JPH082117B2 - Channel switching method - Google Patents

Description

Description: “Industrial field of use” The present invention relates to a during-call channel switching method performed when a mobile station moves between service zones in a mobile communication system.

"Prior art" When a mobile station shifts from the service zone of a base station in communication to the service zone of another base station in a mobile communication system, in order to continue the communication, the radio channel of the base station in communication is set. , It is necessary to switch to the wireless channel of the transfer destination base station.

A conventional technique of this switching system will be described with reference to FIGS. 6 and 7. As shown in FIG. 6, the mobile station 11 transmits / receives data to / from the base station 14 and its wireless channel by the transmitter 12 and the receiver 13, and moves in the direction of arrow 16 while communicating. When the mobile station 11 approaches the boundary of the service zone (area) of the base station 14, the wireless channel is switched so as to communicate with the base station 15 of the destination service zone through the call channel of the wireless channel of the base station 14. A command is given. That is, as shown in FIG. 7, from the currently communicating base station 14 to the mobile station
A new channel is designated for 11. The mobile station 11 receives this and performs processing necessary for switching. For this processing, the frequencies of the transmitter 12 and the receiver 13 are changed, and a continuity test is performed.

When the call signal is digitalized, the continuity test is performed after the establishment processing of the clock synchronization and the frame synchronization is performed.

The mobile station 11 generally has a built-in frequency synthesizer and controls the synthesizer to make the transmission / reception frequency variable. It takes 0.1 to 0.3 seconds to change the frequency in the synthesizer. The pain test is indispensable for confirming whether transmission and reception are normally performed on the wireless channel at the destination. As a confirmation method, for example, a method of sending a pattern of 1010 ... And checking whether or not there is an error is adopted. In the conventional method, the switching process takes about 0.5 seconds in total, and the call is interrupted during this period.

Further, in the case of the digital method, a new time is required to establish signal synchronization, and the call disconnection time becomes longer. Especially in facsimiles and data transmission, information on the period of call disconnection is completely lost, so that the problem of call disconnection is larger than in the case of voice transmission.

In order to solve these drawbacks, a channel switching system has been proposed in which a mobile device simultaneously transmits and receives to and from two base stations, thereby eliminating the disconnection during a channel switching.

That is, as shown in FIG. 1, the mobile station 11 is connected to the transmitter 12a,
Two systems of a receiver 13a, a transmitter 12b, and a receiver 13b are provided. As shown in FIG. 2, the mobile station 11 is an old base station 14 and a transmitter.
12a and the receiver 13a are communicating. When the channel switching starts with the transition between the wireless zones, the frequency of the new wireless channel is first designated by the in-service control signal in the wireless channel used for the call with the old base station 14. Calls are generally made in the frequency band of 300 Hz to 3 KHz, and various control information is transmitted by using a digital signal of about 100 b / s using a frequency of 300 Hz or less. This control information is called an in-service control signal.

As described above, when the frequency of the new wireless channel is designated by this in-service control signal, the transmitter 12b and the receiver 13b, which have not been operating until then, are started at this designated frequency. At the same time, the corresponding transmitting / receiving device of the transfer destination base station 15 is also started. This is performed by a command from the control station, which is a higher-level station of the radio base station. The continuity test of the new call channel begins with the new base station originating mobile station reception (downlink continuity test), and when it is confirmed that the test signal has been received on the mobile station 11 side, the mobile station originating base station reception is next. A test signal is sent (uplink continuity test). The continuity test is completed when the new base station 15 confirms the reception of the test signal. If the call signal is of the digital type, the clock synchronization and frame synchronization of the upstream and downstream lines are established (synchronization establishment) prior to the continuity test. As described above, the mobile station 11 is in a state of communicating with both the new and old base stations 14 and 15 at the same time. Finally, when the call itself is switched from the old channel to the new channel, all channel switching operations are completed without disconnecting the call.

In the case of the digital method, switching between the channels at the frame-to-frame boundary ensures more reliable non-interruption.
When there is a time delay difference between the signals of the old base station 14 and the new base station 15, it is necessary to consider that the base station 15 or the mobile station 11 should match the delay.

[Problems to be Solved by the Invention] As shown in FIGS. 1 and 2, channel switching can be performed without disconnecting a call. However, it is necessary to provide two transceivers in the mobile station, which causes a problem that the device scale of the mobile station becomes large.

Therefore, an object of the present invention is to provide a channel switching method which enables channel switching without increasing the device size of a mobile station, that is, using a single-system transceiver, and without disconnecting a call. is there.

[Means for Solving Problems] According to the present invention, both the base station currently in communication and the base station to which the base station is next switched when switching base stations to communicate with each other as the zone moves. At the same time, time-division transmission / reception is performed using a single-system transceiver. For this purpose, two time division channels are used, one of which is used to communicate with the base station currently in communication, and the other of which is used to communicate with the base station to be switched to next. The wireless channel is switched without interruption of the call after the procedure necessary before starting the communication with the switching destination base station, that is, after completing the wireless continuity test and the establishment of signal synchronization.

