KR20120125691A - Apparatus and method for feedback in wireless mesh system - Google Patents

Abstract

PURPOSE: An apparatus and method for feedback in a wireless mesh system are provided to reduce overheads by providing an HARQ(hybrid automatic repeat request) feedback channel for the wireless mesh system. CONSTITUTION: Data is received in a first sub frame. An HFBCH(HARQ feedback channel) is selected to transmit ACK/NACK(acknowledgement/not-acknowledgement) of the data in a second sub frame corresponding to the first sub frame. The ACK/NACK of the data is transmitted in the selected HFBCH. The HFBCH which can be transmitted from the second sub frame has a mapping relation with an LRU(logical resource unit) of the first sub frame. The first sub frame and the second sub frame are included in a frame which can transmit scheduling information and the data.

Description

Feedback method and apparatus for wireless mesh system {APPARATUS AND METHOD FOR FEEDBACK IN WIRELESS MESH SYSTEM}

The present invention relates to wireless communication, and more particularly, to a feedback method and apparatus for a wireless mesh system.

In a typical wireless communication system, time-varying channels and dynamic interference of adjacent communication devices (nodes) occur. Therefore, there is a probability that the data transmitted from one node fails to receive at another node. In preparation for data reception failure, the wireless communication system provides a hybrid automatic repeat request (HARQ). HARQ feeds back to the transmitting node whether the receiving node has successfully received the data. If the receiving node feeds back the receiving failure, the transmitting node retransmits the previously transmitted data or transmits data consisting of additional codewords for the data. The receiving node receives the data to be retransmitted or data consisting of additional codewords to increase the probability of successful reception of the original data.

For such HARQ, the receiving node needs feedback to inform the transmitting node whether the reception is successful. A channel through which feedback is transmitted is called a feedback channel. In the related art, a HARQ feedback dedicated channel is assigned and assigned within a frame in order to reduce a delay time caused by the feedback channel assignment. The cellular system is composed of a base station and a terminal that performs centralized control. In such an environment, HARQ feedback channels of nodes, that is, nodes connected to the control node, such as a base station, can be easily allocated.

However, in a distributed communication environment, a procedure for channel allocation of a transmit / receive node pair may be required to prevent transmission / reception conflicts between neighboring nodes, which may cause overhead. Distributed communication environments are, for example, wireless mesh systems. A wireless mesh system refers to a communication network composed of wireless nodes organized in a mesh topology.

In this distributed communication environment, since the transmission and reception time points of the nodes are not distinguished on the frame, HARQ feedback channels are required as many times as the transmission and reception switching intervals. However, when a procedure such as exchanging information for channel allocation is required between transmitting and receiving nodes as in the conventional method, overhead may occur, and a plurality of HARQ feedback channels themselves may act as a fixed ratio of a large ratio.

There is a need for a method and apparatus for HARQ feedback in a wireless mesh system.

An object and method of HARQ feedback for a wireless mesh system is provided.

A feedback method in a node of a wireless mesh system according to an aspect of the present invention includes receiving data in a first subframe; Selecting a HARQ feedback channel (HFBCH) to transmit acknowledgment / not-acknowledgement (ACK / NACK) for the data in a second subframe corresponding to the first subframe; And

And transmitting ACK / NACK for the data in the selected HFBCH, wherein the HFBCH that can be transmitted in the second subframe has a mapping relationship with a logical resource unit (LRU) of the first subframe. It is done.

The first subframe and the second subframe may be included in a scheduling and data frame (SDF) capable of transmitting scheduling information and data.

When the data is received through an LRU burst composed of a plurality of LRUs, the HFBCH to transmit the ACK / NACK may be selected as the HFBCH mapped to the LRU having the smallest index in the LRU burst.

When the data is received through an LRU burst composed of a plurality of LRUs, the HFBCH to transmit the ACK / NACK has the highest signal to interference plus noise ratio (SINR) among the HFBCHs mapped to each of the LRUs included in the LRU burst. HFBCH may be selected.

