KR100281095B1 - Mobile communication system cell searching apparatus and method - Google Patents

Abstract

The present invention relates to a method and apparatus for detecting a start point of a base station group and a frame of a second stage when a synchronization channel signal is transmitted from a base station to a mobile station in an asynchronous wideband code division multiple access (CDMA) And more particularly to a mobile communication system cell search apparatus and method capable of finding cells transmitted from a base station more quickly and accurately with hardware having a simpler configuration. According to another aspect of the present invention, there is provided an apparatus for searching for a cell of a mobile communication system, comprising: a correlation unit for obtaining a plurality of correlation values from an input signal; memory means for sequentially storing correlation values obtained by the correlation unit; A slot counter for addressing a plurality of slot data stored in the memory means by an input clock ca_s2_clock, a slot counter for storing a plurality of slot data stored in the memory means, A code group counter for counting an index of a candidate code group according to a carry output from the shift count; and an accumulator for accumulating a correlation value of one frame amount output from the memory means, And an optimum code arrangement for the output signal of the accumulator And a peak detector for detecting the peak value.

Description

Mobile communication system cell searching apparatus and method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cell search method in a mobile communication system, and more particularly, to a cell search method in a mobile communication system using an asynchronous Wideband Code Division Multiple Access (CDMA) And more particularly to a cell search apparatus and method in a mobile communication system adapted to search for a cell in a short period of time.

In an asynchronous wideband code division multiple access (OFDMA) mobile system, a cell search method provided by a base station is roughly divided into three steps.

The first step ST1 detects the synchronization channel signal SCH1 provided by the base station and finds the start point of any one of 16 slots per frame.

The second step ST2 detects the synchronization channel signal SCH2 provided by the base station based on the starting point of the slot found in the first step and transmits the synchronization channel signal SCH2 sent to the base station group to the beginning of the frame Is the step of finding out where.

The third step ST3 detects the CCPCH1 signal using the information on the known base station group and the start of the frame in the second step and detects which base station among the 16 base stations in the base station group identified in the second step It is a step to find out. At this time, if the cell provided by the base station is not found in the third step, the process returns to the first step and all the steps described above are repeatedly executed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for transmitting a synchronization channel signal from a base station to a mobile station in an asynchronous Wideband Code Division Multiple Access (CDMA) The present invention provides a mobile communication system cell search apparatus and method capable of quickly and accurately searching cells transmitted from a base station with hardware having a simple configuration.

According to an aspect of the present invention, there is provided a mobile communication system cell search apparatus including a correlator for obtaining a plurality of correlation values from an input signal,

A memory for storing the correlation value obtained by the correlation unit in order; a code storage unit for storing the code list for each code group and providing a stored value to the memory means, if necessary; and an input clock (ca_s2_clock) A slot count for addressing a plurality of stored slot data; a shift count for counting a start point of a frame by a carry output from the slot counter; and an index of a candidate code group by a carry output from the shift count An accumulator for accumulating a correlation value of one frame amount outputted from the memory means; and a peak detector for detecting an optimal code sequence with respect to an output signal of the accumulator.

According to another aspect of the present invention, there is provided a method for searching for a cell in a mobile communication system, comprising: detecting a synchronization channel signal provided from a base station to find a start point of an arbitrary one of a plurality of slots configured per frame; The method of claim 1, further comprising: storing correlation values obtained by repeatedly performing the correlation in a memory, and determining whether the synchronization channel signals are either And to find out where the start of the frame belongs to the base station group.

1 is a diagram for explaining a general cell search process;

2 is a block diagram of a cell search circuit of a terminal receiving terminal according to the present invention;

FIG. 3 and FIG. 4 are timing diagrams each illustrating a cell search process according to an embodiment of the present invention; FIG.

