KR20080023505A - Cooperative transmission method for ofdma mobile communication system and user equipment - Google Patents

Abstract

A cooperative transmission method of an orthogonal frequency division multiple access mobile communication system and a user terminal are provided to wholly increase capacity of a system by improving gain of a time diversity and a user diversity. An orthogonal frequency division multiple access mobile communication system includes a plurality of user terminals and a base station(100). A cooperative transmission method of an orthogonal frequency division multiple access mobile communication system includes a step of allowing the user terminals to transmit a signal to the base station by using a sub-carrier allocated at the user terminals. Each user terminal receives the signal which the other user terminal transmits to the base station. Each user terminal cooperatively transmits a signal of the other user terminal to the base station by using a sub-carrier equal to the sub-carrier of the other user terminal.

Description

Cooperative transmission method for OFDMA mobile communication system and user equipment

1 is an exemplary diagram illustrating a mobile communication system.

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

3 is a block diagram illustrating a terminal according to an embodiment of the present invention.

4A and 4B are exemplary views illustrating a cooperative transmission method according to an embodiment of the present invention.

5A and 5B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

6a and 6b are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

7A and 7B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

8A and 8B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

9A and 9B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

10A and 10B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

11 is a graph showing user density versus system capacity.

12 is a graph showing user density versus system capacity per user.

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

100: base station

200: terminal

The present invention relates to a cooperative transmission method of a mobile communication system, and more particularly, to a cooperative transmission method of a multi-carrier-based OFDMA mobile communication system and a terminal using the same.

With the emergence of various multimedia services and high quality services, next-generation wireless communication systems are required to guarantee high quality data and differential quality of service (QoS).

Multipath delay has become a big problem as higher data rates are required in 3rd generation and later systems. This is because multipath delay causes Inter-Symbol Interference (ISI). Orthogonal Frequency Division Multiplexing (OFDM) has attracted attention to reduce the ISI effect with low complexity.

OFDM converts serially input data symbols into N parallel data symbols and carries them on N subcarriers, respectively. The subcarriers maintain orthogonality in the frequency dimension. Each orthogonal channel experiences frequency selective fading that is independent of each other, and the interval of transmitted symbols is increased, thereby minimizing ISI. Orthogonal Frequency Division Multiple Access (OFDMA) refers to a multiple access method for realizing multiple access by providing each user with a part of subcarriers available in a system using OFDM as a modulation scheme.

One technique for mitigating a multipath delay is a diversity technique of repeatedly transmitting the same data. If multiple signals are transmitted independently of each other via diversity, even if signals of some paths are received low, signals of the other paths may have large values. Therefore, the diversity technique is to achieve stable transmission and reception by combining a plurality of signals. Types of diversity include frequency diversity for transmitting signals at different frequencies, time diversity for transmitting signals at different points of time, and spatial diversity using a plurality of transmission antennas. diversity).

One of the diversity schemes is known for cooperative transmission over multiple relay stations. A repeater is disposed between a base station and a user equipment, and the repeater relays and transmits a signal transmitted by the base station or the terminal. The repeater first receives information for cooperative transmission in a time division manner and sequentially transmits the information.

However, since the cooperative transmission is based on a single carrier, a cooperative transmission scheme suitable for a multicarrier based system such as OFDMA is not well known.

In the case of cooperative transmission using a single carrier system, time delay due to time division occurs in the repeater in charge of cooperative transmission, which hinders the performance of the system. In the case of an OFDMA-based multicarrier system, if a suitable cooperative transmission scheme is not applied, a data transmission rate may be remarkably reduced when a channel gain of a subcarrier allocated between a base station and a terminal is not good.

An object of the present invention is to provide a cooperative transmission method of an OFDMA mobile communication system suitable for a multi-carrier system and a terminal using the same.

According to an aspect of the present invention, there is provided a cooperative transmission method of an OFDMA mobile communication system including a plurality of terminals and a base station. In the cooperative transmission method, the terminals transmit a signal to the base station using a subcarrier assigned thereto. Each terminal hears the signal transmitted from the other terminal to the base station. In addition, each terminal cooperatively transmits the signal of the other terminal heard by the other terminal to the base station using the same subcarrier as the subcarrier of the other terminal.