The second subframe may be an HFBCH subframe including one orthogonal frequency division muliplexing (OFDM) symbol in the time domain.

The second subframe includes a plurality of HFBCH mini tiles (HMTs) including eight subcarriers, and each of the HMTs includes a sampled physical subcarrier (SPS) in which one of a predetermined number of physical subcarriers is selected. It may contain eight.

A plurality of HMTs included in the second subframe may be grouped by two, and a plurality of HFBCHs may be transmitted in each grouped two HMTs.

The same orthogonal code sequence may be applied to each of the two grouped HMTs.

The first subframe may be located in a first frame, and the second subframe may be located in a second frame that exists after the first frame.

The first subframe may be any one of a plurality of data subframes separated by a switching gap SG.

The first subframe may consist of two consecutive data subframes among a plurality of data subframes, and a switching gap may not exist between the two data subframes.

When the first subframe is an Nth data subframe divided by a switching gap within a first frame SDF capable of transmitting scheduling information and data, the second subframe is contiguous in time with the first frame. It may be the N-th HFBCH subframe separated by the switching gap in the second frame.

The first subframe may include 6 OFDM symbols or 7 OFDM symbols in the time domain.

After the subcarrier mapping is performed, the HFBCH to transmit the ACK / NACK may be inverse fast Fourier transform (IFFT), and in the HFBCH to transmit the ACK / NACK, only one signal of the time domain generated after the IFFT is repeated Can be sent.

Feedback device in a wireless mesh system according to another aspect of the present invention includes an RF unit for transmitting and receiving a radio signal; And a processor coupled to the RF unit, the processor receiving data in a first subframe and acknowledgment / not-ACK for the data in a second subframe corresponding to the first subframe. Select a HARQ Feedback channel (HFBCH) to transmit an acknowledgment, and transmit ACK / NACK for the data in the selected HFBCH, the HFBCH that can be transmitted in the second subframe is the LRU (logical) of the first subframe resource unit) and a mapping relationship.

It provides an HRQ feedback channel for a wireless mesh system and can transmit ACK / NACK while reducing overhead by using the HARQ feedback channel.

1 shows an example of a wireless mesh system.
2 shows an example of a frame structure used in a wireless mesh system.
3 shows an example of a scheduling and data frame (SDF) structure.
4 shows another example of an SDF structure.
5 shows an example of an SDF including a HARQ feedback channel subframe according to an embodiment of the present invention.
6 shows another example of an SDF including an HFBCH subframe.
7 shows the structure of an HFBCH subframe.
8 shows a method of feeding back a HARQ ACK / NACK.
9 shows the characteristics of the frequency domain and the time domain with respect to the signal transmitted in the HFBCH.
10 shows a process of transmitting an HFBCH.
11 shows the structure of a node in a wireless mesh system.

1 shows an example of a wireless mesh system.

The wireless mesh system 100 may include nodes 104A to 102G and a network 104 that serve to provide services to one or more terminals (not shown). Each node may be used to form a wireless link between the network 104 and the terminal. In general, the wireless mesh system 100 enables low-cost and efficient expansion of service area and capacity for high-speed networks 104 such as WLAN and WiBro, and multi-hop with the function of setting up and restoring a wireless link. hop) Refers to a relay system.

There are a variety of wireless technologies that can be used to support the wireless mesh system 100. For example, code division multiple access (CDMA), orthogonal frequency division multiplexing / time division multiplexing (OFDM / TDM), orthogonal frequency division multiple access (OFDMA), time division multiple access (TDMA), frequency division multiple access (FDMA) Or combinations thereof. In the following, it is assumed that the wireless mesh system uses OFDMA.

2 shows an example of a frame structure used in a wireless mesh system.

