JP2002009689A - Portable telephone set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a portable telephone set of a CDMA system which can specify a long code with higher accuracy, even under the influence of fading. SOLUTION: In order to ensure synchronization with the received signal that is subjected to spectrum spreading modulation by obtaining the product of spreading codes, an inverse spreading part 13 and an adding/averaging part 19 decide the correlation between the received signal and each of candidates of plural spreading codes over a prescribed period and compares the correlations concerning these candidates with each other to perform a process for identifying any of candidates with the spreading code related to the received signal. A fading cycle detection part 21 extends the prescribed periods of both parts 13 and 19, according to the fading state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CDMA (Code Divisi
In particular, the present invention relates to an improvement of an initial synchronization method under a fading environment.

[0002]

2. Description of the Related Art In recent years, in the field of mobile communication, a CD which is a multiple access system using a spread spectrum communication system has been used.
MA attracts attention, for example, Wideband CDMA 3GPP (3rd Generat
ion Partnership Project) The standard CDMA system has been realized. In the spread spectrum communication system, the transmitting side further applies spread modulation to a signal that has been narrow-band modulated by PSK or the like and transmits the signal. Spread modulation refers to multiplying a signal by a special waveform called a spreading code. This spreads the narrowband signal into a wideband signal. On the receiving side, the wideband signal is despread to return to a narrowband signal,
Demodulation corresponding to narrowband modulation on the transmission side is performed. The despreading circuit on the receiving side has the same configuration as the spreading circuit on the transmitting side, and in despreading, an operation of multiplying the same spreading code as that used for spreading is performed. In a CDMA system based on the above spread spectrum communication technique, multiple access sharing frequency and time is enabled by using different spreading codes for each call.

Now, a mobile station (cellular phone) in a CDMA system
In order for the mobile station and the base station to transmit and receive correctly, synchronization must be established between the mobile station and the base station. In a CDMA system, synchronization establishment consists of synchronization acquisition and synchronization maintenance.
Performed in two stages. Synchronous acquisition refers to an operation of adjusting the generation timing of the spread code on the receiving side to the spread code of the received signal, and synchronism holding refers to an operation of monitoring the received signal so that the adjusted timing does not deviate.

In particular, in a CDMA system in which the base stations are asynchronous, each base station spreads a downlink signal to a mobile station by a spreading code using a code unique to each base station called a long code. Therefore, a mobile station trying to connect to a base station must be able to specify the spreading code of the base station. Therefore, the mobile station needs to perform a process of identifying the long code of the base station of the cell in which the mobile station is located in synchronization acquisition such as when the power is turned on. The process of identifying a long code in this synchronization acquisition is called initial synchronization.

[0005] The procedure of initial synchronization in a conventional CDMA system will be described below with reference to FIGS. 7 and 8. FIG. 7 shows an example of a physical channel from a base station to a mobile station. The figure shows the CP
ICH (Common Pilot Channel), P-SCH (Primary Synchro
nization Channel) and S-SCH (Secondary Synchronizati
on Channel).

[0006] The P-SCH and the S-SCH are synchronization channels. These are spread-modulated by a spreading code called a short code and transmitted in the first symbol of each 670 μs time slot as shown in FIG. P-SCH is
A channel for slot timing reproduction, which is spread by a short code SC # 0 for each slot and repeatedly transmitted. Here, the short code SC # 0 is a short code common to all base stations in the CDMA system, and the mobile station is a P-SC
By detecting H, the slot timing of the base station can be detected.

[0007] The S-SCH is a channel for reproducing the frame timing of the base station and for specifying the long code group number assigned to the base station. Here, the frame timing is a timing of a cycle of a frame (10 ms) composed of 15 slots. The long code group number is
It shows a group in which a plurality of long codes are divided by a predetermined number. For example, eight long codes belong to one long code group number group. Since one base station corresponds to one long code, one long code group number is assigned to every eight base stations.

