JP3778780B2 - Mobile phone - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mobile phone that performs communication using a CDMA (Code Division Multiple Access) method, and more particularly to an improvement of an initial synchronization method in a fading environment.
[0002]
[Prior art]
In recent years, in the field of mobile communication, CDMA, which is a multiple access method using a spread spectrum communication method, has attracted attention, and, for example, a CDMA system of Wideband CDMA 3GPP (3rd Generation Partnership Project) standard has been realized. In the spread spectrum communication system, the transmission side performs further spread modulation on a signal that has been narrow-band modulated by PSK or the like, and transmits it. Spread modulation refers to multiplying a signal with a special waveform called a spread code. As a result, the narrowband signal is spread into the wideband signal. On the receiving side, the wideband signal is despread to return to a narrowband signal, and demodulation corresponding to the narrowband modulation on the transmitting side is performed. The despreading circuit on the receiving side has the same configuration as the spreading circuit on the transmitting side, and an operation of multiplying the same spreading code as that used for spreading is performed also in despreading. In the CDMA system based on the spread spectrum communication technique as described above, multiple access sharing frequency and time is enabled by using a different spreading code for each call.
[0003]
Now, in order for a mobile station (mobile phone) and a base station in a CDMA system to transmit and receive correctly, synchronization must be established between the mobile station and the base station. In a CDMA system, synchronization is established in two stages: synchronization acquisition and synchronization maintenance. Synchronization acquisition refers to an operation of matching the generation timing of the spread code on the reception side with the spread code of the reception signal, and synchronization holding refers to an operation of monitoring the reception signal so that the timing matched by the synchronization acquisition does not shift.
[0004]
Particularly in a CDMA system in which 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, the mobile station trying to connect to the 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 when acquiring synchronization, such as when the power is turned on. The process of identifying a long code in this synchronization acquisition is called initial synchronization.
[0005]
Hereinafter, an initial synchronization procedure in a conventional CDMA system will be described with reference to FIGS.
FIG. 7 shows an example of a physical channel from the base station to the mobile station.
This figure shows CPICH (Common Pilot Channel), P-SCH (Primary Synchronization Channel) and S-SCH (Secondary Synchronization Channel), respectively.
[0006]
P-SCH and S-SCH are channels for synchronization. As shown in the figure, in the first symbol for each time slot of 670 μs, they are spread-modulated by a spreading code called a short code and transmitted.
P-SCH is a channel for slot timing reproduction and is repeatedly transmitted by being spread with a short code SC # 0 for each slot. Here, the short code SC # 0 is a short code common to all base stations in the CDMA system, and the mobile station can detect the slot timing of the base station by detecting the P-SCH.
[0007]
The S-SCH is a channel for frame timing reproduction of the base station and for specifying a long code group number assigned to the base station.
Here, the frame timing is a cycle timing of a frame (10 ms) consisting of 15 slots. The long code group number indicates a group obtained by dividing a plurality of long codes into 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]
In each S-SCH, each slot (15 slots) is spread-modulated with 15 types of predetermined types of short codes SC # Ck (k is an integer). The predetermined type of short code SC # Ck is a common short code in the CDMA system. Depending on the long code group number assigned to the base station, 15 types of short codes used for S-SCH spread modulation and The permutation is predetermined. Therefore, the mobile station detects the S-SCH at the slot timing, and specifies the long code group number of the base station by specifying the 15 types of short codes SC # Ck and their permutations used for S-SCH spread modulation. In addition, the frame timing can be detected.
[0009]
CPICH is called a common pilot channel and is always transmitted by spreading a pilot signal with a long code unique to the base station, for example, a long code LC # 1 multiplied by a short code SC # 1 unique to CPICH. It is what. The mobile station can specify the long code of the base station from the CPICH.
FIG. 8 is a flowchart showing an initial synchronization processing procedure in the mobile station.
[0010]
In the figure, the mobile station first detects the slot timing by detecting the 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 P-SCH timing of the surrounding mobile stations are detected by taking the correlation, but the mobile station is best suited for communication among the multiple detected correlation peaks that recorded the maximum peak As slot timing of the correct base station (step 1002)
Next, 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 a received signal received at slot timing with a plurality of types of short codes SC # Ck over a predetermined period, and detects a short code SC in which a correlation peak equal to or greater than a threshold is detected. Specify #Ck. Subsequently, the long code group number and the frame timing are identified from the permutations of the identified 15 slots of SC # Ck.
