Solving this and obtaining the desired a results in the following equation (45).

  The obtained a is substituted into the second term on the right side of the equation (40) to obtain an update value (processing of the update value calculation unit 304), and the right side of the equation (40) is calculated (addition units 302-1 to 302-). T process), a hard decision can be made and new transmission signal candidates can be obtained (the process of hard decision units 303-1 to 303-T). Similar to the first embodiment, the number of transmission signal candidates is determined by the number of b (r). Therefore, including the hard decision value of the initial signal, the total number of transmission signal candidates is (M−1) T + 1.

In the first embodiment, since σ _n ² << 1, that is, the signal-to-noise power ratio is high, the search accuracy of transmission signal candidates deteriorates when the signal-to-noise power ratio is low. In the present embodiment, search for transmission signal candidates is performed in consideration of noise power, so that the search accuracy can be improved as compared with the first embodiment.

(Third embodiment)
In the third embodiment, a receiving apparatus that repeatedly performs MLD using a result of error correction decoding will be described. The transmission apparatus for transmitting a signal is the same as that in FIG.

  FIG. 5 is a block diagram illustrating a configuration of a receiving device according to the third embodiment. Reception apparatus 500 includes reception antennas 501-1 to 501-R, reception units 502-1 to 502-R, signal detection unit 503, propagation path estimation unit 504, deinterleaver units 505-1 to 505-T, and decoding unit. 506-1 to 506-T and a parallel-serial converter 507. The signals transmitted from the transmission apparatus 100 are received by the receiving antennas 501-1 to 501-R, converted from radio frequencies to baseband signals by the corresponding receiving units 502-1 to 502-R, respectively, and received signals Is output as The signal detection unit 503 uses the received signal and the propagation path estimation value estimated by the propagation path estimation unit 504 to separate spatially multiplexed signals to obtain the encoded bit LLR. The coded bit LLR obtained by the signal detection unit 503 is deinterleaved by the deinterleaver units 505-1 to 505-T, and reverse processing of the interleaving performed on the transmission side is performed and input to the decoding units 506-1 to 506-T. The Decoding sections 506-1 to 506-T perform error correction decoding on the input coded bits. The bit sequence after error correction decoding is parallel-serial converted by the parallel-serial converter 507, and a transmission bit sequence is output.

  FIG. 6 is a block diagram illustrating a configuration of the signal detection unit 503. The signal detection unit 503 includes a transmission signal candidate generation unit 600, a metric generation unit 605, and a likelihood calculation unit 606. The transmission signal candidate generation unit 600 includes an initial signal generation unit 601, addition units 602-1 to 602-T, hard decision units 603-1 to 603-T, and an update value calculation unit 604. The transmission signal candidate generation unit 600 receives the received signal input from the receiving units 502-1 to 502-R, the propagation path estimation value input from the propagation path estimation unit 504, and the decoding units 506-1 to 506-T. The transmission signal candidate is generated from the bit LLR. The metric generation unit 605 generates a transmission signal candidate metric. The likelihood calculating unit 606 calculates the bit LLR of the maximum likelihood sequence using the metric of the transmission signal candidate and the bit LLR obtained from the decoding units 506-1 to 506-T. Transmission signal candidate generation section 600 first generates an initial signal using received signal or bit LLR in initial signal generation section 601. In the case of generating from reception signals input from the reception units 502-1 to 502-R, for example, the reception signals may be separated by MIMO using the MMSE weight as described in the first embodiment. When generating from the bit LLR input from the decoding units 506-1 to 506-T, a symbol replica that is a replica of the modulation symbol can be generated from the bit LLR and used as an initial signal.

An explanation will be given by taking QPSK modulation as an example. If the bits constituting the QPSK symbol are b ₁ and b ₂ , the symbol replica can be expressed as follows.

  λ () represents a bit LLR, and tanh represents a hyperbolic tangent function.

  The update value calculation unit 604 obtains an update value from the initial signal and the propagation path estimated value by the same method as in the first embodiment. The adders 602-1 to 602-T add the initial signal and the updated value, the hard decision units 603-1 to 603-T make a hard decision to obtain the nearest decision point, perform parallel-serial conversion, and select the transmission signal candidate. Output. The metric generation unit 605 generates a transmission signal candidate metric, and the likelihood calculation unit 606 obtains a bit LLR as shown in the following equation (47).

Note that p (b _{k, n} ) represents the occurrence probability of b _{k, n} . Further, b ⁺ and b ⁻ are sets in which b _{k, n} = 1 and b _{k, n} = 0 respectively in b as described above. Therefore, log p (b _{k ′, n ′} ) in the equation (47) calculates log p (b _{k ′, n ′} = 1) or log p (b _{k ′, n ′} = 0). . λ ^to _{k, n} represent the LLR corresponding to the nth modulation bit of the coded bit LLR output from the decoding unit 506-k.

  As an approximate expression of Expression (47), the coded bit LLR may be obtained from Expression (48).

