KR20090080443A - Method for data coding and transmitter in wireless communication system - Google Patents

Abstract

A data coding method of a wireless telecommunications system and a transmitter are provided to reduce a bit number of unnecessary padding bits and to improve data transmission efficiency by producing previously the bit number of the padding bits according to the number of information bits. A processor of a transmitter includes a padded bit calculation unit(310), a padding unit(320), a CRC encoding unit(330), a fragmentation unit(340), and an encoding unit(350). The padded bit calculation unit produces a padded bit from an inputted information bit. The padded bit calculation unit produces a size of the padded bit from a size of an information bit in order to minimize the size of the padded bit. The padding unit pads the produced padded bit to the information bit. The CRC encoding unit outputs a CRC added packet by adding a CRC to a padded packet. The fragmentation unit fragments divides the CRC added packet by a maximum bit number when the CRC added packet is larger than the maximum bit number. The encoding unit performs a CTC(Convolutional Turbo Code) encoding process for an encoder packet and outputs a transmission packet.

Description

Method for data coding and transmitter in wireless communication system

The present invention relates to wireless communications, and more particularly, to a data coding method and a transmitter.

An error compensation technique for securing communication reliability in a wireless communication system includes 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 ARQ, errors are corrected through data retransmission. 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. 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.

As a channel coding process for using the HARQ scheme, padding, CRC encoding, fragmentation, and encoding are performed on information bits. In the encoding process, an turbo correction code may be used as an FEC scheme. The number of bits input to the encoder is determined according to the size of the internal interleaver of the turbo code. Padding is a process of padding the padded bits to adjust the size of the data to the size of the internal interleaver before input to the encoder. CRC encoding is a process of adding a cyclic redundancy check (CRC), which is an error detection code, to determine whether to retransmit by checking an error. Partitioning is a process of encoding data blocks by dividing them into data blocks of appropriate size when the size of data to which padding bits and CRC are added exceeds the maximum number of bits that an encoder can process. In the padding process, the padding bits are padded so that the size of the data before being divided is a multiple of the size of the internal interleaver of the turbo code. Therefore, data is sequentially divided and sent to the encoder during the partitioning process. The encoder performs encoding using turbo codes for FEC.

The number of bits input to the encoder may be represented by N _EP = K + p + c when there is no partition and N _EP = (K + p + c) / n when there is a partition. In this case, N _EP is the number of bits input to the encoder, K is the number of bits of information bits, p is the number of bits of padding bits, c is the number of bits of the CRC, n is the number of divided data blocks.

Set the N _EP set for the number of bits that can be input to the encoder in advance, and if the number of bits of information bits does not correspond to the N _EP set, pad the appropriate padding bits to match the number of bits that can be input to the encoder. Can be. In this case, when the N _EP set has a large number of elements, the average number of bits of the padding bit may be reduced. However, since the internal interleaver of the corresponding turbo code is required, the system may be more complicated. On the other hand, if the N _EP set has fewer elements, the complexity of the system is reduced, but the average number of bits of padding bits is increased. The padding bit is necessary only in the channel coding process and is unnecessary data from the whole system viewpoint. The more padding bits, the less throughput the system has. In particular, the padding bits are padded so that the data exceeds the maximum number of bits that can be input to the encoder so as to be a multiple of the maximum number of bits, so that the larger number of bits of information bits is padded. For example, assuming that the maximum number of bits that can be input to the encoder is 4800 bits, 4799 bits are padded if the number of bits of information bits is 4785 bits and the number of bits of CRC is 16 bits. The number of bits of padding bits may be larger than the number of bits of information bits. This problem may occur more seriously in systems where the number of elements in the N _EP set is small and it is difficult to variably operate the interleaver size of the turbo code.

There is a need for a method of improving coding efficiency by reducing unnecessary padding bits.

An object of the present invention is to provide a method for improving coding efficiency by minimizing padding bits.

