JP2012028875A - Communication device and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication device and a communication method that request retransmission for each code block.SOLUTION: A communication device 101 has: a communication part 111 that receives a signal configured by a plurality of code blocks for decoding data in the communication device 101 that decodes the data, and to each of which an error detection code and an identifier different from each other are added; and a controller 113 that detects presence or absence of a code error using the error detection code added to the code block for each code block, and specifies the code block from which the code error has been detected, as a retransmission target, and requests retransmission of only the retransmission target code block.

Description

  The present invention relates to a communication device and a communication method, and more particularly to a communication device and a communication method that improve the efficiency of retransmission request processing.

  In a wireless communication system, transmission errors frequently occur compared to a wired communication system. For this reason, in wireless communication systems, retransmission control based on error detection of received information is generally used to improve communication reliability. In this control, the transmission side adds an error detection code to the data and transmits the data, and the reception side detects an error in the transmission data generated during transmission based on the error detection code. For example, CRC (Cyclic Redundancy Check) is used as the error detection code. If an error is detected, the transmission side is requested to retransmit the information, and the transmission side retransmits the information.

  For the purpose of reducing the amount of processing in this retransmission control, there is a conventional technique that divides transmission data into a plurality of code blocks and adds an error detection code to each divided code block (see, for example, Patent Document 1). . The invention described in Patent Document 1 will be briefly described with reference to FIG.

  6A and 6B are block diagrams of a transmitter and a receiver in Patent Document 1, respectively. As shown in FIG. 6A, the receiver in Patent Document 1 includes a code block division unit 601, a CRC addition unit (error detection code addition unit) 602, an error correction coding unit 603, an interleaving unit 604, and a mapping unit. 605. The code block dividing unit 601 divides transmission data into a plurality of code blocks. The error detection code adding unit 602 adds a parity bit (CRC) for error detection to each data divided into code blocks. The error correction encoding unit 603 performs error correction encoding processing on each data to which the parity bit is added. The interleaving unit 604 performs interleaving processing on the error-corrected encoded data. The mapping unit 605 maps each code block on which the above processing has been performed to a physical channel. 6B includes a demapping unit 609, a deinterleaving unit 610, an error correction decoding unit 611, an error detection unit 612, and a code block connection unit 613. On the other hand, the reverse process of the transmitter is performed. That is, deinterleaving, error correction decoding, and error detection are performed on the received data divided into the code blocks by the demapping unit 609, and the code blocks are connected to be received data. Note that if the error detector 612 detects an error in one or more code blocks, a retransmission request process is performed.

JP 2006-203355 A

  However, in the prior art, when there is an error in the received data, the receiver not only receives the error code block but also the entire received data (all code blocks constituting the transmission data before the division). A resend must be requested. Therefore, a code block in which no CRC error has occurred may be retransmitted due to an error in the CRC check result of a certain code block. Retransmission of error-free code blocks is a wasteful process.

  Accordingly, an object of the present invention made in view of the above problems is to provide a communication device and a communication method that make a retransmission request for each code block.

In order to solve the above-described problems, the communication device according to the first invention provides:
In a communication device for decoding data,
A plurality of code blocks for decoding data, a communication unit that receives a signal composed of a plurality of code blocks to which an error detection code and different identifiers are added; and
For each code block, the presence or absence of a code error is detected using an error detection code added to the code block, the code block in which the code error is detected is identified as a retransmission target, and only the code block to be retransmitted is detected. And a control unit that requests retransmission.

  In addition, when there are a plurality of code blocks to be retransmitted, the control unit further prioritizes retransmission of code blocks so that the number of retransmission requests until data is correctly decoded is smaller than the number of code blocks to be retransmitted. It is desirable to determine the ranking.

  Further, the control unit further determines whether error detection should be performed for each code block based on the modulation class and communication quality related to each code block, and the code determined not to perform error detection. It is desirable to set a block as the retransmission target.

  As described above, the solution of the present invention has been described as an apparatus. However, the present invention can be realized as a method, a program, and a storage medium storing the program, which are substantially equivalent thereto, and the scope of the present invention. It should be understood that these are also included.

