KR20080010640A - Method for combining data block and method for hybrid automatic repeat request - Google Patents

Abstract

A method for combining a data block and a method for hybrid automatic repeat request are provided to reduce the time and power consumption for data processing without an unnecessary error correcting process by selectively combining only the reliable data in case of retransmission. A method for combining a data block includes the steps of: receiving a first data block; requesting retransmission when an error is detected at the first data block; receiving a second data block according to the retransmission; and combining the second data block with the first data block when a total reliability is higher than a total threshold(S153), and combining the first data block with the second data block when the total reliability is lower than the total threshold and a reliability of each block is higher than a block threshold(S154).

Description

Method for combining data block and method for hybrid automatic repeat request}

1 is a block diagram illustrating a communication system according to an embodiment of the present invention.

2 is a flowchart illustrating a complex retransmission method using the communication system of FIG. 1.

3 is a flowchart illustrating an operation of step S150 of FIG. 2.

4 is a graph illustrating a frame error rate (FER) according to the reliability of the second data block.

5 is a flowchart illustrating a complex retransmission method according to another embodiment of the present invention.

6 shows an example of a feedback NACK signal.

7 is a flowchart illustrating a data block combining method according to another embodiment of the present invention.

** Explanation of symbols in main part of drawing **

100: transmitter

200: receiver

220: data block combiner

250: retransmission decision unit

The present invention relates to a data block combining method and a complex retransmission method, and more particularly, to a data block combining method and a complex retransmission method for combining retransmitted data.

Recently, in a wireless environment such as a high-speed multimedia wireless communication service, it is essential to guarantee high quality data and differential quality of service (QoS).

Error compensation techniques for securing communication reliability include a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. In the FEC scheme, an error at the receiving end is corrected by adding an extra error correction code to the information bits. In the ARQ scheme, errors are corrected through data retransmission, and there are a stop and wait (SAW), a go-back-N (GBN), and a selective repeat (SR) scheme. The FEC method has a low time delay and does not require information to be transmitted and received separately between the transmitter and the receiver, but has a disadvantage in that the system efficiency is poor in a good channel environment. The ARQ method has a time delay and a poor system efficiency in a poor channel environment. To solve these shortcomings, a hybrid automatic repeat request (HARQ) scheme combining FEC and ARQ is proposed. The HARQ scheme improves performance by requiring retransmission when the received data contains an error that cannot be decoded. As an example of the HARQ method, S. Lin, D.J. Costello, M.J. Miller, Automatic repeat request error control schemes, IEEE Communications Magazine, Vol. 22, no. 12, pp. 5-17, Dec. See 1984.

HARQ can be classified into Type I, Type II, and Type III. Type I discards the data from which an error was detected and requires retransmission of new data. Type II combines retransmitted data with previous data without discarding the data from which an error was detected. Retransmitted data and previous data may have different code rates. Type III differs from Type II in that the retransmitted data is a self-decodable code. That is, the retransmitted data can be decoded without combining with previous data.

In addition, the HARQ scheme may be classified into chase combining and incremental redundancy (IR). Chase combining is a modified method of Type I, which combines the retransmitted data without discarding the data in which an error is detected. IR refers to the Type II or Type III scheme. This is because in Type II or Type III, additional redundant information is incrementally transmitted to retransmitted data. Distinguishing between Type II and Type III, Type II is also known as full IR and Type III is partial IR.

In HARQ, a combination of previous data and retransmitted data is generally required. An example of the agreement is described by D. Chase under the heading "Code Combining: A maximum-likelihood decoding approach for combining an arbitrary number of noisy packets." on Commun., Vol. 33, pp. 593-607, May, 1985. According to the chase, the weight is given to the retransmitted data according to the channel estimation result and reflected in the combining.

If an error is detected in the transmitted data, request retransmission and combine the retransmitted data with the previous data. Previous data received in poor channel conditions continues to adversely affect the combined result despite continued retransmission. Combined results may be deteriorated despite retransmission. This leads to wasted buffers and reduced data throughput. Therefore, there is a need for a method of determining whether to combine according to the channel environment.