A data coding method in a wireless communication system according to an aspect of the present invention includes the steps of obtaining the number of bits p of padding bits to be padded with respect to information bits, and converting the padding bits by the number p of bits of the padding bits. Padding to, dividing the padded information bits into n data blocks and encoding the n data blocks (p, n > 0), wherein the bits of the padding bits The number p is obtained according to the number n of the data blocks and the number of bits of the data block.

In a wireless communication system according to another aspect of the present invention, a data coding method includes determining whether to divide information bits, and when the information bits are divided, the information bits in consideration of the number of bits of the information bits and the number of bits of the CRC. Determining the number of bits of the data block to be input to the encoder in consideration of the number of bits of the information bits, the number of bits of the CRC and the number of information bits to be divided; Padding the padding bits in consideration of the number of bits.

In a wireless communication system according to another aspect of the present invention, a transmitter includes a processor for generating a transmission packet by processing information bits and a transmission circuit for transmitting the transmission packet, wherein the processor defines a number of divisions of the information bits. The padding bit size is calculated according to the defined number.

By calculating the number of bits of padding bits in advance according to the number of bits of information bits, it is possible to reduce the number of bits of unnecessary padding bits, and to transmit the data by lowering the code rate by the number of bits of the reduced padding bits, or by using more radio resources. By transmitting the data transmission efficiency can be improved.

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 showing the structure of a transmitter and a receiver.

Referring to FIG. 2, the transmitter 100 includes a processor 110 and a Tx circuit 120. The processor 110 performs a data processing process on input information bits according to a data processing method of a wireless communication system. Information bits may include text, audio, video or other data. The processor 110 may encode the information bits according to a predetermined coding scheme to form coded data. As a coding scheme, an error correction code for adding an extra code for error correction may be used. The error correction code may be a turbo code. The error correction code is not limited to a turbo code, and a low density parity check code (LDPC) or other convolutional code may be used. The processor 110 outputs a modulation symbol representing the position of the encoded data according to amplitude and phase constellation. The transmission circuit 120 is connected to the processor 110 and transmits a radio signal through the antenna 130.

The receiver 200 includes a reception circuit 220 for receiving a radio signal and a processor 210 for processing the reception signal. The receiving circuit 220 transmits a received signal received through the antenna 230 to the processor 210. The processor 210 of the receiver 200 processes data in reverse of the processor 110 of the transmitter 100 and outputs information bits.

Although the transmitter 100 and the receiver 200 have been described as having one antenna, the transmitter 100 and / or the receiver 200 may have a plurality of antennas. The technical idea of the present invention can be applied to a multiple-input multiple-output (MIMO) system as it is. The transmitter 100 and the receiver 200 may apply various wireless access schemes such as orthogonal frequency division multiple access (OFDMA), time division multiple access (TDMA), and code division multiple access (CDMA).

3 is a flowchart illustrating an example of a HARQ process.

Referring to FIG. 3, a transmitter generates a transmission packet (S110). The transmission packet may be encoded data encoded by adding a Cyclic Redundancy Check (CRC) to information bits to perform HARQ. As a coding method, a turbo code, which is one of error correction codes, may be applied. The turbo code is a structural code that includes information bits as structural bits. In the case of a turbo code with a code rate of 1/3, two parity bits are allocated to one structural bit.

The transmitter performs the first transmission (S120). The transmitter transmits first data which is a bit string of a portion of a transmission packet generated by applying a turbo code.

The receiver detects whether the received first data is in error (S130). The receiver attempts error correction on the received first data and determines whether to retransmit using the CRC, which is an error detection code. If an error is detected in the first data, the receiver transmits a retransmission request signal (NACK signal) to the transmitter (S140).

The transmitter receiving the NACK signal transmits appropriate second data (retransmission data) according to the HARQ mode (chase combining or IR) (S150). In HARQ in the IR mode, the transmitter may transmit second data, which is a bit stream contiguous to the first data. The receiver combines and decodes the first data and the second data to improve reception performance.

