KR100556461B1 - method for gaining frame synchronism in mobile communication system - Google Patents

Abstract

The method of acquiring frame synchronization in a mobile communication system is to reduce an initial synchronization time in a mobile communication system. The method includes matching and verifying a threshold value after matching a transmitted signal, and verifying a first channel when the verification result is verified. Retrieving a long code mask symbol by searching, detecting a long code mask symbol from the transmitted signal, and searching a second channel to detect a group code having a frame code and a maximum correlation value; The present invention is directed to detecting a long code having a maximum correlation value from the transmitted signal according to the detected frame code and group identification code to obtain frame synchronization.

Description

Method for gaining frame synchronism in mobile communication system

The present invention relates to a mobile communication system, and more particularly, to a method of obtaining frame synchronization in a mobile communication system.

In recent years, according to the plan for the use of the IMT-2000 system, many countries have established standard standards for the IMT-2000, and the research and development has been continued accordingly.

Currently, the IMT-2000 system standard is divided into two groups.

First, we proposed a synchronous system as a Cdma-One group centered on the United States, and secondly, an asynchronous method based on Europe and Japan.

In particular, the DoCoMo system was proposed by NTT in Japan as an asynchronous method.

The DoCoMo system is a so-called Code Division Multiple Access (CDMA) scheme that spreads data at a chip rate of 4.096 Mcps (Chip Per Second).

Commercially available CDMA technology is an IS-95 system developed by Qualcomm in the United States. Each base station is synchronized with base stations using a GPS (Global Positioning System) satellite, and a timing offset of the same spreading code is used. Through the identification between base stations.

The DoCoMo system does not use GPS satellites, and identifies base stations by assigning different long codes to each base station.

This allows the DoCoMo system to be developed flexibly even in situations where GPS satellite reception is not possible (from the outdoors to indoors).

Hereinafter, a method of obtaining frame synchronization in a DoCoMo system according to the prior art will be described with reference to the accompanying drawings.

FIG. 1 is a diagram illustrating a signal format of a perch channel in a DoCoMo system, and FIG. 2 is a diagram illustrating a configuration of a downlink long code generator of a DoCoMo system. 1), a first mixer (2) for mixing values of the first bit and the eighth bit of the first shift register (1) and providing them as inputs of the first shift register (1), and 18 bits of data. A second shift register (3) for sequentially shifting the values of the sixth, eighth, and eleventh bits of the second shift register (3) to the input of the second shift register (3). And a third mixer (5) for mixing the output values of the first and second shift registers (1) and (3).

3 is a diagram illustrating a short code generator for a long code mask symbol of a DoCoMo system, in which a third shift register 11 for sequentially shifting 8-bit data and a third to third of the third shift register 11 are shown. A fourth mixer 12 which mixes a 5-bit value and an output value and provides it as an input of the third shift register 11, a fourth shift register 13 which sequentially shifts 8-bit data, and the first A fifth mixer 14 for mixing the values of the fourth, sixth, and seventh bits of the fourth shift register 13 with the output values as inputs of the fourth shift register 13, and the fourth shift register; A bit mixer 15 for searching each bit value of 13 and outputting a control signal according to the result signal, and a sixth mixer for mixing the output values of the first and second shift registers 11 and 13; 16) and the bit searcher (15). In response to the control signal consists of a switch 17 for switching the value or "0" of the sixth mixer (16).

4 is a flowchart illustrating an initial three-step procedure in the DoCoMo system, and FIG. 5 is a view illustrating a perch channel signal transmission format according to the initial three-step procedure in the DoCoMo system.

A method of acquiring frame synchronization in a DoCoMo system according to the related art configured as described above will now be described in detail with reference to the accompanying drawings.

First, in the signal format of the Perch channel in the DoCoMo system as shown in FIG. 1, one super frame has a time interval of 640 ms and is composed of 64 radio frames (10 ms).

In addition, one radio frame is composed of 16 time slots (0.625 ms), and the time slot is composed of 10 symbols in total.

In the DoCoMo system, the symbol rate of the perch channel is defined as 16ksps, and these symbols are spread as a spread code having a chip rate of 4.096 Mcps.

Thus, one symbol (4.096 Mcps / 16ksps) of the Perch channel is spread over 256 chips.

In the DoCoMo system, the perch channel is a physical channel for reception level measurement for cell selection of the mobile station, and is a physical channel first captured when the mobile station is powered on.

The perch channel is composed of first and second perch channels.

In each time slot of the first perch channel, a pilot symbol of four symbols to help identify the channel characteristics at the mobile station is placed at the head, and the next five symbols are symbols for identifying a logical channel.

The four pilot symbols and the five logical channel symbols are spread by a downward long code generator as shown in FIG. 2 having a period of 10 ms and use a Gold sequence of the M series.

