JP2000224639A - Portable telephone set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a portable telephone set which can shorten a silent state at the time of being returned from hand-over operation to an original base station in the case incapable of searching the base station of the switching destination at the hand-over time and can eliminate the silent state while the base station is searched. SOLUTION: By receiving a control signal transmitted from the other base station while using a control channel(CCH) at the time of hand-over start, in a CCH search processing block to search the base station of the switching destination, similar transmission before the start of search to the base station before switching is continued in a time slot used for transmission to that base station. In this case, in the CCH search block, the reception from the base station before switching can also be continued.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a mobile phone as a mobile station in a cordless telephone system that performs communication between a mobile station and a base station using a TDD (time division multiplex two-way communication) method, and particularly to an improvement in a handover operation.

[0002]

2. Description of the Related Art In a cordless telephone system in which an area is constituted by a plurality of wireless zones, in order for a portable telephone to continue communication while moving between the plurality of wireless zones, it is necessary to separate from a base station with which communication has been performed. It is necessary to perform a process of switching communication channels (such a process is called “handover”) for the base station. Standards are set for handover, and detailed descriptions are described in various documents (for example, “2nd generation cordless telephone system standard (RCR STD-28): Published by Radio System Development Center)”. ing.

In order to perform handover, it is necessary that another base station that satisfies the conditions as a base station to be switched to exists. Therefore, in the first stage of the handover process, it is necessary for the mobile phone (hereinafter, also referred to as “slave device”) to perform a process of searching for a switching destination base station. Here, a brief description will be given of the content of the switching destination base station search processing on the slave unit side in the conventional handover.

FIG. 12 is a timing chart for explaining the contents of a search process of a base station to be switched (hereinafter, referred to as "CCH search process") in a conventional portable telephone. Here, in order to explain the “frame signal” in FIG.
A frame configuration in the MA / TDD scheme will be described.

As shown in FIG. 13, TDMA / TD
In the D system, 5 milliseconds are defined as one frame, and one frame is further divided into eight slots, and the first to fourth slots are slots dedicated to downlink (base station to slave) communication (hereinafter, “downlink communication slot”). 5th slot ~
The eighth slot is allocated as a slot dedicated to uplink (slave unit → base station) communication (hereinafter, referred to as “uplink communication slot”).

[0006] One downlink communication slot from the first slot to the fourth slot and one uplink communication slot (any one of the fifth slot to the eighth slot) 2.5 ms later correspond to one downlink communication slot. Make up one channel.
Therefore, in the communication between the base station and the slave unit, if the first slot is used as the downlink slot, the uplink slot to the base station is the fifth slot.

Returning to FIG. 12, the description of the "frame signal" will be continued. The frame signal shown in FIG.
It is a signal indicating whether it is the timing of a downlink communication slot or the timing of an uplink communication slot in a frame in the DMA / TDD system. That is, when the frame signal is low (timing 1201 or the like), communication using the downlink communication slot is performed. When the frame signal is high (timing 1202 or the like), communication is performed.
Communication using the uplink communication slot is performed.

Accordingly, the communication channel shown in FIG.
Also referred to as “channel” or “TCH”. In the figure, "TC
H ". As shown as a downlink signal, during a normal call, voice data is transmitted from the base station to the slave unit at the timing when the frame signal is low. The example in FIG. 12 is an example in which the first slot is used as a downlink slot and the fifth slot is used as an uplink slot.

[0009] Further, a control channel (hereinafter, also referred to as "C channel" or "CCH" in FIG.
H ". As shown as a downlink signal, at the timing of the downlink communication slot, a control signal is transmitted from each base station using the C channel. The conventional mobile phone system described here (so-called second generation cordless phone system, hereinafter referred to as "PH
S system ". ), Each base station transmits a control signal intermittently every 100 milliseconds (20 frames) on the C channel, and adjacent base stations
The control signal is transmitted using different time slots in the 0 frame. Therefore, when searching for a base station in a conventional mobile phone, control signals of up to 80 base stations can be received within 100 milliseconds.

On the slave side, a slave receiving gate of FIG.
At the timing when each of the slave transmission gates is turned on, communication with the base station is performed by receiving a signal from the base station or the like and transmitting a signal to the base station or the like. That is, in a normal call state, the channel is set to the T channel, and the voice data is transmitted to the base station side as shown in the slave unit transmission signal at the timing of the slave unit transmission gate on. .

When the slave unit reception gate is turned on, audio data from the base station is received. Next, a CCH search process at the start of handover will be described. The handover is performed when there is a handover instruction from the base station or when the handset detects the establishment of the handover start condition. Here, as the handover start condition detected on the slave unit side, it is normal to use deterioration of the reception level or the like.