4 is a block diagram illustrating a processor configuration of a transmitter according to an embodiment of the present invention.

Referring to FIG. 4, the processor of the transmitter includes a padding bit calculation unit 310, a padding unit 320, a CRC encoding unit 330, and a fragmentation unit 340. ) And an encoding unit 350.

The padding bit calculator 310 calculates a padding bit from the input information bit. When the encoder 350 uses the turbo code, the number of bits input to the encoder 350 may be determined according to an interleaver size or interleaver depth of the turbo code. Padding bits are added to match the bits input to the encoding unit 350 to a predetermined number of bits. The padding bit calculator 310 calculates the size of the padding bit from the size of the information bit so that the size of the padding bit is minimized. The padding bit calculator 310 may calculate the size of the padding bit by finding the number of pieces of information bits that are efficiently partitioned.

The padding unit 320 pads the calculated sized padding bit to the information bit. If the size of the information bit is not an element of the allowed set for HARQ, a padding bit may be added to the information bit. The acknowledgment set is a set of bits, and the element of the acknowledgment set refers to the number of bits before the CRC, which is an error detection code, is added to the predetermined number N _EP input to the encoding unit 350. For example, the grant set may have {32, 80, 128, 176, 272, 368, 464, 944, 1904, 2864, 3824, 4784, 9584, 14384, 19184, 23984} bits.

Hereinafter, N _EP means the number of bits input to the encoder 350, and N _{EP _ MAX} means the maximum number of bits that can be input to the encoder 350. When the turbo code is used, N _EP has the same value as the size of the interleaver of the turbo code.

The CRC encoding unit 330 outputs a CRC added packet by adding a CRC, which is an error detection code, to a padded packet padded with an information bit. CRC is added to detect an error in the process of performing HARQ. The size of the CRC may be 16 bits. The number of bits of the CRC additional packet may be {48, 96, 144, 192, 288, 384, 480, 960, 1920, 2880, 3840, 4800, 9600, 14400, 19200, 24000} bits.

When the size of the CRC additional packet is larger than the maximum number N _{EP_MAX} that can be input to the encoding unit 350, the _{splitter 340 divides the} CRC additional packet into the maximum number of bits. If the size of the CRC additional packet is n · N _{EP _ MAX,} it is divided into n encoder packets. The encoder packet refers to a data block input to the encoding unit 350, and n refers to the number of data blocks input to the encoding unit 350. The maximum number of bits N _{EP_MAX} input to the encoding unit 350 may be 4800 bits. If the size of the CRC additional packet is smaller than the maximum number of bits, it is not divided. N _EP representing the number of bits per encoder packet that is input to the channel encoder _(EP N) The set N _EP set may be {48, 96, 144, 192, 288, 384, 480, 960, 1920, 2880, 3840, 4800}.

The encoder 350 performs Convolutional Turbo Code (CTC) encoding on the encoder packet and outputs it as a transmission packet. The transmission packet may be composed of structured bits and at least one parity bits related thereto. If the code rate is 1/3, then the transmission packet includes one structured bit and two parity bits.

5 is a block diagram illustrating a process of processing information bits in a processor of a transmitter.

Referring to FIG. 5, a padded packet having a padding bit having a size p calculated by the padding bit calculator is generated in an information bit having a size K (Padding). CRC is added to the padded packet to generate a CRC added packet (CRC addition). The CRC additional packet is divided into n encoder packets according to the number of divisions n calculated by the padding bit calculator (Fragmentation). The encoder packet is subjected to CTC encoding and output as a transmission packet (CTC encoding). The transport packet includes structured bits and at least one parity bits associated therewith. Since the transmission packet may be divided into n encoder packets from the information bit, it may be referred to as a subpacket.

