KR20090043414A - Method of data transmission using harq - Google Patents

Abstract

Provided is a data transmission method using HARQ according to a redundancy version indicating a transmission start position of a data block in a circular buffer. The method includes transmitting the datablock by HARQ according to the first repeated version, and transmitting the datablock by HARQ according to the second repeated version. The second repeated version is determined by referring to the first repeated version. By efficiently selecting a repetitive version, data in a cyclic buffer can be transmitted as quickly as possible, thereby improving data transmission performance by HARQ.

Description

Data transmission method using ハ ＡＲＱ {Method of Data Transmission Using HARQ}

The present invention relates to wireless communication, and more particularly, to a data transmission method using HARQ.

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, the transmitter encodes the information bits using an extra error correcting code and transmits them. In the FEC scheme, the receiver demodulates a received signal and then decodes an error correcting code and restores transmission information. Through this decoding process, the error of the received signal generated by the channel is corrected. In the ARQ scheme, the transmitter corrects an error by retransmitting data, and there are a stop and wait (SAW), a go-back-N (GBN), and a selective repeat (SR) scheme.

The turbo code is a kind of error correcting code and is composed of a recursive systematic convolution encoder and an interleaver. There is a quadratic polynomial permutatiuon (QPP) as an interleaver to facilitate parallel decoding in actual implementation of turbo code. QPP interleaver is known to maintain good performance only for certain data block sizes. The performance of the turbo code is known to be good as the data block size increases. In the actual communication system, for the convenience of the actual implementation, the data block having a predetermined size or more is divided into several small data blocks to perform encoding.

The divided small data block is called a code block. Code blocks are generally the same size, but due to the size limitation of the QPP interleaver, one or more code blocks of several code blocks may have different sizes. Interleaving is performed to reduce the effects of burst errors that occur during transmission on a wireless channel after an error correction encoding process for a predetermined interleaver size or code block unit. The interleaved data is mapped to actual radio resources and transmitted. Since the amount of radio resources used during the actual transmission is constant, rate matching should be performed on the coded code blocks. In general, rate matching consists of puncturing or repetition. Rate matching may be performed in units of code blocks encoded such as WCDMA of 3GPP.

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. ARQ method can improve the transmission reliability, but it has the disadvantage of incurring time delay and inferior system efficiency in poor channel environment. In order to solve these shortcomings, a hybrid automatic repeat request (HARQ) method combining FEC and ARQ is proposed. According to the HARQ method, whether the data received by the physical layer includes an error that cannot be decoded, and when an error occurs, retransmission is requested to improve performance.

The HARQ retransmission scheme can be divided into synchronous and asynchronous. Synchronous HARQ retransmits data at a time point known to both the transmitter and the receiver, thereby reducing signaling required for data transmission such as a HARQ processor number. Asynchronous HARQ is a method of allocating resources at random times for retransmission, and requires overhead for data transmission.

HARQ may be classified into adaptive HARQ and non-adaptive HARQ according to transmission attributes such as resource allocation, modulation technique, transport block size, and the like. Adaptive HARQ is a method in which transmission attributes used for retransmission are changed in whole or in part compared to initial transmission according to a change in channel conditions. Non-adaptive HARQ is a method of continuously using the transmission attribute used for the initial transmission regardless of the change in channel conditions.

If an error is not detected in the received data, the receiver transmits an acknowledgment (ACK) signal as a response signal to inform the transmitter of the reception success. When an error is detected in the received data, the receiver transmits a negative-acknowledgement (NACK) signal as a response signal to inform the transmitter of the error detection. The transmitter may retransmit the data when the NACK signal is received.

A HARQ (Hybrid Auto Repeat Request) receiver basically attempts error correction on received data and determines whether to retransmit using an error detection code. The error detection code may use a cyclic redundancy check (CRC). When the CRC detection process detects an error in the received data, the receiver sends a NACK signal to the transmitter. The transmitter receiving the NACK signal transmits the appropriate retransmission data according to the HARQ mode (chase combined or IR).

