Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-07-29
2002-04-09
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S450000, C455S020000, C455S015000
Reexamination Certificate
active
06370384
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a method of and apparatus for operation of a wireless communications system, and more specifically to methods of and apparatuses for increasing communication capacity through frequency re-use planning particularly for wireless communications systems using wireless translating repeaters.
2. Background of the Invention
A conventional wireless communications network
800
is shown in FIG.
8
. As illustrated in
FIG. 8
, the wireless communications network
800
includes a plurality of cells
810
a
,
810
b
, a mobile unit
820
, a plurality of base station transceivers (BTS)
805
a
,
805
b
, communication lines
840
, a mobile telecommunications switching office (MTSO)
830
, an interface
850
, and a public switched telephone network (PSTN)
860
.
The wireless communications network
800
has a fixed number of channel sets distributed among the BTS
805
a
,
805
b
serving a plurality of cells
810
a
,
810
b
arranged in a predetermined pattern. The mobile unit
820
, in a cell
810
a
or
810
b
, communicates with the BTS
805
a
or
805
b
, respectively, via radio frequency (RF) means. The BTS
805
a
,
805
b
communicate with the MTSO
830
via communication lines
840
. The MTSO
830
communicates with the switched telephone network
860
via the interface
850
.
In the conventional wireless communications network
800
, the cell areas typically range from
1
to
300
square miles. The larger cells typically cover rural areas, and the smaller cells typically cover urban areas. Cell antenna sites utilizing the same channel sets are spaced by a sufficient distance, e.g., typically referred to as the “reuse distance”, to assure that co-channel interference is held to an acceptably low level.
The mobile unit
820
in a cell
810
a
has radio telephone transceiver equipment which communicates with similar equipment in BTS
805
a
,
805
b
as the mobile unit
820
moves from cell to cell.
Each BTS
805
a
,
805
b
relays telephone signals between mobile units
820
and a mobile telecommunications switching office (MTSO)
830
by way of the communication lines
840
.
The communication lines
840
between a cell site,
810
a
or
810
b
, and the MTSO
830
, are typically T
1
lines. The T
1
lines carry separate voice grade circuits for each radio channel equipped at the cell site, and data circuits for switching and other control functions.
The MTSO
830
in
FIG. 8
includes a switching network (not shown) for establishing call connections between the public switched telephone network (PTSN)
860
and mobile units
820
located in cell sites
810
a
,
810
b
and for switching call connections from one cell site to another. In addition, the MTSO
830
includes a dual access feeder (not shown) for use in switching a call connection from one cell site to another. Various handoff criteria are known in the art and utilize features such as delay ranging to indicate the distance of a mobile unit from a receiving cell site, triangulation, and received signal strength to indicate the potential desirability of a handoff. Also included in the MTSO
830
is a central processing unit (not shown) for processing data received from the cell sites and supervisory signals obtained from the switched telephone network
860
to control the operation of setting up and taking down call connections.
The BTS
805
a
or
805
b
provides coverage for multiple subscribers in a specific cell, e.g.,
810
a
or
810
b
. As the mobile unit
820
enters a cell, the BTS
805
a
or
805
b
and the mobile unit
820
communicate with one another. Information from this initial exchange is used by the cellular communication system
800
so that it can route calls to and from the mobile unit
820
.
The BTS
805
a
or
805
b
has a limited coverage area. As a result, one technique for providing coverage for a large geographic area is to install multiple BTS units. Multiple BTS units are installed to provide coverage for a large geographic area. This strategy also provides the benefit of increasing capacity, so that the cellular system
800
can serve a larger number of subscribers within its coverage area. However, a major drawback to this solution is the high cost of a BTS. As an alternative, a repeater is often used to improve coverage area, reduce cost, and to improve clarity.
Generally, repeaters receive a downlink signal from a BTS and retransmit the downlink signal to a mobile unit after the downlink signal has been amplified by a downlink amplifier. The process works similarly in reverse, where the repeater will amplify an uplink signal from a mobile unit to the BTS with an uplink amplifier. The amplifiers provide an increase in signal strength which improves the clarity of the calls and prevents dropped calls. To distinguish the direction of the signals transmitted and received by the repeaters, the path between the repeater and the BTS is referred to as the “backhaul” signal path.
Unfortunately, while the wireless repeaters thus far described provide a relatively large RF coverage area at a relatively low cost and without the need for a wireline backhaul, the operators of the prior art wireless communications networks must pay a penalty in available communication frequency as conventional wireless communications networks would have less number of available communications channels as a result of the addition of the repeaters.
Operators of wireless communications network must provide communications services to increasing number of subscribers using a limited available RF bandwidth. For example, each of operators of wireless systems, e.g., one based on the GSM-1900 standard, may be licensed to use only a total bandwidth of, e.g., 5 MHz to provide communications services to its subscriber.
Each communication channel of conventional wireless communications network, utilizing, e.g., the Gaussian Minimum Shift Keying (GMSK) modulated waveforms in, e.g., GSM-1900, GSM-1800 and GSM-900 standards, occupies 200 KHz of bandwidth. Moreover, because, e.g., according to the GSM standards, signal level from an adjacent channel must at least 9 dB below the desired signal level of a channel, in a conventional wireless communications network, center frequencies of any two adjacent channels must be at least 400 kHz apart from each another.
Thus, in a conventional wireless communication network having a 5 MHz of available RF bandwidth may be afforded at most 12 RF carrier channels (e.g., 5 MHz/400 kHz). The number of available carrier channels is further reduced when repeaters are employed in the network because communication via a repeater requires two rather than one channel to accommodate both the “local” communications, e.g., between the repeaters and the mobile units, and the “backhaul” communications, e.g., between the BTS and the repeaters.
For example, as shown in
FIG. 9
, a wireless communications network having one local cell A, and
5
repeaters B, C, D, E, and F, may utilize every other available frequency carrier channels, and thus would only be afforded 6 carrier channels
1
,
3
,
5
,
7
,
9
,
11
, and
13
(e.g., half of a network without repeaters), and thus may only have a total of
6
cells that may be served by a BTS.
Furthermore, if an operator of a conventional wireless communications network desires to have more available channels, then the operator must reduce the number of repeaters, thus also reducing the coverage area. Thus, in a conventional wireless communications network, a trade-off between efficient utilization of available RF bandwidth and larger coverage area usage must be made.
Accordingly, there is a need in the art for frequency planning that allows the maximum usage of the available RF bandwidth of a wireless communications network while at the same time affording an operator of the network the benefit of employing repeaters for larger coverage area.
SUMMARY OF THE INVENTION
An object of the present invention is to provide the maximum efficiency in RF bandwidth utilization in a wireless communicati
Airnet Communications Corporation
Perez-Gutierrez Rafael
Senterfitt Akerman
Trost William
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