An object of the present invention is to provide a data block combining method and a complex retransmission method for efficiently combining data according to a channel environment.

Another object of the present invention is to provide a data block combining method and a complex retransmission method for preventing data deterioration due to retransmission.

According to an aspect of the present invention, a data block combining method is provided. The data block combining method receives a first data block and requests retransmission when an error is detected in the first data block. The second data block is received according to the retransmission. Subsequently, when the overall reliability is greater than the overall threshold, the second data block and the first data block are combined. When the reliability is smaller than the overall threshold, the reliability of each data block is greater than the block threshold. Join the first data block and the second data block.

According to another aspect of the present invention, a complex retransmission method is provided. The complex retransmission method retransmits data blocks one or more times. The data blocks are combined when the overall reliability is greater than the overall threshold. When the reliability of each data block is greater than the block threshold, the corresponding data blocks are combined when the overall reliability is less than the overall threshold. If an error is detected for the combined data block, request retransmission.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like numbers refer to like elements throughout.

The following techniques can be used in various communication systems. Communication systems are widely deployed to provide various communication services such as voice, packet data, and the like. This technique can be used for downlink or uplink. The downlink means communication from a base station (BS) to a mobile station (MS), and the uplink means communication from a terminal to a base station. A base station generally refers to a fixed station that communicates with a terminal and may be referred to as another terminology, such as a base transceiver system (BTS), an access point, or the like. The terminal may be fixed or mobile and may be called in other terms such as user equipment (UE), user terminal (UT), wireless device (wireless device), and the like.

1 is a block diagram illustrating a communication system according to an embodiment of the present invention. The communication system is a typical wireless communication system implemented in accordance with the present invention.

Referring to FIG. 1, a communication system includes a transmitter 100 and a receiver 200. Here, the transmitter 100 refers to one side receiving the retransmission request and sending retransmission data, and the receiver 200 refers to the other side which detects an error with respect to the received data and requests retransmission, and must be limited to the data transmission side or the data reception side. It is not. The transmitter 100 may be part of a base station. The receiver 200 may be part of a terminal. Alternatively, the transmitter 100 may be part of a terminal and the receiver 200 may be part of a base station. The base station may include a plurality of receivers and a plurality of transmitters. The terminal may include a plurality of receivers and a plurality of transmitters.

The transmitter 100 includes an error detection coder 110, an encoder 120, a data processor 130, a modulator 140, a demodulator 150, and a retransmission controller 160.

The error detection coding unit 110 receives information bits and adds error detection bits to the information bits. The information bits can include text, voice, video or other data. The error detection bits may be cyclic redundancy check (CRC) bits.

The encoding unit 120 encodes the information bits through an error correction code. The error correction code may be a turbo code. The turbo code is a structural code that includes information bits as structural bits. In the case of turbo codes with a code rate of 1/3, two parity bits are allocated to one structural bit. However, the technical concept of the present invention may be applied to an LDPC (low density parity check code) or other convolutional codes as well as the error correction code.

The data processor 130 forms a data block which is an amount to transmit the encoded information bits at one time. The data block may be a packet. That is, the data processor 130 punctures or repeats the information bits to fit the size of a physical channel.

In the case of perforation, the extra bits are deleted to form the first data block in order to reduce the length of the block in one block of information bits. For example, if two parity codes are assigned to two information bits, the code rate is 2/5. In this case, the error correction capability may be degraded, but the transmission rate is improved. The erased bits may be used to form a second data block, a third data block, ..., an n-th data block required for retransmission. n is the maximum number of times a retransmission is made.

Hereinafter, the first data block refers to a data block transmitted first in a block of one information bits, and the nth data block refers to a data block in which an error is detected and retransmitted for the nth time. There is no restriction on the method of forming the n-th data block, and each data block may be formed with different code rates, or the same data block may be repeatedly formed.

