KR100567313B1 - Method for searching cell in orthogonal frequency division multiple access system - Google Patents

Abstract

The present invention relates to a cell search method performed by a user terminal to distinguish a base station to which the user terminal belongs among multiple base stations in an orthogonal frequency division multiple access system.

A cell search method in an orthogonal frequency division multiple access system according to the present invention includes a first step of encoding and transmitting a pilot used for channel estimation and synchronization at an base station using an encoder including a mutual orthogonal code assigned to each base station. And a second step of searching for a cell through the ID cell searcher after receiving the encoded and transmitted pilot.

Therefore, the cell search method in the orthogonal frequency division multiple access system of the present invention is simple in structure because the cell search is possible using only a mutual orthogonal code encoder, a multiple orthogonal code decoder, and an ID cell selector. It does not need to generate a preamble, so the transmission efficiency is excellent. The ID cell index of the base station can be immediately known while extracting the fixed position pilot encoded by the receiver of the terminal, thereby enabling fast cell search. As a result, the cell search performance is excellent because it is resistant to co-channel interference.

Orthogonal Frequency Division Multiple Access, Cell, Search, Mutual Orthogonal Code Encoder, Multiple Mutual Orthogonal Code Decoder, ID Cell Selector, ID Cell Searcher, Pilot

Description

Method for searching cell in orthogonal frequency division multiple access system             

1 is an example of a multi-cell according to one embodiment of the invention.

2 is a schematic diagram of a base station transmitter for cell search in an orthogonal frequency division multiple access system according to an embodiment of the present invention;

3 is an example of a mutual orthogonal code set necessary to perform an operation of a mutual orthogonal code encoder according to an embodiment of the present invention.

4 is an example of a mutual orthogonal code encoder operation for a 0 th base station according to an embodiment of the present invention.

5 is a schematic diagram of a terminal receiver for cell search in an orthogonal frequency division multiple access system of the present invention;

6 is a structure of a multiple mutual orthogonal code decoder used in the receiver of the present invention.

<Description of Symbols for Main Parts of Drawings>

200: Mutual Orthogonal Code Encoder 500: ID Cell Explorer

510: ID cell selector 520: multiple mutual orthogonal code decoder

The present invention relates to a method for searching for a cell in an orthogonal frequency division multiple access (OFDMA) system using an orthogonal frequency division multiple access, and more particularly to a fixed-location pilot (FLP). When a service user exists in a multi-cell made up of base stations transmitting a variable-location pilot (VLP) and a data carrier (DCA), the base station to which the terminal belongs is selected. In order to distinguish, the fixed position pilot is encoded according to a mutually orthogonal code (MOC) selected according to a unique ID cell index of each base station, and transmitted after receiving the encoded pilot ID. The present invention relates to a method of searching for a cell through a cell searcher.

Orthogonal frequency division multiplexing, which is being actively studied in recent years as a method suitable for high-speed data transmission in wired and wireless channels, is a type of multi-carrier transmission using multiple carriers, and the transmission period in each channel is increased by the number of carriers. In this case, the frequency-selective channel appearing in wideband transmission is approximated as a non-selective channel with no intersymbol interference, so a simple single tap equalizer can compensate. The orthogonal frequency division multiplexing method is adopted as a standard method of digital audio broadcasting and digital terrestrial television broadcasting by enabling a single frequency network, such as 4G mobile communication, next generation home phoneline networking alliance and power line communication. It is being considered for high speed transmission in the system.

In an orthogonal frequency division multiple access system, a system that allocates subchannels to each terminal so that multiple terminals can access the base stations, when the base stations are composed of multiple cells and the same frequency bands are used for each base station, one terminal is connected to the downlink ( Downlink: A base station transmits a signal from a base station to a signal transmitted from several base stations. In this case, in order for the terminal to communicate, it is necessary to distinguish a base station to which the terminal can access and transmit a signal transmitted from the base station. You should be able to receive it continuously. Performing this operation is called cell search.

