Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-06-30
2001-09-18
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S561000, C455S091000
Reexamination Certificate
active
06292673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radio signal transmitters, and more specifically, it relates to a radio signal transmitter employed in a radio base station formed by a master station and a slave station (forward station), for example, for receiving radio signals with two or more different frequency bands respectively, multiplexing the signals and transmitting the same between the master station and the slave station.
2. Description of the Background Art
In mobile communication through a portable telephone or a car phone, it is necessary to eliminate a blind zone such as underground or the inside of a tunnel where no radio waves from a radio base station reach. As that solving this problem, there is a radio base station formed by a master station without an antenna function and a plurality of slave stations having only the antenna function. The plurality of slave stations are dispersively arranged as forward stations in a blind zone or the like, and the master station and each slave station are connected to each other by an optical fiber, for example. In this case, signal transmission between the master station and the slave station is performed by an optical transmission system converting a radio signal (RF signal) to an optical signal and transmitting the same.
FIG. 13
is a block diagram showing an exemplary structure of a conventional optical transmission system employed in the aforementioned radio base station for optically transmitting a signal between the master station and the slave station. This type of optical transmission system is described in “Fiber-Optic Transmission System for Radio Base Stations” (Sanada et al., National Technical Report Vol. 39, No. 4, August 1993), for example.
Referring to
FIG. 13
, the conventional optical transmission system comprises an amplification part
90
amplifying an electric signal to be transmitted, an electrical/optical conversion part
91
performing electrical/optical conversion of an output signal from the amplification part
90
, and an optical/electrical conversion part
92
performing optical/electrical conversion of the transmitted optical signal. The amplification part
90
and the electrical/optical conversion part
91
are provided on a sending end and the optical/electrical conversion part
92
is provided on a receiving end, while the electrical/optical conversion part
91
and the optical/electrical conversion part
92
are connected to each other by an optical fiber
93
.
The electrical/optical conversion part
91
has, in relation to the power of the input signal, such a prescribed linear region that change of the strength of the output optical signal with respect to change thereof is linear. That is, when a signal having power exceeding the upper limit of this region is inputted in the electrical/optical conversion part
91
, the output optical signal is distorted.
The optical/electrical conversion part
92
has, in relation to the strength of the input optical signal, such another prescribed linear region that change of the power of the output signal with respect to change thereof is linear. That is, when an optical signal having strength exceeding the upper limit of this region is inputted in the optical/electrical conversion part
92
, the output signal is distorted.
The amplification part
90
has such an amplification factor that the power of the output signal from the optical/electrical conversion part
92
becomes sufficiently larger than that of noise while the power of the input signal in the electrical/optical conversion part
91
will not exceed the upper limit of the aforementioned prescribed linear region and the strength of the input optical signal in the optical/electrical conversion part
92
will not exceed the upper limit of the aforementioned another prescribed linear region. Thus, on the receiving end, a signal having sufficiently large power as compared with noise and with no distortion is obtained.
As described in “CDMA Cellular System” (Association of Radio Industries and Businesses, ARIB STD-T53 Version 1.0), in relation to mobile communication, as lines rapidly increases in number in recent years, there has been proposed employment of the CDMA (code division multiple access) system having a remarkably larger number of lines as compared with the conventional system. Recently mobile communication in the CDMA system is in part put into practice, and it is predicted that hereafter the ratio of the CDMA system occupying the mobile communication increases.
That is, the current system and the CDMA system coexist in the period up until shift to the CDMA system is completed and hence, in consideration of suppressing the facility cost, it is important to cope with the CDMA system while making the best use of the existing facility for the current system.
In the aforementioned conventional optical transmission system, consider optical transmission of an RF signal employed in the current system and a code division multiple access signal employed in the CDMA system. In this case, the receiving end cannot obtain, in relation to the code division multiple access signal, a signal having sufficiently large power as compared with noise. This is because, while in the current system and the CDMA system the power of signals is set in standards respectively, according to the standards, with reference to the power of the input signals supplied to the sending end, the power of the code division multiple access signal employed in the CDMA system is smaller than that of the RF signal employed in the conventional system.
The standards of the current system are described in “Digital Cellular Telecommunication System” (Research & Development Center for Radio Systems, RCR STD-27A) and the standards of the CDMA system are described in the aforementioned “CDMA Cellular System”. An apparatus optically transmitting a code division multiple access signal is disclosed in Japanese Patent Laying-Open No. 6-70362 (Japanese Patent Application No. 4-219894), for example.
In relation to the code division multiple access signal, on the other hand, it is assumed that the amplification factor of the amplification part
90
is set high so that a signal having sufficiently large power as compared with noise is obtained. In this case, however, it is predicted in relation to the RF signal that the power of the input signal in the electrical/optical conversion part
91
exceeds the upper limit of the aforementioned prescribed linear region or the strength of the input optical signal in the optical/electrical conversion part
92
exceeds the upper limit of the aforementioned another prescribed linear region and consequently the signal obtained on the receiving end is distorted.
That is, when optically transmitting the RF signal and the code division multiple access signal in the aforementioned conventional optical transmission system, the receiving end cannot obtain, in relation to both of the RF signal and the code division multiple access signal, signals having sufficiently large power as compared with noise with no distortion whatever amplification factor of the amplification part
90
is set. Incidentally, the aforementioned Japanese Patent Laying-Open No. 6-70362 describes no means of optically transmitting both of the RF signal and the code division multiple access signal.
A problem similar to the above is quantitatively described from another point of view.
FIG. 14
is a block diagram showing the structure of a conventional radio signal transmitter.
Referring to
FIG. 14
, in the conventional radio signal transmitter a master station
200
and a slave station
300
are connected to each other by optical fibers
201
and
202
. The optical fiber
201
is used when transmitting from the master station
200
to the slave station
300
(hereinafter referred to as a down system) an optical signal. The optical fiber
202
is used when transmitting from the slave station
300
to the master station
200
(hereinafter referred to as an up system) an optical signal.
The slave station
3
Maeda Kazuki
Masuda Kouichi
Morikura Susumu
Sasai Hiroyuki
Matsushita Electric - Industrial Co., Ltd.
Maung Nay
Vuong Quochien B.
Wenderoth , Lind & Ponack, L.L.P.
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