For example, a communication method that implements the first invention as a method is as follows:
In a communication method in a communication device for decoding data,
Receiving a signal composed of a plurality of code blocks for decoding data, the error detection code and a plurality of code blocks each having a different identifier added thereto;
For each code block, detecting the presence or absence of a code error using an error detection code added to the code block;
Identifying a code block in which a code error is detected as a retransmission target; and
Requesting retransmission of only the code block to be retransmitted.

  According to the communication apparatus and communication method of the present invention configured as described above, an identifier is assigned to each code block, and a code block with a code error is specified as a retransmission target. Then, retransmission of only the code block to be retransmitted is requested. Since retransmission processing of error-free code blocks, which is useless processing, is not performed, it is possible to increase the efficiency of retransmission request processing.

FIG. 1 is a schematic communication network diagram according to an embodiment of the present invention. FIG. 2 is a functional block diagram showing a schematic configuration of the base station according to the embodiment of the present invention. FIG. 3 is an explanatory diagram of data used in the description of an embodiment of the present invention. FIG. 4 is a flowchart showing processing of the base station according to the embodiment of the present invention. FIG. 5 is a reception status table according to an embodiment of the present invention. FIG. 6 is a block diagram of a transmitter and a receiver in Patent Document 1.

  Hereinafter, a communication device according to an embodiment of the present invention will be described in detail with reference to the drawings. Examples of the communication device include a base station, a wireless communication terminal (for example, a mobile phone terminal, a notebook computer, a PDA (personal digital assistance), a portable game machine, a portable audio player, a portable video player, a portable electronic dictionary, a portable electronic book viewer. Portable electronic devices, etc.). Hereinafter, in the present embodiment, the communication apparatus is a base station and decodes encoded data.

  FIG. 1 is a schematic communication network diagram according to an embodiment of the present invention. The communication network 11 includes a base station 101 and a wireless communication terminal 103. The base station 101 and the wireless communication terminal 103 communicate by establishing a wireless link. It is assumed that the communication network 11 uses HARQ (Hybrid Automatic Repeat reQuest) technology. HARQ is an automatic retransmission request (ARQ) that is a control for requesting the transmitting side to retransmit the data (wrong packet) when the receiving side in the wireless communication system receives wrong data (packet). And a forward error correction code (FEC) that performs error correction decoding on the combined data of the previously received data and the newly retransmitted data. HARQ is adopted in the HSDPA (High Speed Downlink Packet Access) method described in TS25.212, which is a standard of 3GPP (Third Generation Partnership Project).

  FIG. 2 is a functional block diagram showing a schematic configuration of the base station according to the embodiment of the present invention. The base station 101 according to the present embodiment includes a communication unit 111, a storage unit 112, and a control unit 113.

  The communication unit 111 transmits and receives various signals to and from the wireless communication terminal 103. The storage unit 112 stores various information such as the code block itself and the code block identifier, and also functions as a work memory. The control unit 113 controls and manages the entire base station 101 including each functional block of the base station 101. Here, the control unit 113 is configured as software executed on an arbitrary suitable processor such as a CPU (Central Processing Unit) or a dedicated processor specialized for each process (for example, DSP (Digital Signal Processor)). Can be configured. The processing performed by the control unit 113 will be described in detail with reference to FIG.

  Hereinafter, processing of the base station will be described with reference to FIGS. FIG. 3 is an explanatory diagram of data used in the description of an embodiment of the present invention. FIG. 4 is a flowchart showing processing of the base station according to the embodiment of the present invention.

  First, FIG. 3 will be described. In FIG. 3, data D to be transmitted from the wireless communication terminal 103 to the base station 101 is represented by data D. In this case, in the HARQ technique, a redundant bit (error correction code) R for error correction is added to the data D to define the transport block TB. Examples of the error correction code include a block code such as a turbo code and an LDPC (low-density parity-check code) and a convolutional code.

