JPH0573297B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a digital mobile communication system composed of a large number of small zones and a mobile terminal that implements the system.

(Prior Art) A small zone mobile communication system, a so-called cellular system, is used in car telephone systems around the world as a system with high frequency utilization efficiency. Demand for car phones is growing rapidly, and a serious frequency shortage is expected in the near future. In order to fundamentally solve this frequency shortage, it is necessary to reduce the size of the zone and spatially reuse the same frequency many times. For example, if the radius of the zone is reduced to 1/10, the frequency usage efficiency will be increased by 100 times. When the zone radius is greatly reduced in this way, the frequency of zone switching, which occurs when a mobile object moves to another zone during a call, increases significantly, so the method of zone switching becomes a serious problem. In the current NTT car telephone system, the base station monitors the strength of radio waves received by mobile terminals and sends a switching request signal to the exchange when the radio waves become weak. The details of this system are described in detail on pages 197 to 200 of the book "Car Telephone" published by the Institute of Electronics and Telegraph Engineers in 1985. In this conventional small zone mobile communication system, the strength of received radio waves in surrounding zones is measured based on commands from the exchange, and a continuity test is performed after switching to the strongest zone, so there is a momentary interruption of voice for approximately 0.8 seconds each time the switch is made. arise.

(Problems to be Solved by the Invention) Therefore, in the conventional zone switching method, when the zone size is reduced, the speech quality is significantly degraded. Another point that cannot be overlooked is that reducing the zone size significantly increases the throughput of the exchange for zone switching.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a digital mobile communication system in which there is almost no momentary interruption and in which the load on switching equipment does not increase significantly, except for the drawbacks of the conventional zone switching method described above, and a mobile terminal that realizes the same. .

(Means for Solving the Problems) The digital mobile communication system of the first invention of the present application has a communication channel that performs time division multiplexing to accommodate a plurality of voice channels, and a common communication channel that is used by a plurality of zones in a time division manner. Each mobile terminal uses free time during a call to observe the common control channel, and if a base station with better conditions than the base station being used is found, it switches to the base station. It is characterized by transmitting a request signal.

Further, the mobile terminal of the digital mobile communication system provided by the second invention of the present application has a communication circuit that communicates using a specific slot of a time-division multiplexed communication channel, and an idle time when the communication circuit is not used. channel switching means for switching frequencies to connect to a time-division multiplexed common control channel; base station selection means for selecting an optimal base station from received signals of each of the common control channels; The present invention is characterized by comprising zone control means that performs a zone switching procedure when the output of the means differs from that of the base station in use.

(Function) When performing zone switching, if the base station tries to take the initiative, multiple base stations will have to investigate unless there is information about the direction in which the mobile terminal is moving, making control difficult. becomes complex. In contrast, the present invention uses a method in which the mobile terminal observes the strength of the received radio waves and always selects the best base station. In order to observe radio waves from other base stations during communication, multiple channels are time-division multiplexed, and there must be free time even during a call. Also, to facilitate observation, the control channel must be common to all zones and time-division multiplexed. With such a system configuration, the terminal can observe the control channel using the idle time of the call, and the terminal can oscillate a control signal to connect to the base station where the strongest radio waves are observed. . In this way, you can prepare for zone switching while talking, and the burden on the exchange will be reduced.

(Example) Next, the present invention will be described in more detail with reference to the drawings.

FIG. 2 shows an example of the channel and frame configuration of the digital mobile communication system of the present invention. There are multiple call channels in Figure 2 a, each with 8 channels.
The channels are time division multiplexed. Also the second
The control channel in Figure b is time division multiplexed with nine base stations. The reason why the multiplicity, that is, the frame length, of the communication channel and the control channel is different is that even if the control channel is observed in synchronization with the communication channel, all control channels can be observed by observing multiple frames. be. An example of the operation of the terminal is shown in FIG. 2c. Channel (CH) 1
A call is being made by receiving on channel 2 and transmitting on channel 2, and the control channel is received at a timing corresponding to channel 3. At the frame timing shown in FIG. 2, B3 is received on the control channel, but in the next frame B2 is received, and then B1 is received. In this way, in this embodiment, different control channels are received for each frame, so all control channels can be observed in nine frames.

