Westinghouse Electric Corporation

Joseph B Bronder

Brian William Kroeger

Jeffrey S Baird

Tod Andrew Oblak

Raymond R Cooper

William H Gossard

A method and apparatus for synchronizing symbol timing for a QPSK demodulator. A matched filter pair outputs respective 'early-punctual-late' signals. The early and late signals are input to a symbol synchronizing estimator that produces an interpolation control signal used by the filters to synchronize the symbol timing to the sample timing. The punctual signal is output as an information bearing signal representing the received inphase and quadrature signals. The matched filters are interpolating matched filters. The symbol synchronizing estimator normalizes the early and late signals in a manner that allow the demodulator to 'flywheel' over signals having a low signal to noise ratio below a predetermined threshold.

Symbol synchronizer using modified early/punctual/late gate technique

A locally coherent Quadrature Phase Shift Keying (QPSK) detector that uses a normalized fourth power weighting technique to generate an ambiguous local phase reference of a current symbol. A phase adjusted previous symbol reference is used to resolve the ambiguity using differentially coded data and yield current soft symbol information.

Locally coherent QPSK detection with differential decoding for a fading

A superframe lock subsystem includes a correlator which searches for and identifies a first unique word indicative of a frame boundary within a received bit stream during an initial acquisition state. A controller subsequently predicts frame boundaries in accordance with the first unique word. In a tentative frame lock state, the correlator searches for and determines if a second unique word exists at the frame boundary subsequent the frame boundary which corresponds to the first unique word. If the second unique word is determined to exist at the corresponding frame boundary and if a single frame duration separates the first and second unique words, the superframe lock subsystem enters a frame lock state. During the frame lock state, information of the corresponding frames is processed. The correlator searches for and determines if a carrier wave sequence indicative of a superframe boundary exists in the received bit stream at the frame boundary immediately following the frame boundary which corresponds to the second unique word. If the carrier wave sequence exists at the predicted frame boundary, the correlator searches for and determines if a third unique words exists in the received bit stream immediately after the carrier wave sequence. Upon determination that the third unique word exists subsequent the carrier wave sequence, the superframe lock subsystem enters a superframe lock state wherein the correlator searches for and detects only unique words at subsequent predicted frame boundaries to maintain superframe lock.

Mobile telephone single channel per carrier superframe lock subsystem

A method and apparatus for estimating a frequency of a received carrier wave in a Quadrature Phase Shift Keying (QPSK) system. The invention uses a combination of an FFT, DFT bins, and three point interpolation to estimate a frequency of the carrier wave. The system is robust and compensates for multipath fading and other types of signal degradation.

Carrier acquisition technique for mobile radio QPSK demodulator

A carrier tracking loop that uses a frequency locked loop (FLL) and incorporates synchronized matched filters to minimize complexity of the system. The synchronized matched filters eliminate out-of-band interference while minimizing computation. The carrier tracking loop has an improved error signal generation to extend a frequency range and by employing error signal normalization, which extends the dynamic range of the amplitude of the input signal and allows the frequency to flywheel when signal fading occurs.

Carrier tracking loop for QPSK demodulator

A frequency division multiplex guardband communication system is provided which increases the communication capability of conventional FDM systems with negligible effect on overall system performance. The additional capacity is achieved through the use of guardbands which lie between the information bands of the FDM. To avoid interfering with recovery of the FDM information, the amount of new signal energy added to the individual guardbands is well below the guardband noise level.

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Elkridge, MD, United States of America

Joseph B Bronder