KR101527973B1 - Method for relaying data and wireless communication system using the same - Google Patents

Abstract

The data relaying method includes: generating a received bitstream by performing turbo decoding on a received signal received from a source station; Interleaving the received bitstream to generate an interleaved bitstream; Performing a turbo encoding on the interleaved bit stream to generate a relay bit stream; And transmitting the relay bitstream to a destination station. According to the present invention, a signal transmitted from a source station to a destination station or a relay station is constituted by a turbo code, and sufficient error correction is possible even when the channel environment from the source station to the destination station or the relay station is poor. In addition, the turbo codes received at the respective relay stations can be subjected to turbo decoding, interleaving and turbo encoding to obtain an interleaving gain. As a result, even when the channel environment between the source station and the relay station is poor, a transmission quality higher than a certain level can be guaranteed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a data relaying method and a wireless communication system using the same,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to a method for relaying data in a wireless communication system and a wireless communication system using such a relaying method.

Recently, wireless communication systems including relay stations (RS) are widely used. A relay station relays data between a base station and a mobile station. The relay station uses an AF (Amplify and Forward) method and a DF (Decode and Forward) relay method.

The AF method is a method in which a signal received from a base station is amplified and transmitted to a terminal without progressing to a decoding process, and the DF method is a method in which a received signal is decoded and re-encoded and modulated to be transmitted to a terminal. The DF method is advantageous in that a decoding delay is generated with respect to the AF method, an amount of calculation is increased, and a complexity is large, but a decoding gain can be obtained. Since the performance of the AF method and the DF method depends on the system configuration, the transmission environment, and the configuration of the transmission protocol, it is desirable to select an appropriate method considering the service and the user requirements.

The base station can obtain the effect of expanding the cell coverage by serving through the relay station to the terminal located at the cell coverage boundary of the base station. Further, the relay station can increase the transmission capacity of the signal between the base station and the terminal, thereby increasing the transmission capacity. A relay station may be used when the terminal is located within the cell coverage of the base station but located in a shadow area.

A wireless communication system including such a relay station is considered as an alternative to increase the communication capacity of a cellular or Ad-Hoc system. Initially, in a cellular system, a relay station started in a repeater mode in which a signal transmitted from a base station is received and amplified in order to improve the communication quality of a cell edge region where the electric field intensity of the base station is weak, To improve the performance of the wireless communication system efficiently and intelligently.

In recent years, studies have been made to utilize the advantages of turbo codes by applying turbo codes to wireless communication systems including relay stations. Turbo codes have been developed in the early 1990s and have attracted attention due to their excellent performance and realizable implementation.

An example of applying a turbo code to a wireless communication system including a conventional relay station is a distributed turbo code scheme. In the distributed turbo coding scheme, a source station transmits a code block corresponding to a component code to a destination station and a relay station in a first time slot. Then, the relay station decodes the component code and transmits the re-encoded code block to the destination station in the second time slot. The destination station performs turbo decoding using both the code blocks received in the first and second time slots.

In this distributed turbo coding scheme, the RS does not perform turbo decoding but decodes and re-encodes only the received code block. Therefore, when a decoding error occurs in the relay station, such a decoding error is also transmitted to the destination station, which causes deterioration of the overall performance of the wireless communication system.

SUMMARY OF THE INVENTION The present invention provides a reliable data relay method in a wireless communication system and a wireless communication system using the same.

A wireless communication system according to an aspect of the present invention includes a source station; A plurality of relay stations; And a destination station for turbo decoding signals received from the plurality of relay stations, wherein each of the plurality of relay stations performs a turbo decoding on a received signal received from the source station to generate a received bitstream, Generating an interleaved bit stream by performing stream interleaving on the interleaved bit stream, performing a turbo encoding on the interleaved bit stream to generate a relay bit stream, and transmitting the relay bit stream to a destination station, And performs different interleaving on the stream.

According to another aspect of the present invention, there is provided a data relay method including: performing a turbo decoding on a received signal received from a source station to generate a received bitstream; Interleaving the received bitstream to generate an interleaved bitstream; Performing a turbo encoding on the interleaved bit stream to generate a relay bit stream; And transmitting the relay bitstream to a destination station.

