JPH05260018A - Optical transmission system for radio signal - Google Patents

Abstract

PURPOSE:To provide an optical transmission system for radio signal which transmits signals to be transferred through a radio channel by using an optical fiber cable. CONSTITUTION:A transmission terminal station A' is provided with a first electric/optic converting means 2' for modulating light intensity with a carrier signal Sa from a carrier signal output means 4 and outputting light to an optical transmission line (e), second electric/optic converting means 1' for modulating light intensity with an intermediate frequency signal f1 from an output means 3 for an intermediate frequency signal Sb including an information signal, and photocoupling means 10 for coupling optical signals La and Lb from optical transmission lines (d) and (e) and outputting the signal to an optical transmission line (c) for radio signal, and a transmitter B' is provided with a filtering means 8 for filtering one radio frequency component among the signals Sa and Sb outputted from an photoelectric converting means 11, which converts a light intensity modulated signal Lc transmitted through the optical transmission line (c) to an electric signal Sc, and waves mixing the frequencies of these signals and transmitting means 9' for transmitting a filtered radio frequency signal Sd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal for transmission / reception via a wireless line when a transmitting / receiving terminal station for modulating / demodulating a baseband signal and a wireless signal transmitting / receiving device (antenna) are separated. The present invention relates to an optical transmission system for wireless signals for transmission using a fiber cable.

[0002]

2. Description of the Related Art In this type of field, an optical transmission system for transmitting a radio frequency signal according to the intensity of light transmitted through an optical fiber is a conventional optical transmission system utilizing the characteristics of wide band and low loss transmission using the optical fiber. It has attracted attention as an alternative to electric signal transmission means such as a coaxial cable, and the configuration of the transmission system has been studied.

An example of application of this transmission system is a mobile communication system composed of a large number of small zone radio areas. This communication system includes a central station in which a transmitting terminal station is arranged and a base station in which a transmitting device such as an antenna is arranged. Since many base stations will be installed, it is necessary to make the equipment compact, lightweight and simple. In the optical transmission system used in this communication system, generally, an electrical / optical conversion element such as a laser diode,
A light intensity modulation / light intensity detection method using an optical / electrical conversion element such as an optical fiber transmission line and a photodiode is used.

As a configuration of an optical transmission system, a transmitting device (antenna) transmits a radio frequency signal generated from an intermediate frequency signal including a carrier signal and an information signal on the transmitting terminal side by an optical link.
Link configuration (Central Data)
Mixing), and a link configuration (Rem) in which a carrier signal and an intermediate frequency signal are transmitted from the transmitting terminal station side to the transmitting device (antenna) side via an optical link and a radio frequency signal is generated on the transmitting device side.
ote Data Mixing) has been proposed,
Each is being considered for application.

FIG. 3 shows the conventional Remote Dat.
a Mixing type optical transmission system for wireless signals,
Is a transmitting terminal station, B is a transmitting device (antenna), a and b are optical fiber transmission lines, 1 and 2 are electrical / optical conversion circuits including a laser diode module, 3 is an intermediate frequency band modulator, and 4 is a carrier signal source. , 5 and 6 are optical / electrical conversion circuits including a photodiode module, 7 is a frequency mixer, 8 is a bandpass filter, and 9 is a transmitting antenna radiator.

With the above configuration, the optical transmission link α composed of the laser diode module 1, the optical fiber transmission line a, and the photodiode 5 is for intermediate frequency signals, and the laser diode module 2, the optical fiber transmission line b,
The optical transmission link β composed of the photodiode module 6 is for carrier signals.

A carrier signal source 4 having a frequency fo is output from a carrier signal source 4 in the transmitting terminal station A, and an optical signal whose intensity is modulated by the carrier signal So in the laser diode module 2 is sent to an optical fiber b. .. This light intensity modulated optical signal Lo is demodulated by the photodiode module 6 in the transmitter B (antenna) into the carrier signal So ′ having the frequency fo, and sent to the frequency mixer 7.

Similarly, the intermediate frequency signal S1 'of frequency f1 is demodulated by the photodiode module 5 and sent to the frequency mixer 7. In the frequency mixer 7, the frequency fo of the carrier signal So and the frequency f1 of the intermediate frequency signal S1.
From, a two-wave mixed signal S2 including fo + f1 and fo-f1 is generated, a desired radio frequency signal S3 is filtered by the band pass filter 8, and radiated as a radio wave from the transmitting antenna radiator 9.