Referring to FIG. 2, each of the super frames SU (Superframe, SU0, SU1, ..., SU (N + 1)) includes four frames (frame, F0, F1, F2, F3). Each frame in the superframe may have the same length. As an example, the (time) length of the superframe may be 20 ms, and the length of each frame may be 5 ms. However, this is only an example and is not limited thereto. The length of the superframe, the number of frames included in the superframe, the number of subframes included in the frame, and the like may be variously changed. A subframe is used as a sub-unit of a frame and includes at least one OFDMA symbol, and a subframe does not have to be composed of a plurality of OFDMA symbols. The number of subframes included in the frame may be variously changed according to a channel bandwidth and a length of a cyclic prefix (CP).

The superframe may include a network control frame (NCF, F0) and a scheduling and data frame (SDF, F1, F2, F3). The network control frame (NCF) is a frame for transmitting network information or broadcast information of each node, and the scheduling and data frame (SDF) is a frame for transmitting scheduling information and data in a distributed manner.

Since data bursts related to network control transmitted from NCF and scheduling information transmitted from SDF, that is, scheduling related data bursts are broadcast messages, do not perform hybrid automatic repeat request (HARQ) between a receiving node and a transmitting node. On the other hand, data bursts for traffic (eg, user data) transmitted in the SDF perform HARQ.

HARQ feeds back to the transmitting node whether the receiving node has successfully received the data burst, and if the receiving node feeds back the receiving failure, the transmitting node retransmits the previously transmitted data burst or transmits data consisting of additional codewords for the data burst. Means that.

3 shows an example of a scheduling and data frame (SDF) structure.

Referring to FIG. 3, the SDF includes a distributed scheduling subframe (hereinafter referred to as DSCH SF) for transmitting scheduling information and a data subframe (hereinafter referred to as DATA SF) for transmitting traffic data. 3 illustrates a case in which the SDF includes one DSCH SF and four DATA SFs. Each of the DSCH SF and the DATA SF may include a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain. For example, the DSCH SF may include 7 OFDM symbols and the DATA SF may include 6 or 7 OFDM symbols.

The subframe consists of at least one Physical Resource Unit (PRU) in the time and frequency domain. A PRU is defined as a basic physical unit for resource allocation that includes a plurality of consecutive OFDM symbols in the time domain and a plurality of consecutive subcarriers in the frequency domain. The number of OFDM symbols included in the PRU may be equal to the number of OFDM symbols included in one subframe. For example, when one subframe consists of 6 OFDM symbols, the PRU may be defined with 6 OFDM symbols and 18 subcarriers.

Logical Resource Units (LRUs) are basic logical units for distributed resource allocation and localized resource allocation. The LRU is defined by a plurality of OFDM symbols and a plurality of subcarriers and includes pilots used in a PRU. Thus, the appropriate number of subcarriers in one LRU depends on the number of pilots assigned. LRU may be used for data transmission.

Each subframe may be used for transmission or reception. When transmitting in one subframe of two consecutive subframes and receiving in another subframe, or when receiving in one subframe and transmitting in another subframe, and Transmission and reception switching may occur as well. When transmission and reception switching occurs, some idle period (or guard time) is required. This idle period can be used as the time required for switching, such as the stabilization period of the power amplifier. The rest period is hereinafter referred to as a switching gap (SG). One switching gap may be set to 1 OFDM symbol or less.

The SDF may include a switching gap between all subframes to enable transmission and reception switching in each subframe.

4 shows another example of an SDF structure.

4 includes one DSCH SF and four DATA SFs as in FIG. 3. However, in order to reduce the overhead caused by the switching gap, there is a difference in placing the switching gap every two data SFs. Such an SDF structure can reduce resource diversity and increase resource allocation delay time by reducing the diversity of transmission / reception opportunities in a frame, but has an advantage of reducing overhead caused by a switching gap.

3 and 4 are merely examples, and the allocation ratios of the DSCH SF and the DATA SF may be variably changed by network attributes.

5 shows an example of an SDF including a HARQ feedback channel subframe according to an embodiment of the present invention.