[0011]
The base station stores the identified 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 peak is detected for each of the eight long codes with a received signal over a certain period, and the correlation peak is detected for each long code. Then, the one with the maximum addition average is specified and stored as the long code of the base station (step 1006).
[0012]
[Problems to be solved by the invention]
Incidentally, fading is one of the factors that degrade the communication quality of mobile communication. Fading means that multiple radio wave propagation paths from the transmission side to the reception side occur due to the reflection and diffraction of radio waves by topography and buildings, etc., and the reception level of the signal at the reception side is timed by causing a phase shift on the reception side. Is a phenomenon that fluctuates automatically
[0013]
The period in which the reception level of the received signal from the base station deteriorates due to the influence of fading may overlap with the correlation peak detection period in step 1005. In this case, there is a problem that the mobile station cannot specify the long code or cannot specify it correctly.
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. Also, when the correlation peak detection period partially overlaps the reception level degradation period, the correlation peak cannot be detected in the overlapping part, so the long code in which another correlation peak is detected is assigned to that of the base station. If the long code of the part where the correlation peak could not be detected is the long code of the base station of the serving cell, the long code of the base station other than the serving cell is specified. Therefore, it cannot be specified correctly.
[0014]
Further, when the identification of the long code fails as described above, the mobile station regards that the detection of the slot timing is wrong and starts the processing procedure shown in FIG. However, the deterioration period and the correlation peak detection period may overlap each time, no matter how many times the process is repeated. In this case, there is also a problem that the long code cannot be specified over a long period.
[0015]
In view of the above problems, an object of the present invention is to provide a mobile phone that is a CDMA system mobile phone and that can specify a long code more accurately even under the influence of fading.
[0016]
[Means for Solving the Problems]
In order to solve the above-described problem, the mobile phone of the present invention performs synchronization with a received signal that has been spread-modulated by multiplying a spread code, and for each of a plurality of spread code candidates, A mobile phone that obtains a correlation over a predetermined period and compares one of the candidates with a spread code according to the received signal by comparing correlations of the candidates, and extends the predetermined period according to fading It is configured as follows.
[0017]
According to this configuration, for example, when the mobile phone is moved by an automobile or the like, the cycle of the reception level strength due to fading is repeated in units of several ms, but the predetermined period is extended according to fading. Therefore, even if the period of the valley where the reception level is weak overlaps with the predetermined period, the predetermined period is extended so that the correlation can be taken even in the period of the peak where the reception level is strong immediately after the valley. Thus, since the spreading code can be identified using the correlation of the peak period, the spreading code can be specified more accurately.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, mobile stations according to embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the mobile station of this embodiment.
In the figure, a mobile station 100 includes an antenna 11, a BPF (band pass filter) 12 for excluding unnecessary frequency bands, a despreading unit 13, a demodulator 14, a P-SCH detection unit 15, and an S-SCH detection unit 16. A timing generation unit 17, a PN (spreading code) generation unit 18, an addition averaging unit 19, a determination unit 20, a fading cycle detection unit 21, and a control unit 22. Although not shown, it is assumed that the signal received from the antenna 11 is down-converted and converted into a baseband signal and then input to the BPF 12.
[0019]
The despreading unit 13 performs despreading by the product of the reception signal from the BPF 12 and the spreading code output from the PN generation unit 18 and outputs the result to the demodulator 14, the addition averaging unit 19 and the fading period detection unit 21. In the present embodiment, the despreading unit 13 has eight despreaders (not shown), and can simultaneously multiply the received signal for eight spread codes using each despreader.
[0020]
The demodulator 14 PSK-demodulates a narrowband signal from the despreading unit 13, that is, a signal corresponding to a signal that has been narrowband modulated by PSK modulation on the transmission side, and outputs information data such as control information and audio information To do.
