Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-05-29
2002-11-05
Kincaid, Lester G. (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S434000, C455S062000
Reexamination Certificate
active
06477377
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to communications systems and methods, and in particular to radiotelephone communications systems and methods.
BACKGROUND OF THE INVENTION
Cellular radiotelephone systems are commonly employed to provide voice and data communications to a plurality of subscribers. For example, analog cellular radiotelephone systems, such as designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed successfully throughout the world. More recently, digital cellular radiotelephone systems such as designated IS-54B in North America and the pan-European GSM system have been introduced. These systems, and others, are described, for example, in the book titled
Cellular Radio Systems
by Balston, et al., published by Artech House, Norwood, Mass., 1993.
FIG. 1
illustrates a conventional terrestrial cellular telephone communication system
100
. The cellular radiotelephone communication system
100
includes one or more radiotelephones
102
communicating with a plurality of cells
104
, each of which is served by a base station (BS)
106
a
-
106
n
. The base stations
106
a
-
106
n
communicate with a mobile telephone switching office (MTSO)
108
. Although only six cells are shown in
FIG. 1
, a typical cellular network may comprise hundreds of cells, may include more than one MTSO and may serve thousands of radiotelephones.
The cells
104
generally serve as nodes in the communication system
100
from which links are established between radiotelephones
102
and the MTSO
108
by way of the base stations
106
a
-
106
n
serving the cells
104
. Each cell will have allocated to it one or more dedicated control channels
110
a
-
110
n
, and one or more traffic channels
112
a
-
112
n
. The radiotelephone traffic channels are used by the base stations for radiotelephone communications (such as voice and/or data communications) with the radiotelephones. The control channels are used by the base stations to control radiotelephone communications with the radiotelephones over the radiotelephone traffic channels. Thus, for example, the control channel may be used to broadcast system information to the radiotelephones and also to send and receive access messages to and from individual radiotelephones. The base stations
106
a
-
106
n
are connected to the MTSO by a plurality of bidirectional links
114
a
-
114
n
, which may be hardwired or wireless links. Through the cellular network
100
, a duplex radio communication link may be effected between two radiotelephones
102
or between a radiotelephone
102
and a land line telephone user. The base stations
106
a
-
106
n
handle radio communication between the radiotelephones in the associated cell
104
and the MTSO
108
. In this capacity, the base stations
106
a
-
106
n
function chiefly as a relay station for data and voice signals.
As shown in
FIG. 1
, the dedicated control channels
110
a
-
100
n
are generally broadcast using a different radio frequency F
1
-F
n
per cell. The traffic channels
112
a
-
112
n
are allocated among a plurality of radio frequencies to reduce and preferably eliminate interference using conventional frequency allocation techniques that are well known to those having skill in the art. As also shown in
FIG. 1
, several cells may be combined into larger groups
120
, called paging areas in cellular radiotelephone standard IS-136 or location areas in GSM. The grouped paging areas can reduce the paging and registration loads on the system. Pages to radiotelephones may only be transmitted to the paging area
120
in which the radiotelephone is located. Registration need only take place when a radiotelephone moves between paging areas.
Unfortunately, a cellular radiotelephone system
100
as described in
FIG. 1
may have excess control channel capacity in each cell. More specifically, each control channel may have the capacity to control many more radiotelephones than are generally found within the cell. Accordingly, valuable radio spectrum may be wasted.
This wasted control channel radio spectrum may be reduced by distributing a common control channel via many base stations, forming a larger logical cell including many smaller cells around each base station. The common control channel is multicast on the same frequency in every base station. Accordingly, as shown in
FIG. 2
, cellular radiotelephone system
200
includes radiotelephones
102
, cells
104
, MTSO
108
, traffic channels
112
a
-
112
n
and links
114
a
-
114
n
, as was already described in connection with FIG.
1
. However, in contrast with
FIG. 1
, each base station
206
a
-
206
n
broadcasts the same control channel
210
on the same frequency F
1
. Thus, a common control channel is transmitted by the base stations to control radiotelephone communications with the radiotelephones over the radiotelephone traffic channels. By using a common control channel on a common frequency F
1
, excess capacity in the control channel may be reduced.
Unfortunately, it may be difficult to find a frequency F
1
that can be used by the common control channel of all the base stations without interference. Interference may occur in conventional cellular radiotelephone systems, as described in connection with
FIGS. 1 and 2
. Moreover, interference may be exacerbated in Wireless Office Systems (WOS) that are installed in a building to provide cellular radiotelephone communication among cellular radiotelephones that are located in the building. When installing a wireless office system in a building, there may be excess capacity in the control channel. For example, a wireless office system may be designed for installation in offices with up to 450 users. However, the control channel may have a capacity of up to 1000 users. Thus, a common control channel may be preferred to reduce excess capacity. However, it may be difficult to identify a radio frequency that can be used by all of the WOS base stations to transmit the common control channel.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved cellular radiotelephone systems and methods.
It is another object of the present invention to provide cellular radiotelephone systems and methods that can reduce excess capacity in the control channel that is transmitted by the base stations.
It is yet another object of the present invention to provide cellular radiotelephone systems and methods that can reduce the excess capacity of the control channel without incurring excessive control channel interference.
These and other objects are provided, according to the present invention, by transmitting a common control channel in a cellular radiotelephone system from a first one of the base stations over a first radio frequency and from a second one of the base stations over a second radio frequency that is different from the first radio frequency. By providing a common control channel, excess control channel capacity can be reduced and preferably eliminated, thereby conserving control channel radio spectrum. Moreover, by transmitting the common control channel using multiple radio frequencies, the radio frequencies can be selected to reduce and preferably eliminate interference.
More specifically, cellular radiotelephone systems and methods according to the invention communicate with a plurality of cellular radiotelephones via a plurality of base stations. A plurality of radiotelephone traffic channels are used by the base stations for radiotelephone communications with the radiotelephones. A common control channel is transmitted by the base stations to control radiotelephone communications with the radiotelephones over the radiotelephone traffic channels. According to the invention, the common control channel is transmitted by a first one of the base stations over a first radio frequency and is transmitted by a second one of the base stations over a second radio frequency that is different from the first radio frequency. The cellular radiotelephone system also preferably comprises a central control channel handler (CCH) that synchronously transmit
Backstrom Olof Tomas
Freeze John Mark
Ericsson Inc.
Kincaid Lester G.
Myers Bigel & Sibley & Sajovec
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