JP2012100026A - Radio communication device and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To synthesize retransmission packets based on a metric in most likelihood detection, while continuously securing a constant packet multiplexing number without increasing the number of states in the most likelihood detection to separate packets, in transmission in which a plurality of packets channel-coded in an identical time and an identical frequency are multiplexed and retransmitted in a radio section.SOLUTION: A radio communication device 10 which synthesizes the retransmission packets and separates the packets includes: a modulation symbol generation unit 16 for generating a modulation symbol, using the bit sequence of a packet correctly decoded beforehand; an interference elimination MUD unit 14 for reducing the number of states in the most likelihood detection using the modulation symbol, and for calculating a bit LLR from a received signal by the most likelihood detection; and a channel decoding unit 15E for channel decoding the bit LLR and for outputting a packet bit sequence.

Description

  The present invention relates to a wireless communication apparatus and a wireless communication method in a transmission method for simultaneously receiving retransmission packets of a plurality of users.

  In uplink packet transmission of mobile communication, multi-user detection (Multi User Detection: MUD) in which a base station simultaneously receives a plurality of users' packets and separates (detects) each packet has been studied. Further, when a determination error occurs in a packet detected at the base station (receiver), the packet is retransmitted from the mobile station (transmitter) by retransmission control. The retransmitted packet is detected again for error and received without error, or the retransmission is continued up to the maximum number of retransmissions. Here, the method of multiplexing packets of a plurality of users in the radio section using the same frequency channel at the same time as described above is called packet multiplexing. In MUD at the time of retransmission control in packet multiplexing, the base station detects a packet received by retransmission using a received signal corresponding to the initially transmitted and retransmitted packet. Note that each packet is channel-coded with an error correction code.

  There are linear and non-linear MUDs, and a method has been proposed in which the same multiplexed packet as the linear MUD is retransmitted as many times as the number of multiplexed packets and the multiplexed packet is separated by a linear filter at the receiver. It is described in. On the other hand, as a nonlinear MUD, a separation method based on maximum likelihood detection (MLD) has been proposed, and is described in Non-Patent Document 2 to Non-Patent Document 4 below. Further, it is known that nonlinear MUD can realize transmission characteristics superior to linear MUD.

M. K. Tsatsanis, R. Zhang, and S. Banerjee, “Network-assisted diversity for random access wireless networks,” IEEE Trans. Signal Processing, vol.48, March 2000, pp.702-711. R. Nagareda, K. Fukawa, and H. Suzuki, “OFDM mobile packet transmission system with multiuser detection and metric combining ARQ,” IEICE Trans. Commun., Vol.E88-B, no.1, Jan. 2005, pp. 106-114. R. Nagareda, K. Fukawa and H. Suzuki, “Efficient OFDM mobile radio packet system using LLR combining multiuser detection for ARQ with adaptive modulation and coding scheme,” IEICE Trans. Commun., Vol.E90-B, no.6, June 2007, pp.1444-1453. Hideya Mune, Kazuhiko Fukawa, Satoshi Suyama, Hiroshi Suzuki, “Hybrid Combining Multiuser Detection in OFDMA Uplink with Retransmission Control and Scheduling,” IEICE Tech. RCS2010-65, July 2010.

  In the metric synthesis type MUD (MC-MUD) described in Non-Patent Document 2, the square Euclidean distance between the received signal and the replica signal in the MLD is used as a metric, and the receiver synthesizes a retransmission packet using the metric. In MUD that is optimal from the viewpoint of maximum likelihood estimation, the number of MLD states increases exponentially with the number of retransmissions, so in MC-MUD, until all multiplexed packets are successfully received in order to reduce the amount of computation. It is assumed that the same multiple packet is retransmitted. Therefore, it is necessary to retransmit packets that have already been successfully received, resulting in a problem of reduced throughput.

  In order to solve this problem, an LLR synthesis type MUD (LC-MUD) that performs packet synthesis at a receiver using a log-likelihood ratio (LLR) of each encoded bit is disclosed in Non-Patent Document 3. Proposed in LC-MUD eliminates the need to retransmit the same multiplexed packet. When a packet is successfully received, another packet can be multiplexed at the next retransmission. Throughput is improved in the high SNR region. On the other hand, in the low SNR region, packet synthesis by bit LLR is a sub-optimal method, so that LC-MUD has a problem that the characteristics are inferior to MC-MUD.

  Furthermore, in order to compensate for the shortcomings, packet synthesis is performed based on metric synthesis, but when a packet that has been successfully received is generated, the receiver performs packet synthesis using the bit LLR for the newly multiplexed packet. Non-patent document 4 also proposes a hybrid synthesis type MUD (HC-MUD). HC-MUD can achieve the same throughput characteristics as LC-MUD in the high SNR region, but inferior to MC-MUD in the low SNR region.

  However, with conventional MC-MUD, LC-MUD, and HC-MUD, LC-MUD and HC-MUD can achieve the best throughput characteristics in the high SNR region, but MC-MUD in the low SNR region. However, there is a problem that there is no method that can always realize the best throughput characteristics and that always has excellent characteristics in the entire SNR region. This is because the prior art has been studied on the premise that the number of states in the MLD is not increased, and is not the optimum MUD in terms of maximum likelihood estimation. The optimal MUD always achieves excellent characteristics in the entire SNR region, but on the other hand, the number of MLD states increases exponentially with the number of retransmissions, which increases the amount of computation. there were.

  In the wireless transmission system in which a plurality of channel-coded packets at the same time and the same frequency are multiplexed in a wireless section and retransmission control is performed, information on the packet is obtained when a successfully received packet is generated. Provides a wireless communication device and a wireless communication method that can reduce the number of states in the MLD and increase the number of states that are reduced in response to newly multiplexed packets, while reducing the amount of computation and realizing the optimal MUD. The purpose is to do.

