JP2733378B2 - Method and apparatus for switching wireless line in mobile communication - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a radio channel switching system suitable for radio channel switching in a base station.

BACKGROUND ART In recent years, mobile communication for performing communication between a base station and a mobile station using a wireless line has become widespread. Such a mobile communication service area is formed by a large number of cells (or zones), and a base station is provided for each of the cells. Therefore, usually, a mobile station moving in a certain cell communicates with a base station provided in this cell via a predetermined radio line. Here, the wireless line used is not always fixed to a specific line,
Lines can be switched as needed.

There are two types of wireless channel switching required for mobile communication: wireless channel switching between base stations and wireless channel switching within a base station. The radio link switching between base stations is executed when the mobile station changes the base station communicating with the mobile station when moving from the cell of the base station currently communicating to a cell next to another base station. On the other hand, the wireless channel switching in the base station is executed when the quality of the wireless channel is degraded due to interference from another base station or mobile station. Here, a description will be given of a conventional method of switching the radio line in the base station.

In a digital mobile telephone system that is currently in practical use, radio line switching within a base station within the same base station is processed in the same manner as radio line switching between base stations, and the sequence shown in FIG. Proceed according to the chart.

That is, when the base station and the mobile station are communicating with each other using the transmission / reception circuit of the base station, if the transmission / reception circuit detects the deterioration of the quality of the radio line in use, this fact is notified in the form of a circuit switching request. Is notified (step S101). In response, the control circuit selects an unused wire line, frequency and time slot (step S103), and notifies the switching center of the selected wire line. Then, the exchange performs signal transmission on the notified wired line in addition to the currently used wired line (step S105), while the control circuit selects the transmitting / receiving circuit connected to the selected wired line. Notify the frequency and time slot.

The transmitting / receiving circuit that has received the notification generates a switching destination radio line synchronization signal in accordance with the notified frequency and time slot, and transmits the generated switching destination radio line synchronization signal to the mobile station (step S107). Further, the control circuit transmits the switching destination wireless line designation signal to the mobile station via the switching source wireless line, and notifies the mobile station of the switching destination wireless line frequency and time slot (step S109).

Then, the control circuit of the mobile station notifies the notified new frequency and time slot to the transmission / reception circuit of the mobile station, and the transmission / reception circuit switches the frequency and time slot to the notified new frequency and time slot (step S111). Thereafter, the transmission / reception circuit receives the switching destination radio line synchronization signal transmitted from the transmission / reception circuit of the base station, executes synchronization establishment processing for the switching destination radio line (step S113), and connects the mobile station to the base station. Establish wireless network synchronization at the switching side (steps S115 and S117).

When the synchronization is established, the base station stops signal transmission to the switching source wired line and releases the switching source wired line and the wireless line (step S119). Then, communication is started on the newly set wireless line.

By the way, in the radio channel switching in the base station in the TDMA-FDMA system, only the radio section parameters given by the frequency and the time slot need to be changed, whereas the radio channel switching in the base station in the above-described conventional mobile communication system is performed by the mobile station. Since two transmission / reception circuits on the side and the base station are used, it is also necessary to change the wired line connected to the transmission / reception circuit on the base station side, which considerably complicates the switching process.

In order to eliminate the necessity of changing the wired line, it is necessary to switch the wireless section parameters within the same transmitting / receiving circuit. Here, when the radio section parameters are switched in the same transmission / reception circuit, if the switching timing is different between the base station side and the mobile station side, one switch is completed after the switching is completed, and the other is switched. There is a high possibility that the communication will be momentarily interrupted for a considerable period of time before completing. For this reason, it is preferable to perform wireless channel switching at the same timing between the base station and the mobile station. However, in the above-described conventional method, there is no way to notify the switching timing between the base station and the mobile station, so that it is difficult to perform the wireless channel switching between the base station and the mobile station at the same timing. Was.

Even when two transmitting / receiving circuits are used as in the above-mentioned conventional method, the frequency and time slot are switched by the transmitting / receiving circuit of the mobile station to new values selected by the base station, and then the switching destination radio line is switched. The problem remains that the communication between the base station and the mobile station is momentarily interrupted for the time required until the synchronization of the mobile station is established.

DISCLOSURE OF THE INVENTION Accordingly, an object of the present invention is to be able to perform radio line switching at the same timing between a base station and a mobile station,
Further, it is an object of the present invention to provide a wireless line switching method which makes processing for a wired line unnecessary and can prevent instantaneous interruption of communication at the time of wireless line switching.

Another object of the present invention is to provide a wireless line switching method that reduces the probability of wireless line switching failure, switches wireless lines at appropriate timing, and does not interfere with frame order control on the mobile station side. Is to do.

According to one aspect of the present invention, there is provided a method for switching a wireless channel in mobile communication between a base station and a mobile station, wherein communication between the base station and the mobile station is performed via a framed wireless channel. Providing switching timing information composed of data of layer 1 bit in each frame of the radio channel, and switching of the radio channel when it is necessary to switch the radio channel between the base station and the mobile station. So that at least one of the frames of the radio link at the base station
Changing the switching timing information at
A step of transmitting the changed switching timing information from the base station to the mobile station, and a step of changing the switching timing information, the switching timing being a predetermined period after each frame whose switching timing information has been changed, the base station transmits the radio link. A step of switching to the switching destination radio line, a step of detecting changed switching timing information transmitted from the base station in the mobile station, and a predetermined period from each frame detected in the step of detecting the changed switching timing information. At a later switching timing, the mobile station switches the wireless line to the switching destination wireless line.

According to another aspect of the present invention, there is provided a mobile communication system including a base station and a mobile station, wherein communication between the base station and the mobile station is performed via a framed wireless channel, Means for providing switching timing information composed of layer 1-bit data in each frame of the base station, and a base station for indicating the switching of the radio channel when it is necessary to switch the radio channel between the base station and the mobile station. Means for changing the switching timing information in at least one of the frames of the radio line in the station, means for transmitting the changed switching timing information from the base station to the mobile station, and means for changing the switching timing information by the changing means. Means for switching the radio line at the base station to the switching destination radio line at a switching timing after a predetermined period from the frame, Means for detecting the changed switching timing information transmitted from the base station, and switching timing after a predetermined period from each frame detected by the means for detecting the changed switching timing information. For switching to a switching destination wireless line.

Other features and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sequence chart of a conventional wireless channel switching method in a base station.

FIG. 2A is a schematic block diagram of a base station of the mobile communication system according to the present invention.

FIG. 2B is a schematic block diagram of a transmission / reception unit in the base station of FIG. 2A.

FIG. 3A is a schematic block diagram of a mobile station of the mobile communication system according to the present invention.

FIG. 3B is a schematic block diagram of a transmission / reception unit in the mobile station of FIG. 3A.

FIG. 4 is the first of the wireless line switching systems according to the present invention.
5 is a sequence chart of the embodiment.

FIG. 5 is a signal form diagram of a switching destination spread code designating signal used in the system of FIG.