  The wireless communication terminal 103 divides the transport block TB and transmits it to the base station 101 because the size that can be transmitted at one time is limited. This one-time transmission unit is referred to as a segment (signal in claims). Segments S1 and S2 in FIG. 3 show a part of the divided transport block TB. The segments S1 and S2 in FIG. 3 each have information on different positions of the transport block TB. However, the segments may overlap and share some information.

  The segment is composed of a plurality of code blocks for decoding the data D of the transport block TB. For example, the segments S1 and S2 in FIG. 3 are composed of CB1-1 to CB1-6 and CB2-1 to CB2-6, respectively. Note that the number of code blocks constituting a segment is not limited to six. An error detection code is added to each code block. The error detection code is, for example, a CRC or a parity code. Hereinafter, in this embodiment, it is assumed that the error detection code is CRC. Each code block is added with an identifier for identifying the code block by the wireless communication terminal 103. The identifier includes information on the segment to which the code block belongs. For example, identifiers such as 1-2 can be set for the second code block of segment S1, and 2-6 can be set for the sixth code block of segment S2. Further, an NDI (New Data Indicator) is added by the wireless communication terminal 103 for each code block. NDI indicates whether transmission by the wireless communication terminal 103 is initial transmission or retransmission, and 0 and 1 are switched as the value of NDI for each initial transmission. Here, initial transmission refers to transmission of the first segment that is performed to extract data by decoding. Retransmission refers to transmission of a code block of a part of the first segment or transmission of a segment other than the first segment, which is performed when data cannot be extracted by decoding of the first transmission segment. For example, when the NDI value of the code blocks CB1-1 to CB1-6 of the initial transmission segment S1 is 0 and the code block CB1-1 is retransmitted, the NDI value of the retransmission code block CB1-1 is 0. Even when a segment S2 that is a part of the transport block TB and is different from the initial transmission segment S1 is retransmitted, the NDI value of all the code blocks CB2-1 to CB2-6 of the retransmission segment S2 is 0. It becomes. When the data D is taken out and the process proceeds to the next data transmission, the NDI value of the code block in the next data transmission becomes 1.

  Although the segment S is a part of the transport block TB, since the data to be transmitted is a part of the transport block TB, even if all the segments constituting the transport block TB are not complete, In some cases, data D can be extracted by decoding some code blocks.

  Then, the process of the base station which concerns on one Embodiment of this invention is demonstrated using FIG. The data to be decoded is the data D in FIG. 3, and the wireless communication terminal 103 transmits the segment S1 to the base station 101 as an initial transmission.

  First, when the communication unit 111 of the base station 101 receives a signal from the wireless communication terminal 103, the control unit 113 determines whether or not the received signal is a segment (step S101). Since the communication unit 111 receives the segment S1 as an initial transmission (Yes in step S101), the control unit 113 divides the segment S1 into a plurality of code blocks (step S102).

  Then, the control unit 113 performs loop processing S103 to S110 for each code block. The control unit 113 calculates communication quality at the time of code block reception for each code block, for example, SINR (Signal to Interference and Noise power Ratio) and RSSI (Received Signal Strength Indicator). (Step S104). Further, the control unit 113 can confirm the modulation class applied to each received code block (step S105).

  Subsequently, the control unit 113 can determine, for each code block, whether or not the code block is to be decoded (decoded) and subjected to error detection (step S106). This determination is for specifying in advance a code block that is highly likely to have a code error, that is, a code block that is likely to cause an error in the CRC check result even after being decoded. This determination is performed based on, for example, the modulation class and communication quality regarding each code block. The determination method will be described using the reception state table of FIG.

