JP2014039122A - Receiver, reception method, reception program, and processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to appropriately perform MIMO separation.SOLUTION: A channel estimation unit creates a channel matrix between a transmission signal vector and a reception signal vector. A reference metric creation unit calculates a reception signal replica on the basis of one of candidates of the transmission signal vector and the channel matrix, and calculates a reference metric showing difference between the calculated reception signal replica and the reception signal vector received by a receiver. A signal search unit determines whether or not a metric showing difference between a reception signal replica of a transmission signal vector including some elements of the candidates of the transmission signal vector and the reception signal vector is larger than the reference metric, on the basis of the some elements; and performs or does not perform calculation with respect to the transmission signal vector including the some elements, on the basis of a result of the determination.

Description

  The present invention relates to a receiving device, a receiving method, a receiving program, and a processor.

In recent years, MIMO (Multiple Input Multiple Output) communication has attracted attention as a technique for realizing large-capacity high-speed information communication. In this MIMO communication, different information is transmitted and received at the same time and the same frequency.
In MIMO communication, Maximum Likelihood Detection (MLD) is known as a MIMO separation technique that realizes good transmission characteristics. However, in MLD, the receiving apparatus needs to calculate the metric (square Euclidean distance) of all symbol replica candidates that can be transmitted. Therefore, the calculation amount of the receiving apparatus increases exponentially with respect to the number of multiplexed streams. Therefore, when the number of streams increases, the receiving apparatus cannot perform MIMO separation in a realistic processing time.

  Patent Document 1 describes a method using QRM-MLD (MLD with QR decomposition and M-algorithm). Specifically, in Patent Document 1, ranking is performed in the order in which the branch metric is expected to be small with respect to the residual reception signal obtained by subtracting the signal component of the surviving symbol replica candidate from the reception signal obtained by orthogonalizing the transmission signal by QR decomposition. A symbol replica candidate ranking unit for performing symbol processing, a symbol replica candidate selecting unit for selecting a symbol replica candidate in order from a symbol replica candidate ranked highest, a branch metric calculating unit for calculating a branch metric of the selected symbol replica candidate, A threshold comparison unit that compares the calculated branch metric with a predetermined threshold, and when the branch metric becomes larger than the predetermined threshold as a result of the comparison in the threshold comparison unit, symbols after the stage For plica candidate is deleted from the candidate without performing the search.

JP 2006-270430 A

However, the invention described in Patent Document 1 determines whether or not to search for a subsequent stage based on the branch metrics of the same stage. Therefore, the invention described in Patent Document 1 is not guaranteed to reach a result equivalent to, for example, MLD. Further, in the invention described in Patent Document 1, for example, MIMO separation cannot be performed efficiently because, for example, it takes time for the MIMO separation processing.
As described above, the invention described in Patent Document 1 has a problem that MIMO separation may not be performed properly.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a receiving apparatus, a receiving method, a receiving program, and a processor that can appropriately perform MIMO separation.

  (1) The present invention has been made to solve the above-described problems, and one aspect of the present invention is a receiving apparatus that performs communication of a MIMO transmission method, and includes a transmission signal vector and a reception signal vector. A channel estimation unit for generating a channel matrix, a received signal replica based on one of the transmission signal vector candidates and the channel matrix, and the calculated received signal replica and the received signal vector received by the receiving device A reference metric generation unit that calculates a reference metric indicating a difference; and a received signal replica of the transmitted signal vector including the partial component and the received signal vector based on the partial component of the candidate transmitted signal vector It is determined whether or not a metric indicating a difference is larger than the reference metric, and based on the result of the determination, the transmission including the partial component A signal searching unit for switching whether to perform operations on No. vector is a receiving device comprising a.

  (2) In addition, according to one aspect of the present invention, in the reception apparatus, accumulation of the partial components is performed based on the partial components of the transmission signal vector candidates, the channel matrix, and the reception signal vectors. A metric calculation unit configured to calculate a metric, wherein the signal search unit is configured to calculate a difference between the received signal replica of the transmitted signal vector including the partial component and the received signal vector when the accumulated metric is larger than the reference metric. Is determined to be larger than the reference metric.

  (3) In addition, according to one aspect of the present invention, in the reception device described above, a metric calculation that calculates a cumulative metric based on a partial component of the transmission signal vector candidate, the channel matrix, and the reception signal vector. The signal search unit has a metric indicating a difference between the received signal replica of the transmitted signal vector including the partial component and the received signal vector when the accumulated metric is smaller than the reference metric. It is determined that the value is smaller than the metric.

  (4) Further, according to one aspect of the present invention, in the reception device, the signal search unit has a metric indicating a difference between a reception signal replica of a transmission signal vector including the partial component and the reception signal vector. When it becomes smaller than the reference metric, an operation relating to the transmission signal vector including the partial component is performed.

  (5) Further, according to one aspect of the present invention, in the reception device, the signal search unit has a metric indicating a difference between a reception signal replica of a transmission signal vector including the partial component and the reception signal vector. When the reference metric becomes larger than the reference metric, the calculation relating to the transmission signal vector including the partial component is not performed.

  (6) Further, according to one aspect of the present invention, in the reception device, the signal search unit is configured to receive a reception signal replica of a transmission signal vector including the partial component and the reception signal based on the determination result. Switches whether or not to calculate a metric indicating a difference from a vector.

  (7) Further, according to one aspect of the present invention, in the reception apparatus described above, a decomposition unit that performs QR decomposition on the channel matrix to generate a unitary matrix and an upper triangular matrix, and triangulated reception based on the unitary matrix A signal conversion unit that calculates a signal, and a metric calculation unit that calculates a cumulative metric related to the partial component based on the partial component of the transmission signal vector candidate, the triangulated reception signal, and the upper triangular matrix The signal search unit calculates a cumulative metric related to the partial component based on the triangulated received signal and the upper triangular matrix, and the calculated partial metric is smaller than the reference metric, the partial metric A maximum likelihood sequence corresponding to the transmission signal vector including the component is obtained.

  (8) Further, according to one aspect of the present invention, in the reception apparatus, the signal search unit has a metric indicating a difference between the reception signal replica of the transmission signal vector candidate and the reception signal vector based on the reference metric. If the reference metric is determined to be smaller, the reference metric is changed to a metric related to the transmission signal vector candidate.

  (9) Further, according to one aspect of the present invention, in the reception device, the reference metric generation unit calculates the reference metric based on suboptimal maximum likelihood detection.

  (10) Further, according to one aspect of the present invention, in the reception device, the reference metric generation unit calculates the reference metric based on linear detection.

  (11) Further, according to one aspect of the present invention, in the reception device, the reference metric generation unit arbitrarily selects one of the transmission signal vector candidates.

  (12) Further, according to one aspect of the present invention, in the reception device, the signal search unit obtains a maximum likelihood sequence corresponding to a transmission signal vector including the partial component, and information bits are obtained from the maximum likelihood sequence. Ask for.

  (13) Further, according to one aspect of the present invention, in the reception device, the signal search unit obtains a maximum likelihood sequence corresponding to a transmission signal vector including the partial component, and information bits are obtained from the maximum likelihood sequence. Ask for.

  (14) Further, according to one aspect of the present invention, in the reception apparatus described above, the channel matrix sequence may be based on calculation component information indicating a component of the transmission signal vector and a log likelihood ratio component to be calculated. A decomposition unit that performs QR decomposition on a matrix whose vector order has been changed to generate a unitary matrix and an upper triangular matrix, a signal conversion unit that calculates a triangulated received signal based on the unitary matrix, and a log likelihood ratio A calculation unit; and a decoding unit, wherein the reference metric generation unit generates the reference metric for each calculation target candidate that is a candidate for a component indicated by calculation component information, and the signal search unit includes: For each of the calculation target candidates, a minimum metric that minimizes the metric among transmission vectors including the calculation target candidate is calculated, and the log likelihood ratio calculation unit includes the minimum metric. Calculates the log likelihood ratio based on click, the decoding unit decodes based on the log likelihood ratio, and outputs the information bits to the decoding.

  (15) Further, according to one aspect of the present invention, in the reception device, the decoding unit outputs a coded bit log likelihood ratio.

  (16) Further, according to one aspect of the present invention, in the reception apparatus, the signal search unit obtains a maximum likelihood metric from a plurality of the minimum metrics, and the calculation target candidates other than the maximum likelihood sequence are calculated. The minimum metric related to the calculation target candidate is obtained, and a log likelihood ratio is calculated based on the maximum likelihood metric and the minimum metric.

  (17) Further, according to one aspect of the present invention, in the reception apparatus described above, a decomposition unit that performs QR decomposition on the channel matrix to generate a unitary matrix and an upper triangular matrix, and triangulated reception based on the unitary matrix A signal conversion unit that calculates a signal, and a metric calculation unit that calculates a cumulative metric related to the partial component based on the partial component of the transmission signal vector candidate, the triangulated reception signal, and the upper triangular matrix The decomposition unit rearranges the column vectors of the channel matrix so as to calculate a cumulative metric first from a highly reliable component, and then performs QR decomposition.

  (18) Further, according to one aspect of the present invention, in the reception device, the signal search unit may receive a reception signal replica of a transmission signal vector including the partial component and the reception signal based on the determination result. Whether to calculate a metric indicating a difference from the vector is switched, and when the metric of the calculation result falls below a predetermined metric threshold, the metric of the calculation result is output as the minimum metric.

  (19) Further, according to an aspect of the present invention, in the reception device, the metric threshold is generated based on the reference metric.

  (20) Further, according to one aspect of the present invention, in the reception device, when the number of search nodes exceeds a predetermined search threshold, the signal search unit outputs a minimum metric obtained up to that point. .

  (21) According to another aspect of the present invention, there is provided a reception method in a reception apparatus that performs communication of a MIMO transmission method, a channel estimation process for generating a channel matrix between a transmission signal vector and a reception signal vector, A reference metric generation step of calculating a received signal replica based on one of the transmission signal vector candidates and the channel matrix, and calculating a reference metric indicating a difference between the calculated received signal replica and the received signal vector received by the receiving device And a metric indicating a difference between the received signal replica of the transmission signal vector including the partial component and the received signal vector is larger than the reference metric based on the partial component of the transmission signal vector candidate. Based on the result of the determination, an operation relating to the transmission signal vector including the partial component is performed. A signal search process for switching or Ukaina to a receiving method having a.

  (22) One embodiment of the present invention is a reception program that causes a computer to execute the reception method.

  (23) Further, according to one aspect of the present invention, in the above-described reception apparatus, a reception signal replica calculated based on one of transmission signal vector candidates and a channel matrix between the transmission signal vector and the reception signal vector And a received signal vector received by the receiving device, a reference metric indicating a difference between the received signal vector and a received signal vector including the partial component based on the partial component of the candidate transmitted signal vector A processor that determines whether or not a metric indicating a difference from a vector is larger than the reference metric, and switches whether or not to perform an operation on a transmission signal vector including the partial component based on the determination result It is.

  According to the present invention, MIMO separation can be performed appropriately.

It is a conceptual diagram of the communication system which concerns on each embodiment of this invention. It is a schematic block diagram which shows the structure of the transmitter which concerns on the 1st this embodiment of this invention. It is an example of an output of the mapping part which concerns on this embodiment. It is a schematic block diagram which shows the structure of the receiver which concerns on this embodiment. It is a schematic block diagram which shows the structure of the signal search part which concerns on this embodiment. It is a schematic block diagram which shows the detailed structure of the signal search part which concerns on this embodiment. It is another schematic block diagram which shows the detailed structure of the signal search part which concerns on this embodiment. It is another schematic block diagram which shows the detailed structure of the signal search part which concerns on this embodiment. It is the schematic explaining an example of the search of the candidate of a modulation symbol. It is the schematic explaining an example of the search of the candidate of the modulation symbol which concerns on this embodiment. It is another schematic diagram explaining an example of a search for a modulation symbol candidate according to the present embodiment. It is another schematic diagram explaining an example of a search for a modulation symbol candidate according to the present embodiment. It is another schematic diagram explaining an example of a search for a modulation symbol candidate according to the present embodiment. It is a flowchart which shows operation | movement of the receiver which concerns on this embodiment. It is a schematic block diagram which shows the structure of the receiver which concerns on the 2nd Embodiment of this invention. It is a schematic block diagram which shows the structure of the signal search part which concerns on this embodiment. It is a schematic block diagram which shows the detailed structure of the signal search part which concerns on this embodiment. It is another schematic block diagram which shows the detailed structure of the signal search part which concerns on this embodiment. It is another schematic block diagram which shows the detailed structure of the signal search part which concerns on this embodiment. It is another schematic diagram explaining an example of a search for a modulation symbol candidate according to the present embodiment. It is another schematic diagram explaining an example of a search for a modulation symbol candidate according to the present embodiment. It is another schematic diagram explaining an example of a search for a modulation symbol candidate according to the present embodiment. It is a flowchart which shows operation | movement of the receiver which concerns on this embodiment. It is a schematic block diagram which shows the structure of the transmitter which concerns on the 3rd Embodiment of this invention. It is a schematic block diagram which shows the structure of the receiver which concerns on this embodiment. It is a schematic block diagram which shows the structure of the signal search part which concerns on this embodiment. It is a schematic block diagram which shows the detailed structure of the signal search part which concerns on this embodiment. It is another schematic block diagram which shows the detailed structure of the signal search part which concerns on this embodiment. It is the schematic explaining an example of the search of the candidate of the modulation symbol which concerns on this embodiment. It is the schematic showing an example of IQ plane concerning this embodiment. It is a flowchart which shows operation | movement of the receiver which concerns on this embodiment. It is the schematic which shows an example of the simulation conditions of MIMO communication which concern on this embodiment. It is the schematic which shows an example of the simulation result of MIMO communication (8x8) which concerns on this embodiment. It is the schematic which shows an example of the average number of search nodes which concerns on this embodiment. It is the schematic which shows an example of the simulation result of the MIMO communication (16x16) which concerns on this embodiment. It is the schematic which shows another example of the average number of search nodes which concerns on this embodiment.