Description of the Related Art [0002]

10: Correlation unit 20: Address counter

30: ram 40, 70: adder

50: multiplier 60: code storage unit

80: code group counter 90: shift counter

100: Slot counter 110: Group register

120: Shift register 130: Accumulator

140: peak detector 141: comparator

142: buffer

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

2 is a block diagram of a cell search circuit of a terminal receiving terminal according to the present invention.

Referring to FIG. 2, the cell search circuit of the terminal of the present invention includes a correlation unit 10 for obtaining 17 correlation values from an input signal, a RAM (Random Access Memory) for sequentially storing correlation values obtained by the correlation unit 10, A code storage unit 60 for storing a code list for each code group as shown in Table 1 below and providing a stored value to the RAM 30 as needed; A slot counter 100 for addressing 16 slot data stored in the slot counter 30, a shift counter 90 for counting a start point of a frame by a carry output from the slot counter 100, A code-group counter 80 for counting the index of the candidate code group by a carry output from the shift count 90 and a code-group counter 80 for counting one frame amount output from the RAM 30, An accumulator for accumulating the correlation value, And a peak detector 140 for detecting an optimal code sequence with respect to an output signal of the accumulator 130. [

The cell search circuit having such a configuration is for implementing the second step of searching for cells transmitted from the base station. That is, for the code group identification process as the second step in the cell search process, the synchronization channel signal SCH2 transmitted from the base station is selected from 17 orthogonal gold codes, and is divided into 32 code groups . The SCH2 code assigned to each code group is composed of 16 codes selected by allowing overlap among 17 orthogonal Gold codes as shown in Table 1 below. Also, as shown in FIG. 1, 16 codes are transmitted from the base station in 16 slots during one frame period. One code consists of 256 1 or -1 data and is transmitted at the chip rate set at the start of each slot.

In FIG. 2, the signal cs_in_I represents an I channel input signal, cs_in_Q represents a Q channel input signal, cs_s2_slot represents a slot synchronous signal detected in the first step for cell search, and cs_s2_test_frame represents a data Indicates a signal indicating the starting point. The offset of the slot of the starting point of the actual frame detected based on this signal is obtained. Also, Cs_s2_on indicates a signal indicating the start of the second step for cell search, cs_chip indicates a clock of a chip rate, and is used to obtain correlation during 256 chips.

cs_s2_clock denotes a clock used during the secondary cell search period according to the present invention, end_of correlation denotes a signal for starting the secondary search process after the first search process according to the present invention, and corr (b, j) indicates a clock used for the cs_s2_test_frame Represents the output of the b < th > correlator at the j < th >

j represents the contents of the slot counter and is usually increased from 16 to 16 modulo.

i is the value of the slot off being measured by the content of the shift counter 90. It is usually increased from 0 to 16 to 16 by the module.

g is the index of the code group under measurement as the content of the code group counter 80. [ It usually increases from 0 to 31.

Cs_s2_SCH2_detected indicates a signal notifying the external module that the code group and slot off has been detected, and Cs_s2_SCH2_group is valid only when Cs_s2_SCH2_detected is activated as the detected code group.

Cs_s2_SCH2_shift is valid only when Cs_s2_SCH2_detected is active with the detected slot offset.

Code group Group sync code 0 C1, C2, C11, C6, C3, C15, C7, C8, C8, C7, One C1, C2, C9, C3, C10, C11, C13, C13, C11, C10, C3, C9, ..... 31 C2, C5, C7, C5, C2, C11, C10, C9, C15, C13, C15,

Hereinafter, a cell search process according to the present invention will be described with reference to the accompanying drawings.

The first step ST1 detects the synchronization channel signal SCH1 provided by the base station in the conventional manner and finds the starting point of any one of 16 slots per frame.

The second stage ST2 is divided into two stages. That is, in the first step, the output data of the correlator 10 composed of 17 correlators per slot is stored in the RAM 30 during the 16-slot period, and in the second process, Find out the starting point of the frame.

