JP2001111498A - Base station and radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base station inexpensive and simple in configuration without needing any expensive opto-electric transformer to be operated in a radio frequency band, and to provide a radio communication system suitable for the base station. SOLUTION: A control station 10 extracts an outgoing signal from a public network to the base station 20 by an exchange 11 and an optical signal whose intensity is modulated in accordance with the outgoing signal (10 Mbps base band signal) is generated by an E/O element 15. The optical signal is transmitted to the base station 20 via an optical fiber 2 and an optical control VCO 22 is irradiated with the transmitted optical signal in the base station 22. In this case, the optical control VCO 22 is oscillated by ratio frequency band, an oscillation frequency is changed by the light intensity of the irradiation light and a transmitting signal fRF is generated, whose frequency is modulated in accordance with the optical signal. Thus, the base station 20 is constituted without using the expensive opto-electric(O/E) transformer and the control station 10 is constituted without using an expensive and complicated millimeter wave circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base station which is connected to a wired communication network via an optical transmission line for transmitting an optical signal, and performs radio communication with a terminal station existing within a communication area of the own station. The present invention relates to a wireless communication system using a base station.

[0002]

2. Description of the Related Art In recent years, there has been a demand for a large-capacity and high-reliability communication network as a base for realizing multimedia communication and a broadband portable terminal capable of large-capacity data communication as a terminal for this multimedia communication. Demands are growing.

[0003] At present, as a large-capacity communication network,
A communication line using an optical fiber has been put into practical use, and a plan to construct a communication network using an optical fiber up to a subscriber line connected to an office or a home has been proposed in the future. On the other hand, in order to secure a wide bandwidth in mobile communication, it is necessary to increase a frequency band to be used, and a wireless communication technology using a microwave band or a millimeter wave band is receiving attention. In mobile communication, a cellular system in which a large number of base stations having a limited communication area are provided is widely adopted, and the base stations are mutually connected by communication lines.

In other words, when configuring a communication system that can use a broadband portable terminal, it is important to realize a wired / wireless interface. And, for example, "An ATM Wirel
essSystem for Tetherless Multimedia Service ”(MU
mehira, A.Hashimito, H.Matsue; IEEE ICUPC '95) has an ATM wireless access that uses an optical fiber for high-frequency signal transmission and realizes wireless access to the B-ISDN network using millimeter or quasi-millimeter waves. A system has been proposed.

FIG. 13A is a block diagram showing an example of this wireless access system. FIG. 13 (a)
As shown in the figure, a base station 120 that performs wireless communication with a terminal station existing within a predetermined communication area,
0 and a control station 110 that interfaces with a B-ISDN network (hereinafter, referred to as “public network”).

[0006] Then, the control station 110 is connected to a public network, and extracts an exchange 111 for extracting a downlink signal addressed to the base station 120.
A modulator 112 for generating a predetermined modulation signal based on the downlink signal extracted by the exchange 111, a local oscillator 117 for generating a local signal in the intermediate frequency band, a modulation signal from the modulator 112 and the local oscillator Mixer 113 that mixes the local signal from signal 117 and modulates the local signal with a modulation signal to generate an intermediate frequency (IF) signal
And an electrical-optical conversion (E / O) element 115 for generating an optical signal intensity-modulated according to the IF signal from the mixer 13
And an optical amplifier 116 for amplifying the optical signal generated by the E / O element 115. The optical signal amplified by the optical amplifier 116 is transmitted to the base station 120 via the optical fiber 102.
Is configured to be supplied.

On the other hand, the base station 120
Amplifier 121 that amplifies the optical signal supplied through the
And optical-electrical conversion (O / E) for converting the optical signal amplified by the optical amplifier 121 into an electric signal and restoring the IF signal.
Element 122 and IF restored by O / E element 122
An amplifier 123 for amplifying the signal, a local oscillator 127 for generating a second local signal in a radio frequency band, and a frequency conversion (up-conversion) of the IF signal by mixing the IF signal with the second local signal. , An amplifier 125 for amplifying the transmission signal generated by the mixer 124, and an amplifier 125
And a transmission antenna 126 for converting the transmission signal amplified by the radio wave into a radio wave and transmitting the radio wave.

Generally, a laser diode (LD) or a light emitting diode (LE) is used as the E / O element 115.
An element whose optical output changes according to an electric signal, such as D), is used. As the O / E element 122, an element whose output power changes according to the reception intensity of the optical signal, such as a photodiode (PD), is used. Have been.

In the above-described system configured as above, the control station 110 generates an IF signal on which a downlink signal is superimposed, and generates an optical signal intensity-modulated by the IF signal. At 120, I
The F signal is restored, mixed with the local signal and up-converted to generate a transmission signal in a radio frequency band.

[0010]

However, in the above-described system, it is necessary to provide a local oscillator 27 and a mixer 24 operating in a radio frequency band in each base station, so that a millimeter wave device having an expensive and complicated structure is required. Are used, so that the configuration of the base station becomes large and expensive, and especially in a communication system using millimeter waves, it is necessary to arrange a large number of base stations. Therefore, there has been a problem that the cost of the entire system becomes enormous.

[0011] That is, the millimeter wave has a very large propagation loss in the atmosphere and a long delay wave due to multipath propagation is very weak, and the radio wave via multipath cannot be used. It is necessary to provide a large number of base stations so that line-of-sight communication using only radio waves directly propagating between the stations is possible.