(First embodiment)
FIG. 1 is a conceptual diagram of a communication system according to each embodiment of the present invention. In this figure, the communication system includes a transmission device a1 and a reception device b1. For example, the transmission device a1 is a base station device (eNodeB, Home eNodeB, E-UTRAN, wireless LAN access point, broadcast transmission tower), and the reception device b1 is a mobile station device (UE). . However, the transmission device a1 may be a mobile station device, and the reception device b1 may be a base station device.
The transmission device a1 includes transmission antennas a1-1 to a1-T. The receiving device b1 includes receiving antennas b1-1 to b1-R. Here, T is the number of transmitting antennas, and R is the number of receiving antennas. The transmission device a1 and the reception device b1 perform MIMO (multiple input multiple output) communication. In this MIMO communication, the transmission device a1 and the reception device b1 transmit and receive different information at the same time and the same frequency. As a result, the communication system can significantly increase the information bit rate.

  Here, the receiving apparatus b1 generates a channel matrix between the transmission signal vector and the reception signal vector, for example, by channel estimation. The transmission signal vector is a vector having, for example, a transmission signal transmitted from each transmission antenna a1-t (t = 1, 2,..., T) as a component. The received signal vector is a vector whose component is a received signal received by each receiving antenna b1-r (r = 1, 2,..., R), for example. The receiving apparatus b1 calculates a received signal replica based on one of the transmission signal vector candidates and the channel matrix, and a reference metric (D) indicating the difference between the calculated received signal replica and the received signal vector of the signal received by the receiving apparatus b1. Square Euclidean distance) is calculated. The receiving apparatus b1 determines whether or not a metric indicating a difference between the transmission signal vector including the partial component and the reception signal vector is larger than the reference metric based on the partial component of the transmission signal vector candidate. judge. Based on this determination result, the receiving apparatus b1 switches whether or not to perform an operation related to a transmission signal vector including a part of the component.

  FIG. 2 is a schematic block diagram showing the configuration of the transmission device a1 according to the first embodiment of the present invention. In this figure, the transmission device a1 includes a bit allocation unit a101, a modulation unit a102-t, a pilot generation unit a103, a mapping unit a104-t, and a transmission unit a105-t. Here, t = 1, 2,..., T. FIG. 2 also shows the transmission antennas a1-t.

The bit allocation unit a101 allocates information bits to be transmitted to the reception device b1 to each transmission antenna a1-t. Note that the allocation information (for example, information indicating the antenna to be assigned and the order) regarding the allocation of the information bits to the transmission antenna is, for example, as scheduling information (or mapping information) from any of the transmission units a105-t to the reception device b1. To be notified.
The modulation unit a102-t modulates the bits input from the bit allocation unit a101 using a modulation scheme such as PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation), and generates a modulation symbol. Is generated. The modulation unit a102-t outputs the generated modulation symbol to the mapping unit a104-t.
Note that information indicating a modulation scheme used for communication with the reception device b1 is notified from one of the transmission units a105-t to the reception device b1 as, for example, MCS (Modulation and Coding Scheme) information. The modulation method may be different for each modulation unit a102-t, that is, for each transmission antenna a1-t, or may be different for each frequency band (for example, component carrier).

Pilot generation section a103 generates a pilot symbol as a reference signal for receiving apparatus b1 to perform channel estimation, and outputs the pilot symbol to mapping section a104-t.
The mapping unit a104-t maps the modulation symbol input from the modulation unit a102-t and the pilot symbol input from the pilot generation unit a103 at the time based on predetermined mapping information, and transmits the transmission unit a105. Output to -t.
FIG. 3 is an output example of the mapping unit a104-t according to the present embodiment. This figure is an output example when T = 4. In this figure, the horizontal axis represents the time axis. According to the output example in this figure, the transmission device a1 outputs nothing from the other transmission antennas a1-k (k ≠ t) at the timing of transmitting the pilot symbols of a certain transmission antenna a1-t. Thereby, the receiving apparatus b1 can suppress interference of pilot symbols transmitted from the transmission antennas a1-t, and can realize channel estimation in the receiving apparatus b1.

  The transmission unit a105-t performs digital / analog conversion on the signal input from the mapping unit a104-t, and shapes the waveform of the converted analog signal. The transmission unit a105-t upconverts the waveform-shaped signal from the baseband to the radio frequency band, and transmits the signal from the transmission antenna a1-t to the reception device b1.

  FIG. 4 is a schematic block diagram showing the configuration of the receiving device b1 according to this embodiment. In this figure, the receiving device b1 includes a receiving unit b101-r, a channel estimating unit b102, a QR decomposing unit b103, a signal converting unit b104, a reference metric generating unit b105, a reference metric storing unit b106, a candidate sequence storing unit b107, and a signal. The search part b108 is comprised. Here, r = 1, 2,..., R. FIG. 4 also shows the receiving antenna b1-r.

  The reception unit b101-r receives the transmission signal transmitted by the transmission device a1 via the reception antenna b1-r. The receiving unit b101-r performs frequency conversion and analog-digital conversion on the received signal. The reception unit b101-r outputs the converted reception signal to the channel estimation unit b102 and the signal conversion unit b104.

The channel estimation unit b102 performs channel estimation using the received signal at the time when the pilot symbol input from the reception unit b101-r is transmitted, and calculates a channel value. The channel estimation unit b102 outputs the calculated channel value to the QR decomposition unit b103.
The QR decomposition unit b103 uses the channel value input from the channel estimation unit b102 to perform QR decomposition of a channel matrix having the channel value as a component. The QR decomposition unit b103 outputs the unitary matrix Q calculated by the QR decomposition to the signal conversion unit b104, and outputs the calculated triangular matrix R to the reference metric generation unit b105 and the signal search unit b108.
The signal conversion unit b104 performs signal conversion on the reception signal input from the reception unit b101-r based on the unitary matrix Q input from the QR decomposition unit b103. Hereinafter, the reception signal subjected to this signal conversion is referred to as a triangulated reception signal. The signal conversion unit b104 outputs the triangulated reception signal to the reference metric generation unit b105 and the signal search unit b108.

The reference metric generation unit b105 performs MIMO separation based on the signal input from the signal conversion unit b104 and the triangular matrix R input from the QR decomposition unit b103. For MIMO separation, linear processing such as ZF (Zero Forcing) criterion and MMSE (Minimum Mean Square Error) criterion may be performed, or nonlinear processing such as QRM-MLD (MLD with QR decomposition and M-algorithm) may be performed. You may do it. Further, the reference metric generation unit b105 may perform MIMO separation based on the reception signal that is the output of the reception unit b101-r and the channel value that is the output of the channel estimation unit b102. The reference metric generation unit b105 is not limited to these, and any MIMO separation may be used.
The reference metric generation unit b105 calculates a temporary determination value (initial value of the candidate sequence) of the candidate sequence from the obtained MIMO separation result, and stores it in the candidate sequence storage unit b107. Further, the reference metric generation unit b105 calculates a metric using the candidate series and stores the metric in the reference metric storage unit b106. The candidate sequence is a bit sequence obtained by demodulating the following vector x, that is, a symbol replica combination (transmission signal vector) of modulation symbols transmitted from the transmission antennas a1-t. In other words, the candidate sequence is a bit sequence (before modulation of the symbol replica) that is a source for generating the symbol replica. The candidate series includes information bit candidates as components.

The reference metric storage unit b106 outputs the stored reference metric to the signal search unit b108. In addition, when receiving a metric from the signal search unit b108, the reference metric storage unit b106 stores the received metric as a new reference metric.
When the candidate sequence storage unit b107 receives a processing end signal from the signal search unit b108, the candidate sequence storage unit b107 outputs the stored candidate sequence as a maximum likelihood sequence. Further, when the candidate sequence storage unit b107 receives a candidate sequence from the signal search unit b108, the candidate sequence storage unit b107 stores the received candidate sequence as a new candidate sequence.
The signal search unit b108 determines a candidate sequence by performing processing described later, and stores the determined candidate sequence in the candidate sequence storage unit b107. When the process ends, the signal search unit b108 outputs a process end signal to the candidate sequence storage unit b107.
Note that the candidate sequence storage unit b107 or the signal search unit b108 may arrange the information bits of the maximum likelihood sequence in the order of input to the bit allocation unit a101 of the transmission device a1 based on the allocation information of the scheduling information. .

Hereinafter, the process performed by the signal search unit b108 will be described.
FIG. 5 is a schematic block diagram showing the configuration of the signal search unit b108 according to the present embodiment. In this figure, the signal search unit b108 includes a stage t search unit b108-t (t = 1, 2,..., T). Note that the processing performed by the stage t search unit b108-t is also referred to as stage t processing.

  6 to 8 are schematic block diagrams illustrating a detailed configuration of the signal search unit b108 according to the present embodiment. In these figures, a stage t search unit b108-t (t = 1, 2,..., T-1, T) includes a symbol replica generation unit b108-t-1 and a cumulative metric calculation unit b108-t-2. , A metric comparison unit b108-t-3, and a symbol replica subtraction unit b108-t-4. Below, the process of the stage T is demonstrated first using FIG. Next, the process of stage t after stage T-1 will be described using FIG. 7, and the process of stage 1 will be described finally using FIG.

FIG. 6 is a schematic block diagram illustrating a detailed configuration of the signal search unit b108 according to the present embodiment. This figure shows the relationship between the stage T search unit b108-T and the stage (T-1) search unit b108- (T-1). In addition, “-” inside the parenthesis represents minus (the same applies hereinafter).
The triangulated reception signal output from the signal conversion unit b104 is input to the symbol replica generation unit b108-T-1, the cumulative metric calculation unit b108-T-2, and the symbol replica subtraction unit b108-T-4.

When the symbol replica generation unit b108-T-1 detects the input of the triangulated reception signal, the symbol replica generation unit b108-T-1 starts a process of MLD (Maximum Likelihood Detection). Specifically, first, the symbol replica generation unit b108-T-1 selects one information bit candidate (information bit candidate) that can be transmitted from the transmission antenna a1-T, and based on the selected information bit candidate One symbol replica (modulation symbol candidate; transmission vector T component candidate) is generated. Here, the symbol replica generation unit b108-T-1 determines information bit candidates one by one based on the MCS information notified from the transmission device a1, and modulates the determined information bit candidates to generate a symbol replica. Generate one by one. The symbol replica generation unit b108-T-1 outputs the generated symbol replica to the cumulative metric calculation unit b108-T-2 and the symbol replica subtraction unit b108-T-4.
The processing for the one symbol replica thus output is excluded from the candidates by the metric comparison unit b108-T-3, or the symbol replica generation unit b108- (T-1)-of the stage (T-1). When the process end signal is received from 1, the process ends. When the processing for one symbol replica is completed, the symbol replica generation unit b108-T-1 selects and selects an information bit candidate different from the previously selected information bit candidate from the information bit candidates. Modulate information bit candidates. That is, the symbol replica generation unit b108-T-1 generates a symbol replica different from the previously generated symbol replica and performs the same processing. When these processes are performed on all information bit candidates, the stage T ends the process, and outputs a process end signal to the candidate sequence storage unit b107.

  The cumulative metric calculation unit b108-T-2 receives the symbol replica input from the symbol replica generation unit b108-T-1 and the component of the Tth row and Tth column of the triangular matrix R input from the QR decomposition unit b103. Multiply. The cumulative metric calculation unit b108-T-2 subtracts the multiplication result from a value corresponding to the component of the transmission antenna a1-T of the triangulated reception signal input from the signal conversion unit b104. The cumulative metric calculation unit b108-T-2 calculates the square Euclidean norm of the subtraction result (see Expression (23)). The cumulative metric calculation unit b108-T-2 uses the calculated square Euclidean norm as the cumulative metric in the stage T, and the metric comparison unit b108-T-3 and the cumulative metric calculation unit b108- (T in the stage (T-1). -1) Output to -2.

  When the cumulative metric input from the cumulative metric calculation unit b108-T-2 is larger than the reference metric input from the reference metric storage unit b106, the metric comparison unit b108-T-3 is a symbol replica generation unit b108-T-1. Is removed from the candidates and notified to the symbol replica generation unit b108-T-1. That is, the metric comparison unit b108-T-3 excludes candidate sequences (candidate sequences having information bit candidates as T components) including information bit candidates corresponding to the symbol replica from the candidates. If this condition is not met, a signal for continuing processing is output to the symbol replica subtracting section b108-T-4. Specifically, the metric comparison unit b108-T-3, for example, if the cumulative metric input from the cumulative metric calculation unit b108-T-2 is smaller than the reference metric input from the reference metric storage unit b106, the symbol replica A candidate sequence including information bit candidates corresponding to the symbol replica output by the generation unit b108-T-1 is maintained.

The symbol replica subtraction unit b108-T-4 receives the signal of the processing continuation, and the symbol replica input from the symbol replica generation unit b108-T-1 and the triangular matrix R input from the QR decomposition unit b103. Of these, multiplication is performed from the first component to the (T−1) -th component of the T-th column vector. The symbol replica subtraction unit b108-T-4 subtracts the multiplication result from a vector obtained by taking the first component to the (T-1) component of the triangulated reception signal input from the signal conversion unit b104. The symbol replica subtraction unit b108-T-4 outputs the T-1th of the T-1 replica subtraction signals to the accumulated metric calculation unit b108- (T-1) -2 of the stage (T-1). To do.
The symbol replica subtraction unit b108-T-4 converts the 1st to T-2th of the T-1 replica subtraction signals into the symbol replica subtraction unit b108- (T-1) -4 of the stage (T-1). Output to. The symbol replica subtraction unit b108-T-4 outputs a processing start signal to the symbol replica generation unit b108- (T-1) -1 of the stage (T-1).
Note that the symbol replica subtraction unit b108-T-4 does not perform the above process when the process continuation signal is not input.