FIG. 6 is a diagram of a transmission signal in the system of FIG. 4 for explaining a first case in which a unique word is used as switching timing information.

FIG. 7 shows a modification of the first case using a unique word as switching timing information.
FIG. 4 is a diagram of a transmission signal in the system of FIG.

FIG. 8 is a diagram of a transmission signal in the system of FIG. 4 for explaining a second case in which a flag of each frame is used as switching timing information.

FIG. 9 shows a modification of the second case in which the flag of each frame is used as switching timing information.
FIG. 6 is a diagram of a transmission signal in the FIG. 4 system.

FIG. 10 is a diagram of a transmission signal in the system of FIG. 4 for explaining another modification of the second case using a flag of each frame as switching timing information.

FIG. 11 is a signal form diagram of a transmission signal in the second case using a flag of each frame as switching timing information.

FIG. 12 is a diagram of a transmission signal in the system of FIG. 4 for explaining a third case using a housekeeping bit flag as switching timing information.

FIG. 13 is a diagram of a transmission signal in the system of FIG. 4 for explaining a modification of the third case using a housekeeping bit flag as switching timing information.

FIG. 14 is a diagram of a transmission signal in the system of FIG. 4 for explaining another modification of the third case using a housekeeping bit flag as switching timing information.

FIG. 15 is a diagram illustrating a signal form of a transmission signal in the third case in which a housekeeping bit flag is used as switching timing information.

FIG. 16 is a diagram of a transmission signal in the system of FIG. 4 for explaining the number of frames.

FIG. 17 is a diagram of a transmission signal in the system of FIG. 4 for describing a fourth case in which the number of frames is used as switching timing information.

FIG. 18 is a diagram of a transmission signal in the system of FIG. 4 for describing a modification of the fourth case using the number of frames as switching timing information.

FIG. 19 is a signal form diagram of a transmission signal in a fourth case using the number of frames as switching timing information.

FIG. 20 is the second wireless line switching method according to the present invention.
5 is a sequence chart of the embodiment.

FIG. 21 is a diagram of a table used in the system of FIG.

FIG. 22 is a diagram of a transmission signal in the system of FIG. 20 for explaining one possible relationship between the switching timing notification frame and the switching timing.

FIG. 23 is FIG. 20 for explaining another possible relationship between the switch timing notification frame and the switch timing.
FIG. 4 is a diagram of a transmission signal in the system of FIG.

FIG. 24 is a FI to explain yet another possible relationship between the switch timing notification frame and the switch timing.
FIG. 21 is a diagram of a transmission signal in the G.20 scheme.

FIG. 25 is the second of the wireless line switching systems according to the present invention.
9 is a sequence chart of a modification of the embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Here, an embodiment of a wireless line switching system in mobile communication according to the present invention will be described.

First, in mobile communication, a multiple access method is adopted because a plurality of mobile stations communicate with one base station.
Here, the multiple access method includes frequency division multiple access (FDMA)
There are a scheme, a time division multiple access (TDMA) scheme, and a code division multiple access (CDMA) scheme, and these can be used individually or in combination with others. In the present invention, as described below, any of these methods can be used as long as the wireless line has a frame structure capable of including layer 1 bit data representing switching timing information.

The only difference arising from the choice of multiple access method is that
The parameters to specify the radio line are frequency, TD
It is only a time slot in MA and a spreading code in CDMA. The present invention can be similarly applied to the FDMA system and the TDMA system. However, in the following, an embodiment of the present invention will be described for the case of using the CDMA system for explanation.

In this case, a base station suitable for the switching method to the wireless line of the present invention has a configuration as shown in FIG. 2A,
A mobile station suitable for the wireless line switching method of the present invention is shown in FIG. 3A.
Has a configuration as shown in FIG. In FIG. 2A and FIG. 3A, a solid line indicates a communication line, and a dotted line indicates a control line.

In the configuration of FIG. 2A, the base station includes an antenna 11 for transmitting / receiving a radio signal to / from the mobile station, a common amplifying unit 13 for amplifying the transmission signal and the reception signal, encoding and modulation of the transmission signal, and A plurality of (N) transmitting / receiving units 15 (15 ₁ , 15 ₂ ,..., 15 _N ) for performing decoding and demodulation, and base station control for controlling operation in the base station and generating control signals for the mobile station And a unit 17.

Here, each transmitting / receiving unit 15 corresponds to one wireless line. As shown in FIG. 2B, each transmitting / receiving unit 15 includes a switching timing setting unit 15a, a switching timing information flag changing unit 1
5b, a spreading code switching unit 15c, and a control unit 15d for controlling operations in the transmitting / receiving unit 15. In addition, each transmitting / receiving unit 15 is connected to a wired line that is connected to an exchange and transmits data or voice from a user.

On the other hand, in the configuration of FIG. 3A, the mobile station includes an antenna 21 for transmitting / receiving a radio signal to / from the base station, an amplifying unit 23 for amplifying the transmission signal and the reception signal, encoding and modulation of the transmission signal, and modulation of the reception signal. Transmitter / receiver performing decoding and demodulation
25, a mobile station control unit 27 for controlling operation in the mobile station and generating a control signal for the base station, and an operation unit 29 formed by a man-machine interface such as a dial button.
And an input / output circuit 31 for performing input / output processing of voice or user data.

Here, as shown in FIG. 3B, the transmission / reception unit 25 includes a switching timing information change detection unit 25a, a switching timing setting unit 25b, a spreading code switching unit 25c, and control for controlling operations in the transmission / reception unit 25. Includes part 25d.

Next, a first embodiment of the wireless line switching method according to the present invention will be described with reference to the sequence chart of FIG.

That is, in the first embodiment, the wireless line switching method is executed according to the sequence chart of FIG. 4 as follows.

First, the transmission / reception unit 15 of the base station and the transmission / reception unit 25 of the mobile station
Is in communication by setting up a certain radio line.

Then, when the transmission / reception unit 15 of the base station detects the quality deterioration of a certain radio channel (step S1), the transmission / reception unit 15 notifies the control unit 17 of the base station of the quality deterioration (step S3).

In response, the control unit 17 selects an unused switching destination spreading code for each of the uplink (mobile station → base station) and the downlink (base station → mobile station) (step S5), and the selected A switching destination spreading code designating signal including a spreading code is transmitted to the mobile station using the wireless channel before switching (step S7). Here, the switching destination spread code designating signal has, for example, a form as shown in FIG. 5, a signal type 31 indicating that this signal is a switching destination spread code designating signal, and a signal selected for uplink. An uplink spreading code number 32 indicating the spreading code and a spreading code number 33 indicating the spreading code selected for the downlink.

Then, the control unit 27 of the mobile station that has received the switching destination spread code designation signal transmits the uplink and downlink spread code numbers 32, 3
3 is stored, and a switching destination spreading code designation confirmation signal is returned to the base station for confirmation (step S9).