In a cooperative transmission method of an OFDMA mobile communication system according to another aspect of the present invention, a base station transmits a signal for each terminal, and each terminal listens to the signal transmitted by the base station to another terminal. Each terminal cooperatively transmits the signal of the other terminal, which is heard by the other terminal, to the other terminal using the same subcarrier assigned to the other terminal.

According to another aspect of the present invention, a terminal uses a transmitter for transmitting a signal, a receiver for receiving a signal transmitted from another terminal, and a subcarrier identical to a subcarrier of the other terminal as the receiver receives the signal of the other terminal. It includes a controller for cooperative transmission of the signal of the other terminal.

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

The technique disclosed below may be used in various multiple access communication systems using multiple carriers such as orthogonal frequency division multiple access (OFDMA) or multi-carrier code division multiple access (MC-CDMA). Orthogonal Frequency Division Multiplexing (OFDM) partitions an entire system bandwidth into a plurality of subcarriers with orthogonality. The subcarriers may be called subbands, tones, and the like.

1 is an exemplary diagram illustrating a mobile communication system.

Referring to FIG. 1, a mobile communication system includes a base station (BS) 100 and a plurality of UEs 200. Mobile communication systems are widely deployed to provide various communication services such as voice and packet data.

The base station 100 generally refers to a fixed station that communicates with the terminal 200 and includes other terms such as node-B, base transceiver system (BTS), and access point (access point). terminology).

The terminal 200 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.

Downlink (downlink) means communication from the base station 100 to the terminal 200, uplink (uplink) means communication from the terminal 200 to the base station 100.

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

2, the base station 100 includes a transmitter 120, a receiver 140, and a controller 160.

The transmitter 120 includes a channel encoder 121, a symbol mapper 122, an inverse fast Fourier transform unit 123, and a CP remover 124. The transmitter 120 transmits data provided from the data source 110 through the antenna 130.

The channel encoder 121 encodes a series of streams of information bits provided from the data source 110 according to a predetermined coding scheme to form coded data. The information bits can include text, voice, video or other data. The channel encoder 121 may add error detection bits such as a cyclic redundancy check (CRC) to the information bits, and add an extra code for error correction. The error correction code used may be a turbo code, a low density parity check code (LDPC) or other convolution code, or the like.

The symbol mapper 122 modulates the encoded data of the stream of information bits in accordance with a predetermined modulation scheme to provide modulation symbols. The symbol mapper 122 maps the coded data into modulation symbols representing positions according to amplitude and phase constellation. The modulation scheme is not limited, and may be m-quadrature phase shift keying (m-PSK) or m-quadrature amplitude modulation (m-QAM). For example, m-PSK may include BPSK or 8-PSK as well as QPSK. m-QAM may include 256-QAM as well as 16-QAM or 64-QAM.

The IFFT unit 123 performs Inverse Fast Fourier Transformation (IFFT) on the input symbols and converts them into time domain samples. The symbols input to the IFFT unit 123 may include not only modulation symbols of encoded data but also pilot symbols separately modulated. The pilot symbol may be data known a priori to both the base station 100 and the terminal 200.

The CP inserter 124 adds a cyclic prefix (CP) to the time domain samples. CP is also called a guard interval. The sample signal output from the CP insertion unit 124 is converted into an analog signal and transmitted through the antenna 130.

The receiver 140 includes a CP remover 141, an FFT unit 142, a symbol demapper 143, and a channel decoder 144. The receiver 140 decodes a signal received from the antenna 130 and provides the decoded signal to the data sink 150 or the controller 160.

The signal received from the antenna 130 is digitized and the CP is removed by the CP removing unit 141. The samples from which CP is removed are converted into symbols in the frequency domain by performing FFT by the FFT unit 142. The symbol demapper 143 demaps the encoded data back from the symbols. The demodulation scheme corresponds to the modulation scheme provided to the symbol mapper 122 of the transmitter 120. The channel decoder 250 decodes the encoded data and provides the decoded data to the data sink 150.