  In order to solve the above problems, a radio communication apparatus according to the present invention is used in a radio transmission system in which a plurality of channel-coded packets are multiplexed in a radio section at the same time and at the same frequency. A wireless communication device that receives a packet having an error multiple times and separates the multiplexed packet, and generates a modulation symbol using a bit sequence of a packet that has already been correctly decoded; , An interference cancellation MUD (multiple-likelihood ratio) that reduces the number of states in maximum likelihood detection using the modulation symbol generated by the modulation symbol generation unit and calculates a bit LLR (logarithmic likelihood ratio) by maximum likelihood detection from a received signal representing a packet A channel that performs channel decoding on the bit LLR calculated in the user detection) unit and the interference cancellation MUD unit and outputs a bit sequence of the packet. And a decoding unit, a bit sequence of correctly decoded packet channel decoding unit is characterized in that it is supplied to the modulation symbol generator.

  With the above configuration, in a wireless transmission system in which a plurality of channel-coded packets at the same time and the same frequency are multiplexed in a wireless section, the erroneous packet is received a plurality of times and the multiplexed packets are separated. In this case, the number of states in maximum likelihood detection can be reduced when the bit LLR is calculated from the reception signal of the multiplexed packet by using the modulation symbol generated in the modulation symbol generation unit in the interference removal MUD unit.

  In the radio communication apparatus according to the present invention, the interference cancellation MUD unit includes a candidate signal modulation unit that generates a modulation signal in accordance with the state of maximum likelihood detection, and a received signal using the modulation signal generated by the candidate signal modulation unit. The replica generation unit that generates the replica signal, the metric calculation unit that calculates the metric that is the square Euclidean distance between the replica signal generated by the replica generation unit and the reception signal, and the metric calculated by the metric calculation unit are the same. Each time a packet is received, it accumulates for each state of maximum likelihood detection and calculates a storage metric, and a metric storage unit that reduces the number of states of maximum likelihood detection using modulation symbols, and storage calculated by the metric storage unit It is desirable to include a bit LLR calculation unit that calculates a bit LLR using a metric. In this case, every time a multiplexed packet is received, a metric is accumulated for each state of maximum likelihood detection, whereby packet synthesis is performed and packet detection performance is improved. Further, when a metric is accumulated for each state and a packet that has been successfully received is generated, the number of states for maximum likelihood detection can be reduced using the modulation symbol of the packet.

Also, in order to reduce the amount of computation and the accumulated metric, those with large cumulative metrics (that is, those with a low probability of being a correct path) are deleted, and the method described in the following document that stores only M values is applied. May be.
C.-F. Lin and JB Anderson, “M-algorithm decoding of channel convolutional codes,” presented at 20th Annu. Conf. Inform. Sci. Syst., Princeton, NJ, Mar. 19-21, 1986.

Furthermore, when applying the method described in this document, a path is selected so that the LLR calculation unit does not become impossible, or a method of substituting with another value as shown in the following document. Need to apply.
K. Higuchi, H. Kawai, N. Maeda, M. Sawahashi, T. Itoh, Y. Kakura, A. Ushirokawa, and H. Seki, “Likelihood Function for QRM-MLD Suitable for Soft-Decision Turbo Decoding and Its Performance for OFCDM MIMO Multiplexing in Multipath Fading Channel, ”in Proc.IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2004, Barcelona, Spain, 5-8 Sept. 2004, pp.1142-1148.

  The radio communication apparatus according to the present invention further includes a bit LLR accumulation unit, and the bit LLR calculated by the interference cancellation MUD unit is input to the bit LLR accumulation unit, and the same encoded bit sequence is obtained. Each time a packet to which different puncturing is applied is received, the bit LLR is accumulated in the bit LLR accumulating unit, and the bit LLR accumulating unit generates the accumulated bit LLR from the accumulated bit LLR, and the accumulated bit LLR is the channel decoding unit. It is desirable to be input to. In this case, when receiving packets in which different puncturing is applied to the same encoded bit sequence, packet synthesis is performed by accumulating the bit LLR, and encoding of the error correction code is performed. The packet detection performance is improved by decreasing the rate. Since packets to which the same puncturing is applied have the same bit sequence, they can be handled as the same packet, so that packet synthesis is performed based on metrics and packet detection performance is improved.

  In addition, when receiving a packet to which different puncturing is applied, if no error is detected after packet decoding by the channel decoding unit, the modulation symbol generation unit modulates using the bit sequence of the packet that is the decoding result. By generating symbols, the interference cancellation MUD unit uses the modulation symbols of the packet to reduce the number of states of maximum likelihood detection. As a result, when a plurality of channel-coded packets at the same time and the same frequency are multiplexed in the radio section, the characteristics can be improved by decoding another packet again.

  The wireless communication apparatus according to the present invention further includes a GI (guard interval removal unit, a serial-parallel conversion unit, and a Fourier transform unit, in order to perform OFDM (Orthogonal Frequency Division Multiplexing) demodulation. Removes the GI component in the received signal, the received signal from which the GI has been removed is input to the serial-parallel converter, and the serial-parallel converter converts the received signal from which the GI has been removed to the Fourier transform unit The Fourier transform unit calculates the subcarrier reception signal in each subcarrier by performing Fourier transform on the output of the serial-parallel conversion unit, and the interference cancellation MUD unit determines the most from the subcarrier reception signal for each subcarrier. It is desirable to calculate the bit LLR by likelihood detection, in which case the received signal is OFDM demodulated in a system in which packets are multiplexed by OFDM, and then transmitted to each subcarrier. Thus, a process of detecting the multiplexed packet by the interference cancellation MUD unit is performed, so that the retransmitted packet can be optimally combined while suppressing the amount of calculation.