The modulator 140 modulates the data blocks output from the data processor 130. As modulation, quadrature phase shift keying (QPSK), 16 quadrature amplitude modulation (QAM), and 64 QAM may be used. The data block modulated by the modulator 140 is transmitted to the receiver 200 through a channel. The demodulator 150 demodulates the received signals ACK and NACK transmitted from the receiver 200 to be described later. The retransmission control unit 160 controls retransmission of the data blocks according to the received signal.

The receiver 200 includes a demodulator 210, a data block combiner 220, a decoder 230, an error detector 240, a retransmission determiner 250, and a modulator 260.

The demodulator 210 demodulates the received signal. As described below, the data block combiner 220 combines the data block to be retransmitted with the existing data block. The decoder 230 decodes the combined data block, and the error detector 240 checks whether an error is detected in the decoded data block. The retransmission determining unit 250 determines an ACK signal or a NACK signal according to whether an error is detected. If no error is detected in the data block, an ACK signal is generated, and if an error is detected, a NACK signal is generated. The ACK / NACK signal is modulated by the modulator 260 and transmitted to the transmitter 100.

2 is a flowchart illustrating a complex retransmission method using the communication system of FIG. 1.

Referring to FIG. 2, the transmitter 100 first transmits a first data block (S110). The receiver 200 decodes the received first data block and determines whether there is an error (S120). If no error is detected, an ACK signal is transmitted to the transmitter 100, and the transmission of the data block for the next information bits is awaited. However, it is assumed here that an error is detected and the NACK signal is transmitted (S130). When the NACK signal is received, the transmitter 100 transmits a second data block (S140). The receiver 200 selectively combines the received second data block with the existing first data block to detect whether an error occurs (S150).

3 is a flowchart illustrating an operation of step S150 of FIG. 2.

Referring to FIG. 3, first, total reliability (TR) is calculated to perform data block combining (S151). Overall reliability refers to the reliability of the entirety of the received data blocks. The overall reliability TR may be an average of the sum of the reliability BRs of each data block. The reliability of a data block may be viewed as a channel error rate for the data block.

Reliability can be obtained from the signal-to-noise ratio (SNR) of the data block. In this case, the overall reliability TR may be an average of the sum of the reliability BR of each data block, that is, the average of the sum of the SNRs of each data block.

As another example, the reliability may be obtained by calculating an error of a synchronization sequence inserted into each data block. In order to calculate this, sync bits may be further added to the data block as well as information bits and error detection bits.

 As another example, the reliability is estimated by a data block from a block that combines previously received data blocks (here, the first data block), so that the currently received data block (second data block) and bit-by-bit Can be obtained from the difference.

The total reliability TR and the total threshold TT are compared (S152), and if the overall reliability TR is greater than the total threshold TT (TR> TT), all received data blocks are combined. (S153). That is, the first data block and the second data block are combined. If the overall reliability (TR) is above a certain level, the channel environment is considered to be relatively good to combine the entire received data blocks. This is because the quality of service (QoS) may be regarded as satisfying a certain level.

 The overall threshold value TT may be a value preset in the receiver 200. In this case, the overall threshold value TT may be stored in advance in the buffer of the receiver 200. The global threshold TT can be set according to the desired QoS of the system. If the overall threshold value TT is small, the rate at which all data blocks are combined increases, so that data throughput may be increased, but the combined data blocks may be worsened according to the channel environment.

As another example, the receiver 200 may change the set overall threshold value TT according to the channel state. The receiver 200 may change the overall threshold TT through the previous overall reliability TR.

As another example, the overall threshold TT may be transmitted through the transmitter 100. That is, the transmitter 100 may receive the channel environment from the plurality of receivers 200 to determine the overall threshold value TT and transmit the obtained overall threshold value TT to the receiver 200.

If the overall reliability TR is less than the total threshold TT (TR <= TT), the block threshold is calculated (S154).

