KR20090116604A - Method for transmitting synchronization signal - Google Patents

Abstract

In a wireless communication system, a method of transmitting a synchronization signal includes transmitting a first synchronization signal through a first synchronization channel including a plurality of subcarriers in a frequency domain and at least one OFDM symbol in a time domain; And transmitting a second synchronization signal through a second synchronization channel having the same structure, wherein the first synchronization signal and the second synchronization signal are mapped to subcarriers having different indices, and the first synchronization signal includes a plurality of synchronization signals. The second synchronization signal is transmitted in a period of a superframe size including a frame and the second synchronization signal is transmitted in a multiple period of a frame size. By transmitting the synchronization signal through the synchronization channel having a shorter period than the superframe header, the delay in the initial access or handover process of the terminal can be reduced. Various synchronization signals can be obtained without increasing complexity, and additional information can be obtained using various synchronization signals.

Description

Method for transmitting synchronization signal in wireless communication system

The present invention relates to wireless communication, and more particularly, to a method for transmitting a synchronization signal through a superframe.

The Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard provides technologies and protocols to support broadband wireless access. Standardization has been in progress since 1999, and IEEE 802.16-2001 was approved in 2001. This is based on a single carrier physical layer called 'WirelssMAN-SC'. Later, in the IEEE 802.16a standard approved in 2003, 'WirelssMAN-OFDM' and 'WirelssMAN-OFDMA' were added to the physical layer in addition to 'WirelssMAN-SC'. After the completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. In order to correct bugs and errors in the IEEE 802.16-2004 standard, IEEE 802.16-2004 / Cor1 (hereinafter referred to as IEEE 802.16e) was completed in 2005 in the form of 'corrigendum'.

The communication between the base station and the terminal consists of downlink (DL) transmission from the base station to the terminal and uplink (UL) transmission from the terminal to the base station. The conventional IEEE 802.16e based system profile supports a time division duplex (TDD) scheme in which downlink transmission and uplink transmission are divided into time domains. The TDD scheme is a scheme in which uplink transmission and downlink transmission are performed at different times while using the same frequency band. The TDD scheme has an advantage of easy frequency selective scheduling because the uplink channel characteristic and the downlink channel characteristic are reciprocal.

Currently, standardization of IEEE 802.16m, which is a new technical standard standard, is progressing based on IEEE 802.16e. In IEEE 802.16m, not only the TDD scheme but also the frequency division duplex (FDD) scheme are considered. In the FDD scheme, downlink transmission and uplink transmission are simultaneously performed through different frequency bands. In IEEE 802.16e, a 5 ms frame of a TDD scheme is used, whereas in IEEE 802.16m, a 20 ms super-frame for a TDD scheme and an FDD scheme is considered. In IEEE 802.16e, since a preamble is transmitted every frame, the UE can acquire a synchronization signal at 5 ms intervals. The synchronization signal is a signal for synchronizing with the base station during initial access or handover of the terminal, and system performance may vary according to a transmission period of the synchronization signal.

In the superframe structure, it is not clearly suggested how to transmit a synchronization signal.

An object of the present invention is to provide a method for efficiently transmitting a synchronization signal through a superframe.

In a wireless communication system according to an aspect of the present invention, the method for transmitting a synchronization signal includes transmitting a first synchronization signal through a first synchronization channel including a plurality of subcarriers in a frequency domain and at least one OFDM symbol in a time domain. And transmitting a second synchronization signal through a second synchronization channel having the same structure as the first synchronization channel, wherein the first synchronization signal and the second synchronization signal are mapped to subcarriers having different indices. The first synchronization signal is transmitted in a period of a superframe size including a plurality of frames, and the second synchronization signal is transmitted in a multiple period of the frame size.

In a wireless communication system according to another aspect of the present invention, a method for receiving a synchronization signal through a superframe including a plurality of frames includes receiving a first synchronization signal through a first synchronization channel and transmitting the first synchronization signal. And receiving a second synchronization signal transmitted through a second synchronization channel at a multiple interval of a frame size, wherein the first synchronization channel and the second synchronization channel have the same structure, and the first synchronization signal and the first synchronization channel have the same structure. The two synchronization signals are transmitted in different waveforms.

