JP2001346239A - Mobile wireless communication equipment and cell search method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain cell search with high performance independently of a change in a wireless environment by reducing a time required until decision of a base station in path timing from a detection point of time of the path timing by means of a synchronous symbol. SOLUTION: A mobile speed of its own unit is detected, number of divisions for one slot period is variably set so as to change a width of each search window in response to the mobile speed, and detection processing of the path timing by a synchronous symbol spread code by each search window, the reception decision of an information symbol spread code in the path timing and detection processing of its maximum peak are continuously performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a CDMA (Code
The present invention relates to a mobile radio communication device used as a mobile station in a mobile communication system adopting a Division Multiple Access (Division Multiple Access) method, and more particularly to a mobile radio communication device having a function of searching for a receivable base station and a cell search method thereof.

[0002]

2. Description of the Related Art Recently, as one of radio access systems applied to mobile communication systems, CDMA, which is resistant to interference and interference,
The method is receiving attention.

In a mobile communication system adopting the CDMA system, for example, communication is performed as follows. That is, the communication device on the transmitting side first modulates digitized voice data and image data by a digital modulation method such as the PSK modulation method. Next, the modulated transmission data is converted into a wideband baseband signal using a spreading code such as a pseudo noise code (PN code),
The spread transmission signal is converted into a radio frequency signal and transmitted. On the other hand, the communication device on the receiving side first performs spectrum despreading on the received radio frequency signal using the same code as the spreading code used in the communication device on the transmitting side.
Then, the demodulated received signal is digitally demodulated by a digital demodulation method such as the PSK demodulation method to reproduce the received data.

By the way, in this type of system, a so-called cell search is performed in a mobile station in order to review peripheral base stations that can be received when power is turned on.

[0005] In order to enable this cell search, all base stations (cells) transmit a synchronization symbol spread by a synchronization symbol spreading code common to the base stations in a synchronization channel at a predetermined slot period, and further transmit the base station. The information symbol spread by the information symbol spreading code individually set for each is transmitted at the same timing as the synchronization symbol.

When performing a cell search, the mobile station sets the search range to one slot period, and first performs a synchronization symbol reception search in this search period. In the synchronization symbol reception search, the correlation between the received signal and the synchronization symbol spread code is obtained in a matched filter, the reception power is obtained for each path timing, and the synchronous addition is performed. Then, based on the result of the synchronous addition, the peak search unit
This is performed by extracting m pieces of path timings from the plurality of path timings detected during the slot period in descending order of received power, and storing the m pieces of path timings as reception candidates.

Subsequently, the mobile station performs a reception search for information symbols using an information symbol spread code at each of the m path timings. In this information symbol reception search, at each of the m path timings, a plurality of information symbol spreading codes stored in advance in the spreading code storage unit are sequentially read out and set in a finger circuit. To detect the reception power of the information symbol despread. Then, an information symbol having the maximum received power is extracted, and an information symbol spreading code corresponding to the information symbol is stored in the cell path storage unit in association with the path timing.

That is, in the conventional cell search method, after a search for path timing by a synchronization symbol spreading code over one slot period is completed, a base station reception search by an information symbol spreading code is performed at each path timing detected by this search. To do.

[0009]

However, in such a conventional cell search system, a search for a path timing using a synchronization symbol spreading code is started, and then a base station using an information symbol spreading code is used at the path timing detected by the search. A lot of time elapses until a station reception search is performed. For example, when there are 20 paths detected by the synchronization symbol reception search, and there are eight information symbol spreading codes to attempt reception,
At the point of time when the reception with the eighth information symbol spreading code is tried at the path timing detected at the end of one slot period, the reception search of the base station with the information symbol spreading code of 19 × 8 times has already been performed. I will.

[0010] Therefore, for example, in a radio environment where the multipath fluctuates greatly due to the movement of the mobile station, when a search for the base station is performed using the information symbol spreading code,
A path may not already exist at that path timing. For this reason, even though the base station of the path detected in the first half of the one slot period can be specified, the base station of the path detected in the second half of the one slot period cannot be specified. And the cell search performance is degraded.

