KR100308150B1 - Method for Searching Cell in Mobile Communication System - Google Patents

Abstract

The present invention relates to a cell search method in a mobile communication system capable of determining whether a current base station provides reference time information commonly used at a system level while performing a first step of a cell search procedure. As described above, the present invention outputs two new corresponding first and second codes by matching two intermediate values corresponding to each other in some steps of generating a Golay code using a predetermined correlator. And one of the first code and the second code is used to confirm whether the current base station is an asynchronous system and to obtain synchronization of a slot, and the other code is used to confirm whether the current base station is a synchronous system. Is done.

Description

Method for searching cell in mobile communication system {Method for Searching Cell in Mobile Communication System}

The present invention relates to a cell search method corresponding to a physical layer of an air interface in a mobile communication system based on wideband code division multiple access (WCDMA). The present invention relates to a cell search method for confirming whether reference time information commonly used at a system level is provided in a more advanced manner, and a method for allocating a scrambling code (scrambling code) to each base station (base station).

When power is applied to each mobile terminal in the WCDMA IMT-2000 communication network, the mobile terminal performs a search for the current base station (or cell) and exchanges desired data. Thus, each base station transmits (primary and secondary) synchronization signals to all mobile terminals in its area using one or more synchronization channels. Then, the mobile terminal sequentially performs the following three steps of cell search procedure to determine the cell search and scrambling code and to determine frame synchronization.

First, in the first step, the transmitting end of the current base station transmits a primary synchronization code (hereinafter, referred to as a PSC), which can be represented by a ₈ (k), to the corresponding mobile terminal at the beginning of each slot. The mobile terminal detects the start point of each slot by detecting the output signal of the correlator shown in FIG. 1 using a primary synchronization code (PSC). Therefore, slot synchronization of the corresponding cell can be obtained. Here, slot timing of a cell may be obtained by detecting peaks of the correlator output terminal provided in the mobile terminal.

In the second step, the mobile station finds the starting point of each frame and determines the code group of the cell by using a secondary synchronization code (SSC) transmitted together with the primary code at the base station. This process is possible by correlating the signal received from the base station to all possible SSCs and discerning the SSC with the largest correlation value. At this time, if the determined code group is 33. It is determined that the current base station provides reference time information commonly used at the system level to all mobile terminals in its own area. On the other hand, if the determined code group is determined to be a code group other than 33, it is determined that the current base station does not provide each mobile terminal with reference time information commonly used at the system level. Here, frame synchronization is easily performed because cyclic shifts of SSC sequences are unique.

Finally, in the third step, the mobile terminal determines the correct scrambling code of the current base station. The scrambling code is a symbol-by-symbol for all scrambling codes corresponding to the primary common control physical channel (CCPCH) provided to the IMT-2000 mobile communication system and the code group detected in the second step. symbol and take the correlation and store them in order, and determine that the scrambling code having the largest value among the stored correlation values is used for the corresponding base station.

In the first step of the conventional cell search process, the Golay sequence is used by using the PSC. The general binary method of generating the Golay sequence is' s. Z. Budisin, 'Efficient pulse compressor for Golay complementary sequences,' Electronics Letters, vol. 27, no. 3, pp. 219-220, Jan. The iterative relation described in 1991 'is generated as follows.

a ₀ (k) = δ (k)

b ₀ (k) = δ (k)

a _n (k) = a _n-1 (k) + W _n b _n-1 (kD _n )

b _n (k) = a _n-1 (k)-W _n b _n-1 (kD _n ),

Where k = 0, 1, 2, ..., 2N-1, n = 1, 2, ..., N, Is,

a _n (k) and b _n (k) represent a sequence of length 2 ^N ,

δ (k) represents the Kronecker delta function,

k represents an integer representing a time interval,

n represents the number of repetitions,

D _n represents the delay,

P _n (n = 1, 2, ..., N) represents a permutation of {0, 1, 2, ..., N-1},

W _n represents the same number with a value of +1 or -1, respectively.

Thus, it sets _{a 8 (k), k =} 0, 1, 2, ..., and 255 by using the PSC. The structure of an efficient correlator for a ₈ (k) is shown in FIG. 1.

In addition, a Pruned Golay Code having a length of 255 codes having a modified structure of the Golay correlator shown in FIG. 1 has recently been presented. The Pruned Golay Code is used in the above Equations 1 to 4 using the following numerical values.

If N = 8,

If n is 4, b ₄ (k) = a ₄ (k) in Equation 4, and if n is 6, b ₆ (k) = a ₆ (k) in Equation 4 . Thus, it sets _{a 8 (k), k =} 0, 1, 2, ..., and 255 by using the PSC. The structure of an efficient correlator for a ₈ (k) is shown in FIG.