The HARQ mode may be classified into chase combining and incremental redundancy according to a redundancy version (RV) indicating a characteristic of a data block to be retransmitted. Chase combining is a method of obtaining a signal-to-noise ratio (SNR) gain by combining with retransmitted data without discarding the data where an error is detected. IR is a method in which additional redundant information is incrementally transmitted to retransmitted data, thereby reducing the burden of retransmission and obtaining a coding gain.

When circular buffer rate matching is applied in the IR mode, the repetitive version (RV) mainly indicates a transmission start position of a data block transmitted or retransmitted in a circular buffer. That is, as many transmission start positions as the number of repeated versions must be defined in the circular buffer. The need for retransmission means that the channel condition is not good. If the coding rate, modulation technique, or resource allocation used for the initial transmission is used as the retransmission data, the changed channel state cannot be properly reflected when the retransmission data is transmitted. Therefore, when a coding rate or a modulation technique changes over time, a method of adaptively selecting a data transmission start position and retransmitting data to increase an error correction rate is required.

An object of the present invention is to provide a data transmission method using HARQ which increases error correction rate by efficiently selecting a repetitive version.

Another technical problem of the present invention is to provide a data transmission method using a predetermined repetitive version according to the transmission order in synchronous HARQ.

Provided is a data transmission method using HARQ according to a redundancy version indicating a transmission start position of a data block in a circular buffer. The method includes transmitting the datablock by HARQ according to the first repeated version, and transmitting the datablock by HARQ according to the second repeated version. The second repeated version is determined by referring to the first repeated version.

Even if there is no scheduling information, the system can be prevented from malfunctioning by defining a repetitive version in advance. By efficiently selecting a repetitive version, data in a cyclic buffer can be transmitted as quickly as possible, thereby improving data transmission performance by HARQ. Efficiency of uplink transmission using synchronous HARQ can be improved.

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.

1 is a block diagram illustrating a wireless communication system. Wireless communication systems are widely deployed to provide various communication services such as voice and packet data.

Referring to FIG. 1, a wireless communication system includes a user equipment (UE) 10 and a base station 20 (BS). The terminal 10 may be fixed or mobile and may be called by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), and a wireless device. The base station 20 generally refers to a fixed station that communicates with the terminal 10, and in other terms, such as a Node-B, a Base Transceiver System, or an Access Point. Can be called. One or more cells may exist in one base station 20.

Hereinafter, downlink (DL) means communication from the base station 20 to the terminal 10, and uplink (UL) means communication from the terminal 10 to the base station 20. In downlink, the transmitter may be part of the base station 20 and the receiver may be part of the terminal 10. In uplink, the transmitter may be part of the terminal 10 and the receiver may be part of the base station 20.

The wireless communication system may be an Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) based system. OFDM uses multiple orthogonal subcarriers. OFDM uses orthogonality between inverse fast fourier transforms (IFFTs) and fast fourier transforms (FFTs). At the transmitter, data is transmitted by performing an IFFT. The receiver performs FFT on the received signal to recover the original data. The transmitter uses an IFFT to combine multiple subcarriers, and the receiver uses a corresponding FFT to separate multiple subcarriers.

2 is a block diagram illustrating a channel encoding process. Consider a case where one code block is transmitted through a plurality of data streams by performing channel encoding, interleaving, and rate matching. A code block is a data block of a certain size for performing channel coding. Code blocks may have the same size, and a plurality of code blocks may have different sizes.

Referring to FIG. 2, the channel encoder 110 performs channel encoding on an input code block. The channel encoder 110 may be a turbo code, and the turbo code includes a recursive systematic convolution encoder and an interleaver. The turbo code generates structural bits and parity bits on a bit basis from an input code block. In this case, it is assumed that one structural block S and two parity blocks P1 and P2 are output assuming a 1/3 code rate. A structural block is a set of structural bits, and a parity block is a set of parity bits.

