Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-05-29
2004-09-14
Nguyen, Simon (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S560000, C455S561000, C455S502000, C455S524000, C375S220000, C375S377000
Reexamination Certificate
active
06792267
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
is a block diagram of a conventional cellular radiotelephone communication system. As shown in
FIG. 1
, cellular radiotelephone communication system
100
includes a plurality of cells
170
each of which includes a base station
120
a
-
120
n
. Although two cells
170
are shown in
FIG. 1
, it will be understood that a large number of cells and a large number of base stations
120
a
-
120
n
are generally included in the cellular radiotelephone communication system. Cellular radiotelephones
130
in the cells
170
communicate with the base stations
120
a
-
120
n.
Cellular radio exchange
110
is connected to each of the base stations
120
a
-
120
n
via a respective uplink
140
a
-
140
n
and a respective downlink
150
a
-
150
n
. Cellular radio exchange
110
controls communication among the cellular radiotelephones via the base stations. Cellular radio exchange also controls communications between the cellular radiotelephones
130
and wire telephones via a connection
160
to the Public Switched Telephone Network (PSTN). The design of cellular radiotelephone communication system
100
is well known to those having skill in the art and need not be described further herein.
Cellular radiotelephone communication systems are often installed for communications over a large geographic area using large cells, as evidenced by the cellular radiotelephone base stations that have now become a commonplace sight along highways. However, in densely populated cities, the cells may be small, covering several city blocks or less. Recently, it has also been proposed to provide cellular radio communication systems within a building in a DAMPS Wireless Office System (DWOS). In such a wireless office system, base stations may be located in spaced apart locations on one or more floors of an office building, to thereby provide wireless communications within the office building using conventional cellular radiotelephones.
In cellular systems, there may be conflicting requirements that may affect the architecture of the cellular radio exchange and the base stations. For example, it is generally desirable to produce low cost base stations and cellular radio exchanges. On the other hand, high quality voice communications should be provided by the cellular radiotelephone system.
More specifically, in a wireless office system, it is generally desired to maintain low cost of the base stations because many base stations are used in the system compared to the cellular radio exchange. In order to support high quality voice communication, it is also generally desired to use macro diversity, wherein radio frequency communications from a cellular radiotelephone are received by more than one receiver at a base station, to thereby allow diversity reception and improve radio link quality.
FIG. 2
illustrates a conventional cellular radiotelephone system with wideband transmissions between the base stations and cellular radio exchange. More specifically, in
FIG. 2
, cellular radiotelephone system
200
includes a base station
120
′ and a cellular radio exchange
110
′, wherein wideband signals are uplinked from the base station
120
′ to the cellular radio exchange
110
′ over uplink
140
′, and wideband signals are downlinked from cellular radio exchange
110
′ to base station
120
′ over downlink
150
′. It will be understood that although
FIG. 2
illustrates only one base station
120
′, many base stations conventionally are used. Moreover, more than one cellular radio exchange
110
′ may also be used. The uplink
140
′ and downlink
150
′ may be provided by a radio frequency uplink and downlink, or a wired uplink and downlink, as is well known to those having skill in the art.
More specifically, the wideband architecture of
FIG. 2
uses wideband digital distribution of digital Intermediate Frequency (Digital IF) signals, for example at a rate of 10-1000 megabits per second (Mbps). In the wideband architecture, the entire frequency band of received cellular radiotelephone communications is sampled and these samples are uplinked to the cellular radio exchange
110
′ for processing. Thus, the base stations need only act as relays, so that the base stations can be simple and low cost. Signal processing complexity is placed in the cellular radio exchange
110
′, where the central processing power can be shared and used efficiently to further decrease cost.
More specifically, referring to
FIG. 2
, base station
120
′ includes a digital-to-analog converter (DAC)
202
that receives wideband digital distribution signals, for example at rates between 10-1000 Mbps, from downlink
150
′. A first wideband channel filter
204
filters the analog signal. The filtered analog signal is provided to a radio frequency transmitter/receiver (transceiver)
230
that includes a first modulator
206
, a transmit local oscillator (TXLO)
208
, a power amplifier
210
and an isolator
212
. The amplified radio frequency signal from power amplifier
210
is transmitted via antenna
224
, to provide radiotelephone communications with a radiotelephone
130
.
Radiotelephone communications that are received from a radiotelephone
130
at antenna
224
are routed to low noise amplifier
214
by isolator
212
and are then down-converted from radio frequency by a second modulator
216
using receive local oscillator (RXLO)
218
. The output of second modulator
216
is provided to second wideband channel filter
220
and to an analog-to-digital converter (ADC)
222
. The digitized output of analog-to-digital converter
222
is uplinked to cellular radio exchange
100
via wideband uplink
140
′. Accordingly, similar to downlink
150
′, uplink
140
′ is a wideband digital uplink, for example at rates between 10-1000 Mbps.
At the cellular radio exchange
110
′, the wideband uplink
140
is received by digital channelizer
252
and separated into two or more digital channels that are provided to a demodulator
250
. Demodulator
250
includes at least two synchronizer/downsamplers
254
a
and
254
b
, that synchronize and downsample the digital channels created by the digital channelizer
252
. The synchronized and downsampled signals are then provided to a diversity combiner/equalizer
256
that can perform macro-diversity combining. The output of the diversity combiner/equalizer
256
is provided to a channel decoder
258
, the output of which is provided to speech decoder
260
. The decoded speech is then provided to a processor
270
, for example at 64 kilobits per second (Kbps) per call (i.e. per radiotelephone communication), which can perform control functions, such as routing signals to PSTN
160
and other base band and signal processing functions such as echo canceling.
When a signal is received by processor
270
that is to be transmitted to a radiotelephone
130
, the signal is provided to speech coder
272
(for example at 8 Kbps/call) and channel decoder
274
. Channel coder
274
may provide I/Q symbols at 48.6 Kbps per call. The speech coded signal is then provided to modulator
276
to produce the wideband signal that is downlinked to base station
120
′ over downlink
150
′. The overall design of base
Backstrom Olof Tomas
Bexten Ronald L.
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Nguyen Simon
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