JPH08280062A - Mobile communication system - Google Patents

Abstract

PURPOSE: To improve distortion characteristics on an optical transmission line which connects a radio base station to a centralized control station. CONSTITUTION: Plural radio base stations 3 provided with radio function are connected to the centralized control station 4 provided with the modulating/ demodulating function of a signal communicated between the plural radio base stations 3 and mobile terminal machines by the optical transmission line 26. In such a case, a reception signal from the mobile terminal machine is converted to an intermediate frequency by a frequency conversion means 37, and it is synthesized with an auxiliary signal S1 of frequency at a fixed level outputted from an oscillation means 39 and other than a system signal frequency band area by a synthesizing means 40, and so as to be inputted to an electricity/light conversion means 9.

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 using an optical transmission line. This mobile communication system includes a plurality of radio base stations having only a radio function for forming a radio zone in which a mobile phone such as a mobile phone communicates, and signals transmitted between the plurality of radio base stations and mobile terminals. It is connected to a centralized control station having a modulation / demodulation function and the like through an optical transmission line, and is considered to be applied to, for example, PHS (Personal Handyphone System) which is currently under development.

[0002]

2. Description of the Related Art PH described in the above-mentioned industrial application fields
S is located between the mobile phone and the cordless phone, and unlike a cordless phone, S moves from a wireless zone covered by one base station to a wireless zone covered by another base station like a mobile phone. Is possible.

However, unlike a mobile telephone, the upper limit of the moving speed of the mobile station is expected to be about the walking speed of a person, and the radius of one radio zone is as small as about 200 m, so that the mobile station can be made small and inexpensive. You can

In such a PHS, the base stations must be arranged at a much higher density than in the mobile telephone system, and therefore each base station must be small and maintainable. .

Therefore, the radio unit of the base station and the modulation / demodulation unit are separated, and the former is placed in each radio zone as a radio base station.
The latter is being intensively placed in one centralized control station, and it is under study to connect both by an optical transmission line.

FIG. 7 shows an example of a conventional configuration in which an optical transmission line is used for such a PHS, and its description will be given. In FIG. 7, reference numeral 1 is a mobile terminal (mobile station), 2 and 3 are radio base stations, and 4 is a centralized control station. The wireless base stations 2 and 3 have wireless units 5 and 6, and also include E / O converters (electrical / optical converters) 7 and 9 and O / E converters (optical / electrical converters) 8,
10 is configured to perform wireless communication with the mobile terminal 1 in a wireless zone 11 (only the wireless unit 6 is described) formed by the wireless units 5 and 6.

The centralized control station 4 includes O / E converters 12, 13
And E / O converters 14 and 15, a distribution unit 16, modulation / demodulation units 17 and 18, and TDMA (Time Division Multiplex A).
ccess) control units 19 and 20, a power supply unit 21, a common access control unit 22, and a clock supply unit 23.

The pair of O / E converter 12 and E / O converter 14 are the E / O converter 7 and O / O converter of one radio base station 2.
Two-way optical transmission lines (optical fibers) 24 and 25 are connected to the E converter 8. That is, the other pair of O / E converter 13 and E / O converter 15 is also connected to the other one radio base station 3
The two-way optical transmission lines 26 and 27 are connected to the E / O converter 9 and the O / E converter 10.

The distribution unit 16 outputs the electric signal converted by the O / E converters 12 and 13 according to the distribution control signal output from the common access control unit 22 to either of the modulation / demodulation units 17 and 18. , The output signals of the TDMA control units 19 and 20 are modulated by the modulation / demodulation units 17 and 18 to obtain E / O signals.
Control to output to either the converter 14 or 15 is performed.

The modulation / demodulation units 17 and 18 demodulate the signals output from the O / E converters 12 and 13 via the distribution unit 16 in addition to the above-described modulation. The TDMA control units 19 and 20 are
Time-division multiplexing control of signals exchanged between the modulation / demodulation units 17 and 18 and the exchange is performed. In addition, the clock supply unit 23,
The system clock signal of the centralized control station 4 is generated, and the power supply unit 21 supplies power to the centralized control station 4.

In the operation of such a configuration, for example, when the mobile terminal 1 exists in the wireless zone 11 and performs communication, the signal transmitted by the radio wave from the mobile terminal 1 is received by the wireless unit 6 of the wireless base station 3. Then, the E / O converter 9 converts the electric signal into an optical signal, and the converted optical signal is sent to the O / E converter 13 of the centralized control station 4 via the optical transmission line 26.

Then, after being converted into an electric signal by the O / E converter 13, distributed by the distributor 16 to any modulator / demodulator 17 or 18, and converted by the TDMA controller 19 or 20 into an exchange interface signal, It is sent to the exchange.