  The MCS (Modulation and Coding Scheme) in FIG. 5 means a modulation class defined by a combination of a modulation scheme and a coding rate. The modulation method is, for example, BPSK (Binary Phase Shift Keying) capable of transmitting 1 bit per symbol, QPSK (Quadrature Phase Shift Keying) capable of transmitting 2 bits per symbol, and 8PSK (8 Phase Shift Keying) capable of transmitting 3 bits per symbol. It is. The greater the number of bits that can be transmitted in one symbol (the higher the transmission rate, the higher the transmission rate), the better the communication environment required. The coding rate indicates the strength of error correction, that is, the ratio of data allocation. For example, a coding rate of 3/4 means that 3/4 of the signal is data and 1/4 is a redundant bit for error correction. Therefore, the higher the coding rate, the fewer redundant bits allocated for error correction, and thus a better communication environment is required. A larger MCS value means a modulation class in which a modulation scheme having a high transmission rate and a large coding rate are combined. That is, the larger the MCS value, the better the communication environment is required. Communication environments A to Z mean that A has the best communication environment and Z has the worst communication environment. The communication environment standard is determined by parameters indicating communication quality such as SINR and RSSI. For example, the communication environment A can be set as an environment where the SINR value is 25 dB or more and the RSSI value is −40 dB or more. In each of the communication environments A to Z, “OK” is written in the usable modulation class (stable communication is guaranteed), and “NG” is written in the unusable modulation class. That is, if the modulation class related to the code block confirmed by the control unit 113 in step S105 is determined to be “NG” from the communication quality acquired in step S104, there is a possibility that this code block has a code error. Can be judged high.

  Then, the control unit 113 decodes the code block determined to be subjected to error detection, and detects the presence or absence of a code error using the error detection code attached to the code block (step S107). That is, the control unit 113 performs CRC inspection. If there is no sign error, the CRC check result is “error”, and if there is a sign error, the CRC check result is “normal”. If the CRC check result of a certain code block is normal, the control unit 113 sets the code block as a turbo decoding target (step S108). Then, the control unit 113 stores the code block to be turbo decoded in the storage unit 112. Note that turbo decoding is performed on the entire plurality of code blocks set as turbo decoding targets in order to extract data D, and is different from decoding for each code block performed for step S107. Is.

  The control unit 113 identifies the code block determined not to be subjected to error detection in step S106 and the code block in which the CRC check result is error in step S107 by using an identifier, and sets the code block as a retransmission target (step S109). . Then, the control unit 113 stores the identifier of the code block to be retransmitted in the storage unit 112. Hereinafter, in this embodiment, it is assumed that the code block to be retransmitted is the code block CB1-2 in FIG. The identifier is 1-2, for example.

  When the control unit 113 performs the loop processing S103 to S110 for all the code blocks, the control unit 113 determines whether or not the received signal is an initial transmission segment (step S111). Since the received signal is the initial transmission segment S1 (Yes in step S111), the control unit 113 performs turbo decoding on the entire code block to be turbo decoded stored in the storage unit 112 (step S112). When the received signal is not the first transmission segment (No in step S111), that is, when the received signal is a segment or code block by retransmission, the control unit 113 stores the turbo decoding target stored in the storage unit 112 by the past signal reception. The code block and the code block set as the turbo decoding target in the current signal reception are synthesized (HARQ synthesis) (step S113). Then, the control unit 113 performs turbo decoding on the synthesized block (step S112).

  Then, the control unit 113 performs a CRC check on the entire decoded code block (step S114). If the CRC check result is normal (normal in step S114), it means that the data D has been extracted. Therefore, the control unit 113 receives an Ack signal indicating that the data D has been correctly received via the communication unit 111. Is transmitted to the wireless communication terminal 103 (step S115).

  If the CRC check result is an error in step S114, the control unit 113 transmits a Nack signal including a retransmission request to the wireless communication terminal 103 via the communication unit 111 (step S116). An example of a retransmission request is shown below. The control unit 113 can request the wireless communication terminal 103 to retransmit only the code block (CB1-2) to be retransmitted specified by the identifier (1-2) stored in the storage unit 112. In addition, the control unit 113 can request the wireless communication terminal 103 to retransmit a segment other than the segment S1 (for example, the segment S2).

