JPH0738738B2 - Method of switching channel during call of mobile communication system and mobile terminal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for switching channels during a call in a mobile communication system in a small zone system (cellular system) and a mobile terminal for implementing this method.

[Conventional technology]

The small zone system (cellular system) is a system that divides the service area into a number of wireless zones and reuses the same frequency in distant wireless zones to increase the number of accommodations per frequency and is used in car telephone systems. ing. However, the potential demand for car phones far exceeds the capacity of current systems, and higher capacity systems need to be realized. As a method for further increasing the capacity in a limited frequency band, minimization of the wireless zone can be considered. For example, if the radius of the wireless zone is reduced to 1/10, the frequency utilization rate will increase 100 times.

When the wireless zone is minimized in this way, the frequency of channel switching during a call increases because the mobile station moves between wireless zones one after another during a call. As for the method of switching the in-call channel of the current Nippon Telegraph and Telephone Corporation's car telephone system, as described in detail on pages 197 to 200 of a car telephone (supervised by Moruji Kuwahara) published by the Institute of Electronics and Communication Engineers, Constantly monitors the reception level of the uplink speech channel from the mobile station, and when the reception level falls below the threshold value, the adjacent base station measures the uplink speech channel of this mobile station, and the radio network controller compares these measurement results. By doing so, the movement of the mobile station between the wireless zones is detected.

[Problems to be solved by the invention]

In the conventional method of switching channels during a call, the movement of the mobile station between the wireless zones is intensively detected by the base station and the radio network controller. Is increased, the control amount is increased locally, and a device having a large processing capacity is required.

An object of the present invention is to provide a method for channel switching during a call without locally concentrating a control amount, and a mobile terminal that realizes this method.

[Means for solving problems]

According to a first aspect of the present invention, there is provided a method of switching a channel during a call in a mobile communication system, wherein each radio base station transmits a signal including a flag indicating the presence / absence of an idle call channel, and a mobile terminal in a call uses a dedicated receiver. The wireless zone by receiving the signal transmitted from the wireless base station being connected by the wireless base station and the wireless base station adjacent to the wireless base station, and comparing the reception levels of the base stations having the idle communication channels based on the flag. It is configured by monitoring the movement between the terminals and transmitting a switching request signal when the movement is detected to switch the connection to the wireless base station of the moving destination having the idle speech channel.

A mobile terminal according to a second invention of the present application is a measuring device for measuring a reception level of a signal transmitted from a connected wireless base station and a wireless base station adjacent to the wireless base station, and an output of the level measuring device. The movement of wireless zones is monitored by comparing the contents of the memory with a memory that stores a flag indicating the presence or absence of an empty call channel included in the signal. And a control circuit for transmitting a switching request signal requesting switching to the destination wireless base station.

[Operation] If the base station side compares the received level of the mobile station's uplink signal to monitor the movement between wireless zones, multiple base stations are observed and these results are collected somewhere and compared. Therefore, the control amount locally increases as the switching frequency increases.

On the other hand, in the present invention, the mobile stations compare the reception levels of the downlink signals of the respective base stations to monitor the movement between the wireless zones to achieve decentralized control. Therefore, a dedicated measuring receiver is provided for receiving the downlink signal of another base station without disturbing the call. The downlink signal received by this receiver may be a communication channel, but a control channel that is constantly transmitted is preferable. If this control channel is common to all zones and is time-divisionally overlapped by each base station, there is no need to change the reception frequency of the receiver, and the device becomes simple. In addition, the base station transmits in advance a flag indicating the presence / absence of an idle call channel in the downlink signal, and the mobile station compares only the reception level of the downlink signal of the base station with the idle call channel based on this flag. As a result, it is possible to prevent a base station having no idle call channel from being selected as a switching destination. In this way, the mobile station monitors the movement between wireless zones during a call, and when it detects the movement, it transmits a switching request signal to switch to the movement-destination base station having an idle call channel. , It is possible to avoid local concentration of the control amount due to switching of channels during a call.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a method of switching channels during a call according to the present invention. Mobile communication system is exchange 1
0, the base station 20, and the mobile terminal 30. The N base stations communicate with the mobile terminal through their own communication channels and control channels. The downlink signal of each control channel includes a flag 40 indicating the presence / absence of an idle communication channel of the base station. If the flag 40 is, for example, "1", it indicates that there is a free call channel, and the flag
When 40 is "0", it indicates that there is no available communication channel. Frequencies are assigned to these speech channels and control channels so as not to interfere with each other. The first Figure, the frequency f _d to the downlink speech channel of the base station 3, the frequency f _u, also the downlink control channel to the uplink traffic channel and assigning reuse I number of frequency, the base station 2 , 3
And _I are assigned frequencies f ₁ , f ₂ , f ₃ and f I, respectively. The other frequency allocation is omitted. The mobile terminal 30 includes an antenna 31, a duplexer 32, a call transmitter 33, a call receiver 34, a measurement receiver 35, and a control circuit 36. The mobile terminal 30 includes a transmitter 33 for calling.
While talking with the nearest base station by the call receiver 34, the measurement receiver 35 receives the downlink control channel of each base station, that is, the frequencies f ₁ to f _I by switching them one after another, and based on the flag 40. Then, the movement between wireless zones is monitored by comparing the reception levels of base stations with idle communication channels. When the movement is detected, a switching request signal is transmitted on the uplink communication channel in order to inform the exchange of the movement-destination base station.