That is, on the slave side, from the start of communication,
The level and reception quality of the channel used for communication, specifically, the reception field strength (hereinafter, referred to as “RSSI”)
And the status of occurrence of errors (frame error rate) are monitored. Then, when the deterioration of the level or the reception quality is detected, for example, when it is detected that the RSSI falls below a predetermined threshold, the handover operation is started.

[0013] In the example of FIG.
Upon receiving 203, it is assumed that it is detected that the RSSI has fallen below a predetermined threshold, and a handover operation is started. When the handover operation is started, the setting on the slave unit side is changed to a carrier of a predetermined C channel,
The control signal is received continuously for a predetermined period (100 * N milliseconds, usually 100 to several hundred milliseconds) from timing 1204 in the figure. Then, an identifier (hereinafter, referred to as “CSID”) of each base station detected from the received control signal (a signal indicated as “CCH downlink signal” in the figure) and an RSSI value corresponding to the base station Are sequentially stored in the memory. At the time of receiving the control signal, transmission of audio data from the slave unit to the base station is also interrupted (see the slave unit transmission signal).

When the above-mentioned predetermined period has elapsed as a control signal receiving period, a switching destination base station is selected from other base stations whose RSSI value stored in the memory is equal to or greater than a predetermined threshold value, and the other base station is selected. A link channel establishment request is made to the base station. This is a process for requesting the other base station to allocate a T channel. If the assignment of the T channel can be received from the new base station, the operation shifts to communication with the other base station.

Here, in the above CCH search processing,
As shown in FIG. 12, there is not always a switching destination base station. Nevertheless, it is necessary to avoid a situation in which a call disconnection occurs as much as possible, so if the base station of the switching destination cannot be searched, the communication returns to the communication with the original base station that had been communicating so far. Is usually the case. Next, a process of returning to the original base station in the conventional mobile phone will be described with reference to FIG. 12 (as shown in FIG. 12, another base station showing a sufficient RSSI as a CCH downlink signal). In the situation where the control signal can be received, it is not actually shifted to the recovery processing immediately after the end of the CCH search processing. However, since the recovery processing is described here, the base station of the switching destination can be searched. It was not).

When the handset starts the handover operation, the transmission to the original base station is stopped as described above, so that the base station determines that there is no transmission signal from the portable telephone. Becomes In the PHS system, when a predetermined period elapses after the base station cannot receive the transmission signal from the slave unit, the base station side:
Switching from the state of transmitting audio data to the state of transmitting a so-called synchronous burst signal (FIG. 12, 120)
5). The synchronization burst signal 1205 has the same physical slot structure as the control signal, and has a 62-bit preamble period before a unique word for detecting a slot position, so that bit synchronization can be achieved every time one slot is received. . Accordingly, the slave unit loses the bit synchronization information held during the call by starting the CCH search process,
Even if the synchronization with the T channel is lost, the bit synchronization can be established again and the communication state can be restored.

In the PHS system, after the slave unit having received the synchronization burst signal 1205 from the base station establishes bit synchronization by transmitting the synchronization burst signal 1206, the base station transmits a unique word to the physical slot for communication. The switched TCH idle slot (empty slot with no data) 1207 is transmitted. The slave unit that has received the message also transmits the TCH idle slot 1208, and after confirming that bit synchronization has been established as the communication slot, shifts to a voice data transmission / reception state (see 1209 in FIG. 12).

[0018]

In the above-mentioned conventional portable telephone, since the reception of audio data on the slave unit side is interrupted at the start of the CCH search processing, a silent state (100 to several hundred millimeters) is generated in the CCH search processing section. Seconds). Further, when returning to the communication with the original base station, it is necessary to perform the synchronization establishment processing with the original base station again, so that the sound is interrupted even during the synchronization establishment processing (up to about 200 milliseconds). ), There is a problem that the silent state becomes longer.

The present invention has been made in view of the above problems, and will return to the original base station from the handover operation when the base station of the switching destination cannot be searched in the CCH search processing. It is an object of the present invention to provide a mobile phone capable of shortening a silent state in the case where the above condition is satisfied, and a mobile phone capable of eliminating a silent state in a CCH search processing section.

[0020]

In order to achieve the above object, a portable telephone according to the present invention has a handover function of switching a base station during communication and performs time division multiplex communication. At the start of handover, by receiving a control signal transmitted using a control channel from another base station, a search unit that searches for a base station to be switched to, and after the search by the search unit is started, Transmission control means for transmitting communication data in a transmission time slot for a base station before switching.

