JPS5830242A - Mobile radio communication system - Google Patents

Abstract

PURPOSE:To prevent deterioration of a quality of communication, by constituting so that local oscillation frequency of a base station device follows transmission frequency of a mobile terminal machine. CONSTITUTION:A signal received by an antenna 7 passes through a sharing device 6 and an amplifier 8, and after that, is mixed with the first local oscillation frequency outputted from a voltage control oscillator 13, by the first receiving frequency converter 9, is converted to the first intermediate frequency, and after that, is demodulated by a receiving circuit 10, and is sent to a receiver 11. As for an output of an intermediate frequency amplifier of the circuit 10, a variation of its frequency is detected by a frequency discriminator 12, and it is supplied to the oscillator 13. That is to say, an automatic frequency controlling circuit of receiving frequency which follows the transmission frequency of the terminal machine is constituted of the discriminator 12 and the oscillator 13.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a system for performing duplex communication between a mobile terminal and a base station device, and particularly relates to a system that performs duplex communication between a mobile terminal and a base station, and particularly relates to a method that causes drift in the local oscillation frequency of the mobile terminal. The present invention also relates to a mobile radio communication system that does not cause deterioration in communication quality.

2. Description of the Related Art In radio equipment used in mobile radio communication such as a car telephone, a local oscillator in a transmitter and a local oscillator in a receiver are usually shared, as shown in FIG. 1, for example. That is, the transmitter 1
The signal obtained by modulating the audio signal from the modulator 2 is mixed with the first local oscillation frequency from the reference oscillator 4 in the transmission frequency converter 3 and converted to a desired transmission frequency, and then the signal is mixed with the first local oscillation frequency from the reference oscillator 4 and converted to a desired transmission frequency. The signal is transmitted to the antenna 1 via the receiver 6. On the other hand, the signal received by the antenna 1 passes through a duplexer 6 and a low noise amplifier 8, and then passes through a first receiving frequency converter 9.
It is mixed with the first local oscillation frequency output from the reference oscillator 4 and converted into a first intermediate frequency, and then demodulated by the receiving circuit 10 comprising an intermediate frequency amplifier, a second intermediate frequency stage, and a demodulator. and is sent to the receiver 11.

If such a front radio device is installed on the mobile terminal side and the base station side and used facing each other, communication can be performed between the mobile terminal and the base station device using a duplex method.

By the way, the stability of the transmission frequency of this type of wireless TA is
Since the output signal frequency of the modulator 1 is extremely lower than the first local oscillation frequency from the reference oscillator 4, it is determined approximately by that of the first local oscillation frequency. Therefore, if a frequency drift occurs in the reference oscillator 4 of at least one of the mobile terminal and the base station, and the first local oscillation frequencies of both vary relatively, many of the mobile terminal and base station will receive the first local oscillator. 1. The intermediate frequency fluctuates, leading to a decrease in sensitivity and an increase in distortion, resulting in problems such as deterioration of communication quality.

Conventionally, therefore, a temperature-controlled crystal oscillator, a temperature-compensated crystal oscillator, or the like is used as the reference oscillator 4 to stabilize the first local oscillation frequency. However, when an extremely high frequency range signal is used, such as in mobile radio communications, the absolute value of the frequency drift becomes extremely large, so the above method cannot provide sufficient stability. Further, providing such a special oscillator as described above makes the structure of the radio complicated and large, and in particular, installing it in a mobile terminal makes it inconvenient to carry, which is not desirable.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to make the local oscillation frequency of the base station device follow the transmission frequency of the mobile terminal, thereby eliminating the problem caused by the frequency drift of the reference oscillator. An object of the present invention is to provide a mobile radio communication system that prevents deterioration of communication quality by preventing fluctuations in the intermediate frequency of a received signal and that prevents at least the configuration of a mobile terminal from becoming complicated and large.

An embodiment of the present invention will be described below with reference to FIG.