[0008] The S-SCH is provided for each frame (15 slots).
Each slot is spread-modulated by 15 types of short codes SC # Ck (k is an integer) of a predetermined type. The predetermined type of short code SC # Ck is a common short code in the CDMA system, and according to the long code group number assigned to the base station, 15 types of short codes used for spread modulation of S-SCH and The permutation is predetermined. Therefore, the mobile station uses the S-SC
Detecting H, identifying the long code group number of the base station by identifying the 15 types of short codes SC # Ck and their permutations used for S-SCH spreading modulation, and detecting the frame timing it can.

CPICH is called a common pilot channel. A pilot signal is a long code unique to a base station, for example, a long code LC # 1 and a short code SC # unique to CPICH.
It is always transmitted after being spread by a spreading code multiplied by 1. The mobile station can specify the long code of the base station from the CPICH. FIG. 8 is a flowchart showing a procedure of initial synchronization in the mobile station.

Referring to FIG. 1, a mobile station first performs a process of detecting a slot timing by detecting a P-SCH (step 1001). More specifically, the mobile station correlates the received signal with SC # 0 over a certain period. Multiple correlation peaks that match the timing of the P-SCH of the surrounding mobile stations are detected by taking the correlation, but the mobile station optimizes the maximum detected peak among the multiple detected correlation peaks for communication. Then, the mobile station identifies the long code group number of the base station by detecting the S-SCH (step 1003). More specifically, the mobile station correlates the received signal received at the slot timing with a plurality of types of short codes SC # Ck over a predetermined period, and detects a short code SC having a correlation peak equal to or higher than a threshold. Identify #Ck. Next, the long code group number and the frame timing are specified from the permutation of the specified SC # Ck for 15 slots.

The base station stores the specified long code group number (step 1004). Further, the mobile station specifies the long code of the base station by correlating each of the eight long codes belonging to the specified long code group number with the received signal (step 1005). As a specific procedure, for example, a correlation with a received signal is detected for each of the eight long codes over a predetermined period, a correlation peak is detected, and an average of correlation peaks is calculated for each long code. Then, the one with the largest averaging is specified and stored as the long code of the base station (step 1006).

[0012]

However, fading is one of the factors that degrade the communication quality of mobile communication. Fading is a phenomenon in which radio waves are reflected and diffracted by the terrain, buildings, etc., causing a plurality of radio wave propagation paths from the transmitting side to the receiving side. A phenomenon that fluctuates periodically.

The period during which the reception level of the reception signal from the base station has deteriorated due to the effect of the fading is defined as Step 10
May overlap the period of detection of the correlation peak in 05. In this case, there is a problem that the mobile station cannot specify the long code or cannot correctly specify the long code. More specifically, the reception level deterioration period due to fading may reach several ms. Therefore, for example, when the correlation peak detection period falls within the reception level deterioration period, the correlation peak cannot be detected and the long code cannot be specified. When the detection period of the correlation peak partially overlaps with the reception level deterioration period, the correlation code cannot be detected in the overlapping portion. If the long code of the portion where the correlation peak could not be detected is the long code of the serving cell base station, the long code of the base station other than the serving cell is specified. Therefore, it cannot be correctly specified.

Further, when the identification of the long code fails as described above, the mobile station assumes that the detection of the slot timing has been erroneous, and repeats the processing procedure shown in FIG. 8 from step 1001 again. However, the deterioration period and the correlation peak detection period may overlap each time even if the process is repeated many times. In this case, there is a problem that a long code cannot be specified for a long time.

In view of the above problems, an object of the present invention is to provide a mobile phone of a CDMA system, which can specify a long code more accurately even under the influence of fading.

[0016]

In order to solve the above-mentioned problem, a portable telephone according to the present invention comprises a plurality of spreading codes for synchronizing a spread-modulated reception signal by multiplying the spreading codes. A mobile phone that determines a correlation with the received signal with respect to each of the candidates over a predetermined period of time, and compares the correlations with each of the candidates to identify any of the candidates as a spreading code according to the received signal. Is configured to extend the predetermined period according to