Further, the search means receives a control signal transmitted from another base station using a control channel in a time slot other than a time slot of a communication channel with respect to the base station before switching, thereby performing switching. Searching for the previous base station, the mobile phone further comprises:
Even after the search by the search means is started, a reception control means for continuing reception in a reception time slot in a communication channel from the base station before switching can be provided.

Here, one local oscillator circuit may be provided, but by providing two synthesizer circuits, all the time slots other than the time slot for continuing the reception from the original base station are provided. Alternatively, a control signal transmitted from another base station using a control channel may be received.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a portable telephone according to the present invention will be described below with reference to the drawings. (1) Configuration of Mobile Phone FIG. 1 is a functional block diagram showing a configuration of a mobile phone according to one embodiment of the present invention. As shown in the figure,
The mobile phone according to the present embodiment includes an antenna 10, a transmission / reception switching unit 11, a radio unit 12, a modem unit 13, a TDMA / TD.
D (Time Division Multiple Access / Time Division D
uplex) unit 14, an audio processing unit 15, a microphone 16, a speaker 17, and a control unit 18.

The transmission / reception switching unit 11 includes a timing generation unit 1
A switch that switches between transmission and reception by TDD via the antenna 10 according to a timing instruction from 80. The wireless unit 12 includes a transmitting unit 121, a synthesizer 12
2. It includes a receiver 123 and an RSSI detector 124.

The transmitting section 121 is composed of a mixer, an amplifier and the like for converting to a transmission frequency, and converts a modulated signal of voice and control data input from the modem section 13 into a transmission wave and transmits it. Synthesizer 122 stores a table in which carrier numbers and local frequencies (local oscillation frequencies) are associated with each other. When a frequency switching instruction including designation of a carrier number is issued from synthesizer control section 183, synthesizer 122 stores the table. A local frequency signal is generated and supplied to the transmitting unit 121 and the receiving unit 123. Note that in the synthesizer 122 used in the present embodiment, the lock time required from the input of the frequency switching instruction to the generation of a stable local frequency signal is about 300 μsec.

The receiving section 123 converts the C- and T-channel received waves input from the antenna 10 via the transmission / reception switching section 11 into an intermediate frequency signal, amplifies the intermediate frequency signal, and outputs it to the modem section 13. . RSSI detector 1
24 detects the strength of the received signal as RSSI,
Output to MA / TDD section 14. RSS of this embodiment
When performing communication on the T channel, the I detection unit 124 detects the RSSI of the T channel and uses the detected RSSI for monitoring the communication quality.
The RSSI of the channel is detected and used for searching for a base station to be switched to.

Each section of the radio section 12 described above performs transmission and reception by the TDMA / TDD system in accordance with timing control and frequency switching instructions by the control section 18 described later. Since the mobile phone of the present embodiment has only one synthesizer circuit, it is not possible to switch to a channel having a different carrier number between adjacent slots, for example, the first slot and the second slot. As described above, it takes about 300 μs to stabilize the generation frequency of the synthesizer 122 (see FIG. 2). The same applies to other adjacent slots.

Therefore, in order to perform communication in parallel using time slots with different carrier numbers during one frame, it is necessary that time slots with different carrier numbers are not adjacent to each other. For example, as shown in the example of FIG. 2, when the time slots used for communication with the base station that is currently talking are the second slot and the sixth slot, the other base station while continuing the communication, Specifically, if communication is performed with the handover destination base station, the fourth and eighth slots need to be used for communication with the handover destination base station.

In the portable telephone system (PHS system) of the present embodiment, each base station transmits a control signal to C
The channel performs intermittent transmission every 100 milliseconds (20 frames), and adjacent base stations transmit control signals using different time slots in the 20 frames. Therefore, when searching for a base station in the mobile phone of the present embodiment, switching of synthesizer 122 is performed between a time slot of a control signal of a base station to be searched as a switching destination and a time slot used for transmitting voice data. If a lock time of at least one slot is required, the fifth slot or the eighth slot is used as a transmission slot.
Control signals of up to 60 base stations can be received in milliseconds, and when the sixth or seventh slot is used as a transmission slot, up to 80 base stations in 100 milliseconds can be received. The control signal can be received.

The modem unit 13 is connected to the radio unit 12 and TDMA /
A modem that performs modulation and demodulation with the TDD unit 14 using π / 4 shift QPSK (quadrature phase conversion) or the like. T
The DMA / TDD unit 14 controls time-division multiplex bidirectional communication according to the TDMA / TDD method. Audio processing unit 15
Performs audio encoding and decoding of audio input and output via the microphone 16 and the speaker 17, amplification, and the like.