Next, the stage t after T−1, that is, the stage t where t ≦ T−1 will be described.
FIG. 7 is another schematic block diagram showing a detailed configuration of the signal search unit b108 according to the present embodiment. This figure shows the relationship between the stage (t + 1) search unit b108- (t + 1), the stage t search unit b108-t, and the stage (t-1) search unit b108- (t-1). However, since the process is different when t = 1, the process of the stage 1 search unit b108-1 will be described later.

The symbol replica generation unit b108-t-1 starts the process when the processing start signal is input from the symbol replica subtraction unit b108- (t + 1) -4. Specifically, the symbol replica generation unit b108-t-1 selects one information bit candidate (information bit candidate) that can be transmitted from the transmission antenna a1-t, and the symbol replica based on the selected information bit candidate Are generated (modulation symbol candidates; transmission vector t component candidates). Here, the symbol replica generation unit b108-t-1 determines information bit candidates one by one based on the MCS information notified from the transmission device a1, and modulates the determined information bit candidates to generate a symbol replica. Generate one by one. The symbol replica generation unit b108-t-1 outputs the generated symbol replica to the cumulative metric calculation unit b108-t-2 and the symbol replica subtraction unit b108-t-4.
The processing for the one symbol replica thus output is excluded from the candidates by the metric comparison unit b108-t-3, or the symbol replica generation unit b108- (t-1)-of the stage (t-1). When the process end signal is received from 1, the process ends. When the processing for one symbol replica is completed, the symbol replica generation unit b108-t-1 selects and selects an information bit candidate different from the previously selected information bit candidate from the information bit candidates. Modulate information bit candidates. That is, the symbol replica generation unit b108-t-1 generates a symbol replica of a modulation symbol different from the previously generated candidate series and performs the same processing. When these processes are performed on all the modulation symbols, the stage t ends the process and outputs a process end signal to the symbol replica generation unit b108- (t + 1) -1 of the stage (t + 1).

  The cumulative metric calculation unit b108-t-2 receives the symbol replica input from the symbol replica generation unit b108-t-1 and the component of the t-th row and t-column components of the triangular matrix R input from the QR decomposition unit b103. Multiply. The cumulative metric calculation unit b108-t-2 subtracts the multiplication result from the replica subtraction signal input from the symbol replica subtraction unit b108- (t + 1) -4. The cumulative metric calculation unit b108-t-2 calculates the square Euclidean norm of the subtraction result. The cumulative metric calculation unit b108-t-2 adds the calculated square Euclidean norm and the cumulative metric input from the cumulative metric calculation unit b108- (t + 1) -2, and calculates a cumulative metric at the stage t. This accumulated metric is output to the metric comparison unit b108-t-3 and the accumulated metric calculation unit b108- (t-1) -2 of the stage (t-1).

  When the cumulative metric value input from the cumulative metric calculation unit b108-t-2 is larger than the reference metric input from the reference metric storage unit b106, the metric comparison unit b108-t-3 is a symbol replica generation unit b108-t-. The symbol replica output by 1 is removed from the candidates and notified to the symbol replica generation unit b108-t-1. That is, the metric comparison unit b108-t-3 removes candidate sequences (candidate sequences having information bit candidates as T components) including information bit candidates corresponding to the symbol replicas from candidates. If this condition is not met, a signal for continuing processing is output to the symbol replica subtracting section b108-t-4. Specifically, the metric comparison unit b108-t-3, for example, if the cumulative metric input from the cumulative metric calculation unit b108-t-2 is smaller than the reference metric input from the reference metric storage unit b106, the symbol replica A candidate sequence including information bit candidates corresponding to the symbol replica output by the generation unit b108-t-1 is maintained.

The symbol replica subtracting unit b108-t-4, when the processing continuation signal is input, receives the symbol replica input from the symbol replica generating unit b108-t-1 and the triangular matrix R input from the QR decomposition unit b103. Of these, multiplication is performed from the first component to the (t−1) -th component of the t-th column vector. The symbol replica subtraction unit b108-t-4 subtracts the multiplication result from the replica subtraction signal input from the symbol replica subtraction unit b108- (t + 1) -4. The symbol replica subtraction unit b108-t-4 outputs the t-1th of the t-1 replica subtraction signals to the accumulated metric calculation unit b108- (t-1) -2 of the stage (t-1). To do. When t is not 2, the symbol replica subtraction unit b108-t-4 converts the first to t-2th of the t-1 replica subtraction signals into the symbol replica subtraction unit b108- (stage (t-1). output to t-1) -4. The symbol replica subtraction unit b108-t-4 outputs a processing start signal to the symbol replica generation unit b108- (t-1) -1 of the stage (t-1).
Note that the symbol replica subtraction unit b108-t-4 does not perform the above process when the process continuation signal is not input.

Finally, stage 1 will be described.
FIG. 8 is another schematic block diagram showing a detailed configuration of the signal search unit b108 according to the present embodiment. This figure shows the relationship between the stage 2 search unit b108-2 and the stage 1 search unit b108-1. The stage 1 search unit b108-1 is different from the stage t search unit b108-t where t ≧ 2 in that it does not include a symbol replica subtraction unit.

The symbol replica generation unit b108-1-1 starts the process when a processing start signal is input from the symbol replica subtraction unit b108-2-4. Specifically, the symbol replica generation unit b108-1-1 selects one information bit candidate (information bit candidate) that can be transmitted from the transmission antenna a1-1, and based on the selected information bit candidate, the symbol replica 1 (modulation symbol candidate; one component candidate of the transmission vector). Here, the symbol replica generation unit b108-1-1 determines information bit candidates one by one based on the MCS information notified from the transmission device a1, and modulates the determined information bit candidates to generate a symbol replica. Generate one by one. The symbol replica generation unit b108-1-1 outputs the generated symbol replica to the cumulative metric calculation unit b108-1-2.
The processing for the one symbol replica that is output ends when the processing in the metric comparison unit b108-1-3 ends. When the processing for one symbol replica is completed, the symbol replica generation unit b108-1-1 selects and selects an information bit candidate different from the previously selected information bit candidate from the information bit candidates. Modulate information bit candidates. That is, the symbol replica generation unit b108-1-1 generates a symbol replica of a modulation symbol different from the previously generated symbol replica, and performs the same processing. When these processes are performed for all information bit candidates, the stage 1 ends the process and outputs a process end signal to the symbol replica generation unit b108-2-1 of the stage 2.

  The cumulative metric calculation unit b108-1-2 includes the symbol replica input from the symbol replica generation unit b108-1-1 and the first row and first column component of the triangular matrix R input from the QR decomposition unit b103. Multiply. The cumulative metric calculation unit b108-1-2 subtracts the multiplication result from the replica subtraction signal input from the symbol replica subtraction unit b108-2-4. The cumulative metric calculation unit b108-1-2 calculates the square Euclidean distance of the subtraction result. The cumulative metric calculation unit b108-1-2 adds the calculated square Euclidean distance and the cumulative metric input from the cumulative metric calculation unit b108-2-2 to calculate the cumulative metric in stage 1. The accumulated metric is output to the metric comparison unit b108-1-3.

When the cumulative metric value input from the cumulative metric calculation unit b108-1-2 is larger than the reference metric input from the reference metric storage unit b106, the metric comparison unit b108-1-3 is a symbol replica generation unit b108-1- 1 outputs a signal indicating the end of processing. That is, the metric comparison unit b108-1-3 excludes candidate sequences (candidate sequences having information bit candidates as T components) including information bit candidates corresponding to the symbol replica from the candidates. If this condition is not met, the metric comparison unit b108-1-3 outputs the accumulated metric value to the reference metric storage unit b106. Specifically, the metric comparison unit b108-1-3, for example, if the cumulative metric input from the cumulative metric calculation unit b108-1-2 is smaller than the reference metric input from the reference metric storage unit b106, the symbol replica A candidate sequence including information bit candidates corresponding to the symbol replica output by the generation unit b108-1-1 is adopted as a candidate sequence.
Further, the metric comparison unit b108-1-3 outputs a candidate sequence including information bit candidates corresponding to the symbol replicas used in each stage so far to the candidate sequence storage unit b107. Further, the metric comparison unit b108-1-3 outputs a signal indicating the end of processing to the symbol replica generation unit b108-1-1. That is, the metric comparison unit b108-1-3 outputs the candidate series corresponding to the reference metric to the candidate series storage unit b107.

<About the operating principle>
Hereinafter, the operating principle of the receiving device b1 will be described with reference to FIGS.
Of the reception signals received by the reception unit b101 and transmitted to the channel estimation unit b102, the reception signal corresponding to the time when the pilot symbol of FIG. 3 is transmitted is expressed by the following equation (1).

Here, _{y r} is the received signal receiving unit b101-r _{outputs, h rt} channel value between receive antennas b1-r transmitting antennas ^{_{a1-t, s t (p}} ) is transmitted from the transmitting antenna a1-t The pilot symbol, n _r, is noise added by the receiving unit b101-r. Since the pilot symbol is known, the channel estimation unit b102 can obtain the estimated value of the channel value, for example, as in the following equation (2).

However, the variable with ^ (hat) represents an estimated value. In the following description, it is assumed that the estimated channel value is equal to the ideal value _hrt .
The received signal at the time when the data is sent is represented by the following equations (3) to (8) using the R-dimensional received signal vector y.

Here, T is denotes the transpose, s _t represents a modulation symbol transmitted from the transmission antennas a1-t. However, although the same characters as in equations (1) and (2) are used, since they represent signals at different times, the characters in equations (1) and (2) and equations (3) to (7) Letters represent different things.

  Next, the MLD will be described. In MLD, a determination value of a signal sequence x that minimizes a metric (square Euclidean distance) f expressed by the following equation (9) is obtained.

However, x is a replica (symbol replica) of s and is a T-dimensional vector. If the t-th element of x and x _t, the possible values of x _t is equal in number to the number M of modulation symbols used in the transmission antennas a1-t. For example, M = 4 when the modulation method in the modulation unit a102-t is QPSK, M = 16 when 16QAM, and M = 64 when 64QAM.

The search for possible values of x can be described by a tree structure of height T + 1.
FIG. 9 to FIG. 13 are schematic diagrams for explaining the search for modulation symbol candidates according to the present embodiment. This figure shows an example in which a signal is transmitted using a modulation scheme (for example, QPSK) that can take M = 4 modulation symbols with all transmission antennas at T = 3.
9 to 13, the vertical axis represents the height, and this height corresponds to t. White circles (nodes) represent modulation symbol candidates (represent symbol symbols or information bit candidates). That is, the node of height t is a modulation symbol candidate that is modulated by the modulation unit a102-t and transmitted from the transmission antenna a1-t. A combination of white circles traced along a branch (branch) represented by a straight line becomes a candidate (or candidate series) of x. The example of FIG. 9 is a case where the receiving device b1 (signal search unit b108) performs a search in the order from t = T to t = 1. Since the process corresponding to the modulation symbol candidate of height t corresponds to the process in the stage t search unit b108-t described in FIGS. 6 to 8, the height t is hereinafter referred to as a stage t.

(When QR decomposition is not used)
First, a case where QR decomposition is not used will be described. In the present embodiment, the receiving device b1 has a configuration using QR decomposition described later. Hereinafter, the processing unit corresponding to the stage t search unit b108-t is also referred to as a stage t processing unit.

The branch from the node at stage t + 1 to the child node at stage t fixes _xt to modulation symbol b (m), that is, the stage (t + 1) processing unit selects modulation symbol b (m) (node). Represents that. Here, m = 1, 2,..., M. For example, branch 71 in FIG. 9 shows a case of fixing the _{x 3} to b (1). Further, branch 72 shows a case of fixing the _{x 3} in b (2). The relationship between the branch and the modulation symbol is not limited to this, and a combination of a branch other than the above and the modulation symbol number m may be used.

  Next, when the node of stage t is selected, the stage t processing unit calculates a T-dimensional vector y (t) expressed by the following equation (10), and the calculated y (t) is set to stage (t−1). Output to the processing unit.

  However, y (T + 1) is y. Therefore, when the node 73 in FIG. 9 is selected, the stage 3 processing unit calculates y (3) using the following equation (11), and outputs the calculated y (3) to the stage 2 processing unit.

  When the node 74 in FIG. 9 is selected, the stage 3 processing unit calculates y (3) using the following equation (12), and outputs the calculated y (3) to the stage 2 processing unit.

Similarly, branch 75 represents a case of fixing a _{x 2} to b (1). When the node 76 in FIG. 9 is selected, the stage 2 processing unit calculates y (2) using the following equation (13), and outputs the calculated y (2) to the stage 1 processing unit.

When a leaf node that is a node of stage 1 is selected, the stage 1 processing unit calculates not only y (1) but also a square Euclidean norm of y (1). This means that the stage 1 processing unit has calculated f in Expression (9).
In FIG. 9, as encircled by a broken line 77, f is calculated at M ^T (M raised to the power of T) leaf nodes, and the route to the smallest leaf node is the solution of MLD. It should be noted that an increase in memory can be suppressed by searching in the forward scan.
Specifically, the stage 1 processing unit performs subtraction of the T-dimensional vector at a node other than the root node and calculation of the square Euclidean norm of the T-dimensional vector at the leaf node. When QR decomposition is not used, the number of nodes at stage t is M ^{(T−t + 1)} , and the number of scalar subtractions is expressed by the following equation (14).