According to this configuration, for example, when the mobile phone is moving by a car or the like, the cycle of the intensity of the reception level due to the effect of fading is repeated in units of several ms, but the predetermined period is extended in accordance with the fading. Therefore, even when the period of the valley having a weak reception level and the predetermined period overlap, the predetermined period is extended, and the correlation is obtained even in the period of the mountain having the strong reception level immediately after the valley. Since the spread code can be identified using the correlation between the peak periods, the spread code can be specified more accurately.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A mobile station according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a mobile station according to the present embodiment. In FIG. 1, a mobile station 100 includes an antenna 11, a BPF (Band Pass Filter) 12 for eliminating unnecessary frequency bands, a despreading unit 13, a demodulator 14, a P-SCH detecting unit 15, and an S-SCH detecting unit 16. , Timing generating section 17, PN (spreading code) generating section 18, averaging section 19, determining section
20, a fading cycle detecting section 21 and a control section 22. Although not shown, it is assumed that a signal received from the antenna 11 is down-converted and converted into a baseband signal, and then input to the BPF 12.

The despreading unit 13 receives the PN signal from the BPF 12
Despreading is performed by multiplying the product with the spreading code output from the generating unit 18 and output to the demodulator 14, the averaging unit 19, and the fading period detecting unit 21. In the present embodiment, the despreading unit 13
Has eight despreaders (not shown), and can simultaneously multiply eight spread codes with a received signal using each despreader.

The demodulator 14 PSK-demodulates the narrow-band signal from the despreading unit 13, ie, a signal corresponding to a signal narrow-band modulated by PSK modulation or the like on the transmitting side, and outputs information such as control information and audio information. Output data. P-SCH detector 15
Is provided with, for example, a matched filter, a correlation peak detection circuit, a judgment circuit, and the like, and a short code SC common to the received signal output by the matched filter and the CDMA system.
Based on the correlation value with # 0, the correlation peak detection circuit detects the correlation peak, the determination circuit determines which correlation peak is the maximum, and controls the timing of the maximum correlation peak as the slot timing of the base station Output to the unit 22.

At the slot timing detected by the P-SCH detection unit 15, the S-SCH detection unit 16
Detect the S-SCH using SC # Ck, and identify the 15 types of short codes SC # Ck used for spread modulation of the S-SCH for 15 slots and the long code group number of the base station by specifying the permutation thereof , And detects the frame timing, and outputs the group number and the frame timing to the control unit 22.

The timing generator 17 generates a symbol timing in synchronization with the slot timing detected by the P-SCH 15 and outputs it to the PN generator 18. The PN generation unit 18
Under the control of the control unit 22, the spread code specified by the control unit 22 is generated in synchronization with the symbol timing output from the timing generation unit 17, and is output to the despreading unit 13. Especially PN
The generating unit 18 controls each of the eight long codes belonging to the long code group specified by the S-SCH detecting unit 16 and the short code SC # 0 used for CPICH under the control of the control unit 22 in the initial synchronization. Are generated by multiplying by eight, and each of the eight spreading codes is output to the despreading unit 13 according to a period instructed by the control unit 22. In the present embodiment, the PN generator 18 has eight PN generators (not shown), and can generate eight different spreading codes in the same time zone.

The averaging unit 19 includes a correlation peak detection circuit, an adder, etc., operates at the time of initial synchronization under the control of the control unit 22, and determines the threshold value of the signal output from the despreading unit 13 to determine the correlation. The peak is detected, an average value of the correlation peak is calculated for each of the eight spreading codes, and the calculated average value is output to the determination unit 20. At this time, the averaging unit 19 is notified of a period for averaging the correlation peaks from the control unit 22, and calculates an averaging value in the period.

The judging section 20 operates at the time of initial synchronization under the control of the control section 22. The judging section 20 outputs a long code corresponding to the largest averaging value from among the averaging values for each of the eight spreading codes output from the averaging section 19. Identify the long code of the base station and
Notify 22. Here, a method of specifying a long code performed mainly by the PN generation unit 18, the despreading unit 13, the averaging unit 19, and the determination unit 20 will be described.

FIG. 2 is a time chart for explaining the long code specifying method. CPICH 201 indicates the configuration of CPICH for two frames. As shown in the figure, one frame of CPICH201 is composed of 15 time slots, and each time slot is a spreading code obtained by multiplying a long code LC # 1 unique to the base station 100 and a short code SC # 1 unique to CPICH. Are spread modulated.

