JP2012222519A - Radio communication device and retransmission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of re-transmission in retransmission during MIMO transmission.SOLUTION: A radio communication system supporting a MIMO space multiplexing technology comprises a base station eNB forming spatially divided streams S1 and S2 between a radio terminal UE and the base station eNB. The base station eNB transmits data signals #1 and #2 by MIMO transmission which transmits different data signals for each of the streams S1 and S2. When retransmission of the single data signal #1 out of the data signals #1 and #2 transmitted by the MIMO transmission is requested by the radio terminal UE, the base station eNB switches to transmission diversity in which the same data signals are transmitted in each of the streams S1 and S2, and retransmits the data signal #1 having been requested to retransmit.

Description

  The present invention relates to a radio communication apparatus and a retransmission control method that support multi-input multi-output spatial multiplexing technology.

  In recent years, in a wireless communication system, various multiplexing techniques have been realized in order to increase frequency utilization efficiency and improve transmission speed. For example, a plurality of data signals are transmitted through a plurality of transmission antennas using the same time / frequency resource, and the plurality of data signals are received through a plurality of reception antennas, and separated into data signals. A multi-input multi-output (MIMO) spatial multiplexing technique for decoding is known (see, for example, Patent Document 1).

  In the MIMO spatial multiplexing technology, a logical transmission path (referred to as a “stream”) that is spatially divided between a transmission side and a reception side by using different transmission antennas or different transmission directivities for each data signal. ) Are formed. Such a stream may be referred to as a “layer”.

  On the other hand, in a wireless communication system, since transmission errors frequently occur, an automatic retransmission request (ARQ) or a hybrid automatic retransmission request (HARQ) is used to ensure communication reliability. In such a retransmission control technique, when the receiving side fails to decode the data signal received from the transmitting side, the receiving side requests the transmitting apparatus to retransmit the data signal, and the transmitting side retransmits the data signal requested to be retransmitted. I do. Then, when the reception side succeeds in decoding the data signal received from the transmission side, the reception side notifies the transmission device of the successful decoding of the data signal.

  A retransmission request is made by sending a negative acknowledgment (NACK) from the receiving side to the transmitting side, and a successful decoding notification is made by sending an affirmative acknowledgment (ACK) from the receiving side to the sending side. It is common.

JP 2007-19806 A

  By the way, when the transmission side is transmitting a plurality of data signals (MIMO transmission) using the MIMO spatial multiplexing technology, if retransmission of a single data signal is requested among the plurality of data signals, the MIMO transmission is stopped. It is assumed that the single data signal is retransmitted using only a single stream corresponding to the single data signal.

  However, in such a retransmission control method, since the probability of successful decoding of the single data signal on the receiving side is low, the decoding of the single data signal fails by decoding the single data signal. There is a high possibility of requesting retransmission again. When the number of retransmissions is increased by repeating such a retransmission request, there is a problem that the transmission rate is lowered.

  Therefore, an object of the present invention is to provide a radio communication apparatus and a retransmission control method that can reduce the number of retransmissions in retransmission during MIMO transmission.

  In order to solve the above-described problems, the present invention has the following features.

  First, the wireless communication device according to the present invention is characterized in that, in a wireless communication system that supports MIMO spatial multiplexing technology, a plurality of spatially divided streams (for example, stream S1 and stream S2) are transferred to other wireless communication devices (for example, A wireless communication device (e.g., base station eNB) formed between the wireless terminal UE) and a first transmission method (MIMO transmission) for transmitting a different data signal for each of the plurality of streams; and the plurality of streams A transmission unit (for example, the transmission unit 110) configured to transmit a data signal in any one of a second transmission scheme (transmission diversity) for transmitting the same data signal in each of the first transmission scheme and the first transmission scheme Among the plurality of data signals (for example, data signal # 1 and data signal # 2) transmitted by the transmission unit, a single data signal (for example, When retransmission of the data signal # 1) is requested from the other radio communication device, the first transmission scheme is switched to the second transmission scheme, and the single data signal is retransmitted to the second transmission scheme. The gist of the present invention is to include a control unit (for example, the control unit 101) that controls the transmission unit so as to perform the transmission method.

  According to such a wireless communication apparatus, when retransmission of a single data signal is requested among a plurality of data signals transmitted by the first transmission method, the first transmission method is switched to the second transmission method. In addition, diversity gain is obtained by performing retransmission of the single data signal by the second transmission method. This increases the probability of successful decoding of the single data signal on the receiving side, thereby reducing the number of retransmissions. Therefore, according to this feature, there is provided a wireless communication apparatus that can reduce the number of retransmissions in retransmission during MIMO transmission.