The present invention has been made in view of the above circumstances. It is an object of the present invention to reduce the time required from the detection of a path timing by a synchronization symbol to the determination of a base station at the path timing. Accordingly, it is an object of the present invention to provide a mobile radio communication device and a cell search method that enable high-performance cell search regardless of changes in the radio environment.

[0012]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a synchronization symbol transmitted by a plurality of base stations, each forming a cell, at a predetermined slot period and spread by a first spreading code. A mobile wireless communication apparatus having a cell search function for determining a base station capable of communication by sequentially receiving information symbols spread by the second spreading code, Speed detection means, and search section setting means for dividing a period corresponding to the slot cycle into a plurality of search sections whose lengths are variably set according to the moving speed of the own device detected by the moving speed detecting means, A first search for performing a reception search of the synchronization symbol and detecting a path timing as a reception candidate for each search section set by the search section setting means; Each time the search of one search section is completed by the first search means and the first search means, at the path timing of the reception candidate detected by this search, the information symbol of the information symbol is specified by a plurality of second spreading codes specified in advance. A second search unit for performing a reception search and determining a receivable base station.

More specifically, the search section setting means variably sets the number of divisions in one slot period so that the length of each search section decreases in proportion to an increase in the moving speed.

Therefore, according to the present invention, one slot period is divided into a plurality of search sections according to the moving speed,
The reception search of the synchronization symbol and the reception search of the information symbol are continuously performed for each search section. For this reason,
The time required from the detection of the path timing by the synchronization symbol to the determination of the base station at the path timing is shortened, and the determination of the base station at the path timing can be performed without time. Therefore, even in a wireless environment in which the multipath fluctuates greatly due to a high-speed movement of a mobile station, it is possible to more accurately search for a base station using an information symbol spreading code. It can be captured as a receivable base station and cell search performance can be improved.

Further, according to the present invention, when the second search means performs a reception search of a plurality of information symbols based on a reception search result of a synchronization symbol in an arbitrary search section, a plurality of second symbols corresponding to the plurality of information symbols are searched. It is determined whether or not the second spreading code of the base station detected by the reception search of the information symbol in the preceding search section already exists in the spreading code. It is also characterized in that the information symbol reception search is omitted.

By doing so, it is possible to prevent the reception search for the base station that has already been detected in the preceding search section from being executed again and again in subsequent search sections. Can be omitted to improve the efficiency of cell search.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a CDM according to the present invention.
FIG. 3 is a circuit block diagram illustrating an embodiment of a mobile station device A.

In FIG. 1, a transmission voice signal of a speaker output from a microphone 10a is converted into a digital signal by an analog-to-digital converter (AD) 11a, and then is converted to a voice coder-decoder ( speech coder-decoder
, Hereinafter referred to as an audio codec) 12. In the microprocessor (MPU) 13, a control signal and the like are added to the coded transmission signal output from the audio codec 12, thereby generating transmission data.

The transmission data is added with an error detection code and an error correction code by a data generation circuit 14, is encoded by a convolutional encoder 15, and is further processed by an interleave circuit 16 for interleaving. .
The transmission data output from the interleave circuit 16 is spread by a spread code into a wideband signal by a spread code.

This spread spectrum transmission signal is:
After unnecessary frequency components are removed by the digital filter 18, it is converted into an analog signal by a digital-analog converter (DA) 19. The analog transmission signal is up-converted to a predetermined radio channel frequency by the analog front end 20 and power-amplified to a predetermined transmission power level.
Is transmitted to a base station (not shown).

On the other hand, the spread spectrum radio signal received by the antenna 21 is amplified by the analog front end 20 with low noise and down-converted to an intermediate frequency or a baseband frequency. The received signal output from the analog front end 20 is converted into a digital signal at a predetermined sampling period by an analog-to-digital converter (AD) 22, and then input to a CDMA signal processing unit 25. . This CDM
The A signal processing unit 25 has a RAKE receiving function of separating and reproducing each of the multipath received signals and synthesizing the symbols, and a cell search function to be described later.