Next, the control unit 17 of the base station, which has received the switching spread code designation confirmation signal from the control unit 27 of the mobile station, then transmits the uplink and downlink spreading codes used in the switching destination wireless line to the transmitting / receiving unit 15. Notify (step S11). The transmitting and receiving unit 15 of the base station that has received the notification stores the notified uplink and downlink spreading codes, and checks the switching destination spreading code.
It is returned to 17 (step S13).

Next, in the transmission / reception unit 15 of the base station, an appropriate switching timing is set by the switching timing setting unit 15a (Step S
15) The switching timing information included in the frame having a predetermined relationship with the switching timing set by the switching timing setting unit 15a is changed and changed by the switching timing information changing unit 15b as described in detail below. The transmission unit 25 of the mobile station sends the frame including the switched timing information
(Step S17).

Then, in the transmission / reception unit 25 of the mobile station, the switching timing information change detection unit 25a checks whether the switching timing information included in the received frame has been changed, and if the change of the switching timing information is detected (step S2).
1) The switching timing is set in a predetermined relationship with respect to the frame including the detected and changed switching timing information so that the switching timing set in the mobile station is the same as the switching timing set in the base station. Setting unit 25
This is set in b (step S23).

Finally, the spreading code switching unit 15c of the transmitting / receiving unit 15 of the base station
Performs switching of the spreading code at the switching timing set by the switching timing setting unit 15a, and at the same time, the spreading code switching unit 25c of the transmitting / receiving unit 25 of the mobile station performs spreading at the switching timing set by the switching timing setting unit 25b. By performing code switching, simultaneous switching of spread codes is realized in the base station and the mobile station (step S25). After the completion of the switching, the transmitting / receiving section 15 of the base station and the transmitting / receiving section 25 of the mobile station notify the control sections 17 and 27 of the completion of the switching of the spreading code.

If the framing timings of the downlink and the uplink do not match, for the downlink, the spreading code of both the base station and the mobile station is switched after a predetermined number of frames from the frame including the switching timing information changed by the base station. Should be executed. For the uplink, the spreading code switching of both the base station and the mobile station may be performed after a predetermined number of frames from the frame closest to the downlink frame including the switching timing information changed by the base station.

In addition, in the procedure of FIG. 4, when the spreading code is switched between the base station and the mobile station, the synchronization state before the switching is maintained, and the signal transmission is performed in the same synchronization state after the switching. In the wireless channel switching in the base station, the distance between the base station and the mobile station hardly changes immediately before and after the switching, so that the synchronization timing hardly changes. Therefore, the synchronization timing can be maintained at the time of switching without any problem.

Here, when the detection processing result of the switching timing information satisfies the out-of-synchronization condition during the wireless line switching operation, the wireless line switching operation is cleared, and the synchronization establishment processing is performed on the switching source wireless line. However, even when the switching timing information in a frame during the wireless line switching operation is not detected, it is determined that the synchronization is not lost unless the synchronization loss condition is satisfied at the time immediately before the spreading code switching timing, and the switching of the spreading code is performed. Done.

Therefore, according to the first embodiment, since the wireless line switching can be completed in the same transmitting / receiving unit 15 of the base station, the switching station switches the wired line connected to the transmitting / receiving unit 15. No need. Also, by performing switching at the same timing in both the mobile station and the base station,
It is possible to prevent the occurrence of a period during which communication is not possible, and to maintain the synchronization state at the time of switching, thereby making it possible to omit the synchronization establishment processing of the switching destination wireless line. Therefore, it is possible to prevent instantaneous interruption of communication due to synchronization establishment processing. Here, since only one transmission / reception unit of the base station is involved in the radio line switching operation of the first embodiment, the same synchronization state can be maintained very easily.

Here, in order to prevent instantaneous interruption of communication, it is necessary that the time required for wireless channel switching, that is, the time required for changing wireless channel parameters in the transmission / reception unit, is sufficiently shorter than the signal transmission speed. In other words, the upper limit of the signal transmission speed is determined by the time required to switch the radio channel parameters. In this regard, switching of radio channel parameters in CDMA is a change of the spreading code set in the correlator and can be realized very easily at high speed.
MA is suitable for high signal transmission speed. Therefore, the use of CDMA is advantageous in this first embodiment.

In the first embodiment, the switching timing information provided in each frame used in the above procedure can be generally given by layer 1-bit data. There are several possible options, including the case where

As a first case, the switching timing information is provided for the purpose of maintaining frame synchronization in the synchronization establishing process, and can be given by a so-called unique word (UW) including two types of UW0 and UW1. Where UW
0 and UW1 have a sufficient Hamming distance between each other, and the probability of the two types being confused is very low.

In this case, as shown in FIG.
Uses UW0 as downlink switching timing information as in normal frame 61. Then, in step S17 of FIG. 4, the transmission / reception unit 15 changes the switching timing information to UW1 as in the frame 62. afterwards,
The transmission / reception unit 15 uses UW0 again as in the subsequent frames 63 to 66.

Similarly, the transmission / reception unit 25 of the mobile station transmits the switching timing information in the uplink as in the normal frame 71.
Use UW0.

On the other hand, the transmission / reception unit 25 of the mobile station regularly monitors the switching timing information in the downlink to detect the normal UW0. Then, when UW0 cannot be detected, the transmitting / receiving unit 25 detects UW1, and when UW1 is detected, the transmitting / receiving unit 25 recognizes the start of the radio line switching operation. In response to this, as a confirmation notification of the start of the wireless channel switching operation, the transmission / reception unit 25 changes the switching timing information on the downlink to UW1 as in the frame 73. here,
The frame 73 is the first uplink frame in which the switching timing information can be changed after the detection of UW1 in the downlink in the frame 62. Thereafter, the transmission / reception unit 25 continues to use UW1 until the spread code switching timing as in the frames 74 and 75.

On the other hand, the transmission / reception unit 15 of the base station regularly monitors the switching timing information in the uplink to detect the normal UW0. However, in frames 73 to 75 in which use of UW1 is expected in the uplink, the transmitting / receiving unit 15 detects UW1, and when UW1 cannot be detected, the transmitting / receiving unit 15 detects UW0. UW0
If the frame cannot be detected, it is determined that the synchronization by the unique word is impossible in the frame, the synchronization state is maintained, and the same operation is performed for the next frame.

Then, the transmission / reception unit 15 of the base station and the transmission / reception unit 25 of the mobile station
In both cases, for the downlink, the switching timing is set as N frames after the frame 62 in which UW1 is used by the base station, whereas for the uplink, the switching timing is determined by the use of the first UW1 by the mobile station. It is set as M frames after the predicted frame 73.

When at least one UW1 is detected between the frame 73 in which the UW1 is expected to be used first in the uplink and the frame 75 immediately before the switching timing in the uplink, the transmission / reception unit 15 of the base station moves. It is determined that the notification of the switching timing to the station has been successful. In this case, at each switching timing as described above, the uplink and downlink spreading codes are switched to those selected in step S5 of FIG.