  Another feature of the wireless communication apparatus according to the present invention is that, in the wireless communication apparatus according to the above feature, the control unit transmits a plurality of data signals (for example, data signal # 1) transmitted by the transmission unit according to the first transmission method. And data signal # 2), when retransmission of two or more data signals (for example, data signal # 1 and data signal # 2) is requested from the other wireless communication device, the data signal for each of the plurality of streams And the transmission unit is controlled to perform retransmission of the two or more data signals by the first transmission method.

  Another feature of the wireless communication apparatus according to the present invention is that, in the wireless communication apparatus according to the above feature, the control unit is configured to perform the first operation when a propagation path state with the other wireless communication apparatus is deteriorated. Among the plurality of data signals (for example, data signal # 1 and data signal # 2) transmitted by the transmission unit according to one transmission method, retransmission of a single data signal (for example, data signal # 1) is performed for the other wireless communication When requested by the device, the transmission unit is switched from the first transmission method to the second transmission method, and the transmission unit is controlled to perform retransmission of the single data signal by the second transmission method. This is the gist.

  Another feature of the wireless communication apparatus according to the present invention is that, in the wireless communication apparatus according to the above feature, the control unit switches from the first transmission method to the second transmission method, and then performs the second transmission. Controlling the transmitting unit to switch from the second transmission method to the first transmission method when notified of successful decoding of a single data signal retransmitted by the method from the second transmission method; Is the gist.

  Another feature of the wireless communication device according to the present invention is that, in the wireless communication device according to the above feature, a plurality of spatially divided streams are exchanged with other wireless communication devices in a wireless communication system that supports MIMO spatial multiplexing technology. A retransmission control method used in a wireless communication device formed between the plurality of streams, wherein a plurality of data signals are transmitted by a first transmission method for transmitting different data signals for each of the plurality of streams; When the other wireless communication apparatus requests retransmission of a single data signal among the plurality of data signals transmitted by the transmission method, the second data signal transmits the same data signal in each of the plurality of streams. A step of switching to a transmission method of: a step of retransmitting a single data signal requested to be retransmitted by the second transmission method; And summary to include.

  ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless communication apparatus and retransmission control method which can reduce the frequency | count of retransmission in resending at the time of MIMO transmission can be provided.

It is a figure for demonstrating the outline | summary of the radio | wireless communications system which concerns on embodiment of this invention. It is a block diagram which shows the structure of the base station which concerns on embodiment of this invention. It is a block diagram which shows the structure of the radio | wireless terminal which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the base station which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the radio | wireless terminal which concerns on embodiment of this invention.

  Referring to the drawings, for a wireless communication system according to an embodiment of the present invention, (1) an outline of the wireless communication system, (2) a detailed configuration example of the wireless communication system, (3) an operation example of the wireless communication system, (4 ) Effects of the embodiment, (5) Other embodiments will be described in this order. In the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) Overview of Radio Communication System FIG. 1 is a diagram for describing an overview of a radio communication system according to the present embodiment. The wireless communication system according to the present embodiment is configured based on LTE (Long Term Evolution) whose specifications are formulated by 3GPP (3rd Generation Partnership Project).

  As illustrated in FIG. 1A, the radio communication system according to the present embodiment includes a base station eNB and a radio terminal UE that performs radio communication with the base station eNB. In the present embodiment, the base station eNB has two transmission antennas (transmission antenna 11 and transmission antenna 12), and the radio terminal UE has two reception antennas (reception antenna 21 and reception antenna 22). Note that the number of transmission antennas provided in the base station eNB and the number of reception antennas provided in the radio terminal UE may be greater than two.

  The base station eNB and the radio terminal UE support MIMO spatial multiplexing technology in the downlink. In the present embodiment, information on propagation path characteristics between the base station eNB and the radio terminal UE (so-called propagation path state information (CSI)) is not fed back from the radio terminal UE to the base station eNB, that is, MIMO transmission is performed. Loop MIMO is applied.

  In the MIMO spatial multiplexing technique, a plurality of spatially divided streams can be formed between the transmission side and the reception side by using different transmission antennas or different transmission directivities for each data signal. In the present embodiment, the stream S1 and the stream S2 are formed by using different transmission antennas 11 and 12 for each of the data signal # 1 and the data signal # 2.

  The base station eNB transmits the data signal # 1 and the data signal # 2 using the stream S1 and the stream S2, respectively. At that time, the base station eNB inserts and transmits different known signals (pilot signals) for each of the transmission antenna 11 and the transmission antenna 12.