Further, the number of leaf nodes Since M ^T, the case of not using the QR decomposition, the squared Euclidean norm calculation of a scalar is represented by the following formula (15).

  Thus, when QR decomposition is not used, in MLD, the number of operations increases exponentially with respect to T.

(When using QR decomposition)
Next, a case where QR decomposition is used will be described. When QR decomposition is used, the number of operations can be reduced as compared with the case where QR decomposition is not used.
4 performs QR decomposition on the R × T channel matrix H to decompose the channel matrix H into an R × T unitary matrix Q and an T × T upper triangular matrix R. These are represented by the following formulas (16) to (18).

Specifically, the QR decomposition unit b103 decomposes the channel matrix H into the matrix Q and the matrix R by performing Gram-Schmitt orthogonalization, modified Gram-Schmidt orthogonalization, householder transformation, Givens rotation, and the like.
The signal conversion unit b104 uses the matrix Q generated by the QR decomposition unit b103 and the received signal vector y that is an input from the receiving units b101-1 to b101-R as in the following equations (19) and (20). A triangulated reception signal y ′ is generated.

Here, H represents a complex conjugate transpose, and Q ^H is a conjugate transpose matrix of Q. Using the fact that Q ^H Q is a T × T identity matrix, finding a sequence x that minimizes Equation (9) is equivalent to finding x that minimizes Equation (21) below. .

  Since the matrix R is an upper triangular matrix, f can be transformed as in the following equations (22) to (24).

Equation (23) represents the cumulative metric f (T) of stage T. Note that f (t) represents a cumulative metric up to stage t.
Symbol replica generation unit b 108-T-1 of FIG. 6, select the modulation symbols one by one from the candidates of the modulation symbols transmitted from the transmitting antenna a1-T, the symbol replica x _T, the cumulative metric calculation Part b108-T-2. Cumulative metric calculation unit b 108-T-2, based on the T component of the symbol replica x _T and the T rows and T columns of components and triangulated received signal y of the matrix R ', by using the equation (23) f ( T) is calculated.

Note that y ′ (T) represents a vector for calculating the cumulative metric in the stage (T−1). Here, y ′ (t) represents a vector for calculating the cumulative metric at stage (t−1), and represents a vector of dimension t−1. y ′ (t) is also referred to as a replica subtraction signal. The k-th component of y ′ (t) is represented by y ′ _k (t).
The symbol replica subtraction unit b108-T-4 calculates y ′ (T) using Expression (24). The symbol replica subtraction unit b108-T-4 outputs y ′ _T−1 (T) to the cumulative metric calculation unit b108- (T−1) -2. y ′ _T-1 (T) is used to calculate f (T−1) (see Expression (26)). The symbol replica subtraction unit b108-T-4 outputs y ′ ₁ (T) to y ′ _T-2 (T) to the symbol replica calculation unit b108- (T-1) -4. y ′ ₁ (T) to y ′ _T-2 (T) are used to calculate y ′ (T−1) (see Expression (27)).

Next, processing after t = T−1 will be described.
Expression (22) can be further modified to be expressed by the following expressions (25) to (27).

Symbol replica generation unit b 108-t-1 in FIG. 7, select the modulation symbols one by one from the candidates of the modulation symbols transmitted from the transmitting antenna a1-t, the symbol replicas as x _t, cumulative metrics It outputs to calculation part b108-t-2. Cumulative metric calculation unit b 108-t-2, based on the component and symbol replica subtracting unit of the t rows t columns of _{x t} and the matrix R b108- (t + 1) inputted from _{-4 y 't (t + 1} ) The accumulated metric f (t) is calculated using Equation (26).

Further, symbol replica subtracting unit b 108-t-4 is inputted from the _{x t} the first row column t-component and symbol replica subtracting unit of the t-1 row t column of matrix R b108- (t + 1) -4 Based on y ′ ₁ (t + 1) to y ′ _t−1 (t + 1), y ′ (t) is calculated using Expression (27).
By performing the above processing from t = T to t = 1, the cumulative metric calculation unit b108-1-2 can obtain the metric of the equation (21) as the following equation (28).

In this way, when the metric calculation is changed to the cumulative metric calculation from stage T to stage 1 using QR decomposition, the processing of each stage changes.
Referring to FIG. 9 again, at stage t, the stage t search unit b108-t calculates the cumulative metric f (t) and the t−1-dimensional vector y ′ (t), and the stage (t−) of the stage t−1. 1) Output to search unit b108- (t-1). Note that y ′ (t) is not calculated in the leaf node. Since y ′ (t) is calculated by subtraction of a t−1-dimensional vector and is performed at a node other than the root node and the leaf node, the number of scalar subtractions is expressed by the following equation (29).

  This is a smaller value than Expression (14), and the number of scalar subtractions can be reduced. Since the cumulative metric is calculated at a node other than the root node, the scalar square Euclidean norm calculation number is expressed by the following equation (30).

  This is a smaller value than Expression (15), and the number of square Euclidean norms calculated can be reduced. However, there is no change in increasing with an index with respect to T.

  In the present embodiment, the receiving device b1 reduces the amount of calculation by reducing the number of nodes to be searched. Thereafter, the calculation amount is evaluated by the number of search nodes. The metric comparison unit b108-t-3 in FIGS. 6 to 8 is provided to reduce the number of search nodes. According to Expression (26), the cumulative metric f (t) is a value larger than f (t + 1). That is, the fact that the cumulative metric f (t + 1) at stage t + 1 is larger than the reference metric means that the cumulative metric f (t) at the next stage t is also larger than the reference metric. That is, the metric comparison unit b108- (t + 1) -3 receives the received signal replica of the signal sequence x including the (t + 1) th component to the Tth component based on the (t + 1) th component to the Tth component of the signal sequence x. It can be determined whether or not the metric f indicating the difference between Hx and the received signal vector y is larger than the reference metric.

First, the reference metric generation unit b105 in FIG. 4 generates an initial value of the reference metric and a candidate sequence at that time. Specifically, the reference metric generation unit b105 performs MIMO separation to obtain a candidate sequence. Further, the reference metric generation unit b105 sets a metric calculated using the candidate series as a reference metric. For each of the transmission antennas a1-1 to a1-T, one modulation symbol may be selected at random from the modulation symbol candidates transmitted from the transmission antenna a1-t. Note that the reference metric generation unit b105 may select a modulation symbol based on a predetermined rule.
FIG. 10 illustrates an example of selection of candidate series related to the reference metric according to the present embodiment. For example, the reference metric generation unit b105 selects a candidate series represented by a thick line in FIG. 10, that is, a combination of modulation symbol candidates traced along the thick line.

Metric comparison unit b 108-t-3, the cumulative metric is calculated based on x _t is at the time of exceeding the reference metric (determined value is increased), and outputs a signal indicating the processing end. That is, the metric comparison unit b 108-t-3, for the candidate sequence containing the _{x t,} skipping subsequent search (abort; discarded). Thereby, the signal search part b108 can reduce the number of search nodes.

FIG. 11 illustrates an example of processing of the signal search unit b108. In this figure, candidates for modulation symbols connected by bold lines indicate that the cumulative metric has been calculated based on the symbol replicas. This figure is an example in the case where any of the nodes 91 to 94 is selected, and the accumulated metric up to that node exceeds the reference metric. In this case, the signal search unit b108 discards the subsequent search for the candidate series including the nodes 91 to 94. By this discarding process, the X mark is given to the node that has not been searched. Therefore, 32 nodes are excluded from the search.
In FIG. 11, the cumulative metric of the candidate series including the leaf node 95 is lower than the reference metric (it is determined that the value is small). Therefore, this accumulated metric is stored as a new reference metric in the reference metric storage unit b106, and the candidate series up to the node 95 is stored in the candidate series storage unit b107. As described above, when the accumulated metric of the candidate series including the leaf node is smaller than the reference metric, the signal search unit b108 sets the accumulated metric as a new reference metric.

  FIG. 12 illustrates a process subsequent to the process illustrated in FIG. In FIG. 12, it is assumed that the cumulative metric up to the node 101 exceeds the reference metric. For this reason, the signal search unit b108 discards the subsequent search processing for the candidate series including the node 101. Thereby, the signal search part b108 can reduce the number of search nodes for four. In FIG. 12, the cumulative metric of the candidate series including the leaf node 102 is lower than the reference metric (the reference metric based on the candidate series including the node 95 in FIG. 11). For this reason, the cumulative metric of the candidate series including the leaf node 102 is stored in the reference metric storage unit b106 as a new reference metric, and the candidate series up to the node 102 is stored in the candidate series storage unit b107.

FIG. 13 illustrates a process subsequent to the process illustrated in FIG. FIG. 13 shows an example in which the accumulated metric from the nodes 111 to 113 exceeds the reference metric. In this case, the signal search unit b108 discards the subsequent search for the candidate series including the nodes 111 to 113. As a result, the signal search unit b108 can reduce the number of search nodes for twelve. In FIG. 13, it is assumed that no leaf node below the reference metric has been found. In this case, the candidate sequence including the leaf node 102 in FIG. 12 is the final result. That is, the signal search unit b108 (metric comparison unit b108-1-3) stores a candidate sequence including the leaf node 102, and this candidate sequence becomes a maximum likelihood sequence.
9 to 13, the total number of nodes excluding the root node is 84. However, since 48 nodes were not searched, the number of nodes actually searched by the signal search unit b108 is 36. . Thus, the signal search unit b108 can reduce the number of search nodes and the number of operations.

<Operation of Receiving Device b1>
FIG. 14 is a flowchart showing the operation of the receiving device b1 according to this embodiment. The operation shown in this figure is processing after the reception unit b101-r in FIG. 4 outputs the received signal to the channel estimation unit b102 and the signal conversion unit b104. In FIG. 14, a case will be described in which the stage number t, the modulation symbol number m _{t at} the stage t, and the modulation symbol number M _t used at the stage t are used as variables.

(Step S101) The channel estimation unit b102 obtains a channel matrix by performing channel estimation based on the received signal and the pilot symbol. Then, it progresses to step S102.
(Step S102) The QR decomposition unit b103 obtains a unitary matrix Q and an upper triangular matrix R by performing QR decomposition of the channel matrix H configured using the channel values obtained in step S102. Thereafter, the process proceeds to step S103.
(Step S103) The signal conversion unit b104 multiplies the reception signal vector by the unitary matrix Q obtained in step S102 to calculate a triangulated reception signal. Thereafter, the process proceeds to step S104.

(Step S104) The reference metric generation unit b105 performs MIMO separation using the upper triangular matrix R obtained in step S102 and the triangulated reception signal obtained in step S103. The reference metric generation unit b105 calculates a reference metric using the MIMO separation result and stores it in the reference metric storage unit b106. Further, the candidate sequence at that time (initial value of the candidate sequence) is stored in the candidate sequence storage unit b107. Thereafter, the process proceeds to step S105.
(Step S105) The signal search unit b108 sets m _T = 1 and t = T. Thereafter, the process proceeds to step S106.
(Step S106) the symbol replica generation unit b108-t-1 as _{x t,} generates a symbol replica b _{(m t).} Thereafter, the process proceeds to step S107.
(Step S107) cumulative metric calculation unit b 108-t-2, using a _{x t} generated in step S106, to calculate the cumulative metrics of the stage t. Thereafter, the process proceeds to step S108.

(Step S108) When the metric comparison unit b108-t-3 detects that the accumulated metric calculated in Step S107 exceeds the reference metric, the process proceeds to Step S109. If not, the process proceeds to step S113.
(Step S109) When the signal search unit b108 determines that m _t has reached M _t , the process proceeds to step S110. Otherwise, the process proceeds to step S112.
(Step S110) When the signal search unit b108 determines that t is T, the candidate sequence stored in the candidate sequence storage unit b107 is output as the final maximum likelihood sequence. Thereafter, the receiving device b1 ends the operation. If not, the process proceeds to step S111.
(Step S111) The signal search unit b108 substitutes t + 1 for t. Thereafter, the process returns to step S109.

(Step S112) the signal search section b108 substitutes _m t +1 to _{m t.} Thereafter, the process returns to step S106.
(Step S113) If t is 1, the process proceeds to Step S114. Otherwise, the process proceeds to step S115.
(Step S114) The metric comparison unit b108-1-3 stores the cumulative metric obtained in step S107 in the reference metric storage unit b106 as a new reference metric metric. Further, the candidate sequence at that time is stored in the candidate sequence storage unit b107. Thereafter, the process proceeds to step S109.
(Step S115) The symbol replica subtraction unit b108-t-4 calculates a replica subtraction signal using the symbol replica obtained in step S106. Thereafter, the process proceeds to step S116.
(Step S116) The signal search unit b108 substitutes 1 for m _t−1 , and then substitutes t−1 for t. Thereafter, the process returns to step S106.

Thus, according to the present embodiment, the reception device b1 performs communication using the MIMO transmission method. The channel estimation unit b102 generates a channel matrix between the transmission signal vector and the reception signal vector. The reference metric generation unit b105 calculates a reception signal replica Hx based on one of the signal sequences x (candidates of transmission signal vectors; may be candidate sequences) and a channel matrix, and the calculated reception signal replica Hx and the reception device A reference metric f indicating a difference between the received signal and the received signal vector y is calculated. The metric comparison unit b108-t-3 (comparison unit), based on a partial component (information bit candidate) of the signal sequence x, the received signal replica Hx and the received signal vector of the signal sequence x including the partial component It is determined whether or not the metric f indicating the difference from y is larger than the reference metric. Specifically, the metric comparison unit b108-t-3 compares the cumulative metric with the reference metric. Based on the determination result of the metric comparison unit b108-t-3, the signal search unit b108 switches whether or not to perform the calculation related to the signal sequence x including the partial component.
Thereby, the receiving apparatus b1 can determine, for example, whether or not the metric exceeds the reference metric based on some components of the signal sequence x, and based on the determination result, the signal sequence including the some components Whether to calculate the metric of x can be switched.

