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Performance of a carrier-recovery loop in a satellite modem

By SW Cheung and AP Clark

Abstract

The paper describes a carrier recovery loop for the coherent demodulation of a digital satellite modem for mobile systems. The loop is data aided, employing decision feedback. The modem transmits a band-limited differentially encoded quaternary phase-shift-keyed (DEQPSK) signal over a satellite link. Several different earth stations are assumed to have simultaneous access to a given transponder, in an arrangement of frequency-division multiple access (FDMA). Thus the DEQPSK signals that occupy the immediately adjacent frequency bands can introduce adjacent-channel interference (ACI) into the transmitted DEQPSK signal. The high-power amplifier (HPA) at the earth station transmitter introduces AM-AM and AM-PM conversion effects into the DEQPSK signal, but the satellite transponder is linear. A baseband predistorter operates on the baseband signals at the input to the modulator and assumes a prior knowledge of the HPA characteristics. A carrier-recovery loop is used at the receiver to generate the in-phase and quadrature reference carriers employed by the coherent demodulator. The performance of the system is studied by computer simulation, over a range of different conditions and with different arrangements of the modem, and the results are used to determine the preferred modem design.link_to_subscribed_fulltex

Publisher: Institution of Engineering and Technology. The Journal's web site is located at http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=2215
Year: 1991
DOI identifier: 10.1049/ip-i-2.1991.0004
OAI identifier: oai:hub.hku.hk:10722/154939
Provided by: HKU Scholars Hub
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