  The radio terminal UE receives the data signal # 1 and the data signal # 2 in an interference state, and estimates the propagation path characteristics for each of the transmission antenna 11 and the transmission antenna 12 from the known signals for each of the transmission antenna 11 and the transmission antenna 12. Each data signal # 1 and data signal # 2 are separated based on the difference in the propagation path characteristics, and each of the separated data signal # 1 and data signal # 2 is decoded.

  In addition, the wireless communication system according to the present embodiment supports HARQ. As the HARQ method, an existing technology such as a chase combining (CC) method or an incremental redundancy (IR) method can be used. In this embodiment, the CC method is used.

  When the radio terminal UE fails to decode the data signal # 1 and / or the data signal # 2 received from the base station eNB, the radio terminal UE requests the base station eNB to retransmit the data signal that has failed to be decoded. The requested data signal is retransmitted. At that time, the radio terminal UE holds information on the data signal that has failed to be decoded, and uses the held information for decoding the retransmitted data signal. When the radio terminal UE succeeds in decoding the data signal received from the base station eNB, the radio terminal UE notifies the transmission device of the successful decoding of the data signal.

  In this embodiment, a retransmission request is performed by transmitting a NACK from the radio terminal UE to the base station eNB, and a successful decoding notification is performed by transmitting an ACK from the radio terminal UE to the base station eNB.

  For example, if both the data signal # 1 and the data signal # 2 are successfully decoded, the radio terminal UE transmits an ACK for the data signal # 1 and the data signal # 2. When both the data signal # 1 and the data signal # 2 have failed to be decoded, the radio terminal UE transmits a NACK for the data signal # 1 and the data signal # 2. When one of the data signal # 1 and the data signal # 2 is successfully decoded and the other is a decoding failure, the radio terminal UE transmits an ACK for the one data signal and the other data signal Send a NACK for.

  FIG. 1B shows the data signal # 2 in the wireless communication system according to the present embodiment, in which the data signal # 1 of the data signal # 1 and the data signal # 2 shown in FIG. FIG. 6 is a diagram for explaining retransmission control when the decoding is successful, that is, when retransmission of a single data signal # 1 is requested. In this case, the radio terminal UE transmits NACK for the data signal # 1 and transmits ACK for the data signal # 2.

  As illustrated in FIG. 1B, the base station eNB is requested by the radio terminal UE to retransmit a single data signal # 1 of the data signal # 1 and the data signal # 2 illustrated in FIG. Then, switching to transmission diversity in which the same data signal is transmitted in each of the stream S1 and the stream S2, and the data signal # 1 requested to be retransmitted is retransmitted. Thereby, a diversity gain can be obtained. Note that transmission diversity is for transmitting the same data signal in each of the streams S1 and S2, but if the identity of the data signals is maintained, a method of delaying one data signal or one data A system for encoding a signal may be used.

  As described above, the following effects can be obtained by switching to transmission diversity at the time of retransmission of the single data signal # 1 of the data signal # 1 and the data signal # 2. For example, a transmission error occurs in bit b3 among bits b1, b2, and b3 constituting data signal # 1 retransmitted in stream S1, and bits b1 and b2 constituting data signal # 1 retransmitted in stream S2 , B3, even if a transmission error occurs in bit b2, these transmission errors can be complemented by synthesizing data signals # 1 of both streams. As a result, the decoding success rate of the retransmitted data signal # 1 can be increased.

  FIG. 1C shows a case where both the data signal # 1 and the data signal # 2 shown in FIG. 1A have failed to be decoded in the wireless communication system according to this embodiment, that is, retransmission of a plurality of data signals. It is a figure for demonstrating resending control in case a request | requirement is requested | required. In this case, it is assumed that the radio terminal UE transmits NACK for the data signal # 1 and the data signal # 2.

  As shown in FIG. 1 (c), when the base station eNB is requested by the radio terminal UE to retransmit the data signal # 1 and the data signal # 2 shown in FIG. 1 (a), the stream S1 and stream The assignment of the data signal to each of S2 is changed (replaced), and retransmission of data signal # 1 and data signal # 2 is performed by MIMO transmission. Specifically, in FIG. 1A, the data signal # 1 is assigned to the stream S1 and the data signal # 2 is assigned to the stream S2. In FIG. 1C, the data signal # 1 is assigned to the stream S1. 2 is assigned, and the data signal # 1 is assigned to the stream S2.