The P-SCH detection unit 15 includes, for example, a matched filter, a correlation peak detection circuit, a determination circuit, and the like. From the correlation value between the received signal output by the matched filter and the short code SC # 0 common in the CDMA system, the correlation is calculated. The peak detection circuit detects the correlation peak, the determination circuit determines which correlation peak is the maximum, and outputs the timing of the maximum correlation peak to the control unit 22 as the slot timing of the base station.
[0021]
The S-SCH detector 16 detects the S-SCH using the short code SC # Ck at the slot timing detected by the P-SCH detector 15, and is used for the spread modulation of the S-SCH for 15 slots. The long code group number of the base station is specified by specifying the 15 types of short codes SC # Ck and their permutations, the frame timing is detected, and the group number and frame timing are output to the control unit 22.
[0022]
The timing generator 17 generates symbol timing in synchronization with the slot timing detected by the P-SCH 15 and outputs the symbol timing to the PN generator 18.
The PN generation unit 18 generates a spreading code specified by the control unit 22 in synchronization with the symbol timing output from the timing generation unit 17 and outputs the spread code to the despreading unit 13 under the control of the control unit 22. In particular, the PN generation unit 18 controls each of the eight long codes belonging to the long code group specified by the S-SCH detection unit 16 and the short code SC # used for CPICH under the control of the control unit 22 in the initial synchronization. Eight spreading codes multiplied by 0 are generated, and each of the eight spreading codes is output to the despreading unit 13 in accordance with the period instructed by the control unit 22. In the present embodiment, the PN generation unit 18 has eight PN generators (not shown), and can generate eight different spreading codes in the same time zone.
[0023]
The averaging unit 19 includes a correlation peak detection circuit, an adder, and the like, operates at the time of initial synchronization under the control of the control unit 22, and detects the correlation peak by determining the threshold value of the signal output from the despreading unit 13. Then, an average value of correlation peaks is calculated for each of the eight spreading codes and output to the determination unit 20. At this time, the addition averaging unit 19 is notified of the period during which the correlation peaks are added and averaged by the control unit 22, and calculates the addition average value during that period.
[0024]
The determination unit 20 operates at the time of initial synchronization under the control of the control unit 22, and selects the long code corresponding to the maximum addition average value from the addition average values for each of the eight spreading codes output from the addition average unit 19 of the base station. The control unit 22 is notified by identifying the long code.
Here, a long code specifying method performed mainly by the PN generation unit 18, the despreading unit 13, the addition averaging unit 19, and the determination unit 20 will be described.
[0025]
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 CPICH 201 is composed of 15 time slots, and each time slot is a spreading code obtained by multiplying a long code LC # 1 specific to the base station 100 and a short code SC # 1 specific to CPICH. Is spread modulated.
[0026]
Slot 202 shows the configuration of the first slot of the first frame of CPICH 201. As shown in the figure, the slot 202 is composed of 10 symbols of 1 symbol 67 μs.
At timings 203 to 210, the eight PN generators in the PN generation unit 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 obtaining the correlation with each of the eight spreading codes is shown. Here, it is assumed that the eight spreading codes are composed 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.
[0027]
For example, at timing 203, the PN generation unit 18 outputs a spreading code obtained by combining the long code LC # 1 and the short code SC # 1 to the despreading unit 13 every time, and the despreading unit 13 Every time, the correlation value between the spread code and the received 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 operations at timings 203 to 210 over two frame periods in each time slot. In other words, it is repeated 30 times of 2 frames × 15 time slots.
[0028]
The addition averaging unit 19 detects a correlation peak for two frames for each spreading code related to the eight long codes LC # 1 to LC # 8, calculates the addition average value, and outputs it to the determination unit 20. In other words, the addition averaging unit 19 determines eight addition average values corresponding to eight spreading codes by calculating an addition average value from 300 (2 frames × 15 slots) correlation peaks for each spreading code. To be output to the unit 20.
[0029]
The determination unit 20 specifies the long code according to the maximum from the eight average values, that is, in this example, the long code LC # 1 as the long code of the base station and outputs it to the control unit 22.
As described above, the PN generation unit 18, the despreading unit 13, the addition averaging unit 19, and the determination unit 20 specify the long code. However, since these components extend the period in which the despreading unit 13 performs correlation and the period in which the addition averaging unit 19 performs addition averaging in accordance with an instruction from the control unit 22, the correlation peak that is the basis of the addition average value Is not necessarily 300 per spreading code.