The first shift register 1 in the downward long code generator sequentially shifts 18 bits of data.

The first mixer 2 then mixes the value of the first bit and the eighth bit of the first shift register 1 and provides it as an input of the first shift register 1.

In addition, the second shift register 3 sequentially shifts 18 bits of data.

The second mixer 4 then mixes the values of the eighth, eleventh and sixteenth bits of the second shift register 3 as the inputs of the second shift register 3.

Accordingly, the third mixer 5 mixes the output values of the first shift register 1 and the second shift register 3 and outputs the resultant signal.

In this case, the generated polynomials and initial values of the downlink long code generator are shown in Table 1 below.

Produce polynomials Initial value First shift register X ¹⁸ + X ⁷ +1 Long code number (00000h to 3FFFFh) Second shift register X ¹⁸ + X ¹⁰ + X ⁷ + X ⁵ +1 All 1

The generated downward long code has one radio frame (10 msec) periodically.

That is, the pattern from phase 0 to phase 10959 sec 40959 is repeated.

In addition, each base station is assigned a different long code, the long code assigned to each base station is identified by the initial value of the first shift register (1).

On the other hand, the long symbol symbol period, which is the last symbol period, is spread and transmitted with a short code common to all cells by a short code generator for a long code mask symbol for speeding up cell selection when the mobile station powers up.

In the long sign mask symbol section, a long sign is masked during this period, and spreading is performed by a short sign.

3 shows a code generator for a long code mask symbol of a DoCoMo system, in which a third shift register 11 in the code generator for a long code mask symbol shifts 8 bits of data sequentially.

The fourth mixer 12 then mixes the values of the third to fifth bits of the third shift register 11 with the output and provides them to the input of the third shift register 11.

In addition, the fourth shift register 13 sequentially shifts 8 bits of data.

The fifth mixer 14 then mixes the values of the fourth, sixth, and seventh bits of the fourth shift register 13 with the output and provides them as inputs of the fourth shift register 13.

At this time, the bit searcher 15 searches for each bit value of the fourth shift register 13 and outputs a control signal according to the result signal.

That is, the bit searcher 15 outputs a result signal of the sixth mixer 16 if all bit values are 1 as a result of the search of each bit value of the fourth shift register 13, and outputs "0" if not 1. Outputs

The sixth mixer 16 then mixes the output values of the first and second shift registers 11 and 13 and outputs the resultant signal.

Then, the switch 17 switches the value or "0" of the sixth mixer 16 according to the control signal of the bit searcher 15 to output the result signal.

The generation polynomial and initial value of the short code for the long code mask symbol are as shown in Table 2 below.

Produce polynomials Initial value First shift register X ⁸ + X ⁴ + X ³ + X ² +1 Short sign number for long sign mask symbol: N _LMS (0 to 225) Second shift register X ⁸ + X ⁶ + X ⁵ + X ³ +1 All 1

Like the above-mentioned long code, a short code is also identified according to the initial value of the third shift register 11 in FIG. 3, and the initial value of the third shift register 11 is denoted by N _LMS .

The spreading code during the long code mask symbol period on the first perch channel uses a short code of N _LMS = 1 that is common to all base stations.

In addition, the group identification code is transmitted during the long code mask symbol period on the second perch channel, thereby reducing the time for the mobile station to find the long code.

For example, suppose that there are 32 base stations, the long codes used by 16 base stations from base station 1 to base station 16 are allocated as codes with N _LMS = 2, and the next N 17 through 32 N _LMS. By assigning a code of = 3, the mobile station only needs to find one of the 16 codes without having to find all 32 long codes if it only finds the group identification code.

The second perch channel is spread with a short code representing a long code currently used by a base station to which the mobile station belongs and is transmitted only during a long code mask symbol period, and there is no data transmission in the remaining period.

That is, there is a one-to-many correspondence between the short code number for the long code mask symbol of the second perch channel and the downlink long code used in the same base station.

On the other hand, Figure 4 is a flow chart showing an initial three-step procedure in the DoCoMo system, the first step is to find the long sign mask timing interval.

That is, since the base station transmits the same short code in all base stations during the long code mask symbol period of the first perch channel, the mobile station receiver can know the long code mask timing period by using a matched filter.

Here, in the matched filter of the mobile station receiver, a short code spreading the long code mask symbol section of the first perch channel common to all cells is loaded into a memory, and then stored in the code of the received signal and the memory of the matched filter. It derives the output by deriving the correlation between the code.

That is, the main role of the matched filter is to determine whether the coded phase of the received input signal coincides with the coded phase stored in the memory of the matched filter.

If the output value is greater than a predetermined threshold, the mobile station receiver goes through a verification procedure to detect the mask timing.