On the other hand, when at least one UW0 is detected between the frame 73 in which the UW1 is expected to be used first in the uplink and the frame 75 immediately before the switching timing in the uplink, the transmission / reception unit 15 Determines that the transmission / reception unit 25 of the mobile station has failed to detect UW1, and that the notification of the switching timing to the mobile station has not been successful. In this case, the transmitting / receiving unit 15 restarts the wireless channel switching operation using the UW1 again on the downlink.

On the other hand, when UW1 is detected on the downlink,
The transmission / reception unit 25 of the mobile station switches the uplink and downlink spread codes to those specified in step S7 of FIG. 4 at each switching timing as described above.

After the switching of the spreading code, the transmission / reception unit 15 of the base station and the transmission / reception unit 25 of the mobile station resume communication using UW0 as usual.

This first case in which a unique word is used as switching timing information can be modified as follows. That is, as shown in FIG. 7, UW0, UW1, UW2, UW
Five different types of unique words can be used, including 3 and UW4. Here, different types of unique words have a sufficient Hamming distance from each other,
The probability of any two types being confused is very low.

In this case, as shown in FIG.
Usually uses UW0 as downlink switching timing information as in frame 41. Then, in step S17 of FIG. 4, the transmitting and receiving unit 15 sequentially switches the switching timing information.
Change to UW4 as in frame 42, to UW3 as in frame 43, to UW2 as in frame 44, and to UW1 as in frame 45. Thereafter, as in subsequent frames 46-49, transceiver 15 again uses UW0.

Similarly, the transmission / reception unit 25 of the mobile station transmits the switching timing information in the uplink as in the normal frame 51.
Use UW0.

On the other hand, the transmission / reception unit 25 of the mobile station regularly monitors the switching timing information in the downlink and detects the normal UW0. Then, when UW0 cannot be detected, the transmitting / receiving unit 25 sequentially detects UW4 to UW1, and when any of UW4 to UW1 is detected, the transmitting / receiving unit 25 recognizes the start of the wireless line switching operation. In response to this, as a confirmation notification of the start of the wireless channel switching operation, the transmitting / receiving unit 25 transmits the downlink switching timing information to the UW4 as in the frame 53, to the UW3 as in the frame 54, and to the frame 55.
UW2 as in, UW1 as in frame 56
And sequentially. Here, the frame 53 is the frame 42
This is the first uplink frame in which the switching timing information can be changed after the detection of UW4 in the downlink in FIG. After that, the transmission / reception unit 25 continues to use UW1 until the spread code switching timing as in the frames 57 and 58.

Here, the transmission / reception unit 25 of the mobile station transmits an expected type of signal during a period from the detection of one of UW4 to UW1 to the spread code switching timing (that is, a period between frames 42 and 48). The detection of unique words is sequentially performed. Therefore, when UW4 is detected in the frame 42, the detection processing of UW3, UW2 and UW1 is performed in the frames 43, 44 and 4
5 is executed sequentially, and the UW0 detection process
Performed at 48. If a unique word of the expected type cannot be detected, it is determined that synchronization by the unique word is impossible in the frame, and the synchronization state is maintained, and the same operation is performed for the next frame. For example, when UW3 is not detected in frame 43, the synchronization state is maintained, and the process proceeds to UW2 detection processing in frame 44.

On the other hand, the transmission / reception unit 15 of the base station regularly monitors the switching timing information in the uplink to detect the normal UW0. However, corresponding to UW4 to UW1 used in the downlink, frames 53 to
In 58, the transmission / reception unit 15 sequentially performs detection of UW4 to UW1.
Therefore, the detection processing of UW4, UW3 and UW2 is performed in frames 53 and 54.
, And 55, and the UW1 detection process is executed in the subsequent frames 56 to 58. If a unique word of the expected type cannot be detected in a frame in which use of UW4 to UW2 is expected, it is determined that synchronization by the unique word is not possible in that frame, the synchronization state is maintained, and the next frame is maintained. To the execution of a similar operation for. For example, when UW3 is not detected in the frame 54,
The synchronization state is maintained, and the process proceeds to the UW2 detection processing in the frame 55. If UW1 cannot be detected in a frame in which use of UW1 is expected, the transmission / reception unit 15 performs detection of UW0. If UW0 cannot be detected, it is determined that synchronization by a unique word is not possible in that frame.
The process proceeds to the execution of the same operation for the next frame while maintaining the synchronization state.

Then, the transmission / reception unit 15 of the base station and the transmission / reception unit 25 of the mobile station
In both cases, for the downlink, the switching timing is changed from frame 45 in which UW1 is used by the base station to N
On the other hand, for the uplink, it is set M frames after the frame 56 in which the mobile station is expected to use the first UW1.

The transceiver unit 15 of the base station has at least UW4 to UW1 in an expected frame between the frame 53 in which UW4 is expected to be used first in the uplink and the frame 58 immediately before the switching timing in the uplink. When one is detected, it is determined that the notification of the switching timing to the mobile station has been successful. In this case, the uplink and downlink spreading codes are:
At each switching timing as described above, switching is performed to the one selected in step S5 of FIG.

On the other hand, when at least one UW0 is detected between the frame 53 in which the UW4 is expected to be used first on the uplink and the frame 58 immediately before the switching timing in the uplink, the transmission / reception unit 15 of the base station is detected. Determines that the notification of the switching timing to the mobile station has not been successful. In this case, the transmission / reception unit 15 restarts the wireless channel switching operation using the UW4 again in the downlink.

On the other hand, when any one of UW4 to UW1 is detected in the downlink, the transmission / reception unit 25 of the mobile station specifies the uplink and downlink spreading codes at each switching timing as described above in step S7 of FIG. Switch to the one that

After the switching of the spreading code, the transmission / reception unit 15 of the base station and the transmission / reception unit 25 of the mobile station resume communication using UW0 as usual.

In a variation of this first case, the transceiver of the mobile station
25 can detect the start of the spreading code switching operation together with the spreading code switching timing by detecting any one of UW4 to UW1 on the downlink in four frames in which UW4 to UW1 are used, Even in a situation where it is difficult to detect a change in the switching timing information on the downlink due to the deterioration of the quality in the wireless section, it is possible to increase the possibility of successfully completing the wireless channel switching operation.

Here, when the transmission error rate in the wireless section is high,
In order to increase the possibility of successfully notifying the start of the switching operation from the base station to the mobile station, it is necessary to increase the number of unique word types. However, when the number of types of unique words is increased, the switching timing is delayed by that amount, so that the quality degradation period becomes longer in a wireless section in a state where the quality is degraded, which may lead to a decrease in service quality. Then, there is a high probability that the line will be disconnected before the switching is completed. Further, as the number of unique word types used increases, it becomes more difficult to provide a sufficient Hamming distance between any two types of unique words. Therefore, it is not always desirable to increase the number of types of unique words used indefinitely, and an appropriate number of types of unique words to be used should be determined in view of the above requirements.