The block threshold BT may be obtained as in Equation 1 below.

Here, BTn is a block threshold value of the n-th data block, An is the average of the sum of the reliability of the remaining data blocks except the n-th data block, C is a preset value. C can be found statistically according to the FEC method. C may be a value preset in the receiver 200 or may be a value received from the transmitter 100.

4 is a graph illustrating a frame error rate (FER) according to the reliability of the second data block. The SNR (B1) of the first data block and the SNR (B3) of the third data block are fixed, and the FER according to the change of the SNR (horizontal axis, B2) of the second data block is shown.

Referring to FIG. 4, as the SNR (B2) of the second data block is lowered, the FER in the case of including the SNR (B2) of the second data block (B1 + B2 + B3) is sharply lowered, whereas the second data is reduced. If the SNR (B2) of the block is not included (B1 + B3), the FER is not very different. That is, it is better to combine the second data block except the second data block on the left side based on the point X where the two lines intersect, and the performance is very different even if the second data block is included on the right side based on the intersection point X. No influence The intersection point X becomes a block threshold BT2 of a second type of data block.

Accordingly, the block threshold value BT2 is obtained based on the average of the sum of the reliability of the remaining data blocks except for the current data block, as shown in Equation 1, to prevent the combined result from worsening.

However, the technique for obtaining the block threshold BT is not limited to Equation 1, and may be modified with various other techniques to selectively combine the retransmitted data blocks. As another example, the block threshold BT may be a value preset in the receiver 200. The block threshold BT may be stored in a buffer of the receiver 200 in advance. As another example, the receiver 200 may change the block threshold BT according to the channel state. The receiver 200 may change the block threshold BT through the previous partial reliability BR. As another example, the block threshold BT may be transmitted through the transmitter 100. That is, the transmitter 100 may receive a feedback channel environment from a plurality of receivers 200 to determine a block threshold BT, and transmit the obtained block threshold BT to the receiver 200.

Referring back to FIG. 3, the data blocks are selectively combined according to the reliability BR of the data blocks (S155). If the reliability BR of the data block is greater than the block thrshold BT (BR> BT), the corresponding data block is combined (S156). If the reliability BR of the data block is smaller than the block threshold BT (BR <= BT), the corresponding data block is not combined. That is, when the reliability BR1 of the second data block is smaller than the block threshold BT1 of the second data block, the second data block is not combined with the first data block. If the reliability BR2 of the second data block is greater than the block threshold BT2 of the second data block, the second data block is combined with the first data block.

Decoding is performed on the combined data block (S157). An error is detected through the decoded data (S158). If an error is not detected, an ACK is determined as a transmission signal (S159-1), and if an error is detected, a NACK is determined as a transmission signal (S159-2). .

In the present invention, a low reliability data block is not combined with an existing data block even if retransmitted. By selectively combining only reliable data blocks, unnecessary error correction processing is not performed, thereby reducing time and power consumption due to data processing. Data degradation due to unnecessary coupling can be prevented.

Referring back to FIG. 2, if an error is not detected, an ACK signal is transmitted to the transmitter 100 and the data block is awaited for transmission of the next information bits. However, it is assumed here that an error is detected and a NACK signal is transmitted (S160). When the NACK signal is received, the transmitter 100 transmits a third data block (S170).

The receiver 200 selectively combines the received third data block with existing first and second data blocks to detect whether an error occurs (S180). That is, the overall reliability (TR) of the received first to third data blocks is obtained. The total reliability TR is compared with the total threshold TT, and when the total reliability TR is greater than the total threshold TT, all received data blocks are combined (S153). That is, the first data block, the second data block, and the third data block are combined. If the overall reliability TR is less than the overall threshold TT, the data blocks are selectively combined according to the partial reliability BR of each data block. In detail, if the reliability BR2 of the second data block is smaller than the block threshold BT2 of the second data block, it is not combined with the first data block. If the reliability BR2 of the second data block is greater than the block threshold BT2 of the second data block, the second data block is combined with the first data block. Subsequently, when the reliability BR3 of the third data block is smaller than the block threshold BT3 of the third data block, the third data block is not combined with the first data block. If the reliability BR3 of the third data block is greater than the block threshold BT3 of the third data block, the third data block is combined with the first data block. After the combining is completed, decoding is performed on the combined data blocks. An error is detected through the decoded data to determine an ACK as a transmission signal when no error is detected, and a NACK as a transmission signal when an error is detected.