By transmitting the synchronization signal through the synchronization channel having a shorter period than the superframe header, the delay in the initial access or handover process of the terminal can be reduced, and since the synchronization signal is transmitted through the synchronization channel of the same structure, the terminal uses the same algorithm. Various synchronization signals can be obtained without increasing complexity, and additional information can be obtained using various synchronization signals.

1 is a block diagram illustrating a wireless communication system. Wireless communication systems are widely deployed to provide various communication services such as voice and packet data.

Referring to FIG. 1, a wireless communication system includes a user equipment (UE) 10 and a base station 20 (BS). The terminal 10 may be fixed or mobile and may be called by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), and a wireless device. The base station 20 generally refers to a fixed station that communicates with the terminal 10, and in other terms, such as a Node-B, a Base Transceiver System, or an Access Point. Can be called. One or more cells may exist in one base station 20.

Hereinafter, downlink (DL) means transmission from the base station 20 to the terminal 10, and uplink (UL) means transmission from the terminal 10 to the base station 20. In downlink, the transmitter may be part of the base station 20 and the receiver may be part of the terminal 10. In uplink, the transmitter may be part of the terminal 10 and the receiver may be part of the base station 20.

There is no limitation on the multiple access scheme applied to the wireless communication system. Various multiple access techniques such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Single-Carrier FDMA (SC-FDMA), and Orthogonal Frequency Division Multiple Access (OFDMA) are available. Can be.

An orthogonal frequency division multiplexing (OFDM) system uses orthogonality between an inverse fast fourier transform (IFFT) and a fast fourier transform (FFT). The transmitter performs IFFT to transmit data. The receiver recovers original data by performing FFT on the received signal. The transmitter uses an IFFT to combine multiple subcarriers, and the receiver uses an FFT corresponding to the IFFT to separate multiple subcarriers. Hereinafter, it is assumed that the wireless communication system is an OFDM / OFDMA system.

2 illustrates a superframe structure.

Referring to FIG. 2, a super-frame SU includes a plurality of frames F and a frame includes a plurality of sub-frames SF.

Each superframe includes a super-frame header. The superframe header includes system information and resource allocation information in the superframe. The synchronization signal may be transmitted through the superframe header. The synchronization signal is a downlink signal for the terminal to synchronize with the base station. The terminal may acquire a cell ID by synchronizing with the base station during an initial access or handover process through a synchronization signal. The synchronization signal may be called a preamble. Superframe may be defined as the transmission period of the superframe header. The superframe header may be transmitted at 20 ms intervals, and a 20 ms superframe may be defined. A 20ms superframe may include four 5ms frames.

The frame may include a downlink frame in which downlink data is transmitted and an uplink frame in which uplink data is transmitted. The downlink frame and the uplink frame may be allocated in a TDD method or an FDD method. The TDD scheme is a scheme in which uplink transmission and downlink transmission are performed at different times while using the same frequency band. In the FDD scheme, downlink transmission and uplink transmission are simultaneously performed through different frequency bands.

One frame may include eight subframes. The subframe may be a basic unit for resource allocation. The subframe includes a plurality of OFDM symbols. The number of OFDM symbols included in the subframe may vary depending on the length of a cyclic prefix (CP). For example, when the CP length is 1/8 of the OFDM symbol time Tu, six OFDM symbols are included in a subframe, and the frame may include 48 OFDM symbols.

Table 1 shows an example of frame parameters.

