JP2003244742A - Mobile phone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile phone capable of enhancing a success rate of hand-off of a CDMA system mobile phone system. <P>SOLUTION: A mobile phone 100 for searching a base station of a transfer destination corresponding to soft hand-off instruction and hard hand-off instruction accepts the soft hand-off instruction or the hard hand-off instruction able to include designation of a width of a search window from a base station, when the mobile phone 100 receives the hard hand-off instruction, a window control section 83 controls a search section 70 to search a pilot signal from other base stations by using a search window with a wider width than that of the search window included in the instruction or that of the search window used for the soft hand-off instruction. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handoff of a CDMA portable telephone system. 2. Description of the Related Art A mobile phone of the CDMA system performs a handoff for switching a communication channel from a communicating base station to another base station in accordance with movement between cells. In the handoff, before terminating communication with the base station in communication (also called the old base station), another base station (new base station) on the same frequency is used.
There is a soft handoff that starts communication with the base station, and a hard handoff that starts communication with a base station having a different base station group, a different frequency allocation, or a different frame offset after disconnecting the communication with the old base station. [0003] Soft handoff is performed based on the pilot strength of a peripheral base station monitored by the mobile phone. Here, the pilot strength refers to the radio field strength of a pilot signal common to each base station, which is output from each base station at a different spreading timing. By measuring the pilot strength, the mobile phone can specify the spreading timing of each peripheral base station, that is, the synchronization timing. Therefore, when a soft handoff is instructed from the base station, the mobile phone immediately synchronizes with the designated base station. be able to. On the other hand, since the hard handoff is a handoff between base stations having different base station groups, frequency allocations, or frame offsets, the portable telephone sets the pilot strength of the new base station before the handoff due to the hardware configuration. Cannot be measured. Therefore, the mobile phone measures the pilot strength of the new base station after receiving the instruction for hard handoff from the base station, and specifies the synchronization timing of the new base station based on the measurement result. When measuring the pilot strength of the new base station, the mobile phone estimates the synchronization timing of the new base station based on the synchronization timing of the old base station, sets a search window in accordance with the estimated synchronization timing, and indicates the search window. Measure the pilot strength during the period. As described above, in the hard handoff, since the search window is set based on the synchronization timing of the old base station as described above, radio waves from the new base station are greatly reflected due to reflection or the like. In this case, the peak position of the pilot signal of the new base station falls outside the frame of the search window, the synchronization timing of the new base station cannot be acquired, and handoff may fail and communication may be interrupted. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a portable telephone having an improved handoff success rate of a CDMA portable telephone system. [0007] In order to solve the above-mentioned problems, a portable telephone according to the present invention is a portable telephone which searches for a destination base station in response to a soft handoff instruction and a hard handoff instruction. Receiving means for receiving a hard handoff instruction that may include a soft handoff instruction or a search window width designation from a base station, and when a hard handoff instruction is received, a search window width or a soft handoff instruction included in the instruction. Search means for searching for a pilot signal from another base station using a search window wider than the width of the search window to be used. [0008] Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing a configuration of the mobile phone according to the present embodiment. In FIG. 1, a mobile phone 100 includes an antenna 10, a radio unit 20, a modem unit 3
0, an audio processing unit 40, a microphone 50, a speaker 60, a search unit 70, and a control unit 80. The radio unit 20 performs frequency conversion between a radio section between the base station and the antenna 10 and the modem unit 30, and performs frequency conversion according to the traffic channel frequency allocation in accordance with an instruction from the control unit 80. be able to. The modulation / demodulation unit 30 mainly includes a modulation unit that performs narrowband modulation and spread modulation and a demodulation unit that performs despreading and demodulation, and modulates and demodulates data. The audio processing unit 40 performs CODEC processing of audio input and output via the microphone 50 and the speaker 60. The search unit 70 includes a matched filter 71, a pilot strength measurement unit 72, and the like, and performs a pilot search for a nearby base station during communication or a new base station during hard handoff. [0011] The pilot search is to set a search window in which a multi-path component of an available pilot channel (ie, a mobile phone 100 to demodulate a corresponding downlink traffic channel).
This is an operation to search for a multipath component that can be used by. The size of the search window is based on an instruction from the base station. The pilot channel is a signal continuously transmitted by each base station. The pilot channel enables the mobile phone to acquire the timing of the downlink CDMA channel. Different base stations are identified by different pilot PN sequence offsets. That is, since each base station spreads pilot channels at 512 different timings using a PN sequence having a cycle of 2 to the 15th power, the mobile phone can specify the base station by specifying the timing. The mobile phone 100 searches for a pilot channel on the current CDMA frequency allocation by a pilot search of a nearby base station, detects the presence of a pilot channel of another base station, and measures its strength.
