JP3221575B2 - Mobile communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system for performing mutual communication between a mobile terminal and a centralized base station via a base station using a radio frequency signal. In particular, the present invention relates to a communication system in which a base station converts a wireless signal into an optical signal and transmits the optical signal to a centralized base station via an optical fiber. The present invention, when receiving radio signals at different frequencies at a base station from a plurality of mobile terminals,
The level difference between the wireless channels input to the transmitter in the base station, that is, the electric / optical conversion circuit is reduced to converge within the required dynamic range of the electric / optical conversion circuit.

[0002]

2. Description of the Related Art Conventionally, radio channel signals transmitted from mobile terminals in the same zone use the same frequency,
Some employ a time division multiplexing method (TDMA method). In this case, common amplification by frequency multiplexing was unnecessary, and there was no problem of cross-modulation due to nonlinearity, and the level difference between a plurality of channels did not matter.

[0003]

By employing a frequency division multiplexing (FDMA) system, a plurality of radio channel signals transmitted from mobile terminals in the same zone are simultaneously transmitted to a centralized base station using different frequencies by optical signals. , The allowable difference in the reception level between the radio channel signals is limited by the input dynamic range of the electric / optical conversion circuit. If the difference is too large, the communication quality deteriorates.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a mobile communication system capable of adjusting a level difference of a received radio signal input to an electric / optical conversion circuit and reducing a so-called dynamic range.

[0005]

SUMMARY OF THE INVENTION According to the present invention, different frequencies transmitted from a plurality of mobile terminals in the same radio zone are provided.
Receiving a plurality of radio channel signals, comprising: a base Chikyoku you sent to convert it into an optical signal, and a centralized base station for receiving and converting the optical signal transmitted from the base station to the radio frequency signals In the mobile communication system, the base station receives
A reception level detecting means for detecting their reception levels for a plurality of radio channel signals, the reception level detected by this reception level detecting means and level adjusting means for attenuating the level only for a radio channel signal exceeds a predetermined level It is characterized by having.

The reception level detection means inputs the output of the local oscillator whose frequency can be switched and the reception signal to a first mixer, and sweeps the frequency of the local oscillator to convert all the channel signals into one band. Circuit means for detecting a reception level by passing through a filter, wherein the level adjustment means includes a second mixer, a local oscillator whose frequency can be controlled, and a center frequency inserted into an output of the second mixer. The same band rejection filter and band pass filter are provided, and the center frequency of the channel of the radio channel signal exceeding a predetermined level by the reception level detecting means is made to match the center frequency of the band rejection filter and the band pass filter. Means for controlling the local oscillator to perform frequency conversion and attenuate the output of the band-pass filter. Door can be.

The level adjusting means includes a band rejection filter and a band pass filter to which a radio channel signal is applied, and a level attenuating means provided at a subsequent stage of the band pass filter. The signal band is variably controlled by the output of the means, and a radio channel signal exceeding a predetermined level can be provided from the band pass filter to the level attenuating means.

In addition, there is provided means for converting the frequency of the radio signal received by the base station into a plurality of groups according to the signal bands of the band rejection filter and the band pass filter provided in the level adjusting means. Receiving level detecting means and level adjusting means for each group, and the receiving level detecting means and the level adjusting means perform means for detecting the receiving level for each channel included in the group and performing level adjustment for each group. Can be included.

[0009]

In the base station, the level of the radio channel signal input to the electric / optical conversion circuit can be detected and the level difference can be reduced. Therefore, the required dynamic range of the electric / optical conversion circuit can be reduced, which leads to improvement in communication quality.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration of a communication system according to a first embodiment of the present invention. In the first embodiment, a description will be given of a configuration in which the centralized base station 18 and the base station 3 in the mobile communication system are connected by optical fibers 17 and 25 to perform signal transmission. Note that the centralized base station 1 is provided for each of a plurality of base stations, and in the description of this embodiment, only one is illustrated and described.

