Multiplex communications – Generalized orthogonal or special mathematical techniques – Plural diverse modulation techniques
Reexamination Certificate
1998-01-13
2001-07-03
Ngo, Ricky (Department: 2664)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Plural diverse modulation techniques
C370S209000, C370S339000, C370S343000, C370S480000, C375S267000
Reexamination Certificate
active
06256290
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wireless telecommunications in general, and, more particularly, to a multi-carrier code-division multiple access (“CDMA”) transmitter with transmit diversity.
BACKGROUND OF THE INVENTION
FIG. 1
depicts a schematic diagram of a portion of a typical wireless telecommunications system in the prior art, which system provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals
101
-
1
through
101
-
3
) that are situated within a geographic region. The heart of a typical wireless telecommunications system is Wireless Switching Center (“WSC”)
120
, which may also be known as a Mobile Switching Center (“MSC”) or Mobile Telephone Switching Office (“MTSO”). Typically, Wireless Switching Center
120
is connected to a plurality of base stations (e.g., base stations
103
-
1
through
103
-
5
) that are dispersed throughout the geographic area serviced by the system and to local and long-distance telephone and data networks (e.g., local-office
130
, local-office
139
and toll-office
140
). Wireless Switching Center
120
is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal, which is connected to the system via the local and/or long-distance networks.
The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially distinct areas called “cells.” As depicted in
FIG. 1
, each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on the topography of the terrain serviced by the system. Typically, each cell contains a base station, which comprises the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with Wireless Switching Center
120
.
For example, when wireless terminal
101
-
1
desires to communicate with wireless terminal
101
-
2
, wireless terminal
101
-
1
transmits the desired information to base station
103
-
1
, which relays the information to Wireless Switching Center
120
. Upon receipt of the information, and with the knowledge that it is intended for wireless terminal
101
-
2
, Wireless Switching Center
120
then returns the information back to base station
103
-
1
, which relays the information, via radio, to wireless terminal
101
-
2
.
When base station
103
-
1
is capable of communicating with wireless terminals
101
-
1
and
101
-
2
using code-division multiple access (“CDMA”) technology,
FIG. 2
depicts a block diagram of the salient components that base station
103
-
1
uses to prepare the datastream of symbols for transmission on the forward channel in accordance with IS-95. Base station
103
-
1
typically comprises demultiplexor
201
, a bank of c forward channel radios,
203
-
1
through
203
-c, summer
205
, amplifier
207
and transmit antenna
209
, interconnected as shown.
A multiplexed datastream of symbols from wireless switching center
120
, comprising up to c datastreams is received by demultiplexor
201
, in well-known fashion, wherein each of the individual datastreams are intended for transmission over a unique forward channel to a wireless terminal. Demultiplexor
201
demultiplexes the c datastreams, in well-known fashion, and routes each individual datastream to one of c forward channel radios,
203
-
1
through
203
-c. Each forward channel radio spreads the received datastream into a 1.25 wide MHz forward channel signal, in well-known fashion, and then modulates the spread datastream onto a carrier, also in well-known fashion. As is well-known in the prior art, each forward channel radio can modulate the spread datastream onto any one of the available carrier signals available for use by that base station. The output of each of the c forward channel radios,
203
-
1
through
203
-c, is summed by summer
205
, amplified by amplifier
207
and radiated by antenna
209
, in well-known fashion.
FIG. 3
depicts a block diagram of a typical IS-95 compliant forward channel radio in the prior art. Forward channel radio
203
-i typically comprises: convolutional encoder
301
, symbol repeater
303
, block interleaver
305
, multiplier
307
, long code generator
309
, decimator
311
, multiplier
315
, and modulator
317
, interconnected as shown.
One disadvantage with a IS-95 forward channel in the prior art is that it has a rather limited data rate capacity, and, therefore, the need exists for a CDMA forward channel that is capable of a greater data rate. As is well-known in the prior art, one technique for increasing the data rate of the CDMA forward channel is to widen its band to 5 MHz or 10 MHz or more.
SUMMARY OF THE INVENTION
Some embodiments of the present invention are capable of transmitting a wideband CDMA forward channel signal without some of the costs and restrictions associated with techniques in the prior art. In particular, some embodiments of the present invention enjoy three distinct advantages.
First, some embodiments of the present invention are capable of transmitting a wideband (e.g., 5 MHz, 10 MHz, etc.) signal with a high data rate to an appropriately-designed wideband CDMA wireless terminal and are also capable of transmitting a narrowband (e.g., 1.25 MHz, etc.) signal to a CDMA wireless terminal in the prior art. This is advantageous because it means that embodiments of the present invention are backward compatible with millions of existing CDMA wireless terminals. To accomplish this, some embodiments of the present invention generate a wideband forward channel from two or more frequency-disparate sub-channels. Advantageously, each sub-channel is a narrowband signals that can be, but is not necessarily, compliant with an existing narrowband standard (e.g., IS-95).
Second, the generation of a wideband forward channel from multiple frequency-disparate sub-channels enables embodiments of the present invention to utilize spatial transmit diversity (i e., at least one of the frequency-disparate sub-channels is transmitted from an antenna that is some distance from another antenna that is used to transmit the other sub-channels). This is particularly advantageous because a forward channel constructed in this way is more robust to interference, distortion and fading. Furthermore, because the respective sub-channels use different carrier frequencies, and hence are orthogonal, they do not interfere with each other. This is in contrast with the prior art in which delayed versions of the “same” signal are transmitted from different antennas and cause self interference.
Third, some embodiments of the present invention are capable of co-existing in the same frequency spectrum that is allocated to existing narrowband wireless systems. This property, which is also known as “overlay,” is advantageous because the system can simultaneously support narrowband terminals (e.g., IS-95, etc.) and wideband terminals without mutual interference.
An illustrative embodiment of the present invention comprises: receiving a datastream of symbols that is to be transmitted to one wireless terminal; distributing at least some of the datastream of symbols to a first derivative datastream of symbols; distributing at least some of the datastream of symbols to a second derivative datastream of symbols; modulating the first derivative datastream of symbols onto a first carrier frequency to create a first modulated carrier; modulating the second derivative datastream of symbols onto a second carrier frequency that is different that the first carrier frequency to create a second modulated carrier; radiating the first modulated carrier from a first antenna; and radiating the second modulated carrier from a second antenna that is separated from the first antenna.
REFERENCES:
patent: 5521937 (1996-05-01), Kondo et al.
patent: 5652764 (1997-07-01), Kanzaki et al.
patent: 5822359 (1998-10-01), Bruck
Breyer Wayne S.
DeMont Jason Paul
DeMont & Breyer LLC
Lucent Technologies - Inc.
Ngo Ricky
LandOfFree
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