Referring to FIG. 5, the SDF further includes a plurality of HARQ FeedBack CHannel (HFBCH) subframes (SF) in the structure illustrated in FIG. 3. Although FIG. 5 shows one SDF for convenience, a plurality of such SDFs may exist in succession in time. The HFBCH subframe (HFBCH SF) may transmit ACK / NACK (acknowledgement / not-acknowledgement) for traffic data transmitted by each DATA SF included in the previous SDF. The number of HFBCH subframes included in the SDF may be determined according to the number of switching gaps included in the corresponding SDF (i.e., including DATA SFs transmitting data targeted for ACK / NACK), in particular with respect to the DATA SF. Can be. This means that the number of HFBCH subframes is determined according to the number of DATA SFs transmitting traffic data targeted for ACK / NACK. For example, if the SDFs shown in FIG. 5 are continuous, four DATA SFs separated by four switching gaps may be transmitted, and thus four HFBCH subframes may be included in the SDF.

When multiple nodes simultaneously transmit ACK / NACK, a plurality of HFBCH subframes may exist to prevent ACK / NACK transmission / reception failures from the receiving node due to overlapping transmission / reception timings (that is, collisions). The switching gap SG is added between the frames. One HFBCH subframe may have a length of time corresponding to one effective OFDM symbol period. The effective OFDM symbol interval may have a time length of 1 / P _sampling times of a general OFDM symbol included in a DSCH SF or a DATA SF. This will be described later in detail.

6 shows another example of an SDF including an HFBCH subframe.

Referring to FIG. 6, the SDF further includes a plurality of HFBCH subframes in the structure illustrated in FIG. 4. In FIG. 6, only one SDF is illustrated for convenience, but such SDFs are continuously present in the time domain. Compared to FIG. 5, the difference is that there is no switching gap SG between DATA SF0 and DATA SF1, and there is no switching gap between DATA SF2 and DATA SF3. That is, two data SFs for transmitting traffic data targeted for ACK / NACK are configured in units of two. In terms of the transmission and reception switching of the traffic data transmission, it can be seen that the traffic data targeted for ACK / NACK is divided and transmitted by the two switching gaps 61 and 62. Accordingly, under the SDF structure illustrated in FIG. 6, two HFBCH subframes 63 and 64 exist, and each HFBCH subframe is divided by a switching gap.

7 shows the structure of an HFBCH subframe.

Referring to FIG. 7, the HFBCH subframe includes one OFDM symbol in the time domain and includes a plurality of physical subcarriers (hereinafter, PS) except for guard subcarriers and DC subcarriers used as guard regions in the frequency domain. ) May be included. For example, one HFBCH subframe may include N _used PS.

The subcarriers are selected according to the sampling factor P _sampling in the plurality of PSs. Here, Psampling may be a divisor of the size of a fast fourier transform (FFT) or inverse FFT (IFFT) applied to the selected subcarriers. That is, one PS of every PS may be selected. For example, if the sampling factor is 4, the first subcarrier of every four PSs can be selected. The selected subcarrier is called a sampled physical subcarrier (hereinafter referred to as SPS). Referring to FIG. 7, for example, PS (0) corresponds to SPS (0), and PS (4) corresponds to SPS (1).

The HFBCH Mini Tile (HMT) includes eight SPSs. HMTs are permutated on the frequency axis. Permuted HMT is defined as Permuted HMT (hereinafter referred to as PHMT). Two HMTs (PHMTs) form one HFBCH group (hereinafter referred to as HFG). For example, in FIG. 7, PHMT (0,0) and PHMT (0,1) form one HFG. Similarly, PHMT (1,0) and PHMT (1,1) form another HFG. PHMTs are logically continuous but physically distributed on the frequency axis.

The same orthogonal code sequence is applied to each PHMT included in one HFG to obtain a repetition gain. In FIG. 7, orthogonal code sequences are illustrated as C ₀ to C ₇ .

Hereinafter, the process described with reference to FIG. 7 will be described through equations. First, we define some parameters.

N _HMTperHFG represents the number of _HMTs included in one HFG.

