Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-07-30
2002-11-05
Vo, Nguyen T. (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S561000, C455S127500
Reexamination Certificate
active
06477388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a power management system in a base station transceiver system. In particular, the present invention allocates power to channels on a demand-based system for the base station transceiver system.
2. Background of the Invention
A conventional cellular phone system
1300
is shown in FIG.
1
. As illustrated in
FIG. 13
, the cellular phone system
1300
includes a plurality of cells
1310
a,
1310
b,
a mobile unit
1320
, a plurality of base transceiver stations (BTS)
1305
a,
1305
b,
communication lines
1340
, a mobile telecommunications switching office (MTSO)
1330
, an interface
1350
and a switched telephone network
1360
.
The cellular phone system
1300
has a fixed number of channel sets distributed among the BTS
1305
a,
1305
b
serving a plurality of cells
1310
a,
1310
b
arranged in a predetermined reusable pattern. The mobile unit
1320
, in a cell
1310
a
or
1310
b,
communicates with the BTS,
1305
a
or
1305
b,
respectively, via radio frequency (RF) means. The BTS
1305
a,
1305
b
communicate with the MTSO
1330
via communication lines
1340
. The MTSO
1330
communicates with the switched telephone network
1360
via the interface
1350
.
In the cellular phone system
1300
, 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 to assure that co-channel interference is held to an acceptably low level.
The mobile unit
1320
in a cell
1310
a
has radio telephone transceiver equipment which communicates with similar equipment in BTS
1305
a,
1305
b
as the mobile unit
1320
moves from cell to cell.
Each BTS
1305
a,
1305
b
relays telephone signals between mobile units
1320
and a mobile telecommunications switching office (MTSO)
1330
by way of the communication lines
1340
.
The communication lines
1340
between a cell site,
1310
a
or
1310
b,
and the MTSO
1330
, 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
1330
in
FIG. 1
includes a switching network (not shown) for establishing call connections between the public switched telephone network
1360
and mobile units
1320
located in cell sites
1310
a,
1310
b
and for switching call connections from one cell site to another. In addition, the MTSO
1330
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 phase 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
1330
is a central processing unit (not shown) for processing data received from the cell sites and supervisory signals obtained from the switched telephone network
1360
to control the operation of setting up and taking down call connections.
In order to remain competitive in an increasingly crowded market, wireless equipment manufacturers experience constant pressure to reduce their costs. One way to reduce the overall cost of a cellular phone system is to re-design individual system components to operate at a lower cost.
In the conventional cellular phone system, the power amplifier used in a BTS is a significant factor contributor to the overall cost of the BTS. As one of the most expensive components, it would be desirable to have the power amplifier operate as efficiently as possible in terms of power usage, in order to minimize the hardware requirements for this high cost component.
In a typical broadband Base Transceiver System that supports multiple conversations with mobile stations on different frequencies, each carrier signal must be amplified separately. It is possible to provide a single power amplifier for each carrier, along with a frequency selective combiner. This architecture suffers significant loss of efficiency due to the insertion losses encountered in the frequency combiner. Perhaps more significantly, the frequency combiner is physically large, with and typically has “static” frequency selectivity which needs to be manually tuned during base station installation and reconfiguration. The efficiency of a single carrier power amplifier installation can be improved through the installation of antenna combiners, an architecture that generally requires mast mounted power amplifiers, which increases the required geographic area for the base station installation. The arrangement of small power amplifiers in an array, using spatial combination of a number of antenna elements instead of one central power amplifier per antenna, improves the physical space requirements of the system, but it still requires multiple antenna installations, and accordingly requires a relatively large physical space in which to locate the installation.
The installation of a single, high-power multi-carrier power amplifier (MCPA) will overcome these drawbacks of the single carrier power amplifier installation. However, a common limitation of the multi-carrier amplifier is linearity—that is, the typical MCPA provides a fixed amount of power for each carrier in the BTS in a technique known as the “divide among carriers” scheme.
This fixed division of power has some drawbacks. For instance, a fixed amount of power for each carrier necessarily limits the distance that the broadband BTS can transmit. When a carrier wave is initially transmitted, the strength of the carrier wave is close to the fixed amount of power assigned to that carrier. As the carrier wave propagates through space, the power decreases, varying inversely proportionally to the transmission distance R raised to the fourth power, i.e.
Power
∝
1
R
4
Since mobile subscribers cannot detect signals below a minimum threshold level of transmitted power, capping the transmit power of each carrier wave limits how far that carrier wave can travel. Thus, fixing the amount of transmit power limits the cell size that the BTS can serve.
Another drawback of the “divide among carriers scheme” is that it uses the overall power allocated to the BTS inefficiently. The power allocated to the unused carriers is wasted when fewer than all of the carriers are in use.
In the event of failure of a power amplifier module in a MCPA, the “divide among carriers” scheme is incapable of compensating for the failure. Typically, the BTS MCPA has several MCPA modules. If one or more of the MCPA modules fails, there is typically not a way for the remaining modules to compensate for the loss of the failed power amplifier modules. Since in that situation there are less power amplifier modules available for the same number of carriers, the actual power supplied to each carrier is less than the power set for the carrier. This reduction in power to each carrier results in an associated reduction in distance that the carrier propagates, and thus the cell site coverage is reduced.
Similarly, the “divide among carriers” scheme does not automatically compensate when additional MCPA modules are installed in the BTS. Since in the “divide among carriers” scheme the amount of power for each carrier has already been set, the installation of additional power supply units does not automatically increase the power per carrier without significant reprogramming of the BTS.
Furthermore, because an MCPA is typically one of the most expensive components of a BTS, it is desirable to deliver a power supply with the minimum number of MCPA modules while retaining the ability to provide maximum transmit power. Minimizing the size of the power amplifier may lower the cost of the power amplifier, which in turn lowers the overall cost of the BTS.
Accordingly, there is a need for a multicarrier power amplifier that can de
Airnet Communications Corporation
Akerman & Senterfitt
Vo Nguyen T.
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