The slot 202 shows the configuration of the first slot of the first frame of the CPICH 201. Slot 2 as shown in the figure
02 is composed of 10 symbols of 67 μs per symbol. At timings 203 to 210, the eight PN generators in the PN generator 18 generate spreading codes using the long codes LC # 1 to LC # 8, respectively, and the eight despreaders in the despreading unit 13 The timing for correlating with each of the eight spreading codes is shown. Here, it is assumed that the eight spreading codes are obtained by combining each of the long codes LC # 1 to LC # 8 and the short code SC # 1. The long codes LC # 1 to LC # 8 are long codes belonging to the group of the long code group number specified by the S-SCH detection unit 16.

For example, at timing 203, the PN generation unit 1
8 outputs a spread code obtained by combining the long code LC # 1 and the short code SC # 1 to the despreading unit 13 every symbol, and the despreading unit 13 receives the spread code and the spread code every symbol. The correlation value with the signal is output to the averaging unit 19. The same applies to the timings 204 to 210. The PN generation unit 18 and the despreading unit 13 repeat the operation at timings 203 to 210 in each time slot for two frame periods. That is, 30 times of 2 frames × 15 time slots are repeated.

The averaging unit 19 includes eight long codes LC # 1
The correlation peaks for two frames are detected for each of the spread codes related to LC # 8, the average value of the correlation peaks is calculated, and the average value is output to the determination unit 20. That is, the averaging unit 19 calculates the
By calculating the average value from 300 (2 frames × 15 slots) correlation peaks, eight average values corresponding to the eight spread codes are output to the determination unit 20.

The determining unit 20 specifies the long code corresponding to the largest one from the eight averages, that is, in this example, the long code LC # 1 as the long code of the base station,
Output to 22. As described above, the PN generation unit 18 and the despreading unit
13. The averaging unit 19 and the determination unit 20 specify a long code. However, these components extend the period in which the despreading unit 13 takes a correlation and the period in which the averaging unit 19 takes an averaging in accordance with an instruction from the control unit 22, so that the correlation peak serving as a source of the averaging value is extended. Is not necessarily 300 for each spreading code.

The fading period detecting section 21 is provided with a DSP (digita
a signal processor), monitors the reception level of the signal output from the despreading unit 13, and detects a fading cycle when the reception level is deteriorated, determines an extended period of the long code identification process, and Notify. This notification is transmitted to the PN generation unit 18, the averaging unit 19, and the like via the control unit 22, and the period of the long code specifying process is extended.

Here, the term "fading cycle" means that when a relatively high reception level (mountain) and a relatively low reception level (valley) are alternately repeated in a reception level fluctuation caused by fading, the peak and the valley are determined. Refers to the combined period. When the mobile station 100 moves at the speed of a car or an airplane, a fading cycle of several ms to several tens of ms occurs. Control unit
22 controls the other components in the mobile station 100, thereby mainly controlling the timing using the slot timing output from the P-SCH detection unit 15, the PN at the time of initial synchronization.
It issues a spread code generation instruction to the generation unit 18 and an instruction to extend the period of the long code identification processing.

The procedure for determining the extension of the length of the long code specifying process performed mainly by the fading cycle detecting section 21 and the procedure for determining the extension period will be described below. FIG. 3 and FIG. 4 are flowcharts illustrating the processing procedure of the period extension determination process and the extension period determination process in the fading cycle detection unit 21.

In FIG. 3, the fading period detecting section 21
Repeats the processing of steps 301 to 308 for each time slot. When the long code specifying process is started by the despreading unit 13 and the averaging unit 19 in the initial synchronization, the fading period detecting unit 21 counts the slot period from the start to measure the time from the start. Start (Step 301, Step 302). Here, t indicates a slot period from the start of the long code specifying process, and is counted up for each slot.

The fading period detecting section 21 includes a despreading section 13
The reception level L (t) for each slot is detected from the output signal (step 303). More specifically, the fading period detection unit 21 detects the reception level from the correlation value at each of the timings 202 to 201 in FIG.
Detects eight reception levels over eight long codes,
The largest one of them is detected as the reception level L (t). Here, each of the eight reception levels for the eight long codes may be the average value of the correlation peaks for each symbol, or may be the maximum value of the correlation peaks for each symbol.