  In order to solve the above problems, a wireless communication method according to the present invention is used in a transmission system in which a plurality of channel-coded packets are multiplexed at the same time and at the same frequency. A wireless communication method that receives a packet multiple times and separates the multiplexed packet, and generates a modulation symbol by a modulation symbol generation unit using a bit sequence of the packet that has already been correctly decoded Interference reduction MUD that reduces the number of states in maximum likelihood detection using the modulation symbol generated in the step and the modulation symbol generation step, and calculates a bit LLR (log likelihood ratio) by maximum likelihood detection from the received signal representing the packet (Multiuser detection) step, and channel decoding is performed on the bit LLR calculated in the interference cancellation MUD step, Wherein a channel decoding step of outputting the bit sequence of the packet, further comprising a step of supplying a bit sequence of correctly decoded packets in channel decoding step on the modulation symbol generator.

  In the radio transmission system in which a plurality of channel-coded packets transmitted at the same time and at the same frequency are multiplexed in the radio section by the above method, a packet with an error is received a plurality of times and multiplexed. When the bit LLR is calculated from the received signal of the multiplexed packet, the number of states in maximum likelihood detection is reduced by using the modulation symbol generated in the modulation symbol generation step in the interference cancellation MUD step. it can.

  In the wireless communication method according to the present invention, the interference cancellation MUD step includes a candidate signal modulation step for generating a modulation signal in accordance with the state of maximum likelihood detection, and a received signal using the modulation signal generated in the candidate signal modulation step. The replica generation step for generating the replica signal, the metric calculation step for calculating the metric that is the square Euclidean distance between the replica signal generated in the replica generation step and the received signal, and the metric calculated in the metric calculation step are the same. Each time a packet is received, it accumulates for each state of maximum likelihood detection and calculates a storage metric, and a metric storage step that uses modulation symbols to reduce the number of states of maximum likelihood detection, and storage calculated in the metric storage step A bit LLR calculation step of calculating a bit LLR using a metric Theft is desirable. In this case, every time a multiplexed packet is received, a metric is accumulated for each state of maximum likelihood detection, whereby packet synthesis is performed and packet detection performance is improved. Further, when a metric is accumulated for each state and a packet that has been successfully received is generated, the number of states for maximum likelihood detection can be reduced using the modulation symbol of the packet.

  Further, the radio communication method according to the present invention inputs the bit LLR calculated in the interference cancellation MUD step to the bit LLR accumulating unit, and transmits packets in which different puncturing is applied to the same encoded bit sequence. It is desirable that the bit LLR is accumulated in the bit LLR accumulation unit every time it is received, the accumulation bit LLR is generated from the bit LLR accumulated in the bit LLR accumulation unit, and the accumulated bit LLR is supplied to the channel decoding step. In this case, when receiving packets in which different puncturing is applied to the same encoded bit sequence, packet synthesis is performed by accumulating the bit LLR, and encoding of the error correction code is performed. The packet detection performance is improved by decreasing the rate. Since packets to which the same puncturing is applied have the same bit sequence, they can be handled as the same packet, so that packet synthesis is performed based on metrics and packet detection performance is improved.

  The wireless communication method according to the present invention further includes a GI (guard interval) removal step, a serial-parallel conversion step, and a Fourier transform step to perform OFDM (Orthogonal Frequency Division Multiplexing) demodulation, and GI removal The step removes the GI component in the received signal, the serial-parallel conversion step performs the serial-parallel conversion on the received signal from which the GI has been removed, and the Fourier transform step performs the Fourier transform on the output of the serial-parallel conversion step to perform each sub-translation. It is preferable that a subcarrier received signal in a carrier is calculated, and the interference cancellation MUD step calculates a bit LLR by maximum likelihood detection from the subcarrier received signal for each subcarrier. In this case, in a system in which packets are multiplexed by OFDM, a received signal is OFDM demodulated, and thereafter, a process of detecting a multiplexed packet in each subcarrier by an interference removal MUD step is performed. Thereby, it is possible to optimally combine the retransmitted packets while suppressing the calculation amount.

  According to the wireless communication device and the wireless communication method of the present invention, in a wireless transmission system that performs retransmission control in which a packet that has been channel-encoded at the same time and at the same frequency is multiplexed in a wireless section, the maximum likelihood detection metric is used. The transmission characteristics can be improved by combining the packets, and the amount of calculation can be suppressed by reducing the number of states in the maximum likelihood detection using the modulation symbols generated from the packets that have already been correctly decoded.

It is a block diagram of the radio | wireless communication apparatus in the OFDM transmission which concerns on 1st Embodiment of this invention. It is a block diagram of the interference removal MUD part of the radio | wireless communication apparatus which concerns on 1st and 2nd embodiment. It is a block diagram of the modulation symbol production | generation part of the radio | wireless communication apparatus in the OFDM transmission which concerns on 1st and 2nd embodiment. It is a block diagram of the transmitting station assumed by this invention. It is a block diagram of the radio | wireless communication apparatus in the OFDM transmission which concerns on 2nd Embodiment of this invention. It is a figure showing the throughput characteristic which shows the application effect of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment]
First, the configuration of a wireless communication apparatus in OFDM (Orthogonal Frequency Division Multiplexing) transmission according to the first embodiment of the present invention will be described. FIG. 1 is a hardware configuration diagram of a wireless communication device 10 in OFDM transmission. The wireless communication device 10 shown in FIG. 1 may be a base station in a mobile communication system. Alternatively, the wireless communication device 10 may be an access point in a wireless LAN (local area network) or WiMAX (Worldwide Interoperability for Microwave Access). FIG. 1 shows elements related to reception of an uplink signal in the wireless communication apparatus 10.

