Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-07-26
2004-12-14
Nguyen, Chau (Department: 2662)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S338000
Reexamination Certificate
active
06831904
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the benefit of a Japanese Patent Application No.11-214180 filed Jul. 28, 1999, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a mobile communication system having a line control station and a plurality of clustered base stations, a base station for such a mobile communication system, a cluster control station, a line control station, and a mobile station.
2. Description of the Related Art
FIG. 1
is a diagram for explaining an example of a conventional mobile communication system. The mobile communication system shown in
FIG. 1
includes a mobile station (MS)
10
, base stations (BSs)
111
through
117
, a line control station (RNC: Routing Network Controller)
12
, and a mobile communication switching station (MSC: Mobile Switching Center)
13
.
The mobile communication switching station
13
is a switching station designed for a mobile communication network. Lines of this mobile communication switching station
13
are connected to another mobile communication switching station or a switching station of a fixed network such as a Public Switched Telephone Network (PSTN). In the case where the mobile communication switching station
13
is a third generation type, the mobile communication switching station
13
not only supports the circuit switching functions, but also supports packet switching functions, which enables connection to the Internet.
The line control station
12
is connected to the mobile communication switching station
13
, and to the plurality of base stations
11
1
through
11
7
. When a communication request is generated, the line control station
12
controls the allocation of radio channels used by the base stations
11
1
through
11
7
, the start and end of the communication, and the like. In addition, the line control station
12
carries out a handover control when the mobile station
10
moves among the coverage areas of the base stations
11
1
through
11
7
.
The base stations
11
1
through
11
7
are connected to the line control station
12
, and carry out radio communication with a plurality of mobile stations
10
under the control of the line control station
12
. Various kinds of radio signal protocols (air interfaces), such as the Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA), may be employed between the base station and the mobile station.
When making a communication with one mobile station
10
in the mobile communication system shown in
FIG. 1
, radio signals are basically exchanged directly (peer-to-peer) between the mobile station
10
and the base station which is located near the mobile station
10
. In the particular case shown in
FIG. 1
, the base station
11
2
is close to the one mobile station
10
which is shown. Accordingly, the signals from the mobile station
10
are sent to the mobile communication switching station
13
via the base station
11
2
and the line control station
12
. When the mobile station
10
moves from the location near the base station
11
2
towards a location near the base station
11
3
as shown in
FIG. 1
, the handover is made from the base station
11
2
to the base station
11
3
in order to continue the communication. In other words, the line control station
12
controls the base stations so as to change the base station which is used for the communication with the mobile station
10
from the base station
11
2
to the base station
11
3
, and also switches the line to the base station from the base station
11
2
to the base station
11
3
. In
FIG. 1
, a solid line arrow pointing in two directions indicates a normal communication, and a dotted line arrows pointing in two directions indicates a handover communication.
In the case of a microcell mobile communication system in which an area covered by one base station is small, the handover among the base stations occur frequently when the mobile station
10
carries out the communication while moving at a high speed. As a result, the load on the line control station
12
which carries out the necessary control increases considerably in this case, and there is a problem in that it is difficult to appropriately control and carry out the handover.
On the other hand, in a vicinity of a boundary between two adjacent base stations, the electric field intensity decreases and an error may be generated in the received signals. Consequently, the handover may not be carried out smoothly, and the handover may fail, thereby causing a problem particularly in the microcell mobile communication system in which the handover occurs frequently.
In order to eliminate the latter problem, the CDMA mobile communication system employs the diversity handover technique. According to the diversity handover technique, the mobile station
10
during the handover simultaneously exchanges radio signals with the present base station
11
2
and the next base station
11
3
which is to take over, so that even if the signal level exchanged between the mobile station
10
and one of the base stations
112
and
11
3
decreases and the signal error is generated, the signals exchanged between the mobile station
10
and the other of the base stations
11
2
and
11
3
are used for the communication to realize a smooth handover. In this case, in addition to the load caused by the handover control, the line control station
12
must bear the load of the diversity process. Hence, the load on the line control station
12
increases considerably due to the diversity process.
Furthermore, in order to more effectively obtain the diversity effects, it is necessary to transfer to the line control station
12
information related to soft decisions made on the received signals, and information related to the electric field intensity of the received signals. As a result, the amount of information exchanged between the base station and the line control station increases considerably, and there is a problem in that it is necessary to use a line having a large capacity.
The diversity handover is not limited between two base stations, and in some cases, the diversity effects are greater when the diversity handover is carried out among three or more base stations. In addition, the diversity handover can effectively improve the quality of the communication by being carried out not only during the handover, but also when the electric field intensity of the received signals decreases when the mobile station enters within a building, for example. However, the load on the line control station and the load on the line capacity between the base station and the line control station further increases in such cases, thereby making it difficult to realize such a diversity handover in the conventional mobile communication system. Therefore, there was a limit to improving the quality of the communication in the conventional mobile communication system.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a novel and useful mobile communication system, a base station, a cluster control station, a line control station, and a mobile station, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide mobile communication system, a base station, a cluster control station, a line control station, and a mobile station, which can improve the quality of the communication, reduce the load on the line control station and the line between the base station and the line control station, and carry out a distributed autonomous process in the base station, so that an efficient mobile communication system can be realized.
Still another object of the present invention is to provide a mobile communication system comprising a line control station, and a plurality of base stations belonging to a plurality of clusters so that each of the clusters includes a plurality of base stations, wherei
Suda Hirohito
Umeda Narumi
Yamao Yasushi
Mills Donald L
Nguyen Chau
NTT DoCoMo Inc.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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