On the other hand, the signal transmitted from the exchange is TD
Modulator / demodulator 17 or 18 via MA controller 19 or 20
Is modulated by the distribution unit 16, distributed to the E / O converter 15 for example, converted into an optical signal by the E / O converter 15, and then transmitted to the O / E converter 10 via the optical transmission line 27. It Then, after being converted into an electric signal by the O / E converter 10, it is transmitted from the wireless unit 6 to the mobile terminal 1.

According to such a configuration, the radio base stations 2,
Since the size of the wireless base stations 2 and 3 is reduced, the wireless base stations 2 and 3 can be easily installed, and most of the maintenance work can be centrally performed by the centralized control station 4, thus improving maintainability.

Further, the distribution unit 16 of the centralized control station 4 distributes and controls the signals from the modulation / demodulation units 17 and 18, and a zone (for example, 11) in which the radio base station 2 or 3 having a large call volume exists is
Since the signals of a plurality of waves can be assigned, it is possible to improve the overall call loss rate.

Further, in the system having such a configuration, it is necessary to arrange the base stations in a much higher density than in the mobile telephone system as described above, but the optical transmission lines 24, 25, which are low in loss, Since a plurality of wireless base stations 2 and 3 and the centralized control station 4 are connected using 26 and 27, a flexible correspondence is possible.

[0017]

By the way, the above-mentioned P
In the HS, the signals received by the radio base stations 2 and 3 have a wide range of variations in the reception level depending on the position of the mobile phone 1 and the surrounding environment, and it is necessary to satisfy the intermodulation sensitivity characteristic defined as the standard of the receiver. Optical transmission lines 24, 25, 26,
The distortion standard required by No. 27 is quite strict, and the E / O converters 7, 9, 14, 15 used for that purpose and the optical devices including the O / E converters 8, 10, 12, 13 have low distortion. Characteristic characteristics are required.

Particularly, looking at the third-order intermodulation characteristics when the received signal level is lowered, the desired waves (input signals) indicated by the symbols D1 and D2 in FIG. 8 are used instead when the input signal level to the optical device is lowered. There is a problem that the D / U (Desire / Undesire) ratio, which is the ratio of the third-order distortion components indicated by the symbols U1 and U2, is deteriorated and the distortion characteristics are deteriorated.

At present, the reason why the distortion characteristic is deteriorated is considered as follows. As the input signal level to the optical device decreases, the modulation degree of the laser diode that constitutes the optical device decreases, and the modulation state of the laser diode, that is, coherency (coherence), becomes higher than that when the modulation degree is high. It has been known.

When the coherency becomes high, the probability that the phases of the reflected light generated in the optical connector of the optical device and the like coincide with each other as compared with the case where the coherency is low, and the peak value of the distortion variation becomes large. It becomes easy to receive.

Therefore, when the input signal level is lowered by the reflected light, the distortion characteristic is deteriorated, and as a result, as shown by the broken line 30 in FIG. 9, the normal third-order distortion characteristic (third-order inclination with respect to the input level). It is considered that the distortion characteristic deteriorates when the level decreases, as in the portion indicated by the arrow Y1.

However, in the graph of FIG. 9, the vertical axis represents the levels of the input signals D1 and D2 shown in FIG. 8 and the third-order distortion components U1 and U2.
IM ₃ (IM; Inter Modulation), which is the difference from the level of, and the horizontal axis represents the input signal level.

The present invention has been made in view of the above circumstances, and provides a mobile communication system capable of improving distortion characteristics in an optical transmission line connecting a radio base station and a centralized control station. Is intended.

[0024]

FIG. 1 shows a principle diagram of a mobile communication system of the present invention. In the mobile communication system shown in this figure, a plurality of radio base stations 3 having a radio function and a central control station 4 having a function of modulating / demodulating a signal communicated between the plurality of radio base stations 3 and mobile terminals are optical. The transmission lines 26 are connected to each other.

The feature of the present invention is that the radio base station 3 uses the frequency conversion means 37 for converting the received signal from the mobile terminal into an intermediate frequency and the frequency f1 other than the system signal frequency band used in the mobile communication system. Further, the oscillating means 39 for outputting the auxiliary signal S1 of a constant level, the synthesizing means 40 for synthesizing the auxiliary signal S1 and the intermediate frequency signal output from the frequency converting means 37, and the signal synthesized by the synthesizing means 40 Electricity that is converted to an optical signal and sent to the optical transmission line 26
The light conversion means 9 is provided.