The control section 18 has a ROM and a RAM, and controls the entire portable telephone by executing various programs recorded in the ROM. In the mobile phone of the present embodiment, in the first stage of the handover operation,
The control unit 18 performs CCH search processing (search processing for a base station to be switched to) by performing control in the CCH search processing so as to continue transmission of voice data on the T channel that has been in conversation. After the CCH search process, when returning to the original base station, it is possible to return without performing the synchronization establishment process again, and the silent state in the section where the process is performed is eliminated. The control unit 18 includes a timing generation unit 180, a memory 181, a comparison determination unit 182,
It includes a synthesizer control unit 183 and a CPU 184.

The timing generation section 180 has a TDMA / T
A DD slot timing signal is generated, and the comparison / determination unit 1
82, a synthesizer control unit 183, a CPU 184, a wireless unit 12, and a transmission / reception switching unit 11. Memory 181
Stores the RSSI value of the received signal obtained through the TDMA / TDD unit 14, the communication slot position information, the communication slot bit synchronization correction value obtained from the modem unit 13, and the like. That is, the memory 181 of the present embodiment has
As shown in (a), it includes an RSSI storage unit 1811, a communication slot position information storage unit 1812, and a communication slot bit synchronization correction value storage unit 1813.

The RS stored in the RSSI storage unit 1811
The SI is used for monitoring the communication quality by the comparison / determination unit 182 during a call using the T channel. Also, C
In the CH search process, as described above, the CSID and the RSS
I is stored in association with it, and is used for selection of a base station to be switched to. Call slot position information storage section 181
2 stores the absolute slot number included in the message from the base station during a call. By storing the absolute slot number, a reception gate for CCH search can be opened for each slot if the search base station of the switching destination is in slot synchronization with the communication slot.

Talk slot bit synchronization correction value storage unit 18
Reference numeral 13 stores the bit synchronization correction value of the talk slot.
When receiving and demodulating data in a slot, a preamble for generating a bit synchronization clock for demodulation is not sufficiently secured in a talk slot.
The bit synchronization response time constant is lengthened, the bit synchronization correction value used in the previous reception slot is held in a period other than reception, and synchronization fine adjustment is performed in the preamble period of the next reception slot.

However, if a CCH search for a base station different from the call is performed in another slot, it is necessary to synchronize the bit with the CCH. Therefore, it is necessary to store the bit synchronization correction value of the talk slot. Therefore, the bit synchronization correction value for the talk slot is stored in the memory 181 and the correction value is read out and used when the talk slot is received.

During a call on the T channel, the comparison / determination unit 182 compares the RSSI value stored in the RSSI storage unit 1811 with a predetermined threshold value,
Monitors communication quality. When the RSSI value falls below a predetermined threshold, a signal notifying the fact is output to the CPU 184, and the handover operation is started in response to the signal.
Further, in the CCH search process, the comparison determination unit 182 compares the value of the RSSI of each base station stored in the RSSI storage unit 1811 with a predetermined threshold value to determine whether there is a base station that can be a switching destination candidate. It is determined whether or not to perform. If the RSSI value is equal to or greater than a predetermined threshold, the base station is a candidate for a switching destination.

Synthesizer control section 183 outputs a frequency switching instruction specifying a carrier number to synthesizer 122 in synchronization with the slot timing signal output from timing generation section 180. The content of the frequency switching instruction is controlled by the CPU 184. Further, as shown in FIG. 3B, the synthesizer control unit 183 of the present embodiment includes the CCH monitor timing generation unit 1
831. CCH monitor timing generator 1
831 includes a CCH monitor timer, and manages whether or not a period (100 to several hundred milliseconds) for performing the CCH search process has elapsed.

FIG. 4 is a timing chart for explaining the CCH search processing and the return processing according to the present embodiment. The contents in the figure correspond to FIG. 4 is different from FIG. 12 in that the transmission of audio data is continued as a slave unit transmission signal in the CCH search processing section while maintaining the same synchronization as before. 12 is that audio data is output as a TCH downlink signal in a section 401 where a synchronous burst signal and an idle slot are output in FIG. In addition, when the transmission of the voice data is continued in the CCH search processing section, the control signal cannot be received at the timing of the transmission slot for transmitting the voice data using the T channel and the slot adjacent thereto, as shown in FIG. Is different. The reason why the control signal cannot be received at these timings is that the mobile phone according to the present embodiment has only one synthesizer 122, and thus the switching between the T channel and the C channel is performed by the above-described approximately 300 μm. This is because it takes seconds.