That is, in the first step, 17 correlations are performed for 256 chips according to the signal (cs_s2_slot) indicating the start time of the detected slot in the first stage of the cell search. Here, the correlation is performed in 16 slots in order, and the result of the correlation value is stored in the RAM 30 every slot. At this time, the order of the correlators corresponding to the correlation values stored in the RAM 30 is performed for each slot, and the order is performed in the order of the set slots in each slot. However, the address of the data stored in the RAM 30 will increase continuously without being repeated at a predetermined period (for example, 16) as the number of the correlator. At this time, when the value of the address counter 20 becomes 272, the correlation process is completed and the second process is started.

In the second step, the start point of the code-group and the frame is found from the data stored in the RAM 30. The code storage unit 60 of FIG. 2 stores data shown in Table 1 in advance. At this time, the data to be stored is the number of the correlator, minus 1 in the code number in Table 1.

Address data 0 0 One 0 2 One 3 10 4 5 5 2 6 14 7 6 8 7 9 7 10 6 11 14 12 3 13 5 14 10 15 One 16 0 ... ...

In the second step, the starting point of the frame is found as follows.

You can not know the starting point of the frame right now. Therefore, the Cs_s2_test_frame signal is generated at a frame period from an arbitrary slot start point as shown in FIG. Assuming that the g-th code based on the Cs_s2_test_ frame and the frame starts from the i-th slot, the address of the correlator to be observed in the j-th slot can be obtained using Equation 1 as follows.

j = 16 * j? + j-i 16% [9bit]

In FIG. 2, the upper 5 bits of the address are set to the value of the code-group counter 80, and the lower 4 bits are used to subtract the shift counter 90 from the slot counter 100 and then carry out the carry. Here, if the number of the correlator corresponding to the address is expressed by the following expression 2,

the address of the RAM 30 in which the output of the c (g, i, j) -th correlator in the j-th slot is stored can be obtained using Equation 3 below.

a _R (g, i, j) = 17 * j + c (g, i, j)

2, the output of the slot counter 100 is multiplied by 17, and the value of the code table stored in the code storage unit 60 is added to obtain the address of the RAM 30.

Assuming that the g-th code-group with respect to the Cs_s2_test_ frame-group starts from the ith slot, the sum of the 16 slot correlators can be obtained using Equation 4 below.

This process is calculated by the accumulator 130 sharing the clock with the slot counter 100. [

The optimal code-group G and slot offset I are indexes that maximize corr (i) and can be obtained using Equation 5 below.

(G, I) = arg max _{g, i} [corr (g, i)]

This process is performed by a peak detector 140 that shares a clock with the shift counter 90. When the comparator 141 of the peak detector 140 detects a new maximum value, the code-group counter 80 sends the value to the group register 110 and the value of the shift counter 90 is loaded into the shift register 120 , 0 to 31 code-groups, and 0 to 15 slot offsets, the index of the code-group used by the base station is left in the group register 110, and the Cs_s2_test_ frame is stored in the shift register 120 The number of slots to the actual frame remains as a reference.

The second step of the second step of the cell search step according to the present invention will now be described with reference to FIG.

4, the accumulator 130 is cleared to "0" and the values of the slot counter 100, the shift counter 90 and the code group counter 80 are initialized to "0" do. First, a test is performed assuming that the code group is "0" and the slot offset is "0" for 16 clocks while Cs_s2_clock is supplied.

C1, C2, C11, C6, C3, C15, C7, C8, C8, C7, and C8 during the 16 slots since the code-group is assumed to be "0" and the slot offset to be " C15, C3, C6, C11, C2.

At this time, the number of correlators corresponding to the above code is expressed by Equation 6 below.