A signal transmitted from a source station to a destination station or a relay station may be configured with a turbo code so that sufficient error correction is possible even when the channel environment from the source station to the destination station or the relay station is poor. In addition, the turbo codes received at the respective relay stations can be subjected to turbo decoding, interleaving and turbo encoding to obtain an interleaving gain. As a result, even when the channel environment between the source station and the relay station is poor, a transmission quality higher than a certain level can be guaranteed.

1 shows a wireless communication system according to an embodiment of the present invention.

1, a wireless communication system 100 includes a mobile station (MS) 110, a base station (BS) 120, and relay stations 130, 140, and 150.

The terminal 110 may be fixed or mobile and may be a user equipment (UE), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA) ), A portable device (Handheld Device), an AT (Access Terminal), and the like.

The base station 120 generally refers to a fixed station that communicates with the terminal 110 and includes an evolved NodeB (eNB), a base transceiver system (BTS), an access point, an access network (AN) And so on. The base station 120 provides communication services for a specific geographical area. In addition, the BS may perform functions such as connectivity, management, control, and resource allocation between the RS and the MS.

The relay stations 130, 140, and 150 relay data between the terminal 110 and the base station 120, and at least one relay station may be disposed. In FIG. 1, the case where three relay stations are arranged is exemplarily shown, but this is not a limitation. The relaying method used by the relay stations 130, 140 and 150 may be a decode and forward (DF) scheme. The DF scheme is a scheme in which a received signal is decoded and then re-encoded and modulated to be transmitted to the UE.

Hereinafter, downlink (DL) means communication from the base station 120 to the terminal 110, and uplink (UL) means communication from the terminal 110 to the base station 120. In the downlink, the transmitter may be part of the base station 120, and the receiver may be part of the terminal 110. In the uplink, the transmitter may be part of the terminal 110, and the receiver may be part of the base station 120.

In a UL transmission, a source station may be a terminal 110 and a destination station may be a base station 120. In the downlink transmission, the source station may be the base station 120 and the destination station may be the terminal 110. [ In the following description, the source station is the terminal 110 and the destination station is the base station 120, but this is not a limitation.

In the wireless communication system 100 according to the embodiment of the present invention, the source station 110 turbo-encodes the information to be transmitted to generate a source bitstream and transmits the source bitstream. The transmission scheme may be, for example, a broadcast scheme. Each of the relay stations 130, 140 and 150 receives a turbo encoded source bit stream and performs a turbo decoding, interleaving and turbo encoding to generate a relay bitstream, and then transmits the relay bitstream to the destination station. The interleaving performed in each of the relay stations 130, 140, and 150 is different from each other, and the generated relay bitstreams may be different from each other. The destination station 120 receives the source bit stream from the source station 110 and receives different relay bit streams from each of the relay stations 130, 140 and 150 to perform turbo decoding.

2 is a diagram showing a configuration of a source station, a relay station and a destination station in a wireless communication system according to an embodiment of the present invention.

Referring to FIG. 2, the source station 110 may include a turbo encoder 111 and a transmission circuit 112. The turbo encoder 111 is a module for generating a source bit stream by turbo coding information to be transmitted, that is, information bits (d). The transmission circuit 112 receives the source bit stream, modulates the received bit stream into a radio signal, and transmits the modulated signal to the outside through an antenna (not shown).

3 shows an example of a configuration of a turbo encoder.

Referring to FIG. 3, the turbo encoder 111 includes a first component encoder 31, a second component encoder 32, and an internal interleaver 33. When the information bits d are input to the turbo encoder 111, systematic bits x, parity bits 1 and 2, and parity bits 2 ; y2) is output. The systematic bits x are the same as the information bits d.

The first component encoder 31 generates first parity bits y1 from the information bits d. The second component encoder 32 generates second parity bits y2 from the bits output from the inner interleaver 33. [ The first component coder 31 and the second component coder 32 may use a recursive systematic convolution code (RSC) having the same structure. The internal interleaver 33 interleaves the input information bits d. In general, the internal interleaver 33 rearranges the input order of the information bits d in order to convert the correlated information into information that is not correlated effectively, thereby eliminating the error pattern.

