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Asynchronous timing and Doppler recovery in DSP based DPSK modems for fixed and mobile satellite applicationsWhile conventional analog modems employ some kind of clock wave regenerator circuit for synchronous timing recovery, in sampled modem receivers the timing is recovered asynchronously to the incoming data stream, with no adjustment being made to the input sampling rate. All timing corrections are accomplished by digital operations on the sampled data stream, and timing recovery is asynchronous with the uncontrolled, input A/D system. A good timing error measurement algorithm is a zero crossing tracker proposed by Gardner. Digital, speech rate (2400 - 4800 bps) M-PSK modem receivers employing Gardner's zero crossing tracker were implemented and tested and found to achieve BER performance very close to theoretical values on the AWGN channel. Nyguist pulse shaped modem systems with excess bandwidth factors ranging from 100 to 60 percent were considered. We can show that for any symmetric M-PSK signal set Gardner's NDA algorithm is free of pattern jitter for any carrier phase offset for rectangular pulses and for Nyquist pulses having 100 percent excess bandwidth. Also, the Nyquist pulse shaped system is studied on the mobile satellite channel, where Doppler shifts and multipath fading degrade the pi/4-DQPSK signal. Two simple modifications to Gardner's zero crossing tracker enable it to remain useful in the presence of multipath fading.
Document ID
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Koblents, B.
(Queens Univ. Kingston Ontario, Canada)
Belanger, M.
(Queens Univ. Kingston Ontario, Canada)
Woods, D.
(Queens Univ. Kingston Ontario, Canada)
Mclane, P. J.
(Queens Univ. Kingston Ontario, Canada)
Date Acquired
September 6, 2013
Publication Date
January 1, 1993
Publication Information
Publication: JPL, Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)
Subject Category
Communications And Radar
Accession Number
Distribution Limits
Work of the US Gov. Public Use Permitted.
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