FIG. 1 specifically shows an example of a control procedure when switching base stations. Assume that the terminal is currently talking to base station 1. The terminal monitors the control channel during a call, and the control signal from base station 2 is higher than that from base station 1.
When the signal becomes stronger than that of the base station 2, the terminal transmits a connection request signal to the base station 2. The base station 2 specifies a communication channel for this. The terminal sends a test signal to this channel. If this test signal is correctly received by the base station 2, the base station 2 returns a test OK signal. All of these interactions take place during free time on the phone. Since the test result was OK, the terminal transmits a switching request signal to base station 1. The base station 1 reports this to the exchange and transmits a switching instruction to the terminal in accordance with the switching instruction from the exchange. At this point, the terminal switches the communication channel to that of the base station 2 for the first time. By doing this, the zone can be switched without momentary interruption of the call.

FIG. 3 shows an embodiment of a mobile terminal according to the present invention. Reference numeral 10 represents channel switching means, reference numeral 20 represents a communication circuit, reference numeral 30 represents base station selection means, and reference numeral 40 represents zone control means. The zone control means 40 is realized by a microprocessor and controls the entire circuit. The time division signal received from the antenna 100 is sent to the mixer 11 via the hybrid circuit 70.
After being converted into an IF signal and demodulated by a demodulator 50,
The signal is converted into an audio signal by the time division multiplexed signal receiving circuit 21 and output from the terminal 101. One terminal 102
The audio signal input from
0, converted to an RF signal by the mixer 12, and transmitted from the antenna 100 via the hybrid 70. The time division multiplexing method and modulation/demodulation method may be any commonly used method, and will not be described in detail here. When the reception slot is completed, the synthesizer 13 changes its oscillation frequency according to instructions from the microprocessor 40 so that it can receive the control channel signal. This signal is detected by a power detector 31 and integrated for one slot to obtain the average power, which is then sent to the microprocessor 40.
The signal is inputted to the maximum value detection circuit 33 via the gate circuit 32, which opens at a good timing in response to the instruction. The maximum value detection circuit compares the average received power of each control channel and outputs to the microprocessor 40 the number of the channel that provides the maximum average received power. If the base station that gave the maximum received power is different from the base station in use, the microprocessor 40 transmits a connection request signal to an empty slot via the adder 41 and starts the zone switching procedure described above. do.

In this example, a control method is shown in which the base station that provides the maximum received power is selected, but in order to prevent the frequency of zone switching from increasing too much, signals from base stations other than those that are currently in a call will be sent to the base station that is not currently in a call. Of course, it is also possible to prevent switching unless the signal is greater than a certain value than the signal from the base station. Furthermore, as long as the zone switching procedure is such that the terminal takes the initiative and sends a switching request to the base station, almost the same effect as this embodiment can be obtained no matter what the subsequent procedure is. is clear.

(Effect of the invention) As described in detail above, according to the present invention,
It is possible to provide a digital mobile communication system and a mobile terminal in which there are almost no instantaneous interruptions due to zone switching and the load on switching equipment is small.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a procedure for a zone switching method in a digital mobile communication system of the present invention, FIG. 2 is a diagram showing an example of a channel configuration of the present invention, and FIG. 3 is an example of an implementation of a mobile terminal of the present invention. It is a figure which shows an example. In the figure, reference numeral 10 is a channel switching means, 20 is a communication circuit, 30 is a base station selection means,
40 indicates zone control means, respectively.

Claims (1)

[Claims] 1. A call channel that performs time division multiplexing to accommodate a plurality of audio channels, and a common control channel that is used by a plurality of zones in a time division manner. The digital mobile communication system is characterized in that it continues to observe the common control channel by using the above, and if a base station with better conditions than the base station in use is found, it transmits a switching request signal to the base station. 2. In a mobile terminal of a digital mobile communication system, there is a communication circuit that communicates using a specific slot of a time-division multiplexed communication channel, and a communication circuit that performs time-division multiplexing by switching frequencies during free time when the communication circuit is not in use. channel switching means for connecting to a common control channel that has been accessed; base station selection means for selecting an optimal base station from received signals of each channel of the common control channel; A mobile terminal comprising zone control means for performing a zone switching procedure when the station is different from the station.