Referring again to FIG. 2, three relay stations 130, 140 and 150 are shown, but each relay station 130, 140 and 150 includes the same components in terms of functionality, so that one relay station 130 will be described.

The relay station 130 includes a receiving circuit 131, a turbo decoder 132, an external interleaver 133, a turbo re-encoder 134, and a transmission circuit 135 .

The receiving circuit 131 converts the received source bit stream into a digital signal. The source bit stream converted into a digital signal is provided to a turbo decoder 132. [ The turbo decoder 132 is a module for turbo decoding a source bit stream input from a receiving circuit to generate a received bit stream.

4 shows an example of a configuration of a turbo decoder.

Referring to FIG. 4, the turbo decoder 132 may include a first decoder 41, a second decoder 42, two internal interleavers 43 and 44, and an internal deinterleaver 45.

The first decoder 41 and the second decoder 42 may be MAP (Maximum A Posteriori) decoders having the same structure. The first decoder 41 receives the systematic bits x and the first parity bits y1 included in the source bit stream, decodes the systematic bits and sends the systematic bits x and the first parity bits y1 to the internal interleaver 44. The second decoder 42 decodes the signal obtained by interleaving the output of the first decoder 41, the second parity bits y2, and the signal interleaved with the systematic bits x.

The first decoder 41 decodes the output signal of the second decoder 42 by the deinterleaver 45, the systematic bits x and the first parity bits < RTI ID = 0.0 > (y1). After the desired iterative decoding process, the second decoder 42 generates a received bitstream and provides it to the external interleaver 1 (133).

This iterative decoding can be performed until the desired performance is obtained. As the number of iterative decoding processes is increased, the performance of the turbo code is improved. However, when the number of iterations exceeds a certain number of iterations, the performance may be saturated and converged. In general, the performance gain of a turbo code tends to be larger with respect to the existing code as the size of the processed information block increases.

However, if the iterative decoding is not performed, the output signal of the second decoder 42 is deinterleaved by the internal deinterleaver 45 and then hard decision is made through a hard decision unit (not shown) And may generate a bitstream.

2, the external interleaver 133 interleaves the signal input from the turbo decoder 132 to generate an interleaved bit stream. The external interleaver 133 is distinguished from an internal interleaver included in the turbo encoder 111, the turbo decoder 132, and the like.

Each of the relay stations 130, 140, and 150 may use different external interleavers 133, 143, and 153, and in this case, an interleaving gain may be obtained. It is preferable that the outer interleaver 1 (133) maximize the Hamming distance of the entire code according to the component code of the turbo code, the code rate, and the size of the interleaver. The same applies to the case of the external interleaver 2 143 and the external interleaver 3 153.

However, when the number of relay stations is one, it is relatively easy to design an external interleaver. However, when the number of relay stations increases, it is difficult to design an external interleaver used in each relay station. This problem can be solved by changing the external interleaver which is one of the basic elements. For example, if the number of relay stations is N (where N is a natural number equal to or greater than 2), and the size of the outer interleaver is L (L is a natural number of 2 or more), let the outer interleaver be denoted as ILn (i). Here, n is 0, 1, ... , N-1, i is 0, 1, ... , And L-1. That is, ILn (i) is an external interleaver used for the nth relay station, and 0, 1, 2, ... , And L-1 are interleaved. In this case, when the basic external interleaver is denoted by IL0 (i), the remaining external interleavers (i.e., any one of n = 1, 2, ..., N-1) can be obtained as follows.

≪ Equation &

Here, J (n) = (L / N) * n + c, and c is a constant smaller than N. And% is a modulus operator. In the case where J (n) has the form J (n) = (L / N) * n + c, it is the most basic type of cyclic shift. Of course, J (n) may be configured in a random form or a block form.

As the number of relay stations increases and the multiplexing of the turbo codes increases, the performance of the entire codes does not differ greatly according to the specific design of the external interleaver. In this respect, it is advantageous in terms of the complexity and the required amount of memory to utilize the external interleaver of each relay station as a basic external interleaver.

