Fully Digital Burst Modem for Satellite Multimedia Communication Systems


IEICE TRANSACTIONS on Communications   Vol.E80-B    No.1    pp.8-15
Publication Date: 1997/01/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Advances in Satellite Communications toward Multimedia Era)
Category: Modem and Coding
digital burst modem,  TDMA,  satellite communication,  VLSIC,  

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This paper presents fully digital high speed (17.6Mb/s) burst modem for Offset Quadrature Phase Shift Keying (OQPSK), which employs novel digital modem VLSICs. The modulator VLSIC directly generates modulated intermediate frequency (IF) signals in a fully digitalized manner. A newly proposed digital reverse-modulation and pre-filtered carrier filter-limiter scheme realizes low power consumption and stable operation in a low Eb/No condition. The demodulator VLSIC also achieves fast bit-timing acquisition in burst mode. Moreover, it supports stable initial burst acquisition by a novel automatic frequency control (AFC) acquisition detector and a digital burst detector. A digital burst automatic gain control (AGC) compensates burst-to-burst level differences without analog circutits. Performance evaluation results show that the new modem achieves satisfactory bit-error-rate performance in severe environments. The developed modem has been employed in a commercial portable earth station for ISDN services and reduces the hardware size to one third that of the conventional one.