FR2968157A1 - Transmitter for transmitting synchronization signal in wireless communication system, has spreading unit for spreading frame start region and data region, and data transmission unit transmitting spread signal by spreading codes - Google Patents

Abstract

A transmitter (200) transmits a synchronization signal in a frame-based wireless communication system comprising a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols. The transmitter (200) comprises: a spreading code generation unit (260) configured to generate first and second spreading codes used to compensate for synchronization of a receiver receiving a start frame region and a region data having at least one OFDM data symbol; a spreading unit (270) configured to spread the start frame region using the first spreading code and to spread the data region at each predetermined period using the second spreading code; and a transmission unit (280) configured to transmit a spread signal by the first spreading code and the second spreading code.

Description

DEVICE AND METHOD FOR SYNCHRONIZATION SIGNAL TRANSMISSION

The present invention relates to wireless communications and, more particularly, to a device and method for transmitting a synchronization signal. An OFDM (Orthogonal Frequency Division Multiplexing) modulation mode is a method of dividing data into several subcarriers having orthogonality and transmitting the divided data in parallel. An OFDM symbol is generated in a time axis by the OFDM modulation. Because the length of the OFDM symbol is relatively large, the OFDM modulation mode is an effective modulation mode in multipath path environments. The OFDM modulation mode is resistant to selective frequency fading but is sensitive to frequency synchronization and non-linear distortion. Various systems such as Digital Audio Broadcasting (DAB), DVB (Digital Video Broadcasting), DMB (Digital Multimedia Broadcasting), LTE (Long Term Evolution), WiBro and Network System local wireless use such an OFDM modulation mode. In various transceiver systems using an OFDM modulation mode such as Eureka-147, DAB and DMB, a phase reference symbol (hereinafter referred to as "PRS") is inserted into each transmission frame with a length constant so as to implement the synchronization performance of a receiver and the resulting transmission frames are transmitted. The receiver can seek a time point when a symbol is started in a transmission frame using the PRS and can acquire the synchronization. The DAB or DMB system is a system used to receive a mobile broadcast. As a result, when a receiver loses synchronization while moving, a signal must be searched again and synchronization must be acquired again. In order to acquire synchronization, the receiver must first identify a transmission mode, acquire frame synchronization, and then acquire frequency synchronization, symbol synchronization, and sampling synchronization. Fig. 1 is a diagram illustrating a basic synchronization process in the related art. Referring to Fig. 1, at least two frames are needed to identify a transmission mode, about two frames are needed for frame synchronization, one frame is needed for approximate frequency timing. The identification of a transmission mode, the frame synchronization and the approximate frequency synchronization must be performed in the initialization of a system and require at least five frames. A transmission signal of at least six frames is required for stable synchronization. In this way, when the acquisition time of the synchronization is long, the satisfaction of a system is diminished.

Therefore, there is a need for a device and method for transmitting a timing signal to reduce a timing acquisition time in a wireless communication system. An advantage of certain aspects of the invention is to provide a device and a method for transmitting a synchronization signal, which can reduce a synchronization acquisition time.

Another advantage of certain aspects of the invention is to enable a receiver to quickly and accurately acquire ka synchronization and to estimate a channel by further transmitting a signal useful for reception timing and channel estimation without assign an existing transceiver system. Another advantage of certain aspects of the invention is to provide a device and a method for reducing a synchronization acquisition time. Another advantage of certain aspects of the invention is to provide a frame structure that can reduce a synchronization acquisition time. Another advantage of some aspects of the invention is to provide a spreading code signal used to reduce a timing acquisition time. According to one aspect of the invention, there is provided a transmitter that transmits a synchronization signal in a frame-based wireless communication system comprising a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols. The transmitter comprises: a spread code generation unit configured to generate first and second spreading codes used to compensate for synchronization of a receiver receiving a start frame region and a data region having at least one OFDM symbol of data, a spreading unit configured to spread the start frame region using the first spreading code and to spread the data region at each predetermined period using the second spreading code, and a unit transmission configured to transmit a signal spread by the first spreading code and the second spreading code.

