Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-03-12
2002-04-16
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S062000, C455S450000
Reexamination Certificate
active
06374111
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to cellular telecommunications networks and, in particular, to retuning cells within telecommunications networks.
2. Description of Related Art
Reference is now made to
FIG. 1
wherein there is illustrated an exemplary cell structure and frequency plan assignment for use in a radio frequency reuse cellular telephone system. An arbitrary geographic region (hereinafter “the service area”) is divided into a plurality of contiguous cell sites
10
schematically represented by hexagons. Each of these cell sites
10
is sectorized to include three cells
11
. The cell sites
10
are then grouped into clusters
12
(outlined in bold to ease recognition). For example, in the frequency plan of
FIG. 1
, each cluster
12
includes seven cell sites
10
(
1
)-
10
(
7
). It will, of course, be understood that each cluster
12
may have more or less cell sites
10
as required by the selected frequency plan.
The available frequencies in the allocated hyperband are divided in accordance with the frequency plan into channel groups
14
, with the channel groups assigned amongst the cells
11
of each cell site
10
in a cluster
12
such that the radio channels of the allocated hyperband are reused in each cluster. For example, in a plan having seven cell sites
10
per cluster
12
(and three cells
11
per cell site) like that shown in
FIG. 1
, there are twenty-one channel groups
14
identified and differentiated from each other by the alphanumeric labels “A
1
, A
2
, A
3
” through “G
1
, G
2
, G
3
” corresponding to the cells
11
(
1
)
a
-
11
(
7
)
c,
respectively. Thus, each cell
11
(
1
)
a
in the service area is assigned use of radio channels of the allocated hyperband in channel group Al, each cell
11
(
2
)
a
is assigned use of radio channels of the allocated hyperband in channel group B
1
, and so on up to each cell
11
(
7
)
a
being assigned use of radio channels of the allocated hyperband in channel group G
1
. Cells
11
(
1
)
b
through
11
(
7
)
b
are assigned the radio channels of the allocated hyperbands in channel groups A
2
through G
2
, respectively, while cells
11
(
1
)
c
through
11
(
7
)
c
are assigned the radio channels of the allocated hyperbands in channel groups A
3
through G
3
, respectively. An exemplary channel chart correlating three hundred thirty-three available individual analog radio channels to the channel groups
14
in the plan illustrated in
FIG. 1
is shown in TABLE 1.
TABLE 1
A1
B1
. . .
A2
B2
. . .
A3
B3
. . .
G3
333
332
326
325
319
318
313
312
311
305
304
298
297
292
291
290
284
283
277
276
271
270
269
263
262
256
255
250
249
248
242
241
235
234
229
228
227
221
220
214
213
208
207
206
200
199
193
192
187
186
185
179
178
172
171
166
165
164
158
157
151
150
145
144
143
137
136
130
129
124
123
122
116
115
109
108
103
102
101
95
94
88
87
82
81
80
74
73
67
66
61
60
59
53
52
46
45
40
39
38
32
31
25
24
19
18
17
11
10
4
3
It will be noted that in such a frequency plan, adjacent cells
11
are typically not assigned use of the same channel group. Reuse of an identical channel group in the service area is preferably made with a separation of at least more than one cell site
10
along with a regulation of broadcast power from each cell to constrain radio propagation substantially within the cell area. Furthermore, it will be noted that typically no one cell
11
utilizes channels in the allocated hyperband that do not meet some minimal channel separation. Adjacent channel groups are preferably assigned no closer than one cell
11
away from each other. By arranging the cell sites
10
in clusters
12
and dividing cell sites into cells
11
as shown in
FIG. 1
, regulating broadcast power of communications within the cell as mentioned above, and further by assigning channels in the fashion mentioned above, the likelihood of interference is reduced while simultaneously providing effective cellular communications services across a very large service area.
Each of the cell sites
10
in a cellular telephone system such as that illustrated in
FIG. 1
includes at least one base station (BS)
18
configured to facilitate radio channel communications with mobile stations
20
moving throughout the service area. The base stations
18
are illustrated as being positionally located at or near the center of each of the cell sites
10
. However, depending on geography and other known factors, the base stations
18
may instead be located at or near the periphery of, or otherwise away from the centers of, each of the cell sites
10
. Each base station
18
includes three directional antennas
19
, wherein each of the directional antennas are pointed towards and serve a particular cell
11
.
The base stations
18
are connected by communications links (generally shown by arrow
16
) to at least one mobile switching center (MSC)
22
operating to control the operation of the system for providing cellular communications with the mobile stations
20
. Operation of the mobile switching center
22
and base station
18
to provide cellular telephone service is well known to those skilled in the art, and will not be described.
Referring now to
FIG. 2
, an exemplary base station
18
configured in accordance with the present invention is described. Each base station
18
includes three directional antennas
19
a,
19
b,
and
19
c,
each serving a particular cell
11
. Each antenna is connected to a plurality of channel equipments (Tx/Rx)
24
each capable of operating independently on a different radio channel of the channel group
14
assigned to the cell
11
served by the antenna
19
. In the present example, each channel equipment
24
connected to directional antenna
19
a
operates at a different radio channel of the A
1
channel group as described in TABLE 2.
TABLE 2
Tx/Rx
A1 Channel
24 (1)
333
24 (2)
312
24 (3)
291
24 (4)
270
24 (5)
249
24 (6)
228
24 (7)
207
24 (8)
186
The capacity or maximum number of users of a cell site
10
is dictated by the number of assigned channels. In order to accommodate the demand for a cellular telecommunications network, each cell site
10
is strategically placed and sized so that the demand within the cell site is commensurate with the capacity. Accordingly, in high traffic areas such as a metropolitan city, cell sites
10
are generally smaller in size, while in more rural areas, cell sites
10
are larger in size. After the cell sites
10
are strategically positioned and sized, channel assignments are made in accordance with a frequency reuse plan which minimizes co-channel interference.
However, over time the demand for cellular telecommunications services is subject to change. Increasing numbers of persons subscribing to cellular services as well as population growth in the geographic area of the cell site
10
can cause the demand for cellular telecommunications services to exceed the capacity of a cell site
10
. To accommodate the additional demand, additional cell sites
10
are placed in the area and a larger number of smaller cell sites
10
accommodate the same area. The placement of additional cell sites
10
requires a reassignment of the channels for the cells
11
to minimize co-channel interference. The reassignment often requires preexisting cells
11
to be retuned in accordance with the channel reassignment. When the cell
11
is retuned to a new channel assignment, each channel equipment
24
connected to the directional antenna
19
serving the cell must be retuned to one of the new channels. The process of retuning a channel equipment
24
involves temporarily disabling the channel equipment and calibrating the channel equipment to a new channel.
A problem arises when a channel equipment
24
is retuned to a channel that is too close to a channel currently used by another channel equipment
24
. For example, if the channel equipment
24
connected to the directional antenna
19
a
were to be retuned from the A
1
channel group to the G
3
channel group, each channel equipment would have to be retuned from a cha
Briere Sylvain
Murphy Mark
Chow Charles
Cong Le Thanh
Jenkins & Gilchrist
Telefonaktiebolaget LM Ericsson (publ)
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