KR20080009639A - Apparearus and method for transmitting downlink frame in wireless communication system - Google Patents

Abstract

A method for transmitting a downlink frame in a wireless communication system is provided to improve cell search performance by placing main and sub synchronization channels adjacent to the boundary of a sub frame. A method for transmitting a downlink frame in a wireless communication system includes the step of: generating a first synchronization channel by inserting a first guard interval into a first synchronization channel signal; generating a second synchronization channel by inserting a second guard interval into a second synchronization channel signal; arranging the first synchronization channel in the downlink frame to place the first synchronization channel at the front of the boundary of the sub frame; and arranging the second synchronization channel in the downlink frame to place the second synchronization channel at the rear of the boundary of the sub frame. One of the first and second synchronization channels is a main synchronization channel, and the other is a sub synchronization channel.

Description

Method for transmitting downlink synchronization channel in mobile communication system {APPAREARUS AND METHOD FOR TRANSMITTING DOWNLINK FRAME IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a method for transmitting a downlink sync channel in a mobile communication system, and more particularly, to a method for transmitting a downlink sync channel when a sync channel has a variable CP in an OFDM cellular system.

The present invention is derived from the research conducted as part of the IT new growth engine core technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. .

The synchronization channel of an OFDM cellular system consists of a primary synchronization channel and a secondary synchronization channel. The primary and secondary synchronization channels are separated in the time domain and are adjacent to each other on the time axis.

When the base station transmits the primary synchronization channel and the secondary synchronization channel, the cell searcher in the terminal acquires the OFDM symbol synchronization using the primary synchronization channel, and converts the secondary synchronization channel signal into the frequency domain through the fast fourier transform (FFT) using the primary search channel. . In the frequency domain, the cell searcher finds a cell group or a cell number by using a sub-sync channel signal. In this process, the channel can be estimated using the primary synchronization channel, and the value can be used for demodulation.

It is possible to improve the overall system performance by allowing the length of CP to be variable in an OFDM cellular system so that an appropriate CP can be selected according to channel environment and service characteristics. That is, the CP length may be increased for a cell environment having a large time delay or a service requiring high quality. In general, however, the cell searcher correlates the received data with a known main sync channel signal to find the timing of the received signal and averages the correlation values over several times, with one OFDM symbol having a different length of CP. If they are mixed in the frames of the above, this time average cannot be taken, which causes a problem of deterioration of cell search performance.

An object of the present invention is to provide a synchronization channel transmission method that enables a terminal of an OFDM cellular system to efficiently perform cell search when a CP of a synchronization channel is variable.

In order to achieve the above object, the synchronization channel transmission method according to an aspect of the present invention generates a first synchronization channel by inserting a first protection interval in the first synchronization channel signal and a second protection interval in the second synchronization channel signal After generating the second synchronization channel by inserting the first synchronization channel in the downlink frame so that the first synchronization channel is located directly in front of the boundary of the sub-frame, and the second synchronization channel is just the boundary of the sub-frame The second sync channel is disposed in the downlink frame so as to be located later, one of the first sync channel and the second sync channel is a main sync channel, and the other is a sub sync channel.

In order to achieve the above object, a synchronization channel transmission apparatus according to another aspect of the present invention generates a first synchronization channel by inserting a first protection interval into a first synchronization channel signal, and provides a second protection interval to a second synchronization channel signal. A guard interval insertion unit for inserting a second synchronization channel and inserting the first synchronization channel into a downlink frame such that the first synchronization channel is located directly in front of the boundary of the subframe, and the second synchronization channel And a frame arrangement unit for arranging the second synchronization channel in the downlink frame so as to be located immediately after the boundary, wherein one of the first synchronization channel and the second synchronization channel is a primary synchronization channel and the other is a secondary synchronization channel.

According to the present invention, when the CP length of the sync channel is variable, the main sync channel and the sub sync channel are adjacent at the subframe boundary, and the sync channel disposed in the OFDM symbol immediately after the subframe boundary is short from the subframe boundary. The cell search performance can be improved by having the sync channel signal located after CP.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, except to exclude other components unless otherwise stated. In addition, the terms “… unit”, “… group” described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software.

Now, a downlink synchronization channel of a mobile communication system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First, a frame and a synchronization channel of an OFDM cellular system will be described with reference to FIG. 1. 1 is a diagram illustrating the structure of a frame and a synchronization channel in an OFDM cellular system.

As shown in Fig. 1, one frame consists of 20 subframes, and one subframe consists of 7 OFDM symbols. The synchronization channel includes a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH). The primary sync channel consists of one or more sequences, and the secondary sync channel consists of a plurality of sequences.