According to another aspect of the invention, there is provided a method of transmitting a synchronization signal in a frame-based wireless communication system comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols. . The method includes the steps of: generating first and second spreading codes used to compensate for synchronization of a receiver receiving a start frame region and a data region having at least one OFDM data symbol, the spreading of the start of frame region by using the first spreading code, spreading the data region at each predetermined period using the second spreading code, and transmitting a signal spread by the first payload code. spreading and the second spreading code.

According to yet another aspect of the invention, there is provided a receiver receiving a synchronization signal in a frame structure based wireless communication system comprising a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols. The receiver comprises: a receiving unit configured to receive a frame comprising a spread start region using a first spreading code and a spreading data region using a second spreading code, a reverse spreading unit configured to perform reverse spreading of the start frame region using the first spreading code to output a first signal and the reverse spread of the data region at each predetermined period using the second code of spreading to output a second signal, and a synchronization acquisition unit configured to acquire at least one of a frame synchronization, an OFDM symbol synchronization, an accurate frequency synchronization and a sampling synchronization based on the first and second signals. According to yet another aspect of the invention, there is provided a method of receiving a synchronization signal in a frame structure-based wireless communication system comprising a plurality of orthogonal frequency division multiplexing symbols (OFDMs). ). The method comprises the steps of: receiving a frame comprising a spread beginning region using a first spreading code and a spreading data region using a second spreading code; start frame region using the first spreading code to output a first signal; inverse spreading the data region at each predetermined period using the second spreading code to output a second signal, and acquiring at least one of a frame synchronization, an OFDM symbol synchronization, accurate frequency synchronization and sampling timing based on the first and second signals. In accordance with the aforementioned configuration, by further transmitting a specific signal useful for reception timing and channel estimation without affecting system transmission and reception of a synchronization signal, it is possible to enable the receiver to stably perform processes such as a transmission mode acquisition process, a frame acquisition process, a symbol acquisition process, a frequency synchronization process and a synchronization process. sampling in two frames and continuously performing the sampling synchronization process and the channel estimation process throughout the frames. Even when a PRS is inserted into each frame for a transmission structure reason, it is possible to continuously perform the channel estimation process and the sampling synchronization process. The invention will be described in more detail with reference to the accompanying drawings.

Fig. 1 is a diagram illustrating a basic synchronization process according to the related art. Fig. 2 is a block diagram illustrating the configuration of an emitter transmitting a synchronization signal according to an embodiment of the invention. Fig. 3 is a diagram illustrating conceptually the sequence in which a spreading unit spreads a signal according to the embodiment of the invention.

FIG. 4 is a diagram illustrating a frame structure transmitted by the transmitter according to the transmitter. FIG. 5 is a block diagram illustrating the configuration of a receiver receiving a synchronization signal according to another embodiment of the invention. Fig. 6 is a block diagram illustrating the configuration of a synchronization acquisition unit according to the embodiment of the invention. Fig. 7 is a diagram illustrating the sequence in which the receiver acquires synchronization according to the embodiment. Fig. 8 is a flowchart illustrating the flow of an operation of transmitting and receiving a synchronization signal between a transmitter and a receiver according to an embodiment of the invention. Hereinafter, exemplary embodiments of the invention will be described in detail with reference to the accompanying drawings so that one skilled in the art can easily practice the invention. However, the invention can be implemented in different forms and is therefore not limited to the embodiments. Elements not directly involved in the invention are not described to clarify the invention and similar elements are indicated by like reference numerals throughout the description. In this description, if an element "includes" another element, this does not mean that the element excludes another element yet, but means that the element may include yet another element, as long as it is not described differently. . Terms, "unit" and the like, described in this specification, represent units performing at least one function or operation and may be implemented by hardware, software, or a combination of hardware and software. Embodiments of the invention will be described below with reference to the accompanying drawings. Fig. 2 is a block diagram illustrating the configuration of an emitter transmitting a synchronization signal according to an embodiment of the invention.

