KR101054077B1 - Data transmission method based on terminal-relay station system and terminal for same - Google Patents

Abstract

The present invention relates to a terminal-relay station system-based data transmission method and a terminal for the same.

A terminal and a base station that move to a shadow area or a cell coverage area by setting a terminal that meets a preset criterion among the terminals located in a cell of the base station as a relay terminal that is a mobile relay station. Ensure that communications continue to be maintained. Therefore, since there is no packet loss and communication delay occurring during the reconnection of the base station through ranging after the communication is lost between the base station and the terminal, real time communication is possible.

seamless relay station shadowed mode opaque CQI pilot ranging piggyback

Description

A method for transmitting data based on a terminal-relay station system and a terminal for the same

The present invention relates to a terminal-relay station system-based data transmission method and a terminal for the same.

In general, when a terminal communicating with a base station is located in a shadow area or a cell coverage area in a wireless communication system, communication loss with the base station occurs, thus requiring a base station reconnection process through ranging. This will be described with reference to FIGS. 1 and 2.

1 is a diagram illustrating a general fixed relay station based wireless communication environment, and FIG. 2 is a flowchart illustrating a general fixed relay station based relay station access procedure.

As shown in FIG. 1, a general wireless communication system includes a base station 10, a fixed relay station 20, 30, and a terminal 40, 50, 60 that a base station has jurisdiction over. When there are terminals 30 and 50 moving to a shaded area that does not receive the downlink signal from the base station 10 and the terminal 40 moving out of the cell area, the relay stations 20 and 30 are connected to the terminals 40 and 50. , 60) to improve the quality of service. Therefore, by using the relay stations 20, 30, the terminals 40, 50, 60 can obtain a stable transmission effect of data through capacity improvement, bit error rate performance improvement, and transmission distance extension.

In order to improve the stable data transmission performance according to the introduction of the relay stations 20 and 30, the relay stations 20 and 30 receive signals from the base station 10 and then transmit them to the terminals 40, 50, and 60. Amplify and forward and Decode and forward methods are used. The post-amplification transmission method is a method in which the relay station 20, 30 amplifies the power of the signal received from the base station 10 to the transmission power of the relay station 20, 30 and then transmits the signal to the terminal 40, 50, 60.

Communication with the base station 10 through a connection with the relay station 20, 30 after the communication with the base station 10 in a situation that the terminal (40, 50, 60) moves outside the shaded area or the cell in a general wireless communication environment The procedure for reconnecting is as shown in FIG.

Referring to FIG. 2, the base station 10 confirms communication maintenance with the terminal 50 by exchanging an ARQ signal with the terminal 50 (S10). If the base station 10 determines whether a time-out has occurred from the terminal 50 and does not receive an ACK or NACK signal until the time-out occurs, the base station 10 retransmits the previous signal. (S20). However, the base station 10, which has not received the response signal from the terminal 50 until the timeout occurs, stops transmitting the signal to the terminal (S30). At the same time, the terminal 50 that has not received a signal from the base station 10 for a predetermined time recognizes the communication loss with the base station 10 (S40), and performs a ranging process through the connection to the relay station 20.

The relay station 20 performs ranging with the base station 10 for a registration procedure for reconnection of the terminal 50 to the base station 10. The base station 10 allows the terminal 50 to be registered with the base station 10 through the ranging response to the relay station 20. In this process, the terminal 50 transmits / receives messages for ranging to the relay station 20 (S50 and S60), and the relay station 20 again returns to the base station 10 for a registration procedure for reconnection of the terminal to the base station 10. The ranging procedure is performed (S70, S80). Thereafter, the relay station 20 causes the terminal 50 to resume communication with the base station 10 through the ranging response (S90).

Based on the above process, when the base station 10 and the mobile station 50 moving outside the shadow area or the cell reconnect through the repeater after the communication is lost, communication delay and packet loss occur, so that the quality of service (QoS): It is difficult to guarantee quality of service.

Accordingly, the present invention provides a method for transmitting data based on a terminal-relay station system that enables a terminal to continuously communicate without disconnection between a terminal and a base station when the terminal communicating with the base station moves to a cell outer region or a shadowed region. Provides a terminal for.