Transmission Bandwidth (MHz) 5 10 20 Over-sampling factor 28/25 Sampling Frequency (MHz) 5.6 11.2 22.4 FFT Size 512 1024 2048 Sub-carrier Spacing (kHz) 10.94 OFDM symbol time, Tu (us) 91.4 Cyclic Prefix (CP) Ts (us) OFDM symbols per Frame Idle time (us) Tg = 1/4 Tu 91.4 + 22.85 = 114.25 43 87.25 Tg = 1/8 Tu 91.4 + 11.42 = 102.82 48 64.64 Tg = 1/16 Tu 91.4 + 5.71 = 97.11 51 47.39 Tg = 1/32 Tu 91.4 + 2.86 = 94.26 53 4.22

The frame parameter may be variously changed, and accordingly, the number of subframes included in the frame, the number of OFDM symbols included in the subframe, and the like may vary. Even if the frame parameters are different, the proposed synchronization signal transmission method can be applied in the same manner.

3 illustrates an example of a process of performing handover through a TDD superframe.

Referring to FIG. 3, a 20ms superframe includes four 5ms frames, and one frame includes a downlink frame (DL) and an uplink frame (UL) in a TDD scheme, and the first frame of the superframe includes a superframe. Suppose a frame header is allocated. A preamble is transmitted through the superframe header.

The terminal receives a handover command message from the base station through a downlink frame (S110). In this case, it is assumed that the handover command message is transmitted through a downlink frame adjacent to the first superframe header.

After receiving the handover command message, the terminal stops transmitting and receiving data with the base station and starts searching for the preamble (S120). The terminal finds a preamble transmitted from the target base station in order to synchronize time synchronization and frequency synchronization with the target base station. A base station providing a wireless communication service to a terminal is called a serving base station, and a base station targeted for handover is called a target base station. Assuming that the periods of the preamble transmitted from the serving base station and the target base station are the same, the terminal should perform a preamble search for approximately 20 ms to receive the preamble transmitted from the target base station.

The terminal acquires a preamble of the target base station through the second superframe header (S130). The terminal may synchronize time synchronization and frequency synchronization with the target base station using the preamble. The UE can know the cell ID of the target base station through the preamble. The terminal may acquire the uplink parameter and the downlink parameter of the target base station through the system information transmitted through the superframe header.

The terminal starts a ranging process with respect to the target base station (S140). The ranging process is generally a process in which a terminal transmits a ranging request message to a base station and receives a ranging response message in response thereto. The terminal may transmit the ranging request message to the target base station through an uplink frame following the second superframe header.

The terminal may receive the ranging response message through a downlink frame following the uplink frame in which the ranging request message is transmitted (S150). After receiving the ranging response message, the terminal can transmit / receive data to be actually transmitted with the target base station.

The terminal transmits and receives data through an uplink frame or a downlink frame after the downlink frame in which the ranging response message is transmitted (S160). After the terminal receives the handover command message, it takes approximately 30ms to connect to the target base station and transmit and receive actual data. The time it takes for data transmission and reception with the target base station to start after the terminal stops transmitting and receiving data with the serving base station in the handover process, that is, the time when data communication is interrupted due to handover, is called a handover interruption time. do. If a delay occurs in any one of the steps during the handover process, the handover interruption interval may be 30 ms or more. As described above, when the preamble is transmitted through the superframe header having a 20 ms interval, the handover interference interval may be very long, and thus communication quality may be deteriorated.

Hereinafter, a synchronization signal transmission method capable of reducing the handover interference interval and improving system performance will be described.

4 illustrates a synchronization signal transmission method through a superframe according to an embodiment of the present invention. 5 is a diagram illustrating a synchronization signal transmission method through a superframe according to another embodiment of the present invention.

4 and 5, a first sync signal and a second sync signal are transmitted through a superframe. An area in which the first synchronization signal is transmitted on the superframe is called a first synchronization channel, and an area in which the second synchronization signal is transmitted is called a second synchronization channel. The first sync channel may be allocated to a superframe header, and the second sync channel may be allocated between two superframe headers. The sync channel may include a plurality of subcarriers in the frequency domain and at least one OFDM symbol in the time domain.