Also, in this first case, the spread code switching timing does not necessarily have to be set after a predetermined number of frames from the reference timing at which the specific type of unique word is used, as described above. The timing may be set as desired.

The procedure using the uplink and downlink in this first case as described above with reference to FIGS. 6 and 7 also applies to the second, third and fourth cases described below. Applicable equally.

Next, as a second case, the switching timing information is
It can be given by the flag of each frame in either ON or OFF state.

That is, as shown in FIG. 8, the flag F can be set to ON in a specific frame, and the simultaneous wireless channel switching timing of the base station and the mobile station is set after a predetermined period from this frame in which the flag is ON. Is done. In FIG. 8, the switching timing is set to, for example, the timing of the boundary four frames after this frame whose flag is ON.

In this case, the transmitting / receiving unit 15 of the base station normally sets the flag of each frame to OFF as switching timing information, and FIG.
In step S17, the transmission / reception unit 15 changes the switching timing information by setting the flag to ON. And
The transmission / reception unit 15 sets the flag of each frame to OFF again for the subsequent frames.

On the other hand, the transmission / reception unit 25 of the mobile station regularly monitors the switching timing information given by the flag in the frame transmitted from the base station and checks whether the flag is ON. And when it is detected that the flag is ON,
The transmission / reception unit 25 recognizes the start of the radio line switching operation, and sets the switching timing to a timing after a predetermined period from this frame in which the flag is ON, for example, a timing at a boundary four frames after this frame in which the flag is ON. Is done.

Here, instead of fixing the switching timing to a frame whose flag is ON as described above, instead of fixing the switching timing to a constant value, a multi-valued flag in which the number of frames up to the switching timing is indicated by a value, for example, a flag having a value of 5 It is also possible to provide a flag indicating that the frame is five frames ahead and a flag having a value of 4 indicating that the frame is four frames ahead.

This second case using flags as switching timing information as shown in FIG. 9 is modified to prevent a predetermined number of frames preceding the switching timing in order to prevent the switching timing information from being overlooked in the form of flags. It is also possible to use different numbers of flags in. For example, in FIG. 9, the number of flags in each frame indicates the number of frames up to the switching timing, and the number of flags sequentially decreases as the switching timing approaches. in this case,
Even when the first frame with three flags F is overlooked or not recognized due to poor communication conditions, as long as a subsequent frame with fewer flags F can be detected, only one flag F at the end It is possible to surely execute the wireless line switching at a predetermined switching timing after the frame.

This second case using flags as switching timing information is illustrated in FIG.
It is also possible to deform as shown in FIG. That is, PDC (P
In the case of personal digital cellular, one superframe is defined by a series of 36 frames, and the flag F can be set to ON in every frame of the superframe as shown in FIG. Is set at the boundary between this superframe and the next superframe.

In this second case, the flag F can be located in each frame at a position between the associated control link ACCH provided between the preamble PR and the communication ring TCH and the unique word UW, as shown in FIG. .

Next, as a third case, the switching timing information is
This can be provided by a so-called housekeeping bit flag that is in either the ON or OFF state.

The housekeeping bit is used to detect data degradation such as the bit error rate of the communication link or the received power level during communication between the mobile station and the base station for the purpose of detecting the quality degradation of the radio link in the communication station and controlling the transmission power. Is used in many mobile communication systems, such as digital mobile telephone systems currently in practical use, to notify the user of the notification. The housekeeping bits are normally included in a selected number of frames in the transmission frame and are formed using error correction / detection codes, so that reliable signal transmission is guaranteed for the housekeeping bits. it can. In the case of the third case, a flag is provided in the highly reliable housekeeping bit, so that the switching timing from the base station to the mobile station can be notified with high reliability.

In this case, as shown in FIG. 12, a housekeeping bit can be provided for each frame, and the transmitting / receiving section 15 of the base station sets a flag as normal switching timing information.
Use the housekeeping bit R0 that is OFF. Then, in step S17 of FIG. 4, the transmission / reception unit 15 changes the switching timing information by setting the housekeeping bit flag to ON (housekeeping bit R1). Then, the transmission / reception unit 15 sets the flag of the housekeeping bit to OFF (housekeeping bit R0) again for the subsequent frame. The simultaneous wireless channel switching timing for both the base station and the mobile station is set after a predetermined period from the housekeeping bit R1 whose flag is ON. For example, in FIG. 12, the switching timing is set to a boundary timing four frames after the frame including the housekeeping bit R1 whose flag is ON.

On the other hand, the transmission / reception unit 25 of the mobile station regularly monitors switching timing information given by the flag of the housekeeping bit of the frame transmitted from the base station and checks whether the flag is ON. Then, when it is detected that the flag is ON, the transmitting / receiving unit 25 recognizes the start of the wireless line switching operation, and the switching timing is, for example, after a predetermined period from the housekeeping bit whose flag is ON, for example, Housekeeping bit with flag ON
The timing is set at a boundary timing four frames after the frame including R1.

Here, as in the above second case, instead of fixing the switching timing to a frame including the housekeeping bit R1 in which the above flag is ON, the number of frames up to the switching timing is determined by a value. The multi-value flag indicated, for example, the flag whose value is 5 is 5
Indicates that the frame is ahead, and the flag whose value is 4 is 4
It is also possible to provide such a thing as indicating that the frame is ahead.

As shown in FIG. 13, it is also possible to provide housekeeping bits periodically in the selected frame. Fig.
At 13, the transmitted signal is provided in units of a superframe formed by L frames, only the first frame of the superframe contains housekeeping bits. Here, as in the case of FIG. 12 described above, the transmission / reception unit 15 of the base station uses the housekeeping bit R0 whose flag is OFF as the normal switching timing information, and uses the housekeeping bit R0 in the first frame of the appropriate superframe. Turn ON the Keeping Bit Flag (Housekeeping Bit
The switching timing information is changed by setting to R1). Then, the transmitting / receiving unit 15 turns off the housekeeping bit flag again for the subsequent superframe.
(Housekeeping bit R0). The simultaneous wireless channel switching timing for both the base station and the mobile station is set after a predetermined period from the housekeeping bit R1 whose flag is ON. For example, in FIG. 13, the switching timing is set to a boundary timing four frames after the frame including the housekeeping bit R1 whose flag is ON.

Here, as described above, instead of fixing the switching timing to a frame including the housekeeping bit R1 in which the above flag is ON, instead of fixing the switching timing to a fixed value, the multi-value flag indicating the number of frames until the switching timing is indicated by a value. It is also possible to provide. For example, as shown in FIG.
Housekeeping bit R1 with a flag whose value is 3
-3 indicates that it is three superframes before the switch timing, the housekeeping bit R1-2 having a flag with a value of 2 indicates that it is two superframes before the switch timing, The housekeeping bit R1-1 having a flag whose value is 1 indicates that it is one superframe before the switching timing. In this way, the housekeeping bits R1-3 with the flag of value 3 are not recognized even if the first frame is overlooked or not recognized due to poor communication conditions, so the housekeeping bit with the flag of a lower value is also kept. As long as a subsequent superframe having a bit can be detected, the mobile station can recognize the wireless channel switching timing, so that the success rate of wireless channel switching can be increased.