One feature of the present invention for achieving the above technical problem is,

When the channel quality information request signal is received from the base station, transmitting a response signal; Receiving a terminal-relay station conversion request signal from the base station; Receiving a signal transmitted from a neighboring terminal to the base station, measuring channel quality information of the neighboring terminal; Transmitting the measured channel quality information to the base station; And relaying to the base station when receiving data from the neighboring terminal.

Another feature of the present invention for achieving the technical problem of the present invention,

Determining a threshold value based on the plurality of channel quality information received from the plurality of terminals and the previously stored cumulative channel quality information; If there is a first terminal having channel quality information smaller than the threshold among the plurality of channel quality information, transmitting a terminal-to-relay station converted signal to a plurality of second terminals having channel quality information larger than the threshold value, respectively; ; Receiving channel quality information of the first terminal from the second terminals, respectively; And selecting a relay terminal to serve as a relay station of the first terminal based on the received channel quality information of each of the first terminals.

Terminal another feature of the present invention for achieving the technical problem of the present invention,

A signal receiving unit for receiving a terminal-to-relay station converted signal from a base station or a signal transmitted from a neighboring terminal to the base station; A channel quality information measuring unit measuring channel quality information of the neighboring terminal based on the signal transmitted from the signal receiving unit to the base station; A signal transmitter which transmits the channel quality information of the neighboring terminal measured by the channel quality information measuring unit to an uplink slot to the base station; And a control unit that controls to convert the mode from the terminal mode to the relay station mode when the signal receiving unit receives the terminal-relay station conversion signal.

According to the present invention, the communication between the terminal and the base station existing in the shadow area or outside the cell coverage is continuously maintained, so that the packet loss and the communication delay that occur during the base station reconnection process through ranging after the communication is lost between the base station and the terminal. Since there is no real time communication is possible.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise. In addition, the terms “… unit”, “… unit”, “module”, etc. described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software. have.

In the present specification, a terminal is a mobile station (MS), a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), a user equipment (User Equipment). It may also refer to a user equipment (UE), an access terminal (AT), and the like, and may include all or some functions of a mobile terminal, a subscriber station, a portable subscriber station, a user device, and the like.

In the present specification, a base station (BS) is an access point (AP), a radio access station (Radio Access Station, RAS), a Node B (Node B), a base transceiver station (Base Transceiver Station, BTS), MMR ( Mobile Multihop Relay) -BS and the like, and may include all or part of functions such as an access point, a radio access station, a Node B, a base transceiver station, and an MMR-BS.

According to an embodiment of the present invention, a function of a relay station is determined based on a threshold determined based on statistical characteristics of channel quality indicators (CQIs) before a terminal moving outside a shadow area or cell coverage is disconnected from a base station. It provides a method for preventing packet loss and communication delay through a seamless connection to the terminal having a. To this end, it will be described in detail with reference to the drawings.

3 is an exemplary diagram of a mobile relay station based wireless communication system according to an embodiment of the present invention.

As shown in FIG. 3, in a wireless communication system according to an exemplary embodiment of the present invention, a terminal (or a second terminal) 300 that is located outside a cell or in a shaded area is configured to include a base station (B) through a relay terminal which is a mobile relay station in an uplink. A cell environment in communication with 100). Here, the relay terminal refers to a terminal that can perform a function as a terminal and a function as a relay station.

The structure of the terminal 200 which performs both the function of the relay station and the function of the terminal in such an environment, and a procedure in which the terminal is switched to the relay terminal and connected to the base station 100 will be described with reference to FIGS. 4 and 5. Shall be. Here, in FIG. 5, it is assumed that the first terminal 200 is a terminal included in the area controlled by the base station 100 and can also perform a function as a relay station, and the second terminal 300 is a terminal existing in a shaded area. do.

First, the structure of the terminal, Figure 4 is a structural diagram of a terminal according to an embodiment of the present invention.

As shown in FIG. 4, the first terminal 200 according to an embodiment of the present invention includes a signal receiver 210, a channel quality information measurer 220, a signal transmitter 230, and a controller 240. .