The turbo encoder 134 turbo-encodes the interleaved bit stream input from the external interleaver 133 to generate a relay bit stream. The turbo encoder 134 may have the same configuration as the turbo encoder 111 described above.

The transmission circuit 135 modulates the relay bit stream input from the turbo encoder 134 to generate a radio signal and transmits the radio signal to the outside.

A method of relaying data in each of the relay stations 130, 140, and 150 configured as described above will be described. Hereinafter, a method of relaying data to one relay station 130 will be described, but the other relay stations 140 and 150 are the same. However, there is a difference in that the relay stations 130, 140, and 150 perform interleaving using different outer interleavers.

5 is a flowchart showing a method of relaying data by the relay station.

Referring to FIG. 5, the relay station 130 performs a turbo decoding on a received signal received from the source station 110 to generate a received bitstream (S100). That is, the receiving circuit 131 receives the source bit stream transmitted from the source station 110 by turbo encoding, and the turbo decoder 132 performs the turbo decoding on the received source bit stream to generate a received bit stream.

The relay station 130 interleaves the received bit stream to generate an interleaved bit stream (S200). More specifically, the outer interleaver 133 interleaves the received bitstream to generate an interleaved bitstream.

The relay station 130 performs turbo encoding on the interleaved bit stream to generate a relay bit stream (S300). A turbo encoder 134 generates this relay bit stream.

The relay station 130 transmits the relay bit stream to the destination station 120 (S400). Specifically, it transmits the relay bit stream to the destination station 120 via the transmission circuit 135.

 As described above, a plurality of relay stations for relaying data may be arranged in a wireless communication system. A time resource allocation method when the relay station uses DF (decode and forward) as a relay scheme and N nodes are allocated will be described.

6 is a diagram illustrating a method of relaying data by assigning time resources to each relay station in the wireless communication system according to the present embodiment.

Referring to FIG. 6, time resources are divided into (N + 1) time slots having a value 1 greater than the number N of relay stations, and time slots 0, time slots 1, ..., , And time slot N, respectively. In time slot 0, the source station broadcasts the source bit stream to the destination station and N relay stations.

The source bit stream transmitted from the source station is generated as a relay bitstream through the turbo decoding, interleaving and turbo encoding process in each relay station, and then transmitted to the destination station. At this time, the relay station n (1? N? N, n is a natural number) can transmit the relay bitstream to the destination station in the time slot n. That is, the relay station 1 may transmit the relay bitstream to the destination station in time slot 1, and the relay station 2 may transmit the relay bitstream to the destination station in time slot 2.

Hereinafter, a frequency resource allocation method when N relay stations relay data in the wireless communication system according to the present embodiment will be described.

7 is a diagram showing a method of relaying data by assigning frequency resources to each relay station.

Referring to FIG. 7, the frequency resources are divided into (N + 1) frequency bands, which are 1 greater than the number N of relay stations. Then, the time resources are divided into time slot 0 and time slot 1. In time slot 0, the source station broadcasts the source bit stream to the destination station and N relay stations using frequency band 0. In the time slot 1, each relay station transmits its relay bit stream with different frequency bands. For example, relay station n transmits the relay bit stream using frequency band n.

Referring again to FIG. 2, the destination station 120 may include a receiving circuit 121 and a turbo decoder 122.

The receiving circuit 121 receives the source bit stream transmitted from the source station 110 and / or the relay bit stream transmitted from each of the relay stations 130, 140 and 150, and converts the received bit stream into a digital signal. The turbo decoder 122 turbo-decodes the signal input from the receiving circuit 121. The turbo decoder 122 used in the destination station 120 may perform turbo decoding in various ways. For example, turbo decoding may be performed in parallel or serial manner.

FIG. 8 shows an example of a process in which a turbo decoder used in a target station performs turbo decoding in parallel.

Referring to FIG. 8, the turbo decoder 122 used in the destination station 120 includes a plurality of turbo decoding modules 80-0 to 80-N, a plurality of turbo decoding modules And a plurality of deinterleavers for performing deinterleaving between the interleaver and the turbo decoding module.