[0030]
The fading period detector 21 is a DSP (digital signal processor), monitors the reception level of the signal output from the despreading unit 13, detects the fading period when the reception level deteriorates, and performs long code identification processing The extension period is determined and notified to the control unit 22. This notification is transmitted to the PN generation unit 18, the addition averaging unit 19, etc. via the control unit 22, and the period of the long code specifying process is extended.
[0031]
Here, the fading cycle is a period in which peaks and valleys are combined when a relatively high portion (mountain) and a relatively low portion (valley) are alternately repeated in a reception level variation caused by fading. Say. When the mobile station 100 moves at a speed similar to that of a car or an airplane, a fading cycle of several ms to several tens of ms occurs.
The control unit 22 mainly controls the timing control using the slot timing output from the P-SCH detection unit 15 to the PN generation unit 18 at the time of initial synchronization by controlling other components in the mobile station 100. The spread code generation instruction and the long code identification process period extension instruction are performed.
[0032]
In the following, a procedure for determining a period extension and a process for determining an extension period for the long code specifying process performed with the fading cycle detection unit 21 as the center will be described.
FIG. 3 and FIG. 4 are flowcharts showing a processing procedure of the period extension determination process and the extension period determination process in the fading cycle detection unit 21.
[0033]
In FIG. 3, the fading cycle detection unit 21 repeats the processing from step 301 to step 308 for each time slot.
When the long code specifying process is started by the despreading unit 13 and the addition averaging unit 19 in the initial synchronization, the fading period detection unit 21 counts the slot period from the start time and measures the time from the start time. 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.
[0034]
The fading period detection unit 21 detects the reception level L (t) for each slot from the signal output from the despreading unit 13 (step 303). More specifically, the fading period detection unit 21 detects reception levels from their correlation values at each of the timings 202 to 201 in FIG. 2, that is, detects eight reception levels related to eight long codes, of which The maximum is detected as the reception level L (t). Here, 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.
[0035]
The fading cycle detector 21 compares the reception level L (t) with a predetermined threshold value (step 304).
If the reception level L (t) is smaller than the threshold value as a result of the comparison in step 304, the fading period detection unit 21 determines whether or not the long code identification process period has already been extended (step 306). This determination may be made based on the flag value indicating that the fading cycle detection unit 21 has notified the control unit 22 of the extension of the long code identification process period.
[0036]
If it is determined in step 306 that the long code identification process has not been extended, the fading period detection unit 21 performs an extension period determination process that detects the fading period and determines the extension period (step 307). ). This process will be described with reference to FIG.
Finally, the fading cycle detector 21 determines whether or not the period of the long code specifying process has ended. If it has ended, the process of FIG. 3 ends. If not, the process returns to step 302 (step 308 ).
[0037]
Next, FIG. 4 will be described.
In FIG. 4, the fading period detection unit 21 performs fast Fourier transform (FFT) on the reception level L (t) for each slot detected from the start of the long code identification process to the present time, and converts the time domain data into the frequency domain. Data is converted (step 401).
The fading cycle detection unit 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, (1) a frequency component having the highest intensity among a plurality of frequency components is selected and its period is set as a fading period Tf. (2) Frequency component having an intensity higher than a threshold value Any one of the following methods may be used: the average value of the intensity is the fading period Tf, and the period of the lowest frequency among the frequency components whose intensity is higher than the threshold value is the fading period Tf.
[0038]
The fading cycle detection unit 21 notifies the control unit 22 of the fading cycle Tf.
By this notification, the control unit 22 notifies the fading cycle Tf to the PN generation unit 18, the despreading unit 13, and the addition averaging unit 19 so that the period for the long code specifying process is equal to or longer than the fading cycle Tf. The long code specifying process is extended so as to be longer than the fading period Tf (step 403).
[0039]
As described above, the fading cycle detection unit 21 determines the fading cycle Tf from the reception level, and the control unit 22 controls each component so that the long code specifying process is performed over the fading cycle Tf or more. Since the period longer than one period is the long code identification processing period, at least a better part of the reception level during the fading period, that is, a peak part is included in the long code identification processing period, and the despreading unit 13 The addition averaging unit 19 can calculate the addition average value by correlating the portion where the reception level has not deteriorated, so that it is possible to specify the long code more accurately. .