[0012] On the other hand, "60
GHz millimeter wave "(Kenichi Kitayama, Toshiaki Kuri; EMCI998.5.5 N
o.121,1998) to reduce the cost of base stations,
A communication system in which a base station is configured without using a local oscillator has been proposed. In this communication system, FIG.
As shown in (b), as a control station 110a, in addition to the configuration of the control station 110, a local oscillator 118 for generating a second local signal in a radio frequency band and an IF signal generated by a mixer 113 are used. A mixer 114 for generating a transmission signal in a radio frequency band by mixing and upconverting the second local signal from the local oscillator 118 is provided, and the transmission signal is converted into an optical signal by the E / O element 15. Is configured.

On the other hand, the base station 120a is
20 to radio frequency band amplifier 123, local oscillator 12
7, a configuration in which the mixer 124 is omitted, an optical signal supplied via an optical fiber is amplified by an optical amplifier 121, and then converted into an electric signal by an O / E element 122 to restore a transmission signal. After the restored transmission signal is amplified by the amplifier 125, the transmission antenna 1
26.

In the communication system configured as described above,
Each base station 120a has a local oscillator 127 and a mixer 124
, It is possible to minimize the number of millimeter-wave devices, so that the configuration of the base station 120a is very simple, and the base station 120a can be made compact.

However, in this communication system, light intensity modulation is possible corresponding to the frequency of the millimeter wave band, and since the intensity modulation is performed according to the analog signal, a high quality E / O having a linear conversion characteristic is provided. The element 115 and the O / E element 122 are required. At present, since such a photoelectric conversion element is very expensive, the configuration of the base station 120a is simple, but the cost of the base station 120a and the cost of the entire system including the control station 110a are very high. There is a problem that it becomes expensive.

It is an object of the present invention to provide an inexpensive and simple base station which does not require an expensive photoelectric conversion element operating in a radio frequency band, and a radio communication system suitable for such a base station. And

[0017]

According to a first aspect of the present invention, an output of an oscillator oscillating in a radio frequency band is used as a transmission signal, and an antenna is operated in accordance with the transmission signal. To perform wireless communication with a terminal station existing in the communication area of the own station.

The base station is connected to a predetermined wired communication network via an optical transmission line for transmitting an optical signal, and the oscillator is irradiated with an optical signal supplied via the optical transmission line. The oscillation frequency of the transmitter changes according to the intensity of the irradiated light. In other words, an optical signal that is intensity-modulated based on a signal to be transmitted from the base station to the terminal station,
By simply transmitting the signal to a desired base station via an optical transmission line (for example, an optical fiber), the base station modulates the frequency based on the signal to be transmitted to the terminal station by an oscillator that directly responds to a change in the intensity of the optical signal. It is possible to easily obtain a transmission signal in the specified radio frequency band.

As described above, according to the present invention, expensive light-
A base station can be configured with an oscillator whose oscillation frequency changes in accordance with light intensity and an antenna without using an electric conversion element, so that the base station can be reduced in size and cost. In particular, when the intensity modulation waveform of the optical signal is a rectangular wave, the oscillator of the base station only needs to reliably switch the frequency according to the signal level of the rectangular wave. Since the required high-precision linearity is not required, the configuration can be made cheaper and simpler.

In the base station of the present invention, the frequency is changed by changing the characteristics of the oscillator, and the phase of the generated transmission signal is continuous, so that transmission and reception between the base station and the terminal station are performed. The occupied bandwidth of the transmitted radio wave can be made relatively small. By the way, an oscillator whose oscillation frequency changes in response to the intensity of irradiated light is described in claim 2
As described, this can be realized by using a monolithic microwave integrated circuit including a circuit element whose high-frequency characteristics change according to light irradiation.

The circuit element whose high-frequency characteristics change in response to light irradiation is preferably a circuit element having a high frequency characteristic.
It is desirable to use an AlAs / InGaAs high electron mobility field effect transistor (HEMT). That is,
The InGaAs layer is made of infrared light (1.55 μm, which has particularly low loss among them) which is currently used in optical fiber communication.
It is known that the HEMT having the InGaAs layer changes its characteristics according to the amount of infrared light absorbed. In addition, InA formed to include an InAlAs layer
In an AsAs / InGaAs-based HEMT, ordinary InG
Since the electron mobility is higher than that of the aAs layer alone and the performance in the millimeter wave region is improved, it becomes optimal as a circuit element constituting the oscillator of the base station of the present invention.

The oscillator is not limited to an oscillator having a fixed oscillation frequency when no light is radiated, but may be a voltage-controlled oscillator capable of controlling the oscillation frequency by a voltage signal. Is also good. In this case, the center frequency of the transmission signal generated by the base station can be set arbitrarily, and the usability of the base station can be improved.

In the case where the wired communication network to which the above-mentioned base station is connected via an optical transmission line uses an optical fiber as a transmission medium, the optical fiber is connected to the optical fiber. By providing an optical distributor for distributing an optical signal and supplying the optical signal to an optical transmission line in a wired communication network using as a transmission medium, the optical signal distributed by the optical distributor can be directly supplied to the base station. Can be configured.

However, in this case, it is necessary to provide a function for extracting necessary information on the terminal station side, and the terminal station can be suitably used when configuring a broadcast communication system.
Further, by providing an optical switch for extracting an optical signal addressed to a base station and supplying the extracted optical signal to an optical transmission line in a wired communication network using an optical fiber as a transmission medium, as in the wireless communication system according to claim 6, The configuration may be such that only the optical signal extracted by the optical switch is supplied to the base station.

