Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-09-27
2001-11-20
Jung, Min (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C455S277100
Reexamination Certificate
active
06320853
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wireless communication systems. More specifically, the invention relates to methods of phase recovery between a common pilot signal and dedicated traffic signals at a mobile station. This invention pertains to applications in which a base station uses a sector wide beam for transmitting the pilot signals and adaptive spatial beams with the highest possible gain for transmitting the traffic signals.
BACKGROUND
As wireless communications rapidly spread and promise to deliver voice and data to every walk of modern life, a great deal of effort is devoted to enhance the capacity and performance of wireless communication networks.
US IS-95 CDMA cellular standard, the second US digital cellular standard based on CDMA (code division multiple access) technology, is designed to deliver a very high capacity by way of spread-spectrum signal techniques. In IS-95, the downlink (or forward link) channel structure consists of the transmission of up to 64 simultaneous, distinct channels with varying functions that are orthogonally multiplexed onto a common RF carrier. One of these channels is a high-power pilot signal that is transmitted continuously as a coherent phase reference of reception of a radio frequency (RF) carrier modulated by information. Another of these channels is a continuously transmitted synchronization channel that is used to convey system information to all users in the cell. Up to seven paging channels are used to signal incoming calls to mobiles in the cell, and to convey channel assignments and other signaling messages to individual mobiles. The remainder of the channels is designated as traffic channels, each transmitting voice and data to an individual mobile user.
At the mobile station, the common broadcast pilot signal is used to recover the phase of the RF carrier in order to coherently demodulate the received traffic signals. This approach would require that both the pilot and traffic signals received at the mobile station have the same phase as the RF carrier. This phase-matching requirement is easy to accomplish if the pilot signal and the traffic signals are transmitted through the same sector beam, often through a single antenna, as illustrated in FIG.
1
A. In
FIG. 1A
, an antenna
101
at a base station
100
transmits a sector beam carrying, among other things, a pilot signal
103
and a traffic signal designated
104
to a mobile station
102
.
U.S. Pat. No. 6,108,565 describes a system and method for enhancing CDMA communication capacity. In particular, it provides a base station with an adaptive antenna array system, such that a common pilot signal is transmitted through a sector wide beam and one or more traffic signals are transmitted through a narrower adaptive spatial beam, as illustrated in FIG.
1
B. In
FIG. 1B
, an adaptive antenna array system
111
at a base station
110
transmits a sector wide beam carrying a common pilot signal
113
and a narrower adaptive spatial beam carrying a traffic signal
114
designated to a mobile station
112
along with other traffic signals.
The aforementioned adaptive spatial beams render important advantages of providing higher effective radiated power to the desired user and reducing cross-talk interference to other users. However, this novel approach requires that the downlink traffic beam be phase matched with the sector pilot beam, in order to carry out coherent demodulation at individual IS-95 mobile stations. Moreover, care must be taken to ensure that the phase-matching process is achieved not at the expense of compromising the gain of the traffic beam and hence the gain of the downlink system capacity.
There exists a need, therefore, for a simple and effective method for matching the phases of the common pilot beam and the dedicated traffic beams without compromising the downlink system capacity.
OBJECTS AND ADVANTAGES
Accordingly it is a principal object of the present invention to provide methods for recovering the phase mismatch between a common pilot signal and dedicated traffic signals at a mobile station. A significant advantage of the present invention is that it enables the base station to advantageously use a sector beam for transmitting the common broadcast pilot signal and adaptive spatial beams for transmitting the dedicated traffic signals, thereby effectively enhancing the gain of the traffic beams and hence the gain of the downlink system capacity, and reducing the cross-talk interference.
These and other objects and advantages will become apparent from the following description and accompanying drawings.
SUMMARY OF THE INVENTION
This invention provides a CDMA (IS-95) cellular communication system, in which a base station transmits a common broadcast pilot signal through a sector wide beam and traffic signals through narrower adaptive spatial beams by way of an adaptive antenna array system. The present invention further provides methods of recovering the phase mismatch between the common pilot signal and the traffic signals received at a mobile station, thereby providing for coherent demodulation.
In an exemplary embodiment of the present invention, the mobile station is implemented with a novel downlink demodulator, which is configured to construct in-phase and quadrature-phase signals from the received pilot and traffic signals, such that the in-phase and quadrature-phase signals are respectively proportional to cosine and sine functions of the phase mismatch between the common pilot signal and the traffic signals. The demodulator further allows the phase mismatch itself to be extracted and averaged. Moreover, the demodulator uses the thus-constructed in-phase and quadrature-phase signals to produce an output signal that is independent of the phase mismatch, thereby eliminating the effects of the carrier phase in the demodulation process.
By carrying out the aforementioned phase recovery at the mobile station, the present invention eliminates the necessity for the pilot-traffic phase matching process at the base station, thereby enabling the base station to form the traffic beams with maximum power gain and minimum interference.
The novel features of this invention, as well as the invention itself, will be best understood from the following drawings and detailed description.
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patent: 5634199 (1997-05-01), Gerlach et al.
patent: 5940742 (1999-08-01), Dent
patent: 5953325 (1999-09-01), Willars
patent: 5966094 (1999-10-01), Ward et al.
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patent: 6108565 (2000-08-01), Scherzer
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Scherzer Shimon B.
Wong Piu Bill
Fulbright & Jaworski L.L.P.
Jung Min
Metawave Communications Corporation
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