Sync channels in a superframe may be allocated in multiples of a frame size, or may be allocated in 1/2 or 1/4 of a superframe size. As shown in FIG. 4, synchronization channels may be allocated at 10 ms intervals, which are 1/2 intervals of 20 ms superframes and twice intervals of 5 ms frames. Alternatively, as shown in FIG. 5, synchronization channels may be allocated at intervals of 1/4 ms of a 20 ms superframe and intervals of 1 ms of a 5 ms frame. Here, since the first sync channel is allocated for each superframe header, the interval between the first sync channel is 20 ms and the interval between the first sync channel and the second sync channel is 10 ms or 5 ms. That is, the first synchronization signal may be transmitted in a period of a super frame size, and the second synchronization signal may be transmitted in a multiple period of a frame size.

Meanwhile, the first sync channel does not necessarily need to be allocated to the superframe header and may be allocated to a separate area other than the superframe. As described above, when the sync channels are allocated at intervals of 10 ms or 5 ms, the handover interference interval Can be reduced. For example, if sync channels are allocated at intervals of 5 ms in a TDD superframe, the handover interruption interval is reduced to 15 ms.

The first sync channel and the second sync channel may have the same structure, and different sync signals may be transmitted through the first sync channel and the second sync channel. That is, the first sync signal and the second sync signal may be generated in a sequence of different values of the same length. Alternatively, the first sync signal and the second sync signal may be generated in the same sequence and mapped to the sync channel in different ways. Various orthogonal sequences may be used as the first synchronization signal and the second synchronization signal. As the synchronization signal, various sequences such as Hadamard code, DFT sequence, Walsh code, Zadoff-Chu (ZC) Constant Amplitude Zero Auto-Correlation (CAZAC) sequence can be used, and the type of sequence is not limited. . For example, when a ZC sequence is used as a synchronization signal, the first synchronization signal and the second synchronization signal may be generated as ZC sequences having the same length, but the original indexes may be different from each other. Alternatively, the first sync signal and the second sync signal may be generated as ZC sequences having the same source index, but different mapping schemes may be applied.

The base station may provide various types of system information as well as time synchronization and frequency synchronization to the terminal through the first synchronization signal and the second synchronization signal. For example, the base station may express the cell ID information using the original indexes of the first synchronization signal and the second synchronization signal. The cell ID information may be expressed by a combination of a source index of the first sync signal and a source index of the second sync signal. The terminal may obtain a raw index by taking a correlation value with respect to the received first synchronization signal and the second synchronization signal, and may know cell ID information indicated by the source index.

Now, a method of mapping a synchronization signal to a synchronization channel will be described. The sync signal is preferably mapped to the sync channel under the following conditions. (1) A plurality of synchronization channels should be designed in the same structure so that the UE can detect synchronization signals transmitted in different sequences using the same algorithm. (2) The mapping process of the synchronization signal should not degrade the detection performance of the synchronization signal. (3) Synchronization signals transmitted through different synchronization channels should be clearly detected.

6 illustrates a method of mapping a synchronization signal to a synchronization channel according to an embodiment of the present invention.

Referring to FIG. 6, a synchronization channel includes a plurality of subcarriers in a frequency domain, and a synchronization signal is mapped to a plurality of subcarriers in a frequency domain.

The synchronization signal is mapped to a subcarrier whose frequency index k is even (k is an integer). The frequency index indicates a subcarrier included in the frequency domain. The synchronization signal is mapped to a subcarrier having an index of 2 m with respect to the DC subcarrier (m is an integer). The sequence length of the synchronization signal may be determined in various ways according to the size of the FFT window. Accordingly, the mapping method of the synchronization signal may be determined in various ways.

For example, the synchronization signal may be mapped to a subcarrier whose index is even from-(2k + 2) to 2k. When the sequence element of the synchronization signal A is A = {a (0), a (1), a (2), ...}, the 0th sequence element a (0) is the index-(2k + 2). After being mapped to the subcarriers, the sequence elements may be sequentially mapped to subcarriers having an even index. In this case, since data is not transmitted through the DC subcarrier having an index of 0 in consideration of the DC offset in OFDM transmission, the DC subcarrier may be punctured after the sequence is mapped. The sequence in which the sequences are mapped is only an example and a synchronization signal may be mapped from the DC subcarrier.