It is understood that there is no proposed method for a cell search method for an orthogonal division multiple access system. In the conventional wireless communication system, the cell search method has been code division multiple access (CDMA) cell search methods.

The cell search method using the optimal frame synchronization code of the prior art Korea Patent Publication No. 10-2000-0075107 is used for frame synchronization in the downlink to the next generation mobile communication system using the wideband code division multiple access method (W-CDMA) As a method of searching a cell using an optimal pilot sequence, a method of cell searching is provided by mapping a new code pattern on a secondary sync channel to each I-channel feeder and a Q-channel feeder.                         

However, the conventional cell search method using the optimal frame synchronization code as described above is a cell search method used in a wideband code division multiple access system rather than an orthogonal frequency division multiple access system. The structure is complicated because a differential synchronization channel is required. In addition, since each frame sync and code group are identified using a new code sequence for the secondary sync channel, it takes a long time to perform a cell search and has a problem of poor cell search performance due to weak co-channel interference.

In addition, the conventional high-speed cell search apparatus and method of the asynchronous code division multiple access communication system of the Republic of Korea Patent Publication No. 10-2001-0008719 has a first section having the second synchronous code information and scramble code number information Cell searching with a fast cell searching apparatus of an asynchronous code division multiple access communication system comprising a base station transmitting a second synchronous channel consisting of a second section consecutive in one section and a terminal obtaining the scramble code number at the same time as obtaining frame synchronization A method for acquiring a scramble code number at the same time as acquiring time frame synchronization is provided.

However, the conventional fast cell search apparatus and method of the asynchronous code division multiple access communication system described above is a synchronization channel for searching a cell by a cell search method used in an asynchronous code division multiple access system rather than an orthogonal frequency division multiple access system. Since these two and additional scramble codes are needed, the structure is complicated, the transmission efficiency of the system is decreased, and the cell search performance is deteriorated due to the weak interference channel.                         

In addition, the cell search apparatus and method in the conventional wireless communication system of the Republic of Korea Patent Publication No. 10-2001-0081863 The slot synchronization search means for acquiring slot synchronization using the main synchronization channel; Frame synchronization code group searching means for receiving frame synchronization and code group by receiving sub-synchronization channels in accordance with the slot synchronization obtained by the slot synchronization searching means, and timing the frame synchronization obtained by the frame synchronization and code group searching means. And a cell spreading code searching means for searching for a spreading code of a cell using a spreading code corresponding to a code group.

However, the above-described cell search apparatus and method in the conventional wireless communication system do not mention the transmitter of the base station, but only the receiver of the terminal is proposed, and the frame synchronization and code group search means and the cell spreading code Since cell searching is performed through several steps through cell spreading code searching means for searching, there is a problem that the cell searching speed is slow and the structure is complicated.

Accordingly, the present invention is to solve the problems of the prior art as described above, in the orthogonal frequency division multiple access system to encode the pilot that each base station must use for synchronization and channel estimation to its own mutual orthogonal code Cell search method which improves the transmission efficiency of the system, enables fast cell search, and improves cell search performance by being resistant to interference between the same channels by detecting the pilot received from the terminal with a multi-orthogonal decoder and ID cell selector. It is an object of the present invention to provide.

The above object of the present invention is to receive a first step of transmitting a pilot used for channel estimation and synchronization at a base station using an encoder including a mutual orthogonal code assigned to each base station, and then transmitting the encoded and transmitted pilot. A cell search method in an orthogonal frequency division multiple access system comprising a second step of searching for a cell through an ID cell searcher.

A method of searching for a cell by inserting a mutual orthogonal code encoder (MOC encoder) into the transmitter structure of the base station and inserting an ID cell searcher into the receiver structure of the terminal for the cell search. The signal transmitted from the transmitter of the base station can be largely divided into a fixed position pilot, a variable position pilot, and a data carrier.

 The fixed position pilot is used to determine the position of the carrier and information bits to be transmitted. The fixed position pilot is used to synchronize the channel estimation at the receiving end of the terminal. Information bits to be determined are defined. The data carrier also corresponds to information bits transmitted to the terminal.

