JPH05347580A - Mobile communication system - Google Patents

Abstract

PURPOSE:To provide a mobile communication system which can prevent such a case where the amplifier of a base station is saturated when the received signals of different frequencies are amplified in common by the amplifier. CONSTITUTION:The signals of different frequencies which are used for communication of many mobile stations 4 included in a radio wave area of a base station 1 are divided into a 1st signal group of the frequency which is usually used and a 2nd signal group of the frequency which is not usually used. Then the 1st signal group is amplified by a 1st amplifier 13 of the receiver side, and the 2nd signal group is amplified by a 2nd amplifier 14 of the smaller gain than the amplifier 13. These amplified signal groups are synthesized together and these synthetic signals of different frequencies are received by a controller 3 via a MODEM device 2. The levels of the received signals are individually detected. When the detected levels exceed a certain reference level, an instruction is given to the station 4 that is transmitting the signal of the frequency higher than the reference level. Thus the instructed station 4 switches its using frequency to another that is not usually used.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to mobile communication systems. With the recent increase in demand for mobile stations such as mobile phones and car phones, it has become necessary to install a large number of base stations for controlling the mobile stations.

Since the base station is installed in a limited place such as on the roof of a building, its size must be minimized. However, since the base station must be provided with a transmitter / receiver having amplifiers for transmission and reception for each communication channel, if the number of channels handled by the base station is large, the number of amplifiers increases and the overall size increases.

Therefore, it is desired to downsize the base station by using a transmission / reception apparatus capable of properly amplifying transmission / reception signals of a large number of channels with one amplifier for each of transmission and reception by frequency division multiplexing or time division multiplexing technology. ing.

[0004]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional mobile communication system. In this figure, 1a to 1n are a plurality of transmission / reception devices. Each of the transmission / reception devices 1a to 1n is installed as a base station on the rooftop of a building or the like, and is connected to the modem device 2 and the control device 3 of the main station by a cable, and a large number of mobile stations within its own radio area It communicates with 4a-4m.

This communication is performed by frequency division multiplexing for dividing and multiplexing the frequencies of the communication signals of the respective communication channels which differ depending on the mobile stations 4a to 4m. After the transmission signals of different frequencies of the respective channels sent from the control device 3 are modulated by the modulation / demodulation device 2, they are commonly amplified by the transmission side amplifier 5a of the transmission / reception device 1a and transmitted by the antenna 6a. The transmission signal of each channel transmitted by this radio wave is
The signal is received by the mobile station 4a to which the corresponding frequency within the radio wave area of the transmitter / receiver 1a is assigned.

On the other hand, the radio wave signals transmitted from a large number of mobile stations 4a within the radio wave area of the transmitter / receiver 1a are transmitted to the antenna 7
received by a. The reception signals having different frequencies are commonly amplified by the reception-side amplifier 8a, demodulated by the modulator / demodulator 2 and sent to the controller 3.

The transmitter / receiver 1n of another base station communicates with the mobile stations 4m within its own radio wave area in the same manner.

[0008]

By the way, in the system in which the transmission / reception signals of channels having different frequencies are amplified by one transmission / reception amplifier as described above, the distance between each mobile station and the base station is different. The electric field levels of the signals are different.

That is, the signal from the mobile station close to the base station is
Since the level is large, when the signal is received and amplified, the amplifier is saturated and a harmonic is generated, which affects the signals of other channels, and there is a problem that proper communication cannot be performed.

The present invention has been made in view of the above point, and it is possible to prevent the amplifiers from being saturated when the received signals of different frequencies are commonly amplified by the amplifiers of the base station. It is intended to provide a mobile communication system.

[0011]

[MEANS FOR SOLVING THE PROBLEMS] A base station wiredly connected to a main station that controls communication and a large number of mobile stations within a radio area of the base station transmit and receive signals of different frequencies. In a mobile communication system in which a single amplifier performs common amplification for communication, a plurality of mobile stations communicate signals of different frequencies with a first signal group of frequencies normally used and a frequency of frequencies not normally used. Branching means for branching into a second signal group, and a receiving-side first for amplifying the first signal group
The base station is provided with an amplifier, a second amplifier on the reception side that has a gain smaller than that of the first amplifier and that amplifies the second signal group, and a combining unit that combines the signals output from the first and second amplifiers. , Receiving signals of a large number of different frequencies output from the synthesizing means via a modulator / demodulator, individually detecting the levels of the received signals, and when the detected levels are above a certain reference level, The main station is provided with a control device for instructing a mobile station that is transmitting a signal having a frequency higher than the reference level to switch the currently used frequency to the frequency that is not normally used.

The reference level is preferably a signal level output when the first amplifier is in a saturated state.

[0013]

According to the present invention described above, when the control device provided in the main station detects a signal having a level higher than the reference level, the mobile station communicating with the frequency of the detected signal is An instruction is given to switch the currently used frequency to a frequency that is not normally used, and the mobile station switches the frequency according to this instruction.

Since the mobile station communicates with a signal of a frequency that is not normally used, the signal of that frequency is amplified by the second amplifier via the branching means of the base station. In the case of a signal having a frequency higher than the reference level, the first amplifier is saturated and a harmonic is generated, which affects signals of other frequencies. However, in the invention, the first amplifier is switched by switching the frequency as described above. Second gain with a smaller gain
Since it is amplified by the amplifier, the amplification at this time does not result in a saturated state unlike the first amplifier.

That is, since the saturation state of the amplifier can be prevented, as described above, the amplifier enters the saturation state and harmonics are generated, so that signals of other frequencies are not affected.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a mobile communication system according to an embodiment of the present invention. In this figure
The same reference numerals are given to the portions corresponding to the respective portions of the conventional example shown in, and the description thereof will be omitted.