Specifically, the receiving apparatus b1 uses the metric of the signal sequence x obtained by arbitrary MIMO separation as the reference metric f, and corresponds to the accumulated metric when the calculated accumulated metric f (t) exceeds the reference metric f. For the signal sequence x to be performed, the subsequent processing (search for stages (t−1), (t−2),..., 1) is discarded. That is, when the cumulative metric f (t) is larger than the reference metric f, the metric indicating the difference between the received signal replica Hx of the transmission signal vector including a part of the component and the received signal vector y becomes larger than the reference metric f. judge. In this case, the receiving apparatus b1 does not perform an operation related to a transmission signal vector including a part of the components, that is, an accumulated metric or a metric. In other words, when the accumulated metric f (t) is smaller than the reference metric f, the metric indicating the difference between the received signal replica Hx and the received signal vector y of the transmission signal vector including some components is more than the reference metric f. Determined to be smaller. In this case, the receiving apparatus b1 performs a calculation related to a transmission signal vector including a part of the components, that is, a cumulative metric and a metric calculation.
As a result, the receiving device b1 can significantly reduce the amount of calculation compared to a normal MLD. In addition, since the receiving device b1 uses the accumulated metric of the leaf node as the reference metric, it can always reach the maximum likelihood sequence. That is, the performance of the receiving device b1 does not deteriorate as compared with the MLD. Further, for example, the receiving device b1 can reduce the time required for the MIMO separation process, and can efficiently perform the MIMO separation. Thus, the receiving apparatus b1 can appropriately perform MIMO separation.

As a more specific example, as described above, the QR decomposition unit b103 performs QR decomposition on the channel matrix H to generate a unitary matrix Q and an upper triangular matrix R. The signal conversion unit b104 calculates a triangulated reception signal y ′ based on the unitary matrix Q. The cumulative metric calculation unit b108-t-2 obtains a cumulative metric f (t) for some components based on some components of the candidate signal sequence x, the triangulated received signal number y ′ and the upper triangular matrix R. When the calculated cumulative metric f (t) is smaller than the reference metric f, a maximum likelihood sequence corresponding to the signal sequence x including some components is obtained.
Thus, the fact that the cumulative metric f (t + 1) at the stage t + 1 is larger than the reference metric means that the cumulative metric f (t) at the next stage t is also larger than the reference metric. That is, the receiving apparatus b1 receives, for example, the received signal replica Hx and the received signal vector of the signal sequence x including the (t + 1) th component to the Tth component based on the (t + 1) th component to the Tth component of the signal sequence x. It can be determined whether or not the metric f indicating the difference from y is larger than the reference metric.

  Further, according to the present embodiment, when the receiving apparatus b1 determines that the metric indicating the difference between the received signal replica Hx of the signal sequence x candidate and the received signal vector y is smaller than the reference metric f, the metric comparing unit b108-1-3 changes the reference metric f to the accumulated metric value f (1), that is, the metric f (t) relating to the candidate of the signal sequence x.

  In the first embodiment, the number of transmission antennas T and the number of signals to be multiplexed (referred to as the number of streams) are described as the same, but they may be different. For example, when the number of streams よ り 小 さ い is smaller than T, the receiving apparatus b1 performs processing in which the channel matrix shown in Expression (5) is changed to an R × ∪ matrix.

In the first embodiment, the receiving device b1 has been described for searching for all nodes that are not discarded. However, when the number of search nodes exceeds a predetermined threshold (hereinafter referred to as a search threshold), The processing may be interrupted and the sequence stored in the candidate sequence storage unit b107 at that time may be output. In this way, the receiving device b1 can stabilize the calculation amount. The search threshold value may be fixed when the receiving device b1 is designed, or may be updated when updating the firmware or software of the receiving device b1.
The receiving device b1 stops the process when the accumulated metric obtained at the leaf node falls below a predetermined threshold (hereinafter referred to as the metric threshold), and is stored in the candidate sequence storage unit b107 at that time. A certain series may be output. For example, the threshold value may be a value obtained by multiplying the initial value of the reference metric by a coefficient β (0 <β <1). In this way, the receiving device b1 can abort the calculation at an early stage. Β may be fixed when the receiving device b1 is designed, or may be updated when updating the firmware or software of the receiving device b1.

  In the first embodiment, it has been described that QR decomposition can be performed as in the equations (16) to (18). However, the equations (16) to (18) are executed when T> R. Can not. In such a case, the receiving apparatus b1 changes the unitary matrix Q in Equation (16) and the upper triangular matrix R in (17) to change the matrix Q and the matrix R as in the following Equations (31) and (32). It may be used.

  In this case, the receiving apparatus b1 sets the stage t to t = R,..., 1 instead of t = T,. In addition, the receiving device b1 changes to the cumulative metric of the stage R corresponding to the equation (23) and the replica subtraction signal y ′ (t) of the stage R corresponding to the equation (24), and the following equations (33) and (33) 34) is used.

Given the tree structure of FIG. 9, equation (33) and (34) means that the number of branches leading to the root node is _{M R M R + 1 ··· M} T. When T = R + 1 and the transmission antennas a1- (T-1) and a1-T use QPSK (that is, M _T-1 = M _T = 4), the number of branches connected to the root node is 16.

In the above-described first embodiment, the case has been described in which the receiving device b1 performs the metric comparison in all the stages. However, the receiving apparatus b1 may not be all, but may be performed in at least one stage.
In the first embodiment, the reception device b1 may perform the QR decomposition expressed by the equations (16) to (18) after changing the order of the channel matrix expressed by the equation (5). Specifically, the receiving apparatus b1 performs QR decomposition after making the channel matrix into the following equation (35).

  Here, rank (t) is a transmission antenna number in the descending order of the following equation (36).

  That is, the rearrangement is performed so that the square Euclidean norm of the column vector at the right end of H ′ is maximized. By doing so, the lower right element of the upper triangular matrix R can be increased, and the cumulative metric when using the wrong symbol replica at the shallow node can be increased, and the reference metric can be exceeded at the shallow node stage. And the number of search nodes can be reduced.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings. In the first embodiment, the case has been described in which the receiving apparatus b1 scans the tree structure illustrated in FIG. 9 in order and searches for an MLD solution. In the present embodiment, a description will be given of a method in which the receiving apparatus searches a tree structure by scanning in a level order. In the present embodiment, the communication system of FIG. 1 includes a receiving device b2 instead of the transmitting device a1 and the receiving device b1 according to the first embodiment.

  FIG. 15 is a schematic block diagram showing the configuration of the receiving device b2 according to the second embodiment of the present invention. When the receiving apparatus b2 (FIG. 15) according to the present embodiment is compared with the receiving apparatus b1 (FIG. 4) according to the first embodiment, the signal search unit b208 is different. However, the functions of other components (reception unit b101-r, channel estimation unit b102, QR decomposition unit b103, signal conversion unit b104, reference metric generation unit b105, reference metric storage unit b106, candidate sequence storage unit b107) The same as in the first embodiment. A description of the same functions as those in the first embodiment is omitted.

Hereinafter, processing performed by the signal search unit b208 will be described.
FIG. 16 is a schematic block diagram showing the configuration of the signal search unit b208 according to this embodiment. In this figure, the signal search unit b208 includes a stage t search unit b208-t (t = 1, 2,..., T), and the process performed by the stage t search unit b208-t is as follows. Also referred to as stage t processing.

  17 to 19 are schematic block diagrams illustrating a detailed configuration of the signal search unit b208 according to the present embodiment. In these figures, a stage t search unit b208-t (t = 1, 2,..., T−1, T) includes a symbol replica generation unit b208-t−1 and a cumulative metric calculation unit b208-t-2. A metric comparison unit b208-t-3 and a symbol replica subtraction unit b208-t-4. Below, the process of the stage T is demonstrated first using FIG. Next, the process of stage t after stage T-1 will be described using FIG. 18, and the process of stage 1 will be described finally using FIG.

FIG. 17 is a schematic block diagram illustrating a detailed configuration of the signal search unit b208 according to the present embodiment. This figure shows the relationship between the stage T search unit b208-T and the stage (T-1) search unit b208- (T-1).
The triangulated reception signal output from the signal conversion unit b104 is input to the symbol replica generation unit b208-T-1, the cumulative metric calculation unit b208-T-2, and the symbol replica subtraction unit b208-T-4.

  The symbol replica generation unit b208-T-1 starts the MLD process when detecting the input of the triangulated reception signal. The symbol replica generation unit b208-T-1 extracts all information bit candidates that can be transmitted from the transmission antenna a1-T, and generates all symbol replicas based on the extracted information bit candidates. Here, the symbol replica generation unit b208-T-1 extracts all information bit candidates based on the MCS information notified from the transmission device a1, and modulates each extracted information bit candidate to generate a symbol replica. Generate everything. The symbol replica generation unit b208-T-1 outputs the generated symbol replica to the cumulative metric calculation unit b208-T-2.

  The cumulative metric calculation unit b208-T-2 receives the symbol replica input from the symbol replica generation unit b208-T-1 and the component of the Tth row and Tth column of the triangular matrix R input from the QR decomposition unit b103. Multiply. The cumulative metric calculation unit b208-T-2 subtracts the multiplication result from a value corresponding to the component of the transmission antenna a1-T of the triangulated reception signal input from the signal conversion unit b104. The cumulative metric calculator b208-T-2 calculates the square Euclidean norm of the subtraction result. The cumulative metric calculation unit b208-T-2 outputs the calculated square Euclidean norm to the metric comparison unit b208-T-3 as the cumulative metric in the stage T. Further, the cumulative metric calculation unit b208-T-2 outputs the symbol replica input from the symbol replica generation unit b208-T-1 as it is to the metric comparison unit b208-T-2.

  The metric comparison unit b208-T-3 excludes the cumulative metric value input from the cumulative metric calculation unit b208-T-2 that is larger than the reference metric input from the reference metric storage unit b106 from the candidates. That is, the metric comparison unit b208-T-3 excludes candidate sequences (candidate sequences having information bit candidates as T components) including information bit candidates corresponding to cumulative metric values larger than the reference metric from the candidates. The metric comparison unit b208-T-3 outputs the cumulative metric that has not been excluded from the candidates to the cumulative metric calculation unit b208- (T-1) -2. Further, the metric comparison unit b208-T-3 outputs the symbol replica that has not been excluded from the candidates to the symbol replica subtraction unit b208-T-4.

  The symbol replica subtraction unit b208-T-4 uses the first component of the T-th column vector among the symbol replica input from the metric comparison unit b208-T-3 and the triangular matrix R input from the QR decomposition unit b103. Multiply up to the (T-1) -th component. The symbol replica subtraction unit b208-T-4 subtracts the multiplication result from the vector obtained by taking the first to (T-1) th components of the triangulated reception signal input from the signal conversion unit b104. The symbol replica subtraction unit b208-T-4 outputs the T-1th of the T-1 replica subtraction signals to the cumulative metric calculation unit b208- (T-1) -2 of the stage T-1. Further, the symbol replica subtraction unit b208-T-4 converts the 1st to T-2th of the T-1 replica subtraction signals into the symbol replica subtraction unit b208- (T-1) of the stage (T-1). Output to -4. These processes are performed by the number of symbol replicas input from the metric comparison unit b208-T-3. The symbol replica subtraction unit b208-T-4 outputs a processing start signal to the symbol replica generation unit b208- (T-1) -1 of the stage (T-1).

Next, the stage t after T−1, that is, the stage t where t ≦ T−1 will be described.
FIG. 18 is another schematic block diagram illustrating a detailed configuration of the signal search unit b208 according to the present embodiment. This figure shows the relationship between the stage (t + 1) search unit b208- (t + 1), the stage t search unit b208-t, and the stage (t-1) search unit b208- (t-1). However, since the process is different when t = 1, the process of the stage 1 search unit b208-1 will be described later.

  The symbol replica generation unit b208-t-1 starts a process when a processing start signal is input from the symbol replica subtraction unit b208- (t + 1) -4. The symbol replica generation unit b208-t-1 extracts all information bit candidates that can be transmitted from the transmission antenna a1-t, and generates all symbol replicas based on the extracted information bit candidates. Here, the symbol replica generation unit b208-t-1 extracts all information bit candidates based on the MCS information notified from the transmission device a1, and modulates each extracted information bit candidate to generate a symbol replica. Generate everything. The symbol replica generation unit b208-t-1 outputs the generated symbol replica to the cumulative metric calculation unit b208-t-2.

  The cumulative metric calculation unit b208-t-2 receives the symbol replica input from the symbol replica generation unit b208-t-1 and the component in the t-th row and t-column of the triangular matrix R input from the QR decomposition unit b103. Multiply. The cumulative metric calculation unit b208-t-2 subtracts the multiplication result from the replica subtraction signal input from the symbol replica subtraction unit b208- (t + 1) -4. The cumulative metric calculation unit b208-t-2 calculates the square Euclidean norm of the subtraction result. The cumulative metric calculation unit b208-t-2 adds the calculated square Euclidean norm and the surviving cumulative metric input from the metric comparison unit b208- (t + 1) -3 to calculate the cumulative metric at the stage t. This accumulated metric is output to the metric comparison unit b208-t-3. Also, the cumulative metric calculation unit b208-t-2 outputs the symbol replica input from the symbol replica generation unit b208-t-1 to the metric comparison unit b208-t-2 as it is.