When detecting a pilot channel of another base station having sufficient strength, the mobile phone 100 transmits a pilot strength measurement message to the base station in communication, and the base station instructs execution of a handoff in response thereto. [0013] Further, the mobile phone 100 performs synchronization acquisition of the new base station by performing a pilot search for the new base station during hard handoff. 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. The matched filter 71 performs correlation detection by convolution integration of the received signal and the PN sequence while the signal indicating the search window period is input from the window control unit 83. The pilot strength measuring section 72 adds the ratio between the received pilot energy Ec per chip and the total received spectral density (noise and signal) Io of each component based on the result of the correlation detection of the matched filter 71. To measure the pilot strength of the pilot channel. Further, the pilot strength measuring unit 72
Detects the peak position by measuring the intensity and detects the timing of the pilot channel. The control unit 80 includes a CPU (not shown) and a RAM (not shown).
The mobile phone 10 is configured by a CPU that executes various programs recorded in the ROM.
0 various controls are performed. Functionally, the control unit 80 includes a handoff processing unit 81, a frequency setting unit 82, a window control unit 83,
It comprises a search window memory 84 and a search window table 85. When receiving a handoff instruction message from the base station, the handoff processing unit 81 controls each component to perform a handoff. More specifically, the handoff processing unit 81 first analyzes a handoff instruction message to specify a handoff type, a frequency allocation, a pilot PN sequence offset index, search window size information, and the like. Here, the handoff type includes a soft handoff and a hard handoff. The frequency assignment indicates the frequency assigned to the channel of the new base station, and is omitted when the handoff type is soft handoff. The pilot PN sequence offset index is
5 shows a PN offset in units of 64 PN chips per pilot that is proportional to a zero offset pilot sequence for a new base station. The search window size indicates a search window size used for pilot search, and may be omitted in some cases. Next, the handoff processing unit 81 controls the radio unit 20 to perform frequency conversion in synchronization with the specified frequency allocation frequency. Also, the handoff processing unit 81
Using the search window size information, the corresponding search window size is read from the search window table 85, and the search window memory 8 is read.
4 is stored. Further, the handoff processing unit 81 notifies the window control unit 83 of the pilot PN sequence offset index and the handoff type. The frequency setting unit 82 includes a handoff processing unit 8
1 controls the frequency switching of the radio unit 20 in accordance with the frequency assignment of the new base station indicated in the handoff instruction analyzed by the first unit. The search window table 85 stores the search window table shown in FIG. As shown in the figure, the search window table includes search window information shown in the left column and window size parameters shown in the right column. The value indicated by the window size parameter corresponds to the number of PN chips of a search window used when searching for a pilot channel. The search window memory 84 stores the search window information and the window size parameter read from the search window table 85 by the handoff processing unit 81. The window control unit 83 matches the matched filter 7 based on the handoff type, the pilot PN sequence offset, the search window information stored in the search window memory 84, and the window size parameter.
1 is notified of the timing of the search window in the pilot search. During communication, window control section 83 performs a pilot search by setting the center of the search window having the width of the window size parameter indicated in the search window memory to the pilot PN sequence offset of each neighboring base station. When the handoff type is hard handoff, the window control unit 83 reads out the search window information stored in the search window memory 84, increases the value of the search window information by one, and responds to the increased value of the search window information. The window size parameter to be read is read from the search window table 85. Subsequently, window control section 83 sets the center of the search window having the width of the read window size parameter to the pilot PN sequence offset of the new base station, and performs a pilot search for the new base station. That is, with this configuration, the portable telephone 100
Performs a pilot search for a new base station with a search window that is wider than the search window size indicated by the window size parameter stored in the search window memory during hard handoff. As a result, at the time of hard handoff, pilot search is performed using a search window size used for pilot search for soft handoff or a window wider than the search window size specified by the base station. FIG. 3A shows a normal hard handoff point, and FIG. 3B shows an abnormal hard handoff point. 3 (a) and 3 (b), when the mobile phone performs a hard handoff from the base station A to the base station B, the mobile phone sets a search window for the pilot search of the base station B based on the radio wave of the base station A. Set. That is, the timing of the search window is determined based on the delay time of the radio wave from base station A. In FIG. 3A, the mobile telephone (mobile unit in the figure) is located at an intermediate distance between the base station A and the base station B, so that the delay time α1 of the radio wave from the base station A and the base station The time difference of the delay time α2 of the radio wave from the station B is not so large. Therefore, the time difference is absorbed by the search window size specified by the base station at the time of hard handoff or the search window size used at the time of the previous pilot search. However, as shown in FIG. 3 (b), when the mobile phone is located near the base station A (in the figure, the mobile station) and far from the base station B, the radio wave from the base station B is The reflection time increases, so the delay time increases. For this reason, the time difference between the delay time β1 of the radio wave from the base station A and the delay time β2 of the radio wave from the base station B is larger than in the case of FIG. The search window size used in the pilot search may not be absorbed. If it cannot be absorbed, the mobile phone cannot catch the pilot signal of base station B,
