Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2000-11-21
2004-05-11
Maung, Nay (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S517000, C455S519000, C370S327000
Reexamination Certificate
active
06735446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile communication system that carries out digital communication with efficient use of vacant channels in a one-way communication which is performed by separately assigning different channels for the transmission and the receiving. The present invention relates to a method for channel assignment of the mobile communication system. Further, the present related to a control unit for use in the mobile communication system.
2. Description of the Related Art
A mobile communication system that is designed to carry out public service operations, such as fire or police call management operations, by using a multi-channel access (MCA) technique is known.
FIG. 20
shows a conventional mobile communication system of this type.
In the conventional mobile communication system of
FIG. 20
, mobile station units
10
, base station units
20
, and a central control unit
30
are provided. Each of the mobile station units
10
is formed by mounting a radio communication device on a fire engine or the like. The base station units
20
and the mobile station units
10
communicate with each other by using radio channels. The central control unit
30
controls the radio channels of the base station units
20
and is linked to a core network L.
Generally, in the mobile communication system, a multiple access communication is performed by using the frequency division multiple access (FDMA) method or the time division multiple access (TDMA) method. Alternatively, the code division multiple access (CDMA) method may be used to perform the multiple access communication.
In the above conventional mobile communication system, a two-way communication between the mobile station units
10
is normally performed. In the central control unit
30
, upstream and downstream communication channels are assigned to each of the respective mobile station units
10
that perform the two-way communication, in order to achieve the two-way communication between the mobile station units
10
. Another type of the one-way communication between the mobile station units
10
, which is carried out in the conventional mobile communication system of
FIG. 20
, is a one-to-multiple one-way communication in which a single transmitter sends information to multiple receivers.
A description will be given of the one-to-multiple one-way communication (hereinafter, called the group communication) between the mobile station units
10
with reference to FIG.
20
.
Suppose that, in the mobile communication system of
FIG. 20
, the FDMA method is used to carry out the group communication. In the FDMA method, the available channel bandwidth is divided into a number of frequency non-overlapping subchannels and a subchannel is assigned to each mobile station unit
10
upon request by the mobile station units
10
.
As shown in
FIG. 20
, the mobile station units
10
-
1
and
10
-
2
exist in a radio zone “ZoneA” of the base station unit
20
-
1
, and the mobile station units
10
-
3
and
10
-
4
exist in a radio zone “ZoneB” of the base station unit
20
-
2
. In the mobile communication system of
FIG. 20
, the mobile station units
10
-
1
through
10
-
4
pertain to the same group (called group
1
) for the group communication.
When a request for the group communication related to the group
1
is transmitted by the mobile station unit
10
-
1
, the central control unit
30
receives the group communication request via the base station unit
20
-
1
. In response to the request, the central control unit
30
retrieves the radio zone in which the mobile station units pertaining to the group
1
exist, by accessing, through the core network, a home location register (HLR)
50
that is connected to the core network. As described above, the mobile station units
10
-
2
,
10
-
3
and
10
-
4
pertain to the group
1
, the mobile station unit
10
-
2
exists in the radio zone “ZoneA” of the base station unit
20
-
1
, and the mobile station units
10
-
3
and
10
-
4
exist in the radio zone “ZoneB” of the base station unit
20
-
2
.
FIG. 21
shows a channel assignment of the conventional mobile communication system of
FIG. 20
in which radio channels are assigned to the mobile stations.
As shown in
FIG. 21
, in the above case of the group communication request, the central control unit
30
assigns an upstream subchannel f
1
(channel
1
) and a downstream subchannel f
2
(channel
2
) for the radio zone ZoneA of the base station unit
20
-
1
, and assigns an upstream subchannel f
3
(channel
3
) and a downstream subchannel f
4
(channel
4
) for the radio zone ZoneB of the base station unit
20
-
2
. This channel assignment is the same as that in the case of the normal two-way communication.
During the group communication between the mobile station units, the mobile station unit
10
-
1
transmits an upstream group-communication signal at the frequency f
1
to the central control unit
30
, whereas the central control unit
30
transmits a downstream group-communication signal at the frequency f
2
to the mobile station unit
10
-
2
and transmits a downstream group-communication signal at the frequency f
4
to the mobile station units
10
-
3
and
10
-
4
. Hence, the one-to-multiple one-way communication between the mobile station units
10
(or the group communication) is carried out by the conventional mobile communication system.
In the TDMA method, the multiple subchannels for multiple access are created by dividing the frame duration into a number N of non-overlapping subintervals, each of individual durations divided by the number N. Then each mobile station unit that requests the group communication is assigned to a particular time slot within each frame. In the CDMA method, each mobile station unit is assigned a unique code sequence that allows the mobile station unit to spread the information signal across the assigned frequency band. Thus, the multiple subchannels for multiple access are created.
However, the conventional mobile communication system assigns the subchannels to the mobile station units in the group communication (the one-way communication) in a manner that is the same as in the normal two-way communication. According to the channel assignment of the conventional mobile communication system, the subchannels that are not used for the group communication are also assigned to the mobile station units. As a result, the efficiency of use of the available frequency channels is lowered.
As described above, the conventional mobile communication system assigns both the upstream subchannel and the downstream subchannel for each base station unit
20
during the group communication. In the channel assignment of
FIG. 21
, the upstream subchannel f
3
is assigned for the base station unit
20
-
2
, but only the downstream subchannel f
4
is used to transmit the group-communication signal to the mobile station units
10
-
3
and
10
-
4
during the group communication. Therefore, during the group communication of the conventional mobile communication system, the vacant channels (for example, f
3
) are always provided in the base station units
20
that are different than the base station unit
20
including the mobile station unit
10
transmitting the group communication request and include the mobile station units
10
related to the group specified by the request.
Further, in the conventional mobile communication system of
FIG. 20
, the mobile station unit
10
-
2
pertains to the base station unit
20
-
1
that includes the mobile station unit
10
-
1
transmitting the group communication request, and is included in the radio zone of the base station unit
20
-
1
. In this case, the downstream subchannel f
2
is assigned to the mobile station unit
10
-
2
in the base station unit
20
-
1
, and the downstream subchannel f
2
is used to transmit the group-communication signal to the mobile station unit
10
-
2
. However, there is a case in which the mobile station unit
10
related to the group specified by the group communication reques
Hasegawa Hajime
Iwata Yasuharu
Fujitsu Limited
Gantt Alan T.
Katten Muchin Zavis & Rosenman
Maung Nay
LandOfFree
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