Referring to FIG. 2, the transmitter 200 comprises a source coding unit 210, a channel coding and interleaving unit 220, a multiplexing unit 230, a fast information channel synchronization unit (FIC) 240 , an OFDM modulation unit 250, a spreading code generation unit 260, a spreading unit 270 and a transmission unit 280. The source coding unit 210 encodes analog source data such as a signal video and an audio signal based on the MPEG-2 standard and outputs the encoded source data to the channel coding and interleaving unit 220. The channel coding and interleaving unit 220 performs a coding process and channel interleaving to correct an error of encoded source data. The multiplexing unit 230 multiplexes various types of source data or various data channels. The FIC synchronization unit 240 synchronizes a symbol corresponding to a fast information channel (FIC) among OFDM symbols generated by the OFDM modulation unit 250. The OFDM modulation unit 250 configures an input data stream on a plurality of subcarriers in a frequency domain and performs a Fast Fourier Transform (FFT) process and an inverse Fast Fourier Transform (IFFT) process to generate the OFDM symbols. At this point, the several OFDM symbols generated by the OFDM modulation unit 250 constitute a frame in a time domain. Each frame includes a null region and a data region (see Figure 4). Each region has at least one OFDM symbol. The null region includes an OFDM symbol from which a frame begins. The OFDM symbol included in the null region is indicated as a null OFDM symbol and the OFDM symbol included in the data region is indicated as an OFDM data symbol. The spread code generation unit 260 generates a specific signal to be added to an OFDM transmission band. The frequency bandwidth of the specific signal is set so that it does not exceed the bandwidth supported by the system. For example, in the case of the DAB system, the spreading code generation unit 260 sets the frequency bandwidth of the specific signal so as not to exceed 1.36 MHz which is a DAB transmission band. An example of the specific signal is a spreading code having orthogonality. For example, a first spreading code and a second spreading code have an orthogonality between them.

The spread code generation unit 260 generates a specific signal to be added to an existing frame for transmission, i.e. a spreading code, so as to be used for the reception synchronization. and lane estimation.

The specific signal can be transmitted with a lower power than the existing signal. For example, spreading code generating unit 260 generates different spreading codes depending on modes of transmission. A transmission mode defines parameters of a frame. Table 1 is an example of the transmission mode standard for the DAB system.

Table 1 Mode Mode Mode Mode of Parameter Transmission Transmission Transmission Transmission I II III IV L 76 76 153 76 K 1536 384 192 768 TF 196 608 T 49 152 T 49 152 T 98 304 T 96 ms 48 ms 24 ms 24 ms TNULL 2 656 T 664 T 345 T 1 328 T 1.297 ms -324 pS -168 pS -648 pS Ts 2 552 T 638 T 319 T 1 276 T -1.246 ms -312 pS -156 pS -623 pS Tu 2 048 T 512 T 256 T 1024 T 1 ms 250 pS 125 pS 500 pS 0 504 T 126 T 63 T 252 T -246 pS -62 gS -31 pS-123 pS Referring to Table 1, four modes of DAB frame transmission are defined and parameters such as a null region length TNULL are defined different depending on the transmission modes. K represents the number of subcarriers and T 'represents the duration of an effective symbol. A represents the duration of a protection interval and Tr represents the duration of a transmission frame. In this way, since the parameters vary depending on the transmission modes, a receiver must recognize the transmission mode of a frame generated by the transmitter 200 and the transmission modes can be identified by the spreading codes. generated from spreading code generating unit 260. For example, spreading codes 1, 2, 3 and 4 are used for transmission modes 1, 2, 3 and 4, respectively. spreading codes 1, 2, 3 and 4 are guaranteed to be orthogonal to each other. In another example, the spreading code generation unit 260 generates different spreading codes depending on the regions of a frame. For example, a spreading code a may be generated for the null region and a spreading code b may be generated for the data region. In another example, the spreading code generation unit 260 generates different spreading codes depending on the transmission modes and the regions of a frame. For example, a spreading code 1-a may be generated for the null region of a transmission mode 1 and a spreading code 2-a may be generated for the null region of a transmission mode 2. spreading code 1-b can be generated for the data region of a transmission mode 1 and a spreading code 2-b can be generated for the data region of a transmission mode 2. The unit The spreading code 270 adds the spreading codes generated from the spreading code generation unit 260 to the frame using a predetermined method. In particular, the spreading unit 270 spreads the regions of the frame using different spreading codes. For example, the spreading unit 270 spreads the null OFDM symbol of the null region using a spreading code a and spreads the data OFDM symbol of the data region using a spreading code b. The spreading unit 270 spreads the transmission mode frame 1 using the spreading code 1 and spreads the transmission mode frame 2 using the spreading code 2. The transmission unit 280 transmits the signal spread by the spreading unit 270 to a receiver by RF (radiofrequency). In the case of DAB, since differential quadrivalent phase modulation (DQPSK) is used, reception performance can be guaranteed without performing channel estimation. However, in the case of AT-DMB which is developed to increase the transmission capacity of the DAB, the phase information is essential to receive a signal and a channel compensation function should be added to guarantee the performance. By adding the spreading codes, it is possible to efficiently perform reception timing and channel estimation.

