KR20080111788A - Method for transmitting data in multiple antenna system - Google Patents

Abstract

A method for transmitting a data block which a channel is encoded in a multiple antenna system is provided to secure space-diversity gain additionally due to spatial multiplexing by proposing a transmitting method by mapping the code block according to a layer in a multiple antenna system. A code block is channel-encoded. A plurality of data streams is generated by multiplexing the channel-encoded code block. The channel-encoded code block is mapped to a plurality of data streams uniformly. A plurality of data streams is transmitted through a multiple antenna. The channel-encoded code blocks include a structural block and a parity block.

Description

Method for transmitting data in multiple antenna system {Method for transmitting data in multiple antenna system}

1 is a block diagram illustrating a wireless communication system.

2 is a block diagram illustrating a transmitter according to an embodiment of the present invention.

3 is a block diagram illustrating a transmitter according to another embodiment of the present invention.

4 is a block diagram illustrating a channel encoding scheme according to an embodiment of the present invention.

5 shows data transmission according to an embodiment of the present invention.

6 shows data transmission according to another embodiment of the present invention.

7 shows data transmission according to another embodiment of the present invention.

8 shows data transmission according to another embodiment of the present invention.

9 shows data transmission according to another embodiment of the present invention.

The present invention relates to wireless communications, and more particularly, to a method for transmitting a channel encoded data block in a multi-antenna system.

The demand for communication services is rapidly increasing, including the generalization of information and communication services, the emergence of various multimedia services, and the emergence of high quality services. Various wireless communication technologies have been studied in various fields to satisfy these demands.

Next generation wireless communication systems must be able to transmit high quality, high capacity multimedia data at high speed using limited frequency resources. To enable this in bandwidth-constrained wireless channels, it must overcome the intersymbol interference and frequency selective fading that occur during high-speed transmissions while maximizing frequency efficiency. Multiple input multiple output (MIMO) technology is one of the technologies that can improve communication capacity and communication performance without additional frequency allocation or power increase.

MIMO technology is a technique for increasing capacity or improving performance by using multiple antennas in a transmitter or receiver of a wireless communication system. MIMO technology is an application of a technique of gathering and completing fragmented pieces of data received from multiple antennas without relying on a single antenna path to receive one entire message. You can increase the data rate in certain ranges or increase the system range for certain data rates. Increasing the number of transmit antennas and the number of receive antennas simultaneously increases the theoretical channel transmission capacity in proportion to the number of antennas, thereby improving frequency efficiency.

MIMO technology can be classified into a spatial diversity scheme that improves transmission reliability using various channel paths and a spatial multiplexing scheme that improves a transmission rate by simultaneously transmitting a plurality of data streams. In addition, researches on how to appropriately combine these two methods to obtain the advantages of each are being studied in recent years.

The space diversity scheme includes a space-time block code (STBC) scheme and a space-time trellis code (STTC) scheme for simultaneously increasing diversity and coding gains. In general, the bit error rate improvement performance and the freedom of sign generation are better in the STTC method, but the operation complexity is lower in the STBC method. The spatial diversity gain can be obtained by an amount corresponding to a product of the number of transmit antennas and the number of receive antennas.

Spatial multiplexing is a method of transmitting different data streams in each transmit antenna. Since mutual interference occurs between data streams transmitted at the same time, the receiver must remove and process this interference using an appropriate signal processing technique. Depending on the noise cancellation method used, it may be classified into a maximum likelihood (ML) receiver, a zero-forcing (ZF) receiver, a minimum mean square error (MMSE) receiver, and a Bell Labs Layered Space Time (BLAST) receiver. If the transmitter can know the channel information, the SVD (Singular Value Decomposition) method can be used.

If only the spatial diversity gain is taken, the performance improvement gain due to an increase in the diversity order may be gradually saturated. Taking only the spatial multiplexing gain can reduce the transmission reliability. In order to solve this problem, methods of obtaining both gains have been studied. There are double space-time block code (Double-STTD) and space-time bit-interleaved coded modulation (BICM).

Fading channels are one of the major causes of poor performance of wireless communication systems. The channel gain changes with time, frequency, and space, and the lower the channel gain, the more severe the degradation. Diversity, one way to overcome fading, takes advantage of the fact that multiple independent channels are all very unlikely to have low gains. Among the various diversity schemes, the introduction here is multiuser diversity. When there are several users in a cell, the channel gains of each user are stochastically independent of each other, so the probability that they all have low gains is very small. According to information theory, if the base station has sufficient transmission power, allocating all channels to a user having the highest channel gain value when there are several users in a cell can maximize the total capacity of the channel.