The controller 160 controls the overall operation of the base station 100, and a memory for the operation of the base station 100 may be stored in the memory 160. In addition, the controller 160 may adaptively adjust a coding and modulation scheme by receiving channel quality from the terminal 200.

3 is a block diagram illustrating a terminal according to an embodiment of the present invention.

Referring to FIG. 3, the terminal 200 includes a transmitter 220, a receiver 240, and a controller 260.

The configuration and operation of the transmitter 220 and the receiver 240 of the terminal 200 is the same as the structure of the transmitter 120 and the receiver 140 of the base station 100. The transmitter 220 encodes and modulates data provided from the data source 210 and transmits the data through the antenna 230. The receiver 240 demodulates and decodes a signal received from the antenna 230 and provides the demodulated signal to the data sink 250.

The controller 260 controls the overall operation of the terminal 200, and a program for the operation of the terminal 200 may be stored in the memory 260. In addition, the controller 260 may estimate the channel quality and return it to the base station 100. The terminal 200 may further include a display device or an input device for interfacing with a user.

The signal received by the terminal 200 may include a signal transmitted from another terminal to a base station or a signal transmitted from another base station to another terminal. The controller 260 listens to the signals and cooperatively transmits them to other terminals or base stations using the allocated subcarriers.

4A and 4B are exemplary views illustrating a cooperative transmission method according to an embodiment of the present invention. This is an example for uplink. For clarity, the following description will be made of one base station and three terminals UE1, UE2, and UE3. The number of base stations and terminals is not limited, and may be one or more.

Referring to FIG. 4A, a first terminal UE1 transmits a signal to a base station using a subcarrier (frequency band) allocated thereto. The first terminal UE1 becomes a source station and the base station becomes a target station. Hereinafter, a source station refers to a point at which a signal is sent, and a target station refers to a target point at which the signal is transmitted.

While the first terminal UE1 transmits its own signal to the base station, the signals of the first terminal UE1 are heard by the neighboring second terminal UE2 and the third terminal UE3. In the drawing, the dotted line indicates that the terminal hears a signal transmitted from another terminal.

Referring to FIG. 4B, the second terminal UE2 and the third terminal UE3 cooperatively transmit a signal of the first terminal UE1 that they hear using the same subcarrier as the subcarrier of the first terminal UE1 to the base station. do. In addition to the signals of the first UE UE1, the time diversity gain due to the transmission interval and the user diversity gain due to a plurality of users are additionally provided through the signals of the second and third terminals UE2 and UE3 cooperatively transmitted. You can get it. The base station may combine the cooperatively transmitted signals to reproduce the original signal. The combining method may use a maximum ratio combining (MRC) technique.

The second terminal UE2 and the third terminal UE3 may be referred to as relay stations which relay signals between the source station and the target station. A plurality of terminals cooperatively transmit using the same subcarrier to obtain a time diversity gain and a user diversity gain.

The cooperatively transmitted signal may be processed in various ways at the relay station. In an embodiment, the second terminal UE2 and the third terminal UE3 may simply amplify the received signal and cooperatively transmit the received signal. That is, the relay station amplifies the signal of the source station that it heard and performs cooperative transmission. In another embodiment, the second terminal UE2 and the third terminal UE3 may reprocess the received signal and cooperatively transmit the received signal. That is, the relay station decodes the signal of the source station that it heard, reprocesses it, and cooperatively transmits it. The reprocessing may be performed in various ways. For example, the second terminal UE2 and the third terminal UE3 may demodulate and decode the entire received signal, interleave it, and encode and modulate the received signal. Alternatively, after demodulating and decoding the received signal, only extra information such as incremental redundancy (IR) may be transmitted in a hybrid automatic repeat request (HARQ) scheme. In another embodiment, the second terminal UE2 and the third terminal UE3 may selectively select whether to simply amplify and transmit the signal or reprocess the signal. In another embodiment, the second terminal UE2 and the third terminal UE3 may take different processing schemes. For example, the second terminal UE2 may simply amplify the received signal and cooperatively transmit it, and the third terminal UE3 may reprocess the received signal and cooperatively transmit the received signal.