Spread codes can be added to a part that does not affect the existing signal. In this way, a signal that can be received by a receiver is constituted using the signal strongly affecting the existing system.

Fig. 3 is a diagram illustrating conceptually the sequence in which a spreading unit spreads a signal according to the embodiment of the invention. Referring to FIG. 3, the spreading unit 270 adds a spread signal in which the spread codes are applied to data on an OFDM signal. Fig. 3 shows an example in which the spread signal comprising data is added to the OFDM signal, but this is only an example. The spreading unit 270 may spread the OFDM signal using only the spread signal that does not include data. The bandwidth of the spread signal added by the spreading unit 270 should be within the transmission bandwidth of the system. For example, in the case of DAB, the bandwidth of the spread signal should not exceed 1.536 MHz. FIG. 4 is a diagram illustrating a frame structure transmitted by the transmitter according to the embodiment of the invention. FIG. 4 shows the frame structure in transmission mode 1. Referring to FIG. 4, a transmission frame is defined as 96 ms and comprises a synchronization channel, a fast information channel (FIC) and a channel Main Service (MSC). The synchronization path includes a null region, and the FIC and the MSC are called a data region. A null region is defined as a start frame region, which includes at least one OFDM symbol. Each region has at least one OFDM symbol.

The number of OFDM symbols in each region in Figure 4 is only an example. The number of OFDM symbols in each region is not limited to the number indicated but can be defined differently depending on the transmission modes and systems.

The null region is spread using the first spreading code and the data region is spread using the second spreading code. Since the frame shown in Fig. 4 is the transmission mode frame 1, it is assumed that the first spread code and the second spread code are involved in the transmission mode 1. The length of each code of spreading and the period of each spreading code can be adjusted according to the characteristics of the system. For example, the length of the spreading code is equal to an OFDM symbol and the period with which the spreading code is added is equal to two OFDM symbols. In particular, Fig. 4 shows that the data region is spread using the spreading code at each OFDM symbol of even degree indices.

Specifically, the same second spreading code is applied to the second, fourth, sixth, and seventh OFDM symbols. This is just an example. The data region may be spread using the spreading code at each odd-degree index OFDM symbol or the spreading code may be applied with a period of at least two OFDM symbols. FIG. 5 is a block diagram illustrating a receiver receiving a synchronization signal according to one embodiment of the invention. The receiver may be a comb receiver. Referring to FIG. 5, the receiver 500 comprises a reception unit 510, an inverse spreading unit 520, a synchronization acquisition unit 530, an OFDM demodulation unit 540, a channel decoding unit and a decoder unit. interleaving 550 and a source decoding unit 560. The receiving unit 510 receives a signal (or a frame) transmitted from a transmitter, filters the received signal in a baseband and transmits the resulting signal to the inverse spreading unit 520 and the synchronization acquisition unit 530. The inverse spreading unit 520 inversely spreads the received signal using the first and / or second spreading codes. The sync acquisition unit 530 acquires synchronization from the inverted spread signal. For example, when the inverse spreading unit 520 inversely spreads the received signal using the first spreading code and a signal is detected, the synchronization acquisition unit 530 can recognize the corresponding OFDM symbol as an OFDM symbol no. This is because it is defined that the null OFDM symbol is spread using the first spreading code for the purpose of acquiring frame synchronization. Accordingly, the synchronization acquisition unit 530 can acquire the OFDM symbol synchronization using the first spreading code. On the other hand, when the inverse spreading unit 520 inversely spreads the received signal using the second spreading code and a signal is detected, the synchronization acquisition unit 530 can recognize the corresponding OFDM symbol as a OFDM symbol of data. This is because it is defined that the OFDM data symbol is spread using the second spreading code for purposes of acquiring symbol timing. Accordingly, synchronization acquisition unit 530 can acquire frame synchronization using the second spreading code.