The fading period detecting section 21 detects the reception level
L (t) is compared with a predetermined threshold value (step 304). If the result of the comparison in step 304 is that the reception level L (t) is smaller than the threshold value, the fading cycle detecting section 21 determines whether or not the period of the long code specifying process has already been extended (step 306). This determination may be made based on a flag value indicating that the fading cycle detection unit 21 has notified the control unit 22 of the extension of the period of the long code specifying process.

If it is determined in step 306 that the long code specifying process has not been extended, the fading period detecting section 21 performs an extended period determining process for detecting a fading period and determining an extended period. (Step 307). This processing will be described with reference to FIG. Finally, the fading cycle detection unit 21 determines whether or not the period of the long code specifying process has ended. If the period has ended, the process of FIG. 3 ends, and if not, the process returns to step 302 (step 308). ).

Next, FIG. 4 will be described. In FIG. 4, the fading cycle detection unit 21 performs a fast Fourier transform (FFT) on the reception level L (t) of each slot detected from the start of the long code identification processing to the present time, and converts the data in the time domain into the data in the frequency domain. Convert to data (Step 40
1). The fading cycle detector 21 selects a main frequency component from the conversion result and determines the fading cycle Tf (Step 402). As a specific determination method, for example, a frequency component having the highest intensity among a plurality of frequency components is selected, and the cycle is set as a fading cycle Tf.
Either the average value of the intensity of the frequency components higher in intensity than the threshold is set to the fading period Tf, or the period of the lowest frequency of the frequency components higher in intensity than the threshold is set to the fading period Tf. May be used.

The fading cycle detecting section 21 notifies the controlling section 22 of the fading cycle Tf. The control unit
22, the PN generation unit 18, such that the period required for the long code identification process is equal to or longer than the fading period Tf,
The fading period Tf is notified to the despreading unit 13 and the averaging unit 19, and the period of the long code specifying process is extended so as to be longer than the period of the fading period Tf (step 40).
3).

As described above, the fading cycle detecting section 21 determines the fading cycle Tf from the reception level,
By controlling each component such that the long code specifying process is performed over the fading period Tf or more, the period of one or more fading periods is the long code specifying process period. The better part of, that is, the peak part will be included during the long code identification processing period,
Since the despreading unit 13 and the averaging unit 19 can calculate the averaging value by correlating the portion where the reception level has not deteriorated, it is possible to more accurately specify the long code. .

Although the mobile station according to the present invention has been described based on the embodiments, the present invention is not limited to the above embodiments, and may be as follows. That is, (1) In the present embodiment, the fading period detecting unit 21
Is configured to detect the fading cycle by monitoring the reception level of CPICH, but may be configured to detect the fading cycle by monitoring the reception level of the S-SCH instead of CPICH. In that case, the fading period detecting unit 21
Is the S-SCH despread by the P-SCH detection unit 15 instead of monitoring the reception level of the signal output from the despreading unit 13.
This is realized by configuring to monitor the reception level of the signal. Here, the reception level is monitored when the P-SCH is detected immediately after the start of the initial synchronization processing, and the reception level at that time may be stored or may be constantly monitored. In short, the monitoring of the reception level of the P-SCH can be performed prior to the long code specifying process, so that the fading cycle can be detected prior to the long code specifying process, and the period is set at the same time as the start of the long code specifying process. There is an advantage that it can be extended in accordance with the fading cycle. (2) In the present embodiment, the fading cycle is detected by the fast Fourier transform. It may be configured as follows.

FIG. 5A shows a detailed flowchart. In the figure, the fading period detecting section 21 calculates an approximate curve f (t) from the past reception level L (t) (step 50).
1). Here, the past reception level L (t) is a reception level for each slot detected from the start of the long code specifying process to the present time. However, as reception level
When using the S-SCH, the reception level detected from the S-SCH prior to the start of the long code specifying process may be used.