The base station 3 includes an antenna 4 for forming a wireless transmission path with a plurality of mobile terminals 2 in the wireless zone 1;
A transmission / reception separator 5, a reception level detection circuit 30 for detecting a reception level of a radio channel signal, and a level of a radio channel signal exceeding a reference value is attenuated based on a detection output of the reception level detection circuit 30 to reduce a level of a channel. A level adjusting circuit 29 for adjusting the level so as to reduce the level difference, an electrical / optical converting circuit 16 for performing electrical / optical conversion of an output of the level adjusting circuit 29 and transmitting the output to the centralized base station 18 via the optical fiber 17; An optical / electrical conversion circuit 24 for converting an optical signal transmitted from the centralized base station 18 through the optical fiber 25 into an electric signal.
And a mobile terminal 2 that amplifies the converted electric signal and transmits the amplified electric signal from the antenna 4 via the transmission / reception separator 5.

A feature of the present invention resides in a reception level detection circuit 3 for detecting the reception level of each radio channel signal.
Level adjustment circuit 2 for attenuating the level of a radio channel signal exceeding a reference value based on 0 and the output of reception level detection circuit 30 to adjust the level of the radio channel signal.
9 has been provided.

The configuration will be described in more detail. There is provided a duplexer 6 for splitting the wireless channel signal from the transmission / reception duplexer 5 to a level adjustment circuit 29 and a reception level detection circuit 30. The level adjustment circuit 29 includes a mixer 7 for converting the frequency of the wireless channel signal, a duplexer 8 for splitting the wireless signal output from the mixer 7, and a wireless signal output from the duplexer 8 that exceeds a reference value. A band rejection filter (BDF) 9 for blocking a channel signal of the received level, a low pass filter (LPF) 10 connected to the band rejection filter for blocking an image signal generated by the mixer 7, and output from the duplexer 8. Band-pass filter (BDF) 1 that passes a channel signal of a reception level exceeding a reference value among wireless signals
2. An attenuator 13 for attenuating the level of the channel signal exceeding the reference value, a combiner 14 for combining the output signals from the low-pass filter 10 and the attenuator 13, and an output signal of the combiner 14 is used as an original radio signal. A mixer 32 for converting the signal into a signal, a low-pass filter 33 for blocking an image signal generated by the mixer 32, and an automatic gain control for amplifying the output level of the low-pass filter 33 to a constant value and applying the output level to the electric / optical conversion circuit 16 A circuit (AGC) 15, a local oscillator 11 for supplying a radio frequency signal to the mixer 7 and the mixer 32, these two mixers 7,
A demultiplexer 39 for demultiplexing the output signal of the local oscillator 11 to 32
It has.

The reception level detection circuit 30 outputs a local oscillator 19 for extracting each channel, and a frequency control signal connected to the local oscillator 19 and a channel level circuit (LFD) 22 for sweeping the oscillation frequency. The output sweep control signal generator (SWP) 36 and the local oscillator 19
, And a band-pass filter 21 for extracting a band signal for one channel from the output of the mixer 20, and a channel output from the band-pass filter 21. A channel level detector (LFD) 2 for identifying a signal level and a frequency control signal from a sweep control signal generator (SWP) 36
2 is provided. The output of the channel level detector 22 is provided to the local oscillator 11 and the level attenuator 13 of the level adjustment circuit 29.

Next, the operation of the first embodiment of the present invention will be described.

First, the basic operation will be described. The reception signal output from the transmission / reception separator 5 is split by the splitter 6, and one output of the splitter 6 is input to the reception level detection circuit 30 and the other output is input to the level adjustment circuit 29. When a reception level exceeding the reference value is detected by the reception level detection circuit 30, the level of the channel signal exceeding the reference value is attenuated by the attenuator 13 by the level adjustment circuit 29 and input to the electrical / optical conversion circuit 16. The level difference between the radio channel signals.

Next, the operation of the reception level detection circuit 30 will be described. The received signal output from the duplexer 6 and the signal of the local oscillator 19 are mixed by the mixer 20 to convert the frequency of the received signal. At this time, the frequency of the output signal of the local oscillator 19 also changes due to the change in the output voltage of the sweep control signal generator 36. As the frequency of the mixer 20 changes, all channel signals are sequentially output from the bandpass filter 21. The channel level detector 22 identifies the frequency of the channel signal exceeding the reference value and its level from the control voltage value of the sweep control signal generator 36 and the output signal level of the band-pass filter 21. The frequency information of the channel signal exceeding the reference value is input from the channel level detector 22 to the local oscillator 11, and the level information is input to the attenuator 13.