In the orthogonal frequency division multiple access system of the present invention, a base station-specific mutual orthogonal code encoder determined according to an ID cell index to distinguish a base station where a user is located when each base station transmits a fixed position pilot, a variable position pilot, and a data carrier. When the pilot is encoded and transmitted using the UE, the receiver may transmit the encoded and transmitted pilot through the ID cell searcher including a multiple MOC decoder and an ID cell selector. Searching.

The ID cell index is a value for determining a subchannel of each base station and subcarriers constituting the subchannel, and the mutual orthogonal code encoder performs one row according to an ID cell index, which is a unique value of the base station among mutual orthogonal code sets. An encoder having mutually orthogonal codes determined by selection. In addition, the multi-orthogonal code decoder outputs respective values by taking parallel correlation between pilots received from a terminal and codes of multi-orthogonal cross-orthogonal codes and pilots and multi-orthogonal codes. The ID cell index having the maximum value is output by comparing the values output from the mutually orthogonal code decoders.

In addition, the pilot of the first stage may be divided into using only a fixed position pilot, using only a variable position pilot, or using both a fixed position pilot and a variable position pilot. And the information bits to be transmitted are determined, and the signal transmitted from the transmitter is received first in the terminal, so it is most commonly used in a cell search method. The variable position pilot is used when the terminal is orthogonal frequency when the number of base stations increases or co-channel interference is severe. It is used when it is possible to estimate the position of the variable position pilot that changes for each divided multiple access symbol.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, Figure 1 is an example of a multi-cell according to an embodiment of the present invention. Referring to FIG. 1, one base station (BS) forms one cell of a regular hexagon and service users (SSs) are uniformly distributed in the cell. If a plurality of base stations form a multi-cell and the frequency bands used by each base station are the same, the user's terminal receives all signals transmitted by the base station. Therefore, the user cannot know which base station he will be communicating with, so he must find a base station to which he will communicate among the received signals.

2 is a schematic diagram of a base station transmitter for cell search in an orthogonal frequency division multiple access system according to an embodiment of the present invention. As shown in FIG. 2, the transmitter of the base station is a pilot pseudo random binary sequence (PRBS) generator for generating information bits to be carried on a subcarrier (SCA) used as a pilot, and a pilot splitter for selecting information bits used as a pilot. (Pilot splitter), fixed position pilot modulator (Fix.pilots modulator) and variable position pilot modulator (Var. Pilots modulator) for modulating the fixed position pilot and variable position pilot information bits respectively, mutually orthogonal code set according to the ID cell index ( A mutual orthogonal code encoder 200 for processing an input signal by selecting one mutual orthogonal code from a MOC set, a multiple data generator for generating data to be delivered to service users, and an information bit of the service user Is assigned to the sub-channel (SCH: Subchannel) of the service user according to the ID cell index Data carrier allocation, a data carrier modulator for modulating the information bits of the service user, a DC & Null inserter for generating 0 bits, and an input signal on the frequency axis to an output signal on the time axis It consists of a CP inserter inserting a cyclic prefix to prevent the destruction of orthogonality caused by the inverse fast fourier transform (IFFT) and the delay of the subcarrier.

3 is an example of a mutual orthogonal code set required to perform an operation of a mutual orthogonal code encoder according to an embodiment of the present invention. C represents a mutually orthogonal code. As shown in FIG. 3, each mutual orthogonal code set is determined according to an ID cell index, and the determined mutual orthogonal code is assigned to each base station. There are several ways to generate the mutual orthogonal code set, and any code that is orthogonal to each other is possible if the length is equal to the number of bits of the fixed position pilot.

Next, FIG. 4 is an example of a mutual orthogonal code encoder operation for a 0 th base station according to an embodiment of the present invention. p denotes a fixed position pilot and q denotes a signal obtained by multiplying a fixed position pilot and a mutually orthogonal code. As shown in FIG. 4, the mutual orthogonal code encoder sequentially multiplies and outputs a mutual orthogonal code to a pilot transmitted from a base station.