  Thus, the following diversity gain can be obtained by exchanging both data signals # 1 and # 2 when retransmitting the data signals. For example, in FIG. 1A, a case is assumed in which a transmission error occurs in bit b3 among bits b1, b2, and b3 constituting data signal # 1 transmitted in stream S1, and decoding fails. In this case, the decoding information related to the bits b1 and b2 is held in the radio terminal UE by the HARQ function. Here, if data signal # 1 is transmitted with stream S1 at the time of retransmission, there is a high possibility that bit b3 will be erroneous again, and decoding will fail even if the stored decoding information is used. On the other hand, if data signal # 1 is transmitted by stream S2 at the time of retransmission, the possibility that bit b3 will be erroneous again is low, and the probability of successful decoding using the stored decoding information can be increased.

(2) Detailed Configuration Example of Radio Communication System Next, a detailed configuration example of the radio communication system according to the present embodiment will be described in the order of (2.1) configuration of base station and (2.2) configuration of radio terminal. .

(2.1) Configuration of Base Station FIG. 2 is a block diagram showing the configuration of the base station eNB according to this embodiment. Here, the configuration related to the present invention will be mainly described.

  As shown in FIG. 2, the base station eNB includes a control unit 101, a data generation unit 102, a stream division unit 103, an error correction coding unit 104 # 1, an error correction coding unit 104 # 2, and a modulation unit. 105 # 1 and modulation section 105 # 2, mapping precoding section 106 # 1 and mapping precoding section 106 # 2, inverse fast Fourier transform (IFFT) section 107 # 1 and IFFT section 107 # 2, and transmission An antenna 11 and a transmission antenna 12 are included.

  The control unit 101 includes, for example, a central processing unit (CPU) and a memory. The control unit 101 controls the transmission unit 110.

  The transmission unit 110 transmits a data signal, and includes a digital signal processor (DSP), for example, and includes a data generation unit 102, a stream division unit 103, an error correction coding unit 104 # 1, and an error correction. Encoding section 104 # 2, modulation section 105 # 1, modulation section 105 # 2, mapping / precoding section 106 # 1, mapping / precoding section 106 # 2, IFFT section 107 # 1 and IFFT section 107 # 2 is constituted.

  Error correction coding section 104 # 1, modulation section 105 # 1, mapping / precoding section 106 # 1, IFFT section 107 # 1, and transmitting antenna 11 correspond to stream S1 shown in FIG. Is provided. The error correction encoding unit 104 # 2, the modulation unit 105 # 2, the mapping / precoding unit 106 # 2, the IFFT unit 107 # 2, and the transmission antenna 12 correspond to the stream S2 shown in FIG. Is provided.

  The data generation unit 102 generates a data signal to be transmitted to the radio terminal UE under the control of the control unit 101, and outputs the generated data signal to the stream division unit 103. The data signal before being formatted for transmission may be referred to as a code word. Specifically, the data generation unit 102 generates two different data signals (multicode words) at the time of MIMO transmission, and outputs the generated two data signals to the stream division unit 103. Further, the data generation unit 102 performs buffering of the generated data signal in order to perform retransmission processing related to HARQ. The data generation unit 102 outputs one data signal (single codeword) to the stream division unit 103 during transmission diversity.

  The stream division unit 103 performs processing for distributing the data signal input from the data generation unit 102 to each of the error correction encoding unit 104 # 1 and the error correction encoding unit 104 # 2. Since two different data signals are input to the stream division unit 103 during MIMO transmission, the stream division unit 103 outputs one data signal to the error correction coding unit 104 # 1 and error correction of the other data signal Output to encoding section 104 # 2. On the other hand, since one data signal is input to the stream division unit 103 during transmission diversity, the stream division unit 103 creates a copy of the data signal and converts one data signal into the error correction coding unit 104 #. 1 and the other data signal is output to the error correction encoding unit 104 # 2.

  Error correction coding section 104 # 1 and error correction coding section 104 # 2 perform error correction coding on the data signal input from stream division section 103 and output the data signal to modulation section 105 # 1 and modulation section 105 # 2, respectively. .

  Modulation section 105 # 1 and modulation section 105 # 2 modulate the data signals input from error correction coding section 104 # 1 and error correction coding section 104 # 2, respectively, and perform mapping / precoding section 106 # 1 and The data is output to the mapping / precoding unit 106 # 2.

  The mapping / precoding unit 106 # 1 and the mapping / precoding unit 106 # 2 map the data signal respectively input from the modulation unit 105 # 1 and the modulation unit 105 # 2 to each subcarrier and transmit the data (MIMO) Precoding is performed according to (transmission / transmission diversity) and output to IFFT section 107 # 1 and IFFT section 107 # 2.

