KR20070099172A - Method of allocating and searching relay station region in mobile communications system - Google Patents

Abstract

A method for allocating and searching for a relay station area in a mobile communication system is provided to make it unnecessary for a terminal to synchronize between a relay station and a preamble regarding all the frames in order to search for the relay station area and to enable the terminal to find start location of the relay station area though the location of the relay station area is varied. A method for allocating a relay station area in a mobile communication system comprises the following several steps. A BS(Base Station) transmits the first message to a relay station wherein the first message includes ID information which allocates location of the relay station area in one and more next frames. The relay station transmits the second message to at least one terminal through the relay station area of a current frame wherein the second message includes the ID information. The ID information includes a start point of a relay station preamble. The ID information includes an offset value from a specific reference point to a start point of the relay station preamble in the next frame.

Description

Method of allocating and searching relay station region in mobile communications system

1 illustrates a frame structure of a physical layer of an orthogonal frequency division multiple access (OFDMA) broadband wireless access system.

2 exemplarily shows three subchannels composed of two subcarriers.

3 shows a data region defining resource allocation of OFDMA.

4 and 5 illustrate subchannel mapping methods in downlink and uplink frames, respectively.

6 shows the structure of a mesh frame.

7 shows an example of networking using a relay station.

8 is a view for explaining the operation of the network using a relay station in accordance with IEEE 802.16.

9 is an example of a frame structure proposed for communication through a relay station.

10 and 11 illustrate structures of frames transmitted and received from a base station and a relay station to a terminal according to an exemplary embodiment of the present invention, respectively.

The present invention relates to a mobile communication system. More specifically, the present invention relates to a method for designating a relay station area and a method for searching for a relay station area in a communication system using a relay station.

1 illustrates a frame structure of a physical layer of an orthogonal frequency division multiple access (OFDMA) broadband wireless access system. A frame is a data sequence channel for a predetermined time due to physical characteristics, and is composed of a downlink subframe and an uplink subframe. The downlink subframe starts with a preamble used for synchronization and equalization in the physical layer, and then broadcasts defining the size, location, and use of bursts allocated to the downlink and uplink. A structure of the entire frame is defined through a DL-MAP message and an UL-MAP message. A burst is a unit of data transmitted to or received from one terminal.

The DL-MAP message defines the use allocated for each burst for the downlink period in the burst mode physical layer, and the UL-MAP message defines the use of the burst allocated for the uplink period. The information element constituting the DL-MAP is a user based on the Downlink Interval Usage Code (DIUC), the Connection ID (CID), and the position information (subchannel offset, symbol offset, subchannel number, symbol number) of the burst. However, the downlink traffic section is distinguished. On the other hand, the information elements constituting the UL-MAP message is determined by the Uplink Interval Usage Code (UIUC) for each CID (Connection ID), the location of the interval is defined by the 'duration'. Here, the use of each section is determined according to the UIUC value used in the UL-MAP, and each section starts at a point separated by the 'duration' defined in the UL-MAP IE from the previous IE start point.

Downlink Channel Descriptor (DCD) message and Uplink Channel Descriptor (UCD) message are physical layer related parameters to be applied in burst periods allocated to downlink and uplink, respectively, as modulation type (Modulation type), Forward Error Correction (FEC) code type (FEC Code type), etc. In addition, it defines the necessary parameters (eg, K, R value of RS Code, etc.) according to various forward error correction code types. These parameters are given by a burst profile defined for each UIUC and DIUC inside the UCD and DCD.

A general burst allocation method in IEEE 802.16, the international standard for broadband wireless access systems, is as follows. In the downlink, the burst allocation scheme in the general MAP is a base station to teach the terminal a rectangular shape consisting of a time axis and a frequency axis, as shown in FIG. 1, through a DL-MAP message. In other words, it teaches the starting symbol number, the starting subchannel number, the number of symbols used and the number of subchannels used. Uplink uses a method of assigning the symbol axis in sequence so that the burst of uplink can be allocated by only teaching the number of symbols used.

The physical layer of the broadband wireless access system is largely divided into a single carrier (Single Carrier) and a multi-carrier (OFDM / OFDMA). The multi-carrier method employs OFDM and introduces OFDMA as an access method for allocating resources in subchannel units in which a part of carriers is grouped.

