Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-11-27
2002-03-19
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06359714
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a relay system for covering silent zones in a mobile communications system, and in particular to a relay system capable of providing radio communication of desired communication quality throughout a complicated-shaped silent zone, repeating various kinds of signals with a simple configuration, and facilitating the system management.
2. Description of the Related Art
A public vehicular communications system such as a mobile and portable telephone system, a personal handyphone system (PHS) or a radio paging system (hereinbelow, generically called a “mobile communications system”) is equipped with vehicular communication base stations (hereinbelow, simply called “base stations”) connected by wire to an upper network such as a public telecommunication network (PSTN or ISDN), in which the base stations realize radio communication with mobile stations such as portable telephones.
In case of the mobile and portable telephone system, each base station has an area communicable by radio (coverage area) that ranges from several kilometers to ten and several kilometers. To secure a wider service area while effectively using the frequencies, such a system that coverage areas are arranged like cells, called a cellular system, has been adopted.
In a mobile communications system using such a cellular system, it would be possible to provide good radio communication with mobile radio terminals in outdoor environments such as ones on the ground, but difficult to realize radio communication with terminals inside a tunnel, an underground shopping center, a basement and aboveground stories in a large-scale building because of the difficulty of delivering radio waves.
Such an area as to make radio communication impossible is called a “silent zone,” and commonly appears not only in the mobile communications but also any other communications using radio waves, such as radio communications for business use including police radio, fire fighting radio and train radio, television broadcasting and radio broadcasting.
To enable radio communication in the silent zone, an apparatus, called a repeater-amplifier, is typically used as auxiliary means.
The apparatus is accompanied with a first antenna installed at a point to which a base station (or a broadcasting station) can transmit radio waves for proper communication, and a second antenna installed in the silent zone. In such a configuration, an incoming radio-frequency signal to the first antenna is amplified and transmitted through a cable to the second antenna in the silent zone. The amplified radio-frequency signal is then radiated from or broadcast through the second antenna.
A down link from the base station to a mobile station can thus be secured. An up link from a mobile station to the base station can also be allowed by amplifying a radio-frequency signal from the mobile station, transmitting it to the first antenna through the cable and radiating the amplified radio-frequency signal from the first antenna for transmission to the base station. It is therefore possible to realize radio communication in the silent zone.
So far, two methods of installing the second antenna have been used: one using a leakage coaxial system and the other using an optical fiber system. But in using either of the methods without any consideration, especially for mobile communications such as portable telephones, the installation of the second antenna can merely expand the coverage area of the base station at which a relay is received from the silent zone. This increases the amount of communication to be processed by the base station, and may cause the base station to exceed its capacity when used in an area such as a metropolitan area in which demand for communication is so great that incoming and outgoing lines from portable stations in the coverage area could not be processed.
Since an upper wired network of high quality such as an ISDN network has recently been popularized, installation of a radio modulator-demodulator directly connected by wire to the upper network such as ISDN is considered nowadays.
Such a radio modulator-demodulator modulates a radio-frequency signal with an input signal from the upper network and distributes or allots the radio-frequency signal to an antenna in the silent zone (the above-mentioned second antenna), while it receives a radio-frequency signal from a mobile station in the silent zone through the antenna and demodulates it for output to the upper network.
Referring now to
FIGS. 9 and 10
, such conventional relay systems will be described.
FIG. 9
is a diagram for explaining the concept of a conventional relay system using a leakage coaxial cable, and
FIG. 10
is a diagram for explaining the concept of another conventional relay system using optical fiber.
The relay system using a leakage coaxial cable shown in
FIG. 9
is constituted of a public telecommunication network
1
such as PSTN or ISDN, a radio modulator
2
connected by wire to the public telecommunication network
1
, a coaxial cable
3
, an amplifier
4
, a leakage coaxial cable
5
and auxiliary amplifiers
6
.
In
FIGS. 9 and 10
, only the down link is shown for simplification.
Hereinbelow, description is specifically made with respect to each portion.
The radio modulator
2
modulates a carrier with an incoming signal from the public telecommunication network
1
through a cable to obtain a radio-frequency signal and outputs the radio-frequency signal through the coaxial cable
3
.
The amplifier
4
amplifies the radio-frequency signal taken in through the coaxial cable
3
and outputs the amplified signal to the leakage coaxial cable
5
.
Parts of the leakage coaxial cable
5
are disposed linearly across the silent zone so as to transmit the radio-frequency signal from one end to the other while gradually leaking it to the outside. Thus the leakage coaxial cable
5
serves as an antenna.
Each auxiliary amplifier
6
is inserted between two sections or parts of the leakage coaxial cable
5
to amplify the radio-frequency signal passing through the leakage coaxial cable
5
so as to extend the extension distance of the leakage coaxial cable
5
.
Next, operation of the relay system using the leakage coaxial cable of
FIG. 9
will be described.
The radio modulator
2
modulates a radio-frequency signal with the incoming signal from the public telecommunication network
1
for output to the amplifier
4
through the coaxial cable
3
.
The amplifier
4
amplifies the radio-frequency signal for output to the leakage coaxial cable
5
.
The leakage coaxial cable
5
, like an antenna, transmits the radio-frequency signal from the amplifier
4
while leaking it to the outside. The auxiliary amplifier
6
amplifies the radio-frequency signal attenuated due to a leak from the preceding part of the leakage coaxial cable
5
and outputs it to the subsequent part of the leakage coaxial cable
5
. The subsequent part of the leakage coaxial cable
5
in turn leaks the amplified radio-frequency signal. Thus, the radio-frequency signal is imparted through the public telecommunication network
1
to a mobile station existing in the silent zone.
The relay system using optical fiber shown in
FIG. 10
is constituted of a public telecommunication network
1
, optical fiber
7
, a fixed central station
10
, an optical star coupler
20
and a plurality of fixed relay stations
30
.
The fixed central station
10
includes, in addition to a radio modulator
2
and an amplifier
4
similar to those in the relay system of
FIG. 9
, an electro-optic transducer (E/O) transducer
11
for transducing the radio-frequency signal amplified by the amplifier
4
into an optical signal. Each of the fixed relay stations
30
includes, in addition to an amplifier
34
similar to the amplifier
4
in the relay system of
FIG. 9
, an opto-electric (O/E) transducer
31
for transducing the optical signal into a radio-frequency signal and an antenna
32
from which the signal amplified by the amplifier
34
is radiated.
Hereinbel
Jacobson & Holman PLLC
Kokusai Electric Co. Ltd.
Pascal Leslie
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