N _HFBCHperHFG represents the number of HFBCHs allocated to one HFG. In the example of FIG. 7, N _HMTperHFG is 2 and N _HFBCHperHFG is 4.

L _seq means the length of an orthogonal code sequence applied to PHMT. In the example of FIG. 7, L _seq is 8.

P _sampling is a sampling factor indicating how many physical subcarriers are sampled among the remaining physical subcarriers (N _used subcarriers) except for the guard subcarrier and the DC subcarrier.

Then, in FIG. 7, the HMT corresponding to the m th PHMT of the k th HFBCH included in the HFBCH SF may be defined as follows.

[Formula 1]

An orthogonal code sequence having a length of L _seq is applied to two PHMTs included in one HFG so that a plurality of HFBCHs may be code division multiplexed (CDM). Orthogonal code sequence may vary depending on the number of HFBCH CDM in one HFG.

The following table shows examples of orthogonal code sequences.

[Table 1]

In Table 1, for example, when four HFBCHs are CDM, ACK / NACK for each of the four HFBCH can be distinguished and transmitted by a total of eight orthogonal code sequences.

The physical subcarrier to which the orthogonal code sequence of each HMT is mapped may be defined as follows.

[Formula 2]

In Equation 2, SPS means subcarriers sampled for every P _sampling physical subcarriers and can be defined as Equation 3 below.

[Equation 3]

In Equation 3, PS means a physical subcarrier excluding a guard subcarrier and a DC subcarrier, and PS, not an SPS, is a null subcarrier in which no data is carried.

Hereinafter, a method and apparatus for feeding back HARQ ACK / NACK using the above-described structure of HFBCH SF will be described.

8 shows a method of feeding back a HARQ ACK / NACK.

Referring to FIG. 8, the receiving node receives data in a first subframe (S110). The first subframe may be any one of the above-described SDF, that is, a plurality of DATA SFs included in the scheduling and data frame, and may be included in the first frame. The data may be traffic data requiring feedback of ACK / NACK. At this time, the data may be transmitted through the LRU of the DATA SF.

The receiving node selects an HFBCH to transmit ACK / NACK in a second subframe corresponding to the first subframe (S120). The second subframe may be the above-described HFBCH subframe, and the second subframe may be included in a next frame of the first frame, that is, a second frame located after the first frame in the time domain. Since the receiving node takes a predetermined time to decode the received data, the second subframe for transmitting the ACK / NACK should be positioned at a predetermined time interval. Therefore, the second subframe may be located in the second frame. Alternatively, the second subframe may be located in the first frame when the predetermined time required for the decoding is satisfied, or in the second frame.

The second subframe corresponding to the first subframe may correspond to the order of the first subframe and the order of the second subframe in the SDF. For example, referring to FIG. 5, when the first subframe is the first data subframe DATA SF0 of the first frame, the second subframe transmitting ACK / NACK is the first HFBCH subframe of the second frame. Can be. In the HFBCH subframe, a plurality of HFBCHs may be transmitted. The receiving node selects an HFBCH to transmit ACK / NACK for the data.

In this case, the LRU of the first subframe has an implicit mapping relationship of 1: 1 with the HFBCH of the second subframe. That is, there may be a predetermined mapping relationship between the LRU of the first subframe in which the receiving node receives data and the HFBCH in which the receiving node may transmit ACK / NACK. This mapping relationship may be known in advance by the receiving node and the transmitting node which has transmitted the data.

For example, index i of the LRU of the first subframe and index k of the HFBCH that can be transmitted in the second subframe may have a mapping relationship as shown in the following equation.

[Formula 4]

In the above formula, N _HFBCH is the number of HFBCHs that can be transmitted in the second subframe, and N _LRU is the number of _LRUs in the first subframe. For all bandwidths, there may be extra HFBCHs that are not allocated because N _HFBCH is larger than N _LRU .