From the above differences, in the portable telephone of the present embodiment, even when the CCH search process is started on the slave unit, the audio data from the slave unit is maintained in a state where the synchronization up to that point is maintained. Is still being sent,
The state where the base station recognizes that the communication with the slave unit is continuing as it is is continued. Therefore, since the TCH downlink signal from the base station does not shift to the synchronization burst, in the recovery process, only the channel setting by the synthesizer 122 is changed to the T channel after the end of the CCH search process, and the process is repeated. It is possible to return to a normal call without performing the synchronization establishment process.

(2) Processing Content of Control Unit 18 Next, the processing content of the control unit 18 when performing the CCH search processing and the return processing to the original base station will be described. FIG.
5 is a flowchart showing the processing contents of the control unit 18 when performing a handover operation. Hereinafter, the specific processing content of the control unit 18 will be described with reference to FIG.

As described above, the comparison / determination unit 182 monitors the value of the RSSI as the communication quality of the T channel used for communication with the base station from the start of the call. And
When the RSSI value falls below a predetermined threshold, that is, when a deterioration in communication quality is detected or when a handover instruction is issued from the base station, a handover (“H” in the figure) is performed.
O ". ) When the start condition is satisfied (S
101: Yes), a signal notifying the fact is sent to the CPU.
184 and the handover operation is started. In the present embodiment, the description will be continued on the assumption that the deterioration of the communication quality is detected at the timing of 402 shown in FIG.

In the handover operation, first, CCH
A search process is performed (S102). FIG. 6 is a flowchart showing the details of the CCH search process. As shown in the figure, in the CCH search process according to the present embodiment, the CCH monitor timer is first activated at the timing of 402 in FIG. 4 (S201). CCH
The monitor timer is a timer for determining the end of the CCH search processing section, and is therefore set to measure the time for performing the CCH search processing (specifically, about 100 * N (millisecond)). (In this embodiment, since the CCH monitor timer is started at the timing 402, the actual set time of the timer is 100
* N milliseconds + α. ).

Thereafter, the control unit 18 determines whether or not it has entered the transmission slot area, specifically, whether or not the timing of turning on the slave unit transmission gate has come (S202), and turns on the transmission gate at that timing. (S203) Wait for the transmission to end (S204), and when the transmission ends, turn off the transmission gate (S205). This process corresponds to turning on the slave unit transmission gate at the timing 403 shown in FIG. When this transmission ends,
The slot position information and the bit synchronization information during the call are stored in the slot position information storage unit 1812 and the bit synchronization information storage unit 1813, respectively, and the carrier setting of the synthesizer 122 is changed to the C channel (S206). Hereinafter, the description will be made with reference to the timing chart of FIG. FIG.
FIG. 5 is an enlarged view of a CCH search processing section shown in FIG. 4. The timing of turning on the slave unit transmission gate on the left end in FIG. 7 corresponds to the timing 403 in FIG.

After the setting is changed to the C channel in step S206, since no control signal is transmitted from the base station in the uplink communication slot area, the control unit 18 waits until the mobile station enters the reception slot area ( S20
7: Yes, corresponding to timing 701 in FIG. ),
The control signal is received by opening the reception gate (S
208). Here, in order to determine whether or not the data has entered the reception slot area, the slot position information stored in the slot position information storage unit 1812 and the bit synchronization information storage unit 1812 are determined.
13 is used. Also,
Here, the CSID and RS of the base station from which the control signal was received.
The SI is sequentially stored in the RSSI storage unit 1811.

Thereafter, the process waits until the reception slot area ends (S209: Yes, timing 702 in FIG. 7).
Corresponding to ), And turns off the reception of the control signal (S21).
0), the carrier setting of the synthesizer is changed to the communication channel (S211). If the CCH monitor timer has not expired (S212: No), the control unit 18 returns to step S202 in order to repeat the above-described operation within the time specified as the CCH search processing section (S212: No). Wait to enter the transmission slot area. afterwards,
By turning on the slave unit transmission gate in the transmission slot area (S203), audio data is transmitted from the slave unit side. This corresponds to, for example, transmission of audio data at timing 703 in FIG. Note that there is a section that is neither the T channel nor the C channel prior to the timing 703 because a lock time of about 300 μs is required to switch between the two channels in the configuration of the present embodiment, and a certain transition time must be secured. Because there is.