The interleaver 120 performs interleaving on the channel coded code block to reduce the influence of burst error that occurs when the interleaver 120 is transmitted over the wireless channel. The interleaver 120 may perform interleaving on the structural block S and each of the two parity blocks P1 and P2.

The rate matching unit 130 fits the channel coded code block according to the size of the radio resource. Rate matching may be performed in units of channel coded code blocks. Alternatively, the structural block S and the two parity blocks P1 and P2 may be separated.

3 is a block diagram showing a transmission start position according to a repetitive version (RV) in a system applying rate matching in a circular buffer. In this case, it is assumed that the coding rate of the turbo code is 1/3, and that a scheduling entity for data transmission is present in the receiver. That is, when a receiver transmits a transport format and resource indicator (TFRI), which is an indicator indicating a transmission format and a resource of data to be transmitted by the transmitter, to the transmitter, the transmitter transmits data according to the transmission format and resource indicator. Send it. Hereinafter, the repetitive version is called RV.

Referring to FIG. 3, a circular buffer consists of 36 logical data blocks horizontally. Of these, one-third part (12 data blocks) of the circular buffer is the systematic part, and the second two-third part (24 data blocks) represent the parity part. There are four RVs in the repetitive version from RV0 to RV3. The interval between RVs is the size of the total cyclic buffer divided by the number of RVs. If transmission of data using HARQ fails, the repetition version is determined, and the start position of the transmission or retransmission of the data block is changed according to the repetition version.

RV0 to RV3 represent repetitive versions indicating starting positions of different transmissions or retransmissions. When the repetitive version is the 0th repetitive version (hereinafter RV0), it is transmitted from the second data block in the circular buffer, and when the repetitive version is the first repetitive version (hereinafter RV1), it is transmitted from the 11th data block in the circular buffer. When the repetitive version is the second repetitive version (hereinafter RV2), it is transmitted from the 20th data block in the recursive buffer, and when the repetitive version is the third repetitive version (hereinafter RV3), the 29th data block in the recursive buffer Is sent from.

Here, the coding rate of the turbo code is 1/3, and the number of RVs is assumed to be four, but this is only an example. Of course, another coding rate, another number of RVs, or a starting position of another RV may be applied to the present invention.

Scheduling information for initial transmission (eg, scheduling grant) should be transmitted, but scheduling information for retransmission is not necessarily transmitted. As such, in case there is no scheduling information for retransmission, an RV to be used for retransmission needs to be newly defined.

Hereinafter, a method of adaptively selecting an RV and retransmitting data in a HARQ process is disclosed.

As an example, data using HARQ may be transmitted by fixing an RV to be used in initial transmission and retransmission of data in a circular buffer regardless of a coding rate. As shown in FIG. 3, when the transmission start position of the RV is fixed by dividing the entire cyclic buffer into equal number of data blocks, a good performance can be obtained by selecting the data based on the cyclic buffer as soon as possible.

When the total size of the circular buffer of FIG. 3 is 4, the portion occupied by the circular buffer according to the coding rate is shown in Table 1.

Coding Rate portion 2/3 ≤ coding rate ≤ 1 1 <portion <2 4 / 9≤ coding rate≤2 / 3 2 <portion <3 1 / 3≤coding rate≤4 / 9 3 <portion <4

Referring to Table 1, when the coding rate is 2/3 or more and 1 or less, four data transmissions may transmit all data blocks in the entire circular buffer. If the coding rate is 4/9 or more and 2/3 or less, two transmissions may transmit all data blocks in the entire circular buffer. On the other hand, if the coding rate is 1/3 or more and 4/9 or less, two data transmissions may transmit all data blocks in the entire circular buffer.

From the above-described results, a set of fixed RVs to be used in each transmission regardless of the coding rate may be selected as shown in Table 2. Here, it is assumed that RV0 is always the RV used for the initial transmission.