  FIG. 7 is a flowchart of the reception process in the third embodiment. In step s701, the initial signal generator 601 of the signal detector 503 generates an initial signal. If error correction decoding processing has never been performed, the received signals received by the receiving units 502-1 to 502-R are separated using MMSE weights to generate an initial signal. When the error correction decoding process is performed, an initial signal is generated by generating a symbol replica from the coded bit LLR obtained by the decoding process of the decoding units 506-1 to 506-T. In step s702, the update value calculation unit 604 generates an update value from the initial signal in a direction in which reception performance such as noise enhancement deteriorates. In step s703, the update value is added to the initial signal, and a hard decision is made to generate a transmission signal candidate. In step s704, the metric generation unit 605 generates a metric for the obtained transmission signal candidate. In step s705, the coded bit LLR is calculated from the metric obtained by the likelihood calculation unit 606. In step s706, the reordering performed by the deinterleaver units 505-1 to 505-T in the transmission interleaver units 103-1 to 103-T is performed on the bit LLR output from the signal detection unit 503. Then, error correction decoding is performed on the coded bits input by the decoding units 506-1 to 506-T. Then, the parallel / serial conversion unit 207 performs parallel / serial conversion on the bit sequence after error correction decoding, and outputs a transmission bit sequence.

  In step s707, it is determined whether the signal detection unit 503 has performed a predetermined number of decoding processes, or whether an error has been detected in the decoding result, and the predetermined number of processes have been performed, or an error has been detected. If not, information bits are output and the reception process is terminated. If the predetermined number of times of processing has not been performed and an error has been detected, the processing of steps s701 to s706 is performed again. Whether or not there is an error in the decoding result may be detected using an error detection code such as CRC (Cyclic Redundancy Check).

  As described above, in the third embodiment, the low-computation-type MLD is repeatedly performed using the error correction decoding result. By repeatedly performing MLD, the MIMO separation performance can be further improved.

  In the third embodiment, the channel estimation value can be updated using the error correction decoding result. In this case, propagation path estimation accuracy is improved, and transmission signal candidate search accuracy is improved.

  In the above embodiment, the case of narrowband single carrier MIMO has been described. However, the present invention is not limited to this, and all systems capable of MLD such as MIMO-OFDM (Orthogonal Frequency Division Multiplexing) which is multicarrier transmission are used. Can be applied to.

  In the above embodiment, error correction coding is performed after the transmission bits are spatially divided. However, the present invention is not limited to this, and the case where the transmission bits are subjected to error correction coding, interleaving, and then space division is performed. Is also applicable.

  In the above-described embodiment, different data is transmitted by each transmission antenna. However, the present invention is not limited to this, and a plurality of transmission antennas are used and a plurality of different data less than the number of transmission antennas is transmitted. But it can be applied.

DESCRIPTION OF SYMBOLS 100 Transmission apparatus 101 Serial / parallel conversion part 102-1 to 102-T Encoding part 103-1 to 103-T Interleaver part 104-1 to 104-T Modulation part 105-1 to 105-T Transmission part 106-1 106-T transmitting antenna unit 200 receiving apparatus 201-1 to 201-R receiving antenna 202-1 to 202-R receiving unit 203 signal detecting unit 204 propagation path estimating unit 205-1 to 205-T deinterleaver unit 206-1 ˜206-T decoding unit 207 parallel-serial conversion unit 300 transmission signal candidate generation unit 301 initial signal generation unit 302-1 to 302-T addition unit 303-1 to 303-T hard decision unit 304 update value calculation unit 305 metric generation unit 306 Likelihood calculation unit 500 receiving apparatus 501-1 to 501-R receiving antenna 502-1 to 502-R receiving unit 503 signal detecting unit 504 propagation Estimator 505-1 to 505-T Deinterleaver 506-1 to 505-T Decoder 507 Parallel / serial converter 600 Transmission signal candidate generator 601 Initial signal generator 602-1 to 602-T Adder 603-1 ˜603-T Hard decision unit 604 Update value calculation unit 605 Metric generation unit 606 Likelihood calculation unit

Claims (15)