For example, the mobile terminal 30 connected to the base station 3 by the downlink call channel of the frequency f _d and the uplink call channel of the frequency f _u moves from the radio zone of the base station 3 to the radio zone of the base station 2 having an idle call channel. Consider the case. With the movement, the output of the measurement receiver 35 has the highest reception level of the frequency f ₂ instead of the frequency f ₃ . Control circuit 36
As a result of comparing the reception levels of the base stations having the idle communication channels based on the flag 40, knowing that the mobile station has moved to the wireless zone of the base station 2 and sends a switching request signal requesting the switching to the base station 2 to the upstream communication channel. Send with. The base station 3 receiving this signal reports it to the exchange 10. The switching center 10 selects an idle communication channel of the base station 2 and gives the number to the mobile terminal 30 via the base station 3. Mobile terminal
30 switches to the communication channel of the base station 2 according to this instruction. In this manner, by monitoring the movement between wireless zones on the mobile terminal side and decentralizing the control of channel switching during a call, it is possible to avoid local concentration of the control amount. In the present embodiment, different frequencies are assigned as control channels, but it is also possible to assign the same frequency by time division multiplexing. In this case, it is possible to eliminate the need to change the reception frequency of the measuring receiver.

FIG. 2 is a block diagram of an embodiment of the mobile terminal of the present invention. The mobile terminal includes an antenna 31, a duplexer 32, a mixer 331 and a modulator 332 that make up a call transmitter, a mixer 341 and a demodulator 342 that make up a call receiver, and a mixer 351 and demodulator that makes up a measurement receiver. It includes a device 352, a level measuring device 353 and an oscillator 350, an oscillator 330 for the mixers 331 and 341, a control circuit 36, and a telephone 37. The RF signal received by the antenna 31 is transmitted via the duplexer 32 to the mixer 34.
1 and distributed to mixer 351. Outgoing call channel RF
The signal is mixed with the output of oscillator 330 by mixer 341 and IF
After being converted into a signal, the call signal is demodulated by the demodulator 342 and sent to the telephone 37, and the control signal included in the call channel is sent to the control circuit 36. Further, the call signal output from the telephone 37 and the control signal output from the control circuit 36 are the modulator 332.
Is converted into an IF signal by the mixer 331, mixed with the output of the oscillator 330 by the mixer 331, and then transmitted from the antenna 31 as an RF signal of a communication channel via the duplexer 32. The modulation / demodulation method may be any method that is normally used, and will not be described in detail here. Further, one call channel may be assigned to one frequency, or a plurality of call channels may be assigned by time division multiplexing. On the other hand, the RF signal of the downlink control channel is transmitted to the oscillator 350 by the mixer 351.
Demodulator 352 and level measurer 3 after being mixed with the output of
Divided into 53. The output of the mixer 351 is demodulated by the demodulator 352 and sent to the control circuit 36 as a control signal including a base station identification code, a flag indicating the presence / absence of a free communication channel, and at the same time, its level is measured by the level measuring device 353. It is sent to the memory 354. The control circuit 36 changes the oscillation frequency of the oscillator 350 so that the downlink control channels of the respective base stations can be sequentially received. When the base station identification code in the output of the demodulator 352 is recognized, the level measuring device 353 at that time is detected.
And a flag indicating the presence / absence of an idle call channel are stored in the memory 354 for each base station identification code. Further, the control circuit 36 monitors the movement between the wireless zones by comparing the reception levels of the base stations having the idle call channels in the contents of the memory 354, and includes the identification code of the movement destination base station when the movement is detected. Send the switching request signal. Further, by storing a plurality of reception levels for each base station and comparing their average values, it is possible to reduce the influence of measurement errors due to fading. In this case, a flag indicating the presence / absence of a plurality of empty call channels is stored, but the reception levels may be compared based on the latest flag. By monitoring the movement between the wireless zones on the mobile station side in this manner, it is possible to avoid the concentration of the control amount due to the channel switching during a call.

〔The invention's effect〕

As described above, according to the present invention, there is an effect that it is possible to provide the in-call channel switching method and the mobile terminal of the mobile communication system in which the control amount hardly locally increases with the increase in the frequency of the in-call channel switching. .

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a channel switching method during a call of the present invention, and FIG. 2 is a block diagram showing an embodiment of a mobile terminal of the present invention. 20 ... Base station, 30 ... Mobile terminal, 36 ... Control circuit, 353
…… Level measuring instrument, 354 …… Memory.

Claims (2)

[Claims] 1. Each radio base station transmits a signal including a flag indicating the presence / absence of an idle call channel, and a mobile terminal in a call uses a dedicated receiver to connect with the radio base station and the radio base station. When the signal is transmitted from an adjacent wireless base station and the movement between wireless zones is monitored by comparing the reception levels of base stations having idle communication channels based on the flag, and movement is detected A method for switching channels during a call in a mobile communication system, comprising: transmitting a switching request signal to switch the connection to a destination wireless base station having an idle speech channel. 2. A measuring device for measuring a reception level of a signal transmitted from a connected wireless base station and a wireless base station adjacent to the wireless base station, and an output of the level measuring device and included in the signal. The movement of wireless zones is monitored by comparing the contents of the memory with a memory that stores a flag indicating the presence / absence of an empty call channel, and if movement is detected, the wireless base of the move destination that has an empty call channel A mobile terminal comprising: a control circuit that transmits a switching request signal that requests switching to a station.