Since one sync channel is allocated to every four subframes, there are five sync channels in one frame. In this way, when several synchronization channels are provided in one frame, when the terminal acquires the synchronization, the terminal can average the correlation value between the received data and the known main synchronization channel signal for several hours, thereby speeding up the synchronization acquisition.

As shown in FIG. 1, when one main sync channel is arranged for every two subcarriers, the main sync channel may have a pattern repeated twice in the time domain, thereby obtaining synchronization without knowing an accurate waveform of the main sync channel.

Next, a downlink sync channel transmission apparatus and a downlink sync channel transmission method of a base station of an OFDM cellular system according to an embodiment of the present invention will be described with reference to FIGS. 2 to 9.

2 is a block diagram showing an apparatus for transmitting a downlink sync channel of a base station according to an embodiment of the present invention.

As shown in FIG. 2, the apparatus for transmitting synchronization channels according to an embodiment of the present invention includes a frequency allocator 210, an inverse fast Fourier transformer (IFFT) 220, and a guard interval inserter 230. ), A frame arrangement unit 240 and a radio frequency (hereinafter referred to as "RF") 250 transmitter.

The frequency allocator 210 determines a frequency to which the primary and secondary synchronization channels are allocated.

The IFFT 220 converts the main sync channel signal and the sub sync channel signal to be transmitted into a transmission signal in the time domain through an inverse fast Fourier transform, and the guard interval inserter 230 converts the main sync channel signal and the sub sync channel signal into a transmission signal in the time domain. A cyclic prefix (hereinafter referred to as "CP") corresponding to a guard interval is inserted into the channel signal and the sub-sync channel signal to generate a main sync channel and a sub-sync channel.

The frame arrangement unit 240 arranges the main sync channel and the sub sync channel in a frame.

The RF transmitter 250 converts an analog transmission signal into a radio frequency and transmits the same through a transmission antenna.

3 is a flowchart illustrating a downlink sync channel transmission method according to an embodiment of the present invention.

As shown in FIG. 3, the frequency allocator 210 determines a frequency to allocate a sync channel (310).

According to an embodiment of the present invention, a frequency for allocating a synchronization channel is determined for a case where sub-channels are arranged in an OFDM symbol immediately after a subframe boundary and a case where sub-channels are arranged in an OFDM symbol immediately before a subframe boundary. Explain how.

First, a method of determining a frequency to which a sync channel is to be allocated when the sub sync channel is disposed in an OFDM symbol immediately after the subframe boundary will be described with reference to FIG. 4. FIG. 4 is a diagram illustrating the arrangement of a main sync channel and a sub sync channel in a frequency domain when the sub sync channel is arranged in an OFDM symbol immediately after a subframe boundary.

P-SCH means primary synchronization channel, and S-SCH indicates secondary synchronization channel. Pilot 1 and pilot 2 each represent a pilot for one antenna.

As shown in FIG. 4, the primary synchronization channel is arranged at two subcarrier intervals. By arranging the main sync channels in this way, not only the cross correlation technique but also the sync acquisition method using a repeated pattern can be used.

The pilot is located in the first OFDM symbol of the subframe. 4 shows that pilots for two antennas are distributed at six subcarrier intervals, respectively. Therefore, when the sub-sync channel is arranged at a frequency where the pilot is not located, the sub-sync channel is divided into a pilot channel and a frequency. That is, the sub-channel code is assigned to a frequency where the pilot is not distributed. As a synchronization channel code, a generalized chirp like (GCL) code such as Equation 1 may be used.

Where N is the length of the sequence. In particular, each code length N in the GCL sequence is prime and there are a total of N-1 sequences.

Next, a method of determining a frequency to which a sync channel is to be allocated in case of arranging the sub-sync channel in an OFDM symbol immediately before the subframe boundary will be described with reference to FIG. FIG. 5 is a diagram illustrating the arrangement of a main sync channel and a sub sync channel in a frequency domain when the sub sync channel is arranged in an OFDM symbol immediately in front of a subframe boundary.

As shown in FIG. 5, sub-sync channels are arranged at two subcarrier intervals. That is, the sub-sync channel codes are sequentially arranged at two subcarrier intervals.

 In the first OFDM symbol of the subframe, pilot 1 and pilot 2 are arranged at six subcarrier intervals, respectively, and the main sync channel is divided into two subcarrier intervals separated by pilot and frequency. In this way, there is an advantage that the sub-synchronous channels are distributed at regular intervals in the frequency domain.