The transmitter using the HARQ in the IR mode transmits initial data, which is a bit string of a part of the generated transmission packet, and transmits retransmission data, which is a bit string different from the initial data, in response to a retransmission request from the receiver. After transmitting the retransmission data, when the retransmission request is received, the transmitter transmits a bit string different from the previously transmitted bit string. The retransmitted bit string may be transmitted cyclically in a transmission packet.

HARQ data retransmission may be performed synchronously to retransmit data at a time point known to both the transmitter and the receiver, or asynchronously to retransmit data by allocating resources at random times. HARQ may be performed according to a stop and wait (SAW), a go-back-N (GBN), a selective repeat (SR) scheme, and the like. The proposed scheme adopts adaptive HARQ scheme in which transmission attributes such as resource allocation, modulation technique, transport block size, etc. are adaptively changed according to channel conditions, or transmission attributes used for initial transmission. It can be used in the non-adaptive HARQ scheme which is continuously used regardless of the change of. In the above, the number of bits of the grant set, the number of bits of the CRC additional packet, the maximum number of bits, and the number of bits of the encoder packet are merely examples and are not limiting.

6 is a flowchart illustrating a method of calculating padded bits according to an embodiment of the present invention.

Referring to FIG. 6, when the sum of the size K of information bits and the size c of the CRC is greater than the maximum number of bits N _{EP_MAX} among the number of bits that can be input to the encoder, the plurality of encoder packets are divided into a plurality of encoder packets. By defining the number n in advance, the size of the padded bits can be reduced.

If an information bit of size K is input (S210), it is determined whether the sum of the information bits and the CRC size (K + c) is greater than the maximum number of bits (N _{EP_MAX} ) to determine whether the information bits are fragmented. Determine (S220).

When the sum of the information bits and the CRC size is larger than the maximum number of bits (K + c> N _{EP _ MAX} ), the number n divided into a plurality of encoder packets is defined (S230). The encoder packet means a data block input to the encoder, and n means the number of data blocks. The number n of encoder packets from the information bits may be defined as in Equation 1.

은 *보다 큰 최소 정수이다. here,

Is the smallest integer greater than *.

Applying a number (n) of the defined EP is obtained by at least N _EP satisfying the expression (2) in _EP N set _{(N EP set) (S240)} .

The number of bits p of padding bits is calculated as in Equation 3 by applying n and N _EP obtained in Equations 1 and 2 (S250).

p = (N _EP * n)-(K + c)

If the size and the sum of the CRC size of the information bits is not greater than the maximum number of bits _{(K + c ≤ N EP_MAX)} , N EP is selected to be at least N _EP satisfying the expression (4) in N _EP three (N _EP set) (S260).

K + c ≤ N _EP

According to the selected N _EP , the number of bits c of padding bits is calculated as in Equation 5 (S270).

p = N _EP- (K + c)

In the proposed technique, assuming K = 4785, c = 16, and N _{EP _ MAX} = 4800, n = 2 according to Equation 1. When n = 2, N _EP = 2880 according to Equation 2. According to Equation 3, the number of bits of the padding bit is c = (2880 * 2)-(4785 + 16) = 959. Two encoder packets of 2880 bits are generated.

In the conventional technique of not calculating the size of the padding bit in advance, when K = 4785, 9584 bits are selected from the allowed set and 16 bits of CRC are added to generate a 9600-bit CRC additional packet. The size of the CRC portion of packets divided into the size N is larger than N _{MAX _ EP EP _ MAX,} to generate the encoder packets 2 of 4800 bits. Here, the number of bits of padding bits c = 9584-4785 = 4799 bits. As such, when the size of the CRC additional packet in which the CRC is added to the information bit exceeds the maximum number of bits N _{EP_MAX} input to the channel encoder, the maximum number of bits N _{EP _ MAX} regardless of the exceeding number of bits is exceeded. Padding in multiples greatly increases the number of bits in the padding bits, which in turn lowers the throughput of the system.