In addition, in the case of a base station having reference time information commonly used at the system level, a method of allocating a scrambling code corresponding to each base station in a communication system based on the entire wideband code division multiple access scheme is one of 40960 code lengths. The sequence is shifted by 80 code lengths and assigned to 512 base stations, respectively.

However, in order to determine whether the current base station provides the reference time information commonly used at the system level, the conventional technology must perform the cell search procedure of the second step of the entire cell search procedure.

In addition, since one scrambling code having an 80 code length is used for different base stations, it is easy to cause the radio wave emitted from the base station to delay the transition time of the scrambling code due to various causes. In this case, the mobile terminal may fail accurate cell search and degrade the quality of the communication service.

SUMMARY OF THE INVENTION The present invention has been made to improve the prior art, and it is possible to determine whether the current base station provides reference time information commonly used at the system level while the mobile terminal performs the first step of the cell search procedure. It is to provide a cell search method in a mobile communication system.

Another object of the present invention is to provide a method for allocating a scrambling code for each base station in a mobile communication system that can greatly increase the transition length of a scrambling code allocated to the base station when the base station provides reference time information to each mobile terminal. It is for.

According to a first aspect of the present invention for achieving the above object, in the step of generating a Golay code using a predetermined correlator, two new values corresponding to each other by matching two intermediate values are matched. Outputting a first code and a second code, respectively, one of the first code and the second code is used to confirm whether the current base station is an asynchronous system and to obtain synchronization of the slots, and the other is used by the current base station. It is a step used to check whether the system is synchronous.

According to a second aspect of the present invention for achieving the other object of the present invention, the scrambling code allocation method for each base station in the mobile communication system is a transition length of the preset code to one scrambling code having a predetermined unit length In the mobile communication system which divides by as many as each base station, at least two or more different scrambling codes are divided by a transition length of a predetermined code and assigned to a plurality of base stations, respectively.

According to the characteristics of the present invention as described above, in order to determine whether the current base station provides the reference time information commonly used at the system level to each mobile terminal, the second step of the cell search process can be known, In the present invention, it can be known even by executing only the first step of acquiring synchronization of the corresponding cell. In addition, it provides an advantage that the transition of the scrambling code allocated to each base station can be expanded four times to 320 code lengths instead of 80 code lengths.

1 is a block diagram of a conventional Golay correlator.

2 is a block diagram of a conventional Pruned Golay correlator.

3 is a block diagram of a Pruned Golay correlator according to the present invention.

4 is a flowchart illustrating a cell search procedure according to the present invention.

Explanation of symbols for important parts of the drawings

D ₁ -D _N : Delay A1-An: Adder

M1-Mn: Multiplier S1-Sn: Subtractor

r (k): Input signal of correlator

R _ra (τ): output of correlator corresponding to a ₈ (k)

R _rb (τ): output of correlator for b ₈ (k)

In order to realize the present invention, new functions must be implemented in the base station and the mobile terminal. First, the base station transmits a primary sync code of a ₈ (k) or b ₈ (k) to the synchronization channel (SCH) at the start of each slot. That is, when the base station does not provide the reference time information commonly used at the system level, the base station transmits a ₈ (k) to the synchronization channel at every start point of the slot, and provides the reference time information commonly used by the base station at the system level. If so, b ₈ (k) is transmitted at the beginning of the slot on the synchronization channel.

Here, the reference time information is provided when the base station is a synchronous system, and the reference time information is not provided when the base station is a synchronous system.

In addition, each mobile terminal receives a primary synchronization code (PSC) of a ₈ (k) or b ₈ (k) transmitted from a base station, and a ₈ (k) and b ₈ ( k) shall be used simultaneously as PSC.

First, as shown in FIG. 1, the use of the Golay sequence as the PSC in the correlator for a ₈ (k) and b ₈ (k) will be described. Equations 1 to 4 shown in the related art use the following numerical values.

At this time, in the present invention, unlike the prior art, not only a ₈ (k), k = 0, 1, 2, ..., 255 but also b ₈ (k), k = 0, 1, 2, ..., 255 Also used as PSC.

In addition, as shown in FIG. 3, the case where Pruned Golay sequence is used as the PSC in the correlator for a ₈ (k) and b ₈ (k) will be described.

In Equations 1 to 4 shown in the prior art, if N is 8,

Satisfy the condition.

If n is 4, b ₄ (k) = a ₄ (k) in Equation 4, and if n is 6, b ₆ (k) = a ₆ (k) in Equation 4 . At this time, in the present invention, as well as a ₈ (k), k = 0, 1, 2, ..., 255, b ₈ (k), k = 0, 1, 2, ..., 255 is also used as the PSC. .