In an OFDM system, a transmitter performs an inverse fast fourier transform (IFFT). A synchronization signal mapped to a plurality of subcarriers in a frequency domain is converted into a signal in a time domain through an IFFT. The synchronization signal mapped to the even subcarriers with an even index is converted into a signal in which the waveform is repeated twice in the form of [A A] in the time domain.

7 illustrates a method of mapping a synchronization signal to a synchronization channel according to another embodiment of the present invention.

Referring to FIG. 7, a synchronization signal is mapped to a subcarrier having an odd frequency index k. The synchronization signal is mapped to a subcarrier whose index is 2m + 1 around the DC subcarrier (m is an integer). For example, the synchronization signal may be mapped to a subcarrier whose index is odd from-(2k + 1) to 2k + 1. When the sequence element of the synchronization signal B is B = {b (0), b (1), b (2), ...}, the 0th sequence element b (0) is the index-(2k + 1). After being mapped to the subcarriers, the sequence elements may be sequentially mapped to subcarriers having an odd index.

A synchronization signal mapped to an odd subcarrier in the frequency domain is converted into a signal in which a waveform is repeated twice in the form of [B -B] in the time domain through an IFFT.

According to a method of mapping a synchronization signal to an even-numbered subcarrier in the frequency domain and a method of mapping a synchronization signal to an odd-numbered subcarrier in the frequency domain, the mapped synchronization signal is divided into different types of signals in the time domain through an IFFT. It can be seen that it is converted. 6 illustrates a method of mapping a first synchronization signal to a first synchronization channel, and FIG. 7 illustrates a method of mapping a second synchronization signal to a second synchronization channel. 6 illustrates a method of mapping a second synchronization signal to a second synchronization channel, and FIG. 7 illustrates a method of mapping a first synchronization signal to a first synchronization channel.

The first sync signal and the second sync signal may be transmitted in the same sequence. Even when the first sync signal and the second sync signal are transmitted in the same sequence, the first sync channel and the second sync channel may be distinguished according to the mapping method of the sync signal. For example, the same sequence may be used as the first sync signal and the second sync signal for the same cell ID, and only the mapping method to the frequency domain may be different. If the number of synchronization signals is 114, the amount of information through the first synchronization signal and the second synchronization signal is 114 * 2 = 228, but the number of necessary sequences is 114.

The first synchronization signal and the second synchronization signal may be transmitted in different sequences. When the first synchronization signal and the second synchronization signal are transmitted in different sequences, a larger frequency offset tolerance can be obtained. For example, when 114 sequences are used as the first sync signal and 114 sequences different from the first sync signal are used as the second sync signal, the first sync signal and the second sync signal are divided into different sequences in the frequency domain. The information of 114 * 114 = 12996 may be transmitted in a combination of the first synchronization signal and the second synchronization signal.

The terminal may process the synchronization signal according to the following procedure. (1) Symbol synchronization is obtained by differential correlation with respect to the received synchronization signal. (2) Assuming that the repeated synchronization signals have the same sign, a differential frequency offset is estimated and compensated by differential correlation. (3) Whether the synchronization signal is mapped to an even subcarrier or an odd subcarrier is detected. As a method for detecting a synchronization method mapping method, an ML (maximum likelihood) method may be used. The ML method detects the received signal by comparing all combinations corresponding to the sequence of the synchronization signal with the received signal, and a sequence that provides an optimal value for any criterion is selected. An energy detection method may be used as a method for detecting a synchronization method mapping method. The energy detection method is a method of determining the presence or absence of a signal at each frequency position, and can detect the cell ID based on the presence or absence of a signal at the frequency position. The energy detection method requires a very small amount of calculation compared to the ML method.

8 illustrates a synchronization signal transmission method through a superframe according to another embodiment of the present invention.