As a method of selecting an HFBCH to which the receiving node transmits ACK / NACK, one of the following two methods may be selected. 1) When the receiving node receives data through an LRU burst composed of a plurality of LRUs, the receiving node may select an HFBCH corresponding to the smallest LRU index in the LRU burst to transmit ACK / NACK. For example, the receiving node may receive the first data in LRU bursts from LRU index 11 to LRU index 15 of the first DATA SF, and receive the second data in LRU bursts from LRU index 14 to LRU index 15 of the second DATA SF. Can be. At this time, the receiving node transmits ACK / NACK for the first data through the HFBCH corresponding to LRU index 11 in the first HFBCH SF corresponding to the first DATA SF. In addition, the receiving node transmits an ACK / NACK for the second data through the HFBCH corresponding to LRU index 14 in the second HFBCH SF corresponding to the second DATA SF.

2) ACK / NACK may be transmitted by selecting an HFBCH having the highest signal to interference plus noise ratio (SINR) among a plurality of HFBCHs corresponding to the LRU burst. The interference considered in the SINR may be interference due to time and frequency synchronization errors from other nodes. The receiving node may transmit information on the selected HFBCH to the node that will receive the ACK / NACK. For example, when data is received through LRU bursts from LRU index 11 to LRU index 14 in the first DATA SF, there is an HFBCH mapped to each LRU. Among them, one HFBCH having the highest SINR is selected and selected. Through ACK / NACK is to be transmitted. In this case, the receiving node may transmit information on one HFBCH having the highest SINR, for example, the index of the HFBCH to a node to receive the ACK / NACK first, and then transmit the ACK / NACK through the corresponding HFBCH.

The receiving node transmits ACK / NACK for data received on the selected HFBCH (S130).

9 shows the characteristics of the frequency domain and the time domain with respect to the signal transmitted in the HFBCH.

Referring to FIG. 9, the HFBCH is eventually allocated and transmitted to a plurality of SPSs, and each SPS is selected from one of the P factor _sampling physical subcarriers. Inverse fast Fourier transform (IFFT) of a set of signals spaced at regular intervals in the frequency domain results in a repetitive signal in the time domain.

The following equation shows the OFDMA modulation equation after IFFT.

[Equation 5]

In Equation 5, t means the elapsed time from the start of the OFDMA symbol, 0 <t <T _S. s (t) means a signal in the time domain. c _k is a complex number and means a data symbol transmitted on a subcarrier having a frequency offset index k in the OFDMA symbol, and Tg is a guard time or CP interval time. fc is the radio carrier frequency.

When transmitting ACK / NACK on the HFBCH, only a signal for any one of the signal sections repeated in the time domain may be transmitted. Therefore, one OFDM symbol for transmitting the HFBCH is reduced by 1 / P _sampling compared to the OFDM symbol in the DATA SF. That is, the effective OFDM symbol interval of the HFBCH subframe is reduced by 1 / P _sampling compared to the OFDM symbol in the DATA SF.

The node receiving the HFBCH receive only a section of a repetitive signal, so you can copy the back rest of symbol periods, remove the CP by P _sampling dog by taking the rear FFT (Fast Fourier Transform) is configured of the original OFDM symbol for every P _sampling subcarriers Data symbols can be obtained. All nodes must have the same P _sampling value and the same starting subcarrier for allocating data symbols can also satisfy the above property for signals multiplexed from multiple nodes.

10 shows a process of transmitting an HFBCH.

Referring to FIG. 10, a receiving node that receives data performs subcarrier mapping to transmit ACK / NACK on the HFBCH (S210). That is, in order to transmit ACK / NACK using the HFBCH structure as described above, the SPS is selected among physical subcarriers according to a sampling factor.

After performing the IFFT (S220), the receiving node selects and transmits only one signal among a plurality of signals repeated in the signal in the time domain (S230).

11 shows the structure of a node in a wireless mesh system.

Referring to FIG. 11, a node includes a processor 910 and an RF unit 920.