[0026]

According to the present invention described above, the received signal from the mobile terminal is converted into the intermediate frequency by the frequency conversion means 37,
Auxiliary signal S1 of a constant level output from the oscillation means 39
Since it is combined by the combining means 40 and input to the electric / optical converting means 9, the auxiliary signal S1 is always supplied to the electric / optical converting means 9 even if the level of the received signal from the mobile terminal is lowered.
Is input, and as a result, the coherency of the optical device becomes higher to the extent that the phase of the reflected light generated by the optical device forming the electrical / optical conversion means 9 matches the received signal from the mobile terminal. Will disappear.

As a result, the coherency is increased due to the decrease of the received signal level as in the prior art, and the phases of the reflected light and the received signal coincide with each other and the third-order distortion component does not increase, so that the distortion characteristic is improved. To do.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram according to the first embodiment of the present invention. In this figure, parts corresponding to those of the conventional example shown in FIG. 7 are designated by the same reference numerals, and the description thereof will be omitted.

However, the first embodiment shown in FIG. 2 shows only the configuration of the upstream line system from one radio base station 3 to the centralized control station 4, and the O / E conversion in the centralized control station 4 is shown. The components on the upstream side of the container 13 are omitted.

The characteristic configuration of the first embodiment shown in FIG. 2 is that the antenna 34, the amplifier 35, the local oscillator 36, the mixer 37, and the band pass filter (BP) which are the conventional components.
F) radio unit 6 that was configured with 38 (see FIG. 7)
In addition, an oscillator 39, which is a characteristic element of this embodiment, and a combiner 40 using a hybrid circuit are provided.

That is, the signal from the mobile terminal (not shown) received by the antenna 34 is amplified by the amplifier 35 and then mixed in the mixer 37 with the oscillation signal of the local oscillator 36 to be frequency-converted. IF (Inter
mediate Frequency) band signal.

This IF band signal is supplied to the combiner 40 via the BPF 38 that passes only the intermediate frequency, and is combined with the oscillation signal (hereinafter referred to as an auxiliary signal) S1 of the oscillator 39 in the combiner 40, and E / O It is adapted to be input to the converter 9.

As shown in FIG. 3, the frequency f1 of the auxiliary signal S1 is a frequency other than the system signal frequency band FB and lower than the system signal frequency band FB, and the level of the auxiliary signal S1 is constant. And

In this way, the auxiliary signal S1 having a constant level is
The combiner 40 combines the received signal with the IF band signal, and E /
By inputting to the O converter 9, the signal level input to the E / O converter 9 does not fall below the level of the auxiliary signal S1 regardless of the received signal level at the antenna 34, so that the optical device (E / O The coherency of the laser diode that constitutes the converter 9) does not rise above a certain level.

That is, as in the prior art, the coherency is increased due to the decrease in the received signal level, and the probability that the phases of the reflected lights generated in the optical device match each other increases.
The influence of reflected light such as the increase of the peak value of the distortion variation is eliminated, and the distortion characteristic with respect to the input signal level of the optical device is the normal third-order distortion characteristic (see the solid line 42 in FIG. 9). It becomes a third-order slope with respect to the input level).

Therefore, unlike the conventional case, the third-order distortion component does not increase when the input signal level decreases, so that the deterioration of the distortion characteristic can be improved. Next, a second embodiment will be described with reference to FIG. However, in FIG.
The same reference numerals are given to the portions corresponding to the respective portions of the first embodiment shown in, and the description thereof will be omitted.

The second embodiment shown in FIG. 4 corresponds to the first embodiment shown in FIG.
The difference from the embodiment is that a distortion compensation circuit 42 is connected between the combiner 40 and the E / O converter 9. Distortion compensation circuit 4
A predistorter or the like can be used as 2.

By connecting the distortion compensating circuit 42 to the input side of the E / O converter 9 as described above, the distortion of the input signal of the E / O converter 9 can be reduced. Therefore, in the first embodiment. The distortion characteristics can be improved more than described above.

Next, a third embodiment will be described with reference to FIG. However, in FIG. 5, parts corresponding to the respective parts of the second embodiment shown in FIG. 4 are designated by the same reference numerals, and description thereof will be omitted. The third embodiment shown in FIG. 5 differs from the second embodiment shown in FIG. 4 in that the distortion compensation circuit 42 connected between the combiner 40 and the E / O converter 9 is connected to the BPF 38 and the combiner. The point is that the connection with 40 was changed.

By configuring in this way, the BPF
Since it is possible to reduce the distortion of the IF band signal obtained by converting the reception signal at the antenna 34 that has passed through 38, it is possible to reduce the distortion of the signal input to the E / O converter 9 as a result. It is possible to obtain substantially the same effect as that of the second embodiment.

Next, a fourth embodiment will be described with reference to FIG. However, in FIG. 6, parts corresponding to the respective parts of the first embodiment shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted. The fourth embodiment shown in FIG. 6 is different from the first embodiment shown in FIG. 2 in that the reception signal at the antenna 34 is directly combined with the auxiliary signal S1 of a constant level output from the oscillator 39,
The frequency conversion of the received signal to the IF band signal is performed by the O / E converter 13 and the subsequent devices of the centralized control station 4.