The reason for the checking procedure is that the output of the matched filter may exceed the threshold even if the phase of the signal of the currently received signal and the sign of the matched filter memory are out of phase due to noise or signal processing error on the channel transmission. This is to reduce the false alarm probability.

If an incorrect code phase is detected in the verification procedure, the synchronization procedure using the code phase information does not perform properly due to the wrong code phase information and the synchronization procedure must be performed again. Printing is a way to increase system reliability.

If the output of the matched filter is larger than the threshold value in the verification procedure, the long code mask timing is obtained. Otherwise, the received signal is continuously input through the shift register to derive a correlation value.

The second step is to identify the group code, and find out the group identification code indicating the long code of the base station to which the mobile station belongs by using the mask timing.

That is, since all base stations transmit a group identification code (GIC) through a second perch channel during the same time interval as the long code mask timing interval of the first perch channel, the mobile station receiver transmits the group identification code (GIC). Find out the group identification code transmitted during the interval.

On the other hand, the third step is to find the long code currently used by the base station by using the found group code, using a sliding correlator (sliding correlator) for all the long code corresponding to the found group identification code The code with the highest correlation among them is selected.

If the wrong long code is selected due to an error in the channel transmission process or the signal processing, the verification process is once again performed.

If there is no abnormality even in the confirmation procedure, if the frame synchronization is detected using the found long code, all initial synchronization procedures are completed.

5 is a diagram illustrating one embodiment of an initial synchronization three-step procedure in a DoCoMo system, where each base station has a different timing offset (T _SECT ) with respect to a reference time.

If the same timing as the reference time is transmitted from the base station A, the base station B is transmitted with a timing offset _equal to the reference time and T _{SECT_B} , and the base station C is transmitted with an offset _equal to T _{SECT_C} .

Then, the mobile station detects the mask timing of the base station located closest to itself by using a short code common to all base stations spreading the long code mask symbol on the first perch channel at initial power-up, and then the second perch Search for the group identification code transmitted during the long code mask period on the channel.

Accordingly, the mobile station receiver searches all long codes assigned to the group identification code detected as a result of the search and selects the largest one regardless of the long one currently used by the base station, thereby terminating all initial synchronization processes.

However, in the method of acquiring frame synchronization in the DoCoMo system according to the prior art, since the downlink long code transmitted on the perch channel is periodically transmitted in units of one radio frame (10 ms), the start of the frame is exactly long. Since there is a coincidence with the start of, there is a problem that even after the long code is found, the frame synchronization search procedure is performed again, causing a large delay in the initial synchronization time of the overall system.

Accordingly, an object of the present invention is to provide a method for obtaining frame synchronization in a mobile communication system for reducing an initial synchronization time in a mobile communication system.

According to an aspect of the present invention, there is provided a method of obtaining frame synchronization in a mobile communication system. The method includes: verifying by comparing a threshold after matching a transmitted signal; Detecting a long code mask symbol by searching a channel, detecting a long code mask symbol from the transmitted signal, and searching a second channel to detect a group code having a frame code and a maximum correlation value; And detecting a long code having a maximum correlation value from the transmitted signal according to the detected frame code and group identification code to obtain frame synchronization.

Another aspect of the method for acquiring frame synchronization in a mobile communication system according to the present invention for achieving the above object is that the long code mask symbol and the group identification code include the first channel and the second signal in the transmitted signal. Listed at the beginning of each time slot on the channel.

According to another aspect of the present invention, there is provided a frame synchronization acquisition method according to the present invention. In the frame code and group identification code detecting step, a frame identification code is detected after detecting a group identification code from the second channel. The code must be detected to perform the next step.

Here, the first channel and the second channel are reception level measurement target physical channels for cell selection of the mobile station, such as the first perch channel and the second perch channel as described above in the prior art. The physical channel that is captured for the first time at power-up. However, in the following description of the embodiment, for convenience of description, the first perch channel and the second perch channel are used.

Hereinafter, a preferred embodiment of a method for obtaining frame synchronization in a mobile communication system according to the present invention will be described with reference to the accompanying drawings.

First, FIG. 6 is a diagram illustrating a perch channel signal transmission format of a frame synchronization acquisition method in a mobile communication system according to the present invention. One radio frame (10 ms) has 16 time slots (0.625 ms). Each time slot consists of 10 symbols.

Each symbol is spread with 256 spreading codes. In particular, during the long sign mask symbol period on the first perch channel and the second perch channel, spreading is performed by short codes rather than spreading by long codes. Is done.

A long code mask symbol (SC _LMS ) is positioned at the beginning of each time slot on the first perch channel, and a frame is placed at the beginning of each time slot on the second perch channel. Insert and transmit a group identification code (SC _FRAME ) to indicate the start of.