Next, the fading period detecting section 21 calculates f (t0)
The time t0 when = 0, that is, the time at the zero cross point of the approximate curve f (t) is obtained. In FIG. 5B, the portion at time t0 is the zero cross point. Finally, the fading period detection unit 21
The period of the long code specifying process is extended for a period N times (t0−t) (N is 1 or more). Here, t in (t0-t) indicates t shown in FIG. 5B, that is, the time at which the reception level deteriorated below the threshold is detected. For example, the fading cycle detection unit 21 may be configured to make the value of N variable, such as increasing the value of N as the slope is smaller, according to the degree of the slope at (t0−t). (3) Instead of the flowcharts shown in FIGS. 3 and 4, the following processing may be performed. That is, in the long code specifying process, the number of reception levels L (t) exceeding the threshold value detected for each slot is counted for each corresponding long code, and the number of times the maximum reception level is recorded is the most. Identify many long codes.

FIG. 6 is a flowchart showing the detailed procedure. In the figure, the fading cycle detection unit 21 performs an initial setting of a variable i and LC # [i] (steps 601 to 604). Where the variable i is the long code LC # 1 to LC # 8
The variable LC # [i] is a variable for counting the number of reception levels exceeding the threshold for each long code.

The fading cycle detector 21 sets the value of the time t for each slot (steps 605 and 606),
A reception level L (t) is detected for each slot (step 60).
7). The fading cycle detection unit 21 determines whether the reception level L (t) is larger than the threshold, and if the result of the determination is smaller than the threshold, discards the reception level L (t) (step 609). . That is, the reception level L (t) is not subjected to the averaging.

When the long code identification processing period has elapsed, the fading cycle detection section 21 determines that the identification of the long code has failed and ends the processing (steps 610 and 61).
1). If the identification has ended with failure, the fading cycle detection unit 21 restarts the long code identification process from the beginning. By temporarily ending the long code specifying process as described above, the period of the long code specifying process is prevented from being uselessly prolonged. Here, S-SCH
May be redone from the detection of.

If it is determined in step 610 that the long code specifying processing period has not ended, the process returns to step 606. If the reception level L (t) is larger than the threshold value in step 608, the fading cycle detection unit 21 determines the long code number i of the reception level L (t), that is, the maximum reception level of the eight long codes. Long code number i
Is selected (step 612). Then, 1 is added to the variable LC # [i] corresponding to the long code number i (step 61).
3). As a result, the number of times the maximum reception level is recorded is counted for each long code.

The fading cycle detector 21 determines whether or not each LC # [i] exceeds a predetermined number (determination criterion) (step 614). As a result of the determination, if there is a variable LC # [i] exceeding the predetermined number, the corresponding long code is specified as the target (step 615), and the variable L # exceeding the predetermined number is determined.
If there is no C # [i], the process proceeds to step 610. (4) In the long code identification processing, the number of reception levels L (t) that are detected for each slot and are equal to or greater than a threshold value is counted, and the long code identification processing period is extended until the number exceeds a predetermined number. You may comprise. It should be noted that a period longer than two frames is set as a limit period of extension, and when the period extended by the extension means has exceeded the limit period, the extension is stopped and the long code specifying process is terminated. Is also good.

Further, after the long code specifying process is completed, the initial synchronization process may be restarted from the beginning. (5) A part where the reception level is equal to or lower than the threshold value may be determined to be a valley of the fading cycle, and the long code specifying process may be extended from the period of the valley to the next valley. (6) Any combination of the embodiments and (1) to (5) may be combined.

[0049]

According to the portable telephone of the present invention, in order to synchronize a spread-modulated received signal by multiplying a spread code, a plurality of spread code candidates can be synchronized with the received signal for a predetermined period. A mobile phone that identifies one of the candidates as a spreading code according to the received signal by comparing the correlations of the candidates, and extending the predetermined period according to fading. Is done.

According to this configuration, for example, when the mobile phone is moving by car or the like, the cycle of the intensity of the reception level due to the effect of fading is repeated in units of several ms, but the predetermined period is extended in accordance with the fading. Therefore, even when the period of the valley having a weak reception level and the predetermined period overlap, the predetermined period is extended, and the correlation is obtained even in the period of the mountain having the strong reception level immediately after the valley. Since the spread code can be identified using the correlation between the peak periods, the spread code can be specified more accurately.