  As shown in FIG. 1, the wireless communication device 10 physically includes a GI (guard interval) removal unit 11, a serial-parallel conversion unit 12, a Fourier transform unit 13, and an interference removal MUD (multiuser detection) unit. 14, a plurality of received bit calculation units 15, and a modulation symbol generation unit 16. Each received bit calculation unit 15 includes a parallel / serial conversion unit 15A, a deinterleave unit 15B, a depuncture unit 15C, a channel decoding unit 15E, and an error detection unit 15F.

  FIG. 2 is a configuration diagram of the interference removal MUD unit 14. The interference removal MUD unit 14 includes a replica subtraction unit 21, a metric calculation unit 22, a candidate signal modulation unit 23, a replica generation unit 24, a metric accumulation unit 25, and a bit LLR calculation unit 26. FIG. 3 is a block diagram of the modulation symbol generator 16 of the present embodiment in OFDM transmission. The modulation symbol generation unit 16 includes a channel encoding unit 31, a puncturing unit 32, an interleaving unit 33, a symbol generation unit 34, and a serial / parallel conversion unit 35.

  In the following, in OFDM transmission with N subcarriers, packets transmitted from a plurality (L units) of transmitting stations are multiplexed at the same frequency and at the same time, and the wireless communication apparatus 10 as a receiving station separates the packets. Assume a system. It is assumed that the multiplexed packets are ideally time and frequency synchronized.

  First, the configuration of the transmission station assumed in the following description will be described. FIG. 4 shows the transmitting station 40. The transmission station 40 is, for example, a mobile station in a mobile communication system, or a terminal in a wireless LAN or WiMAX. In the transmission station 40 shown in FIG. 4, the cyclic redundancy check (CRC) encoding unit 41 performs CRC encoding on the input information bit sequence, and the channel encoding unit 42 performs channel encoding on the output. Is done. The encoded bit sequence is punctured by the puncturing unit 43 in accordance with the coding rate and then interleaved by the interleaving unit 44. Further, the interleaved encoded bit sequence is converted into a modulation signal by the signal modulation unit 45, converted into a modulation signal of a plurality of sequences corresponding to each subcarrier by the serial / parallel conversion unit 46, and then inverted by N points. A Fourier transform unit 47 converts the signal into a time domain signal. Finally, the output is parallel-serial converted by the parallel-serial conversion unit 48, and a GI (guard interval) is inserted by the GI (guard interval) insertion unit 49, and transmitted as a transmission signal.

  Subsequently, the operation of the wireless communication apparatus 10 and the wireless communication method according to the present embodiment will be described. The GI removal unit 11 shown in FIG. 1 removes the GI component in the received signal of the multiplexed packet. The received signal from which the GI has been removed is input to the serial-parallel conversion unit 12, and is subjected to serial-parallel conversion, and then Fourier-transformed by the Fourier transform unit 13 to calculate the received signal in each subcarrier.

となる。ここで、上付き文字^Tは転置を表し、N(n,q)は雑音であり、

はL次元チャネルベクトルであり、

はL次元変調信号ベクトルであって、それぞれ以下の式で表せる。

なお、H_ｊ(n,q)は第q回目の再送時における第j(1≦j≦L)送信局４０、第nサブキャリアの伝達関数であり、s_j(n,q)は第q回目の再送時における第j送信局４０の第nサブキャリアの変調信号である。 When a determination error is detected in the received packet by an error detection unit 15F described later, the packet is retransmitted. Further, when a packet is normally received, it is assumed that a new packet is multiplexed and always L-multiplexed (that is, the radio communication apparatus 10 always receives packets from L transmitting stations 40). To do). Now, let Q be the maximum number of retransmissions of the same packet, and let R (n, q) be a received signal representing a packet of the nth (1 ≦ n ≦ N) subcarrier in the qth (1 ≦ q ≦ Q) retransmission Then, R (n, q) is expressed by Equation (1).

It becomes. Where the superscript ^T represents transposition, N (n, q) is noise,

Is the L-dimensional channel vector,

Are L-dimensional modulation signal vectors, which can be expressed by the following equations, respectively.

H _j (n, q) is a transfer function of the jth (1 ≦ j ≦ L) transmitting station 40 and the nth subcarrier at the time of the q-th retransmission, and s _j (n, q) is the qth This is a modulated signal of the n-th subcarrier of the j-th transmitting station 40 at the time of retransmission.

Next, a method for detecting the packet of the first transmitting station from the received signal R (n, q) will be described. However, hereinafter, in order to simplify the description, it is assumed that the modulated signal s ₁ (n, q) of the first transmitting station is retransmitted up to the maximum number of retransmissions Q. That is, Formula (4) is materialized.

は、q≦Q'では

であり、Q'+1≦q≦Qにおいては

である。 In addition, the same packet is continuously transmitted from the initial transmission (q = 1) to the Q'th time, and L 'transmitted from a transmitting station other than the first transmitting station at the time of the Q'th retransmission (≦ L−1) packets are correctly received by the wireless communication apparatus 10, and new L ′ packets are multiplexed by transmission from a transmitting station other than the first transmitting station from the Q ′ + 1th retransmission. Assume that. That is, the L-dimensional modulation signal vector at the q-th retransmission

Is q ≦ Q '

Where Q '+ 1 ≤ q ≤ Q

It is.

がL次元のベクトルのため、M^Lとなる。 The interference cancellation MUD unit 14 in FIG. 2 calculates the bit LLR of the first transmitting station using the received signal R (n, q). First, the metric calculation unit 22 calculates the metric α (k, n, q) in the state k (1 ≦ k ≦ K) of the MLD. Note that the number of states K in MLD is a vector assuming that M-value quadrature amplitude modulation (QAM) is used as the modulation method.