"Embodiment" FIG. 3 shows an embodiment of the present invention. Normally, a base station talks with a plurality of mobile stations on the same frequency in a time division manner. Third
The figure shows only when the base station 14 and the mobile station 11 are communicating through the channel 1ch when there are two time-division channels (channels), 1ch and 2ch. In digital transmission, the in-service control signal is arranged in one frame, for example, after the voice signal. In this case, the device configuration has only one set of transmitter and receiver as in the case of FIG. Communication with the new base station is performed after a predetermined process by designating a new frequency by the in-service control signal during communication with the old base station 14 as in the case of FIG. This frequency designation information is sent from the upper control station to the new base station 15, and the new base station is also started. The exchange signal with the new base station is performed by the designated wireless channel (frequency) and the designated time division channel, but in this example, it is performed through the channel 2ch. When transmitting and receiving with this channel 2ch, the synthesizer is controlled to set the transmitter 12 and the receiver 13 of the mobile station 11 to the designated wireless channel. In this way, the mobile station 11 becomes the channel 1c.
While communicating with the old base station 14 through h, it is possible to establish synchronization with the new base station 15 and conduct a continuity test through the channel 2ch, and after that test, switch to communication only with the new base station 15. In this example, the mobile station 11 performs intermittent transmission / reception with the base station 14 and continuous transmission / reception with both the bases 14 and 15 during the switching operation. At this time, in order to reduce the guard time slot, high-speed switching between the radio channel with the old base station 14 and the radio channel with the new base station 15 is required. This high-speed frequency switching can be achieved by, for example, preparing two frequency synthesizers. As shown in FIG. 3, when the mobile station 11 performs channel switching, the call time shifts in frame units. If this is left as it is, a time delay occurs with respect to the other party. Therefore, the system needs a function of compensating for the delay. It is also possible to use the control channel instead of the in-service control signal to instruct the start of the frequency of the new channel and the channel switching operation. When the mobile station uses two-system transceivers, the transceivers that are not communicating may always receive the control channel. When the transmitter / receiver has one line in the time division transmission system, the control channel is received during the idle time of transmission / reception. That is, a specific time slot other than the time channel assigned to the call at the mobile station can be used as the control channel. Since the control channel is common to all mobile stations, all mobile stations can receive at this time slot. New channel information can be sent using this time slot. In other words, when using the in-service control signal,
The channel information is sent within the time corresponding to the call channel, but when using the control channel, a different time slot is used, but in either case the new channel information is available during the time when there is no call signal. There is no difference in sending.

Although the above description has been made with respect to the time division of two channels, it is needless to say that the present invention can be applied to the case of time division of three channels or more. The present invention can also be applied to a so-called ping-pong method in which the transmission and the reception are complementarily performed so as not to overlap in time by the two-channel time division method. In ping-pong transmission, transmission and reception are performed alternately, and the transmission frequency and the reception frequency are different. A flow chart in which the present invention is applied to this system is shown in FIG. If a new channel is specified by the in-service control signal while the mobile station is transmitting to the old base station 14 using the ping-pong transmission method, at the same time, the new base station 15 from the upper control station to the mobile station And start ping-pong transmission on the newly specified wireless channel. In the illustrated example, when the mobile station is transmitting to the old base station 14 on the old wireless channel, the new base station 15 transmits on the new wireless channel for establishing synchronization. When the mobile station is in the reception state from the old base station 14 by the old radio channel, the mobile station is in the transmission state by the new radio channel to the new base station 15. When the synchronization with the new base station and the continuity test are completed in this way, the signal exchange with the old base station 14 is stopped and the communication state with the new base station 15 is switched to.

FIG. 5 shows an example in which the present invention is applied to a signal having a time diversity branch incorporated therein. This embodiment is a case of two branches. The symbol in the figure indicates the branch number of time diversity. However, adjacent frames do not necessarily become diversity branches, and in general, branches and are arranged at intervals with a sufficiently low fading correlation. During normal communication, this time diversity is applied to perform high-quality transmission / reception, but at the time of channel switching, transmission / reception of one of the branches (branch in this example) is stopped and the branch of the wireless channel of the new base station 15 at the transfer destination is established. To start communication and establish continuity test. During channel switching, the transmission quality is reduced due to the lack of the time diversity effect, but the call is not interrupted.

[Advantages of the Invention] As described above, according to the present invention, there is no interruption of a call at the time of channel switching when a mobile station moves between service areas, so that the call quality is improved, especially in facsimile and data transmission. It has a great effect.

Moreover, in the present invention, the mobile station only needs to be provided with a single-system transceiver, and the device scale of the mobile station is the same as the conventional one, which is economical.

One of the means for increasing the subscriber capacity in mobile communication is to reduce the zone radius, but the problem is that the frequency of channel switching increases. The present invention becomes more effective in the future increase in subscriber capacity.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration in which a proposed mobile station has transceivers of two systems and performs channel switching without disconnecting a call, and FIG. 2 is a diagram showing channel switching of the configuration shown in FIG. FIG. 3 is a diagram showing an operation flow, FIG. 3 is a diagram showing an operation flow of channel switching when there is only one transmitter / receiver system by time division transmission in the embodiment of the present invention, and FIG. 4 is a channel in the ping-pong transmission system. FIG. 5 is a diagram showing an operation flow of switching, FIG. 5 is a diagram showing an operation flow of a channel switching flow in a system to which time diversity is applied, and FIG. 6 is a diagram showing a configuration when a conventional mobile station is a transceiver of one system. , FIG. 7 is a diagram showing an operation flow of conventional channel switching.

Claims (1)

[Claims] 1. In a mobile communication method for forming a service area in a plurality of zones and performing time division communication, when switching a base station to be communicated with transition between zones, a base station currently communicating with The wireless continuity test and signal transmission, which are the procedures necessary before starting communication with the switching destination base station, by performing transmission / reception in time division using the transceiver of one system simultaneously with the switching destination base station. A channel switching method, characterized in that a wireless channel is switched without interruption of a call after establishment of synchronization and the like is completed.