In this case, since only necessary information is transmitted to the terminal station, the processing load on the terminal station can be reduced. In addition, when a wired communication network uses an optical fiber as a transmission medium, the conventional device requires a circuit in which a control station temporarily converts an optical signal into an electric signal and then converts the signal into an optical signal again. Although there is a possibility that the transmission speed is limited by the operation limit, in the invention according to claim 5 or 6, the optical signal obtained from the wire communication network converts the carrier wave (signal generated by the oscillator) into a radio frequency band carrier. Since the modulation can be directly applied, not only the circuit configuration is simplified, but also very high-speed communication can be realized.

Next, when the above-mentioned wired communication network to which the base station is connected via an optical transmission line transmits electric signals using a coaxial cable or the like as a transmission medium, this wired communication network is used. It is necessary to provide a control station because an optical transmission line cannot be directly connected to the network.

In such a case, in the control station, the data extracting means extracts a downlink signal addressed to the base station from the wired communication network, and the optical signal transmitting means in the control station. The optical signal formed by superimposing the extracted downstream signal may be transmitted to the optical transmission line. The data extracting means may be an electronic exchange that extracts only a downlink signal addressed to the base station, or a power distributor that simply branches a transmission signal in a wired communication network.

According to the wireless communication system of the present invention configured as described above, it is not necessary for the control station to process a signal in a radio frequency band, and an element for converting an electric signal to an optical signal is also provided.
A relatively low-speed signal that can be intensity-modulated according to the transmission rate of the downlink signal addressed to the base station can be used, and the control station can be configured simply and at low cost.

The down signal destined for the base station, which is extracted by the data extracting means of the control station, is represented by a so-called baseband signal having an unmodulated digital waveform. It is desirable. Thus, when the downlink signal addressed to the base station is represented by a baseband signal, it is possible to easily cope with various modulation schemes by adding the following processing.

For example, as described in claim 9, the optical signal transmitting means of the control station sets n (n is an integer of 1 or more) information bits of the downlink signal addressed to the base station as one symbol, and During this period, when a level signal that is held at a signal level set in advance according to the value represented by the symbol is generated, and the signal strength of the optical signal is modulated by this level signal, The oscillator can generate a frequency-modulated transmission signal by changing the oscillation frequency according to the optical signal supplied from the control station.

When n = 1, the baseband signal is directly used as a level signal, and the transmission signal transmits information using two types of frequency components. On the other hand, when n ≧ 2, a level signal having 2 ⁿ kinds of signal levels is generated, and the transmission signal transmits information using 2 ⁿ kinds of frequency components.

Each value represented by the symbol is defined in claim 1
0 may be associated with the frequency of the transmission signal, or as described in claim 11, may be associated with the frequency difference of the transmission signal. However, in the former case (claim 10), the optical signal transmitting means sets the signal level of the level signal so that the frequency corresponding to the symbol value matches the frequency of the transmission signal generated by the base station. In the latter case (Claim 11), the optical signal transmitting means changes the level signal so that the frequency of the transmission signal generated by the base station changes by the frequency difference corresponding to the symbol value. What is necessary is just to comprise so that a level may be set.

By the way, when the light intensity applied to the oscillator is changed into a pulse for a very short time compared to the symbol, the phase of the signal generated by the oscillator changes at the time of generation of the pulse. It will be. Therefore, it is understood that a phase-modulated transmission signal can be obtained by appropriately adjusting the amount of phase change at this time. When the oscillation frequency of the oscillator is instantaneously increased, the phase of the generated signal is advanced. Conversely, when the oscillation frequency is instantaneously lowered, the phase of the generated signal is increased. Will be late.

Therefore, for example, as described in claim 12,
The optical signal transmitting means of the control station determines that the signal n to the base station (where n is 1)
A pulse signal having a signal level or pulse width set in advance according to the value represented by the symbol is generated at the timing when the symbol changes, with the (integer) information bits as one symbol. When configured to modulate the signal strength of an optical signal, the oscillator of the base station changes the oscillation frequency for a short time according to the pulse signal in accordance with the optical signal supplied from the control station. , A phase-modulated transmission signal can be generated.

Each value represented by the symbol is defined in claim 1
As described in the third aspect, it may be associated with the phase of the transmission signal, or may be associated with the phase difference of the transmission signal. However, in the case of the former (claim 13), the optical signal transmitting means determines the signal level of the pulse signal or the signal level of the pulse signal so that the phase corresponding to the symbol value matches the phase of the transmission signal generated by the base station. The pulse width may be set, and in the latter case (claim 14), the optical signal transmitting means may adjust the phase of the transmission signal generated by the base station by the phase difference corresponding to the symbol value. May be configured so that the signal level or pulse width of the pulse signal is set so as to change.

Next, in the wireless communication system according to the fifteenth aspect, in the optical signal transmitting means of the control station, the local oscillator generates a local signal in an intermediate frequency band lower than the radio frequency band. An intermediate frequency signal is generated by mixing the downstream signal addressed to the station with a mixer,
The signal intensity of the optical signal supplied to the base station is modulated according to the intermediate frequency signal.