The demodulated symbols output from the CDMA signal processing unit 25 are input to a deinterleave circuit 26 together with timing information, and the deinterleave circuit 26 performs a deinterleave process. Subsequently, the demodulated symbols after the deinterleaving are output to the Viterbi decoder 27.
, And the demodulated symbol after the Viterbi decoding is subjected to error correction decoding processing by an error correction circuit 28 to become received data, which is input to the microprocessor 13. In the microprocessor 13, the input received data is separated into voice data and control data. The audio data is subjected to audio decoding by the audio codec 12 and then to a digital-analog converter (DA) 11b.
Is converted to an analog signal by the speaker 10b.
From the speaker.

The keypad / display 29 is
It is provided for a user to input dial data, control data, and the like, and to display various information relating to the operation state of the mobile station. The operation of the keypad display 29 is controlled by the microprocessor 13.

Incidentally, the CDMA signal processing section 25 is configured as follows. FIG. 2 is a block diagram showing the functional configuration.

In the figure, the received signal output from the A-D 22 is input to the matched filter 31 and the finger circuit unit 34, respectively. The matched filter 31
When executing the cell search procedure, a correlation between the received signal and a preset synchronization symbol spread code (short code) common to each base station is obtained, and a synchronization addition signal representing the correlation value is generated. Then, the generated synchronous addition signal is input to the peak search unit 32.

The pick search unit 32 is provided with a cell search window position information generation unit 36 and a multipath search window position information generation unit 37. The cell search window position information generating unit 36 first divides one slot period into a plurality of cell search windows (sections) in a cell search procedure.
Generate At this time, the own moving speed detection signal output from the moving speed detecting unit 24 is fetched, and the number of divisions of one slot period is set so that the length of each cell search window becomes shorter in proportion to the increase of the moving speed. Is set variably. Then, the timing of each cell search window set in this way is given to the peak search unit 32 in order.

On the other hand, in the multipath detection procedure, the multipath search window position information generation section 37 determines the range where the multipath exists around the path timing for each base station (cell) obtained in the cell search procedure. The peak search unit 32 is set as a multipath search window using this range.
Give to.

First, in the cell search procedure, the peak search section 32 outputs the synchronous addition signal output from the matched filter 31 during the cell search window provided from the cell search window position information generation section 36. Among the peaks in, n peaks are detected in descending order of their values. Then, the timings of these n peaks are set as path timings serving as reception path candidates as the path candidate storage unit 3.
Store it in 3. On the other hand, in the multi-path search procedure, during the period of the multi-path search window provided from the multi-path search window position information generating unit 37, the peaks in the synchronous addition signal output from the matched filter 31 are selected. , M peaks are detected in descending order of their values. Then, the timings of these m peaks are stored in the path candidate storage unit 33.

The cell path information setting section 38 stores a plurality of information symbol spreading codes individually assigned to each base station, and stores these information symbol spreading codes from the path candidate storage section 33 in the cell search procedure. The signal is supplied to the finger circuit unit 34 in synchronization with the read path timing.

In the multipath detection procedure, the multipath information setting section 39 reads out the path timing from the path candidate storage section 33 and sends the information symbol spread code of the detection target cell synchronized with this path timing to the finger circuit section 34. give.

In the cell search procedure, finger circuit section 34 despreads the received signal using the information symbol spreading code provided from cell path information setting section 38, and despreads the despread signal into a code power measurement determination section. 40. In the multipath detection procedure, the received signal is despread by the information symbol spreading code given to the multipath information setting section 39, and the despread signal is supplied to the path power measurement determination section 41.

The code power measurement / determination section 40 stores the information symbol spread code having the maximum received power value and its path timing in the corresponding sector path storage sections 35a, 35b and 35c in the cell search result storage section 35. The path power measurement determination unit 41 determines the path timing of the signal that exceeds the threshold value among the signals after despreading, by using the information symbol spreading code in the cell search result storage unit 35 and the sector path storage units 35a and 35b corresponding to the cells. , 35c.

Next, a cell search operation and a multipath detection operation by the CDMA mobile station device configured as described above will be described. FIG. 3 is a flowchart showing control procedures and control contents of the cell search operation and the multipath detection operation.