In this third case, the housekeeping bit R is given in the form shown in FIG. 15 consisting of received power data, received bit error rate (BER) and a flag. Here, the flag can be given by one bit when it takes only two states, ON and OFF, and by a plurality of bits when it takes multiple values.

Next, as a fourth case, the switching timing information is:
This can be given by the number of frames that label each frame.

In this case, a serial frame number is assigned to the frame as shown in FIG. Then, the transmission / reception unit 15 of the base station uses the number of frames in numerical order as the normal switching timing information. Then, in step S17 of FIG. 4, as shown in FIG. 17, the transmission / reception unit 15 assigns an appropriate frame number to the frame number of the preceding frame and the frame number of the subsequent frame so as to be discontinuous. By changing, the switching timing information is changed. In FIG. 17, the frame number of the frame between frame F7 and frame F9 is usually F8, but F50
To make the arrangement of frame numbers discontinuous. Then, the simultaneous wireless channel switching timing for both the base station and the mobile station is set after a predetermined period from this frame having the changed frame number. For example,
In FIG. 17, the switching timing is set to the boundary timing four frames after the frame having the changed frame number F50.

On the other hand, the transmitting / receiving unit 25 of the mobile station regularly monitors switching timing information given by the frame number of the frame transmitted from the base station, and checks whether the frame numbers are discontinuous. Then, when a discontinuous frame number is detected, the transmission / reception unit 25 recognizes the start of the radio line switching operation, and the switching timing is, for example, after a predetermined period from this frame having the discontinuous frame number, for example. It is set at the timing of the boundary four frames after this frame having a continuous frame number.

Here, instead of fixing the switching timing to the frame having the changed frame number as described above in the second and third cases, for example, the frame number 50 is five frames ahead. Indicating that
The frame number 40 may be added to the changed frame number to indicate the number of frames up to the switching timing, such as indicating that the frame number is four frames ahead. A meaning may be attached to the changed frame number by using some symbol other than a number.

As shown in FIG. 18, the sequentially increasing frame number is changed so that the changed frame number indicates the number of frames from the switching timing to the switching timing before a predetermined number of frames before the switching timing. Can also be changed. Therefore, in FIG. 18, the frame numbers of the three frames after the frame number F7 are usually F8, F9, and F10 in that order, but they must be 3, 2, and 1 frame before the switching timing, respectively. F3, indicating
Changed to F2, F1. In this way, even when the first frame with the changed frame number F3 is overlooked or not recognized due to poor communication conditions, as long as a subsequent frame with the sequentially reduced frame number of the changed frame can be detected. Since the mobile station can recognize the wireless channel switching timing, the success rate of wireless channel switching can be increased.

Here, when changing the frame number of a plurality of frames before the switching timing, it is necessary to sufficiently consider the number of frames whose frame numbers are changed.
That is, in normal communication, since it is assumed that frames are transmitted in the order of frame numbers, there is no problem even if the frame number is changed with only a small number of frames, but the change is made in an excessively large number of frames. If a frame number is used, frame transmission and reception order control becomes impossible.

In this fourth case, the frame number FN is associated with the associated control link ACCH provided between the preamble PR and the communication link TCH as shown in FIG.
And the unique word UW.

In any of the first to fourth cases described above, the switching timing information of the present invention can generally or directly indicate the time until the switching timing in one or more frames.

In the first embodiment, the method for determining the number of frames in which the changed switching timing information is provided remains unspecified during the period between the time when the need for radio line switching occurs and the switching timing. It is.

At this point, if the number of frames including the changed switching timing information is fixed to a small number, the rate of failure of frame reception at the mobile station increases when the quality of the radio link is significantly deteriorated. The probability of failing to notify the changed switching timing information to the mobile station increases, and therefore the probability of failing the radio line switching operation increases.

On the other hand, if the number of frames including the changed switching timing information is fixed to a large number, the period required between the wireless channel switching request and the wireless channel switching timing is always considerably long, so that an appropriate It becomes difficult to perform wireless line switching at a timing. Furthermore, when the frame number is used as the switching timing information and the number of frames including the changed switching timing information is fixed to a large number, the period in which the frame transmission order cannot be specified by the frame number becomes considerably long. Sisters,
A problem is apt to occur in order control of the received frame in the mobile station.

To eliminate these potential problems in the first embodiment, the number of frames provided with the changed switching timing information during a period between the time when the need for radio line switching occurs and the switching timing is determined. The preferred method can be defined as in the second embodiment of the wireless line switching method according to the present invention described in detail below.

In the following, for the sake of explanation, the frame number is used as the switching timing information as in the fourth case of the first embodiment, the CDMA system is used as the access method as in the first embodiment, A second embodiment will be described for an example of a case using an SIR (Signal Interference Ratio) indicating the ratio between the signal radio wave reception level and the interference radio wave reception level as the quality of the signal. However, the second embodiment is equally applicable to other types of switching timing information, other types of access methods, and other types of wireless channel quality.

In the second embodiment, the wireless line switching method is executed according to the sequence chart of FIG. 20 as follows.

First, steps S1 to S13, which are the same as those in FIG. 4 for the first embodiment described above, are executed.

Then, after the switching destination spreading code confirmation is returned from the transmission / reception unit 15 to the control unit 17 in step S13, the control unit 17 transmits a line quality measurement request signal to the transmission / reception unit 15 (step 14).
1). In response, the transmitting / receiving unit 15 measures the SIR of the wireless line currently used for communication (step 143), and the control unit 17
Then, a line quality measurement response signal indicating the measured SIR value is reported (step 145).

Next, the control unit 17 determines the switching timing notification frame number indicating the number of frames for providing the changed switching timing information according to the SIR value transmitted from the transmission / reception unit 15 (step S147). Here, the number of switching timing notification frames is determined according to a table of predetermined switching timing notification frames and SIR values as shown in FIG. For example, when the measured SIR value is 3.5 dB, 3 is selected as the number of switching timing notification frames according to the table in FIG. In the table of FIG. 21,
The number of switching timing notification frames is set to be larger for lower SIR values and smaller for higher SIR values. After that, the control unit 17 notifies the transmission / reception unit 15 of the number of switching timing notification frames determined by the switching timing notification frame number designation signal (step S149).

Thereafter, steps S15 to S25 similar to those in FIG. 4 for the first embodiment described above are executed. In this case, the transmission / reception unit 15 switches the switching timing setting unit 15a according to the switching timing notification frame number specified in step S15A.
The switching timing is set in. For example, as shown in FIG. 22, when the designated number of switching timing notification frames is 3, the switching timing
It is set after the number of frames designated by the number of switching timing notification frames from the end of the frame transmitted while S149 is completed. Then, in step S17, the frame number of the switching timing notification frame is changed to F3, F2, and F1, which indicate the number of frames up to the switching timing as in the fourth case in the first embodiment.