When the CCH monitor timer has expired (S212: Yes), a search is made for a candidate base station to be switched to based on the RSSI value of the received control signal.
CSID stored in the RSSI storage unit 1811 and R
A list of base stations that are switching destination candidates is created from the SSI detection result (S213), and the CCH search process ends. In the present embodiment, for the sake of convenience of the subsequent processing, when creating a list of base stations, it is assumed that sorting is performed in the order of the RSSI values of the base stations, but this sorting is not necessarily performed. Absent.

When the CCH search process is completed as described above, returning to the flowchart of FIG. 5, the control unit 18 determines whether or not a candidate for a base station to be switched has been searched (S103). Here, whether or not a base station has been searched is determined based on whether or not there is a base station whose RSSI value is equal to or greater than a predetermined threshold in the list of base stations. Therefore, among the base stations included in the list of base stations, if the RSSI of any of the base stations does not reach the predetermined threshold, it is determined that the base station of the switching destination has not been searched (S103). : No), and a setting change process is performed (S104). The setting change process is a process of returning to communication via the original base station by changing the channel setting of the slave unit to the T channel, as described above. It is not necessary to perform the synchronization establishment process.

In the present embodiment, processing other than returning to the original base station with which communication has been performed so far and continuing the call using the same T channel as before is not performed. However, a method of performing various other processes is also conceivable. Details will be described as a modified example described later. On the other hand, if the base station of the switching destination can be searched (S103: Yes), the base station determined to be the most appropriate among the base stations whose RSSI is equal to or more than the predetermined threshold, specifically, the value of the RSSI is A link channel establishment request is made to the largest base station (S105). The processing after the link channel establishment request is a well-known processing defined in, for example, the above-described standard (RCR STD-28), and thus detailed description thereof will be omitted.

(Embodiment 2) Next, a second embodiment of the present invention will be described. The configuration of the mobile phone according to the present embodiment is almost the same as that shown in FIG. 1, but when returning to the original base station by increasing the frequency of channel switching as compared with the first embodiment. In addition, it is intended to eliminate a silent state in the CCH search section.

FIG. 8 is a timing chart showing the processing contents of the CCH search processing section in the present embodiment. This diagram corresponds to FIG. 7 in the first embodiment, and the timing of changing the channel setting and the timing of turning on the slave unit reception gate are different from those of the first embodiment. The following description focuses on the differences from the first embodiment.

In this embodiment, even if the transmission of audio data from the slave unit to the base station at timing 801 is completed, the slave unit does not immediately switch channels, and maintains the synchronization up to that point. In this state, audio data transmitted from the base station is received (timing 802). Thereafter, in response to a frequency switching instruction from the synthesizer control unit 183, a lock time (approximately 300 μsec) until the frequency generated by the synthesizer 122 stabilizes, and after changing the channel to the C channel, the slave unit receives the signal. The gate is turned on to receive a control signal from the base station (timing 803).

Thereafter, the channel is again set to T on the slave unit side.
Switching to the channel, transmission and reception of audio data are performed (timing 804). The above processing is repeated until the CCH monitor timer expires. By performing such processing, communication via the original base station can be continued even in the CCH search processing section, so that a silent state occurring in the section can be eliminated.
The fact that the base station does not shift to the synchronous burst state is the same as in the first embodiment.

Although the example of FIG. 8 shows the case where the first slot and the fifth slot are used for communication with the base station, the present invention can be easily applied to other cases. However, for example, when the third slot and the seventh slot are used for communication with the base station, it is necessary to switch the channel after the end of the transmission of the audio data from the first slave unit to the base station side. That is, it is necessary to change the timing of channel switching depending on the time slot used for transmission and reception with the original base station.
Need to be added to the beginning of the flowchart.

Specifically, the first signal is received from the original base station.
When the slot or the second slot is used, after the transmission of the audio data at timing 801, the reception of the audio data from the base station is waited, and the channel is switched to the C channel after the end of the reception. On the other hand, when the third slot or the fourth slot is used for reception from the original base station, the channel is switched to the C channel after the transmission of the audio data at timing 801, and another channel is used in the first slot or the second slot. After receiving the control signal from the base station, the channel is switched to the T channel again.

The above-described channel switching timing and on / off control of the transmission / reception gate are performed in the first manner.
Similarly to the embodiment, the slot position information storage unit 181
2 and the bit synchronization information stored in the bit synchronization information storage unit 1813. Also, since the absolute slot number of the time slot used for communication with the original base station is stored in the call slot position information storage unit 1812, it is possible to determine the channel switching timing by referring to the information. it can.