IFFT 220 converts the synchronous channel signal to be transmitted to the transmission signal in the time domain through the inverse fast Fourier transform (S320).

The guard interval inserting unit 230 inserts a CP into the main sync channel signal and the sub sync channel signal converted into the transmission signal in the time domain to generate a main sync channel and a sub sync channel (S330).

In an OFDM cellular system, if the CP length is variably set so that an appropriate CP can be selected according to channel environment and service characteristics, overall system performance can be improved. Accordingly, the length of the CP of the downlink synchronization channel of the OFDM cellular system according to the embodiment of the present invention may be appropriately set according to the channel environment and service characteristics.

Hereinafter, a method of inserting a CP for each of a downlink sub-sync channel of an OFDM cellular system according to an embodiment of the present invention having a short CP and a long CP will be described with reference to FIGS. 6 to 8.

In the embodiment of the present invention, a method of inserting a CP into a sub-sync channel signal when the main sync channel is located in the time domain is described. The same applies to the case where a CP is inserted into a signal.

6 is a diagram illustrating a synchronization channel configuration method and a synchronization acquisition method according to an embodiment of the present invention when the secondary synchronization channel has a short CP, and FIG. 7 illustrates a synchronization channel configuration method and a synchronization method when the secondary synchronization channel has a long CP. 8 is a diagram illustrating an acquisition method, and FIG. 8 is a diagram illustrating a synchronization channel configuration method and a synchronization acquisition method according to an embodiment of the present invention when a sub-sync channel has a long CP.

First, when the sub-sync channel has a short CP, as shown in FIG. 6, the last part of the sub-sync channel signal IFFTed in step S320 is cut by the length of N _S and attached to the front part of the IFFT sub-channel signal. . Where N _S is the length of the short CP. At this time, the main synchronization channel may have a short CP or may have a long CP.

When receiving the same synchronization channel as the transmission structure of FIG. 6, the cell searcher of the mobile station performs fast Fourier transform by taking accurate timing using the main synchronization channel and taking a certain period of data separated by N _S samples from the main synchronization channel. The signal is converted into a signal in the frequency domain, and cell search is performed using the signal in the frequency domain.

Next, a method of inserting a CP when the sub-sync channel has a long CP will be described.

As shown in FIG. 7, a case in which the CP is inserted by pasting the last part of the IFFT sub-channel signal by N _{L, which} is the length of the long CP, is added to the front part of the IFFT sub-channel signal in step S320. When the cell search unit of the terminal receives a synchronization channel as shown in FIG. 7 and sets a timing using the main synchronization channel, takes a predetermined period of data separated by N _S samples from the main synchronization channel, and performs fast Fourier transform. It is shifted in time from the IFFT sub-sync channel signal transmitted by the. Therefore, the channel value estimated as the primary synchronization channel cannot be used as the channel value for the secondary synchronization channel.

In order to solve the above problems, in the embodiment of the present invention, as shown in FIG. 8, the last part of the IFFT sub-sync channel signal is cut by N _S and pasted to the front part of the IFFT sub-sync channel signal, and the IFFT sub-sync is performed. CP is inserted by cutting the front part of the channel signal by N _L -N _S and attaching it to the last part of the IFFT sub-sync channel signal. At this time, the main synchronization channel may have a short CP or may have a long CP.

In such a structure, when the cell searcher of the terminal receives a synchronization channel as shown in the transmission structure of FIG. 8, sets a timing using the main synchronization channel, and takes a certain period of data separated by Ns samples from the main synchronization channel, the base station transmits the data to the base station. It coincides in time with the IFFT sub-sync channel signal. Therefore, the main sync channel and the sub sync channel have the same channel value in the frequency domain.

Next, the base station arranges a sync channel into which the CP is inserted in the frame (S340).

9 is a diagram illustrating a synchronization channel arranged in a frame according to an embodiment of the present invention. In FIG. 9, one of SCH1 and SCH2 represents a primary synchronization channel and the other represents a secondary synchronization channel. That is, if SCH1 represents a primary synchronization channel, SCH2 represents a secondary synchronization channel, and if SCH1 represents a secondary synchronization channel, SCH2 represents a primary synchronization channel.

As shown in Fig. 9, the main sync channel and the sub sync channel arrange a sync channel in a frame adjacent to each other at the boundary of a subframe. That is, the primary sync channel is placed in an OFDM symbol immediately before the subframe boundary and the subsync channel is placed in an OFDM symbol immediately after the subframe boundary, or the primary sync channel is placed in an OFDM symbol immediately after the subframe boundary and The channel is placed in the OFDM symbol immediately before the subframe boundary.