C (0, 0, j)

0, 0, 1, 10, 5, 2, 14, 6, 7, 7, 6, 14, 2, 5, 10, 1

Here, the correlator number is obtained by substituting g = 0 and i = 0 in Equation 1 and then obtaining the address of the code-group while increasing the slot, that is, j from 0 to 15 and then obtaining from the code-group table shown in Table 2 . The output value of the code-group table corresponds to c (g, i, j) in Equation 2. Here, the output of the correlator is stored in the RAM 30 during the first course of the process. At this time, the corresponding address can be obtained by Equation 3

a _R (0, 0, j)

17,35,61,73,87,116,125,143,160,176,201,206,226,248,256

As the j increases, that is, as the slot counter increases, the address value is applied to the RAM 30 and the corresponding data (Correlation value) is output to the RAM_out 16 times in order. (See Equation 4). This value is compared to " 0 " initially stored in max_value as the output of the initial accumulator 130 and a large value is stored in max_value. At this time, if the output x of the accumulator 130 is larger than max_value y, w becomes 1, the value "0" of the code-group counter 80 is loaded into the group register 110, 0 " is loaded into the shift register 120.

As described above, when the test is performed when the value of the group register 110 is "0" and the value of the shift register 120 is "0", a carry is generated in the slot counter 100, Quot; 0 " and the slot offset " 1 ".

In this case, since the slot offset is one slot, the code numbers to be received are the same as the order of C2, C1, C1, C2, C11, C6, C3, C15, C7, C8, C8, C7, C15, C3, .

Since the slot offset is assumed to be " 1 ", the frame start code C1 must be received in the first slot and the last code C2 must be received in the 0th slot.

The process of obtaining the address of the RAM 30 and the process of obtaining the address of the RAM 30 can be performed by setting i = 1 and repeating the previous process.

When the value of the shift counter 90 exceeds 15, the second-order process described above is repeated, and the value of the code-group counter 80 is increased.

Finally, when the value of the code-group counter 80 exceeds 31, a carry occurs. This indicates that the test for all the code groups and all the slot offsets has been completed. Therefore, cs_s2_SCH2_detected is activated and the cell search The process ends. In this case, the optimal code group is stored in the group register 110, and the optimal slot offset is stored in the shift register 120.

According to the present invention as described above, the second stage of the cell search step for searching for a cell transmitted from the base station in the asynchronous Wideband Code Division Multiple Access (CDMA) mobile system can be performed more quickly and accurately So that it is possible to guarantee an optimum search when power is supplied to the terminal.

Claims (4)

A correlation unit for obtaining a plurality of correlation values from the input signal, Memory means for sequentially storing the correlation values obtained by the correlation portion, A code storage unit for storing a code list for each code group and providing the stored value to the memory means when necessary, A slot counter for addressing a plurality of slot data stored in the memory means by an input clock ca_s2_clock, A shift count for counting a start point of a frame by a carry output from the slot counter, A code group counter for counting an index of a candidate code group by a carry output from the shift count, An accumulator for accumulating a correlation value of one frame amount outputted from said memory means; And a peak detector for detecting an optimal code sequence with respect to an output signal of the accumulator. Detecting a synchronization channel signal provided by a base station and determining a start point of an arbitrary one of a plurality of slots formed per frame, Performing a correlation a predetermined number of times for a set period based on a start point of the slot; Storing a correlation value obtained by repeatedly performing the correlation in a memory, and determining, by using the stored data, which base station group the synchronization channel signal belongs to and where the start of the frame is And a cell search method in the mobile communication system. 3. The method of claim 2, wherein assuming that a predetermined frame signal is a reference time point, and that the g-th code-group starts from the ith slot, the address of the code list to be observed at the j- The mobile communication system comprising: j = 16 * j? + j-i 16% [9bit] 3. The method of claim 2, wherein, when the synchronization channel signal belongs to a certain base station group and the beginning of the frame is found, the number of the correlator corresponding to the address , The address of the memory means in which the output of the correlator c (g, i, j) in the jth slot is stored is obtained using the following equation. a _R (g, i, j) = 17 * + c (g, i, j)