The long code mask symbol (SC _LMS ) is a short code transmitted during a long code mask symbol period. When the initial state of the first shift register 11 illustrated in FIG. 3 is '00000001' This is the spread code generated by.

This code is accepted by all base stations, but each base station transmits at a constant timing offset with respect to the reference time to facilitate inter-base station identification.

In addition, the group identification code (SC _FRAME ) is a code used by all base stations in the same manner and is a spreading code indicating the start of a frame, and the initial state of the first and second shift registers 11 and 13 shown in FIG. This code is generated when 10000000 'is displayed.

SC _i is a group code indicating a long code currently used by the base station to which the mobile station belongs.

The one group code represents sixteen long codes.

FIG. 7 illustrates a three-step initial synchronization procedure using a frame code of a frame synchronization acquisition method in a mobile communication system according to the present invention. The mobile station receiver uses a matched filter to form a long code mask on a first perch channel. Attempt one-step synchronization to detect timing.

If the output of the matched filter is larger than a preset threshold, a verification procedure is performed to confirm whether the phase match between the spread code phase of the received signal actually input and the spread code stored in the matched filter memory of the mobile station receiver is checked again. do.

If the phase coincidence between the two codes in the confirmation procedure is confirmed, the synchronization procedure enters step 2.

The mobile station confirms the group identification code on the second perch 13 channel existing during the detected mask timing interval as a two-step synchronization.

That is, the group code and frame code detection in the second step uses a total of 17 sliding correlators.

In the frame structure, a frame code (SC _FRAME ) always comes to the _beginning of each frame, and the group code SC _i representing the current base station is repeatedly transmitted during the next 15 mask timing intervals. When detecting a code, a frame code must be detected to enter a three-step synchronization procedure.

For example, if a group code is identified in the current time slot, the two-step procedure continues to find the frame code until the frame code in the next consecutive time slot is identified instead of immediately entering the three-step synchronization procedure.

Once the frame code is found first, the two-step procedure enters step three immediately after identifying only the group code of the next time slot.

The reason for necessarily finding the frame code is to reduce the long sign search time in the three-step synchronization procedure by finding the exact starting point of the frame.

When the two-step synchronization procedure is completed, the mobile station receiver searches for the long code used by the base station to which the mobile station belongs. Here, the detected group identification code and frame code are used.

Since one group identification code represents 32 long codes, a long code is detected by placing a total of 32 sliding correlators using the group identification code found in step 2.

Since the long sign period is the same as the frame period, if the start of the frame is known, the search time of the long sign is much shorter.

When the long code is detected and the three-step process is completed, the mobile station receiver completes the initial synchronization and then despreads the received user information signal to restore the original data.

If the receiver is out of synch during the steady state operation, the 3-step synchronization process is performed again.

As described above, the method for acquiring frame synchronization in a mobile communication system according to the present invention reduces the initial synchronization time by easily applying a signal transmission format of a new channel to easily adjust the frame synchronization and reduces the overhead of the system for searching for a frame. There is an effect that can improve the reliability of the operation.

1 illustrates the signal format of a perch channel in a DoCoMo system.

2 is a diagram showing the configuration of a downlink long code generator of a DoCoMo system;

3 shows a short code generator for a long sign mask symbol of a DoCoMo system.

4 is a flow chart illustrating an initial synchronization three step procedure in a DoCoMo system.

5 is a diagram illustrating a perch channel signal transmission format according to an initial three-step procedure in a DoCoMo system;

6 illustrates a perch channel signal transmission format of a frame synchronization acquisition method in a mobile communication system according to the present invention.

7 is a diagram illustrating a three-step initial synchronization procedure using a frame code of a method for obtaining frame synchronization in a mobile communication system according to the present invention

Claims (5)

Verifying by comparing the thresholds after matching the transmitted signals; Detecting a long sign mask symbol by searching a first channel when the verification result is verified; Detecting a long code mask symbol from the transmitted signal and searching for a second channel to detect a group code having a frame code and a maximum correlation value; And obtaining a frame synchronization by detecting a long code having a maximum correlation value from the transmitted signal according to the detected frame code and the group identification code. The method of claim 1, The long signal mask symbol and the group identification code are included in the transmitted signal at the beginning of each time slot on the first channel and the second channel. The method of claim 1, The frame code and group identification code detection step of the frame synchronization acquisition method in the mobile communication system, characterized in that after detecting the group code from the second channel must detect the frame code. The method of claim 1, The frame code and the group identification code is detected by a plurality of sliding correlator (sliding correlator) according to the verification frame acquisition method in a mobile communication system. The method of claim 1, And the long code is detected by a plurality of sliding correlators in accordance with the detection of the frame code and the group identification code.