  The metric comparison unit b208-t-3 excludes the cumulative metric value input from the cumulative metric calculation unit b208-t-2 that is larger than the reference metric input from the reference metric storage unit b106 from the candidates. That is, the metric comparison unit b208-t-3 excludes candidate sequences (candidate sequences having information bit candidates as T components) including information bit candidates corresponding to cumulative metric values larger than the reference metric from the candidates. The metric comparison unit b208-t-3 outputs the cumulative metric that has not been excluded from the candidates to the cumulative metric calculation unit b208- (t-1) -2. Also, the metric comparison unit b208-t-3 outputs the symbol replica that has not been excluded from the candidates to the symbol replica subtraction unit b208-t-4.

  The symbol replica subtraction unit b208-t-4 uses the first component of the t-th column vector from the symbol replica input from the metric comparison unit b208-t-3 and the triangular matrix R input from the QR decomposition unit b103. Multiply up to the (t−1) -th component. The symbol replica subtraction unit b208-t-4 subtracts the multiplication result from a vector obtained by extracting the first to (t-1) th components of the triangulated reception signal input from the signal conversion unit b104. The symbol replica subtraction unit b208-t-4 outputs the t−1th of the t−1 replica subtraction signals to the accumulated metric calculation unit b208- (t−1) -2 of the stage t−1. Also, the symbol replica subtraction unit b208-t-4 converts the first to t-2th of the t-1 replica subtraction signals into the symbol replica subtraction unit b208- (t-1) of the stage (t-1). Output to -4. These processes are performed for the number of symbol replicas input from the metric comparison unit b208-t-3. The symbol replica subtraction unit b208-t-4 outputs a processing start signal to the symbol replica generation unit b208- (t-1) -1 of the stage (t-1).

Finally, stage 1 will be described.
FIG. 19 is another schematic block diagram illustrating a detailed configuration of the signal search unit b208 according to the present embodiment. This figure shows the relationship between the stage 2 search unit b208-2 and the stage 1 search unit b208-1. The stage 1 search unit b208-1 is different from the stage t search unit b208-t where t ≧ 2 in that it does not include a symbol replica subtraction unit.

  The symbol replica generation unit b208-1-1 starts the process when a processing start signal is input from the symbol replica subtraction unit b208-2-4. The symbol replica generation unit b208-1-1 extracts all information bit candidates that can be transmitted from the transmission antenna a1-1, and generates all symbol replicas based on the extracted information bit candidates. Here, the symbol replica generation unit b208-1-1 extracts all information bit candidates based on the MCS information notified from the transmission device a1, and modulates each extracted information bit candidate to generate a symbol replica. Generate everything. The symbol replica generation unit b208-1-1 outputs the generated symbol replica to the cumulative metric calculation unit b208-1-2.

  The cumulative metric calculation unit b208-1-2 includes the symbol replica input from the symbol replica generation unit b208-1-1 and the first row and first column component of the triangular matrix R input from the QR decomposition unit b103. Multiply. The cumulative metric calculation unit b208-1-2 subtracts the multiplication result from the replica subtraction signal input from the symbol replica subtraction unit b208-2-4. The cumulative metric calculator b208-1-2 calculates the square Euclidean norm of the subtraction result. The cumulative metric calculation unit b208-1-2 adds the calculated square Euclidean norm and the surviving cumulative metric input from the metric comparison unit b208-2-3 to calculate the cumulative metric in stage 1. This accumulated metric is output to the metric comparison unit b208-1-3.

  The metric comparison unit b208-1-3 selects the smallest one of the cumulative metric values input from the cumulative metric calculation unit b208-1-2. The metric comparison unit b208-1-3 outputs the candidate series corresponding to the symbol replica of each stage corresponding to the selected cumulative metric to the candidate series storage unit b107.

<About the operating principle>
Hereinafter, the operation principle of the receiving device b2 will be described.
In the first embodiment, the case where the tree structure as shown in FIG. 9 is scanned in the forward order has been described. In the second embodiment, the tree structure is scanned in level order. This shows an example in which search nodes are reduced. In addition, the figure showing an example of selection of the candidate series regarding the reference metric according to the present embodiment is the same as FIG.

20 to 22 are schematic diagrams illustrating an example of a search for modulation symbol candidates according to the present embodiment.
FIG. 20 illustrates an example of processing of the signal search unit b208 according to the present embodiment. In this figure, candidates for modulation symbols connected by bold lines indicate that the cumulative metric has been calculated based on the symbol replicas. As shown in FIG. 20, in this embodiment, the search is first performed on nodes at the same level (stage T). This figure shows a state in which a search for nodes 221 to 224 has been performed. This figure is an example in the case where the node 222 is selected and the accumulated metric up to that node exceeds the reference metric. In this case, the signal search unit b108 discards the subsequent search for the candidate series including the node 222.

  FIG. 21 illustrates processing subsequent to the processing illustrated in FIG. This figure shows the nodes 231-1 to 231-4, 232-1 of the next level (stage T-1) for the nodes 221, 223, and 224 other than the node (node 222) excluded from the candidates in FIG. The state in which searches for ˜232-4 and 233-1 to 233-4 are performed is shown. In FIG. 21, as a result, it is assumed that the accumulated metrics of the nodes 231-1, 231-2, 231-4, 232-3, 233-1, and 233-3 exceed the reference metric.

  FIG. 22 illustrates a process subsequent to the process illustrated in FIG. In this case, the signal search unit b208 searches for candidate sequences including the nodes 231-3, 232-1, 232-2, 232-4, and 233-4. For candidate sequences including other nodes, the signal search unit b208 discards the search. As a result, the signal search unit b208 searches for 24 leaf nodes, and the number of search nodes for 40 can be reduced. Then, the signal search unit b208 stores, in the candidate sequence storage unit b107, a candidate sequence including the 24 leaf nodes to be searched, that has the smallest metric.

<Operation of Receiving Device b2>
FIG. 23 is a flowchart showing the operation of the receiving device b2 according to this embodiment. In addition, the operation | movement which this figure shows is a process after receiving part b101-r of FIG. 15 outputs a received signal to the channel estimation part b102 and the signal conversion part b104.

(Step S201) The channel estimation unit b102 obtains a channel matrix by performing channel estimation based on the received signal and the pilot symbol. Thereafter, the process proceeds to step S202.
(Step S202) The QR decomposition unit b103 obtains a unitary matrix Q and an upper triangular matrix R by performing QR decomposition of the channel matrix H configured using the channel values obtained in step S202. Then, it progresses to step S203.
(Step S203) The signal converter b104 multiplies the received signal vector by the unitary matrix Q obtained in Step S202, and calculates a triangulated received signal. Thereafter, the process proceeds to step S204.

(Step S204) The reference metric generation unit b105 performs MIMO separation using the upper triangular matrix R obtained in step S202 and the triangulated reception signal calculated in step S203. The reference metric generation unit b105 calculates a reference metric using the MIMO separation result and stores it in the reference metric storage unit b106. Further, the candidate sequence at that time is stored in the candidate sequence storage unit b107. Thereafter, the processing of S205 to S208 is repeated. Here, the signal search unit b108 subtracts t by 1 from t = T to t = 1, and repeats the processing of S205 to S208.

(Step S205) The symbol replica generation unit b208-t-1 generates all symbol replicas. Thereafter, the process proceeds to step S206.
(Step S206) The cumulative metric calculation unit b208-t-2 calculates the cumulative metric of the stage t using the symbol replica obtained in step S205. Thereafter, the process proceeds to step S207.

(Step S207) The metric comparison unit b208-t-3 excludes the cumulative metric obtained in step S206 that exceeds the reference metric from the candidates. If t = 1, the minimum value is selected from the cumulative metrics obtained in step S206, and the corresponding candidate sequence is stored in the candidate sequence storage unit b107. Thereafter, the process proceeds to step S208.
(Step S208) The symbol replica subtraction unit b208-t-4 calculates a replica subtraction signal using the symbol replica obtained in step S205. However, this is not performed when t = 1. After that, when exiting the loop, the candidate sequence stored in the candidate sequence storage unit b107 is output as the final maximum likelihood sequence. Thereafter, the receiving device b2 ends the operation.

Thus, according to the present embodiment, by scanning the tree structure in level order, the same effect as that of the first embodiment can be realized with a simplified circuit configuration.
In the second embodiment, the case where level order scanning is performed has been described. However, it may be combined with the previous order scanning described in the first embodiment.

(Third embodiment)
Hereinafter, the third embodiment of the present invention will be described in detail with reference to the drawings. In the first embodiment and the second embodiment, a metric corresponding to a candidate sequence serving as an MLD solution is calculated. In this embodiment, a method for calculating a log likelihood ratio (LLR) will be described. In the present embodiment, the communication system of FIG. 1 includes a transmission device a3 and a reception device b3 instead of the transmission device a1 and the reception device b1.

  FIG. 24 is a schematic block diagram showing the configuration of the transmission device a3 according to the third embodiment of the present invention. When the transmission apparatus a3 (FIG. 24) according to the present embodiment is compared with the transmission apparatus a1 (FIG. 2) according to the first embodiment, the transmission apparatus a3 newly includes an encoding unit a306. However, the functions of other components (the bit allocation unit a101, the modulation unit a102-t, the mapping unit a104-t, and the transmission unit a105-t) are the same as those in the first embodiment. A description of the same functions as those in the first embodiment is omitted.

  The encoding unit a306 encodes information bits to be transmitted to the receiving apparatus b3 using an error correction code such as a convolutional code, a turbo code, and an LDPC (Low Density Parity Check) code, Is generated. The encoding unit a306 outputs the generated encoded bits to the bit allocation unit a101. Note that the information indicating the code used for this encoding is notified from one of the transmission units a105-t to the reception device b3 as, for example, MCS information. The code may be different for each modulation unit a102-t, that is, for each transmission antenna a1-t, or may be different for each frequency band (for example, component carrier).

  FIG. 25 is a schematic block diagram showing the configuration of the receiving device b3 according to this embodiment. When the receiving apparatus b3 (FIG. 25) according to the present embodiment is compared with the receiving apparatus b1 (FIG. 4) according to the first embodiment, the receiving apparatus b3 includes a QR decomposition unit b303, a reference metric b305, and a reference metric storage unit b306. The operation of the signal search unit b308 is different. Also, the receiving device b3 does not have the candidate sequence storage unit b107, but newly includes an LLR calculation unit b309 and a decoding unit b310. However, the functions of other components (reception unit b101-r, channel estimation unit b102, signal conversion unit b104) are the same as those in the first embodiment. A description of the same functions as those in the first embodiment is omitted.

The QR decomposition unit b303 replaces the column vector of the channel matrix input from the channel estimation unit b102 in order to calculate the LLR of the bits output from the transmission antenna a1-p (p is also referred to as calculation component information). Specifically, QR decomposition section b303 has replaced a column vector h _t of the channel matrix H of as h _p shown in equation (6) becomes rightmost equation (5), the matrix after swapping QR decomposition is performed on the image. However, p = 1,..., T.
The QR decomposition unit b303 outputs the unitary matrix Q calculated by the QR decomposition to the signal conversion unit b104, and outputs the calculated upper triangular matrix R to the reference metric generation unit b305 and the signal conversion unit b308. In addition, the QR decomposition unit b303 outputs the rightmost transmission antenna number p to the LLR calculation unit b309. When the processing up to the LLR calculation unit b309 is completed, the LLR calculation unit b309 outputs the LLR of the bits output from the transmission antennas a1-p. By repeating this T times for different antennas, the LLRs of the bits output from all the transmitting antennas are calculated.
In the following description, it is assumed that the QR decomposition unit b303 outputs a unitary matrix Q and an upper triangular matrix R by performing rearrangement in the order of p = T,. Note that the rearrangement may not be in this order. In the following description, p = T, that is, no rearrangement will be described. However, even if p is a different value, the processing content does not change.

The reference metric generation unit b305 performs MIMO separation based on the triangulated reception signal input from the signal conversion unit b104 and the upper triangular matrix R input from the QR decomposition unit b303. However, the reference metric generation unit b305 performs MIMO separation of the modulation symbols _{s T} on the assumption with that fixed at b (m). Reference metric generation unit b305 is the process m = 1, · · ·, performs _{M T} Street _{M T,} stores the respective metrics based metric storage unit B 306.
Reference metric storage unit b306 outputs _{M T} number of reference metric which is stored in the signal search section B308.

Hereinafter, processing performed by the signal search unit b308 will be described.
FIG. 26 is a schematic block diagram showing the configuration of the signal search unit b308 according to this embodiment. When the signal search unit b308 (FIG. 26) according to the present embodiment is compared with the signal search unit b108 (FIG. 5) according to the first embodiment, the signal search unit b308 includes the stage T search unit b308-T and the stage. The operation of one search unit b308-1 is different, and a reference metric selection unit B30 is newly provided. However, the functions of other components (stage t search unit b308-t (t = 2, 3,..., T-1) are the same as those in the first embodiment. The same as those in the first embodiment. A description of the function is omitted.

  27 and 28 are schematic block diagrams illustrating a detailed configuration of the signal search unit b308 according to the present embodiment. When the signal search unit b308 (FIGS. 27 and 28) according to the present embodiment is compared with the signal search unit b108 (FIGS. 6 to 8) according to the first embodiment, the signal search unit b308 generates a symbol replica. The operations of the unit b308-T-1 and the metric comparison unit b308-1-3 are different. Further, the stage T search unit b308-T does not include the metric comparison unit b308-T-3, but newly includes a reference metric selection unit B30. However, the functions of other components (symbol replica generation unit b108-t (t = 1 to T-1) and cumulative metric calculation unit b108-t-2 (t = 1 to T) are the same as those in the first embodiment. The description of the same function as in the first embodiment is omitted.