As described above, the cell searcher of the terminal correlates the received data with a known main sync channel signal in order to find the synchronization of the received signal, and averages the correlation values for several hours, and has a different CP length in one frame. If OFDM symbols are mixed, there is a problem that the average cannot be performed for several hours.

However, when the synchronization channel is positioned in the first or last OFDM symbol in the subframe as in the embodiment of the present invention, the length of the subframe is always a constant value, so a time average can be applied.

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

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

1 is a diagram illustrating the structure of a frame and a synchronization channel in an OFDM cellular system.

2 is a block diagram showing an apparatus for transmitting a downlink sync channel of a base station according to an embodiment of the present invention.

3 is a flowchart illustrating a downlink sync channel transmission method according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating the arrangement of a main sync channel and a sub sync channel in a frequency domain when the sub sync channel is arranged in an OFDM symbol immediately after a subframe boundary.

FIG. 5 is a diagram illustrating the arrangement of a main sync channel and a sub sync channel in a frequency domain when the sub sync channel is arranged in an OFDM symbol immediately in front of a subframe boundary.

6 is a diagram illustrating a synchronization channel configuration method and a synchronization acquisition method according to an embodiment of the present invention when the secondary synchronization channel has a short CP.

7 is a diagram illustrating a synchronization channel configuration method and a synchronization acquisition method when a secondary synchronization channel has a long CP.

8 is a diagram illustrating a synchronization channel configuration method and a synchronization acquisition method according to an embodiment of the present invention when the secondary synchronization channel has a long CP.

9 is a diagram illustrating a synchronization channel arranged in a frame according to an embodiment of the present invention.

Claims (13)

Inserting a first guard period into the first sync channel signal to generate a first sync channel; Generating a second synchronization channel by inserting a second guard interval into the second synchronization channel signal; Disposing the first sync channel in a downlink frame such that the first sync channel is located immediately before a boundary of a subframe; And Disposing the second synchronization channel in the downlink frame such that the second synchronization channel is located immediately after a boundary of the subframe; One of the first synchronization channel and the second synchronization channel is a primary synchronization channel and the other is a secondary synchronization channel. The method of claim 1, The second guard period may optionally have one of a plurality of lengths including a first length or a second length, And the second length is longer than the first length. The method of claim 2, Generating the second sync channel And cutting the last portion of the second synchronization channel signal by the first length and inserting the last portion of the second synchronization channel signal in front of the second synchronization channel signal. The method of claim 3, Generating the second sync channel If the second guard period has the second length, cutting the front part of the second sync channel signal by a difference between the second length and the first length and inserting the second guard channel signal into the last part of the second sync channel signal. Downlink synchronization channel transmission method further comprising. The method according to any one of claims 1 to 4, And determining a frequency to which the primary sync channel and the sub sync channel are allocated. The method of claim 5, The first synchronization channel is a primary synchronization channel and the second synchronization channel is a secondary synchronization channel, Determining the frequency And assigning the second sync channel to a frequency where no pilot is located. The method of claim 6, Determining the frequency And disposing the first synchronization channel at two subcarrier intervals. The method of claim 5, The first sync channel is a sub-sync channel and the second sync channel is a main sync channel, Determining the frequency And disposing the second synchronization channel at two subcarrier intervals. The method of claim 8, Determining the frequency And disposing the first sync channel at two subcarrier intervals at a frequency at which a pilot is not located. A guard interval insertion unit inserting a first guard interval into the first sync channel signal to generate a first sync channel and inserting a second guard interval into the second sync channel signal to generate a second sync channel; And Place the first sync channel in a downlink frame such that the first sync channel is located directly in front of the boundary of the subframe, and direct the second sync channel to the downlink so that the second sync channel is just behind the boundary of the subframe. Including a frame arranging unit disposed in the frame, And one of the first synchronization channel and the second synchronization channel is a primary synchronization channel and the other is a secondary synchronization channel. The method of claim 10, The guard period may optionally have one of a plurality of lengths including a first length or a second length longer than the first length, The protective section insertion portion When the second guard period has the second length, the last part of the second sync channel signal is cut by the first length and inserted into the front part of the second sync channel signal, and the front part of the second sync channel signal is included. And inserting into the last portion of the second synchronization channel signal by cutting the second length by the difference between the first length and the first length. The method according to any one of claims 10 to 11, And a frequency allocator configured to determine a frequency to which the primary sync channel and the sub sync channel are allocated. The method according to any one of claims 10 or 11, And an inverse fast Fourier transform unit for converting the first sync channel signal and the second sync channel signal into a transmission signal in a time domain through an inverse fast Fourier transform.

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