Transmission order One 2 3 4 First RV Combination RV0 RV2 RV1 RV3 Second RV Combination RV0 RV2 RV3 RV1

From the fifth transmission sequence, the RV set of Table 2 may be repeated again, or a new fixed RV combination may be defined to transmit data. In this case, even when scheduling information for retransmission is transmitted and the coding rate is changed, data may be transmitted according to the existing fixed RV set. Table 5 shows RV combinations (third to sixth RV combinations) for the fifth or more retransmissions.

Transmission order One 2 3 4 5 6 7 ... Third RV Combination RV0 RV2 RV1 RV3 RV0 RV2 RV1 ... Fourth RV Combination RV0 RV2 RV1 RV3 RV2 RV1 RV3 ... Fifth RV Combination RV0 RV2 RV3 RV1 RV0 RV2 RV3 ... 6th RV Combination RV0 RV2 RV3 RV1 RV2 RV3 RV1 ...

Referring to Table 3, the third RV combination is a combination of repeating the first RV combination of Table 1 twice, and the fourth combination repeats the first RV combination of Table 1 twice, but the tissue bit (second time) A combination that repeats except for RV0 having systematic bits). On the other hand, the fifth RV combination is a combination of repeating the second RV combination of Table 1 twice, and the sixth combination repeats the second RV combination of Table 1 twice, but the systematic bits are set twice. It is a combination that repeats except RV0.

By choosing RV based on transferring data stored in circular buffers as quickly as possible, you can get good performance. The fixed RV combination described above is merely an example, and the RV combination may be changed in advance according to the transmission order.

As another example, after the RV combination is determined in advance according to the coding rate, when scheduling information for retransmission is transmitted, data using HARQ may be transmitted by selecting the RV in consideration of the changed coding rate.

For example, it is assumed that an RV set shown in Table 4 is determined according to a coding rate (hereinafter referred to as CR) of an initial transmission.

Coding Rate RV combination according to the transmission order 2 / 3≤CR0 <1 RV0-> RV1-> RV2-> RV3 4 / 9≤CR1 <2/3 RV0-> RV2-> RV1-> RV3 1 / 3≤CR2 <4/9 RV0-> RV3-> RV2-> RV1

Referring to Table 4, the next RV is determined according to what the previous RV is. For example, if the previous RV is RV2 when transmitting data at the coding rate CR0, the next RV becomes RV3. Table 5 describes how RV is selected when the coding rate is changed by transmitting scheduling information for retransmission when the RV combination according to the coding rate is determined as shown in Table 4 below.

Transmission order One 2 3 4 Coding rate CR0 CR1 CR1 CR2 RV RV0 RV1 RV3 RV0

Referring to Table 5, since the coding rate is CR0 in the first transmission order, the first transmission is determined as RV0 according to Table 4. Since the coding rate is changed to CR1 in the second transmission order, the next RV is determined as RV1. This is to adjust the amount of data according to the changed coding rate by selecting the RV immediately after the most recent RV at the time when the coding rate is changed.

Since the coding rate is now maintained at CR1 in the third transmission order, the order of RVs is determined by the RV combination according to CR1. Since the previous RV is RV1, according to Table 4, the next RV is determined as RV3. In the last fourth transmission order, since the coding rate is changed to CR2, RV0, which is the next RV of RV3, is selected again. As such, the transmission efficiency can be improved by adaptively selecting the RV according to the previous RV and the coding rate.

In the case of uplink transmission, synchronous HARQ may be used to reduce signaling overhead. In this case, by using a predetermined RV, it is possible to reduce signaling and improve performance of HARQ.

Now, a signaling method for informing a selected RV is disclosed.

In general, in synchronous HARQ, a transmitting and receiving end knows a time point at which a data block is transmitted. Therefore, when the order of the RVs is clearly determined between the transmitting and receiving end, signaling for the RV is unnecessary. In consideration of this, a method of informing RV using existing control information without additional signaling is required.