5 is a schematic diagram of a receiver in an orthogonal frequency division multiple access system of the present invention. As shown in FIG. 5, the structure of the receiver is a coarse symbol synchronizer that determines whether a signal is received, detects a start point of a received orthogonal frequency division multiple access symbol, and removes a cyclic prefix. Fast fourier transform (FFT) to transform the signal on the frequency axis, fixed position pilot extractor (Fix.pilot extractor) to extract the information bits of the fixed position pilot that the service user already knows, and the fixed position pilot information bits back to the time axis signal Multiple mutual orthogonal code decoder 520 which processes and outputs the values of the channel fixed impulse response (CIR) position which finds the exact time of FFT execution using the input IFFT, the input signal, and the encoded fixed position pilot received by the terminal. ID cell selector 510 for outputting an input index having the largest value among the signals The ID cell searcher 500 including the frequency offset and the frequency offset (FO) & channel (CH) estimator used for estimating the frequency offset and the channel, and using the output values of the FO & CH evaluation unit for the input signal An FO & CH compensator performing a compensating function, and a variable position pilot extractor (Var. Pilot extractor) extracting information bits of a position by finding a position of a subcarrier used as a variable position pilot.

6 is a structure of a multiple mutual orthogonal code decoder used in the receiver of the present invention. As shown in FIG. 6, the multiple mutual orthogonal code decoder receives an encoded fixed position pilot received by a terminal after being input to a multiple mutual orthogonal code decoder having codes in a form of multiplication of the multiple orthogonal codes of the base station and the fixed position pilot. The codes and the encoded fixed position pilot received by the terminal are correlated in parallel to output respective values.                     

Although the present invention has been shown and described with reference to preferred embodiments as described above, it is not limited to the above-described embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

Therefore, the cell search method in the orthogonal frequency division multiple access system of the present invention is simple in structure because the cell search is possible using only a mutual orthogonal code encoder, a multiple orthogonal code decoder, and an ID cell selector. It does not need to generate a preamble, so the transmission efficiency is excellent, and since the ID cell index of the base station is immediately known while extracting the fixed position pilot encoded at the receiver, the fast cell search is possible. It is resistant to co-channel interference and has an excellent cell search performance.

Claims (11)

A cell search method in an orthogonal frequency division multiple access system, A first step of encoding and transmitting a pilot used for channel estimation and synchronization at a base station using an encoder including a mutual orthogonal code assigned to each base station; and A second step of searching for a cell through an ID cell searcher after receiving the encoded and transmitted pilot; Cell search method in an orthogonal frequency division multiple access system comprising a. The method of claim 1, The mutual orthogonal code is determined by selecting one row from a mutual orthogonal code set according to an ID cell index, which is a unique value of each base station, and assigned to each base station. The method of claim 2, And the ID cell index is a value for determining a subchannel of each base station and subcarriers constituting the subchannel. The method of claim 1, The ID cell searcher includes a multiple mutual orthogonal code decoder and an ID cell selector. The method of claim 4, wherein The multi-orthogonal code decoder multi-orthogonal frequency division multiplexing, characterized in that to take the parallel correlation of the pilot multi-orthogonal codes and the code of the form multiplied by the base station and the pilot received from the terminal and output the respective values Cell search method in the access system. The method of claim 4, wherein And the ID cell selector outputs an ID cell index having a maximum value by comparing values output from the multiple mutual orthogonal code decoders. The method of claim 1, And the pilot of the first step uses a fixed position pilot. The method of claim 7, wherein Wherein the fixed position pilot is used to synchronize with channel estimation at a receiving end of a terminal. The method of claim 1, And the pilot of the first step uses a variable position pilot. The method of claim 9, The variable position pilot is used when the terminal can estimate the position of the variable position pilot that changes for each orthogonal frequency division multiple access symbol. The method of claim 1, And the pilot of the first step uses both a fixed position pilot and a variable position pilot.

Images