In the OFDMA physical layer, active carriers are divided into groups and transmitted to different receivers for each group. The group of carriers transmitted to the receiver is called a subchannel. 2 exemplarily shows three subchannels composed of two subcarriers. Carriers constituting each subchannel may be adjacent to each other or spaced at equal intervals. In this way, by allowing multiple access in subchannel units, implementation complexity increases, but there is an advantage in that frequency diversity gain, power concentration gain, and forward power control can be efficiently performed.

3 shows a data region defining resource allocation of OFDMA. The slot assigned to each user is defined by the data area of two-dimensional space, which is a set of consecutive subchannels allocated by bursts. One data area in OFDMA is shown as a rectangle determined by time coordinates and subchannel coordinates, as shown in FIG. Such a data area may be allocated to an uplink of a specific user or a base station may transmit the data area to a specific user in downlink. To define such a data region in two-dimensional space, the number of OFDM symbols in the time domain and the number of consecutive subchannels starting at a position separated by an offset from the reference point in the frequency domain should be given.

4 and 5 illustrate subchannel mapping methods in downlink and uplink frames, respectively. That is, it indicates how a PDU (Protocol Data Unit) is mapped to a subchannel allocated to a burst of the corresponding PDU in a specific subchannel region through encoding and modulation. The region of the allocated subchannel is displayed in two dimensions, and data is mapped from the subchannel of the first symbol with respect to the allocated two-dimensional subchannel region.

In the case of uplink, the allocated subchannel first determines an allocation region in one dimension. That is, the decision is made as 'duration', and the subchannel is allocated to the symbol axis after the subchannel previously assigned to another PDU burst. At this time, when the end symbol of the specific subchannel region is reached, allocation continues from the next subchannel. As shown in FIG. 5, data is sequentially mapped from the subchannel of the first symbol.

Since the IEEE 802.16a standard considers non-linear wave communication in the 2-11 GHz band, the multipath fading may be severely suffered, and the ARQ protocol is introduced in the MAC layer to secure reliability. In addition, Advanced Antenna System (AAS) technology is being considered to improve cell coverage and system capacity through beamforming using multiple antennas, and to solve coexistence problems with other systems in an unlicensed band. In order to support DFS (Dynamic Frequency Selection), a procedure has been added.

In addition to the point-to-multipoint topology (PMP) structure generally considered in a broadband MAN system, the frame structure of a mesh network as shown in FIG. 6 may be selectively supported. have. In this mesh mode, access to the base station is made possible through relays of other subscribers, and the non-linear wave communication environment of the urban area, which has a radio wave area due to a large building, is considered.

The mesh mode is composed of a control subframe and a data subframe instead of using a conventional frame. The control subframe has two basic functions. In the network control subframe, a function of making and maintaining a coupling between different systems is performed, and in a schedule control frame, an equivalent scheduling function is performed before data between systems. The network descriptor after the network entry is assigned during the network control schedule control subframe, and the network descriptor indicating distributed scheduling during the schedule control subframe is generated in the control frame.

Hereinafter, a process in which the terminal performs initialization with the base station at the cell boundary will be described. First, when the UE enters into the cell, it scans starting from the most recently used downlink channel until it finds an available downlink channel and synchronizes with the base station. . Next, the UCD message is received from the base station to perform a ranging process, to adjust transmission parameters, and to obtain a basic CID and a primary CID.

After the ranging process, the base station authenticates the terminal, and the authenticated terminal registers with the base station. The mobile terminal managed by IP is assigned a secondary management CID (Secondary management CID) from the base station. Then set up the IP connection. After the IP connection, the terminal sets the current date and time. Finally, the configuration file of the terminal is downloaded from the TFTP server and a connection to a service prepared in advance is established.

As described above, the DL-MAP message defines the use allocated per burst for the downlink period in the burst mode physical layer, and the UL-MAP message defines the use of the burst allocated for the uplink period. The information element constituting the DL-MAP is determined by the downlink interval usage code (DIUC), connection ID (CID), and location information (subchannel offset, symbol offset, subchannel number, symbol number) of burst. Downlink traffic intervals are identified in. An example of the data format of DL MAP IE of Table 1 is shown.