(Embodiment 3) Next, a third embodiment of the present invention will be described. FIG. 9 illustrates a configuration of the mobile phone in this embodiment. The configuration shown in the figure is almost the same as that shown in FIG. 1, but differs from the first and second embodiments in that the radio section 12 is provided with two synthesizers 122A and 122B. I have. Incidentally, accompanying this, the synthesizer control unit 183
Has a function of switching between the two synthesizers 122A and 122B.

By providing two synthesizer circuits in this way, the following operation can be realized. In other words, in the TDMA / TDD frame configuration diagram of FIG.
Slot), one synthesizer (eg, 1
While the T channel is being received using 22A), the frequency of the other synthesizer (eg, 122B) is stabilized in the C channel in parallel with the T channel reception.
By doing so, the third slot is changed to the third slot.
By switching between the two synthesizers when shifting to a slot, communication using different carriers can be performed in the second slot and the third slot (the same applies to other adjacent time slots). It becomes possible. Therefore, it is not necessary to provide a transition time for switching channels as in the first and second embodiments.

That is, in the first embodiment, in the CCH search processing, it is not possible to receive a control signal from another base station in a time slot adjacent to a time slot used for transmitting voice data. In the second embodiment, control signals cannot be received from other base stations in time slots adjacent before and after a time slot used for receiving voice data. (Each of these means that the absolute number of other base stations to be searched as a switching destination may be reduced.) In the mobile phone of the present embodiment, reception of voice data It is possible to search for a base station at the timing of all reception slots other than the time slot in which the base station is performed.

Next, processing contents of the control unit 18 in the mobile phone according to the present embodiment will be described. The processing itself of the control unit 18 of the present embodiment is similar to the difference between the first embodiment and the second embodiment, and is different from the above-described embodiment in the channel switching (this embodiment). In the embodiment, the timing of switching between the two synthesizers 122A and 122B) and the ON / OFF of the transmission / reception gate on the slave side.
The timing of switching off is different. This will be described with reference to the timing chart of FIG. This figure corresponds to FIGS. 7 and 8.

As shown in the figure, there is no need to provide a lock time for channel switching. For example, the synthesizer 122A is set to the T channel,
If the channel 22B is set to the C channel, then the channel can be switched by switching between the two synthesizers 122A and 122B. Therefore, after transmitting the audio data at the timing 1101, communication is performed using the T channel until the transmission of the audio data at the timing 1102, and then the synthesizer is switched to switch to the C channel. It is possible to receive a control signal from the base station in all downlink-only slots other than the time slots used for.

Although the example of FIG. 11 is an example in which the first slot and the fifth slot are used for communication with the base station using the T channel, it can be easily applied to other cases. It is. That is, as in the second embodiment, based on the slot position information stored in the slot position information storage unit 1812 and the bit synchronization information stored in the bit synchronization information storage unit 1813, the synthesizer switching timing, When performing on / off control of a transmission / reception gate and receiving a control signal from a base station,
The reception gate is turned on at the timing of the reception-only slot, and T is set only at the timing of receiving audio data.
The synthesizer may be switched so that the channel is used.

As described above, by performing the operations described in the first to third embodiments, the base station communicates with the slave even after the handover is started on the slave. When the mobile station returns to the original base station, for example, when the base station of the switching destination cannot be searched in the CCH search process, the synchronization between the slave unit and the base station is again performed. Without performing the establishment process,
Since it is possible to return instantaneously only by changing the channel setting of the slave unit, it is possible to prevent a silent state from being generated when performing the synchronization establishment processing again, and thereby to reduce the silent state upon return. It can be shortened.

In the CCH search processing section, T
If audio data is received from a base station using a channel, it is possible to eliminate a silent state in the section. <Modifications> Although the embodiment of the present invention has been described above, it goes without saying that the content of the present invention is not limited to the specific example described in detail in the above embodiment. An example can be considered.

(1) In the above embodiment, CCH
If the switching destination base station is not found in the search process, or if the switching destination base station can be found, but a new T channel cannot be allocated in the link channel establishment process, The processing other than returning to the original base station by changing the setting or performing the synchronization establishment processing again is not performed, and the determination in step S101 is performed again immediately after the recovery (FIG. 5, S
104, S106 and S101). However,
If the deterioration of the communication quality is detected once and the handover operation is performed once, the process returns to the step S101 immediately after the process returns to the original base station in the step S104.
Is very likely to have the same determination result again, and even if the handover operation is performed again, as in the previous case, the switching destination base station cannot be searched, or However, there is a large possibility that a new T channel cannot be allocated, resulting in a poor processing efficiency.