The ACK signal or the NACK signal is transmitted to the transmitter 100 according to whether an error is detected (S190).

When the ACK signal is sent, retransmission for the corresponding block of information bits is terminated. The retransmission may be made up to the nth preset time. If the error is still detected by the n-th retransmission, the retransmission process can be reset and transmission of the next block of information bits can be started. Or transmission may be done again from the beginning for the block of current information bits.

5 is a flowchart illustrating a complex retransmission method according to another embodiment of the present invention.

Referring to FIG. 5, the transmitter 100 transmits a first data block (S210). The receiver 200 decodes the first data block and determines whether an error occurs (S220). If no error is detected, an ACK signal is transmitted to the transmitter 100, and the transmission of the data block for the next information bits is awaited. However, it is assumed here that an error is detected and the first NACK signal is transmitted (S230). When the first NACK signal is received, the transmitter 100 transmits a second data block (S240). The receiver 200 selectively combines the received second data block with the existing first data block to detect whether an error occurs (S250).

If no error is detected, an ACK signal is transmitted to the transmitter 100, and the data block is awaited for transmission of the next information bits. However, it is assumed here that an error is detected and the second NACK signal is transmitted (S260). When the second NACK signal is received, the transmitter 100 transmits a third data block (S270). The receiver 200 selectively combines the received third data block with existing first and second data blocks to detect whether an error occurs (S280). The ACK signal or the third NACK signal is transmitted to the transmitter 100 according to whether an error is detected (S290).

The above-described embodiment of FIG. 5 differs from the embodiment of FIG. 2 in that a NACK signal indicating that an error is detected is distinguished and transmitted into a first NACK signal, a second NACK signal, and a third NACK signal. That is, in the embodiment of FIG. 2, the NACK signal may always transmit a constant signal. However, in the embodiment of FIG. 5, additional information may be carried through different NACK signals.

Each NACK signal may take a different level. The level of the NACK signal can be changed by varying the phase of the signal. Depending on the level of the NACK signal, the number of retransmissions or whether data blocks are combined may be transmitted to the transmitter 100. For example, the phase of the second NACK signal may be different from that of the first NACK signal, so that one retransmission is performed to the transmitter 100. The phase of the third NACK signal may be different from that of the first and second NACK signals, so that two retransmissions may be transmitted to the transmitter 100. The transmitter 100 may determine the number of retransmissions according to the received NACK signal level. In addition, the transmitter 100 may transmit a new data block again from the beginning according to the received NACK signal level, or may transmit a subsequent data block by increasing transmission power.

As another example, each NACK signal may include additional information. 6 shows an example of a feedback NACK signal.

Referring to FIG. 6, the NACK signal includes additional bits for including retransmission information as well as bits for NACK. The retransmission information may include the number of retransmissions or whether the data blocks are combined. For example, the first NACK signal may be transmitted to the transmitter 100 by adding a bit for one retransmission together with the NACK signal. In addition to the NACK signal, the second NACK signal may be transmitted to the transmitter 100 by adding a bit for two retransmissions. The transmitter 100 may determine the number of retransmissions according to the additional information of the received NACK signal. In addition, the transmitter 100 may transmit a new data block again from the beginning according to the additional information of the received NACK signal, or may transmit a subsequent data block by increasing the transmission power.

7 is a flowchart illustrating a data block combining method according to another embodiment of the present invention.