Syntax Size Notes DL-MAP_IE () { DIUC 4 bits if (DIUC == 15) { Extended DIUC dependent IE variable See clauses following 8.4.5.3.1 } else { if (INC_CID == 1) { The DL-MAP starts with INC_CID = 0. INC_CID is toggled between 0 and 1 by the CID-SWITCH_IE () (8.4.5.3.7) N_CID 8 bits Number of CIDs assigned for this IE for (n = 0; n <N_CID; n ++) { CID 16 bits } } OFDMA  Symbol offset 8 bits Subchannel  offset 6 bits Boosting 3 bits 000: normal (not boosted); 001: +6 dB; 010: -6 dB; 011: +9 dB; 100: +3 dB; 101: -3 dB; 110: -9 dB; 111:-12 dB; No. OFDMA  Symbols 7 bits No. Subchannels 6 bits Repetition Coding Indication 2 bits 0b00-No repetition coding of 0b01-Repetition coding of 2 used 0b10-Repetition coding of 4 used 0b11-Repetition coding of 6 used } }

On the other hand, the information elements constituting the UL-MAP message is determined by the Uplink Interval Usage Code (UIUC) for each CID (Connection ID), the location of the interval is defined by the 'duration'. Here, the use of each section is determined according to the UIUC value used in the UL-MAP, and each section starts at a point separated by the 'duration' defined in the UL-MAP IE from the previous IE start point. Table 2 shows an example of the data format of the UL MAP IE.

Syntax Size Notes UL-MAP_IE () { CID 16 bits UIUC 4 bits if (UIUC == 12) { OFDMA  Symbol offset 8 bits Subchannel  offset 7 bits No. OFDMA  Symbols 7 bits No. Subchannels 7 bits Ranging Method 2 bits 0b00-Initial Ranging / Handover Ranging over two symbols 0b01-Initial Ranging / Handover Ranging over four symbols 0b10-BW Request / Periodic Ranging over one symbol 0b11-BW Request / Periodic Ranging over three symbols reserved 1 bit Shall be set to zero } else if (UIUC == 14) { CDMA_Allocation_ IE () 32 bits else if (UIUC == 15) { Extended UIUC  dependent IE variable See clauses following 8.4.5.4.3 } else { Duration 10 bits In OFDMA slots (see 8.4.3.1) Repetition coding indication 2 bits 0b00-No repetition coding of 0b01-Repetition coding of 2 used 0b10-Repetition coding of 4 used 0b11-Repetition coding of 6 used } Padding nibble, if needed 4 bits Completing to nearest byte, shall be set to 0. }

Hereinafter, a networking method using a relay station in a broadband wireless access system will be described. 7 shows an example of networking using a relay station.

In IEEE 802.16, work is being carried out to improve the frame structure of the physical layer and to add a new protocol of the MAC layer for relay networking. Its main features include a tree structure with the base station as the base point of the relayed data path, compatible with existing Point to Multi-Point (PMP) schemes, and relay and point-to-multiple schemes have the same frequency. Use bands or other adjacent frequencies. As the type of relay station, fixed, temporary nomadic and mobile relay stations are considered.

When a relay station first enters a cell of a base station, the relay station performs an initialization process, that is, an initial network entry process, like the terminal. The base station decides whether to provide services to the terminals registered to the base station through the relay station or whether the base station communicates directly. If the base station needs to communicate through the relay station, the base station determines to transmit data to the terminal through the relay station.

8 is a view for explaining the operation of the network using a relay station in accordance with IEEE 802.16. The purpose of the relay station can be summarized into two types, namely, service coverage expansion and throughput improvement of the base station. The operation of the relay station may be differently defined as shown in FIG. 8 according to each purpose.

When the relay station is used to extend service coverage of the base station as shown in relay station type 1 of FIG. 8, the relay station 34 may not only transmit and receive data between the terminal 35 and the base station 31, but also the base station 31 or the terminal. Relay all control messages from 35. When using a relay station for throughput improvement as shown in relay station type 2 of FIG. 8, the relay station 32 relays only user data exchanged between the terminal 33 and the base station 31, and controls the broadcast type of the base station 31. The terminal 33 and the base station 31 may exchange the message or the uplink control message of the terminal 33 directly. As such, the data relayed using the relay station may have a delay compared to when the terminal and the base station directly transmit and receive data, and the relay station provides a good signal quality to the terminal to which the data is relayed, and accordingly, an appropriate channel coding rate. And by using the modulation (modulation) method to relay to the terminal, the overall throughput can be increased.