In general, in order for the base station to know the channel gain with the terminal, the terminal must accurately predict this and transmit feedback information to the base station. According to the present invention, it is possible to secure a stable transmission rate without feedback information on the channel gain of the user.

The relay station may dynamically decide whether to transmit cooperatively according to the return signal of the target station. For example, the target station broadcasts success if the signal received from the source station is greater than or equal to a certain Signal-to-Noise Ratio (SNR), and no cooperative transmission is made. If the SNR is below the reference value, the failure is broadcast, where the relay station can cooperatively transmit the signal it has heard.

5A and 5B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

Referring to FIG. 5A, a first terminal UE1 transmits a signal to a base station using a subcarrier allocated to the first terminal UE1. The first terminal UE1 becomes the source station and the base station becomes the destination station. While the first terminal UE1 transmits its own signal to the base station, the signals of the first terminal UE1 are heard by the neighboring second terminal UE2 and the third terminal UE3.

Referring to FIG. 5B, the second terminal UE2 and the third terminal UE3 cooperatively transmit signals of the first terminal UE1 heard by using different subcarriers to the base station. The second terminal UE2 and the third terminal UE3 serve as relay stations for relaying signals between the source station and the target station, and the base station combines the cooperatively transmitted signals for each subcarrier to reproduce the original signal.

When the second terminal UE2 and the third terminal UE3 cooperatively transmit using different subcarriers, a gain due to frequency diversity may be additionally obtained in addition to the time diversity.

6a and 6b are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention. This is a case where a plurality of terminals are connected by uplink and a plurality of source stations are arranged.

Referring to FIG. 6A, a subcarrier is allocated from a base station to a first terminal UE1, a second terminal UE2, and a third terminal UE3, respectively. The first terminal UE1, the second terminal UE2, and the third terminal UE3 transmit signals to the base station using subcarriers allocated to the first terminal UE1, the second terminal UE2, and the third terminal UE3, respectively. The source station becomes a first terminal UE1, a second terminal UE2, and a third terminal UE3, and the target station becomes a base station. While the first terminal UE1 transmits its own signal to the base station, the signals of the first terminal UE1 are heard by the neighboring second terminal UE2 and the third terminal UE3. In addition, while the second terminal UE2 transmits its own signal to the base station, the signal of the second terminal UE1 is heard by the neighboring first terminal UE1 and the third terminal UE3, and the third terminal UE3. ) Transmits its own signal to the base station, the signal of the third terminal (UE3) is heard by the surrounding first terminal (UE1) and the second terminal (UE2).

Referring to FIG. 6B, the first terminal UE1 cooperatively transmits a signal of the second terminal UE2 and a signal of the third terminal UE3 to the base station. The first terminal UE1 may load a signal of the terminal on a subcarrier corresponding to a signal of a terminal heard by the first terminal UE1. For example, the first terminal UE1 may carry a signal of the second terminal UE2 on the same subcarrier as the subcarrier of the second terminal UE2, which is heard by the first terminal UE1, and the subcarrier of the third terminal UE3. A signal of the third terminal UE2 may be carried on the same subcarrier. The second terminal UE2 receives the signal of the first terminal UE1 and the signal of the third terminal UE3, which are heard by the second terminal UE2, respectively, and the same subcarrier as the subcarrier of the first terminal UE1 and the subcarrier of the third terminal UE3, respectively. Cooperative transmission to the base station. The third terminal UE3 receives the signal of the first terminal UE1 and the signal of the second terminal UE2, which are heard by the third terminal UE3, respectively, with the same subcarrier as the subcarrier of the first terminal UE1 and the subcarrier of the second terminal UE2. Cooperative transmission to the base station.

When there are a plurality of source stations, the diversity gain can be increased by cooperatively transmitting a signal on each corresponding subcarrier.