The operation of the level adjustment circuit 29 will be described. The mixer 7 mixes the received signal output from the duplexer 6 and the signal of the local oscillator 11 from the duplexer 39, and converts the frequency of the received signal. The signal frequency of the local oscillator 11 is controlled by the channel level detector 22 so that the frequency of the output signal of the mixer 7 becomes the cut-off frequency band of the band rejection filter 9 and the pass frequency band of the band-pass filter 12. The output of the mixer 7 is split by the splitter 8 and input to the band-elimination filter 9 and the band-pass filter 12. The channel signal exceeding the reference value is extracted using the band-pass filter 12, and the attenuation of the attenuator 13 is adjusted by controlling the channel level detector 22 so that the level of the channel signal falls within the reference value. Further, the output of the band rejection filter 9 for blocking a channel signal having a reception level exceeding the reference value is input to the low-pass filter 10, and the image signal generated by the mixer 7 is blocked. The output of the attenuator 13 and the output of the low-pass filter 10 are multiplexed by the coupler 14, and
9 together with the signal of the local oscillator 11 from the mixer 9. The output of the mixer 32 is input to the low-pass filter 33, and the image signal generated by the mixer 32 and the duplexer 39
Block the signal from After inputting the output of the low-pass filter 33 to the AGC 15 and adjusting the level, the output signal is converted into an optical signal by the electric / optical conversion circuit 16 and transmitted to the centralized base station 18.

FIG. 2 shows the operation principle of this embodiment. The upper part shows the level of the radio signal input to the duplexer 6, and the lower part shows the level of the radio signal output from the coupler 14. When this method is not used, the required dynamic range of the electrical / optical conversion circuit 16 is determined by CH7 and CH10 at the time of input to the duplexer 6 shown in the upper part. When this method is used, the required dynamic range of the electrical / optical conversion circuit 16 is, as shown in the lower part, the CH7 attenuated to the reference level reception level.
And CH10, the dynamic range is reduced from the required dynamic range when the present method shown in the upper part is not used.

FIG. 3 shows the structure of a second embodiment of the present invention. In the second embodiment, as compared with the first embodiment shown in FIG. 1, in the base station 3, the reception level detection circuit 30 and the level adjustment circuit 29 are provided in a plurality of groups each including several channels of radio channel signals. There are different points.

The operation will be described. A plurality of bandpass filters 27 to 28 having different center frequencies are used to split a radio channel signal having a different frequency into a group including a plurality of adjacent channels. Each band pass filter 27-
The wireless channel signals output from the controller 28 are input to the respective reception level detection circuits 30, and the reception levels of the respective channel signals are detected. If the level exceeds the reference value, each level adjusting circuit 29 sets a channel exceeding the reference value.
The signal level is attenuated by the attenuator 13. In this method, level adjustment is performed on a channel signal exceeding a reference value in each channel group, and if there is a radio signal exceeding the reference value in another channel group, the dynamic range of the received signal level is set to the first level. It is better in that it is smaller than the examples.

FIG. 4 shows the configuration of a third embodiment of the present invention. The third embodiment differs from the first embodiment shown in FIG. 1 in that a branching filter 45 is used in place of the mixer 32 in the base station 3, and the centralized base station has the frequency converted by the mixer 7 as it is. The point of transmission to the station 18 and the centralized base station 1
8, the point at which the radio signal is reconverted to the frequency at the time of the output of the duplexer 6 using the duplexer 41, the low-pass filter 42, the high-pass filter 43, the mixer 35, the amplifier 44, and the band-pass filter 37. Are different.

The operation of the level adjusting circuit 29 and the centralized base station 18 different from the first embodiment of the second embodiment will be described. The frequency conversion in the mixer 7 is determined by the frequency of the output signal of the local oscillator 11. The output signal of the local oscillator 11 is input from the demultiplexer 39 to the coupler 45, and transmitted to the centralized base station 18 together with the radio channel signal. Local oscillator 1
The frequency of the first output signal uses a frequency band different from the radio frequency of the output of the coupler 14. In the centralized base station 18, the low-pass filter 4
In step 2, the output signal of the duplexer 14 is extracted, and in the high-pass filter 43, the output signal of the local oscillator 11 is extracted. After the output signal of the high-pass filter 43 is input to the amplifier 44 and amplified, the output is input to the mixer 35 together with the output signal of the low-pass filter 42. The mixer 35 converts the output signal of the low-pass filter 42 into the output signal frequency of the duplexer 6 again. The band pass filter 37 is used to cut off the image signal generated by the mixer 35 and the output signal of the amplifier 44.