Technically speaking, relay stations can be divided into two categories. The first method is an analog method in which the relay station simply amplifies the signal received at the transmitter (amplifies only the signal strength) and delivers the signal to the receiver. In this method, there is almost no delay and the relay station has only basic amplification function, which is advantageous in terms of cost efficiency, but has a disadvantage in that noise can be amplified at the amplification stage. Secondly, the digital signal is decoded, re-encoded, and transmitted to the receiver to achieve high throughput using noise reduction and higher data rate coding. There is a disadvantage that a delay may occur in the encoding process.

When communication is performed between the base station and the terminal through the relay station, an area for performing communication between the relay station and the terminal should be allocated to the frame, which is called a relay station area (or RS area). 9 is an example of a frame structure proposed for communication through a relay station. In FIG. 9, a portion indicated by 'RS DL' is a downlink relay station region, and a portion denoted by 'RS UL' is an uplink relay station region.

Data transmitted from the base station to the relay station is allocated to the downlink of the existing frame in a burst form, and data transmitted from the relay station to the terminal is allocated to the downlink relay station area. If there is data to be transmitted to the base station by the terminal, the uplink region indicated by UL-MAP of the relay station transmits through the area allocated to the terminal, and the relay station transmits the data received from the terminal to the uplink relay station Transmit to the base station through the area (RS UL).

In the downlink relay station region, RS-FCH (Frame Control Header) including length, coding information of RS DL / UL MAP, RS-preamble (RS-) for synchronization of the UE Premable) area, relay station downlink and uplink map area, and relay station downlink and uplink data burst area. The RS preamble may have a different sequence for each relay station. The map (MAP) structure of the relay station area and the burst allocation in the relay station area are determined by the base station.

In the frame structure of the conventional mobile communication system as described above, the terminal receiving the service from the base station cannot determine the exact starting position of the relay station downlink region and the relay station uplink region using only information received from the relay station, and every frame. Each time it should synchronize with the relay station through the RS preamble. For example, when the location of the relay station area is changed by the base station, the terminal may not only recognize the changed relay station area but also may incorrectly recognize the relay station area, which may cause a transmission / reception error with the base station. There is a problem.

The present invention has been made to solve the problems of the prior art as described above, an object of the present invention is to specify a relay station area designation method and a retrieval method in a mobile communication system to quickly and accurately determine the location of the relay station area in the terminal; To provide.

One feature of the present invention for achieving the above technical problem is that the base station transmits identification information specifying the location of the relay station area in at least one or more next frames to the terminal via the relay station, the terminal through the identification information Determining the location of the relay station area in the at least one next frame. Due to this technical feature, the UE does not need to synchronize with the RS-preamble to find the relay station area for every frame, and even when the relay station area is changed, it can quickly and accurately find the start position of the relay station area. Can be.

In one aspect of the present invention, a relay station area designation method in a mobile communication system according to the present invention is a communication system for performing communication between a base station and at least one or more terminals via a relay station, the base station having at least Transmitting a first message to the relay station, the first message comprising identification information designating a location of the relay station area in one or more subsequent frames, the second station including the identification information via the relay station area of the current frame; And transmitting to the at least one terminal.

In another aspect of the present invention, a method for searching for a relay station area in a mobile communication system according to the present invention is a communication system for performing communication between a base station and at least one terminal through a relay station, wherein the relay station area of the current frame is transmitted from the relay station. Receiving a message including identification information designating a location of the relay station area in at least one or more next frames through the search; and searching for a start point of the relay station area in the at least one or more next frames using the identification information; Characterized in that it comprises a step.

The construction, operation and other features of the present invention will be readily understood by the preferred embodiments of the present invention described below with reference to the accompanying drawings.

10 and 11 illustrate structures of frames transmitted and received from a base station and a relay station to a terminal according to an exemplary embodiment of the present invention, respectively.

11 shows a structure of an n-th frame transmitted and received between a base station BS and relay stations RS 1 and RS 2. In an OFDM or OFDMA communication system, a frame may be defined by a two-dimensional plane of a symbol (or time) horizontal axis and a subchannel (or frequency) vertical axis. The entire frame includes a downlink subframe (DL subframe) and an uplink subframe (UL subframe).