The portable telephone has a measuring means for measuring a reception level of a reception signal, a calculation means for calculating a fading cycle using the reception level measured by the measuring means, and a period of the fading cycle or more. Extending means for extending the predetermined period. According to this configuration, the mobile phone performs the correlation process at least for one fading period, so that the correlation of the portion corresponding to the peak of the fading period, that is, the portion of the high reception level is always obtained. As a result, a clear correlation peak appears in the correlation relating to the target spread code, and there is an effect that the spread code can be more accurately identified.

The calculation means is configured to convert the time-series signal of the reception level into a frequency spectrum and calculate a fading period from the conversion result. According to this configuration, a configuration in which the fading period is easily obtained by applying the fast Fourier transform can be realized. The calculating means can calculate a fading period from a change in a plurality of reception levels in a time series.

[0053] The portable telephone includes measuring means for measuring the reception level of the received signal by taking the correlation, and extension means for extending the predetermined period until the number of reception levels equal to or higher than a predetermined threshold reaches a predetermined number or more. Is provided. According to this configuration, the mobile phone has an effect that a predetermined number of reception levels equal to or higher than a predetermined threshold can be secured at the time of spreading code identification processing even in an environment where the reception level periodically fluctuates due to fading. is there.

The portable telephone further comprises control means for causing the extension means to stop extension when the predetermined time period extended by the extension means has passed a second predetermined time period. In a situation in which a predetermined number of levels cannot be secured, the extended predetermined period can be limited to a second predetermined period without extending the predetermined period by the extension means.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a mobile station according to the present embodiment.

FIG. 2 is a time chart for explaining a long code specifying method.

FIG. 3 is a flowchart illustrating a processing procedure of a period extension determination process in a fading cycle detection unit 21.

FIG. 4 is a flowchart illustrating a processing procedure of an extension period determination process in a fading cycle detection unit 21.

FIG. 5A is a flowchart illustrating a processing procedure of another form of extension period determination processing in the fading cycle detection unit 21. (B) An approximate curve f (t) is shown.

FIG. 6 is a flowchart illustrating a processing procedure of another form of extension period determination processing in the fading cycle detection unit 21.

FIG. 7 shows an example of a physical channel from a base station to a mobile station.

FIG. 8 is a flowchart illustrating a processing procedure of initial synchronization in a mobile station.

[Explanation of symbols]

 100 Mobile station 11 Antenna 12 BPF 13 Despreader 14 Demodulator 15 P-SCH detector 16 S-SCH detector 17 Timing generator 18 PN generator 19 Averaging unit 20 Judgment unit 21 Fading period detection unit 22 Control unit

Claims (7)

[Claims] In order to synchronize a spread-modulated received signal by multiplying a spread code, a correlation of each of a plurality of spread code candidates with the received signal over a predetermined period is determined. A mobile phone for identifying any of the candidates as a spreading code according to the received signal by comparing the correlation according to (1), wherein the predetermined period is extended in accordance with fading. 2. The mobile phone, comprising: measuring means for measuring a reception level of a received signal; calculating means for calculating a fading cycle using the reception level measured by the measuring means; 2. The mobile phone according to claim 1, further comprising: extension means for extending the predetermined period. 3. The mobile phone according to claim 2, wherein the calculation unit converts a time-series signal of a reception level into a frequency spectrum, and calculates a fading cycle from the conversion result. 4. The mobile phone according to claim 2, wherein the calculation unit calculates a fading period from a plurality of time-series fluctuations in reception levels. 5. The mobile phone, comprising: measuring means for measuring a reception level of a reception signal by taking the correlation; and extending the predetermined period until reception levels equal to or higher than a predetermined threshold reach a predetermined number or more. 2. The mobile phone according to claim 1, comprising means. 6. The mobile phone according to claim 1, wherein the mobile phone includes a calculating unit that calculates a fading period from a received signal, and an extending unit that extends the predetermined period so as to be longer than the fading period. Mobile phone. 7. The mobile phone according to claim 1, further comprising control means for causing the extension means to stop the extension when the predetermined period extended by the extension means has passed a second predetermined period. 5 described mobile phone.