When the power of the apparatus is turned on, the CDMA signal processing unit 25 first executes a cell search procedure in accordance with an instruction from the microprocessor 13. That is, first, in step 3a, the moving speed of the own device is fetched from the moving speed detecting unit 24 into the cell search window position information generating unit 36, and the length of each cell search window is reduced in proportion to the increase in the moving speed. Then, the number of divisions in one slot period is variably set.

For example, when the mobile station is moving at high speed by train or car, it is expected that the propagation environment changes rapidly. Therefore, the width of the cell search window is set small so that the peak search range becomes narrow. I do. On the other hand, when the mobile station is stopped or moving at a low speed at about the walking speed, the width of each cell search window is set large so that the peak search range is widened. Then, the timing of each cell search window set in this way is sequentially provided to the peak search unit 32.

When the cell search window is set, the CDM
The A signal processing unit 25 activates the matched filter 31 and the peak search unit 32. Then, in matched filter 31, in step 3b, the correlation between the received signal and a preset synchronization symbol spreading code common to each base station is detected, and a synchronization addition signal representing the correlation value is sent to peak search section 32. Supplied. In the peak search unit 32, in step 3c, for each period of the cell search window given from the cell search window position information generation unit 36,
From the synchronous addition signal supplied from the matched filter 31, n peaks are detected in descending order of peak value. Then, the detected timings of the n peaks are stored in the path candidate storage unit 33 as path timings serving as reception path candidates.

When the peak search in one cell search window is completed, the CDMA signal processing unit 25
Shifts to step 3d, where a recognizable information symbol spreading code is determined for each of the n path timings.

That is, the cell path information setting unit 38 includes:
A plurality of information symbol spread codes individually allocated to each base station are stored, and the cell path information setting unit 38 stores these information symbol spread codes in the path candidate storage unit 3.
3 is supplied to the finger circuit section 34 in synchronization with the path timing read out from the third path. Then, the finger circuit unit 34 performs despreading processing of the received signal using the information symbol spreading code given from the cell path information setting unit 38,
The signal after the despreading is input to the code power measurement determination section 40.

In step 3e, the code power measurement determination section 40 detects the information symbol spread code having the maximum received power value and its path timing, and these are detected by the corresponding sector path storage section 3 in the cell search result storage section 35.
5a, 35b, and 35c.

When the cell search procedure for one search window is completed, the CDMA signal processing unit 25 determines in step 3f whether the cell search procedure for all search windows is completed, and ends. If not, the next search window is selected in step 3g. And step 3
b, and from step 3b to step 3e,
The above-described peak search process, code determination of the information symbol spreading code, and the process of detecting the maximum peak are repeated. Thereafter, similarly, every time an unselected search window is selected in step 3g, peak search processing, code determination of an information symbol spread code, and maximum peak detection processing are repeatedly executed.

When the code power measurement determination section 40 stores the maximum peak detected in each of the search windows in the path storage sections 35a, 35b, 35c, the maximum power detected in the preceding search window is the same. It is determined whether or not it is already stored in the sector path storage units 35a, 35b, 35c. If not stored, the new detected maximum peak value is directly stored in the path storage unit 35.
a, 35b, and 35c. When the peak value is already stored, the already stored peak value is compared with the newly detected peak value, and the higher power is stored in the path storage units 35a, 35c. 35b and 35c.

When the cell search procedure is completed as described above, the CDMA signal processing unit 25 subsequently executes a multipath detection procedure. That is, first, in step 3h, in order to detect a multipath for each cell, an information symbol spreading code assigned to a cell to be searched is set in the matched filter 31, and the information symbol spreading code and The path timing detected in the cell search procedure is provided to the multipath search window position information generation unit 37. In the multipath search window position information generating section 37, a range in which a multipath exists around the path timing is set for each base station (cell) obtained in the cell search procedure. Is given to the peak search unit 32.

Then, in step 3i, the matched filter 31 detects a correlation between the received signal and the set information symbol spreading code, and supplies a synchronous addition signal representing the correlation value to the peak search unit 32. You. In the peak search unit 32, in step 3j,
During the period of the multipath search window provided from the multipath search window position information generating unit 37, m peaks are detected from the synchronous addition signal supplied from the matched filter 31 in descending order of peak value. . Then, the timing of the detected m peaks is stored in the path candidate storage unit 33.