FIG. 2 is a block configuration diagram showing a radio device of a base station apparatus to which the mobile radio communication system in the same embodiment is applied. Note that since the mobile terminal has the same configuration as that shown in FIG. 1, a description thereof will be omitted here. Also, in the configuration of FIG. 2, the same parts as in FIG. 1 are given the same reference numerals.

In FIG. 2, the output of an intermediate frequency amplifier (not shown) of the receiving circuit 10 has a frequency variation detected by a frequency discriminator 12 and is supplied to a voltage controlled oscillator IS. This voltage controlled oscillator 13 acts as a reference oscillator and supplies its output frequency and the tb first local oscillation frequency to the transmitting frequency converter 1 and the first receiving frequency converter 9. That is, the frequency discriminator 12 and the voltage controlled oscillator 13 constitute an automatic frequency control circuit for the reception frequency that follows the transmission frequency of the mobile terminal.

With such a configuration, even if a frequency drift occurs in the reference oscillator 4 of the mobile terminal, the oscillation frequency of the voltage controlled oscillator 13 changes to follow the fluctuation in the transmission frequency, and as a result, the first reception The output of the frequency converter 9 always has a constant frequency. On the other hand, due to the change in the oscillation frequency of the voltage controlled oscillator 13, the transmission frequency sent to the mobile terminal also changes, but this change in frequency is only due to the change in the oscillation frequency in the reference oscillator 4 of the mobile terminal. Since the frequency is followed, the first intermediate frequency in the mobile terminal that receives and converts the transmission frequency is also always constant. The first intermediate frequencies of the terminal, mobile terminal, and base station device are always controlled to be constant.

As described above, according to this embodiment in which the first local oscillation frequency in the base station device is changed to follow the transmission frequency of the mobile terminal, stable mobile communication can be achieved without quality deterioration due to frequency drift. I can do things like that. In addition, since the mobile terminal does not have any special oscillators or new additional circuits as in the past, the configuration does not become complicated or large, which makes it inconvenient to carry.
Alternatively, the disadvantage of shortening battery life due to increased power consumption does not occur.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, the transmission frequency is obtained by shifting the oscillation frequency of the modulator 2, but it is not necessarily limited to this configuration.
may be deleted, the transmission frequency converter 3 is replaced with a phase modulator, and the output frequency of the reference oscillator 4 is phase-modulated by the audio signal from the transmitter 1 using the phase modulator. Furthermore, the automatic frequency control circuit does not have to be configured to simply control the oscillation frequency of the voltage-controlled oscillator 13 using the output voltage of the frequency discriminator 12; for example, a control circuit for a microconbeater may be provided, and this control circuit may be used. Complex controls such as searching for a transmission frequency from a mobile terminal and measures against instantaneous interruptions in transmission signals may be performed at the same time. This allows the automatic frequency control operation to be more complete. As a result, the configuration of the automatic frequency control circuit becomes somewhat complicated, but this is only within the base station apparatus and does not affect the configuration of the mobile terminal in any way. Further, in the embodiment described above, the output of the intermediate frequency amplifier of the receiving circuit 10 is guided to the newly provided frequency discriminator 12 to control the voltage controlled oscillator 13, but in the case of the angle modulation method, the receiving circuit 10 The stain pressure control oscillator may be controlled by the output of a frequency discrimination circuit for demodulation provided inside.

[Brief explanation of the drawing]

11. A block diagram showing the configuration of a conventional radio device. FIG. 2 is a block diagram showing a radio device of a base station device to which a mobile radio communication system is applied in an embodiment of the present invention. 3... Transmission frequency converter, 4... Reference oscillator, 9...
...First reception frequency converter, 1o...Reception circuit, 12
...Frequency discriminator, 13...Voltage controlled oscillator.

Claims (1)

[Claims] In a mobile radio system where communication is carried out using a duplex method between a mobile terminal and a base station device that share the same local oscillation frequency for transmission and reception, the base station device receives the frequency of the transmission signal from the mobile terminal. A mobile radio communication system characterized by having an automatic frequency control circuit that monitors the local oscillation frequency and controls the local oscillation frequency according to the frequency.