Multiuser diversity can be divided into three categories. First, temporal multi-user diversity is a method of allocating a channel to a user having the highest gain at that time when the channel changes over time. Second, frequency multi-user diversity is a method of allocating subcarriers to a user having a maximum gain in each frequency band in a multi-carrier system such as orthogonal frequency division multiplexing (OFDM). If the channel changes very slowly in a system without multiple carriers, the user with the highest channel gain will monopolize the channel for a long time and other users will not be able to communicate. In this case, in order to use multi-user diversity, it is necessary to induce channel changes. Third, spatial multi-user diversity is a method of using different channel gain values of users according to space, and an example thereof may include random beamforming (RBF). RBF is also referred to as opportunistic beamforming, and the transmitter induces a channel change by performing beamforming with arbitrary weights using multiple antennas.

In a typical wireless communication system, channel coding is performed for reliable data transmission. Channel coding refers to a transmitter performing encoding of a transmission information using a forward error correction code so that a receiver corrects an error experienced in a channel. The receiver demodulates the received signal and then decodes the error correcting code to recover the transmission information. In this decoding process, the error of the received signal generated by the channel is corrected.

An example of an error correcting code is a turbo code. The turbo code is composed of a recursive systematic convolution encoder and an interleaver. The performance of the turbo code is known to be good as the size of the input data block increases. In an actual communication system, encoding is performed by dividing the data block over a certain size into several small data blocks for the convenience of the actual implementation. The divided small data block is called a code block. After the error correction encoding process by the unit of code block of a predetermined size, it is mapped to the radio resource and transmitted.

However, in the MIMO system, after performing channel encoding on a code block basis, it is necessary to consider spatial multiplexing in mapping radio resources. Since each MIMO channel is independent, transmission efficiency can be improved if spatial multiplexing is performed so that a code block is suitable for multiple transmit antennas.

There is a need for a technique for efficiently transmitting channel encoded data through multiple transmit antennas.

An object of the present invention is to provide a method for efficiently transmitting data in a multi-antenna system.

According to an aspect of the present invention, a data transmission method of a multiple antenna system is provided. The method includes channel encoding code blocks, spatially multiplexing the channel encoded code blocks to generate a plurality of data streams, wherein the channel encoded code blocks are mapped equally to the plurality of data streams and the plurality of data streams. Transmitting the data stream of the multiple antennas.

According to another aspect of the present invention, a data transmission method of a multiple antenna system is provided. The method includes channel encoding a code block, distributing and mapping the channel encoded code block to a subframe, wherein the subframe includes a plurality of subcarriers in a frequency domain and a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain. And transmitting the subframe through multiple antennas.

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.

A radio communication system may be based on Orthogonal Frequency Division Multiplexing (OFDM). OFDM uses multiple orthogonal subcarriers. OFDM uses orthogonality between inverse fast fourier transforms (IFFTs) and fast fourier transforms (FFTs). At the transmitter, data is sent 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. According to OFDM, the complexity of the receiver can be reduced in a frequency selective fading environment of a wideband channel, and the spectral efficiency can be improved through selective scheduling in the frequency domain by using different channel characteristics between subcarriers. . Orthogonal Frequency Division Multiple Access (OFDMA) is a multiple access scheme based on OFDM. According to OFDMA, the efficiency of radio resources can be improved by assigning different subcarriers to multiple users.

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 referred to 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 means communication from the base station 20 to the terminal 10, and uplink 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.

2 is a block diagram illustrating a transmitter according to an embodiment of the present invention.

Referring to FIG. 2, the transmitter 100 includes a CRC attachment unit 110, a codeblock segmentation unit 115, a channel encoder 120, an interleaver 130, and a rate matching unit. (rate matching unit 140), mapper 150, layer mapper 160, and precoding unit 170. The transmitter 100 includes Nt (Nt> 1) transmit antennas 190-1,..., 190 -Nt.

The CRC adding unit 110 adds a cyclic redundancy check (CRC) code for error detection to the input data. The code block dividing unit 155 divides the code to which the CRC is added in units of code blocks. Here, the CRC is added to the data and then divided into code block units, but the CRC may be added to the code block units.

The channel encoder 120 performs channel encoding on the code block. The interleaver 130 interleaves the channel encoded code. The rate matching unit 140 matches the interleaved code according to the amount of radio resources used for the actual transmission. Rate matching can be achieved through puncturing or repetition. The mapper 150 maps the rate matched code to a symbol representing a location on the signal constellation. An interleaver (not shown) may be further added between the front end of the mapper 150, that is, between the rate matching unit 140 and the mapper 150.