As an example, the RV may be informed by a new data indicator (NDI). When transmitting a data block, signaling is needed to indicate whether a currently transmitting data block is a new data block, which is called a new data indicator (NDI). This method does not inform RV externally, but implicitly through a new data indicator. Therefore, overhead due to separate RV signaling can be reduced.

Table 6 is a table showing how to select the RV according to the new data indicator of 1 bit when using the third RV combination of Table 3. In this case, when the new data indicator (NDI) is 1, new data transmission is performed and 0 means retransmission. Of course, this correspondence could change.

Transmission order One 2 3 4 5 6 7 ... Third RV Combination NDI One 0 0 0 0 0 0 ... RV RV0 RV2 RV1 RV3 RV0 RV2 RV1 ...

Referring to Table 6, the new data indicator is 1 in the first transmission order, indicating that the data is new. Therefore, since it is the first transmission, data is transmitted to RV0. Since the new data indicator continues to zero, this indicates retransmission. Accordingly, data may be transmitted by applying the next RV according to what the previous RV is with reference to the third RV combination.

As another example, the RV may be informed by a retransmission sequence number (RSN). If synchronous HARQ, since both ends of the transmission and reception know the time point at which the data block is transmitted, the RV may be informed using a retransmission sequence number (RSN) instead of the new data indicator. At this time, the specific value of the retransmission sequence number promises to indicate the first transmission. For example, when the retransmission sequence number is 1 bit information, the retransmission sequence number is either 0 or 1, and 0 may be referred to as initial transmission and 1 may be referred to as retransmission.

If the retransmission sequence number is 2 bit information, the value '0' is called the first transmission, and the retransmission sequence number is transmitted in the order of 0-> 1-> 2-> 3, and the retransmission sequence after the fourth transmission. By keeping the number 3, you can indicate the order of retransmission. This signaling method is used in 3GPP HSUPA. The retransmission sequence number is sent from the transmitter to the receiver.

Table 7 is a table showing a method of selecting the RV according to the 1-bit retransmission sequence number when using the fourth and fifth RV combination of Table 3.

Transmission order One 2 3 4 5 6 7 ... Fourth RV Combination RSN 0 One One One One One One ... RV RV0 RV2 RV1 RV3 RV2 RV1 RV3 ... Fifth RV Combination RSN 0 One One One One One One ... RV RV0 RV2 RV1 RV3 RV0 RV2 RV1 ...

Referring to Table 7, if the retransmission sequence number is 0 in the first transmission sequence, this indicates that the transmission is the first transmission, and since the retransmission sequence number is 1 in the second to seventh transmission sequences, the transmission is continued. In this case, the RV may be determined according to the fourth and fifth RV combinations in Table 3.

As described above, the retransmission sequence number is not always transmitted, but only when there is scheduling information. Therefore, even if the retransmission sequence number is not transmitted in the middle, the receiver should use the retransmission sequence number in consideration of this.

Table 8 is a table showing a method of selecting the RV according to the two-bit retransmission sequence number when using the third and fourth RV combination of Table 3.

Transmission order One 2 3 4 5 6 7 ... Third RV Combination RSN 0 One 2 3 3 3 3 ... RV RV0 RV2 RV1 RV3 RV0 RV2 RV1 ... Fourth RV Combination RSN 0 One 2 3 One 2 3 ... RV RV0 RV2 RV1 RV3 RV2 RV1 RV3 ...

Referring to Table 8, when the third RV combination is used, when the retransmission sequence number is 3, the actually transmitted RV may be different according to the transmission sequence. This should be promised in advance in the transmission and reception period. As an example, a subframe number currently being transmitted may be used. When the fourth RV combination is used, the retransmission sequence number and the transmitted RV have a 1: 1 matching relationship. Therefore, the RV can be known from the retransmission sequence number included in the retransmission scheduling information. That is, the method used to display the retransmission sequence number as 2 bits indicates that the retransmission sequence number is 0, 1, 2, 3, 3, 3, 3, 3. Or 0, 1, 2, 3, 1, 2, 3... As shown in the figure, RV corresponding to each retransmission sequence number is allocated.