  IFFT section 107 # 1 and IFFT section 107 # 2 perform IFFT on the data signals input from mapping precoding section 106 # 1 and mapping precoding section 106 # 2, respectively, and output the result. Each data signal output from IFFT section 107 # 1 and IFFT section 107 # 2 is added with a CP by a cyclic prefix (CP) adding section (not shown), and then an up converter and a power amplifier (not shown), etc. Is converted to the RF band. The transmission antenna 11 and the transmission antenna 12 each transmit an RF band data signal.

(2.2) Configuration of Radio Terminal FIG. 3 is a block diagram showing a configuration of the radio terminal UE according to the present embodiment.

  As illustrated in FIG. 3, the radio terminal UE includes a reception antenna 21 and a reception antenna 22, a fast Fourier transform (FFT) unit 201 # 1 and an FFT unit 201 # 2, a transmission method determination unit 203, and a MIMO detection unit 204. A demodulation unit 205 # 1, a demodulation unit 205 # 2, an error correction decoding unit 206 # 1, an error correction decoding unit 206 # 2, a cyclic redundancy check (CRC) unit 207 # 1, and a CRC unit 207 # 2. HARQ control unit 208 # 1, HARQ control unit 208 # 2, and stream synthesis unit 209 are included.

  Each of the receiving antenna 21 and the receiving antenna 22 receives an RF band data signal from the base station eNB. The RF band data signals received by the receiving antenna 21 and the receiving antenna 22 are converted into a baseband band via a low-noise amplifier and a down converter (not shown).

  The FFT unit 201 # 1 performs FFT on the baseband data signal from the reception antenna 21 and outputs the result to the transmission method determination unit 203. The FFT unit 201 # 2 performs FFT on the baseband data signal from the receiving antenna 22 and outputs the result to the transmission method determination unit 203.

  The transmission method discrimination unit 203 discriminates a transmission method (MIMO transmission / transmission diversity) based on data signals input from the FFT unit 201 # 1 and the FFT unit 201 # 2. For example, the transmission method determination unit 203 can determine the transmission method (MIMO transmission / transmission diversity) from the transmission method information included in the data signal.

  The MIMO detection unit 204 performs a MIMO detection process for separating data signals for each stream during MIMO transmission. As a method of MIMO detection processing, existing methods such as Zero Forcing, MMSE, MRC, MLD can be used. For example, the MIMO detection unit 204 estimates the propagation path characteristics for each of the transmission antennas 11 and 12 from the known signals (pilot signals) for the transmission antennas 11 and 12, and based on the difference between these propagation path characteristics. Each data signal is separated, one data signal is output to demodulation section 205 # 1, and the other data signal is output to demodulation section 205 # 2. In contrast, since the same data signal is received for each stream during transmission diversity, MIMO detection section 204 outputs the same data signal only to demodulation section 205 # 1.

  Demodulating section 205 # 1 and demodulating section 205 # 2 demodulate the data signals input from MIMO detecting section 204 and output them to error correction decoding section 206 # 1 and error correction decoding section 206 # 2, respectively.

  Error correction decoding section 206 # 1 and error correction decoding section 206 # 2 perform error correction decoding on the data signals input from demodulation section 205 # 1 and demodulation section 205 # 2, respectively, and perform CRC section 207 # 1 and CRC section 207. Output to # 2 respectively. In addition, the error correction decoding unit 206 # 1 and the error correction decoding unit 206 # 2 perform a HARQ-related combining process under the control of the HARQ control unit 208 # 1 and the HARQ control unit 208 # 2.

  The CRC unit 207 # 1 and the CRC unit 207 # 2 perform error detection by CRC on the data signals respectively input from the error correction decoding unit 206 # 1 and the error correction decoding unit 206 # 2 to check whether there is a transmission error. (Decoding success / decoding failure) is notified to the HARQ control unit 208 # 1 and the HARQ control unit 208 # 2. Each of the CRC unit 207 # 1 and the CRC unit 207 # 2 outputs a data signal to the stream synthesis unit 209 when decoding is successful.

  HARQ control unit 208 # 1 and HARQ control unit 208 # 2 perform ACK / NACK depending on the presence / absence of transmission error (decoding success / decoding failure) notified from CRC unit 207 # 1 and CRC unit 207 # 2, respectively. Processing for transmitting to the base station eNB is performed. Also, the HARQ control unit 208 # 1 and the HARQ control unit 208 # 2 hold the decoding information related to the data signal that has failed to be decoded, and the decoding information held by the error correction decoding unit 206 # 1 and the error correction decoding unit It outputs to 206 # 2.

  The stream combining unit 209 combines the data signals respectively input from the CRC unit 207 # 1 and the CRC unit 207 # 2, restores the original data signal, and outputs the original data signal to an upper layer block (not shown).