FIG. 5 shows the configuration of the fourth embodiment of the present invention. The fourth embodiment is different from the first embodiment shown in FIG. 1 in that a filter capable of changing the signal band is used as the band rejection filter 9 and the band pass filter 12 in the level adjustment circuit 29. The difference is that the signal band can be changed and a channel signal exceeding a reference value can be extracted. In this case, the local oscillator 11, the mixers 7, 32, and the low-pass filters 10, 33 can be omitted as compared with the first embodiment.

[0026]

As described above, according to the present invention, when a base station receives radio channel signals having different frequencies from a plurality of mobile terminals, if the level of each channel signal exceeds a reference value, The level of the channel is attenuated by the adjustment circuit. As a result, the level difference between the radio channel signals is reduced, and it is possible to converge within the dynamic range of the electrical / optical conversion circuit. In a mobile communication system using a plurality of mobile terminals, higher communication quality can be achieved. Can be secured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is an operation principle diagram of the first embodiment.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a third embodiment of the present invention.

FIG. 5 is a configuration diagram of a fourth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 wireless zone 2 mobile terminal 3 base station 4 antenna 5 transmission / reception separator 6, 8, 14, 26, 38, 39, 41 duplexer 7, 20, 32, 35 mixer 9 band rejection filter 10, 33, 42 low Band-pass filter 11, 19 Local oscillator 12, 21, 27, 28, 37 Band-pass filter 13 Attenuator 14, 31, 46 Coupler 15 Automatic gain control circuit 16 Electric / optical conversion circuit 17, 25 Optical fiber 18 Centralized base station Reference Signs List 22 channel level detector 23, 44 amplifier 24 optical / electrical conversion circuit 29 level adjustment circuit 30 reception level detection circuit 36 sweep control signal generator 43 high-pass filter

────────────────────────────────────────────────── ─── Continued on the front page Examiner Ken Aoki (56) References JP-A-4-124919 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04Q 7/00-7 / 38 H04B 7/24-7/26

Claims (4)

(57) [Claims] 1. A receives a plurality of radio channel signals having different transmitted frequencies from the same plurality of mobile terminals in a wireless zone, a group Chikyoku sent and converts it into an optical signal, the base station received level in a mobile communication system that includes a centralized base station for converting a radio frequency signal by receiving an optical signal transmitted, which in the base station, detects their reception levels for a plurality of radio channel signals received from A mobile communication system comprising: a detection unit; and a level adjustment unit that attenuates only a radio channel signal whose reception level detected by the reception level detection unit exceeds a predetermined level. 2. The reception level detection means inputs a local oscillator output whose frequency can be switched and a reception signal to a first mixer, and sweeps the frequency of the local oscillator to convert all channel signals into one band. Circuit means for detecting a reception level by passing through a filter, wherein the level adjustment means comprises a second mixer, a local oscillator whose frequency can be controlled, and a center frequency inserted into an output of the second mixer. The same band rejection filter and band pass filter are provided, and the center frequency of the channel of the radio channel signal exceeding a predetermined level by the reception level detecting means is made to match the center frequency of the band rejection filter and the center frequency of the band pass filter. Means for controlling the local oscillator to perform frequency conversion and attenuate the output of the band-pass filter. Item 1. The mobile communication method according to Item 1. 3. The level adjusting means includes a band rejection filter and a band pass filter to which a radio channel signal is supplied, and a level attenuating means provided at a subsequent stage of the band pass filter. The band rejection filter and the band pass filter detect a reception level. The signal band is variably controlled by an output of the means, and a radio channel signal exceeding a predetermined level is supplied from the band-pass filter to the level attenuating means.
Mobile communication system as described. 4. A means for converting the frequency of a radio signal received by a base station into a plurality of groups in accordance with a signal band of a band rejection filter and a band pass filter provided in a level adjusting means, The reception level detection means and the level adjustment means are provided for each group of
2. The mobile communication system according to claim 1, further comprising means for detecting a reception level of each channel included in the group and adjusting a level.