However, if the number n of encoder packets is defined in advance according to the proposed scheme, and N _EP is determined accordingly, the number of bits p of padding bits can be reduced. By reducing the number of bits (p) of unnecessary padding bits, the yield of the system can be improved. Unnecessary padding bits are reduced, allowing data to be transmitted at lower code rates. In addition, even when data is transmitted at the same code rate as the conventional technique, since the amount of data is reduced due to the reduction in the padding bit, the system yield is improved.

7 is a graph showing the yield of a system according to an embodiment of the present invention.

Referring to FIG. 7, a system throughput according to a signal-to-noise ratio (Es / No) is shown.

When the number of bits of the information bit K = 4785, when two encoder packets of 4800 bits are generated and data is transmitted (4785/9600 conventional) as in the prior art, the code rate is reduced by the number of bits of the padding bits reduced according to the proposed scheme. The system yield is shown in the case of lower transmission (4785/9600 proposed) and two encoder packets of 2880 bits generated and transmitted (4785/5760 proposed).

It can be seen that the yield of the system according to the proposed technique is improved compared to the conventional technique.

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 an example of a transmitter.

3 is a flowchart illustrating an example of a HARQ process.

4 is a block diagram illustrating a processor configuration of a transmitter according to an embodiment of the present invention.

5 is a block diagram illustrating a process of processing information bits in a processor of a transmitter.

6 is a flowchart illustrating a method of calculating padded bits according to an embodiment of the present invention.

7 is a graph showing the yield of a system according to an embodiment of the present invention.

Claims (9)

Obtaining the number of bits p of padding bits to be padded with respect to the information bits; Padding the padding bits to the information bits by the number of bits p of the padding bits; Dividing the information bits padded by the padding bits into n data blocks; And And encoding the n data blocks (p, n > 0), wherein the number of bits p of the padding bits is obtained according to the number n of the data blocks and the number of bits of the data blocks. Data coding method. 2. The method of claim 1, further comprising adding a CRC to the information bits padded with the padding bits. The number of bits p of the padding bit is p = (N _EP × n)-(K + c) _Wherein N _EP is the number of bits of the data block, K is the number of bits of the information bit, and c is the number of bits of the CRC (N _EP , n, K, an integer with c> 0). Data coding method in communication system. The method of claim 1, wherein the number n of the data blocks is

K is the number of bits of the information bits, c is the number of bits of the CRC, N _{EP _ MAX} is the maximum number of bits of the data block that can be input to the encoder,

A method of data coding in a wireless communication system, characterized in that is a minimum integer greater than * (an integer of N _{EP _ MAX} , K, c> 0). The method of claim 1, wherein the number of bits N _EP of the data block is a predetermined number of bits.

Is determined as the minimum N _EP , where K is the number of bits of the information bit, c is the number of bits of the CRC (N _EP , n, K, an integer of c> 0). . Determining whether to divide the information bits; When the information bits are divided, determining the number of divided information bits by considering the number of bits of the information bits and the number of bits of the CRC; Determining the number of bits of the data block to be input to the encoder in consideration of the number of bits of the information bits, the number of bits of the CRC, and the number of divisions of the information bits; And And padding the padding bits in consideration of the number of bits of the data block. 7. The method of claim 6, further comprising encoding the data block using a turbo code after the padding bits are padded. A processor for generating a transmission packet by processing an information bit; And And a transmission circuit for transmitting the transmission packet, wherein the processor defines a number of divisions of the information bits and calculates a size of a padding bit according to the defined number. The apparatus of claim 8, wherein the processor comprises: a padding bit calculator configured to calculate a size of the padding bit; A padding unit configured to generate a packet in which the padding bit is padded on the information bit; A CRC encoding unit generating a CRC addition packet by adding a CRC to the padded packet; A divider for dividing the CRC additional packet to generate an encoder packet; And And an encoder configured to encode the encoder packet.

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