Processor 910 implements the proposed functionality, process and / or method. For example, the processor 910 receives data from another node, performs decoding, and transmits an ACK / NACK for the data. At this time, ACK / NACK can be transmitted using the above-described HFBCH structure. The RF unit 920 is connected to the processor 910 to transmit and / or receive a radio signal. Although not shown in FIG. 11, a node may include a memory, and the memory may be connected to the processor 910 to store various information for driving the processor 910. The node may include an antenna 990, and there may be one or a plurality of antennas 990. The antenna 990 may be included in the RF unit 920.

Method according to an embodiment of the present invention is implemented in the form of program instructions that can be executed by various computer means may be recorded on a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

Claims (16)

In a feedback method in a node of a wireless mesh system,
Receiving data in a first subframe;
Selecting a HARQ feedback channel (HFBCH) to transmit acknowledgment / not-acknowledgement (ACK / NACK) for the data in a second subframe corresponding to the first subframe; And
Transmitting ACK / NACK for the data on the selected HFBCH;
The HFBCH that can be transmitted in the second subframe has a mapping relationship with a logical resource unit (LRU) of the first subframe. The method of claim 1, wherein the first subframe and the second subframe are included in a scheduling and data frame (SDF) capable of transmitting scheduling information and data. The HFBCH for transmitting the ACK / NACK is selected as the HFBCH mapped to the LRU having the smallest index in the LRU burst when the data is received through an LRU burst composed of a plurality of LRUs. Feedback method of the wireless mesh system. The HFBCH for transmitting the ACK / NACK is a signal to interference plus among HFBCHs mapped to each of the LRUs included in the LRU burst when the data is received through an LRU burst composed of a plurality of LRUs. A feedback method of a wireless mesh system, wherein the HFBCH having the highest noise ratio is selected. The feedback method of claim 1, wherein the second subframe is an HFBCH subframe including one orthogonal frequency division muliplexing (OFDM) symbol in a time domain. 6. The method of claim 5, wherein the second subframe includes a plurality of HFBCH mini tiles (HFBCH mini tiles, HMTs) including eight subcarriers, and each of the HMTs includes a sampled physical subcarrier in which one of a predetermined number of physical subcarriers is selected. A feedback method of a wireless mesh system, characterized in that it comprises eight sampled physical subcarriers (SPS). The method of claim 6, wherein the plurality of HMTs included in the second subframe are grouped by two, and a plurality of HFBCHs are transmitted in each of the two grouped HMTs. 8. The method of claim 7, wherein the same orthogonal code sequence is applied to each of the two grouped HMTs. The method of claim 1, wherein the first subframe is located in a first frame, and the second subframe is located in a second frame that exists after the first frame. The method of claim 1, wherein the first subframe is any one of a plurality of data subframes separated by a switching gap (SG). The wireless mesh system of claim 1, wherein the first subframe consists of two consecutive data subframes among a plurality of data subframes, and a switching gap does not exist between the two data subframes. Feedback method. The method of claim 1, wherein when the first subframe is an N-th data subframe divided by a switching gap within a first frame SDF through which scheduling information and data can be transmitted, the second subframe includes the first subframe. And a N-th HFBCH subframe divided by a switching gap in a second frame temporally continuous to one frame. 2. The method of claim 1, wherein the first subframe includes 6 OFDM symbols or 7 OFDM symbols in the time domain. The feedback method of claim 1, wherein the HFBCH to transmit the ACK / NACK is inverse fast Fourier transform (IFFT) after subcarrier mapping is performed. 15. The method of claim 14, wherein only one repetitive signal of a time domain signal generated after the IFFT is transmitted in the HFBCH to transmit the ACK / NACK. An RF unit for transmitting and receiving a radio signal; And
A processor connected to the RF unit, wherein the processor
Receiving a data in a first subframe, selecting a HARQ feedback channel (HFBCH) to transmit an acknowledgment / not-acknowledgement (ACK / NACK) for the data in a second subframe corresponding to the first subframe, and The ACK / NACK for the data is transmitted in the selected HFBCH, but the HFBCH that can be transmitted in the second subframe has a mapping relationship with a logical resource unit (LRU) of the first subframe. Feedback device.

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