According to the wireless communication system of the present invention configured as described above, the control station is the control station of the conventional device (FIG. 13).
(A)), a conventional control station can be used. If a conventional wireless communication system exists, only the base station is changed,
The transition to the wireless communication system of the present invention can be made easily and at low cost.

In this case, however, the electro-optical conversion element for generating an optical signal in the control station must perform intensity modulation in accordance with the analog signal in the intermediate frequency band, so that it is necessary to use a high-speed and good linearity element. is there. In order to adjust the relationship between a level signal or a pulse signal for modulating an optical signal and a frequency shift amount in an oscillator constituting the base station, the base station is provided with the control station as described in claim 16. And a light intensity adjusting means for adjusting a light intensity variation width of an optical signal supplied from the optical transmission line via the optical transmission line, or the control signal is supplied to the control station via the optical transmission line. Light intensity adjusting means for adjusting the light intensity fluctuation width of the optical signal to be transmitted.

When phase modulation is performed using a pulse signal, not only the light intensity fluctuation width but also the light pulse width may be adjusted by the light intensity adjusting means. Further, in such a wireless communication system, a base station is installed on or near a road, and a wireless communication is performed between the base station and a terminal station mounted on a vehicle running on the road. The present invention can be suitably used for a communication system in which a large number of base stations having a narrow communication area need to be installed, for example, when performing communication.

[0040]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a block diagram showing a schematic configuration of a wireless communication system according to a first embodiment.

As shown in FIG. 1, the radio communication system of the present embodiment transmits radio waves in the radio frequency band (in this embodiment, millimeter waves of the 60 GHz band) to and from the terminal station T existing in the communication area. A base station 20 for performing wireless communication using the base station 20 is connected to the base station 20 via the optical fiber 2, and is connected to a public network (telephone line network, data line network, ISDN line, B-IS
And a control station 10 that interfaces the base station 20 with a DN line network or the like. In the present embodiment, it is assumed that the public network uses a coaxial cable or the like as a transmission medium and transmits information by electric signals.

Hereinafter, the control station 10 which is a main part of the present invention will be described.
Only the configuration related to a downlink signal from the terminal to the base station 20 will be described. First, the control station 10 relays and exchanges signals transmitted over the public network, and particularly, an exchange 11 for extracting a downlink signal addressed to the base station 20 and a downlink signal (electric signal) extracted by the exchange 11. To generate an intensity-modulated optical signal whose signal intensity varies according to
O) An element 15 and an optical amplifier 16 for amplifying the optical signal generated by the E / O element 15 are provided.

A signal obtained by modulating a baseband signal is transmitted in the public network, and the exchange 11 demodulates the transmission signal transmitted in the public network into a baseband signal and performs switching processing. The extracted downlink signal addressed to the base station is supplied to the E / O element 15 as a baseband signal. The transmission capacity of the channel for the downlink signal addressed to the base station 20 is 10 Mbps.
It is assumed that is set to

The E / O element 15 has a wavelength of 1.55 μm.
It consists of a direct modulation laser diode that emits m infrared light and changes the signal intensity of an output signal (optical signal) according to the signal intensity of an input signal (electric signal). Accordingly, as the optical fiber 2 connecting the control station 10 and the base station 20, a dispersion shift fiber for infrared light having a wavelength of 1.55 μm is used.

In the figure, only one system of the E / O element 15 and the optical amplifier 16 is connected to the exchange 11, but a plurality of these systems are connected, and a plurality of base stations are connected to one control station 10. 20 may be configured to be connectable. on the other hand,
The base station 20 oscillates at an optical amplifier 21 for amplifying an optical signal supplied via the optical fiber 2, and oscillates at a frequency in the above-described radio frequency band. An optical / voltage controlled oscillator (hereinafter referred to as “optically controlled VCO”) 22 capable of shifting the oscillation frequency in accordance with the optical intensity, and an amplifier for amplifying a radio frequency transmission signal fRF output from the optically controlled VCO 22 2
5 and a transmission antenna 26 for transmitting a radio wave according to the transmission signal fRF amplified by the amplifier 25. The light control VCO 22 and the amplifier 25 are integrally formed as a monolithic microwave integrated circuit (MMIC).

The light control VCO 22 is composed of InAl
This is a well-known voltage-controlled oscillator that operates in the millimeter wave band and is configured using an As / InGaAs-based HEMT (High Electron Mobility Field Effect Transistor), and an optical signal radiated from the end face of the optical fiber 2 is a HEMT. It is configured to irradiate the arrangement portion. The high frequency characteristics of the HEMT change according to the signal intensity of the irradiated optical signal, so that the light control VCO 22 has a characteristic that its oscillation frequency changes by about several tens of MHz.

The optical amplifier 21 is configured such that its amplification factor and, consequently, the fluctuation range of the light intensity of the light signal applied to the light control VCO 22 can be adjusted by an external operation. The light intensity of the light signal applied to the light control VCO 22 is adjusted according to the light intensity incident through the optical fiber 2 so as to be within a preset range.

Hereinafter, the operation of the wireless communication system according to the present embodiment thus configured will be described. Here, FIG. 2 is an explanatory diagram for illustrating the operation of each unit of the wireless communication system according to the present embodiment, in which (a) is a waveform diagram of a downlink signal (baseband signal) extracted by the exchange, and (b) is a diagram. ) Is a graph showing the time change of the signal intensity of the optical signal intensity-modulated by the downlink signal shown in (a), and (c) is a transmission signal SRF generated by the optical control VCO 22 irradiated with the optical signal shown in (b). Is a graph showing the time change of the frequency of FIG.