[0040]
The mobile station of the present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and may be as follows. That is,
(1) In the present embodiment, the fading cycle detection unit 21 is configured to detect the fading cycle by monitoring the CPICH reception level. However, the fading cycle detection unit 21 monitors the S-SCH reception level instead of the CPICH. You may comprise so that a period may be detected. In that case, the fading period detection unit 21 monitors the reception level of the S-SCH signal 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. Here, the reception level is monitored at the time of detection of the P-SCH 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, since the monitoring of the P-SCH reception level can be performed prior to the long code identification process, the fading period can be detected prior to the long code identification process, and the period is set simultaneously with the start of the long code identification process. There is an advantage that it can be extended in accordance with the fading period.
(2) In this embodiment, the fading period is detected by fast Fourier transform, but an approximate curve is obtained from the reception level L (t), and the fading period is calculated by obtaining the zero cross point of the approximate curve. You may comprise.
[0041]
FIG. 5 (a) shows a detailed flowchart. In the figure, the fading cycle detector 21 obtains an approximate curve f (t) from the past received level L (t) (step 501). Here, the past reception level L (t) is the reception level for each slot detected from the start of the long code identification process to the present time. However, when an S-SCH signal is used as the reception level, the reception level detected from the S-SCH prior to the start of the long code identification process may be used.
[0042]
Next, the fading cycle detection unit 21 obtains the time t0 when f (t0) = 0, that is, the time of the zero cross point of the approximate curve f (t). In FIG. 5B, the portion at time t0 is the zero cross point.
Finally, the fading cycle detection unit 21 extends the period of the long code specifying process by 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 when the reception level deteriorated below the threshold is detected. For example, the fading cycle detection unit 21 may be configured such that the value of N is variable, for example, the value of N is increased as the inclination is smaller, depending on the degree of inclination 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 identification process, the number of reception levels L (t) detected for each slot exceeding the threshold is counted for each corresponding long code, and the number of times the maximum reception level is recorded is the largest. Identify many long codes.
[0043]
FIG. 6 is a flowchart showing the detailed procedure.
In the figure, the fading cycle detection unit 21 performs initial setting of a variable i and LC # [i] (steps 601 to 604). Here, variable i corresponds to long code numbers 1 to 8 of long codes LC # 1 to LC # 8, and variable LC # [i] counts the number of received levels exceeding the threshold for each long code. It is a variable to do.
[0044]
The fading cycle detector 21 sets the value of time t for each slot (step 605, step 606), and detects the reception level L (t) for each slot (step 607).
The fading cycle detection unit 21 determines whether or not the reception level L (t) is larger than the threshold value, and discards the reception level L (t) when the determination result is smaller than the threshold (step 609). . That is, the reception level L (t) is not subjected to addition averaging.
[0045]
When the long code identification process period has elapsed, the fading cycle detection unit 21 determines that the long code identification has failed and ends the process (steps 610 and 611). When the identification is unsuccessful and the process ends, the fading cycle detection unit 21 starts the long code identification process again from the beginning. Thus, once the long code specifying process is terminated, the long code specifying process period is prevented from being unnecessarily prolonged. Here, the S-SCH detection may be repeated.
[0046]
If it is determined in step 610 that the long code identification processing period has not ended, the process returns to step 606.
When the reception level L (t) is larger than the threshold value in step 608, the fading period detection unit 21 sets the long code number i related to the reception level L (t), that is, the maximum reception level of the eight long codes. The 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 613). As a result, the number of times of recording the maximum reception level is counted for each long code.
[0047]
The fading cycle detection unit 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 identified as the target (step 615), and if there is no variable LC # [i] exceeding the predetermined number Proceed to step 610.
(4) In the long code identification process, count the number of reception levels L (t) that are detected for each slot and exceed the threshold, and extend the long code identification process period until the number exceeds the predetermined number. It may be configured. It should be noted that a period longer than 2 frames is set as the extension limit period, and when the extension period has exceeded the limit period, the extension is stopped and the long code specifying process is terminated. Also good.