[0009]

However, in the optical transmission system for radio signals shown in FIG. 3, the transmitter (antenna) is used.
On the B side, two photodiode modules 5 and 6 and one frequency mixer 7 are required, and two optical interfaces are required. This means that the transmitter B is small and
This is disadvantageous in a mobile communication system that needs to be lightweight. In view of the above problems of the conventional technique, the present invention is to provide an optical transmission system for wireless signals, which simplifies the components and optical interface provided on the transmitter side.

[0010]

The above-mentioned problems of the prior art can be solved by the present invention by adopting the novel characteristic construction means listed below. That is, the first feature of the present invention is that a transmitting terminal station, a radio signal transmitting device provided at a predetermined distance from the transmitting terminal station, and a radio connecting these transmitting terminal station and the transmitting device. A wireless communication system comprising a signal optical transmission line, wherein the transmitting terminal station modulates light intensity with a carrier signal output means and a carrier signal from the carrier output means and outputs the modulated light intensity to a first optical transmission line. A first electric / optical conversion means, an intermediate frequency signal output means including an information signal, and an intermediate frequency signal from the intermediate frequency signal output means for modulating the light intensity and outputting the second optical transmission line to the second optical transmission line. The optical transmission system for wireless signals, comprising: the electrical / optical conversion means and the optical coupling means for coupling the optical signals from the first and second optical transmission lines and outputting the optical signals to the optical transmission line for wireless signals.

A second feature of the present invention is that the wireless signal transmitting device according to the first feature has a non-linear optical-electrical conversion characteristic in which the optical-electrical conversion characteristic is changed by a bias voltage. An optical / electrical converting means for converting a light intensity modulated signal transmitted through an optical transmission line into an electric signal, and the carrier wave signal, the intermediate frequency signal and a frequency mixed wave of these outputted from the optical / electrical converting means. An optical transmission system for a radio signal, comprising: a filtering means for filtering one predetermined radio frequency component, and a transmitting means for wirelessly transmitting the radio frequency signal filtered by the filtering means.

[0012]

In the present invention, since the above-mentioned means are taken, the first electric / optical converting means and the second electric / optical converting means are connected by the optical coupler.
Since the optical signals sent from the optical conversion means and the optical conversion means are combined in advance by the optical coupling means in the transmission terminal station and sent to the transmission path to the transmission device, only one optical interface is required, and the equipment on the transmission device side is required. The configuration is also simplified.

[0013]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the optical transmission system for wireless signals of this embodiment, and FIG.
It is a circuit diagram which shows the structure of an electrical conversion circuit. In the figure, A'is a transmitting terminal station, B'is a transmitting device (antenna), c is an optical fiber transmission line, and d and e are optical fibers.

Reference numerals 1'and 2'represent an electrical / optical conversion circuit including a laser diode module, 9'an antenna radiating element, 1 '
0 is an optical coupler, 11 is an optical-electrical conversion circuit including an avalanche photodiode module, 11a is an avalanche photodiode module, 11b is a load, and 11c.
Is a bias power supply, and 11d is a bias circuit. In addition,
The same elements as those in the conventional example are designated by the same reference numerals.

Since the specifications of the present embodiment present such a concrete embodiment, the operation of the present embodiment will be described with reference to the drawings. The laser diode module 1'sends the optical signal Lb intensity-modulated with the intermediate frequency signal Sb to the optical fiber d, and the laser diode module 2'has a carrier signal S.
The optical signal La intensity-modulated by a is sent to the optical fiber e. In the optical coupler 10, the optical signal Lb input from the optical fiber d and the optical signal La input from the optical fiber e are combined and sent to the optical fiber transmission line c.

Therefore, in the optical fiber transmission line c,
The optical signal Lb intensity-modulated by the carrier signal Sa and the optical signal La intensity-modulated by the intermediate frequency signal Sa are transmitted as a mixed signal Lc and output to the avalanche photodiode module 11a of the optical / electrical conversion circuit 11.