7A and 7B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

Referring to FIG. 7A, a subcarrier is allocated from a base station to a first terminal UE1, a second terminal UE2, and a third terminal UE3, respectively. The first terminal UE1, the second terminal UE2, and the third terminal UE3 transmit signals to the base station using subcarriers allocated to the first terminal UE1, the second terminal UE2, and the third terminal UE3, respectively. That is, the source station becomes the first terminal UE1, the second terminal UE2, and the third terminal UE3, and the target station becomes the base station. While the first terminal UE1 transmits its own signal to the base station, the signals of the first terminal UE1 are heard by the neighboring second terminal UE2 and the third terminal UE3. In addition, while the second terminal UE2 transmits its own signal to the base station, the signals of the second terminal UE1 are heard by the neighboring first terminal UE1 and the third terminal UE3, and the third terminal UE3. ) Transmits its own signal to the base station, the signal of the third terminal (UE3) is heard by the surrounding first terminal (UE1) and the second terminal (UE2).

Referring to FIG. 7B, the first terminal UE1, the second terminal UE2, and the third terminal UE3 cooperatively transmit a signal they hear using a subcarrier originally assigned to them. The first terminal UE1 transmits a signal of the second terminal UE2 and a signal of the third terminal UE3 to the base station. The first terminal UE1 may transmit an identifier together with the base station to distinguish the signal of the second terminal UE2 from the signal of the third terminal UE3. The second terminal UE2 transmits the signal of the first terminal UE1 and the signal of the third terminal UE3 to the base station. The third terminal UE3 transmits the signal of the first terminal UE1 and the signal of the second terminal UE2 to the base station.

8A and 8B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention. This is an example of downlink.

Referring to FIG. 8A, a base station transmits a signal to a first terminal UE1 using a predetermined subcarrier. At this time, the base station becomes the source station, and the first terminal UE1 becomes the destination station. While the base station transmits a signal to the first terminal UE1, a signal transmitted by the base station is heard by the surrounding second terminal UE2 and the third terminal UE3.

Referring to FIG. 8B, the second terminal UE2 and the third terminal UE3 cooperatively transmit a signal of the base station that they heard using the same subcarrier as the first terminal UE1 to the first terminal UE1. That is, the second terminal UE2 and the third terminal UE3 become relay stations which relay signals between the source station and the target station. The first terminal UE combines these for each subcarrier to reproduce the original signal. The combining method may use the MRC technique.

By cooperatively transmitting a signal through the same subcarrier, a gain by time diversity can be obtained.

9A and 9B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention.

Referring to FIG. 9A, a base station transmits a signal to a first terminal UE1 using a predetermined subcarrier. At this time, the base station becomes the source station, and the first terminal UE1 becomes the destination station. While the base station transmits a signal to the first terminal UE1, a signal transmitted by the base station is heard by the surrounding second terminal UE2 and the third terminal UE3.

Referring to FIG. 9B, the second terminal UE2 and the third terminal UE3 cooperatively transmit signals of the base station heard by the second terminal UE2 to the first terminal UE1 using different subcarriers. The first terminal UE combines these for each subcarrier to reproduce the original signal. The combining method may use the MRC technique.

The second terminal UE2 and the third terminal UE3 may cooperatively transmit using different subcarriers to further obtain gain due to frequency diversity in addition to time diversity.

10A and 10B are exemplary views illustrating a cooperative transmission method according to another embodiment of the present invention. This is a case where a plurality of terminals are connected by downlink, and a plurality of target stations are arranged.

Referring to FIG. 10A, a first terminal UE1, a second terminal UE2, and a third terminal UE3 receive signals from a base station. At this time, the base station may transmit the same signal to each terminal, and may transmit a different signal for each terminal. The first terminal UE1, the second terminal UE2, and the third terminal UE3 each receive signals to the base station using subcarriers assigned to them. At this time, the source station is a base station, and the target station is a first terminal UE1, a second terminal UE2, and a third terminal UE3. While the base station transmits a signal to the first terminal UE1, the signal of the base station is heard by the surrounding second terminal UE2 and the third terminal UE3. In addition, while the base station transmits a signal to the second terminal (UE2), the signal of the base station is heard by the surrounding first terminal (UE1) and the third terminal (UE3), the base station transmits the signal to the third terminal (UE3) In the meantime, the signal of the base station is heard by the neighboring first terminal UE1 and the second terminal UE2.