First, in the control station 10, the exchange 11 extracts a downlink signal addressed to the base station 20 from the public network, and the E / O element 1
5 generates an optical signal (see FIG. 2B) that is intensity-modulated according to the downstream signal, that is, a 10 Mbps baseband signal (see FIG. 2A). This optical signal is amplified by the optical amplifier 16 and then transmitted to the base station 20 via the optical fiber 2.

Next, in the base station 20, the optical signal supplied via the optical fiber 2 is amplified by the optical amplifier 21 and irradiated to the optical control VCO 22. Then, the light control VCO 22
Is a transmission signal whose oscillation frequency changes in accordance with the signal strength of an irradiated optical signal (see FIG. 2C), and which is frequency-modulated using a radio frequency band frequency (here, two types of frequencies f1 and f2). fRF (see FIG. 2D) is output. The transmission signal fRF is amplified by the amplifier 25 and then transmitted via the transmission antenna 26.

When the terminal station T that has entered the communication area of the base station 20 receives the radio wave from the base station 20, it converts the received signal in the radio frequency band into an IF signal in the intermediate frequency (for example, 3 GHz) band. After performing frequency conversion (down-conversion), demodulation for frequency modulation can obtain a desired downlink signal (baseband signal).

As described above, in the radio communication system according to the present embodiment, the control station 10 generates an optical signal that is intensity-modulated by the downlink signal addressed to the base station 20, and the base station 20 generates the optical signal. Is applied to the light control VCO 22, thereby changing the oscillation frequency of the light control VCO 22 to obtain a transmission signal fRF in a radio frequency band frequency-modulated according to the downstream signal.

Therefore, according to the wireless communication system of the present embodiment, the base station 20 is an expensive optical-electrical converter (O / E).
It can be configured without using elements, and the control station 10
It can be configured without using an expensive and complicated millimeter wave circuit, and as the E / O element 15, the speed of the downstream signal (10M
(about bps) can be used, so that the base station 20 and the control station 10 can be reduced in size and cost, and the entire wireless communication system can be configured at low cost. can do.

In the wireless communication system of the present embodiment, since the downstream signal for intensity-modulating the optical signal is a baseband signal, that is, a rectangular wave, the E / O element 15 and the optical control V
Since the electrical-optical conversion characteristic and the optical intensity-frequency shift amount characteristic of the CO 22 do not require high-precision linearity as in the case of performing intensity modulation of an optical signal with an analog signal, the E / O element 15 Selection and design of the light control VCO 22 can be performed relatively easily.

Further, in this embodiment, the light control VCO
The frequency-modulated transmission signal fRF generated by 22 has a continuous phase even at a frequency change point and has a relatively small frequency band, so that the design of the millimeter wave circuit portion of the terminal station T can be facilitated. . [Second Embodiment] Next, a second embodiment will be described.

FIG. 3 is a schematic configuration diagram of the wireless communication system of the present embodiment. In the present embodiment, since the configuration of the control station is only partially different from that of the first embodiment, the same components are denoted by the same reference numerals, and description thereof will be omitted. Will be described.

As shown in FIG. 3, in the radio communication system according to the present embodiment, the control station 10a includes a modulator 12 that modulates the downlink signal extracted by the exchange 11, and the modulator 12 The modulated signal is configured to be supplied to the E / O element 15.

Then, the modulator 12 detects the rising edge and the falling edge at which the signal level of the downstream signal (see FIG. 4A) supplied from the exchange 11 changes, and
As shown in (b), a pulse signal having a pulse width sufficiently shorter than the information bits of the downlink signal is generated.

When an optical signal whose intensity is modulated according to the pulse signal is generated and supplied to the optical control VCO 22, the oscillation frequency of the optical control VCO 22 normally oscillates at the frequency f1 and the pulse width of the pulse signal becomes For the corresponding period,
A transmission signal having a frequency f2 (> f1) is generated.

Since the phase of the signal generated by the light control VCO 22 is continuous at the boundary between the period of the frequency f1 and the period of the frequency f2, the phase of the frequency f1 is changed before and after the period of the frequency f2. The phase of the signal will shift. The pulse width of the pulse signal is set such that the phase shift amount is 180 °. Note that the pulse width of this pulse signal increases as the amplitude of the pulse signal increases, that is, the oscillation frequency f of the light control VCO 22 at the time of pulse generation.
The higher the number 2, the smaller it can be.

In the wireless communication system of the present embodiment configured as described above, according to the optical signal from the control station 10a,
In the base station 20, the phase θ = 0 ° for the information bit value “0” of the downlink signal and the phase θ = 180 ° for the information bit value “1”.
Is generated, and a radio signal is transmitted according to the transmission signal fRF.

As described above, according to the radio communication system of the present embodiment, not only the same effects as those of the radio communication system of the first embodiment are obtained, but also the radio communication system of the first embodiment is compared with the radio communication system of the first embodiment. The modulator 12 is provided to the control station 10a.
By simply adding, the modulation method of the transmission signal fRF can be changed without changing the configuration of the base station 20 at all, so that it is possible to easily cope with various modulation methods.

In this embodiment, when a pulse is generated,
The light intensity is increased (that is, the oscillation frequency of the light control VCO 22 is increased) so that the phase of the transmission signal fRF is advanced by 180 °. Conversely, when the pulse is generated, the light intensity is reduced (that is, the light control VCO 22). The oscillation frequency may be lowered) so that the phase of the transmission signal fRF is delayed by 180 ° to realize the binary phase modulation.