However, although a plurality of base stations are hard-wired to the main station as described in the conventional example, in FIG.
Only one base station is shown. The transmitter / receiver 1 serving as a base station shown in FIG. 1 includes a transmitter-side amplifier 5, a transmitter antenna 6, a receiver antenna 7, hybrid circuits 11 and 12, and receiver-side first and second amplifiers 13 and 14. It is configured to include.

The first amplifier 13 has a larger gain than the second amplifier 14, and for example, the first amplifier 13 is provided.
, The gain of the second amplifier 14 is 5 to 1
It is set to 0 times.

The first amplifier 13 has a frequency f of the signal frequencies f _{1 to} f _z of the respective speech channels shown in FIG.
It is intended for amplifying the received signal of ₁ ~f _m, the second amplifier 14 amplifies the received signal in the frequency f _n ~f _z.

[0020] From a number of mobile stations 4 within the same area, each because radio signals of different frequencies f ₁ ~f _z is sent, they were received by the antenna 7, the frequency f ₁ in the hybrid circuit 11 ~f The signal of _{m and} the signals of frequencies f _{n to} f _z are branched into groups, and the branched frequencies f ₁
~ F _m signal is amplified by the first amplifier 13, frequency f _n ~
The signal of f _z is amplified by the second amplifier 14.

The signals amplified by the first and second amplifiers 13 and 14 are combined in the hybrid circuit 12 and transmitted to the controller 3 via the modulator / demodulator 2.

Signals of channels of frequencies f _{1 to} f _m are used for normal communication, and signals of frequencies f _{n to} f _z are idle channels. Further, the control device 3 constantly detects the level of each received signal sent via the modulation / demodulation device 2, and when the detected level becomes equal to or higher than the reference level, the frequency which becomes equal to or higher than the reference level. It also has a function of outputting a control signal for instructing the mobile station 4 communicating with the channel to switch to the idle channel.

However, the reference level is a signal level output when the first amplifier 13 for amplifying the signals of the frequencies f _{1 to} f _m used for normal communication is saturated.

In such a configuration, it is assumed that the control device 3 detects a signal having a reference level or higher. As shown in FIG. 3, it is assumed that the detected signal is a signal of frequency f _g among frequencies f _{1 to} f _m used for normal communication.

In this case, after the control signal for switching from the control device 3 to one of the frequencies f _{n to} f _z of the empty channels is sent to the transmission side amplifier 5 of the transmission / reception device 1 via the modulation / demodulation device 2, and is amplified. A radio wave is transmitted from the antenna 6.
When the control signal transmitted by radio waves is received by the corresponding mobile station 4, the mobile station 4 switches to the frequency of the idle channel designated by the control signal. For example, assume that the frequency is switched to the frequency f _{p as} shown in FIG.

By this switching, the mobile station 4 has the frequency f.
Communication will be performed with the signal of _p . The signal of the frequency f _p , which was an empty channel, is input to the second amplifier 14 via the hybrid circuit 11 of the transmission / reception device 1 and amplified.

Since the gain of the second amplifier 14 is considerably smaller than that of the first amplifier 13, in the amplification at this time,
It does not become saturated like the amplifier 13. That is,
As in the conventional case, when a high level signal is received from the mobile station 4 close to the transmitter / receiver 1, the amplifier on the receiving side is saturated and a harmonic is generated, which affects the signals of other channels, It will not happen that proper communication cannot be performed.

[0028]

As described above, according to the present invention,
Since it is possible to prevent the amplifier from becoming saturated when the received signals of different frequencies are commonly amplified by the amplifier of the base station, the amplifier becomes saturated and harmonics are generated. There is an effect that proper communication can be performed without affecting the communication.

[Brief description of drawings]

FIG. 1 is a block diagram of a mobile communication system according to an embodiment of the present invention.

FIG. 2 is a frequency spectrum diagram of each signal amplified by the first and second amplifiers on the receiving side shown in FIG.

FIG. 3 is a diagram for explaining a communication frequency switching operation between a base station and a mobile station shown in FIG.

FIG. 4 is a block diagram of a conventional mobile communication system.

[Explanation of symbols]

 2 modulator / demodulator 3 controller 4 mobile station 11 branching means 12 combining means 13 first amplifier 14 second amplifier

Claims (2)

[Claims] 1. An amplifier for transmitting and receiving signals of different frequencies, which are communicated between a base station hard-wired to a main station that controls communication and a large number of mobile stations within the radio area of the base station. In a mobile communication system in which communication is performed by commonly amplifying with a plurality of mobile stations, a plurality of mobile stations perform communication with signals of different frequencies, a first signal group of frequencies normally used and a second signal group of frequencies not normally used. Branching means (11) for branching to, a first amplifier (13) on the receiving side for amplifying the first signal group, and a second signal group having a gain smaller than that of the first amplifier (13). The base station is provided with a second amplifier (14) on the receiving side for amplification and a synthesizing means (12) for synthesizing the signals output from the first and second amplifiers (13, 14). ), The signals of a large number of different frequencies are received via the modulator / demodulator (2). Detected signal level individually, and when this detected level exceeds a certain reference level, the frequency currently in use is sent to the mobile station transmitting the signal of the frequency above the reference level. A mobile communication system characterized in that a control device (3) for instructing switching to a frequency not normally used is provided in a main station. 2. The reference level is set to the first amplifier (13).
The mobile communication system according to claim 1, wherein the signal level is output when the signal is saturated.