As described above, an operation of a preferred embodiment of the present invention using the newly added functions of the base station and each mobile terminal and the correlator provided in each mobile terminal as illustrated in FIGS. 1 to 3 will be described below.

First, a primary sync code of a ₈ (k) or b ₈ (k) is transmitted to the synchronization channel at the start point of each slot in the transmission channel of the base station (S1). That is, the base station when not providing the reference time information used in common by the system dimension and sends each entry point of the a ₈ (k) to the sync channel every slot, providing the reference time information, the base station is common to use a system-wide If so, b ₈ (k) is transmitted to the synchronization channel at the beginning of every slot.

Then, the mobile terminal finds the starting point of the slot by using the correlator provided as shown in FIG. 1 or 3 and determines whether the base station currently provides reference time information commonly used at the system level. Determine (S2). That is, when a peak is detected at an output corresponding to R _ra (τ) in the correlator of FIG. 1, the base station determines that it is not providing reference time information commonly used at the system level, and R _rb (τ). If a peak is detected at the output corresponding to the base station, the base station determines that the base station provides reference time information commonly used at the system level. This operation takes advantage of the fact that a ₈ (k) and b ₈ (k) are complementary sequences satisfying R _ra (k) + R _rb (k) = 2δ (k). At this time, slot synchronization is performed using the instant when the peak is detected regardless of R _ra (τ) and R _rb (τ) as the starting point of the slot.

Subsequently, the mobile terminal uses the result determined in step S2 to determine whether the current base station provides reference time information commonly used in the system level (S3). If it is determined that the current base station does not provide the reference time information commonly used at the system level, the subsequent cell search method sequentially executes the second step and the third step mentioned in the prior art (S4).

However, in the first step, if it is determined that the current base station provides the reference time information commonly used at the system level, the current base station does not perform the procedure of searching for the code group executed in the second step of the conventional cell search procedure. The allocated scrambling code is found (S5).

Here, a method of allocating a scrambling code corresponding to each base station when the base station provides reference time information commonly used at the system level to each mobile terminal will be described.

In another embodiment of the present invention, four different sequences of 40960 code lengths are shifted by 320 code lengths and allocated to 512 base stations. In other words, the transition length of the scrambling code allocated to each base station is changed from the conventional base station by changing the transition of four different scrambling codes by 320 code lengths rather than changing the transition of one scrambling code having a 40960 code length by base station. It can be increased four times.

Here, although different scrambling codes can be allocated using two or more sequences, the present invention proposes four because there are disadvantages in that the calculation process becomes complicated when the number is too large.

According to the present invention as described above, each mobile terminal has greatly reduced the time required for cell search when the current base station provides the common reference time information of the system level. That is, in the conventional method, the second base station of the cell search procedure must be performed to determine whether the current base station provides common reference time information at the system level. However, in the present invention, by using different PSCs in the first step, it is possible to confirm whether or not the current base station is providing system-wide common reference time information. At this time, it is not necessary to increase an additional calculation amount or add hardware elements according to the execution of this operation.

In addition, when the current base station is provided with the system-wide reference time information, when assigning a scrambling code corresponding to the base station, by assigning different scrambling code using two or more sequences, the scrambling code assigned to each base station The transition length can be increased by a multiple equal to the number of scrambling code lengths allocated.

Claims (5)

Outputting two new corresponding first and second codes by matching two intermediate values corresponding to each other in some of the steps of generating a Golay code using a predetermined correlator; One of the first code and the second code is used to confirm whether the current base station is an asynchronous system and to obtain slot synchronization, and the other is used to confirm whether the current base station is a synchronous system. A cell search method in a mobile communication system, characterized by the above-mentioned. The method of claim 1, wherein when the base station is a synchronous system, a scrambling code assigned to the base station is divided according to an offset and used for each cell. The method of claim 2, wherein some of the cells use different scrambling codes. One of the two complementary sequences output from the Golay code generator is used to confirm whether the current base station is an asynchronous system and to acquire slot synchronization, and the other is to check whether the current base station is a synchronous system. Cell search method in a mobile communication system, characterized in that it is used to obtain synchronization of a slot. Selectively transmitting, by the base station, one primary synchronization code to the corresponding mobile station through the synchronization channel at the beginning of every slot according to the scheme of the base station system among the two types of primary synchronization codes; Determining, by the mobile terminal, a starting point of a slot for the base station by using a correlator provided with the primary sync code, and identifying a scheme of the base station system; And searching for a scrambling code assigned to the base station when the identified base station system method is a synchronous system.