Since the first spreading code or the second spreading code is divided by code according to the transmission modes, the synchronization acquisition unit 530 can confirm the transmission mode from the spreading code added. to the received signal. The OFDM demodulation unit 540 performs the IFFT process and the FFT process on the received signal and transmits the resulting signal to the channel decoding and de-interleaving unit 550. The channel decoding and decoding unit interleaving 550 performs the channel decoding process and the de-interleaving process on the signal and transmits the resulting signal to the source decoding unit 560. The source decoding unit 560 performs the source decoding process on the signal and outputs source data. In this manner, the comb receiver searches for a multiple path characteristic from the spread code signal and uses the multipath feature for channel estimation. As a result, it is possible to estimate and compensate for channel characteristics even in an interval that does not include a PRS. Fig. 6 is a block diagram illustrating the configuration of the synchronization acquisition unit according to one embodiment of the invention. Referring to FIG. 6, the synchronization acquisition unit 600 comprises a down-conversion unit and a band-pass filter 610, a transmission mode detection unit 620, a frame synchronization unit 630, a unit frequency synchronization unit 640, a symbol synchronization unit 650, a sampling synchronization unit 660 and an FFT / IFFT unit 670. The transmission mode detection unit 620, the frame synchronization unit 630, the frequency synchronization unit 640, the symbol synchronization unit 650 and the sampling synchronization unit 660 analyze a spread signal inversely using the spreading codes and acquire necessary information such as transmission, frame synchronization information, frequency synchronization information, symbol synchronization information, and synchronization information. sampling. For example, when the spreading code is 1-a, the transmission mode detection unit 620 can confirm that the corresponding frame is in transmission mode 1 from the spreading code 1. The synchronization unit frame 630 can confirm that the detected symbol is a null OFDM symbol from the spreading code a.

Figure 7 is a diagram illustrating the sequence in which the receiver according to one embodiment of the invention acquires synchronization. This sequence comprises operations processes of the inverse spread unit and the synchronization acquisition unit.

Referring to Fig. 7, after the receiver begins to receive a frame, it is possible to acquire the symbol timing in two OFDM symbols based on the period with which the second spreading code is added. Because the spreading codes have orthogonality as a function of the transmission mode, the receiver can acquire the types of the transmission modes. Then, the receiver can acquire frame synchronization in a frame from the first spreading code by which the null region as a start portion of the frame is spread. In the following frame, it is possible to estimate the precise frequency timing and sampling timing using the received OFDM signal. Symbol synchronization and accurate frequency synchronization operate in the OFDM symbol interval other than the null OFDM symbol. Since the approximate frequency timing estimate may operate at the time of receiving a next PRS signal after the frame synchronization process has been executed, it may operate after one frame. Therefore, the receive synchronization can stably converge in two frames after the reception of the signal.

FIG. 8 is a flowchart illustrating transmission and reception operations of a synchronization signal between a transmitter and a receiver according to one embodiment of the invention. Referring to Fig. 8, the transmitter generates first and second spreading codes to compensate for the synchronization of the receiver receiving a null region having at least one null OFDM symbol and a data region comprising at least one OFDM data symbol. (5800). Here, the first and second spreading codes are divided by code to identify the transmission mode of a frame. The transmitter spreads the null region of the frame using the first spreading code and spreads the data region of the frame using the second spreading code (5810).

The transmitter transmits the spread signals using the first spreading code and the second spreading code to the receiver (5820). The receiver which has received the spread signals spreads the null region of the frame inversely using the first spreading code and outputs a first signal. In addition, the receiver inversely spreads the data region of the frame using the second spreading code at each predetermined period and outputs a second signal (5830). Here, the predetermined period is promised in advance between the transmitter and the receiver. The receiver acquires at least one of the frame timing of the frame, the OFDM symbol timing, the precise frequency synchronization and the sampling timing based on the first and second signals (5840). For example, the frame synchronization is acquired on the basis of the first signal and the OFDM symbol synchronization is acquired on the basis of the second signal.

While the technical spirit of the invention has been described with reference to the embodiments, the invention is not limited to the embodiment, but may be modified in various forms by those skilled in the art without departing from the concept. technical aspect of the invention. Therefore, the aforementioned embodiments are not intended to define the technical spirit of the invention but to explain the technical spirit of the invention, and the scope of the invention is not limited to the embodiments . The scope of the invention is to be defined by the appended claims and all technical minds within their range of equivalents must fall within the scope of the invention.