Since M is an L-dimensional vector, M ^L.

を生成する。変調信号候補ベクトルはレプリカ生成部２４に入力され、レプリカ生成部２４は、チャネルベクトル

と変調信号候補ベクトルとの内積により受信信号のレプリカ信号

を以下のように計算する。

The state of the MLD output from the metric calculation unit 22 is input to the candidate signal modulation unit 23, and the candidate signal modulation unit 23 receives the L-dimensional modulation signal candidate vector corresponding to the state k.

Is generated. The modulation signal candidate vector is input to the replica generation unit 24, and the replica generation unit 24 receives the channel vector.

And the replica signal of the received signal by the inner product of the modulation signal candidate vector

Is calculated as follows.

同様に、全ての状態におけるメトリックが計算され、メトリック蓄積部２５に入力される。 Then, the replica subtraction unit 21 subtracts this replica signal from the reception signal R (n, q). The metric calculation unit 22 calculates the metric α (k, n, q) as follows using the result. That is, the square Euclidean distance between the replica signal and the received signal is calculated as a metric.

Similarly, metrics in all states are calculated and input to the metric storage unit 25.

ただし、q≦Q'であり、β(k,n,0)=0である。 Since the same packet is retransmitted until the Q'th time, the metric accumulation unit 25 adds the metric α (k, n, q) at the time of each retransmission for each state of the MLD based on the principle of maximum likelihood estimation. Packet synthesis. The storage metric β (k, n, q) in the q-th (q ≦ Q ′) retransmission can be expressed by the following equation (9).

However, q ≦ Q ′ and β (k, n, 0) = 0.

In order to detect a packet transmitted from the first transmitting station, it is necessary to calculate an accumulation metric up to the maximum number of retransmissions Q. However, it is necessary to consider the modulation signal of L ′ packets transmitted from another newly multiplexed transmission station from the time of Q ′ + 1-th retransmission as a state, and simply use equation (9) I can't. Therefore, the metric accumulation unit 25 reduces the number of MLD states by using information of L ′ packets correctly received at the time of the Q′th retransmission. Specifically, the modulation symbol generated by the modulation symbol generation unit 16 from the bit sequence of the correctly received packet (the bit sequence of the packet correctly decoded by the channel decoding unit 15E described later) is used. A method for generating a modulation symbol by the modulation symbol generator 16 will be described later. Since the state corresponding to the modulation symbols of the L ′ packets that have been correctly received has already been determined, only the number of states of M ^{L-L ′} need be considered. Using the accumulation metric β (k ′, n, Q ′) of the surviving state k ′ having the number of states M ^{L−L ′} , the metric accumulating unit 25 calculates the accumulation metric in the Q ′ + 1th and subsequent retransmissions.

ここで、q=Q'+1の場合、式（１０）右辺のβ'(k,n,Q')は以下の式で計算できる。

The accumulated metric at the time of Q ′ + 1 retransmission is obtained by adding the metric α (k, n, Q ′ + 1) to the accumulated metric β (k ′, n, Q ′) of the surviving state k ′. Can be calculated. However, the relationship between the state k ′ that survived the Q′th retransmission and the state k (1 ≦ k ≦ K) in the Q ′ + 1th retransmission is the relationship between the newly multiplexed L ′ packets. Depending on how the modulated signal is assigned to state k, here the surviving state k ′ corresponding to state k is k ′ = f (k). At this time, the accumulation metric β ′ (k, n, q) in the q-th (Q ′ + 1 ≦ q ≦ Q) retransmission can be calculated by the following equation.

Here, when q = Q ′ + 1, β ′ (k, n, Q ′) on the right side of Expression (10) can be calculated by the following expression.

と計算できる。ただし、κ(1,b_m=0)とκ(1,b_m=1)は第1送信局の変調信号における第m番目のビットb_mが0、あるいは1となるMLDにおける状態の集合である。同様に、干渉除去MUD部１４は、第1送信局だけでなく他の送信局から送信される全サブキャリアにおけるビットLLRを計算する。 The accumulated metric updated for each retransmission by the metric accumulation unit 25 is input to the bit LLR calculation unit 26. The bit LLR calculator 26 calculates a bit LLR (log likelihood ratio) necessary for detecting a packet transmitted from the first transmitting station from the accumulated metric. Here, assuming that the bit LLR corresponding to the m-th bit of the modulation signal s _j (n, q) of the _j- th transmission station is λ _j (n, m, q), λ ₁ (n , m, Q) using the accumulation metric β ′ (k, n, Q)

Can be calculated. However, κ (1, b _m = 0) and κ (1, b _m = 1) are a set of states in the MLD in which the _mth bit b _m in the modulation signal of the first transmitting station is 0 or 1. is there. Similarly, the interference cancellation MUD unit 14 calculates bit LLRs in all subcarriers transmitted from not only the first transmitting station but also other transmitting stations.

  The bit LLRs of all subcarriers calculated by the interference cancellation MUD unit 14 are input to the received bit calculation unit 15 corresponding to each transmission station. The bits LLR of all subcarriers of the first transmitting station are input to the parallel / serial conversion unit 15B of the received bit calculation unit 15 corresponding to the first transmission station, and are subjected to parallel / serial conversion. Then, after deinterleaving by the deinterleaving unit 15B, the depuncturing unit 15C performs depuncturing in accordance with the coding rate in channel coding. Finally, the depunctured bit LLR is input to the channel decoding unit 15E for channel decoding. The bit sequence decoded by the channel decoding unit 15E is input to the error detection unit 15F and the modulation symbol generation unit 16. The error detection unit 15F detects a determination error in the packet by using the cyclic redundancy check code added to the information bits of the packet. When an error is detected, a retransmission request is made to the transmitting station.