Accordingly, for example, the following measures can be considered. That is, the timer is started when the handover is performed once and the process returns to the original base station after passing through step S104. Thereafter, until the timer ends counting, the handover process is not started even if the deterioration of the communication quality is detected in step S101,
Keep the call through the original base station. As the count value of the timer, for example, a fixed value of several seconds to several tens of seconds can be considered, but a variable value is also possible. Specifically, based on the number of base stations searched in the CCH search process when the handover process succeeded immediately before, for example, when the number of searched base stations is small, the count value of the timer is reduced. And the like.

(2) When the mobile station returns to the original base station, the number of times the mobile station has returned may be counted. By doing so, every time the count value increases,
It is also possible to lengthen the time for performing the base station search in the CCH search process, or to lower the predetermined threshold used for the CCH search in the CCH search process. (3) Further, in the present embodiment, the case where the mobile phone of the present invention is applied to the PHS system has been described in detail. However, when the CCH search process is performed, transmission to the original base station is continued. The gist of the present invention that prevents communication with a base station from shifting to a synchronous burst can be applied to other cordless telephone systems.

[0067]

As described above, according to the portable telephone according to the present invention, even when the search for the base station to be switched to is started at the start of the handover, communication is performed in the transmission time slot for the base station before switching. Since the data is transmitted, the state where the original base station side recognizes that communication with the slave unit is being performed continues even after the handover operation is started on the slave unit side. Therefore, when handover is performed on the handset side, when it is necessary to return to communication with the original base station, for example, when the base station of the switching destination cannot be searched, it is not necessary to perform the synchronization establishment process again. Thus, it is possible to prevent the occurrence of a silent state that occurs when the synchronization establishment processing is performed again, and thus it is possible to shorten the silent state at the time of handover.

Further, in a time slot other than the time slot of the communication channel with respect to the base station before switching, a control signal transmitted from another base station using a control channel is received, so that the base station to be switched can be changed. If the search is started and the reception is continued in the reception time slot of the communication channel from the base station before the switching even after the search is started, silence in the CCH search processing section after the start of the handover operation is performed. There is an effect that the state can be eliminated.

[Brief description of the drawings]

FIG. 1 is a functional block diagram illustrating an overall configuration of a mobile phone according to a first embodiment of the present invention.

FIG. 2 is a frame configuration diagram for describing channel switching when a single synthesizer 122 is provided.

3A is a diagram showing an example of contents stored in a memory 181. FIG. (B) It is a figure for explaining CCH monitor timing generation part 1831.

FIG. 4 is a timing chart for explaining a handover operation.

FIG. 5 is a flowchart showing processing contents of a control unit 18 in a handover operation.

FIG. 6 is a flowchart showing details of a CCH search process.

FIG. 7 is a timing chart for explaining a CCH search process according to the first embodiment.

FIG. 8 is a timing chart for explaining a CCH search process according to the second embodiment.

FIG. 9 is a functional block diagram illustrating an overall configuration of a mobile phone according to a third embodiment of the present invention.

FIG. 10 is a frame configuration diagram for describing channel switching when two synthesizers 122A and 122B are provided.

FIG. 11 is a timing chart for explaining a CCH search process according to the third embodiment.

FIG. 12 is a timing chart for explaining a handover operation in a conventional mobile phone.

FIG. 13 is a diagram showing a frame configuration in TDMA / TDD communication.

[Explanation of symbols]

 Reference Signs List 10 antenna 11 transmission / reception switching unit 12 radio unit 121 transmission unit 122 synthesizer 122A, 122B synthesizer 123 reception unit 124 RSSI detection unit 13 modem unit 14 TDMA / TDD unit 15 sound processing unit 16 microphone 17 speaker 18 control unit 180 timing generation unit 181 memory 182 comparison / determination unit 183 synthesizer control unit 184 CPU

Claims (2)

[Claims] A mobile phone having a handover function of switching a base station during communication and performing time division multiplex communication, wherein a control signal transmitted from another base station using a control channel at the start of handover A search means for searching for a base station to be switched to, and a transmission control means for transmitting communication data in a transmission time slot for the base station before switching even after the search by the search means is started. A mobile phone comprising: 2. The method according to claim 1, wherein the search unit receives a control signal transmitted from another base station using a control channel in a time slot other than a time slot of a communication channel with respect to the base station before the switch. The mobile phone further includes a reception control unit that searches for a previous base station, and continues reception in a reception time slot in a communication channel from the base station before switching even after the search by the search unit is started. The mobile phone according to claim 1, wherein: