Pulse or digital communications – Synchronizers
Reexamination Certificate
1998-08-06
2001-11-13
Chin, Stephen (Department: 2634)
Pulse or digital communications
Synchronizers
C342S357490, C342S387000
Reexamination Certificate
active
06317474
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to wireless communication systems, and more specifically to a method and apparatus for estimating a time-of-arrival of a synchronization signal sent simultaneously from at least two non-collocated transmitters.
BACKGROUND OF THE INVENTION
Modern simulcast messaging systems are evolving towards ever increasing data rates to accommodate increasing messaging traffic. A promising solution for obtaining higher data rates is the use of quadrature amplitude modulation (QAM) techniques. In a system employing QAM, synchronization is a key determinant of system performance.
Simulcast systems pose unique challenges, in that multiple signals arrive at a messaging receiver with time-of-arrival offsets. It is the job of the synchronization system to properly synchronize the receiver in the presence of such distortion. Prior-art synchronization techniques are unable to estimate the time-of-arrival of synchronization signals accurately enough for desired QAM performance in a simulcast environment.
Thus, what is needed is a new, more accurate method and apparatus for estimating a time-of-arrival of a synchronization signal in a simulcast environment.
SUMMARY OF THE INVENTION
An aspect of the present invention is a method in a wireless communication system for estimating a time-of-arrival (TOA) of a synchronization signal sent simultaneously from at least two non-collocated transmitters. The method comprises, in the at least two non-collocated transmitters, the step of transmitting the synchronization signal such that it includes at least three predetermined tone frequencies. The method further comprises, in a receiver, the steps of receiving the synchronization signal, and separating the synchronization signal into a plurality of segments. The method further comprises the steps of calculating segment Fourier transform values corresponding to the at least three predetermined tone frequencies, for ones of the plurality of segments, thereby creating a set of segment Fourier transform values; and computing a set of segment TOA values corresponding to the set of segment Fourier transform values. The method further comprises the steps of determining a set of segment weights from the set of segment Fourier transform values, and estimating the TOA of the synchronization signal from the set of segment TOA values and the set of segment weights.
Another aspect of the present invention is a receiver in a wireless communication system for estimating a time-of-arrival (TOA) of a synchronization signal including at least three predetermined tone frequencies sent simultaneously from at least two non-collocated transmitters. The receiver comprises a receiver element for receiving the synchronization signal, and a processing system coupled to the receiver element for processing the synchronization signal. The processing system is programmed to separate the synchronization signal into a plurality of segments, and to calculate segment Fourier transform values corresponding to the at least three predetermined tone frequencies, for ones of the plurality of segments, thereby creating a set of segment Fourier transform values. The processing system is further programmed to compute a set of segment TOA values corresponding to the set of segment Fourier transform values, and to determine a set of segment weights from the set of segment Fourier transform values. In addition, the processing system is programmed to estimate the TOA of the synchronization signal from the set of segment TOA values and the set of segment weights.
Another aspect of the present invention is a controller in a wireless communication system for facilitating estimation of a time-of-arrival (TOA) of a synchronization signal by a receiver. The controller comprises a network interface for receiving a message from a message originator, and a processing system for processing the message. The controller further comprises a transmitter interface coupled to the processing system for controlling at least two transmitters to transmit the message. The processing system is programmed to control the at least two transmitters to simultaneously transmit, prior to sending the message, the synchronization signal such that it includes at least three predetermined tone frequencies; and to rely upon the receiver to estimate the TOA of the synchronization signal so that the receiver can decode the message.
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Al-Beshrawi Tony
Breeden R. Louis
Chin Stephen
Motorola Inc.
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