The avalanche photodiode module 11a is supplied with a constant voltage V from a bias power supply 11c via a bias circuit 11d, but a load 11b causes a voltage drop i × R (i: photocurrent, R: resistance value). ), The voltage of V−i × R is effectively applied. Here, i is a value proportional to the input light intensity of the mixed signal Lc,
In the case of FIG. 1, the carrier signal Sa and the intermediate frequency signal Sb are included. Here, avalanche photodiode module 1
1a is a bias voltage applied, and its photocurrent multiplication coefficient changes.

Therefore, although the constant voltage is supplied from the bias power source 11c, the optical-electrical conversion characteristic of the avalanche photodiode module 11a becomes non-linear, and the carrier wave signal Sa and the intermediate frequency signal Sb as electric signals and the frequencies of these two waves are generated. Fo generated as a result of mixing
The mixed signal Sc of the signal components of + f1, fo-f1, etc. is output. Therefore, the desired radio frequency signal Sd is filtered by the bandpass filter 20, and the transmitting antenna radiator 9'is provided.
More radio waves can be emitted.

In the present invention, an avalanche photodiode is used as the photoelectric conversion element,
The present invention is not limited to this, and other opto-electrical conversion elements (photodiodes or the like) having nonlinearity in which the opto-electrical conversion characteristics change due to a slight change in bias voltage may be used. Also,
In the present invention, the optical fibers d and e are used in the transmitting terminal station, but the present invention is not limited to this, and other optical lines such as an optical waveguide may be used.

[0020]

As described above, according to the present invention, the carrier signal and the intermediate frequency signal are separately transmitted from the transmitting end station by using the optical fiber transmission link, and these signals are transmitted by the transmitting device (antenna) side. In the case of mixing and generating a radio frequency signal, in the conventional example, two optical-electrical converters and one frequency mixer were required on the transmitter side. It can perform the same function as the device of (1), and at the same time, can change the conventional optical interface from "2" to "1". This simplifies the electric circuit and the optical fiber interface on the transmitting device side, and has the excellent effect that the transmitting device can be made smaller and lighter than conventional ones.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical transmission system for wireless signals according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical / electrical conversion circuit of the same.

FIG. 3 is a configuration diagram of a conventional optical transmission system for wireless signals.

[Explanation of symbols]

 A, A '... Transmission terminal station B, B' ... Transmission device (antenna) a, b, c ... Optical fiber transmission line d, e ... Optical fiber 1, 1 ', 2, 2' ... Electric / optical conversion circuit 3 ... Intermediate frequency band modulator 4 ... Carrier signal source 5,6,11 ... Optical / electrical conversion circuit 7 ... Frequency mixer 8 ... Bandpass filter 9 ... Transmission antenna radiator 9 '... Transmission antenna element 10 ... Optical coupling Device 11a ... Avalanche photodiode module 11b ... Load 11c ... Bias power supply 11d ... Bias circuit So, So ', Sa ... Carrier wave signal S1, S1', Sb ... Intermediate frequency signal S2, Sc, Lc ... Mixed signal S3, Sd ... Radio Frequency signal Lo, La ... Optical intensity modulation optical signal L1, Lb ... Intermediate frequency optical signal

Claims (2)

[Claims] 1. A transmission terminal station, a radio signal transmission device provided at a predetermined distance from the transmission terminal station, and a radio signal optical transmission line connecting the transmission terminal station and the transmission device. In the wireless communication system configured, the transmitting terminal station includes a carrier signal output means and a first electrical / electrical device that modulates light intensity with a carrier signal from the carrier output means and outputs the modulated light intensity to a first optical transmission line. Optical conversion means, intermediate frequency signal output means including information signal, and second electric-optical conversion means for modulating the light intensity with the intermediate frequency signal from the intermediate frequency signal output means and outputting the modulated light intensity to the second optical transmission line. And an optical coupling means for coupling the optical signals from the first and second optical transmission lines and outputting the optical signals to the optical transmission line for wireless signals. 2. A wireless signal transmitting apparatus transmits an optical intensity modulation signal transmitted through an optical transmission line for wireless signals, which has a nonlinear optical-electrical conversion characteristic in which an optical-electrical conversion characteristic is changed by a bias voltage. Optical-electrical conversion means for converting into an electric signal,
The carrier wave signal output from the optical-electrical converting means,
A filtering means for filtering a predetermined one of the radio frequency components of the intermediate frequency signal and these frequency mixed waves; and a transmitting means for wirelessly transmitting the radio frequency signal filtered by the filtering means. The optical transmission system for wireless signals according to claim 1.