Next, the operation of the modulation symbol generator 16 shown in FIG. 3 will be described. When no error is detected by the error detection unit 15F, the correctly decoded bit sequence that is the output of the channel decoding unit 15E is input to the modulation symbol generation unit 16, and the modulation symbol corresponding to the transmission station is the modulation symbol generation unit. 16 is generated. The decoded bit sequence is input to the channel encoder 31 in the modulation symbol generator 16 and is channel-encoded by the channel encoder 31 in the same manner as the channel encoder 42 of the transmission station 40. The encoded bit sequence is punctured and interleaved by the puncturing unit 32 and the interleaving unit 33, respectively, and then assigned to the modulation symbol by the symbol generating unit 34. The method of puncturing by the puncturing unit 32 is the same as the method of the puncturing unit 43 of the transmitting station 40, and the method of interleaving by the symbol generating unit 34 is the same as the method of the interleaving unit 44 of the transmitting station 40. Unlike the modulation signal, the modulation symbol indicates a modulation point number in the M-value QAM. The modulation symbol is used only for reducing the number of states in the MLD by the metric accumulation unit 25 of the interference cancellation MUD unit 14 described above, and the state of the MLD is determined by a combination of L modulation symbols.
[Second Embodiment]

  Next, the configuration of the wireless communication apparatus and the wireless communication method according to the second embodiment of the present invention will be described. FIG. 5 is a configuration diagram of the wireless communication device 10 in OFDM transmission according to the second embodiment. The wireless communication device 10 includes a bit LLR (log likelihood ratio) storage unit 15D in addition to the same configuration as the wireless communication device 10 according to the second embodiment of FIG. The interference removal MUD unit 14 of the wireless communication apparatus 10 has the same configuration as the interference removal MUD part 14 shown in FIG. 2 and described above, and the modulation symbol generation unit 16 of the wireless communication apparatus 10 is shown in FIG. 2 and described above. The configuration is the same as that of the modulation symbol generator 16. The features of the second embodiment that are different from the first embodiment will be described below, but the other features are the same as those of the first embodiment.

  In the description according to the first embodiment described above, it is assumed that the same packet of the first transmitting station is retransmitted up to the maximum number of retransmissions Q. However, as a method for the puncturing unit 43 to puncture the bit sequence channel-encoded by the transmitting station 40, there is a method of performing puncturing different from the initial transmission at the time of retransmission. In this method, the punctured information can be restored by synthesizing the retransmitted packets at the receiving side, that is, the wireless communication device 10, and the coding rate before puncturing by the transmitting station 40 is determined by the wireless communication device 10. realizable. When the number of retransmissions increases, the transmitting station 40 retransmits again using the same puncturing as in the initial transmission. However, since the same packet (that is, the packet subjected to the same puncturing) is not received at the time of all retransmissions, packet synthesis cannot be performed only by the metric as in the first embodiment. Therefore, in the second embodiment, for the packets retransmitted by the transmitting station 40 using the same puncturing, the metrics are accumulated by the metric accumulation unit 25 in FIG. 1 is synthesized by accumulating the bit LLR in the bit LLR accumulating unit 15E of FIG.

ただし、β_o(k,n,-1) = β_e(k,n,0) = 0である。同様に、Q'/2+1≦i≦Q/2における蓄積メトリックに関しても、第2i-1回目（奇数回目）の再送時の蓄積メトリックβ_o'(k,n,2i-1)と第2i回目（偶数回目）の再送時の蓄積メトリックβ_e'(k,n,2i)を以下の式（１４）および式（１５）のように計算する。

ここで、i=Q'/2+1の場合、式（１４）右辺のβ_o'(k,n,Q'-1)は以下の式で計算できる。

ここで、i=Q'/2+1の場合、式（１５）右辺のβ_e'(k,n,Q')は以下の式で計算できる。

Hereinafter, in order to simplify the explanation, it is assumed that the packet of the first transmitting station is retransmitted up to the maximum number of retransmissions Q (here, Q is assumed to be an even number), and the second i-1 (1 ≦ i ≦ Q / 2 ) It is assumed that the puncturing in the second retransmission is different from the puncturing in the 2i-th retransmission. However, the same puncturing is applied in the 2i-1 or 2i-th retransmission (that is, the first puncturing is used in the odd-numbered retransmissions and the first puncturing is performed in the even-numbered retransmissions). Different puncturing is used). At this time, the metric storage unit 25 stores the storage metric β _o (k, n, 2i) for the second i-1th (odd number) retransmission packet in i ≦ Q ′ / 2 (Q ′ is assumed to be an even number). -1) and the accumulation metric β _e (k, n, 2i) for the 2i-th (even-numbered) retransmission packet is calculated as follows.

However, β _o (k, n, −1) = β _e (k, n, 0) = 0. Similarly, with respect to the accumulation metric in Q ′ / 2 + 1 ≦ i ≦ Q / 2, the accumulation metric β _o ′ (k, n, 2i−1) at the second i−1th (odd number) retransmission and the second The storage metric β _e ′ (k, n, 2i) at the 2i-th (even-numbered) retransmission is calculated as in the following equations (14) and (15).

Here, when i = Q ′ / 2 + 1, β _o ′ (k, n, Q′−1) on the right side of Expression (14) can be calculated by the following expression.

Here, when i = Q ′ / 2 + 1, β _e ′ (k, n, Q ′) on the right side of the equation (15) can be calculated by the following equation.