As a result, the hard handoff fails and the call drops. In the soft handoff, prior to the soft handoff, the pilot search of the neighboring base station is performed, and the soft handoff is performed after the timing of the pilot channel is captured. Therefore, such a problem does not occur. On the other hand, in the hard handoff, such a problem is likely to occur because the pilot search of the transfer destination is not performed before the handoff. Therefore, the present invention, in the case of hard handoff, even if the time difference between the delay time of the radio wave from the old base station and the new base station is large, by making the search window wider, the time difference can be absorbed, Prevent handoff failure. FIG. 4 shows the relationship between the field intensity of each channel of the base stations A and B in FIG. 3B and the search window. The figure shows the flow of time from left to right. PN100 is the pilot PN offset index of base station A, PN2
00 indicates the pilot PN offset index of the base station B. The mobile phone 100 detects the peak position of the radio wave from the radio wave intensity of the signal of the base station A during communication with the base station A (frequency allocation 25 ch), and determines the detected position and the PN
The delay time β1 is obtained from the 100 reference times and stored. When a hard handoff instruction is issued to the base station B (frequency allocation 50 ch), the window control unit 83 determines the timing of the PN200 and the timing delayed by the delay time β1 from the PN200 based on the reference time of the PN100 and the delay time β1. Is estimated. Then, the window control unit 83 sets the PN 200
A search window size wider than the search window size specified by the base station (or the search window size stored in advance) is opened based on the timing delayed by delay time β1 minutes from the base station. The peak position of the radio wave of the signal of the base station B is P
Although a delay time β2 has been sent from the position of N200, a peak is detected in the search window due to the large search window size. FIG. 5 is a flowchart showing a processing procedure centered on the control unit 80. Handoff processing unit 81
Obtains the handoff instruction message from the communicating base station, and obtains the handoff type, the pilot PN sequence offset index of the new base station, the frequency allocation of the new base station, the search window size, etc. by analyzing the handoff instruction message. Then, necessary information is transmitted to the frequency setting unit 82, the window control unit 83, and the like (Step S401, Step S402). The window control unit 83 identifies whether or not the handoff type of the handoff instruction message is a hard handoff.
Proceed to 404, otherwise proceed to step S405 (step S403). The window control unit 83 acquires from the search window table 85 a search window size one size larger than the search window size stored in the search window memory 84 or included in the handoff instruction message (step S404). Subsequently, at the timing estimated by the method described with reference to FIG. 4, the matched filter 71 is controlled so as to open the search window of the search window size acquired in step S404, and the matched filter 71 and the pilot strength measurement unit 72 perform a pilot search. (Step S406). On the other hand, when the handoff type is not the hard handoff, the window control unit 83
The matched filter 71 and the pilot strength measurement unit 72 perform a pilot search using the search window size stored in the H.264 or included in the handoff instruction message. The portable telephone of the present invention is a portable telephone for searching for a destination base station in response to a soft handoff instruction and a hard handoff instruction. Receiving means for receiving a soft handoff instruction or a hard handoff instruction that may include designation of a search window width; and when receiving a hard handoff instruction, a search window width included in the instruction or a search window used for the soft handoff instruction. Search means for searching for a pilot signal from another base station using a search window having a width wider than the width. In the soft handoff, prior to the soft handoff, a pilot search for a neighboring base station is performed, and the soft handoff is performed after the timing of the pilot channel is captured. Therefore, such a problem does not occur. On the other hand, in the hard handoff, such a problem is likely to occur because the pilot search of the transfer destination is not performed before the handoff. Therefore, the present invention makes it possible to absorb the time difference by making the search window wider in the case of hard handoff, even if the time difference between the radio wave delay times from the old base station and the new base station is large. Thus, failure of handoff can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of a mobile phone according to the present embodiment. FIG. 2 is a diagram showing a search window table. FIG. 3 (a) shows a normal hard handoff point. (B) shows an abnormal hard handoff point. FIG. 4 shows the relationship between the radio field intensity of each channel of base stations A and B and a search window. FIG. 5 is a flowchart showing a processing procedure centered on a control unit 80; [Description of Signs] 10 Antenna 20 Radio unit 30 Modulation / demodulation unit 40 Audio processing unit 50 Microphone 60 Speaker 70 Search unit 71 Matched filter 72 Pilot strength measurement unit 80 Control unit 81 Handoff processing unit 82 Frequency setting unit 83 Window control unit 84 Search window Memory 85 Search window table 100 Mobile phone

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Michiyuki Yamaoka             Sanyo-cho, 1-1, Sanyocho, Daito-shi, Osaka             Communications Inc. (72) Inventor Masaka Masuda             Sanyo-cho, 1-1, Sanyocho, Daito-shi, Osaka             Communications Inc. F term (reference) 5K067 AA33 BB04 CC10 DD36 EE02                       EE10 EE24 GG11 JJ39

Claims (1)

Claims 1. A portable telephone for searching for a destination base station in response to a soft handoff instruction and a hard handoff instruction, wherein the base station issues a soft handoff instruction or a designation of a search window width. Accepting means for accepting a hard handoff instruction that may be included, and using a search window having a width wider than the width of a search window included in the hard handoff instruction or the width of a search window used for a soft handoff instruction when the hard handoff instruction is accepted. A search means for searching for a pilot signal from the base station.