However, since retransmission scheduling information may not be transmitted, when there is no retransmission sequence number, an RV to be used for retransmission may be differently selected according to the RV used in the previous transmission. Table 9 shows a method of selecting an RV when the retransmission scheduling information is not transmitted when the third and fourth RV combinations of Table 3 are not transmitted.

Third RV Combination Fourth RV Combination i-1th RV i th RV i th RV i th RV RV0 RV2 RV0 (first transfer only) RV2 (first transfer only) RV1 RV3 RV1 RV3 RV2 RV1 RV2 RV1 RV3 RV0 RV3 RV2

Referring to Table 9, when the i-1 th RV is RV0 in the third RV combination, and there is no retransmission sequence number in the i th transmission sequence, the i th RV refers to the previous RV0. RV2, which is the next RV of RV0, is selected according to the order of the third RV combination. On the other hand, in the fourth RV combination, when the i-1 th RV is RV3, and the retransmission scheduling information is not transmitted in the i th transmission sequence, and there is no retransmission sequence number, the i th RV refers to the previous RV3 and the fourth RV combination. In order of RV3, RV2 is selected as the next RV.

Next, a signaling scheme for informing RV externally is disclosed. Table 10 shows a signaling method for notifying the RV externally according to the fourth RV combination of Table 3.

Transmission order One 2 3 4 5 6 7 Fourth RV Combination RV value 0 2 One 3 2 One 3 RV RV0 RV2 RV1 RV3 RV2 RV1 RV3

All of the above functions may be performed by a processor such as a microprocessor, a controller, a microcontroller, an application specific integrated circuit (ASIC), or the like according to software or program code coded to perform the function. The design, development and implementation of the code will be apparent to those skilled in the art based on the description of the present invention.

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. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

1 is a block diagram illustrating a wireless communication system.

2 is a block diagram illustrating a channel encoding process.

3 is a block diagram showing a transmission start position according to a repetitive version (RV) in a system applying rate matching in a circular buffer.

Claims (12)

In a data transmission method using HARQ according to a redundancy version indicating the transmission start position of a data block in a circular buffer, Transmitting the data block by HARQ according to the first repetitive version; Transmitting the data block by HARQ according to the second repetitive version, And the second repetitive version is determined by referring to the first repetitive version. The method of claim 1, The repeating version is four, each of the repeating version is a data transmission method using HARQ to indicate the four different transmission start position in the circular buffer. The method of claim 2, The four transmission start positions are spaced at equal intervals in the circular buffer, the data transmission method using HARQ. The method of claim 2, A transmission start position of another repetitive version exists between the transmission start positions of the first and second repetitive versions. The method of claim 2, The four iterative versions of the data transmission method using HARQ, the order is predetermined. The method of claim 1, The second repeated version is determined by further referring to a coding rate as well as the first repeated version, data transmission method using HARQ. The method of claim 6, The coding rate is a data transmission method using HARQ, the coding rate according to the turbo code. The method of claim 6, If the coding rate of the data according to the first repetition version and the coding rate of the data according to the second repetition version are different, the second repetition version is the transmission start immediately after the transmission start position indicated by the first repetition version. A data transmission method using HARQ, which is a repetitive version indicating a location. The method of claim 8, And transmitting the data block by HARQ according to the second repetitive version after transmitting the data block by the HARQ according to the second repetitive version. Data transfer method. The method of claim 1, The method of claim 1, further comprising transmitting the first and second repetitive versions. The method of claim 1, Further comprising the step of transmitting a new data indicator (New Data Indicator), The second repeated version is a data transmission method using HARQ determined by referring to the first repeated version and the new data indicator. The method of claim 1, The method may further include transmitting a retransmission sequence number. And the second repetitive version is determined by referring to the first repetitive version and the retransmission sequence number.

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