By the way, in the present embodiment, the modulator 1
In No. 2, binary phase modulation is realized by detecting a rising edge and a falling edge of a downlink signal and generating a pulse signal. For example, as shown in FIG. A pulse signal may be generated such that the phase of the transmission signal fRF is shifted by 180 ° at the timing of the information bit which becomes '1' (or '0').

In this case, according to the optical signal from the control station 10a, the base station 20 sets the information bit of the downlink signal to “0”.
At the time of transition to, the phase difference from the immediately preceding information bit is Δθ =
0 °, when the information bit transits to “1”, the phase difference from the immediately preceding information bit is Δθ = 180 ° (or −180 °)
Thus, the transmission signal fRF subjected to the differential binary phase modulation is generated.

In the present embodiment, the modulator 12 performs modulation control in units of information bits. However, a combination of two consecutive information bits may be used as a symbol, and modulation control may be performed for each symbol. . When performing modulation control for each symbol in this manner, for example, as shown in FIG.
Four possible values' 00 ',' 01 ',' 1 for the symbol
A level signal is generated by associating four different signal levels with 0 'and' 11 '(FIG. 6 (a)
(See (b)), the modulator 12 may be configured.

In this case, according to the optical signal from the control station 10a, the base station 20 generates four types of frequencies f1, f corresponding to each signal level (ie, symbol value) of the level signal.
A transmission signal fRF (see FIGS. 6C and 6D) frequency-modulated by 2, 2, and 3 is generated.

Similarly, when modulation control is performed for each symbol, for example, as shown in FIG. 7, at the start timing of each symbol, four possible values of the symbol are replaced with four different amplitudes ( The modulator 12 may be configured to generate pulse signals corresponding to the respective signal levels (see FIGS. 7A and 7B).

In this case, according to the optical signal from the control station 10a, the base station 20 instantaneously changes the oscillation frequency during the pulse width at the generation timing of the pulse signal, thereby obtaining the phase-modulated transmission signal. fRF will be generated. The phase shift amount of the transmission signal fRF increases as the change amount of the oscillation frequency (that is, the amplitude of the pulse signal) increases.
It will be big.

In particular, as shown in FIG.
At the time of transition to 0 ″ 01 ″ 10 ″ 11 ′, the phase shift amounts Δθ of the transmission signal fRF are 0 °, 90 °, and 18 °, respectively.
If the amplitude of the pulse signal (ie, the frequency at the time of shifting) is set to be 0 ° (or −180 °) or 270 ° (or −90 °), differential four-level phase modulation can be realized. .

Further, as shown in FIG.
When 0 ″ 01 ″ 10 ″ 11 ′, the phase θ of the transmission signal fRF is 0 °, 90 °, 180 ° (or −18), respectively.
0 °) and 270 ° (or −90 °), quaternary phase modulation can be realized by setting the amplitude of the pulse signal.

Further, in the above-described quaternary phase modulation and differential quaternary phase modulation, the phase shift of the transmission signal fRF is realized by changing the amplitude of the pulse signal, as shown in FIG. May be realized by changing the pulse width of the pulse signal. FIG. 9 shows a case of differential quaternary phase modulation. Third Embodiment Next, a third embodiment will be described.

FIG. 10 is a block diagram showing a schematic configuration of the wireless communication system of the present embodiment. In the present embodiment, since the configuration of the control station is only partially different from that of the first embodiment, the same components are denoted by the same reference numerals, and description thereof will be omitted. Will be described.

However, in the present embodiment, the public network to which the control station is connected is configured using an optical fiber as a transmission medium. As shown in FIG.
In the wireless communication system of the present embodiment, the control station 10b
Is an optical switch 11a capable of performing an exchange process on an optical signal branched from a public network in place of the switch 11 as an optical signal, and a downstream signal (optical signal) addressed to the base station 20 extracted by the optical switch 11a. ) Is amplified only by the optical amplifier 16.

The downstream signal extracted by the optical switch 11a has a format in which the intensity is modulated by the baseband signal, and the output of the E / O element 15 in the first embodiment (FIG. 2B) Reference). In the wireless communication system of the present embodiment configured as described above, only the portion for converting the electric signal to the optical signal is omitted, and after the downstream signal is converted to the optical signal, It works exactly the same as in the case.

As described above, in the radio communication system of the present embodiment, the control station 10b does not include any configuration for processing electric signals.
Not only becomes very simple, but also the control station 1
In the case of 0b, the operation speed is not limited by characteristics of an electronic circuit for processing an electric signal, a photoelectric conversion element, and the like, and an extremely high-speed operation can be realized.

In this embodiment, the optical exchange 1
1a is provided with a control station 10b.
As shown in (b), the control station 10b may be omitted and the optical signal branched from the public network may be directly supplied to the base station 20 via the optical fiber 2.

In this case, it is necessary to provide the function of selecting and processing the information signal on the terminal side, which is suitable for a communication system mainly intended for performing broadcast-type communication. [Fourth Embodiment] Next, a fourth embodiment will be described.

FIG. 11 is a schematic configuration diagram of the wireless communication system of the present embodiment. In the present embodiment, since the configuration of the control station is only partially different from that of the first embodiment, the same components are denoted by the same reference numerals, and description thereof will be omitted. explain.