Each of the plurality of turbo decoding modules 80-0 to 80-N includes a turbo decoding module 0 (80-0) for turbo decoding a source bit stream received directly from the source station 110, And turbo decoding modules 80-1 to 80-N for turbo decoding the relay bitstream. For example, the turbo decoding module 1 (80-1) corresponds to the signal transmitted by the relay station 1, and the turbo decoding module N corresponds to the signal transmitted from the relay station N (1). The plurality of turbo decoding modules 80-0 to 80-N may all have the same configuration. FIG. 8 shows an example of a turbo decoding module configuration 80-1.

The soft decision information processed in the turbo decoding module 0 (80-0) is interleaved in the interleaver 1 and then transmitted to the turbo decoding module 1 (80-1). This process proceeds from turbo decoding module 0 to turbo decoding module N. [ The soft decision information processed in the turbo decoding module N (80-N) in the opposite direction is deinterleaved in the deinterleaver (N-1), and then transmitted to the turbo decoding module (N-1). This process proceeds from the turbo decoding module N to the turbo decoding module 0.

9 is an example of a process in which a turbo decoder used in a target station performs turbo decoding in serial.

9, the turbo decoder 122 used in the destination station 120 is provided with a plurality of turbo decoding modules 90-0 to 90-N and turbo decoding modules 90-0 to 90- And a plurality of interleavers for performing a plurality of interleavers.

The plurality of turbo decoding modules 90-0 to 90-N includes a turbo decoding module 0 (90-0) for turbo decoding a source bit stream received directly from the source station 110, And turbo decoding modules 90-1 to 90-N for turbo decoding the bit stream. The plurality of turbo decoding modules 90-0 to 90-N may all have the same configuration. FIG. 9 shows an example (90-1) of the turbo decoding module configuration.

The process in which the turbo decoder 122 performs turbo decoding serially is different from the process of performing the parallel turbo decoding described above in that the turbo decoding modules 90-0 to 90- And provides soft decision information with a certain level of confidence to the next turbo decoding module after decoding. That is, in the process of performing turbo decoding in parallel, for example, if the turbo decoding module 1 (80-1) has performed the decoding once, the turbo decoding module 1 (90-1) And then transmits the soft decision information processed by the turbo decoding module 2 (90-2).

10 is an example of data transmission of a relay station and turbo decoding timing at a destination station in the wireless communication system according to the present embodiment.

Referring to FIG. 10, the destination station 120 turbo decodes the relay bitstream received in the immediately preceding time slot for each time slot in which the source station 110 or the relay station 120 transmits a signal. For example, the destination station 120 turbo decodes the relay bit stream transmitted from the relay station 1 in the time slot 1 (S130-1) in the time slot 2 (S120-1), and transmits the relay bit stream transmitted from the relay station 1 (S130-2) turbo-decodes the relay bit stream in time slot 3 (S120-2).

This turbo decoding timing is particularly suitable for performing turbo decoding serially in the destination station 120. [

11 shows a data relaying method combined with a Hybrid Automatic Repeat reQuest (HARQ) scheme when a relay method of DF scheme is used in a relay station.

Referring to FIG. 11, in time slot 0, source station 110 transmits source signal 1 (i.e., source bitstream 1) to destination station 120 and relay station 130. When the destination station 120 receives the source signal 1 (11) and succeeds in turbo decoding, it transmits an ACK (acknowledgment, acknowledgment) 14 to the relay station 130 and the source station 110 in the time slot 1. Then, the relay station 130 does not transmit the relay signal 1 (i.e., the relay bit stream 1) that has turbo encoded the source signal 1 to the destination station.

Source station 110 broadcasts source signal 2 (12, i.e., source bitstream 2) in time slot 2. If the destination station 120 fails to receive or receive the source signal 2 12 and the turbo decoding fails, the destination station 120 transmits a NACK 15 (Negative Acknowledgment) to the source station 110 and the relay station 130). The relay station 130 transmits the relaying signal 2 (16, that is, the relay bitstream 2) to the destination station 120 only when the NACK is received from the destination station 120. When the destination station 120 receives the relay signal 2 16 and the turbo decoding is successful, the destination station 120 transmits the ACK 17 to the source station 110 and the relay station 130. The source station 110 then broadcasts the source signal 3 (13, i.e., source bitstream 3) to the destination station 120 and the relay station 130.