When the peak search in one multipath search window is completed, the CDMA signal processing unit 25 proceeds to step 3k. Then, the multi-path information setting unit 39 sets the path candidate storage unit 33 to m
The path timings are sequentially read out, and the information symbol spread code of the detection target cell synchronized with the path timing is given to the finger circuit unit 34.

Then, the finger circuit 34 performs a process of despreading the received signal using the information symbol spreading code given to the multipath information setting unit 39. The despread signal is sent to the path power measurement determination unit 41. Is entered.
In step 3m, the path power measurement determination section 41 detects a path of a signal exceeding the threshold value among the signals after the despreading, and determines this path as an information symbol spreading code and a cell in the cell search result storage section 35. The data is stored in the corresponding sector path storage units 35a, 35b, 35c.

When the multipath detection procedure for one cell is completed, the CDMA signal processing unit 25 determines in step 3n whether the multipath detection procedure for all cells is completed, and ends. If not, the next cell is selected in step 3o. And step 3i
Then, from step 3i to step 3m, the above-described peak search processing, the determination of the path power, and the processing of storing the path exceeding the threshold value are repeated. Thereafter, similarly, every time an unselected cell is selected in step 3n, the peak search processing, the determination of the path power, and the processing of storing the path exceeding the threshold are repeatedly executed.

As described above, in this embodiment, the moving speed of the own device is detected, and the number of divisions in one slot period is variably set so that the width of each search window changes according to the moving speed. . FIG. 4 shows an example. In this example, one slot period is divided into four and four search windows S1 to S
4 is set. And for each of these search windows,
For example, as shown in FIG. 6, a process of detecting a path timing using a synchronization symbol spreading code (peak search process), a process of determining whether an information symbol spreading code is received at this path timing and a process of detecting a maximum peak thereof are continuously executed. I have.

Therefore, the time required from the detection of the path timing by the synchronization symbol to the determination of the base station at the path timing is shortened, whereby the determination of the base station at the path timing is executed without time. For this reason, even in a wireless environment in which the multipath fluctuates greatly due to high-speed movement of the mobile station or the like, it is possible to more accurately search for the base station using the information symbol spreading code. As a receivable base station, and cell search performance can be improved.

By the way, the conventional cell search method, for example, as shown in FIG. 5, performs a peak search process over the entire period of one slot, and after completion of the peak search process over this one slot period, reception of an information symbol spreading code. In the method of executing the judgment and the detection processing of the maximum peak (code judgment), for example, as shown in FIG. 7, a lot of time is required until all the code judgments are completed, and in a wireless environment where multipath fluctuations are severe. Therefore, deterioration of cell search performance is inevitable.

The present invention is not limited to the above embodiment. For example, when the reception determination of the information symbol spread code is performed based on the peak search result in an arbitrary search window, the path storage units 35a, 35a are detected in these information symbol spread codes and detected in the preceding search window.
It is configured to determine whether or not the information symbol spread codes stored in 35b and 35c already exist, and if so, omit the reception determination of the information symbol spread codes.

In this way, it is possible to prevent the reception search for the base station already detected in the preceding search window from being executed again in the subsequent search windows, thereby omitting useless search. Thus, the efficiency of cell search can be improved.

In addition, the type and configuration of the mobile station device,
The configuration of the DMA signal processing unit, the procedure of cell search and multipath detection, and the contents thereof can be variously modified without departing from the scope of the present invention.

[0053]

As described above in detail, according to the present invention, the slot period is divided into a plurality of search sections whose lengths are variably set according to the moving speed of the own apparatus, and each of the divided search sections is A process of detecting a path candidate that is a reception candidate by performing a synchronization symbol reception search, and performing a reception search of an information symbol using a plurality of second spreading codes at the reception candidate path timing detected by the search. The process of determining a possible base station is continuously performed.