As shown in FIG. 11, in the radio communication system of the present embodiment, the control station 10c includes a modulator 12 for modulating the downlink signal extracted by the exchange 11, an intermediate frequency band lower than the radio frequency band. (In the present embodiment, 3GH
z) a local oscillator 17 for generating a local signal, and a mixer 14 for mixing the signal modulated by the modulator 12 with the local signal generated by the local oscillator 17 to generate an intermediate frequency (IF) signal. And the IF signal generated by the mixer 14 is supplied to the E / O element 15.

The configuration of the control station 10c is exactly the same as the configuration of the control station 110 (see FIG. 13A) in the prior art described above. Note that the specific configuration of the modulator 12 may employ any one of those described in the description of the second embodiment according to the modulation format to be used.

In the wireless communication system according to the present embodiment thus configured, the control station 10c generates an optical signal intensity-modulated by the IF signal,
Through the base station 20. This optical signal has an analog waveform in which the signal intensity changes continuously unlike the above embodiment.

On the other hand, the base station 20 generates a transmission signal in which the transmission signal in the radio frequency band is frequency-modulated so that the frequency changes continuously according to the signal strength of the optical signal (ie, IF signal). From the transmitting antenna 26. Then, the terminal station T receiving the radio wave from the base station 20
Then, first, demodulation for frequency modulation in a radio frequency band is performed to reproduce an IF signal, and further, demodulation for digital modulation is performed, so that a downlink signal composed of a baseband signal can be obtained.

As described above, in the radio communication system of the present embodiment, the control station 10c has the same configuration as the conventional radio communication system. For this reason, if a conventional wireless communication system already exists, simply replacing the base station from the conventional one (the base station 120) with the one of the present embodiment (the base station 20) is simple and extremely low cost. Then, it is possible to shift to the wireless communication system of the present embodiment.

As described above, several embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and may be implemented in various modes without departing from the gist of the present invention. it can. For example, in each of the above embodiments, the amplitude variation of the optical signal is adjusted by adjusting the amplification factor of the optical amplifier 21 from the outside, but instead of the optical amplifier 21 or the optical amplifier 21 is configured. An optical AGC circuit 30 that automatically adjusts the signal intensity of the optical signal applied to the light control VCO 22 to a value within a predetermined range may be provided at a stage subsequent to 21.

As shown in FIG. 12, the optical AGC circuit 30 is provided on a transmission path of an optical signal, and attenuates an optical signal passing according to a control signal.
And an optical coupler 34 that branches a part of the optical signal that has passed through the optical attenuator 32, a light detection circuit 36 that detects the intensity of the optical signal that is branched by the optical coupler 34, and a light detection circuit 36 that detects the light. The control circuit 38 generates a control signal to the optical attenuator 32 so that the intensity of the optical signal becomes a preset magnitude according to the intensity of the optical signal.

In this case, the optical control VCO 22 of the base station 20
The signal intensity of the optical signal applied to the device can be kept constant irrespective of the aging of the element or the arrangement state of the optical fiber, so that the frequency and phase of the transmission signal can be adjusted accurately. , The reliability of the system can be improved. Such an optical AGC circuit 30 may be provided in place of the optical amplifier 16 on the control station side or at a subsequent stage of the optical amplifier 16.

In each of the above embodiments, the optical control VCO 22 capable of controlling the oscillation frequency by a voltage signal is used as an oscillator that generates a signal in the radio frequency band and shifts the oscillation frequency in accordance with the signal strength of the optical signal. Although used, an oscillator having a fixed oscillation frequency when not irradiating an optical signal may be used.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a wireless communication system according to a first embodiment.

FIG. 2 is a waveform chart for explaining the operation of each section of the system shown in FIG.

FIG. 3 is a schematic configuration diagram of a wireless communication system according to a second embodiment.

FIG. 4 is a waveform chart for explaining the operation (differential binary phase modulation) of each section of the system shown in FIG. 3;

FIG. 5 is a waveform chart for explaining an operation (binary phase modulation) when another modulator is used in the system shown in FIG. 3;

FIG. 6 shows an operation when another modulator is used in the system shown in FIG. 3 (frequency modulation using four kinds of frequencies).
FIG. 6 is a waveform diagram for explaining the operation of FIG.

FIG. 7 is a waveform diagram for explaining an operation (differential quaternary phase modulation) when another modulator is used in the system shown in FIG. 3;

FIG. 8 is a waveform diagram for explaining an operation (four-level phase modulation) when another modulator is used in the system shown in FIG. 3;

FIG. 9 is a waveform diagram for explaining an operation when the phase shift amount is changed according to the pulse width of the pulse signal.

FIG. 10 is a schematic configuration diagram of a wireless communication system according to a third embodiment.

FIG. 11 is a schematic configuration diagram of a wireless communication system according to a fourth embodiment.

FIG. 12 is a block diagram illustrating a configuration of an optical AGC circuit.

FIG. 13 is a schematic configuration diagram of a conventional wireless communication system.