  When there are a plurality of code blocks to be retransmitted in step S116, the control unit 113 determines that the number of retransmission requests until the data D is correctly decoded (until the CRC check result in step S114 becomes normal) is the code to be retransmitted. The retransmission priority order can be set to be smaller than the number of blocks. For example, the control unit 113 can set the highest retransmission priority for the code block set as the retransmission target by the initial transmission. When HARQ is HARQ based on IR (Incremental Redundancy) combining method, data D of transport block TB is included in the initial transmission segment, and the retransmission segment is error correction that is not normally transmitted by puncturing (decimation transmission of information). This is composed of a part of the redundant bit R. Therefore, it is considered that the possibility of obtaining a normal result in step S114 is increased by setting a high priority to the code block related to the first transmission segment including a lot of data itself. In addition, the control unit 113 can set a high retransmission priority order for a code block having good communication quality at the time of reception. It is considered that a code block having better communication quality is transmitted from the wireless communication terminal 103 with better communication quality even in retransmission. And the better the communication quality, the lower the possibility that a code error will occur. That is, it is considered that there is a high possibility that a normal result is obtained in step S114 due to retransmission of a code block having good communication quality at the time of reception.

  As described above, in this embodiment, the control unit 113 of the base station 101 detects the presence / absence of a code error (error) for each code block using the error detection code added to the code block, and detects a code error. The received code block is identified as a retransmission target, and the wireless communication terminal 103 is requested to retransmit only the code block to be retransmitted. That is, by using the identifier assigned to each code block, it is possible to request retransmission only of the code block having a code error. Since the code block having no code error is not retransmitted, it is possible to increase the efficiency of the retransmission request process.

  Further, in the present embodiment, when there are a plurality of code blocks to be retransmitted, the control unit 113 performs code so that the number of retransmission requests until the data D is correctly decoded is smaller than the number of code blocks to be retransmitted. The resending priority of the block can be determined. That is, it is possible to reduce the number of retransmission requests until the data D is correctly decoded by making a retransmission request from a code block with a large amount of data or from a code block that is highly likely to be received without error. By reducing the number of retransmission requests, it is possible to reduce the time and the amount of calculation required to make a retransmission request, and it is possible to further increase the efficiency of retransmission request processing.

  In the present embodiment, the control unit 113 determines whether or not to perform error detection for each code block based on the modulation class and communication quality related to each code block, and determines that error detection should not be performed. The coded code block can be set as a retransmission target. That is, a code block having a high possibility of having a code error from the modulation class and communication quality is determined as a retransmission target without being subjected to decoding and CRC check. By reducing the processing of decoding and CRC check, it is possible to reduce the time and the amount of calculation required for decoding and CRC check. Therefore, the efficiency of retransmission request processing can be further increased.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each functional unit, each step, etc. can be rearranged so that there is no logical contradiction, and a plurality of functional units, steps, etc. can be combined into one or divided. It is.

DESCRIPTION OF SYMBOLS 11 Communication network 101 Base station 103 Wireless communication terminal 111 Communication part 112 Storage part 113 Control part TB Transport block D Data R Redundant bit S1, S2 Segment CB1-1 to CB1-6, CB2-1 to CB2-6 Code block

Claims (4)

In a communication device for decoding data,
A plurality of code blocks for decoding data, a communication unit that receives a signal composed of a plurality of code blocks to which an error detection code and different identifiers are added; and
For each code block, the presence or absence of a code error is detected using an error detection code added to the code block, the code block in which the code error is detected is identified as a retransmission target, and only the code block to be retransmitted is detected. And a control unit that requests retransmission.   2. The communication device according to claim 1, wherein when there are a plurality of code blocks to be retransmitted, the control unit further determines the number of retransmission requests until data is correctly decoded from the number of code blocks to be retransmitted. A communication apparatus that determines a retransmission priority order of code blocks so as to be reduced.   3. The communication apparatus according to claim 1, wherein the control unit further determines whether error detection should be performed for each code block based on a modulation class and communication quality related to each code block, and detects an error. The communication apparatus is characterized in that a code block determined not to be performed is set as the retransmission target. In a communication method in a communication device for decoding data,
Receiving a signal composed of a plurality of code blocks for decoding data, the error detection code and a plurality of code blocks each having a different identifier added thereto;
For each code block, detecting the presence or absence of a code error using an error detection code added to the code block;
Identifying a code block in which a code error is detected as a retransmission target; and
Requesting retransmission of only the code block to be retransmitted.

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