As described above, in the second embodiment, when it is difficult to notify the mobile station of the radio channel switching timing due to deterioration of the radio channel quality such as the SIR value, the number of radio channel switching timing notification frames is increased. Therefore, the probability of failing to notify the mobile station of the changed switching timing information can be reduced, and therefore, the probability of failing in the wireless channel switching operation can be reduced. On the other hand, when the radio channel quality such as the SIR value does not deteriorate, the number of radio channel switching timing notification frames is reduced, so that the loss of the appropriate radio channel switching timing due to unnecessary extension of the switching timing can be prevented. It is possible to eliminate the possibility of trouble in the transmission order control based on the frame number on the side.

Instead of the SIR used above, the absolute reception level,
Wireless channel quality can be indicated by any parameter that can estimate the probability of successful frame reception on the wireless channel, such as a bit error rate (BER).

Instead of using the frame number of the fourth case of the first embodiment as the switching timing information, the unique word of the first case, the flag of the second case, or the flag of the third case of the first embodiment is used. The flag of the housekeeping bit may be used.

Further, instead of indicating the switching timing directly by the frame number as described above, the frame number may be indirectly indicated according to a predetermined relationship between the switching timing information and the period up to the switching timing.

Also, the contents of the table in FIG. 21 used for determining the number of wireless line switching timing notification frames are required without changing the basic principle of increasing the number of switching timing notification frames for those with lower quality wireless lines. It should be determined according to the communication performance of the mobile communication system.

Further, the relationship between the switching timing notification frame and the switching timing may be different from that shown in FIG. For example, as shown in FIG. 23, the switching timing is a predetermined number of frames from the last one end of the changed switching timing information (2 in FIG. 23).
) May be set later. The setting of FIG. 23 is effective when the mobile station needs more time than one frame to set the switching destination wireless channel parameters or the switching timing.

On the other hand, as shown in FIG. 24, the switching timing is set to a predetermined number of frames from the first end of the changed switching timing information regardless of the number of switching timing notification frames (FIG. 5) later. In this case, for obvious reasons, the predetermined number of frames should be larger than the maximum value of the settable number of switching timing notification frames. In the setting of FIG. 24, the appropriateness of the wireless line switching timing is not so important, but it is important to prevent trouble in the transmission order control by the frame number, and the mobile station should follow the switching timing notification frame number determined by the base station. It is suitable when it is difficult to control the switching timing.

The procedure of FIG. 20 described above can be modified as shown in FIG. That is, in the procedure of FIG. 25, the radio channel quality for determining the switching timing notification frame number is given by the measurement quality at the time of the radio channel switching request. Therefore, in this case, during communication with the mobile station, the transmitting and receiving unit 15 always measures the current SIR value of the wireless channel, and the degradation of the wireless channel quality is such that the SIR measured value is lower than a predetermined threshold. Is detected in step S1A. Then, in step S3A, the quality deterioration notification signal including the latest measured SIR value is transmitted from the transmission / reception unit 15 to the control unit 17.

After the spreading code is selected in step S5, in step S147, the number of switching timing notification frames is determined using the table in FIG. 21 according to the latest SIR value included in the quality deterioration notification signal. The determined switching timing notification frame number is notified from the control unit 17 to the transmission / reception unit 15 as a part of the switching destination spread code specification signal transmitted in step S11A, and the transmission / reception unit 15 performs the spreading specified for the uplink and the downlink. The designated switching timing notification frame number is stored together with the code, and a confirmation signal is returned in step S13A.

Then, in step S15A, the transmission / reception unit 15 sets the switching timing in the switching timing setting unit 15a according to the specified number of switching timing notification frames as in the case of FIG. 20 described above. FIG.
Steps S17 to S25 similar to 4 are executed thereafter.

In addition, many modifications and changes may be made to the above embodiments without departing from the novel and advantageous features of the invention, other than those already described above. Accordingly, all such changes and modifications are intended to be included within the scope of the appended claims.

Continued on the front page (31) Priority claim number Japanese Patent Application No. 6-158846 (32) Priority date Hei 6 (1994) July 11 (33) Priority claim country Japan (JP) (31) Priority claim number Special No. 6-158852 (32) Priority Date Hei 6 (1994) July 11, (33) Priority Country Japan (JP)

Claims (54)