[Explanation of symbols]

2: Optical fiber 10, 10a to 10c: Control station
11: Switch 11a: Optical switch 12: Modulator 13,
14 mixer 15 E / O element 16, 21 optical amplifier 17
Local oscillator 20: Base station 22: Optical control VCO 23,
25 amplifier 26 transmission antenna 30 optical AGC circuit 32
Optical attenuator 34 Optical coupler 36 Photodetector circuit 38
Control circuit 21: Optical amplifier T: Terminal station

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K002 AA01 AA03 AA04 BA05 CA14 DA05 DA13 FA01 5K067 AA41 BB02 EE02 EE10 EE16 EE34 EE37 EE67

Claims (18)

[Claims] 1. A base station which is connected to a predetermined wired communication network via an optical transmission line for transmitting an optical signal and performs wireless communication with a terminal station existing in a communication area of the own station. An oscillator that oscillates in a band and whose oscillation frequency changes in accordance with the intensity of irradiated light; and an antenna that uses the output of the oscillator as a transmission signal and sends out a radio wave in accordance with the transmission signal. A base station configured to irradiate the oscillator with the supplied optical signal. 2. The base station according to claim 1, wherein the oscillator comprises a monolithic microwave integrated circuit including a circuit element whose high-frequency characteristics change according to light irradiation. 3. The method according to claim 1, wherein the circuit element is InAlAs / I
3. The base station according to claim 1, further comprising an nGaAs high electron mobility field effect transistor. 4. The base station according to claim 1, wherein the oscillator is a voltage-controlled oscillator whose oscillation frequency can be controlled by a voltage signal. 5. An optical distributor for distributing an optical signal from a wired communication network using an optical fiber as a transmission medium and supplying the optical signal to the optical transmission line, the base station according to any one of claims 1 to 4, A wireless communication system comprising: 6. An optical signal addressed to the base station is extracted from a base station according to claim 1 and a wired communication network using an optical fiber as a transmission medium and supplied to the optical transmission line. A wireless communication system comprising: an optical switch. 7. A base station according to claim 1, a data extracting unit for extracting a signal addressed to the base station from a wired communication network for transmitting an electric signal, and the data extracting unit. And a control station having an optical signal transmitting means for transmitting an optical signal obtained by superimposing the signal transmitted to the base station to the optical transmission line, wherein the base station performs the wired communication via the control station. A wireless communication system connected to a network. 8. The wireless communication system according to claim 7, wherein the signal addressed to the base station extracted by the data extraction means of the control station has an unmodulated digital waveform. 9. The wireless communication system according to claim 8, wherein the optical signal transmitting unit of the control station is configured to transmit the signal n to the base station.
(N is an integer equal to or more than 1) information bits as one symbol, and during the symbol period, a level signal held at a signal level preset according to a value represented by the symbol is generated. By modulating the signal strength of the optical signal, the oscillator of the base station, by changing the oscillation frequency according to the optical signal supplied from the control station, to generate a frequency-modulated transmission signal, Wireless communication system. 10. The wireless communication system according to claim 9, wherein each value represented by said symbol is associated with a frequency of said transmission signal, and said optical signal transmitting means includes a frequency corresponding to said symbol value. And setting the signal level of the level signal so that the frequency of the transmission signal generated by the base station matches. 11. The wireless communication system according to claim 9, wherein each value represented by the symbol is associated with a frequency difference of the transmission signal, and the optical signal transmitting unit corresponds to the value of the symbol. A wireless communication system, wherein a signal level of the level signal is set such that a frequency of a transmission signal generated by the base station changes by a frequency difference. 12. The wireless communication system according to claim 8, wherein the optical signal transmitting means of the control station is configured to transmit n of the signal addressed to the base station.
(N is an integer of 1 or more) information bits as one symbol, and at a timing when the symbol changes, a pulse signal having a signal level or pulse width preset according to a value represented by the symbol is generated; By modulating the signal intensity of the optical signal by the pulse signal, the oscillator of the base station, according to the optical signal supplied from the control station, by changing the oscillation frequency for a short time according to the pulse signal, A wireless communication system for generating a phase-modulated transmission signal. 13. The wireless communication system according to claim 12, wherein each value represented by said symbol is associated with a phase of said transmission signal, and said optical signal transmitting means comprises a phase corresponding to said symbol value. And a signal level or a pulse width of the pulse signal is set so that a phase of a transmission signal generated by the base station matches. 14. The wireless communication system according to claim 12, wherein each value represented by the symbol is associated with a phase difference of the transmission signal, and the optical signal transmitting unit corresponds to the value of the symbol. A wireless communication system, wherein a signal level or a pulse width of the pulse signal is set such that a phase of a transmission signal generated by the base station changes by a phase difference. 15. The radio communication system according to claim 8, wherein the optical signal transmitting means of the control station generates a local signal in an intermediate frequency band lower than the radio frequency band, and a local oscillator from the local oscillator. A mixer that mixes the signal addressed to the base station with the signal to generate an intermediate frequency signal, and modulates the signal strength of the optical signal supplied to the base station according to the intermediate frequency signal generated by the mixer. A wireless communication system, characterized by: 16. The optical communication system according to claim 7, wherein said base station is provided with light intensity adjusting means for adjusting a light intensity fluctuation width of an optical signal supplied from said control station via an optical transmission line. Item 16. The wireless communication system according to any one of Items 15. 17. The control station according to claim 7, further comprising an optical intensity adjusting means for adjusting an optical intensity variation width of an optical signal supplied to said base station via an optical transmission line. 15. The wireless communication system according to any one of 15. 18. The wireless communication system according to claim 5, wherein the base station is installed on or near a road, and performs wireless communication with the terminal station mounted on a vehicle running on the road.
A wireless communication system according to claim 17.