(Time slots 1 and 3 in FIG. 11) for transmitting an ACK / NACK signal than a time slot (time slot 0, time slot 2, time slot 4, etc. in FIG. 11) , Time slot 5, etc.) may be short in time. In this case, when the channel from the source station 110 to the destination station 120 is highly reliable, it is effective in terms of bandwidth efficiency. This is because unnecessary data transmission from the relay station 130 to the destination station 120 is reduced by using an ACK signal having a short time interval.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- A processor, another electronic unit, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. 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.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

1 shows a wireless communication system according to an embodiment of the present invention.

2 is a diagram showing a configuration of a source station, a relay station and a destination station in a wireless communication system according to an embodiment of the present invention.

3 is an example of a configuration of a turbo encoder according to the present embodiment.

4 shows an example of a configuration of a turbo decoder used in a relay station according to the present embodiment.

5 is a flowchart illustrating a method of relaying data by a relay station in the wireless communication system according to the present embodiment.

6 is a diagram illustrating a method of relaying data by assigning time resources to each relay station in the wireless communication system according to the present embodiment.

7 is a diagram illustrating a method of relaying data by assigning frequency resources to each relay station in the wireless communication system according to the present embodiment.

8 is a diagram illustrating a process in which a turbo decoder used in a target station of a wireless communication system according to the present embodiment performs parallel turbo decoding.

FIG. 9 is a diagram illustrating a process in which a turbo decoder used in a target station of the wireless communication system according to the present embodiment performs turbo decoding in serial.

10 is a diagram illustrating data transmission of a relay station and turbo decoding timing at a destination station in a wireless communication system according to the present embodiment.

11 shows a data relaying method combined with an ARQ (Automatic Repeat reQuest) scheme when a relay method of the DF scheme is used in a relay station.

Claims (6)

Source station; A plurality of relay stations; And A destination station for turbo decoding a signal received from the plurality of relay stations, Each of the plurality of relay stations generates a received bitstream by performing turbo decoding on a received signal received from the source station, generates an interleaved bitstream by interleaving the received bitstream, Generating a relay bit stream by performing turbo encoding, and transmitting the relay bit stream to a destination station, Each of the plurality of relay stations performing different interleaving on the received bitstream, When the number of the plurality of relay stations is N and an external interleaver performing interleaving in n (0? N? N-1, n is a natural number) relay station is represented as ILn (i) Wherein the outer interleaver has a relationship as expressed by the following equation. ≪ Equation &

In the above equation, i is 0, 1, ... , And L-1. And J (n) = (L / N) * n + c, c is a constant smaller than N, and% is a modulus operator. The method according to claim 1, Wherein each of the plurality of relay stations transmits a relay bit stream to the destination station in a time slot assigned to the relay station. The method according to claim 1, Wherein each of the plurality of relay stations transmits a relay bit stream to the destination station in a frequency band assigned to itself in the same time slot. The method according to claim 1, Wherein the destination station turbo decodes a signal received from the source station and the plurality of relay stations. delete A method of relaying data carried out by n (0? N? N-1, n is a natural number) relay station in a wireless communication system including a source station, a destination station and N relay stations, Performing turbo decoding on a received signal received from the source station to generate a received bitstream; Interleaving the received bitstream to generate an interleaved bitstream; Performing a turbo encoding on the interleaved bit stream to generate a relay bit stream; And And transmitting the relay bit stream to the destination station, Wherein, when an outer interleaver performing interleaving in the nth relay station is represented as ILn (i), the outer interleaver of each of the plurality of relay stations has a relationship expressed by the following equation. ≪ Equation &

In the above equation, i is 0, 1, ... , And L-1. And J (n) = (L / N) * n + c, c is a constant smaller than N, and% is a modulus operator.

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