Referring to FIG. 10B, the first terminal UE1 transmits a signal of the second terminal UE2 that it hears to the second terminal UE2, and transmits a signal of the third terminal UE3 to the third terminal UE3. Cooperative transmission. The first terminal UE1 may load the signal of the terminal on a subcarrier corresponding to the signal of the terminal heard by the first terminal UE1. For example, the first terminal UE1 may carry a signal of the second terminal UE2 on the same subcarrier as the subcarrier of the second terminal UE2, which is heard by the first terminal UE1, and the subcarrier of the third terminal UE3. A signal of the third terminal UE2 may be carried on the same subcarrier. The second terminal UE2 cooperatively transmits the signal of the first terminal UE1 heard to the first terminal UE1 by using the same subcarrier as the subcarrier of the first terminal UE1, and the third terminal heard by the second terminal UE2. The signal of UE3 is cooperatively transmitted to the third terminal UE3 using the same subcarrier as that of the third terminal UE3. The third terminal UE2 cooperatively transmits the signal of the first terminal UE1 heard by the third terminal UE2 to the first terminal UE1 using the same subcarrier as the subcarrier of the first terminal UE1, and the second terminal heard by the third terminal UE2. The signal of the UE2 is cooperatively transmitted to the second terminal UE2 using the same subcarrier as the subcarrier of the second terminal UE2.

Even when there are a plurality of destination stations, the relay station can cooperatively transmit a signal on each corresponding subcarrier to increase diversity gain.

Hereinafter, the simulation results for the cooperative transmission according to the present invention and the prior art will be described. The system environment sets the cell radius to 1 km and adjusts the user density while increasing the number of users in the cell. In other words, the user density is the number of users / cell width.

11 is a graph showing user density versus system capacity. 12 is a graph showing user density versus system capacity per user. System capacity per user is calculated by dividing the overall system performance by the number of users.

11 and 12, as user density increases, system capacity rises more steeply than in the prior art. In the prior art without cooperative transmission, the data rate per user decreases significantly as the number of users increases rather than the number of subcarriers. However, when the cooperative transmission is made, the capacity of the system increases as the number of users increases due to user diversity gain.

In the above description, single-input single-output (SISO) having one transmit antenna and one receive antenna has been described, but the technical idea of the present invention is multiple-input multiple-output; MIMO) system can be applied as it is.

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

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand. 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, in the OFDMA mobile communication system using a multi-carrier, cooperative transmission using a plurality of terminals can be implemented to increase overall system capacity by further increasing time diversity and user diversity gain.

Claims (7)

In the cooperative transmission method of an OFDMA mobile communication system comprising a plurality of terminals and a base station, The terminals transmitting a signal to the base station using a subcarrier assigned to the terminals; Each terminal listening to the signal transmitted from another terminal to the base station; And And each terminal cooperatively transmitting a signal of the other terminal heard by the terminal to the base station using the same subcarrier of the other terminal. The method of claim 1, Each terminal is a cooperative transmission method of the OFDMA mobile communication system for amplifying and transmitting the signal of the other terminal that they heard. The method of claim 1, Each terminal is a cooperative transmission method of the OFDMA mobile communication system to decode and re-process the signal of the other terminal that they hear after transmitting. In the cooperative transmission method of an OFDMA mobile communication system comprising a plurality of terminals and a base station, Transmitting, by the base station, a signal for each terminal; Each terminal listening to the signal transmitted by the base station to another terminal; And And each terminal cooperatively transmitting a signal of the other terminal heard by the other terminal to the other terminal using the same subcarrier assigned to the other terminal. Transmitting, by the source station, a signal using subcarriers assigned to the destination station; The partner station listening to the signal; And And the cooperative station cooperatively transmitting the signal to the target station using the same subcarrier as the subcarrier of the source station. A transmitter for transmitting a signal; A receiver for listening to a signal transmitted from another terminal; And And a controller for cooperatively transmitting a signal of the other terminal using the same subcarrier as the subcarrier of the other terminal when the receiver receives the signal of the other terminal. A transmitter for transmitting a signal; A receiver for listening to a signal transmitted from another terminal; And And a controller for cooperatively transmitting a signal of the other terminal by using a subcarrier different from the subcarrier of the other terminal when the receiver receives the signal of the other terminal.

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