(3) Operation Example of Radio Communication System Next, a detailed configuration example of the radio communication system according to the present embodiment will be described in the order of (3.1) operation of the base station and (3.2) operation of the radio terminal. Here, the operation in the system configuration shown in FIG. 1 will be described as an example.

(3.1) Operation of Base Station FIG. 4 is a flowchart showing the operation of the base station eNB according to this embodiment.

  As shown in FIG. 4, in step S101, the control unit 101 determines whether it is initial transmission or retransmission. When the NACK for at least one of the stream S1 or the stream S2 is received from the radio terminal UE, it is determined that the NACK is retransmitted. When the ACK for both the stream S1 and the stream S2 is received from the radio terminal UE, it is determined that the initial transmission is performed. In addition, when the upper limit of the number of retransmissions is provided and the number of retransmissions has reached the upper limit, it may be determined that the retransmission is aborted and the initial transmission is performed.

  If it determines with it being the first transmission, the control part 101 will advance a process to step S102. On the other hand, if it determines with it being resending, the control part 101 will advance a process to step S203.

  In step S102, the control unit 101 controls the data generation unit 102 to generate two data signals # 1 and # 2 (multicodeword) to be transmitted to the radio terminal UE in order to perform MIMO transmission. To do.

  On the other hand, in step S103, the control unit 101 determines whether retransmission of the data signals of both the stream S1 and the stream S2 is requested based on ACK / NACK or only the data signal of either the stream S1 or the stream S2. It is determined whether or not retransmission is requested.

  When determining that retransmission of the data signals of both the streams S1 and S2 is requested, the control unit 101 advances the processing to step S104. On the other hand, if it is determined that retransmission of only one of the data signals of stream S1 or stream S2 (here, data signal # 1) is requested, control unit 101 advances the process to step S105.

  In step S104, the control unit 101 controls the data generation unit 102 to output the data signal # 1 and the data signal # 2 for retransmission, and sets the output destination of the data signal # 1 and the data signal # 2. The stream dividing unit 103 is controlled so as to be changed. For example, when the data signal # 1 is output to the error correction encoding unit 104 # 1 and the data signal # 2 is output to the error correction encoding unit 104 # 2 at the first transmission, the data signal # 1 is transmitted at the time of retransmission. Is output to the error correction encoding unit 104 # 2, and the stream division unit 103 is set to output the data signal # 2 to the error correction encoding unit 104 # 1.

  In step S105, the control unit 101 controls the data generation unit 102 so as to output the data signal # 1 for retransmission, and the data signal # 1 is subjected to error correction coding unit 104 # 1 and error correction coding. The stream division unit 103 is set to output to each of the unit 104 # 2.

  In step S106, the stream division unit 103 outputs the input data signal to the error correction coding unit 104 # 1 and the error correction coding unit 104 # 2 according to the control from the control unit 101.

  In step S107, the error correction encoding unit 104 # 1 and the error correction encoding unit 104 # 2 perform error correction encoding on the data signal input from the stream division unit 103 to perform modulation unit 105 # 1 and modulation unit 105 # 2. Respectively.

  In step S108, modulation section 105 # 1 and modulation section 105 # 2 modulate the data signals input from error correction coding section 104 # 1 and error correction coding section 104 # 2, respectively, and perform mapping / precoding sections 106 # 1 and mapping / precoding section 106 # 2.

  In step S109, the mapping / precoding unit 106 # 1 and the mapping / precoding unit 106 # 2 map the data signals respectively input from the modulation unit 105 # 1 and the modulation unit 105 # 2 to each subcarrier, and Precoding according to the transmission scheme (MIMO transmission / transmission diversity) is performed and output to IFFT section 107 # 1 and IFFT section 107 # 2.

  In step S110, IFFT section 107 # 1 and IFFT section 107 # 2 perform IFFT on the data signals input from mapping / precoding section 106 # 1 and mapping / precoding section 106 # 2, respectively, and output the result.

  In step S111, the transmission antenna 11 and the transmission antenna 12 each transmit an RF band data signal.

(3.2) Operation of Radio Terminal FIG. 5 is a flowchart showing the operation of the radio terminal UE according to this embodiment.

  As shown in FIG. 5, in step S201, each of the reception antenna 21 and the reception antenna 22 receives an RF band data signal from the base station eNB.

  In step S <b> 202, the FFT unit 201 # 1 performs FFT on the baseband data signal from the reception antenna 21 and outputs the result to the transmission method determination unit 203.