The base station includes identification information for designating the downlink and uplink relay station regions in the frame in a downlink map (DL-MAP) and transmits the information to the relay station and the terminal, and identifies the downlink and uplink relay station regions. The information may be included in the RS DL Zone IE and the RS UL Zone IE.

The relay station area identification information includes identification information of a start point of the relay station area. In addition, the relay station region identification information may include not only the identification information regarding the start point of the relay station region in the current frame, but also the start point of the relay station region in at least one or more next frames. In FIG. 10, the start point of the relay station area is the start point of the RS preamble. The relay station area identification information may be included in the data bursts A and B assigned to each relay station. The location of the data burst assigned to each relay station is specified by a message included in the DL-MAP region of the frame.

The base station transmits RS DL-MAP information and RS UL-MAP information to each RS. The relay station downlink and uplink map information includes a frame number (for example, the (n + 1) th frame) to which the relay station transmits data of the terminal received from the base station, and the position of RS DL / UL MAP of each relay station. FCH information including information (for example, symbol and subchannel offset value based on RS preamble), RS DL / UL MAP length, coding information, etc., and downlink for each UE in downlink and uplink relay station areas. It includes link and uplink map information. The downlink and uplink map information for each terminal includes downlink data bursts for transmitting the data to each terminal by the respective relay stations and information for allocating uplink data bursts for transmitting data to the relay stations. Include.

The base station includes downlink map (DL-MAP) area and uplink, respectively, along with downlink and uplink map information allocated to the terminal that directly communicates with the base station without the relay station downlink and uplink map information. It can be included in the link map (UL-MAP) area. Each relay station transmits the relay station downlink / uplink map information included in the downlink map area and the uplink map area to a relay station downlink map area of the downlink relay station area RS DL or an uplink relay station area RS UL. It is included in the RS DL-MAP Zone and the RS UL-MAP Zone and transmitted to the UE. Each UE is responsible for receiving data from the RS according to the RS downlink / uplink map information included in the RS DL-MAP Zone and the RS UL-MAP Zone. A downlink data burst to be received and an uplink data burst to transmit data to the relay station are allocated.

The base station may include the relay station downlink and uplink map information in a data burst allocated to each relay station and transmit the information to each relay station. That is, when there is data to be transmitted to the terminals MS 1, MS 2, and MS 3 through the relay stations RS 1 and RS 2, the base station allocates a data burst to each relay station in the downlink data burst region and assigns the data burst. The data over a burst of data. In FIG. 10, an area 'A' is allocated to RS 1 as a data burst including data to be transmitted to the MS 1 and MS 3 through RS 1, and an area 'B' is assigned to MS 2 through RS 2. Is assigned to RS 2 as a data burst containing the data to be transmitted. At this time, the data of the relay station downlink and uplink map (RS1 DL / UL-MAP, RS2 DL / UL-MAP) information to the data burst (A, B) allocated to RS 1 and RS 2 to the terminals Included with. The base station uses the DL-MAP information element (IE) in the downlink map (DL-MAP) area to indicate the location of data bursts (A, B) allocated to RS 1 and RS 2 and the number of frames to transmit data to the terminal. Assign to RS 1 and RS 2.

RS 1 and RS 2 identify the location of data bursts (A, B) assigned to them through the DL-MAP information element, and the relay station downlink and uplink map (RS1 DL / UL) included in the data burst It configures a downlink relay station area using the MAP, RS2 DL / UL-MAP) information and transmits it to the UE.

11 is a frame (n + 1) th frame in which the base station designates RS 1 to transmit data to MS 1 and MS 3, that is, a (n + 1) th frame in which RS 1 transmits to MS 1 and MS 3 The structure of the is shown. Referring to FIG. 11, RS 1 transmits RS1 DL / UL-MAP information included in a data burst A allocated from the base station to RS1 UL- of the RS downlink region. Included in the MAP region and the RS1 DL-MAP region, and transmitted to each terminal in the data burst (C, D) for each terminal (MS 1, MS 3) indicated by the relay station downlink and uplink map information Include data and send it.

The RS 1 constructs a message including the relay station region identification information received from the base station and transmits the message to the terminal through an RS1 DL-MAP region. As described above, the relay station area identification information includes not only the identification information regarding the start point of the relay station area in the current frame, but also the start point of the relay station area in at least one or more next frames. The starting point of the relay station area is the starting point of the RS-preamble.