The layer mapper 160 maps input symbols for each layer according to spatial multiplexing. Data mapped and output by each layer by the layer mapper 160 is called a data stream. The precoding unit 170 performs precoding on the input data stream in a multiple input multiple output (MIMO) scheme according to the transmission antennas 190-1,..., 190 -Nt.

Here, since several data streams are generated from one channel encoded code, this is called a single codeword system.

3 is a block diagram illustrating a transmitter according to another embodiment of the present invention. This is referred to as a multiple codeword system because it produces multiple data streams from one or more channel encoded codes compared to the transmitter 100 of FIG.

Referring to Figure 3, the transmitter 200 is CRC addition unit (210-1, ..., 210-K) (K> 1), code block division unit (215-1, ..., 215-K) , Channel encoders 220-1, ..., 220-K, interleavers 230-1, ..., 230-K, rate matching units 240-1, ..., 240-K, mappers (250-1,..., 250-K), layer mapper 260 and precoding unit 270. The transmitter 200 includes Nt (Nt> 1) transmit antennas 290-1,..., 290 -Nt.

The CRC adding units 210-1, ..., 210-K add CRC codes for error detection to the input data. The code block dividing unit 155 divides the code to which the CRC is added in units of code blocks. The channel encoders 220-1, ..., 220-K perform channel encoding on the code block. Interleavers 230-1, ..., 230-K interleave the channel encoded code. The rate matching units 240-1, ..., 240-K match the interleaved codes according to the amount of radio resources used for the actual transmission. Rate matching can be achieved through puncturing or repetition. The mappers 250-1,..., 250 -K map the rate matched codes into symbols representing positions on the signal constellation. An interleaver (not shown) may be further added between the rate matching units 240-1,..., 240 -K and the mappers 250-1,..., 250 -K.

The layer mapper 260 maps input symbols for each layer according to spatial multiplexing. Data mapped and output by each layer by the layer mapper 260 is called a data stream. The data stream may be called a layer. The precoding unit 270 performs precoding on the input data stream by the MIMO scheme according to the transmission antennas 290-1,..., 290 -Nt.

4 is a block diagram illustrating a channel encoding scheme according to an embodiment of the present invention. Consider a case where one code block is transmitted in multiple data streams by performing channel coding, interleaving, and rate matching. A code block is a data block of a certain size for performing channel encoding. Code blocks may have the same size, and a plurality of code blocks may have different sizes.

Referring to FIG. 4, the channel encoder 320 performs channel encoding on an input code block. The channel encoder 320 may be a turbo code, and the turbo code may include 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 330 performs interleaving on the channel encoded code block to reduce the influence of burst error that occurs as it is transmitted to the wireless channel. The interleaver 330 may perform interleaving on the structural block S and each of the two parity blocks P1 and P2.

The rate matching unit 340 adjusts the channel encoded code block according to the size of the radio resource. Rate matching may be performed in units of channel encoded code blocks. Alternatively, the structural block S and the two parity blocks P1 and P2 may be separated.

Now, a data transmission method using spatial multiplexing will be described.

To clarify the description, consider the case where it is transmitted in two data streams (layer 2).

The structural block S and the two parity blocks P1 and P2 generated from one code block may be divided into two data streams and transmitted. When code blocks are divided and transmitted in two data streams, spatial diversity gain can be obtained, thereby improving performance. Since the structural block S plays a more important role in decoding than the two parity blocks P1 and P2, when the structural block S is transmitted in a data stream having a better channel state, performance may be further improved. In this case, a specific pattern may be used when mapping two data streams to radio resources.

Next, assume that the number of code blocks to be transmitted is two or more. Here, a case of transmitting three code blocks divided into two data streams is considered.

5 shows data transmission according to an embodiment of the present invention.

Referring to FIG. 5, two data streams (layer 2) are divided and allocated in one subframe in the frequency domain. One subframe includes a plurality of resource blocks in the frequency domain. One resource block includes a plurality of subcarriers, for example, one resource block may include 12 subcarriers. One subframe includes 2 slots in the time domain, and one slot includes 7 OFDM symbols. However, the number of resource blocks included in one subframe, the number of slots, and the number of OFDM symbols included in one slot are only examples and are not limited.

One code block is evenly mapped to two data streams. Radio resources allocated to one code block are equally allocated to two data streams. After mapping of one code block is completed, the next code block is mapped in the same manner. Here, three code blocks are equally divided and mapped into two data streams. In this case, the interval occupying in the time domain is minimal.