Referring to FIG. 8, a first sync signal, a second sync signal, and a third sync signal are transmitted through a superframe. An area in which the first synchronization signal is transmitted on the superframe is called a first synchronization channel, an area in which the second synchronization signal is transmitted is a second synchronization channel, and an area in which the third synchronization signal is transmitted is a third synchronization channel. The first sync channel may be allocated to the superframe header, and the second sync channel and the third sync channel may be allocated between the two superframe headers. The second sync channel may be allocated to a position 10 ms apart from the first sync channel, and the third sync channel may be allocated to a position 5 ms apart from the first sync channel. That is, three sync channels are arranged at 5 ms intervals. Sync channels may be allocated at intervals of 1/4 of a 20 ms superframe size or interval of 1 times a 5 ms frame.

The first sync channel, the second sync channel, and the third sync channel may have the same structure, and different sync signals may be transmitted through each sync channel. That is, the first synchronization signal, the second synchronization signal, and the third synchronization signal may be generated in a sequence of different values having the same length. Alternatively, the first sync signal, the second sync signal, and the third sync signal may be generated in the same sequence and mapped to the sync channel in different ways. When each synchronization signal is mapped to a subcarrier in the frequency domain using a different mapping scheme, the synchronization signal is converted into a signal of a different type in the time domain through an IFFT.

9 illustrates a method of mapping a synchronization signal to a synchronization channel according to another embodiment of the present invention. 10 illustrates a method of mapping a synchronization signal to a synchronization channel according to another embodiment of the present invention. 11 illustrates a method of mapping a synchronization signal to a synchronization channel according to another embodiment of the present invention.

9 to 11, when a first sync signal, a second sync signal, and a third sync signal are transmitted through a superframe, FIGS. 9 to 11 illustrate a method of mapping a sync signal to each of three sync channels. . The first synchronous signal, the second synchronous signal, and the third synchronous signal are mapped to subcarriers in the frequency domain in different ways among the three mapping methods. For explanation, the first synchronization signal is mapped to the synchronization channel as shown in FIG. 9, the second synchronization signal is mapped as shown in FIG. 10, and the third synchronization signal is mapped as shown in FIG. 11. Assume that

The first synchronization signal is mapped to a subcarrier having an index of 3 m around the DC subcarrier (m is an integer). The first synchronization signal may be mapped to subcarriers having three intervals from index − (3k + 3) to 3k. For example, when the sequence element of the synchronization signal A is A = {a (0), a (1), a (2), ...}, the 0th sequence element a (0) is the index-(3k The sequence element of the synchronization signal may be sequentially mapped to subcarriers of three intervals in such a manner that the first sequence element a (1) is mapped to a subcarrier having an index of -3k and is mapped to a subcarrier of +3).

The second synchronization signal may be mapped to a subcarrier having an index of 3m + 1 around the DC subcarrier, and the third synchronization signal may be mapped to a subcarrier having an index of 3m + 2 (m is an integer). The second synchronization signal may be mapped to subcarriers having three intervals from the index-(3k + 2) to 3k + 1. The third synchronization signal may be mapped to subcarriers having three intervals from the index-(3k + 1) to 3k + 2. As such, the first sync signal, the second sync signal, and the third sync signal are mapped to subcarriers having different indices.

The first synchronization signal is converted into a signal in which the waveform is repeated three times in the form of [A A A] in the time domain through the IFFT. The second synchronization signal is converted into a signal in which the waveform is repeated three times in the form of [B B · exp (j · 2π / 3) B · exp (j · 2π · 2/3)] in the time domain through the IFFT. The third synchronization signal is converted into a signal in which the waveform is repeated three times in the form of [C C · exp (j · 4π / 3) C · exp (j · 4π · 2/3)] in the time domain through the IFFT.

Since the synchronization signal mapping method is different for each synchronization channel, even when the first synchronization signal, the second synchronization signal, and the third synchronization signal are transmitted in the same sequence, the terminal may distinguish the synchronization channel by the ML method or the energy detection method. . When different sequences are used as the first synchronization signal, the second synchronization signal, and the third synchronization signal, more various information may be reported as the synchronization signal. For example, assume that 114 sequences are used as the first synchronization signal, another 114 sequences are used as the second synchronization signal, and another 114 sequences are used as the third synchronization signal. The cell ID information may be informed by a combination of the first synchronization signal and the second synchronization signal. Up to 114 * 114 = 12996 cell ID information can be represented by the first synchronization signal and the second synchronization signal. The third synchronization signal may indicate system information such as CP length of an OFDM symbol, information on a TDD / FDD frame, whether a multimedia broadcast multicast service (MBMS), and the like. When a ZC sequence is used as a synchronization signal, the raw index of the ZC sequence may be divided to indicate various system information.