The signal receiver 210 receives a signal transmitted by the base station 100 to measure channel quality information of the terminal, or transmits the signal to the base station 100 to request that the first terminal 200 also perform a function of the relay station. Receive the terminal-relay station converted signal. In addition, when the first terminal 200 is performing the function of the relay station, the second terminal 300 in the shaded area may receive a signal transmitted to the base station 100 and transmit the received signal to the base station 100. The channel quality information of the second terminal 300 may also be measured.

The channel quality information measuring unit 220 receives the signal of the second terminal 300 received by the signal receiving unit 210 and measures channel quality information of the second terminal 300.

The signal transmitter 230 transmits a response signal of a signal transmitted by the base station 100 to measure the channel quality information on the terminal itself to the base station 100, or the second terminal 300 transmits to the base station 100. It also relays and transmits the signal. In addition, the channel quality information measuring unit 220 transmits the channel quality information of the shaded area.

When the control unit 240 receives the terminal-to-relay station conversion signal from the base station 100, the controller 240 controls the change of the terminal mode so that the first terminal 200 may also perform a function of the relay station.

In a system where such a terminal is located, a signal transmission and reception procedure through a relay station of the terminal will be described with reference to FIG. 5.

5 is a flowchart illustrating a signal transmission and reception procedure using a relay station in a mobile relay station based system according to an embodiment of the present invention.

 As shown in FIG. 5, when the base station 100 transmits a message for measuring channel quality information to the first terminal 200 and the second terminal 300 (S100), the first terminal 200 and the first terminal 200 are transmitted. 2 terminal 300 transmits a message indicating that the received message to the base station 100 (S110, S115). At this time, if the base station 100 does not receive the ACK or NACK signal until the timeout occurs from the terminals, the base station 100 retransmits the signal transmitted in step S100.

The base station 100 measures the channel quality information in real time by monitoring the channel quality information of each terminal based on the signals received from the first terminal 200 and the second terminal 300 through steps S110 and S115 (S120). ). Then, the base station 100 determines a threshold value for the channel quality information of the first terminal 200 and the second terminal 300 measured based on the statistical characteristics of the previously monitored channel quality information. In operation S130, channel quality information of the first and second terminals 200 and 300 is newly received.

 In this case, the threshold for the channel quality information is determined using the Gaussian distribution shown using the statistical characteristics shown in FIG. 7, and an embodiment of the distribution for determining the threshold will be described with reference to FIG. 7.

7 is a distribution chart for threshold determination according to an embodiment of the present invention.

As shown in FIG. 7, in order to reduce the probability of outage, the base station 100 analyzes channel quality information of each terminal and extracts a distribution map of channel quality information of the corresponding terminal. The threshold is determined based on the distribution. If it is assumed that the terminal moves to the shadowed area or the cell outward as shown in Figure 3, it can be seen that the relationship as shown in the following equation (1).

That is, Equation 1 shows that the relationship between the moving speed of the terminal and the channel quality information, the relationship between the distance between the terminal and the base station and the channel quality information has an inverse relationship. In addition, the reciprocal of the channel quality information according to the amount of time change in a predetermined section based on the speed based on the amount of change in distance according to the change in time indicates that the movement speed of the terminal is proportional.

In Equation 1, V (t) denotes the speed of a terminal moving to a shadow area or a cell outside, and CQI (t) denotes channel quality information of the current terminal. And CQI (t-1) means the channel quality information of the terminal up to the time before calculating the CQI (t), ΔT means a time change for a certain period.

The channel quality information measured by the pilot of each terminal has a Rayleigh distribution, and the sum of the channel quality information measured by all pilots is expressed by a central limit theory. It can be expressed in Gaussian form as shown in 2. Here, the Rayleigh distribution and the central limit theory are already known, and detailed descriptions thereof will be omitted in the embodiments of the present invention.

Each element in Equation 2 is as follows.