When using a turbo code, one code block may be divided into a structural block (S) and a parity block (P1, P2). The structural block S and the parity blocks P1 and P2 may be transmitted evenly divided into two data streams. The mapping of the structural block S and the parity blocks P1 and P2 may have a specific pattern. In particular, since the structural block S plays a more important role in error correction than the parity blocks P1 and P2, the structural block S may be divided into two data streams and transmitted. Accordingly, the spatial diversity gain for the structural block S can be obtained. Alternatively, the structural block S may be mapped to a data stream having a good channel state.

By mapping code blocks distributed to two data streams and transmitting the two data streams through multiple antennas, a spatial diversity gain by the data streams can be secured. By uniformly mapping the code blocks to the two data streams, it is possible to reduce the decoding delay due to the transmission of the data streams.

When mapping a codeblock to an N (N> 1) data stream, it can be mapped evenly if N is an even number. If N is odd, the code blocks can be mapped as evenly as possible. Even when mapping the structural block S, if N is odd, the structural block S may be mapped as evenly as possible.

6 shows data transmission according to another embodiment of the present invention. This is a case where two code blocks are divided into two data streams and transmitted.

Referring to FIG. 6, after mapping a first code block to one data stream, a second code block is mapped to another data stream. The third codeblock maps over two data streams.

When mapping one code block to one data stream, extra code blocks may be generated. That is, when M (M> 1) code blocks are mapped to N (N> 1) data streams, M and N are not multiples, that is, M = k × N + q (k is an integer, 0 <q <N -1) case. In this case, the q code block may be divided and mapped to N data streams.

When one code block includes the structural block S and the parity blocks P1 and P2, the structural block S and the parity blocks P1 and P2 may be mapped to one data stream with a specific pattern.

7 shows data transmission according to another embodiment of the present invention.

Referring to FIG. 7, a first code block and a second code block are mapped to two data streams in a specific pattern. The first code block and the second code block are alternately arranged in OFDM symbol units. The third codeblock maps over two data streams.

When the M code block is transmitted during the L OFDM symbol period, the first code block is mapped to the N data stream during the ceil (L / M) period, and the second code block is mapped. ceil (x) is the minimum integer greater than x. From the first OFDM symbol to each ceil (L / M) -1 OFDM symbol of each data stream is filled, only a part of the ceil (L / M) OFDM symbol can be filled. Then map the next block of code.

When one code block includes the structural block S and the parity blocks P1 and P2, the structural block S and the parity blocks P1 and P2 may be evenly mapped over two data streams. The mapping of the structural block S and the parity blocks P1 and P2 into two data streams may have a specific pattern.

8 shows data transmission according to another embodiment of the present invention.

Referring to FIG. 8, the first code block and the second code block are mapped to two data streams in a specific pattern. The first code block and the second code block are alternately arranged in units of resource blocks. The third codeblock maps over two data streams.

When one code block includes the structural block S and the parity blocks P1 and P2, the structural block S and the parity blocks P1 and P2 may be evenly mapped over two data streams. The mapping of the structural block S and the parity blocks P1 and P2 into two data streams may have a specific pattern.

9 shows data transmission according to another embodiment of the present invention.

Referring to FIG. 9, three code blocks are mapped over all subframes. Three code blocks are transmitted together in two data streams. Three code blocks may be mapped to two data streams in a specific pattern.

Here, three code blocks are mapped one by one on a resource block basis (by frequency axis), but three code blocks may be mapped one by one by OFDM symbol (by time axis).

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 embodiments, and the present invention will include all embodiments within the scope of the following claims.

As described above, according to the present invention, a technique for mapping and transmitting code blocks according to layers in a multi-antenna system may additionally secure a spatial diversity gain due to spatial multiplexing.

Claims (5)

In the data transmission method of a multi-antenna system, Channel encoding the codeblocks; Spatially multiplexing the channel encoded code blocks to generate a plurality of data streams, wherein the channel encoded code blocks are mapped equally to the plurality of data streams; And Transmitting the plurality of data streams through multiple antennas. The method of claim 1, And the channel encoded code block comprises a structural block and a parity block. The method of claim 2, And said structural block is mapped evenly to said plurality of data streams. In the data transmission method of a multi-antenna system, Channel encoding the codeblocks; Distributing and mapping the channel encoded coded blocks to subframes, the subframes including a plurality of subcarriers in a frequency domain and a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols in a time domain; And Transmitting the subframe through multiple antennas. The method of claim 4, wherein The subframe is divided into a plurality of layers in a frequency domain, and the channel encoded code block is mapped to each layer.

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