(57) [Claims] 1. A method for switching a wireless channel in mobile communication between a base station and a mobile station, comprising: performing communication between the base station and the mobile station via a framed wireless channel; Providing switching timing information composed of layer 1 bit data in each frame of the base station; and, when it is necessary to switch the radio channel between the base station and the mobile station, the base station is configured to indicate the radio channel switching. Changing the switching timing information in at least one of the frames of the radio line in the station; transmitting the changed switching timing information from the base station to the mobile station; and changing the switching timing information in the changing step. At the switching timing after a predetermined period from the frame, the base station switches the wireless channel to the switching destination wireless channel. Detecting the changed switching timing information transmitted from the base station in the mobile station; and the switching timing after a predetermined period from each frame detected in the step of detecting the changed switching timing information. And the step of switching the wireless line to the switching destination wireless line in the mobile station. 2. The method of claim 1, wherein the switching timing information is provided by a unique word for maintaining frame synchronization. 3. The method according to claim 2, wherein the unique word is usually set to one type, and is changed to another type different from the one type in the changing step. 4. The method according to claim 2, wherein the unique word is usually set to one type, and in the changing step, the unique word in each of a plurality of consecutive frames is sequentially changed to another type different from the one type. The described method. 5. The method according to claim 1, further comprising the step of changing the switching timing information in at least one frame of the radio channel at the mobile station in response to detecting the changed switching timing information in the detecting step. Transmitting the changed switching timing information from the mobile station to the base station, and the base station switches the radio line only when the changed switching timing information from the mobile station is received before the switching timing. Execute, and otherwise, repeat the step of transmitting the changed switching timing information from the base station to the mobile station. 6. The method according to claim 1, wherein the switching timing information is changed in the changing step such that a value of the changed switching timing information indicates a time until the switching timing. 7. The method according to claim 6, wherein the switching timing information is changed in a plurality of frames in the changing step. 8. The method according to claim 1, wherein the switching timing information is provided by a flag provided in each frame. 9. A method according to claim 8, wherein the flag is provided in a housekeeping bit of each frame for notifying a reception state of a radio channel between the base station and the mobile station. 10. The method of claim 8, wherein the flag is normally set to take one value, and in the changing step is changed to another value different from the one value. 11. The method according to claim 11, wherein in the step of changing any one of a large number of values, one of the plurality of values takes one value, the value of the changed flag in each frame indicates the number of frames from each frame to the switching timing. The method of claim 8, wherein the method is changed to 12. The method according to claim 11, wherein the step of changing the flag includes:
12. The method according to claim 11, wherein the flag is changed to a flag having a sequentially decreasing value in a plurality of consecutive frames. 13. The switching timing information is provided by a plurality of flags provided in each frame, and is changed so that the number of changed flags sequentially decreasing in a plurality of continuous frames is included in a continuous frame. The method of claim 1, wherein the method is modified in steps. 14. The method of claim 1, wherein the switching timing information is changed in a step of changing in units of a superframe formed by a frame. 15. The method according to claim 1, wherein the switching timing information is given by a frame number assigned to each frame. 16. The method according to claim 15, wherein the frame numbers are sequentially assigned in the order of transmission of the normal frames, and the changing step is changed so as to take a value that is not continuous with the frame numbers of the immediately preceding and succeeding frames. 17. The method of claim 15, wherein the frame number is changed in the step of changing the value of the changed frame number in each frame to indicate the number of frames from each frame to the switching timing. 18. The method according to claim 17, wherein the frame number is changed in the step of changing to a frame number of a sequentially decreasing value in a plurality of consecutive frames. 19. The method according to claim 1, wherein the base station and the mobile station maintain the same synchronization state before and after the switching of the radio channel. 20. The method of claim 1, wherein the switching timing information is changed in a variable number of frames in the changing step. 21. The method according to claim 20, further comprising: measuring the quality of the radio link; and changing the switching timing information in the changing step according to the quality measured in the measuring step. Controlling the number. 22. The method according to claim 21, wherein in the controlling step, the variable number is increased when the quality measured in the measuring step is lower, and decreased when the quality measured in the measuring step is higher. The described method. 23. In the controlling step, the variable number is determined by using a table specifying a desired number of frames for which switching timing information is to be changed for each level of quality measured by the measuring step. 22. The method of claim 21, wherein the method is controlled. 24. The method according to claim 21, wherein the step of measuring measures the quality at a timing when it is necessary to switch the radio channel between the base station and the mobile station. 25. The method according to claim 21, wherein the measuring step measures the quality at a timing before the switching timing information is changed at the base station. 26. The method of claim 1, wherein the switching timing is specified in advance as a predetermined number of frames after the beginning of each frame including the changed switching timing information.
The described method. 27. The method according to claim 1, wherein the switching timing is specified in advance as a predetermined number of frames after the end of each frame including the changed switching timing information. 28. A mobile communication system including a base station and a mobile station, wherein communication between the base station and the mobile station is performed via a framed radio channel, and a layer is formed in each frame of the radio channel. Means for supplying switching timing information constituted by 1-bit data; and a radio link in the base station for indicating the radio link switching when it is necessary to switch the radio link between the base station and the mobile station. Means for changing the switching timing information in at least one of the following frames: means for transmitting the changed switching timing information from the base station to the mobile station; and means for changing the switching timing information from the frames for which the switching timing information has been changed by the changing means. Means for switching a radio line to a switching destination radio line in a base station at a switching timing after a predetermined period; Means for detecting the changed switching timing information transmitted from the mobile station, and switching the radio line at the mobile station at a switching timing after a predetermined period from each frame detected by the means for detecting the changed switching timing information. Means for switching to the destination wireless line. 29. The switching timing information is provided by a unique word for maintaining frame synchronization.
The system of claim 28. 30. The system according to claim 29, wherein the unique word is usually set to one type, and the changing means changes the unique word to another type different from the one type. 31. A method according to claim 29, wherein the unique word is generally set to one type, and the changing means sequentially changes the unique word in each of a plurality of consecutive frames to another type different from the one type. The described system. 32. The system according to claim 28, further comprising: means for changing the switching timing information in at least one frame of the radio line at the mobile station in response to the detection of the changed switching timing information by the detecting means. Means for transmitting the changed switching timing information from the mobile station to the base station, and the base station switches the radio line only when the changed switching timing information from the mobile station is received before the switching timing. Executed, and at other times, transmission of the changed switching timing information from the base station to the mobile station is repeated. 33. The system according to claim 28, wherein the changing means changes the switching timing information so that the value of the changed switching timing information indicates a time until the switching timing. 34. The system according to claim 33, wherein the changing means changes the switching timing information in a plurality of frames. 35. The system according to claim 28, wherein the switching timing information is provided by a flag provided in each frame. 36. The system according to claim 35, wherein the flag is provided in a housekeeping bit of each frame for notifying a reception state of a radio line between the base station and the mobile station. 37. The method of claim 35, wherein the flag is normally set to take one value, and the changing means changes the flag to another value different from the one value. 38. The flag, wherein one of a number of values takes one value, and the changing means includes means for changing the value of the changed flag in each frame to indicate the number of frames from each frame to the switching timing. The system of claim 35, wherein the system is modified. 39. The system according to claim 38, wherein the changing means changes the flag to a flag having a sequentially decreasing value in a plurality of consecutive frames. 40. The switching timing information is provided by a plurality of flags provided in each frame, and the changing means includes a number of changed flags for sequentially decreasing the number of changed flags in a plurality of consecutive frames. The system of claim 28, wherein the system is modified to have 41. The system according to claim 28, wherein the changing means changes the switching timing information in a unit of a superframe formed by a frame. 42. The system according to claim 28, wherein the switching timing information is given by a frame number assigned to each frame. 43. The system according to claim 42, wherein the frame numbers are sequentially assigned in the order of transmission of the normal frames, and the changing means changes the frames so as to take values that are not continuous with the frame numbers of the immediately preceding and succeeding frames. 44. The system according to claim 42, wherein the changing means changes the frame number so that the value of the changed frame number in each frame indicates the number of frames from each frame to the switching timing. 45. The system according to claim 44, wherein the changing means changes the frame number in a plurality of consecutive frames to a frame number having a sequentially decreasing value. 46. The system according to claim 28, wherein the base station and the mobile station maintain the same synchronization state before and after the switching of the radio line. 47. The system according to claim 28, wherein the changing means changes the switching timing information in a variable number of frames. 48. The system according to claim 47, further comprising: a means for measuring the quality of the radio link; and a variable means for changing the switching timing information by the changing means according to the quality measured by the measuring means. Means for controlling the number. 49. The controlling means increases the variable number when the quality measured by the measuring means is lower, and decreases the variable number when the quality measured by the measuring means is higher.
The system of claim 48. 50. The means for controlling the variable number by using a table which specifies for each level of quality measured by the measuring means the desired number of frames for which the switching timing information is to be changed. Control, claim
48 described system. 51. The system according to claim 48, wherein the measuring unit measures the quality at a timing when it is necessary to switch the radio line between the base station and the mobile station. 52. The measuring means measures the quality at a timing before the base station changes the switching timing information.
The system of claim 48. 53. The switching system according to claim 28, wherein the switching timing is specified in advance as a predetermined number of frames after the beginning of each frame including the changed switching timing information.
The described system. 54. A method according to claim 1, wherein the switching timing is specified in advance as a predetermined number of frames after the end of each frame including the changed switching timing information.
The system according to 28.