That is, the radio base station 3 amplifies the signal received by the antenna 34 by the amplifier 35, and then synthesizes it with the auxiliary signal S1 output from the oscillator 39 by the synthesizer 40, and the synthesized signal is E / The O converter 9 is configured to convert into an optical signal.

In the centralized control station 4, the signal that has passed through the optical fiber 26 is converted into an electric signal by the O / E converter 13, and then mixed with the output signal of the local oscillator 36 by the mixer 37 so that the IF band is obtained. Frequency conversion to the signal,
After that, it is configured to output to the distribution unit 16 shown in FIG. 7 via the BPF 38.

With such a structure, it is possible to obtain substantially the same effect as that of the first embodiment. In addition, the above-mentioned first
In the fourth embodiment, the auxiliary signal S1 of a constant level output from the oscillator 39 is combined with the signal received by the antenna 34, but instead of this, for example, E /
Since the output signal of the O converter 9 is sent to the O / E converter 13, the FSK (Frequency Shift Keyin) is set on the E / O converter 9 side.
g) An FSK signal for performing modulation and FSK demodulation on the O / E converter 13 side, or FM (Frequency Modulation)
Similar effects can be obtained as long as the signal can be regarded as a signal having a constant level on average, such as a signal.

[0045]

As described above, according to the present invention,
There is an effect that the distortion characteristic in the optical transmission line connecting the wireless base station and the centralized control station can be improved.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a block diagram according to the first embodiment of the present invention.

FIG. 3 is a frequency spectrum diagram showing an input signal to the optical device, a third-order distortion component, and an auxiliary signal.

FIG. 4 is a block diagram according to a second embodiment of the present invention.

FIG. 5 is a block diagram according to a third embodiment of the present invention.

FIG. 6 is a block diagram according to a fourth embodiment of the present invention.

FIG. 7 is a block diagram of a conventional example of the present invention.

FIG. 8 is a frequency spectrum diagram showing an input signal to the optical device and a third-order distortion component.

FIG. 9 is a third-order distortion characteristic diagram.

[Explanation of symbols]

 3 Radio Base Station 4 Centralized Control Station 9 Electric / Optical Converter 26 Optical Transmission Line 37 Frequency Converter 39 Oscillator 40 Synthesizer S1 Auxiliary Signal f1 Frequency of Auxiliary Signal S1

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoshiaki Watanabe 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Ryutaro Omoto 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph Telephone Corporation (72) Inventor Yuji Aburagawa 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. A plurality of wireless base stations having a wireless function,
In a mobile communication system in which a plurality of wireless base stations and a centralized control station having a modulation / demodulation function for signals communicated between mobile terminals are connected by an optical transmission line, the wireless base station is connected from the mobile terminal. Frequency conversion means for converting the received signal of the above into an intermediate frequency, oscillating means for outputting an auxiliary signal of a constant level at a frequency other than the system signal frequency band used in the mobile communication system, the auxiliary signal and the intermediate frequency And the electric / optical conversion means for converting the signal combined by the combining means into an optical signal and transmitting the optical signal to the optical transmission line. Communications system. 2. The mobile communication system according to claim 1, wherein the frequency of the auxiliary signal is a frequency other than the system signal frequency band and a frequency lower than the system signal frequency band. 3. The mobile communication according to claim 1, wherein the frequency of the auxiliary signal is a frequency other than a frequency used between the mobile terminal and the radio base station in the system signal frequency band. system. 4. A distortion compensating means for reducing distortion of a signal output from the synthesizing means is connected between the synthesizing means and the electrical / optical converting means.
The mobile communication system according to any one of 3 above. 5. The distortion compensating means for reducing the distortion of the signal output from the frequency converting means is connected between the frequency converting means and the synthesizing means. A mobile communication system according to claim 1. 6. A plurality of wireless base stations having a wireless function,
In a mobile communication system in which a plurality of radio base stations and a centralized control station having a modulation / demodulation function for signals communicated between mobile terminals are connected by an optical transmission line, the radio base station is used in a mobile communication system. And a synthesizing means for synthesizing the auxiliary signal and a received signal from the mobile terminal, and an oscillating means for outputting an auxiliary signal of a frequency other than the system signal frequency band. And an electric / optical converting means for converting the signal into an optical signal and transmitting the optical signal to the optical transmission line, wherein the central control station controls the optical signal transmitted through the optical transmission line as an electric signal. A mobile communication system, comprising: an optical / electrical conversion unit for converting the electrical signal into an intermediate frequency and a frequency conversion unit for converting the electrical signal into an intermediate frequency.