M _{t is the} mean of the sum of the channel quality information measured from the pilot with Rayleigh distribution

Y _i : Value of channel quality information measured from a pilot with Rayleigh distribution

M: number of pilots transmitted when the terminal accesses upstream from the relay station

: 레일레이 분포를 갖는 파일롯에서 측정한 채널 품질 정보의 분산·

: Distribution of channel quality information measured from pilot with Rayleigh distribution

: 분산을 나타내기 위한 상수 값·

: Constant value to represent variance

를 바탕으로 한 가우시안 분포도Ρ (t): mean value m _t and variance

Gaussian distribution based on

Using Equation 2, a Gaussian distribution can be obtained as shown in FIG. 7. Assuming that the base station 100 can determine the channel quality information 540 and the channel quality information 510 in which no error occurs based on a packet error rate (PER), the base station ( 100 may determine the threshold 520 of the channel quality information by using the distribution of the channel quality information.

However, simply determining the threshold using a distribution of channel quality information may cause a problem of ping-pong in the case of fast channel fading. Therefore, in order to determine the threshold 520, the value is slowly changed using a low-pass as shown in Equation 3 below to relax the ping-pong calculation.

Here, each element is as follows.

M (t): channel quality information currently measured at time t

: 일정구간 내에서 t 시간 이전까지의 누적된 채널 품질 정보의 값·

: Value of accumulated channel quality information up to t hours before

Α: a constant value to represent the variance present in 0 ≦ α ≦ 1

In FIG. 6, the threshold is determined by the following equation (4).

Here, each element is as follows.

: 일정구간 내에서 t 시간 이전까지의 누적된 채널 품질 정보의 값·

: Value of accumulated channel quality information up to t hours before

Ρ _error : Outage probability calculated from statistical characteristics of channel quality information

Β: margin value, scale factor to prevent ping-pong phenomenon

(550)와 채널 품질 정보아웃티지 확률의 임계치 ρ_error(530)의 값을 뺀 값에 핑퐁 현상을 방지하기 위한 마진 값인 크기 변수 β의 곱에 누적된 채널 품질 정보의 평균 값

(550) 차에서 제1 임계값(THR₁)을 구한다.Average value of accumulated channel quality information up to the past

The average value of the channel quality information accumulated in the product of the magnitude variable β, which is a margin value for preventing the ping-pong phenomenon, minus the value of 550 and the threshold value of the channel probability information probability ρ _error (530).

A first threshold value THR ₁ is obtained from a difference 550.

(705)내에서 적응적으로(adaptive) 움직인다. 이와 같은 방법으로 산출한 제1 임계값을 바탕으로, 채널 품질 정보 아웃티지 확률의 임계치 ρ_error(530)와 비교하여 큰 값을, 끊김 없는 중계국 접속을 위한 임계치(520)로 결정한다.The range of the first threshold is an average of an area having an outage occurrence probability ρ _error 530 and accumulated channel quality information by channel quality information.

Move adaptively within 705. Based on the first threshold value calculated in this manner, a large value is determined as the threshold value 520 for seamless relay station access compared with the threshold value ρ _error 530 of the channel quality information outage probability.

Next, referring to FIG. 5, when the terminal having channel quality information less than the threshold calculated in step S120 exists in the cell, the relay station is required for communication with the terminal, so that the base station 100 converts the terminal to the relay station. The signal is transmitted to terminals other than the terminal having the channel quality information below the threshold (S140). Since it is assumed that only one first terminal 200 among the terminals illustrated in FIG. 3 has channel quality information greater than or equal to the threshold value, the base station 100 transmits a terminal-to-relay station converted signal to the first terminal 200.

Under the control of the control unit 240 of the first terminal 200 receiving the terminal-to-relay station conversion signal from the base station 100, the mode switching is performed in the form of performing the function of the relay station in the terminal function (S150). . Based on this, the first terminal 200 becomes a relay terminal that performs a function as a relay station between the second terminal 300 and the base station 100.

Thereafter, the second terminal 300 transmits data to the base station 100 by using an uplink frame as the general terminal uses when transmitting data (S160 and S170). On the other hand, the relay terminal not only measures the channel quality information of the second terminal 300 by receiving the pilot of the frame transmitted by the second terminal 300 to the base station 100 (S180), the second terminal 300 ) Also transmits data to be transmitted to the base station 100.

The relay terminal transmits the channel quality information of the second terminal 300 to the base station 100 using a piggyback method, which is a method of transmitting the channel quality information of the terminal including the channel quality information at the end of the uplink data. In this case, the frame structure used will be described with reference to FIG. 6.