Claims (20)

REVENDICATIONS1. A transmitter (200) transmitting a synchronization signal in a frame structure based wireless communication system comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols, comprising: a spreading code generation unit ( 260) configured to generate first and second spreading codes used to compensate for synchronization of a receiver receiving a start frame region and a data region having at least one OFDM data symbol; a spreading unit (270) configured to spread the start frame region using the first spreading code and to spread the data region at each predetermined period using the second spreading code; and a transmission unit (280) configured to transmit a spread signal by the first spreading code and the second spreading code. The transmitter (200) according to claim 1, wherein the spread code generating unit (260) is configured to set the values of the first spreading code and the second spreading code according to the mode of transmission determining the structure of the frame. The transmitter (200) of claim 2, wherein the transmission mode is a transmission mode based on an audio broadcast transmission standard. An emitter (200) according to claim 1, wherein the spreading code generation unit (260) is configured to set the predetermined period on the basis of at least one OFDM symbol. An emitter (200) according to claim 1, wherein the spread code generating unit (260) is configured to set the length of the first spreading code and the length of the second spreading code to the length. at least one OFDM symbol. The transmitter (200) of claim 1, wherein the spread code generation unit (260) is configured to set the bandwidths of the first and second spreading codes to not exceed a frequency band. predetermined. The transmitter (200) according to claim 1, wherein the receiver synchronization comprises at least one of frame synchronization, OFDM symbol synchronization, sampling synchronization and precise frequency synchronization. A method of transmitting a synchronization signal in a frame structure-based wireless communication system comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols, comprising the steps of: second spreading codes used to compensate for synchronization of a receiver receiving a start of frame region and a data region having at least one OFDM data symbol; spreading of the start of frame region using the first code spreading; spreading the data region at each predetermined period using the second spreading code; and transmitting a spread signal by the first spreading code and the second spreading code. The method of claim 8, wherein the values of the first spreading code and the second spreading code are set to vary depending on the transmission mode determining the structure of the frame. The method of claim 9, wherein the transmission mode is a transmission mode based on an audio broadcast transmission standard. The method of claim 8, wherein the predetermined period is set based on at least one OFDM symbol. 20 The method of claim 8, wherein the length of the first spreading code and the length of the second spreading code are set at a length of at least one OFDM symbol. The method of claim 8, wherein the transmission bandwidths of the first and second spreading codes are set so as not to exceed a predetermined frequency band. A receiver (500) receiving a synchronization signal in a frame-based wireless communication system comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols, comprising: a configured receiving unit (510) for receiving a frame comprising a spread beginning region using a first spreading code and a spreading data region using a second spreading code; an inverse spreading unit (520) configured to perform reverse spreading of the start frame region by using the first spreading code to output a first signal and the inverse spread of the data region at each predetermined period using the second spreading code to output a second signal; and a synchronization acquisition unit (530) configured to acquire at least one of a frame synchronization, an OFDM symbol synchronization, an accurate frequency synchronization, and a sampling synchronization based on the first and second signals. The receiver (500) of claim 14, wherein the synchronization acquisition unit (530) is configured to acquire frame synchronization based on the first signal. The receiver (500) of claim 14, wherein the synchronization acquisition unit (530) is configured to acquire the OFDM symbol timing based on the second signal. 30 The receiver (500) of claim 8, wherein the values of the first spreading code and the second spreading code are set to vary according to the transmission mode determining the structure of the frame. A method of receiving a synchronization signal in a frame structure based wireless communication system comprising a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols, comprising the steps of: receiving a synchronization signal; frame comprising a start of frame region spread using a first spreading code and a spreading data region using a second spreading code; inverse spreading of the start frame region using the first spreading code to output a first signal; inverse spreading of the data region at each predetermined period using the second spreading code to output a second signal; and acquiring at least one of frame synchronization, OFDM symbol synchronization, accurate frequency synchronization, and sampling timing based on the first and second signals. The method of claim 18, wherein the frame synchronization is acquired based on the first signal. 20. The method of claim 18, wherein the OFDM symbol synchronization is acquired based on the second signal.