  In step S203, the transmission method determination unit 203 determines the transmission method (MIMO transmission / transmission diversity) based on the data signals input from the FFT unit 201 # 1 and the FFT unit 201 # 2. If it is determined that the transmission is MIMO transmission, the process proceeds to step S204. On the other hand, if it is determined that there is transmission diversity, the process proceeds to step S205.

  In step S204, the MIMO detection unit 204 performs a MIMO detection process for separating the data signal # 1 and the data signal # 2 for each stream, outputs one data signal to the demodulation unit 205 # 1, and outputs the other data The signal is output to demodulation section 205 # 2. On the other hand, in step S205, since the MIMO detection unit 204 receives the same data signal # 1 for each stream, it outputs the same data signal # 1 only to the demodulation unit 205 # 1. The following processing will be described at the time of MIMO transmission.

  In step S206, the demodulation unit 205 # 1 and the demodulation unit 205 # 2 demodulate the data signals respectively input from the MIMO detection unit 204 and output them to the error correction decoding unit 206 # 1 and the error correction decoding unit 206 # 2, respectively. To do.

  In step S207, error correction decoding section 206 # 1 and error correction decoding section 206 # 2 perform error correction decoding on the data signals input from demodulation section 205 # 1 and demodulation section 205 # 2, respectively, and perform CRC section 207 # 1. And output to the CRC unit 207 # 2. In addition, the error correction decoding unit 206 # 1 and the error correction decoding unit 206 # 2 perform HARQ combining processing under the control of the HARQ control unit 208 # 1 and the HARQ control unit 208 # 2 at the time of retransmission.

  In step S208, the CRC unit 207 # 1 and the CRC unit 207 # 2 perform error detection by CRC for the data signals respectively input from the error correction decoding unit 206 # 1 and the error correction decoding unit 206 # 2, The presence / absence of transmission error (decoding success / decoding failure) is notified to the HARQ control unit 208 # 1 and the HARQ control unit 208 # 2, respectively. Each of the CRC unit 207 # 1 and the CRC unit 207 # 2 outputs a data signal to the stream synthesis unit 209 when decoding is successful (step S208; YES).

  In step S209, the stream combining unit 209 combines the data signals respectively input from the CRC unit 207 # 1 and the CRC unit 207 # 2 to restore the original data signal, and outputs the original data signal to an upper layer block (not shown) To do.

(4) Effect of Embodiment As described above, the base station eNB according to this embodiment requests retransmission of a single data signal # 1 among the data signal # 1 and the data signal # 2 transmitted by MIMO transmission. Then, the MIMO transmission is switched to the transmission diversity, and the data signal # 1 is retransmitted by the transmission diversity. As a result, diversity gain can be obtained, and the probability of successful decoding of data signal # 1 on the receiving side increases, so that the number of retransmissions can be reduced.

  In addition, when the base station eNB according to the present embodiment is requested to retransmit both data signals # 1 and # 2 transmitted by MIMO transmission, the allocation of the data signal to each of the stream S1 and the stream S2 Are changed (replaced), and retransmission of the data signal # 1 and the data signal # 2 is performed by MIMO transmission. As a result, a spatial diversity effect can be obtained, and the probability of successful decoding of the data signal # 1 and the data signal # 2 on the receiving side increases, so that the number of retransmissions can be reduced.

  Thus, the base station eNB according to the present embodiment can reduce the number of retransmissions in retransmission during MIMO transmission.

  Furthermore, after the base station eNB according to the present embodiment switches from MIMO transmission to transmission diversity and is notified from the radio terminal UE of successful decoding of the single data signal # 1 retransmitted by transmission diversity, the base station eNB Switch to MIMO transmission. Thereby, the transmission rate can be improved.

(5) Other Embodiments As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

(5.1) Modification 1
For example, a condition that the channel state between the base station eNB and the radio terminal UE is deteriorated may be added as a condition for switching from MIMO transmission to transmission diversity. The control unit 101 of the base station eNB determines whether the SINR of the signal received from the radio terminal UE has fallen below the threshold, or the fading frequency of the signal has exceeded the threshold, between the base station eNB and the radio terminal UE. It is determined that the propagation path state of is deteriorated. Alternatively, the control unit 101 of the base station eNB determines that the propagation path state between the base station eNB and the radio terminal UE is that SINR information (CQI; Channel Quality Indicator) fed back from the radio terminal UE is below the threshold. Judge that it has deteriorated.