First, the symbol replica generation unit b308-T-1 and the reference metric selection unit B30 will be described with reference to FIG.
The symbol replica generation unit b308-T-1 starts the process when detecting the input of the triangulated reception signal. Specifically, first, one information bit candidate (information bit candidate) that can be transmitted from the transmission antenna a1-T is selected, and one symbol replica is generated based on the selected information bit candidate. Here, the symbol replica generation unit b308-1-1 determines information bit candidates one by one based on the MCS information notified from the transmission device a3, and modulates the determined information bit candidates to generate a symbol replica. Generate one by one. The symbol replica generation unit b308-T-1 outputs the generated symbol replica to the cumulative metric calculation unit b108-T-2, the symbol replica subtraction unit b108-T-4, and the reference metric selection unit B30.
In the processing for the one symbol replica that has been output, a processing end signal is received from the symbol replica generation unit b108- (T-1) -1 of the stage (T-1) search unit b308- (T-1). If so, the process ends. When the processing for one symbol replica is completed, the symbol replica generation unit b308-T-1 selects and selects an information bit candidate different from the previously selected information bit candidate from the information bit candidates. Modulate information bit candidates. That is, the symbol replica generation unit b308-T-1 generates a symbol replica of a modulation symbol different from the previously generated symbol replica, and performs the same processing. When these processes are performed on all information bit candidates, the stage T ends the process and outputs a process end signal to the LLR calculation unit b309.

Reference metric selecting unit B30, from the M _T number of reference metric input from the reference metric storage section B 306, those corresponding to the symbol replica input from the symbol replica generation unit b308-T-1 1 single selected , The metric comparison unit b308-1-3 and the metric comparison units b108-2-3 to b108- (T-1) -3.
The metric comparison units b108-2-3 to b108- (T-1) -3 use the reference metric input from the reference metric selection unit B30 instead of the reference metric input from the reference metric storage unit b106. Thus, the same processing as in the first embodiment is performed.

Next, stage 1 will be described.
FIG. 28 is another schematic block diagram illustrating a detailed configuration of the signal search unit b308 according to the present embodiment. This figure shows the relationship between the stage 2 search unit b308-2 and the stage 1 search unit b308-1.

  When the cumulative metric input from the cumulative metric calculation unit b108-1-2 falls below the reference metric input from the reference metric selection unit B30, the metric comparison unit b308-1-3 The accumulated metric is saved as a new reference metric. However, the reference metric storage unit b306 stores the reference metric corresponding to the symbol number output by the symbol replica generation unit b308-1-1. Thereafter, the metric comparison unit b308-1-3 outputs a signal indicating the end of processing to the symbol replica generation unit b308-1-1.

Returning to FIG. 25, the remaining functions will be described.
The LLR calculation unit b309 calculates the LLR based on the reference metric input from the reference metric storage unit b306. The LLR calculation unit b309 outputs the calculated LLR to the decoding unit b310 when the calculation of LLRs for all the transmission antennas has been completed. Otherwise, the LLR calculation unit b309 notifies the QR decomposition unit b303 of a process end signal related to the transmission antenna a1-p.

  The decoding unit b310 uses the LLR input from the LLR calculation unit b309, for example, maximum likelihood decoding, maximum a posteriori probability (MAP), log-MAP, Max-log-MAP, SOVA (Soft Decoding processing is performed using Output Viterbi Algorithm), Sum-product, or the like.

<About the operating principle>
Hereinafter, a method for outputting the LLR using the MLD will be described. Specifically, a method will be described in which the receiving device b3 obtains the LLR of the bits output from the transmission antenna a1-T.
FIG. 29 is a schematic diagram illustrating an example of a search for modulation symbol candidates according to the present embodiment. In order to obtain the bit LLR from the transmission antenna a1-T, first, the reference metric generation unit b305 in FIG. 25 obtains the minimum metric of the path including each node of the stage T as shown in FIG. Here, the minimum metric is the one having the smallest value among the metrics of the candidate series. There are M ways. In FIG. 29, for example, the metric of the candidate series including the leaf node 325 represents the minimum metric of the candidate series including the node 321. This is the minimum metric for fixed x _T to b (1). The same applies to the other leaf nodes.

In order to obtain such a minimum metric, the reference metric generation unit b305 applies the minimum metric to the subtree having the node at the stage T as a root node by the method described in the first embodiment or the second embodiment. You can ask for. Accordingly, in the present embodiment, in order to perform metric calculation with a fixed _{x T} to b (m) m = 1, ···, against the M, the reference metric generation unit b305 has a reference metric calculating M Street.

In FIG. 27, the stage T search unit b308-T does not have a metric comparison unit. Further, in FIG. 28, the metric comparison unit b308-1-3 stage T searching unit b308-1, among the reference metric of street M of reference metric storage unit b306 is stored, and is fixed as _{x T} symbol Update the baseline metric corresponding to the replica.
After the end of processing signal searching unit B308, the metric stored in the reference metric storage unit b306 and f _m. f _m is the metric in the case _{where x T} is fixed to the b (m). For example, in FIG. 29, the metric of the candidate sequence including the leaf node 325 includes f ₁ , the metric of the candidate sequence including the leaf node 326 includes f ₂ , the metric of the candidate sequence including the leaf node 327 includes f ₃ , and includes the leaf node 328. candidate sequence of metric becomes the f _4.

Next, a method of calculating the LLR using the obtained metric f _m. The q-th bit of transmit antennas a1-T is mapped to a modulation symbol is b _q. For example, when the transmission antenna a1-T uses QPSK, modulation symbols 311 to 314 can be considered as shown in the IQ plane of FIG. It is assumed that b (1), b (2), b (3), and b (4) are in the order of the modulation symbols 311 to 314. At this time, (b ₁ , b ₂ ) = (0, 0) is a modulation symbol 311 (b (1)), and (b ₁ , b ₂ ) = (0, 1) is a modulation symbol 312 (b (2)). , (B ₁ , b ₂ ) = (1, 0) as modulation symbol 313 (b (3)), (b ₁ , b ₂ ) = (1, 1) as modulation symbol 314 (b (4)) Shall be assigned to This is an example, and other combinations may be used.

Next, when the bit b _q is 0, a set of modulation symbol numbers that can be taken is B _{q, 0,} and when the bit b _q is 1, a set of modulation symbol numbers that can be taken is B _{q, 0. Set} to ₁ . For example, in the example of FIG. 30, B _1,0 = [1,2], B _1,1 = [3, 4], B _2,0 = [1, 3], B _2,1 = [2, 4 ].
If the LLR of the bit b _q is λ (b _q ), λ (b _q ) is expressed by the following equation (37).

However, σ ² is noise power and may be estimated simultaneously with channel estimation by the channel estimation unit b102, for example. The LLR calculation unit b309 calculates the LLR based on Expression (37). Equation (37) is a calculation method when λ (b _q ) is defined by the following equation (38).

However, p (A | B) is a conditional probability of A when B is a condition. When the definition of λ (b _q ) is the following equation (39), the calculation is performed as the following equation (40).

The decoding unit b310 may use either λ (b _q ) in the above formula (38) or (39), and which one is used depends on the specification of the decoding unit b310.
The method for calculating the bit LLR of the transmission antenna a1-T has been described above.

  Next, a method for calculating the bit LLRs of the transmission antennas a1-p (p ≠ T) other than t = T will be described. First, before performing QR decomposition, the QR decomposition unit b303 rearranges the column vectors of the channel matrix shown in Expression (5) so that the column vector hp of the channel matrix shown in Expression (6) comes to the rightmost. To. By doing so, the node having the height T of the tree structure in FIG. 29 is deformed so as to correspond to xp. Therefore, by applying the above-described LLR calculation method, the bit LLR of the transmission antenna a1-p is applied. Can be calculated. This may be performed for p = T−1,. For this purpose, the LLR calculation unit b309 in FIG. 25 notifies the end of the LLR calculation to the QR decomposition unit b303, and the QR decomposition unit b303 rearranges the channel matrix and repeats the process.

<About the operation of the receiving device b3>
FIG. 31 is a flowchart showing the operation of the receiving device b3 according to this embodiment. The operation shown in this figure is processing after the receiving unit b101-r in FIG. 25 outputs the received signal to the channel estimation b102 and the signal converting unit b104. FIG. 31 illustrates a case where the stage number t, the modulation symbol m _{t at} the stage t, and the modulation symbol number M _t used at the stage t are used as variables.

(Step S301) The channel estimation unit b102 obtains a channel matrix by performing channel estimation based on the received signal and the pilot symbol. Thereafter, the process proceeds to step S302.
(Step S302) QR decomposition unit b303 is, QR from rearranges to the channel matrix H constituted by using the obtained channel value in step S302, the p column vector _{h p} becomes rightmost By performing the decomposition, a unitary matrix Q and an upper triangular matrix R are obtained. Thereafter, the process proceeds to step S303.
(Step S303) The signal conversion unit b104 multiplies the reception signal vector by the unitary matrix Q obtained in step S302 to calculate a triangulated reception signal. Thereafter, the process proceeds to step S304.

(Step S304) reference metric generation unit b305 uses a triangular matrix R and triangulation received signal calculated at step S303 on obtained in step S302, the MIMO separation by fixing the _{x T} to b _{(m T)} Do. This _is done with respect to _{m T = 1, ···, M} T. Reference metric generation unit b305 calculates the reference metric of street _{M T} using MIMO separation results of street _{M T,} stores the reference metric storage unit B 306. Thereafter, the process proceeds to step S305.
(Step S305) The signal search unit b308 sets mT = 1 and t = T. Thereafter, the process proceeds to step S306.
(Step S306) the symbol replica generation unit b108-t-1 (t = 1, ···, (T-1)) or the symbol replica generation unit b308-T-1 as _{x t,} symbol replica b _{(m t} ) Is generated. Thereafter, the process proceeds to step S307.

(Step S307) cumulative metric calculation unit b 108-t-2, using a _{x t} generated in step S306, to calculate the cumulative metrics of the stage t. Thereafter, the process proceeds to step S308.
(Step S308) If t is T, the process proceeds to Step S314. If not, the process proceeds to step S309.
(Step S309) If the metric comparison unit b108-t-3 detects that the accumulated metric obtained in Step S307 exceeds the reference metric, the process proceeds to Step S310. Otherwise, the process proceeds to step S314.
(Step S310) If the signal search unit b308 determines that mt has reached Mt, the process proceeds to step S311. Otherwise, the process proceeds to step S313.

(Step S311) When the signal search unit b308 determines that t is T, the process proceeds to the end of the loop. Thereafter, in the case of the end of the loop, the receiving device b3 ends the operation. Otherwise, the process proceeds to step S312.
(Step S312) The signal search unit b308 substitutes t + 1 for t. Thereafter, the process returns to step S310.
(Step S313) the signal search section b308 substitutes _m t +1 to _{m t.} Thereafter, the process returns to step S306.
(Step S314) If the signal search unit b308 determines that t is 1, the process proceeds to Step S315. Otherwise, the process proceeds to step S316.

(Step S315) The metric comparison unit b308-1-3 stores the accumulated metric obtained in step S307 in the reference metric storage unit b306 as a new reference metric metric. However, it updates the reference metric corresponding to m _T at that time. Thereafter, the process proceeds to step S310.
(Step S316) The symbol replica subtraction unit b108-t-4 calculates a replica subtraction signal using the symbol replica obtained in step S306. Thereafter, the process proceeds to step S317.
(Step S317) The signal search unit b308 substitutes 1 for m _t −1, and then substitutes t−1 for t. Thereafter, the process returns to step S306.

As described above, according to the present embodiment, the QR decomposition unit b303 is a column vector of the channel matrix H based on the calculated component information indicating the component p of the signal sequence x and the log likelihood ratio to be calculated. QR decomposition is performed on the matrix whose order is changed to generate a unitary matrix Q and an upper triangular matrix R. The signal conversion unit b104 calculates a triangulated reception signal y ′ based on the unitary matrix Q. The reference metric b305 generates a reference metric f for each calculation target candidate (information bit candidate) that is a candidate for the component p indicated by the calculated component information. The signal search unit b308 calculates, for each calculation target candidate, the minimum metric having the minimum metric among the signal series x including the calculation target candidate. The LLR calculation unit b309 calculates the LLR based on the minimum metric calculated by the signal search unit b308. The decoding unit b310 decodes based on the LLR calculated by the LR calculation unit b309 and outputs the decoded information bits.
Thereby, the receiving device b3 can calculate LLR.

  In the third embodiment, the rearrangement shown in the equation (35) cannot be applied as it is. In order to apply this in the present embodiment, when obtaining the bit LLR of the transmission antenna a1-t, the rightmost of H ′ is fixed to ht, and the first to T-1 columns are arranged in ascending order of power. It should be in the form of

  In the third embodiment, the case has been described in which the QR decomposition unit b303 performs T reordering and QR decomposition. However, the number may not be T. In FIG. 29, the minimum metric of the path including the node of the stage T is obtained for calculating the LLR of the stage T, but the minimum metric of the path including the node of the stage t is also obtained for the stage t other than t = T. Thus, the LLR can be calculated. For example, when the LLR is calculated simultaneously not only for the stage T but also for the stage T-1, the number of QR decompositions can be reduced to T / 2 times because the LLR obtained by one QR decomposition is equivalent to two transmission antennas. .

  In the third embodiment, the maximum likelihood metric and the candidate sequence at that time are the same no matter what sort is performed by the QR decomposition unit b303. Therefore, at the time of the first signal search (when p = T) You may save them. In this way, one of the subtree searches as shown in FIG. 29 reaches the maximum likelihood metric, so that one search can be omitted.

In the third embodiment, the case of performing the forward order scan as in the first embodiment has been described. However, the level order scan may be performed as in the second embodiment. Also, the forward scan and the level order may be combined.
In the third embodiment, the decoding unit b310 may output the encoded bit LLR. When the coded bit LLR is output, it can be applied to a repetitive receiving apparatus that performs turbo equalization or decision-directed channel estimation.