[0048]
Further, after the long code specifying process is completed, the initial synchronization process may be restarted from the beginning.
(5) A portion where the reception level is equal to or less than the threshold value may be determined as a trough of the fading cycle, and the long code specifying process may be extended until the next trough comes after the trough period.
(6) You may combine what can be combined among embodiment and (1)-(5).
[0049]
【The invention's effect】
The mobile phone of the present invention obtains a correlation over a predetermined period with the received signal for each of a plurality of spread code candidates in order to synchronize with a spread modulated reception signal by multiplying a spread code, A mobile phone that identifies any of the candidates as a spreading code related to the received signal by comparing the correlations related to the candidates, and is configured to extend the predetermined period according to fading.
[0050]
According to this configuration, for example, when the mobile phone is moved by an automobile or the like, the cycle of the reception level strength due to fading is repeated in units of several ms, but the predetermined period is extended according to fading. Therefore, even if the period of the valley where the reception level is weak overlaps with the predetermined period, the predetermined period is extended so that the correlation can be taken even in the period of the peak where the reception level is strong immediately after the valley. Thus, since the spreading code can be identified using the correlation of the peak period, the spreading code can be specified more accurately.
[0051]
The mobile phone includes a measurement unit that measures a reception level of a received signal, a calculation unit that calculates a fading period using the reception level measured by the measurement unit, A calculation means for converting the time series signal of the reception level measured by the measurement means into a frequency spectrum, and calculating a fading period from the conversion result; Extending means for extending the predetermined period so as to be equal to or longer than the fading period.
According to this configuration, since the mobile phone performs correlation processing at least for the time corresponding to one fading cycle, a correlation corresponding to a portion corresponding to a peak of the fading cycle, that is, a portion with a high reception level is always obtained. As a result, a clear correlation peak appears in the correlation for the target spreading code, and the spreading code can be identified more accurately. By applying the fast Fourier transform, it is possible to realize a configuration for easily obtaining the fading period There is an effect.
[0053]
The mobile phone includes measurement means for measuring the reception level of the received signal by taking the correlation, and extension means for extending the predetermined period until a reception level equal to or higher than a predetermined threshold reaches a predetermined number or more.
According to this configuration, the mobile phone can secure a predetermined number of reception levels that are equal to or greater than a predetermined threshold at the time of spreading code identification processing even in an environment in which the reception level fluctuates periodically due to fading. is there.
[0054]
The mobile phone further includes a control unit that causes the extension unit to stop the extension when the predetermined period extended by the extension unit has exceeded a second predetermined period. In a situation where the number cannot be secured, the extended predetermined period can be limited to the second predetermined period without the predetermined period being continuously extended 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 showing a processing procedure of period extension determination processing in a fading cycle detection unit 21;
FIG. 4 is a flowchart showing a processing procedure of an extension period determination process in a fading cycle detection unit 21.
FIG. 5 is a flowchart showing a processing procedure of another form of extension period determination processing in (a) fading cycle detection unit 21; (B) An approximate curve f (t) is shown.
FIG. 6 is a flowchart showing 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 showing an initial synchronization processing procedure in a mobile station.
[Explanation of symbols]
100 mobile stations
11 Antenna
12 BPF
13 Despreading section
14 Demodulator
15 P-SCH detector
16 S-SCH detector
17 Timing generator
18 PN generator
19 Addition averaging section
20 Judgment part
21 Fading period detector
22 Control unit

Claims (2)

In order to synchronize the spread-modulated received signal by multiplying the spread codes, a correlation over a predetermined period with the received signal is obtained for each of a plurality of spread code candidates, and the correlations related to the candidates are compared. A mobile phone that identifies any of the candidates as a spreading code associated with the received signal,
Measuring means for measuring the reception level of the received signal by taking the correlation;
Extending means for extending the predetermined period until a reception level equal to or higher than a predetermined threshold reaches a predetermined number or more;
A mobile phone comprising: The mobile phone further includes:
Control means for causing the extension means to stop the extension when the predetermined period extended by the extension means exceeds a second predetermined period.
The mobile phone according to claim 1.

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