Apparatus and method for sharing a signaling channel

Details Apparatus and method for sharing a signaling channel Apparatus and method for sharing a signaling channel

1997-08-29

2003-01-14

Ton, Dang (Department: 2661)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S328000

Reexamination Certificate

active

06507575

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to telecommunications system and, in particular, to wireless communications system using a common transmission line to connect a plurality of base stations to a base station controller.
BACKGROUND OF THE RELATED ART
Wireless communication systems generally use transmission lines that are configured in a channelized format, such as T
1
or E
1
facilities, to connect a set of base stations to a base station controller (BSC).
FIG. 1
illustrates a wireless communication system
10
in which a BSC
12
is individually connected to base stations
14
-i via respective T
1
facilities
16
-i, where i=1, 2, . . . , n. Each of the T
1
facilities
16
-i includes a downlink path
17
-i and an uplink path
19
-i, as shown in
FIG. 2
, for the transmission of data to and from the base stations
14
-i, respectively. Each of the paths
17
-i,
19
-i is configured into a channelized format—that is, the paths are divided into transmission time slots.
FIG. 3
illustrates a manner for channelizing the paths
17
-i,
19
-i. Each of the paths
17
-i,
19
-i is divided into frames having a framing time slot and twenty-four DS
0
j
time slots, where j=1, 2, . . . , 24 and each of the DS
0
j
time slots has a 64 Kbps bandwidth. Thus, the wireless communication system
10
has a 24·n number of DS
0
j
time slots in the downlink direction and 24·n number of DS
0
j
time slots in the uplink direction.
The DS
0
j
time slots are used to form communication channels, including a signaling channel and a plurality of traffic channels. Each communication channel includes at least one DS
0
j
time slot in the downlink path
17
-i and the uplink path
19
-i. For purposes of discussion, a DS
0
j
time slot shall be hereinafter deemed to refer to both a DS
0
j
time slot in the downlink path and a DS
0
j
time slot in the uplink path, unless otherwise specified.
Each of the base stations
14
-i uses x number of DS
0
j
time slots as a signaling channel for transmitting control information between the base station
14
-i and the BSC
12
, where x≧1. Each of the base stations
14
-i can support enough user traffic to consume p number of traffic channels (for transmitting the user traffic between the base station
14
-i and the BSC
12
and a voice switch, not shown), wherein a traffic channel comprises y number of DS
0
j
time slots and y≧1. Thus, the T
1
facilities
16
-i should at least have a bandwidth that includes q number of DS
0
j
time slots, where q=y·p+x.
Generally, each of the T
1
facilities
16
-i has a bandwidth that includes more than q number of DS
0
j
time slots—that is, the user traffic supported by an individual base station (and the control information) does not consume the entire bandwidth available on a T
1
facility (i.e., q<n). Thus, the base station does not use some DS
0
j
time slots resulting in inefficient utilization of the T
1
facility.
To more efficiently utilize T
1
facilities and reduce the cost of a wireless communication system, one or more T
1
facilities may be shared by a plurality of base stations.
FIG. 4
illustrates a wireless communication system
20
in which a daisy chain configuration is used to connect n number of base stations
22
-i to a BSC
24
via a common T
1
facility
26
. Unlike the wireless communication system
10
, the wireless communication system
20
has a total of 24 number of DS
0
j
time slots (compared to 24·n number of DS
0
j
time slots in the wireless communication system
10
). Like the base stations
14
-i, each of the base stations
22
-i has its own signaling channel comprising x number of DS
0
j
time slots—that is, n·x number of DS
0
j
time slots on the T
1
facility
26
are used as signaling channels. The remaining DS
0
j
time slots in the T
1
facility
26
, i.e., m−n·x, can be used as traffic channels. The number of remaining DS
0
j
time slots should be at least equal to the total number of DS
0
j
time slots needed by the base stations
22
-i to support user traffic, i.e., 24−n·x·y·p·n. Recall that n represents the total number of base stations, x represents the number of DS
0
j
time slots composing a signaling channel, y represents the number of DS
0
j
time slots composing a traffic channel, and represents the number of traffic channels consumable by user traffic per base station.
In some cases, the total number of DS
0
j
time slots needed by the base stations to support user traffic is greater than the number of remaining DS
0
j
time slots. In these cases, more DS
0
j
time slots (or traffic channels) are required to support the user traffic. For example, suppose the wireless communication system
20
includes five base stations (i.e., n=5), each signaling channel and traffic channel comprises one DS
0
j
time slot (i.e., x=1 and y=1), and the user traffic supported by each of the base stations
22
-i consumes four traffic channels (i.e., p=4). If each base station
2
-i has its own signaling channel (for a total of five DS
0
j
time slots), then there would only be nineteen DS
0
j
time slots available for use as traffic channels by the five base stations. Since each base station supports enough user traffic to consume four traffic channels, twenty DS
0
j
time slots are needed by the wireless communication system for traffic channels. Because the T
1
facility has only nineteen DS
0
j
time slots available for use as traffic channels, the needs of the wireless communication system
20
would exceed the capacity of the T
1
facility.
One way to increase the number of DS
0
j
time slots available for use as traffic channels is to use additional T
1
facilities. Such a solution would undesirably increase the cost of the wireless communication system. Accordingly, there exists a need for increasing the number of DS
0
j
time slots available for use as traffic channels in a T
1
facility connecting two or more base stations to a base station controller.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and a method for increasing the number of DS
0
j
time slots available for use as traffic channels in a T
1
or E
1
facility connecting two or more base stations to a base station controller by sharing a signaling channel among the base stations. The present invention is based on the concept that a single base station does not utilize the entire bandwidth of the signaling channel for the transmittal of signaling messages, i.e., control information for managing resources at one or more base stations. Better utilization of the signaling channel bandwidth can be achieved if two or more base stations can share the same signaling channel which, in turn, results in making more DS
0
j
time slots available fox use as traffic channels. To share a signaling channel, the wireless communication system should be configured such that each of the base stations can receive its signaling over a downlink the signaling channel, and transmit its signaling messages to the base station controller over an uplink signaling channel without interfering with signaling messages transmitted by other base stations over the uplink signaling channel.
In one embodiment, the base station controller transmits over the downlink signaling channel a downlink signaling message with an associated identifier which specifies the base station to which the signaling message is intended. Each of the base stations bridges or taps onto the transmission facility to receive the downlink signaling message and identifier. This permits downlink signaling messages and identifiers to pass transparently through the receiving base station and to other base stations in the wireless communication system. The receiving base station examines the identifier to determine whether the associated downlink signaling message is intended for that base station. If yes, the base station executes instructions contained within the downlink signaling message. Otherwise, the downlink signaling message is ignored.
In another embodiment of the present

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