  And the control part 101 is a case where the propagation path state between the base station eNB and the radio | wireless terminal UE has deteriorated, And among data signal # 1 and data signal # 2 transmitted by MIMO transmission, When retransmission of a single data signal # 1 is requested from the radio terminal UE, the transmission unit 110 is controlled to switch from MIMO transmission to transmission diversity and perform retransmission of the single data signal # 1 by transmission diversity. To do. In this way, when the propagation path state is degraded, the probability of successful decoding of the data signal # 1 on the receiving side becomes very low. Therefore, retransmission of the single data signal # 1 is performed as transmission diversity. This increases the probability of successful decoding of the single data signal # 1 on the receiving side, so that the number of retransmissions can be reduced.

(5.2) Modification 2
In the embodiment described above, a retransmission request is performed by transmitting a NACK from the radio terminal UE to the base station eNB, and a successful decoding notification is performed by transmitting an ACK from the radio terminal UE to the base station eNB. However, an implicit retransmission request / decoding success notification may be applied instead of such an explicit retransmission request / decoding success notification. For example, in a system that does not use NACK, the base station eNB may perform retransmission by assuming that retransmission is implicitly requested by not receiving ACK from the radio terminal UE. Further, in a system that does not use ACK, the base station eNB may consider that decoding success has been implicitly notified by not receiving NACK from the radio terminal UE.

(5.3) Modification 3
In the embodiment described above, transmission of data signals mainly for the downlink has been described. However, the present invention is not limited to the downlink, and the present invention can also be applied to the uplink. In this case, the process performed by the base station eNB in the above-described embodiment is performed by the radio terminal UE, and the process performed by the radio terminal UE in the above-described embodiment is performed by the base station eNB. Moreover, not only the radio communication between the base station eNB and the radio terminal UE, but also the radio communication between the base station eNB and the radio relay station (relay node), and the radio between the radio relay station and the radio terminal UE. The present invention can also be applied to communication.

  Further, in the above-described embodiment, the wireless communication system based on LTE has been described as an example. However, the present embodiment is not limited to the wireless communication system based on WiMAX (IEEE802.16 series), wireless LAN (IEEE802.11 series), next-generation PHS, or the like. The invention may be applied.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

  eNB ... base station, UE ... wireless terminal, 11, 12 ... transmission antenna, 21, 22 ... reception antenna, 101 ... control unit, 102 ... data generation unit, 103 ... stream division unit, 104 # 1, # 2 ... error correction Encoding section, 105 # 1, # 2 ... modulation section, 106 # 1, # 2 ... mapping precoding section, 107 # 1, # 2 ... IFFT section, 110 ... transmission section, 201 # 1, # 2 ... FFT , 203... Transmission method discriminating unit, 204... MIMO detecting unit, 205 # 1, # 2, demodulating unit, 206 # 1, # 2, error correction decoding unit, 207 # 1, # 2, CRC unit, 208 # 1 , # 2 ... HARQ control unit, 209 ... stream synthesis unit

Claims (4)

In a wireless communication system that supports multiple-input multiple-output (MIMO) spatial multiplexing technology, a wireless communication device that forms a plurality of spatially divided streams with other wireless communication devices,
The data signal is transmitted in either one of a first transmission method for transmitting a different data signal for each of the plurality of streams and a second transmission method for transmitting the same data signal in each of the plurality of streams. A configured transmitter, and
Of the plurality of data signals transmitted by the transmission unit according to the first transmission method, when the retransmission of a single data signal is requested from the other wireless communication device, the retransmission of the single data signal is performed A control unit that controls the transmission unit to perform the second transmission method;
A wireless communication apparatus comprising: When the control unit receives a request from the other wireless communication apparatus to retransmit two or more data signals among the plurality of data signals transmitted by the transmission unit according to the first transmission method, the control unit Changing the allocation of the data signal to each of them, and controlling the transmission unit to perform retransmission of the two or more data signals by the first transmission method,
The wireless communication apparatus according to claim 1. The control unit is configured to use a single data among a plurality of data signals transmitted by the transmission unit according to the first transmission method when a propagation path state with the other wireless communication device is deteriorated. When retransmission of a signal is requested from the other wireless communication device, the transmission unit is controlled to perform retransmission of the single data signal by the second transmission method.
The wireless communication apparatus according to claim 1, wherein the wireless communication apparatus is a wireless communication apparatus. This is a retransmission control method used in a wireless communication apparatus that forms a plurality of spatially divided streams with another wireless communication apparatus in a wireless communication system that supports multiple-input multiple-output (MIMO) spatial multiplexing technology. And
Transmitting a plurality of data signals according to a first transmission scheme for transmitting a different data signal for each of the plurality of streams;
Of the plurality of data signals transmitted by the first transmission method, when the retransmission of a single data signal is requested from the other wireless communication device, the retransmission is requested by the second transmission method. Retransmitting a single data signal;
Including a retransmission control method.

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