6 is an exemplary view showing a frame structure according to an embodiment of the present invention.

As shown in FIG. 6, the downlink frame structure maintains the same form as a general WiBro frame, and the second terminal 300 does not have a function of a relay station and operates as a function of a generally known terminal. Looking at the uplink frame structure, the second terminal 300 transmits uplink data to the relay terminal. The relay terminal maintains a form of a terminal-relay station capable of relay station function, and measures channel quality information of the second terminal 300 through a pilot in a frame received from the second terminal 300.

The channel quality information of the second terminal 300 measured by the first terminal 200 is added to the end of the uplink data of the terminal-relay station to transmit the channel quality information of the second terminal 300. Send to 100. It is assumed that the second terminal 300 transmits data using the frame shown in FIG. 5, and the second terminal 300 transmits upward data of two slots or more.

Then, the relay terminal measures the channel quality information of the second terminal 300 with only one slot at the data transmission time of the second terminal 300. In addition, since the UE is switched to the uplink by the R-RTG at the next slot time, fast data transmission is possible because there is no additional overhead.

In more detail, it is assumed that the slot used by the second terminal 300 and the relay terminal when transmitting data to the base station 100 using the uplink is two slots. Then, the second terminal 300 transmits data to the base station 100 using both slots. On the other hand, the relay terminal uses one of two slots to transmit its data to the base station 100, and the other slot is used to receive a signal transmitted from the second terminal (300). In addition, the relay terminal uses a method of transmitting data received from the second terminal 300 to the base station 100 in a piggyback method.

Next, referring to the procedure of FIG. 5, when there is a terminal having channel quality information smaller than a threshold as a result of the determination of step S130, and if there are a plurality of terminals having channel quality information larger than the threshold, the procedure is transmitted to piggyback at step S190. Based on the channel quality information, the base station 100 determines an optimal terminal as a relay terminal (S200). Then, before the communication with the second terminal 300 is lost, the data of the second terminal 300 is received.

That is, in the embodiment of the present invention, since it is assumed that only the first terminal 200 has channel quality information larger than the threshold, the first terminal 200 is selected as the relay terminal through step S200. However, assuming that a plurality of terminals have channel quality information larger than a threshold, when each terminal measures channel quality information of the second terminal 300 through step S180 and transmits these information to the base station 100, The base station selects the terminal measuring the best channel quality information as a relay terminal. Therefore, when the base station 100 selects an optimal terminal as a relay terminal, the second terminal 300 can continuously maintain communication with the base station 100 through the relay terminal (S210).

As described above, according to the access method according to the embodiment of the present invention, the second terminal 300 existing in the shadowed area or the cell outside is seamlessly connected with the relay terminal before the communication with the base station 100 is lost. Through this process, packet loss and communication delay can be minimized. In addition, in transmitting the channel quality information of the second terminal 300 to the base station 100 through the relay terminal, a piggyback method of transmitting the channel quality information of the second terminal 300 to the end of the uplink data of the relay terminal. In this way, the overhead in the frame can be reduced and data can be transmitted quickly. In order to show this, experimental results using frames of IEEE 802.16j are shown in FIGS. 8A and 8B.

8A and 8B are exemplary views showing experimental results according to an embodiment of the present invention.

8A illustrates a case where a distance between a base station 100 and a relay terminal, which is a mobile terminal, is 2 km according to an embodiment of the present invention, and the terminal performs uplink to the base station in a situation in which the terminal moves outside the cell. The cell coverage was calculated based on the hata open model. Here, the hata open model refers to a path loss model applied to the open region in the hata model for predicting the signal strength level, and the detailed description is omitted in the exemplary embodiment of the present invention. Let's do it.

In FIG. 8A, the solid line shows a case where there is no relay station, and the dotted line shows a case where a general relay station connection method is used. And the line indicates the case of using the seamless relay station access method. The packet error rate (PER) is set to a value that allows QoS guarantee up to 1% outage.