Table 3 shows an example of a data format of a message (RS1 DL-MAP message) including identification information of a start point of a relay station preamble.

Syntax Size (bits) Notes RS1_DL-MAP_Message_Format () { Management Message Type = 2 8 PHY Synchronization Field variable See appropriate PHY specification DCD Count 8 Base Station ID 48 Current Preamble Offset 8 Next Preamble Offset 8 Begin PHY Specific Section { See applicable PHY section For (i = 1; i <= n; i ++) { For each DL-MAP element 1 to n DL-MAP_IE () variable See corresponding PHY specification } } if! (byte boundary) { Padding nibble 4 Padding to reach byte boundary. } }

In Table 3, identification information of the start point of the RS preamble is represented by a 'Current Preamble Offset' field and a 'Next Preamble Offset' field. The 'Current Preamble Offset' field means the symbol offset from the specific reference point to the start position of the current RS-Preamble, and the 'Next Preamble Offset' field is from the specific reference point to the start position of the relay station preamble in the next frame. Means symbol offset. Preferably, the specific reference point is a symbol position of a message including identification information of a start point of the RS preamble, but is not limited thereto.

Identification information of the start point of the relay station preamble can be expressed in various ways in addition to the example of Table 3. For example, the 'Current Preamble Offset' field means a symbol offset from a specific reference point to the start position of a current RS-Preamble, and the 'Next Preamble Offset' field indicates a start point of the relay station preamble in the current frame. This symbol may mean a symbol offset from the RS to the start position of the RS preamble in the next frame, and may include only the 'Next Preamble Offset' field. In addition, although the identification information may designate the start position of the relay station preamble in one next frame after the current frame, it may be possible to designate the start position of the relay station preamble in two or more next frames.

Since the terminal can easily search the start position of the relay station preamble in the next frame from the identification information, there is no need to synchronize with the relay station preamble to find the relay station area for every frame, and the position of the relay station area is variable. In this case, the starting position of the relay station area can be found quickly and accurately.

It is apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit and essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

According to the present invention, the terminal does not need to synchronize with the relay station preamble to find the relay station region for every frame, and even when the position of the relay station region is changed, it is possible to find the start position of the relay station region quickly and accurately. have.

Claims (14)

In a communication system for performing a communication between a base station and at least one terminal via a relay station (Relay Station), Sending, by the base station, a first message to the relay station, the first message comprising identification information specifying the location of the relay station area in at least one or more next frames; And Transmitting, by the relay station, a second message including the identification information to the at least one terminal through the relay station region of the current frame. The method of claim 1, And the identification information includes a start point of a relay station preamble (RS-preamble). The method of claim 2, And the identification information includes an offset value from a specific reference point to a start point of the relay station preamble of the next frame. The method of claim 2, And the identification information includes an offset value from a symbol position of the message to a start point of the relay station preamble of the next frame. The method of claim 4, wherein And the identification information further includes an offset value from a symbol position of the message to a start point of a relay station preamble of the current frame. The method of claim 2, The identification information may include an offset value from a specific reference point to the start point of the relay station preamble of the current frame and an offset value from the start point of the relay station preamble of the next frame to the relay station preamble of the current frame. How to specify the relay station area The method of claim 6, And the specific reference point is a symbol position of the message. In a communication system for performing communication between a base station and at least one terminal via a relay station, Receiving a message from the relay station via the relay station area of the current frame, the message including identification information specifying the location of the relay station area in the at least one next frame; And And searching for a starting point of a relay station area in the at least one or more next frames using the identification information. The method of claim 8, The identification information includes a start point of a relay station preamble (RS-preamble). The method of claim 9, And the identification information includes an offset value from a specific reference point to a start point of the relay station preamble of the next frame. The method of claim 9, And the identification information includes an offset value from a symbol position of the message to a start point of the relay station preamble of the next frame. The method of claim 11, The identification information further includes an offset value from a symbol position of the message to a start point of a relay station preamble of the current frame. The method of claim 9, The identification information may include an offset value from a specific reference point to the start point of the relay station preamble of the current frame and an offset value from the start point of the relay station preamble of the next frame to the relay station preamble of the current frame. How to search for the relay station area. The method of claim 13, And the specific reference point is a symbol position of the message.

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