All of the above functions may be performed by a processor such as a microprocessor, a controller, a microcontroller, an application specific integrated circuit (ASIC), or the like according to software or program code coded to perform the function. The design, development and implementation of the code will be apparent to those skilled in the art based on the description of the present invention.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

1 is a block diagram illustrating a wireless communication system.

2 illustrates a superframe structure.

3 illustrates an example of a process of performing handover through a TDD superframe.

4 illustrates a synchronization signal transmission method through a superframe according to an embodiment of the present invention.

5 is a diagram illustrating a synchronization signal transmission method through a superframe according to another embodiment of the present invention.

6 illustrates a method of mapping a synchronization signal to a synchronization channel according to an embodiment of the present invention.

7 illustrates a method of mapping a synchronization signal to a synchronization channel according to another embodiment of the present invention.

8 illustrates a synchronization signal transmission method through a superframe according to another embodiment of the present invention.

9 illustrates a method of mapping a synchronization signal to a synchronization channel according to another embodiment of the present invention.

10 illustrates a method of mapping a synchronization signal to a synchronization channel according to another embodiment of the present invention.

11 illustrates a method of mapping a synchronization signal to a synchronization channel according to another embodiment of the present invention.

Claims (9)

Transmitting a first synchronization signal on a first synchronization channel including a plurality of subcarriers in a frequency domain and at least one OFDM symbol in a time domain; And And transmitting a second synchronization signal through a second synchronization channel having the same structure as the first synchronization channel, wherein the first synchronization signal and the second synchronization signal are mapped to subcarriers having different indices. 1. A synchronization signal transmission method in a wireless communication system in which a first synchronization signal is transmitted in a period of a superframe size including a plurality of frames and the second synchronization signal is transmitted in a multiple period of a frame size. The method of claim 1, wherein the first sync channel is allocated to a header of the superframe and the second sync channel is allocated between a plurality of superframe headers. The method of claim 1, wherein the same sequence is used as the first synchronization signal and the second synchronization signal. The method of claim 1, wherein different sequences are used as the first synchronization signal and the second synchronization signal. The method of claim 1, further comprising transmitting a third synchronization signal through a third synchronization channel having the same structure as the first synchronization channel, wherein the first synchronization signal, the second synchronization signal, and the third synchronization signal are transmitted. A signal transmission method in a wireless communication system, characterized in that the signal is mapped to subcarriers of different indexes. In the wireless communication system receiving a synchronization signal through a superframe including a plurality of frames, Receiving a first synchronization signal through a first synchronization channel; And And receiving a second synchronization signal transmitted through a second synchronization channel at multiple intervals of a frame size after transmitting the first synchronization signal, wherein the first synchronization channel and the second synchronization channel have the same structure. And the first synchronization signal and the second synchronization signal are transmitted in different waveforms. 7. The method of claim 6, wherein the first sync channel and the second sync channel include a plurality of subcarriers in a frequency domain, wherein the plurality of subcarriers are indicated by a frequency index. One of the synchronization signals is mapped to a subcarrier having an even frequency index and the other is mapped to a subcarrier having an odd frequency index. 8. The method of claim 7, wherein an ML (maximum likelihood) comparing all combinations corresponding to a sequence of synchronization signals whether the first synchronization signal and the second synchronization signal are mapped to an even subcarrier having an even frequency or an odd subcarrier. A synchronization signal receiving method, characterized in that the detection method. 8. The method of claim 7, wherein detecting whether the first synchronization signal and the second synchronization signal are mapped to an even subcarrier with an even number or an odd subcarrier with an energy detection method for determining the presence or absence of a signal at a frequency position. Characterized in that the synchronization signal receiving method.

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