Referring to FIG. 7, first, a total reliability (TR) is calculated (S310). Comparing the overall reliability (TR) with the total threshold (TT) (S311), if the overall reliability (TR) is greater than the overall threshold (TT) (TR> TT), all received data blocks are combined (S3122). .

If the overall reliability TR is less than the overall threshold TT (TR <= TT), the block threshold is calculated (S313). The data blocks are selectively combined according to the reliability BR of the data blocks (S314). If the reliability BR of the data block is greater than the block threshold BT (BR> BT), the corresponding data block is combined (S315). If the reliability BR of the data block is smaller than the block threshold BT (BR <= BT), the corresponding data block is discarded.

Decoding is performed on the combined data block (S317). An error is detected through the decoded data (S318). If an error is not detected, an ACK is determined as a transmission signal (S320). If an error is detected, a NACK is determined as a transmission signal (S319).

The above-described embodiment of FIG. 7 differs from the embodiment of FIG. 3 in that the data block is discarded without being stored in the buffer when the reliability of the data block is smaller than the block threshold. In other words, data blocks with low reliability are discarded without being stored in the buffer, so that subsequent combining is not reflected. Discarded data blocks are not reflected in the overall reliability in subsequent retransmission steps. In this case, the overall reliability is high, which increases the probability that the data blocks are combined at once.

That is, by selectively discarding a data block having low reliability, only a reliable data block may be selectively combined even if there is a retransmission later. Therefore, unnecessary error correction processing is not performed, thereby reducing time and power consumption due to data processing. In addition, data degradation due to unnecessary coupling can be prevented. The discarding of data blocks can save buffer capacity at the receiver.

The aforementioned data block combining technique and complex retransmission technique may be implemented by various means. For example, the data block combiner may be implemented in hardware, software, or a combination thereof. In hardware implementation, an application specific integrated circuit (ASIC), a digital signal processing (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, and a microprocessor are designed to perform the above functions. , Other electronic units, or a combination thereof. In a software implementation, the data block combiner may be implemented as a module that performs the above-described function. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand.

As described above, according to the present invention, by selectively combining only reliable data during retransmission, unnecessary error correction processing is not performed, thereby reducing time and power consumption according to data processing. In addition, data degradation due to unnecessary coupling can be prevented.

Claims (12)

Receiving a first data block; Requesting retransmission when an error is detected in the first data block; Receiving a second data block according to the retransmission; And Combine the second data block with the first data block when the overall reliability is greater than the overall threshold; and when the reliability of each data block is greater than the block threshold when the overall reliability is less than the overall threshold Combining the data block with the second data block. The method of claim 1, And said overall reliability is an average of the sum of the reliability of each data block. The method of claim 1, And the reliability is obtained by a signal-to-noise ratio (SNR). The method of claim 1, And the reliability is calculated by calculating an error of a synchronization sequence inserted into each data block. The method of claim 1, And the reliability is obtained by estimating a data block from the first data block and comparing the second data block with a bit-by-bit. In claim 1, And discarding the corresponding data block when the reliability of each data block is less than the block threshold. The method of claim 1, The block threshold is obtained by the following equation.

Here, BTn is a block threshold value of the n-th data block, An is the average of the sum of the reliability of the remaining data blocks except the n-th data block, C is a preset value. In the complex retransmission method, Retransmitting the data blocks one or more times; Combining the data blocks when the overall reliability is greater than the overall threshold, and combining the corresponding data blocks when the reliability of each data block is greater than the block threshold when the overall reliability is less than the overall threshold; And Requesting retransmission when an error for the combined data block is detected. The method of claim 8, And discarding the corresponding data block when the reliability of each data block is less than the block threshold. The method of claim 8, The request for retransmission is a complex retransmission method of transmitting a NACK signal. The method of claim 10, The NACK signal is a retransmission method of the level is changed depending on the number of retransmissions. The method of claim 10, The NACK signal includes a retransmission information bit.

Images