A receiving device that receives a transmission signal transmitted from a transmitting device in a MIMO transmission scheme,
A channel estimation unit that performs channel estimation using the received signal and obtains a channel estimation value;
A signal detection unit for generating a bit log likelihood ratio by MIMO-separating the received signal based on the transmission path estimation value;
A decoding unit that performs error correction decoding on the bit log likelihood ratio;
With
The signal detector is
An initial signal generation unit for generating an initial signal by multiplying the received signal by a weight calculated from the transmission path estimation value;
From the propagation path estimated value and the initial signal, an update value calculation unit for obtaining an update value in consideration of a plurality of directions in which noise is amplified,
An adder for adding the initial signal and the updated value;
A hard decision unit that makes a hard decision on the signal added by the addition unit and generates a transmission signal candidate;
A metric generator for calculating a metric from the transmission signal candidates;
A likelihood calculator that generates a bit-log-likelihood ratio of the maximum likelihood sequence from the metric;
A receiving apparatus comprising: The update value calculator is
The receiving apparatus according to claim 1, wherein the update value is obtained so that an inverted bit sequence of the maximum likelihood sequence remains in the transmission signal candidate. The update value calculator is
The receiving apparatus according to claim 2, wherein a singular value is obtained from the propagation path estimated value, and the update value is obtained from the singular value so that the initial signal becomes a different modulation symbol point. The update value calculator is
The receiving apparatus according to claim 3, wherein the update value is obtained only from a singular value equal to or greater than a certain threshold among the singular values. The update value calculator is
5. The receiving apparatus according to claim 4, wherein an eigenvalue and an eigenvector are obtained from the propagation path estimation value, and the update value is obtained from the eigenvalue and the eigenvector so that the initial signal becomes a different modulation symbol point. The update value calculator is
The receiving apparatus according to claim 2, wherein the update value is obtained only from eigenvalues greater than or equal to a certain threshold among the eigenvalues and eigenvectors of eigenvalues greater than or equal to the threshold.   The receiving apparatus according to claim 4, wherein the threshold value is noise power. A receiving device that receives a transmission signal transmitted from a transmitting device in a MIMO transmission scheme,
A channel estimation unit that performs channel estimation using the received signal and obtains a channel estimation value;
A signal detection unit for generating a bit log likelihood ratio by MIMO-separating the received signal;
A decoding unit that performs error correction decoding on the bit log likelihood ratio;
With
The signal detector is
An initial signal generation unit for generating an initial signal by multiplying the received signal by a weight calculated from the transmission path estimation value;
From the propagation path estimated value and the initial signal, an update value calculation unit for obtaining an update value in consideration of a plurality of directions in which noise is amplified,
An adder for adding the initial signal and the updated value;
A hard decision unit for making a hard decision on a signal output from the addition unit and generating a transmission signal candidate;
A metric generator for calculating a metric from the transmission signal candidates;
A likelihood calculating unit that generates a bit log likelihood ratio of a maximum likelihood sequence from the metric and the bit log likelihood ratio output by the decoding unit;
A receiving apparatus comprising: The initial signal generator is
The receiving apparatus according to claim 7, wherein an initial signal is generated from a bit log likelihood ratio output by the decoding unit. The update value calculator is
The receiving apparatus according to claim 7, wherein the update value is obtained so that an inverted bit sequence of the maximum likelihood sequence remains in the transmission signal candidate. The update value calculator is
9. The eigenvalue and eigenvector are obtained from the propagation path estimated value, and the update value is obtained from the eigenvalue and eigenvector so that the initial signal becomes a different modulation symbol point. Receiver device. The update value calculator is
The receiving apparatus according to claim 11, wherein the update value is obtained only from eigenvalues greater than a certain threshold and eigenvectors of eigenvalues greater than or equal to the threshold among the eigenvalues. A receiving method in a receiving apparatus for receiving a transmission signal transmitted from a transmitting apparatus in a MIMO transmission method,
A channel estimation step for performing channel estimation using the received signal and obtaining a channel estimation value;
A signal detection step of generating a bit log likelihood ratio by MIMO-separating the received signal based on the transmission path estimation value;
Performing error correction decoding on the bit log likelihood ratio;
With
The signal detection step includes
An initial signal generation step of generating an initial signal by multiplying the received signal by a weight calculated from the transmission path estimation value;
An update value calculation step for obtaining an update value in consideration of a plurality of directions in which noise is amplified from the propagation path estimation value and the initial signal;
An adding step of adding the initial signal and the updated value;
A hard decision step of making a hard decision on the signal added in the addition step and generating a transmission signal candidate;
A metric generation step of calculating a metric from the transmission signal candidates;
A likelihood calculating step for generating a bit log likelihood ratio of a maximum likelihood sequence from the metric;
A receiving method comprising: A receiving method in a receiving apparatus for receiving a transmission signal transmitted from a transmitting apparatus in a MIMO transmission method,
A channel estimation step for performing channel estimation using the received signal and obtaining a channel estimation value;
A signal detection step of MIMO separating the received signal to generate a bit log likelihood ratio;
A decoding step for performing error correction decoding on the bit log likelihood ratio;
With
The signal detection step includes
An initial signal generation step of generating an initial signal by multiplying the received signal by a weight calculated from the transmission path estimation value;
An update value calculation step for obtaining an update value in consideration of a plurality of directions in which noise is amplified from the propagation path estimation value and the initial signal;
An adding step of adding the initial signal and the updated value;
A hard decision step of generating a transmission signal candidate by making a hard decision on the signal output by the adding step;
A metric generation step of calculating a metric from the transmission signal candidates;
A likelihood calculating step of generating a bit log likelihood ratio of a maximum likelihood sequence from the metric and the bit log likelihood ratio output by the decoding step;
A receiving method comprising:   The reception method according to claim 14, wherein the signal detection step and the decoding step are repeatedly performed.

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