Referring to FIG. 8B showing the result of FIG. 8A, when the relay station is not used, it can be seen that outage occurs at a point where the distance between the base station and the terminal is about 3.51 km. In case of using general relay station connection method, outage occurred at the same 3.51km as no relay station, and outage occurred once again at 4.5km after re-communication at 3.55km. In this case, re-communication at 3.55 km after outage at 3.51 km indicates that the terminal has moved outward of the cell for about 0.05 km, and thus communication with the base station has been lost.

In the case of using the seamless RS connection method according to the embodiment of the present invention, the cell coverage is substantially the same as the existing RS connection method, but it can be seen that the QoS is continuously guaranteed to the increased cell coverage through seamless communication. . By using the seamless RS connection method as described above, it can be seen that the UE moving to the base station and the shadow area or the cell can maintain the seamless communication through the mobile RS.

The embodiments of the present invention described above are not only implemented by the apparatus and method but may be implemented through a program for realizing the function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded, The embodiments can be easily implemented by those skilled in the art from the description of the embodiments described above.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 is a diagram illustrating a general fixed relay station based wireless communication environment.

2 is a flowchart illustrating a general fixed relay station based relay station access procedure.

3 is an exemplary diagram of a mobile relay station based wireless communication system according to an embodiment of the present invention.

4 is a structural diagram of a terminal according to an embodiment of the present invention.

5 is a flowchart illustrating a signal transmission and reception procedure using a relay station in a mobile relay station based system according to an embodiment of the present invention.

6 is an exemplary view showing a frame structure according to an embodiment of the present invention.

7 is a distribution chart for threshold determination according to an embodiment of the present invention.

8A and 8B are exemplary views showing experimental results according to an embodiment of the present invention.

Claims (8)

In the method for the terminal relays data transmitted and received between the neighboring terminal and the base station, When the channel quality information request signal is received from the base station, transmitting a response signal; Receiving a terminal-relay station conversion request signal from the base station; Measuring channel quality information of the neighboring terminal by receiving a signal transmitted from the neighboring terminal to the base station; Transmitting the measured channel quality information to the base station; And Relaying to the base station when receiving data from the neighboring terminal; Terminal-based relay system based data transmission method comprising a. The method of claim 1, Measuring the channel quality information, Receiving a signal from the neighboring terminal through a preset portion of an uplink slot for transmitting data to the base station; And Measuring channel quality information of the neighboring terminal through the pilot of the signal; Terminal-based relay system based data transmission method comprising a. The method of claim 2, The step of transmitting to the base station, Transmitting to the base station including the channel quality information at the end of data to be transmitted to the base station through the uplink slot. Terminal-based relay system based data transmission method comprising a. Determining a threshold value based on the plurality of channel quality information received from the plurality of terminals and the previously stored cumulative channel quality information; If there is a first terminal having channel quality information smaller than the threshold among the plurality of channel quality information, transmitting a terminal-to-relay station converted signal to a plurality of second terminals having channel quality information larger than the threshold, respectively. ; Receiving channel quality information of the first terminal from the second terminals, respectively; And Selecting a relay terminal to serve as a relay station of the first terminal based on the received channel quality information of each of the first terminals; Terminal-based relay system based data transmission method comprising a. 5. The method of claim 4, Determining the threshold value, The terminal-relay station system-based data transmission method of determining based on the received plurality of channel quality information, the accumulated channel quality information, the channel quality information, the outage probability and the ping-pong phenomenon. 5. The method of claim 4, After the step of selecting the relay terminal, Receiving a data signal of the first terminal through the relay terminal Terminal-relay station system-based data transmission method further comprising. A signal receiving unit for receiving a terminal-to-relay station converted signal from a base station or a signal transmitted from a neighboring terminal to the base station; A channel quality information measuring unit measuring channel quality information of the neighboring terminal based on the signal transmitted from the signal receiving unit to the base station; A signal transmitter which transmits the channel quality information of the neighboring terminal measured by the channel quality information measuring unit to an uplink slot to the base station; And A control unit which controls to convert the mode from the terminal mode to the relay station mode when the signal receiving unit receives the terminal-relay station conversion signal; Terminal comprising a. The method of claim 7, wherein The signal receiver, A terminal for receiving a data signal from the neighboring terminal when the mode is switched to the relay station mode.

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