In the first to third embodiments, examples of application to single carrier communication have been described. However, the present invention can also be applied to OFDM (Orthogonal Frequency Division Multiplexing), SC-FDMA, and the like. In particular, in SC-FDMA, since there is inter-symbol interference even if it is not MIMO, the relational expression (3) can be created. The present invention is not limited to this, and can be applied to all cases where the same relational expression as Expression (3) is obtained, such as inter-carrier interference, inter-cell interference, and inter-code interference. It can also be applied to multi-user MIMO.
In the first to third embodiments, the case where the reception signal vector and the transmission signal vector are longitudinal vectors and QR decomposition is performed on the channel matrix has been described. However, the reception signal vector and the transmission signal vector are horizontal vectors. Also good. When the reception signal vector at that time is yw, the transmission signal vector is sw, the channel matrix is Hw, and the noise vector is nw, the following equation (41) is obtained.

In this case, LQ decomposition is performed on Hw.
Further, error detection may be performed on a MIMO separation result such as MMSE detection, and the present invention may be performed when there is an error. In the case of error correction decoding, the decoding result may be used as a reference metric. Alternatively, MAP (Maximum A posteriori Probability) detection may be performed using the bit occurrence probability that can be obtained from the LLR of the decoding result.

<Experimental result>
Hereinafter, the result of the computer simulation performed to show the effectiveness of the communication system according to the present embodiment will be described.

  FIG. 32 is a schematic diagram illustrating an example of simulation conditions for MIMO communication according to the present embodiment. In the simulation of this example, the simulation was performed under the conditions of FIG. The first embodiment is used, and the rearrangement shown in Expression (31) is performed.

  FIG. 33 is a schematic diagram illustrating an example of a simulation result of MIMO communication (8 × 8) according to the present embodiment. In this figure, the horizontal axis represents average Eb / N0 (average received energy per bit to noise power density ratio), and the vertical axis represents average bit error rate (BER) characteristics. This figure shows the result of a simulation performed under the simulation conditions of FIG. In FIG. 33, characteristic 1 is a characteristic when MIMO separation is performed using linear processing by MMSE, and characteristic 2 is a characteristic of MLD using the method of the present invention. It can be confirmed that the characteristics are greatly improved compared to MMSE.

  FIG. 34 is a schematic diagram illustrating an example of the average number of search nodes according to the present embodiment. This figure shows an example of the number of nodes for each stage and the average number of search nodes when the method of the present invention is used when the BER characteristic with the average Eb / N0 of 15 dB in FIG. 33 is measured. Stage 8 always arrives to calculate the initial cumulative metric, so it is not reduced and all 16 nodes are always searched. It can be seen that nodes other than stage 8 have been reduced. In particular, for stage 1, which is a leaf node, only an average of 586 is searched out of about 4.2 billion nodes. It can be seen that the node search rate can be compressed to 7.80 × 10 −7 even in the total number of searches.

  FIG. 35 is a schematic diagram illustrating an example of a simulation result of MIMO communication (16 × 16) according to the present embodiment. In this figure, the horizontal axis represents average Eb / N0, and the vertical axis represents average BER characteristics. This figure shows the result of a simulation performed under the simulation conditions of FIG. In FIG. 35, characteristic 1 is a characteristic when MIMO separation is performed using linear processing by MMSE, and characteristic 2 is a characteristic of MLD using the technique of the present invention. It can be confirmed that the characteristics are greatly improved compared to MMSE.

  FIG. 36 shows an example of the number of nodes for each stage and the average number of search nodes when the method according to the present embodiment is used when the BER characteristic with an average Eb / N0 of 14 dB is measured in FIG. FIG. The number of search nodes is reduced more than the example of FIG. 34, and it can be seen that the node search rate can be compressed to 2.42 × 10 −15 in the total number of searches.

In each of the embodiments described above, t is an example of information for identifying a transmission antenna and information for identifying a component of a candidate sequence. However, the present invention is not limited to this, and t is a transmission antenna port, a stream, a layer, It may be information for identifying. T may be the number of transmission antenna ports, the number of streams, or the number of layers.
In addition, although r is an example of information identifying a receiving antenna and information identifying a received vector component, the present invention is not limited to this, and r is information identifying a receiving antenna port, a stream, and a layer. May be. R may be the number of reception antenna ports, the number of streams, or the number of layers.

Note that some of the transmission devices a1 and a3 and the reception devices b1 to b3 in the above-described embodiment, for example, the QR decomposition unit b103 and the signal search unit b108 may be realized by a computer. In that case, the program for realizing the control function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read by a computer system and executed.
Here, the “computer system” is a computer system built in the transmission devices a1 and a3 or the reception devices b1 to b3, and includes hardware such as an OS and peripheral devices. Further, the “computer-readable recording medium” refers to a storage device such as a portable medium such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and a hard disk built in the computer system. Furthermore, the “computer-readable recording medium” is a medium that dynamically holds a program for a short time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, In such a case, a volatile memory inside a computer system serving as a server or a client may be included and a program that holds a program for a certain period of time. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.
Further, part or all of the transmission devices a1 and a3 and the reception devices b1 to b3 in the above-described embodiments may be realized as an integrated circuit such as an LSI (Large Scale Integration). Each functional block of the transmission devices a1 and a3 and the reception devices b1 to b3 may be individually made into a processor, or a part or all of them may be integrated into a processor. Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. Further, in the case where an integrated circuit technology that replaces LSI appears due to progress in semiconductor technology, an integrated circuit based on the technology may be used.
As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to

a1, a3... transmitting device, b1, b2, b3... receiving device, a1-1 to a1-T... transmitting antenna, b1-1 to b1-R. Bit allocation unit, a102-1 to a102-T ... modulation unit, a103 ... pilot generation unit, a104-1 to a104-T ... mapping unit, a105-1 to a105-T ... transmission unit , A306 ... coding part, b101-1 to b101-R ... receiving part, b102 ... channel estimation part, b103, b303 ... QR decomposition part, b104 ... signal conversion part, b105, b305 ... reference metric generation unit, b106, b306 ... reference metric storage unit, b107 ... candidate sequence storage unit, b108, b208, b308 ... signal search unit, b108-t, b20 -T ... stage t search unit, b308-T ... stage T search unit, b308-1 ... stage 1 search unit, b108-1-1 to b108-T-1, b208-1-1 b208-T-1, b308-T-1,... stage t search unit,... symbol replica generation unit, b108-1-2 to b108-T-2, b208-1-2 to b208-T-2 ... Cumulative metric calculation unit, b108-1-3 to b108-T-3, b208-1-3 to b208-T-3, b308-1-3 ... Metric comparison unit, b108-1-4 to b108-T-4, b208-1-4 to b208-T-4 ... symbol replica subtraction unit, b309 ... LLR calculation unit, b310 ... decoding unit, B30 ... reference metric selection unit

Claims (23)

A receiving apparatus that performs MIMO transmission communication,
A channel estimator for generating a channel matrix between the transmission signal vector and the reception signal vector;
Reference metric generation for calculating a received signal replica based on one of the transmission signal vector candidates and the channel matrix, and calculating a reference metric indicating a difference between the calculated received signal replica and the received signal vector received by the receiving device And
Whether or not a metric indicating a difference between the received signal replica of the transmission signal vector including the partial component and the received signal vector is larger than the reference metric based on the partial component of the transmission signal vector candidate A signal search unit that switches whether or not to perform an operation on a transmission signal vector including the partial component based on the determination result;
A receiving device. A metric calculation unit that calculates a cumulative metric related to the partial component based on the partial component of the transmission signal vector candidate, the channel matrix, and the received signal vector;
When the accumulated metric is larger than the reference metric, the signal search unit has a metric indicating a difference between the received signal replica of the transmission signal vector including the partial component and the received signal vector larger than the reference metric. The receiving device according to claim 1, wherein the receiving device is determined to be. A metric calculation unit that calculates a cumulative metric based on a partial component of the transmission signal vector candidate, the channel matrix, and the reception signal vector;
The signal search unit, when the cumulative metric is smaller than the reference metric, a metric indicating a difference between the received signal replica of the transmission signal vector including the partial component and the received signal vector is smaller than the reference metric. The receiving device according to claim 1, wherein the receiving device is determined to be.   The signal search unit transmits the partial component when a metric indicating a difference between the received signal replica of the transmission signal vector including the partial component and the received signal vector is smaller than the reference metric. The receiving apparatus according to any one of claims 1 to 3, wherein an operation relating to a signal vector is performed.   The signal search unit transmits the partial component when a metric indicating a difference between the reception signal replica of the transmission signal vector including the partial component and the received signal vector is larger than the reference metric. The receiving device according to any one of claims 1 to 4, wherein an operation relating to a signal vector is not performed.   The signal search unit is configured to switch whether to calculate a metric indicating a difference between a received signal replica of a transmission signal vector including the partial component and the received signal vector based on a result of the determination. The receiving device according to any one of claims 1 to 5. A decomposition unit that performs QR decomposition on the channel matrix to generate a unitary matrix and an upper triangular matrix;
A signal converter that calculates a triangulated reception signal based on the unitary matrix;
With
The signal search unit calculates a cumulative metric related to the partial component based on the triangulated reception signal and the upper triangular matrix, and if the calculated cumulative metric is smaller than the reference metric, the partial search The receiving device according to any one of claims 1 to 6, wherein a maximum likelihood sequence corresponding to a transmission signal vector included is obtained.   When the signal search unit determines that a metric indicating a difference between the reception signal replica of the transmission signal vector candidate and the reception signal vector is smaller than the reference metric, the reference metric is determined as the transmission signal vector candidate. The receiving apparatus according to claim 1, wherein the receiving apparatus is changed to a metric related to.   The receiving device according to any one of claims 1 to 8, wherein the reference metric generation unit calculates the reference metric based on sub-optimal maximum likelihood detection.   The receiving device according to any one of claims 1 to 8, wherein the reference metric generation unit calculates the reference metric based on linear detection.   The receiving apparatus according to claim 1, wherein the reference metric generation unit arbitrarily selects one of the transmission signal vector candidates. The signal search unit obtains a maximum likelihood sequence corresponding to a transmission signal vector including the partial component;
The receiving apparatus according to claim 1, wherein information bits are obtained from the maximum likelihood sequence. The signal search unit obtains a maximum likelihood sequence corresponding to a transmission signal vector including the partial component;
The receiving apparatus according to any one of claims 1 to 11, further comprising a log likelihood ratio calculation unit that obtains a log likelihood ratio sequence based on the maximum likelihood sequence. Based on the calculated component information indicating the component of the transmission signal vector and the log likelihood ratio component to be calculated, QR decomposition is performed on the matrix in which the order of the column vectors of the channel matrix is changed, and a unitary matrix and A decomposition unit that generates an upper triangular matrix;
A signal converter that calculates a triangulated reception signal based on the unitary matrix;
A log likelihood ratio calculation unit;
A decryption unit;
With
The reference metric generation unit generates the reference metric for each calculation target candidate that is a candidate for the component indicated by the calculated component information,
The signal search unit calculates, for each of the calculation target candidates, a minimum metric that minimizes the metric among transmission vectors including the calculation target candidates,
The log likelihood ratio calculation unit calculates the log likelihood ratio based on the minimum metric,
The receiving device according to claim 7, wherein the decoding unit performs decoding based on the log likelihood ratio and outputs the decoded information bits.   The receiving apparatus according to claim 14, wherein the decoding unit outputs a coded bit log likelihood ratio. The signal search unit includes:
A maximum likelihood metric is obtained from a plurality of the minimum metrics,
Obtaining the minimum metric related to a calculation target candidate other than the maximum likelihood sequence among the calculation target candidates;
The receiving apparatus according to claim 14, wherein a log likelihood ratio is calculated based on the maximum likelihood metric and the minimum metric. A decomposition unit that performs QR decomposition on the channel matrix to generate a unitary matrix and an upper triangular matrix;
A signal converter that calculates a triangulated reception signal based on the unitary matrix;
With
17. The QR decomposition according to claim 1, wherein the decomposition unit performs QR decomposition after rearranging the column vectors of the channel matrix so as to calculate a cumulative metric from a highly reliable component first. Receiver device. The signal search unit switches whether to calculate a metric indicating a difference between a reception signal replica of a transmission signal vector including the partial component and the reception signal vector based on the determination result,
The receiving device according to any one of claims 1 to 16, wherein when the calculation result metric falls below a predetermined metric threshold, the calculation result metric is output as a minimum metric.   The receiving device according to claim 18, wherein the metric threshold is generated based on the reference metric.   The receiving device according to claim 14 or 15, wherein the signal search unit outputs a minimum metric obtained up to that point when the number of search nodes exceeds a predetermined search threshold. A receiving method in a receiving apparatus that performs MIMO transmission communication,
A channel estimation process for generating a channel matrix between the transmitted signal vector and the received signal vector;
Reference metric generation for calculating a received signal replica based on one of the transmission signal vector candidates and the channel matrix, and calculating a reference metric indicating a difference between the calculated received signal replica and the received signal vector received by the receiving device Process,
Whether or not a metric indicating a difference between the received signal replica of the transmission signal vector including the partial component and the received signal vector is larger than the reference metric based on the partial component of the transmission signal vector candidate A signal search process for switching whether or not to perform an operation on a transmission signal vector including the partial component based on the determination result;
Receiving method.   A reception program causing a computer to execute the reception method according to claim 21. A reference metric indicating a difference between one of transmission signal vector candidates and a reception signal replica calculated based on a channel matrix between the transmission signal vector and the reception signal vector, and a reception signal vector received by the reception apparatus Get
Determining whether a metric indicating a difference between a transmission signal vector including the partial component and a reception signal vector is larger than the reference metric based on a partial component of the transmission signal vector candidate;
A processor for switching whether or not to perform an operation related to a transmission signal vector including the partial component based on the result of the determination.

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