Multi-point optical transmission system

Details Multi-point optical transmission system Multi-point optical transmission system

1999-05-26

2002-05-21

Negash, Kinfe-Michael (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C379S056200

Reexamination Certificate

active

06392770

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical transmission systems, more particularly to a multi-point optical transmission system for optically transmitting code-division multiplex signals in an analog fashion from a plurality of slave stations to a master station through an optical fiber.
2. Description of the Background Art
FIG. 4
is a block diagram showing an exemplary functional configuration of a conventional multi-point optical transmission system.
The system in
FIG. 4
includes radio base stations
40
1
to
40
n
(where n is an arbitrary integer of 2 or more) and a switching station
41
, and each of the radio base stations
40
1
to
40
n
is connected to the switching station
41
via an optical fiber
43
. Each radio base station
40
1
to
40
n
includes an antenna
401
, a driving section
402
, and an uplink electrical-optical converting section
403
. The switching station
41
includes uplink optical-electrical converting sections
411
1
to
411
n
, demodulating sections
412
1
to
412
n
, and a switching section
413
.
The antenna
401
receives an uplink radio signal. The uplink radio signal herein is a code-division multiplex signal into which radio signals outputted from a plurality of terminals (not shown) in each cell
42
are multiplexed in a code-division system. Each uplink radio signal is equal in frequency as predetermined. The driving section
402
applies a bias to the uplink radio signal. The uplink electrical-optical converting section
403
converts the uplink radio signal into an optical signal whose intensity is modulated by the uplink radio signal. The uplink optical-electrical converting sections
411
1
to
411
n
convert the optical signal into an electrical signal (an uplink radio signal). The demodulating sections
412
1
to
412
n
demodulate the uplink radio signal outputted from the radio base stations
40
1
to
40
n
to base band digital data (Note that a process of demodulation herein includes “reverse diffusions”. Specifically, a radio signal is subjected to reverse diffusion before demodulation so as to obtain base band digital data; the same is applicable to the description below). The switching section
413
goes through a switching process in accordance with the base band digital data.
The operation whereby the system in
FIG. 4
optically transmits a plurality of uplink radio signals outputted from the radio base stations
40
1
to
40
n
to the switching station
41
in a multi-point fashion is described next below. Each cell
42
in the system in
FIG. 4
includes a plurality of terminals (not shown), and each of the terminals transmits a radio signal in a code-division multiplex system to one of the radio base stations
40
1
to
40
n
located in the same cell
42
. Thereafter, each of the uplink radio signals obtained after the code-division multiplexing of radio signals from the terminals is then received by the antenna
401
of the respective radio base stations
40
1
to
40
n
.
The received uplink radio signals are respectively biased in the driving section
402
, and sent to the uplink electrical-optical converting section
403
. In response thereto, the uplink electrical-optical converting section
403
outputs an optical signal whose intensity is modulated by the uplink radio signal. In this manner, each optical signal outputted from the radio base stations
40
1
to
40
n
is transmitted to the switching station
41
through the optical fiber
43
. Each of the transmitted optical signals is subjected to optical-electrical conversion in the uplink optical-electrical converting sections
411
1
to
411
n
. Each electrical signal obtained after the conversion (uplink electrical signals outputted from the radio base stations
40
1
to
40
n
) is demodulated to base band digital data in the demodulating sections
412
1
to
412
n
, and then sent to the switching section
413
. The switching section
413
goes through a switching process in accordance with the respective base band digital data.
As will be known from the above, a plurality of uplink radio signals outputted from the radio base stations
40
1
to
40
n
can be optically transmitted in a multi-point fashion to the switching station
41
in the system in FIG.
4
.
The system, however, necessitates the uplink optical-electrical converting sections
411
1
to
411
n
as many as the radio base stations
40
1
to
40
n
in the switching station
41
. Consequently, if the system has a large number of cells
42
, the switching station
41
accordingly becomes larger and costs more.
Thus, another type of multi-point optical transmission system was proposed, in which, with only a single optical-electrical converting section provided in a switching station, uplink radio signals outputted from a plurality of radio base stations are optically transmitted to the switching station in a multi-point fashion.
FIG. 5
is a block diagram showing an exemplary configuration of another conventional multi-point optical transmission system.
The system in
FIG. 5
includes radio base stations
50
1
to
50
n
(where n is an arbitrary integer of
2
or more) and a switching station
51
, and each of the radio base stations
50
1
to
50
n
is connected to the switching station
51
via an optical fiber
53
. Each of the radio base stations
50
1
to
50
n
includes an antenna
501
, a driving section
502
, and an uplink electrical-optical converting section
503
. The switching station
51
includes an optical multiplexing section
511
, uplink optical-electrical converting section
512
, a branching section
513
, demodulating sections
514
1
to
514
n
, and a switching section
515
.
The optical multiplexing section
511
multiplexes optical signals outputted from the radio base stations
50
1
to
50
n
. The uplink optical-electrical converting section
512
converts an optical signal obtained by multiplexing into an electrical signal. The branching section
513
branches the electrical signal into n signals. Other components in this system perform each task in a similar manner to those in the system in FIG.
4
.
The operation whereby the system in
FIG. 5
optically transmits a plurality of uplink radio signals outputted from the radio base stations
50
1
to
50
n
in a multi-point fashion to the switching station
51
is described next below.
Referring to
FIG. 5
, each cell
52
in the system includes a plurality of terminals (not shown), and each of the terminals transmits a radio signal in a code-division multiplex system to one of the radio base stations
50
1
to
50
n
located in the same cell
52
. Each of the radio signals obtained after the code-division multiplexing is then received by the antenna
501
of the respective radio base stations
50
1
to
50
n
. The received uplink radio signals are respectively biased in the driving section
502
, and then sent to the uplink electrical-optical converting section
503
. In response thereto, the uplink electrical-optical converting section
503
outputs an optical signal whose intensity is modulated by the uplink radio signal.
In this manner, each of the optical signals outputted from the base radio stations
50
1
to
50
n
is transmitted to the switching station
51
through the optical fiber
53
. The transmitted optical signals are multiplexed in the optical multiplexing section
511
, and a signal obtained by multiplexing is then subjected to optical-electrical conversion in the uplink optical-electrical converting section
512
. An electrical signal obtained by the conversion is branched into n signals in the branching section
513
. The respective electrical signals obtained by n-branching are inputted to the demodulating sections
514
1
to
514
n
, and the uplink radio signals outputted from the radio base stations
50
1
to
50
n
are selectively demodulated to base band digital data therein. The base band digital data is then respectively sent to the switching section
515
, and a switching process is performed therein in accordance with the respective ba

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