と計算できる。λ₁(n,m,Q-1)は、受信ビット算出部１５の並直列変換部１５Aと、デインターリーブ部１５Bと、デパンクチャ部１５Cとで処理された後、ビットLLR蓄積部15Dが有するメモリに保存される。また、第Q回目の再送時における第1送信局のビットLLRλ₁(n,m,Q)は蓄積メトリックβ_e'(k,n,Q)を用いて、

と計算でき、同様にビットLLR蓄積部15Dに入力される。ビットLLR蓄積部15Dは、第Q-1回目の再送時に送信局４０で使用されたパンクチャリングと第Q回目の再送時に送信局４０で使用されたパンクチャリングの比較により、同一のビット毎に第Q-1回目のビットLLRと第Q回目のビットLLRを足し合わせる（無線通信装置１０にとって送信局４０で使用されるパンクチャリングのパターンは既知である。）。こうして、ビットLLR蓄積部１５Ｄは、蓄積されたビットLLRから蓄積ビットLLRを生成し、蓄積ビットLLRをチャネル復号部１５Ｅに供給する。 At this time, the bit LLRλ ₁ (n, m, Q-1) of the first transmitting station at the time of the Q-1th retransmission is stored using the accumulation metric β _o ′ (k, n, Q-1),

Can be calculated. λ ₁ (n, m, Q−1) is processed by the parallel-serial converter 15A, deinterleaver 15B, and depuncturer 15C of the received bit calculator 15, and then the memory included in the bit LLR accumulator 15D Saved in. Also, the bit LLRλ ₁ (n, m, Q) of the first transmitting station at the time of the Q-th retransmission uses the accumulation metric β _e ′ (k, n, Q),

And is similarly input to the bit LLR accumulating unit 15D. The bit LLR accumulating unit 15D compares the puncturing used at the transmitting station 40 at the Q-1th retransmission with the puncturing used at the transmitting station 40 at the Qth retransmission, for each same bit. The Q-1th bit LLR and the Qth bit LLR are added together (the puncturing pattern used by the transmitting station 40 is known to the radio communication device 10). In this way, the bit LLR accumulation unit 15D generates the accumulation bit LLR from the accumulated bit LLR and supplies the accumulation bit LLR to the channel decoding unit 15E.

  In the above description according to the present embodiment, the wireless communication device 10 and the wireless communication method assuming that two different types of puncturing are used in the transmission station 40 have been described. However, other types of puncturing are possible. Even when the transmitting station 40 uses, the above method is used to reduce the amount of calculation in the same puncturing and realize packet combining based on the metric. For different puncturing, the bit LLR calculated based on the metric is used. Packet synthesis.

  In the above description regarding the first and second embodiments, an example of application to OFDM transmission has been shown, but the present invention can also be applied to single carrier transmission. In the single carrier transmission, the GI removal unit 11, the serial-parallel conversion unit 12, and the Fourier transform unit 13 are not required. The present invention can also be applied to OFDM transmission that performs antenna diversity reception and MIMO-OFDM (Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing) transmission that performs spatial multiplexing.

  Examples according to the first embodiment of the present invention will be described with reference to the drawings. In order to confirm the effectiveness of the present invention, a computer simulation result when the first embodiment of the present invention is applied to an OFDM transmission is shown below. The number of transmitting stations L to be multiplexed was 2, and the number of FFT points N was 64. Other OFDM parameters conform to 5GHz band wireless LAN. The modulation method was 16QAM, a convolutional code was used for channel coding, and the coding rate was 1/2. The maximum number of retransmissions Q is 4.

  FIG. 6 shows the throughput characteristics of a metric synthesis type MUD (CMC-MUD) that performs interference cancellation according to the present invention. For comparison, the characteristics of MC-MUD described in Non-Patent Document 2 and HC-MUD described in Non-Patent Document 4 are also shown. Note that the characteristics of LC-MUD described in Non-Patent Document 3 were not compared with HC-MUD in Non-Patent Document 4, and thus comparison was not performed. In the figure, CMC-MUD can achieve almost the same throughput characteristics as MC-MUD that performs packet combining based on metrics in the low SNR region, and can achieve characteristics that are higher than HC-MUD. On the other hand, in the high SNR region, CMC-MUD can achieve better throughput characteristics than MC-MUD. This is because CMC-MUD is always L-multiplexable at the time of retransmission. It can also be seen that CMC-MUD can achieve superior throughput characteristics by combining packets with metrics when the average SNR is 23 dB or less compared to HC-MUD.

DESCRIPTION OF SYMBOLS 10 ... Wireless communication apparatus, 11 ... GI (guard interval) removal part, 12 ... Serial-parallel conversion part, 13 ... Fourier transformation part, 14 ... Interference removal MUD (multiuser detection) part, 15 ... Receive bit calculation part, 15A ... Parallel-serial conversion unit, 15B ... deinterleave unit, 15C ... depuncture unit, 15D ... bit LLR (log likelihood ratio) storage unit, 15E ... channel decoding unit, 15F ... error detection unit, 16 ... modulation symbol generation unit, 21 ... Replica subtraction unit, 22 ... Metric calculation unit, 23 ... Candidate signal modulation unit, 24 ... Replica generation unit, 25 ... Metric storage unit, 26 ... Bit LLR (log likelihood ratio) calculation unit, 31 ... Channel encoding unit, 32 Puncture unit, 33 interleaving unit, 34 symbol generation unit, 35 serial-parallel conversion unit, 40 transmitting station, 41 CRC (cyclic redundancy check) encoding unit, 42 channel Encoding unit 43 ... Puncture unit 44 ... Interleave unit 45 ... Signal modulation unit 46 ... Series-parallel conversion unit 47 ... Inverse Fourier transform unit 48 ... Parallel-serial conversion unit 49 ... GI (guard interval) insertion unit .