Therefore, according to the present invention, it is possible to reduce the time required from the detection of the path timing by the synchronization symbol to the determination of the base station at the path timing. A mobile radio communication device and a cell search method capable of performing a cell search can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment of a CDMA mobile station apparatus according to the present invention.

FIG. 2 is a diagram illustrating C in the CDMA mobile station apparatus shown in FIG.
FIG. 2 is a block diagram showing a functional configuration of a DMA signal processing unit.

FIG. 3 is a flowchart showing a control procedure and control contents of a cell search operation and a multipath detection operation in the CDMA signal processing unit shown in FIG. 2;

FIG. 4 is a view showing an example of setting a cell search window by the cell search procedure shown in FIG. 3;

FIG. 5 is a diagram showing a setting example of a cell search window according to a conventional method.

FIG. 6 is a diagram showing an example of operation timing according to the cell search procedure shown in FIG.

FIG. 7 is a diagram showing an example of operation timing according to a conventional method.

[Explanation of symbols]

 11a, 22 ... Analog-to-digital converter (AD) 11b, 19 ... Digital-to-analog converter (DA) 12 ... Speech encoding / decoding (speech codec) 13 ... Microprocessor (MPU) 14 ... Data generation circuit 15 Convolutional encoder 16 Interleave circuit 17 Spectrum spreader 18 Digital filter 20 Analog front end 21 Antenna 24 Moving speed detection unit 25 CDMA signal processing unit 26 Deinterleave circuit 27 ... Viterbi decoder 28 ... Error correction circuit 29 ... Keypad / display 31 ... Matched filter 32 ... Peak search unit 33 ... Path candidate storage unit 34 ... Finger circuit unit 35 ... Cell search result storage unit 35a, 35b, 35c ... Sector path storage unit 36: Cell search window position information generation 37 ... multipath search window position information generating unit 38 ... Serupasu information setting unit 39 ... multipath information setting unit 40 ... Code Power measurement determination section 41 ... path power measurement determination section

Claims (4)

[Claims] 1. A synchronization symbol spread by a first spreading code and an information symbol spread by a second spreading code, which are transmitted by a plurality of base stations each forming a cell in a predetermined slot cycle, sequentially. By receiving, in a mobile radio communication device having a cell search function of determining a base station with which communication is possible, a moving speed detecting means for detecting a moving speed of the own device, and a period corresponding to the slot cycle, Search section setting means for dividing into a plurality of search sections whose lengths are variably set according to the moving speed of the own device detected by the moving speed detecting means; and for each search section set by the search section setting means. A first search means for performing a search for reception of the synchronization symbol to detect a path timing which is a reception candidate, and one search section by the first search means. Every time the search is completed, at the path timing of the reception candidate detected by the search, a reception search for information symbols is performed using a plurality of second spreading codes specified in advance to determine a receivable base station. A mobile wireless communication device comprising: a second search unit. 2. The search section setting means according to claim 1, wherein the length of each search section decreases in proportion to an increase in the moving speed.
2. The mobile radio communication device according to claim 1, wherein the number of divisions of the slot period is variably set. 3. The method according to claim 2, wherein the second search means performs a reception search of a plurality of information symbols based on a reception search result of a synchronization symbol in an arbitrary search section. During the search, it is determined whether or not the second spreading code of the base station detected by the reception search of the information symbols in the preceding search section already exists. 2. The mobile radio communication device according to claim 1, further comprising a function of omitting a reception search. 4. A mobile radio communication apparatus, comprising: a plurality of base stations, each forming a cell, transmitting at a predetermined slot period, a synchronization symbol spread by a first spreading code;
Detecting a moving speed of the own apparatus in a cell search method for determining a base station with which communication is possible by sequentially receiving information symbols spread by a second spreading code; Dividing the search period into a plurality of search sections whose length is variably set in accordance with the detected moving speed of the own apparatus; and performing a reception search of the synchronization symbol for each of the divided search sections. And detecting a path timing to be a reception candidate, and each time a synchronization symbol reception search in said one search interval is completed, the path timing of a reception candidate detected by this search is specified in advance. Performing a reception search for information symbols using a plurality of second spreading codes to determine a receivable base station. Cell search method according to claim.