Claims (8)

Used in a wireless transmission system in which a plurality of channel-coded packets at the same time and the same frequency are multiplexed in a radio section, and the multiplexed packet is received a plurality of times, and the multiplexed packet is received. A wireless communication device for separating received packets,
A modulation symbol generator that generates a modulation symbol using a bit sequence of a packet that has already been correctly decoded;
An interference cancellation MUD (reducing the number of states in maximum likelihood detection using the modulation symbol generated by the modulation symbol generation unit, and calculating a bit LLR (log likelihood ratio) by maximum likelihood detection from a received signal representing a packet) Multi-user detection),
A channel decoding unit that performs channel decoding on the bit LLR calculated in the interference cancellation MUD unit and outputs a bit sequence of the packet;
And a bit sequence of a packet correctly decoded by the channel decoding unit is supplied to the modulation symbol generating unit. The interference cancellation MUD unit is a candidate signal modulation unit that generates a modulation signal in accordance with the state of maximum likelihood detection;
A replica generation unit that generates a replica signal of a reception signal using the modulation signal generated by the candidate signal modulation unit;
A metric calculation unit that calculates a metric that is a squared Euclidean distance between the replica signal generated by the replica generation unit and the received signal;
The metric calculated by the metric calculation unit is accumulated for each maximum likelihood detection state every time the same packet is received to calculate the accumulated metric, and the number of maximum likelihood detection states is reduced using the modulation symbols. A metric storage unit to
A bit LLR calculation unit that calculates the bit LLR using the storage metric calculated by the metric storage unit;
The wireless communication apparatus according to claim 1, further comprising: A bit LLR accumulator
The bit LLR calculated by the interference cancellation MUD unit is input to the bit LLR accumulation unit, and each time a packet in which different puncturing is applied to the same encoded bit sequence is received, the bit LLR is changed to the bit LLR. Accumulated in the LLR accumulating unit, the bit LLR accumulating unit generates an accumulated bit LLR from the accumulated bit LLR, and the accumulated bit LLR is input to the channel decoding unit,
The wireless communication apparatus according to claim 1, wherein the wireless communication apparatus is a wireless communication apparatus. In order to perform OFDM (Orthogonal Frequency Division Multiplexing) demodulation, it further includes a GI (guard interval) removal unit, a serial-parallel conversion unit, and a Fourier transform unit,
The GI removal unit removes the GI component in the received signal, and the received signal from which the GI has been removed is input to the serial-parallel conversion unit,
The serial-parallel conversion unit performs serial-parallel conversion on the received signal from which GI has been removed, and then inputs it to the Fourier transform unit.
The Fourier transform unit calculates a subcarrier reception signal in each subcarrier by performing a Fourier transform on the output of the serial-parallel transform unit,
The interference cancellation MUD unit calculates a bit LLR by maximum likelihood detection from the subcarrier received signal for each subcarrier,
The wireless communication device according to claim 1, wherein the wireless communication device is a wireless communication device. Used in a wireless transmission system in which a plurality of channel-coded packets at the same time and the same frequency are multiplexed in a radio section, and the multiplexed packet is received a plurality of times, and the multiplexed packet is received. A wireless communication method for separating packets,
A modulation symbol generation step of generating a modulation symbol by a modulation symbol generation unit using a bit sequence of a packet that has already been correctly decoded;
An interference cancellation MUD (reducing the number of states in maximum likelihood detection using the modulation symbol generated in the modulation symbol generation step) and calculating a bit LLR (log likelihood ratio) by maximum likelihood detection from a received signal representing a packet ( Multi-user detection) step;
A channel decoding step of performing channel decoding on the bit LLR calculated in the interference cancellation MUD step and outputting a bit sequence of the packet;
Supplying a bit sequence of the packet correctly decoded in the channel decoding step to the modulation symbol generating unit;
A wireless communication method comprising: The interference cancellation MUD step includes a candidate signal modulation step for generating a modulation signal in accordance with the state of maximum likelihood detection;
A replica generation step of generating a replica signal of a received signal using the modulation signal generated in the candidate signal modulation step;
A metric calculation step of calculating a metric that is a squared Euclidean distance between the replica signal generated in the replica generation step and the received signal;
The metric calculated in the metric calculation step is accumulated for each maximum likelihood detection state every time the same packet is received to calculate the accumulated metric, and the number of maximum likelihood detection states is reduced using the modulation symbols. A metric accumulation step to
A bit LLR calculation step of calculating the bit LLR using the accumulation metric calculated in the metric accumulation step;
The wireless communication method according to claim 5, further comprising: The bit LLR calculated in the interference cancellation MUD step is input to the bit LLR accumulation unit, and each time a packet in which different puncturing is applied to the same encoded bit sequence is received, the bit LLR is changed to the bit LLR. Accumulating in the accumulating unit, generating an accumulated bit LLR from the bit LLR accumulated in the bit LLR accumulating unit, and supplying the accumulated bit LLR to the channel decoding step;
The wireless communication method according to claim 5 or claim 6, wherein In order to perform OFDM (Orthogonal Frequency Division Multiplexing) demodulation, a GI (guard interval) removal step, a serial-parallel conversion step, and a Fourier transform step are further included.
The GI removal step removes the GI component in the received signal,
The serial-parallel conversion step performs serial-parallel conversion on the received signal from which GI has been removed,
The Fourier transform step calculates a subcarrier received signal in each subcarrier by performing a Fourier transform on the output of the serial-parallel transform step,
The interference cancellation MUD step calculates a bit LLR by maximum likelihood detection from the subcarrier received signal for each subcarrier.
The wireless communication method according to claim 5, wherein the wireless communication method is a wireless communication method.

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