A Study of Maritime Mobile Satellite Service Requirements, Frequency Planning, Modulation and Interference Analysis. Volume III. Modulation, Signal Processing and System Access

摘要

The report analyzes, compares and recommends signal modulation and system access techniques considered appropriate for a global commercial maritime communication system. It begins with a review of the practical capacities of currently available spacecraft systems suitable for use in synchronous orbit and of the constraining characteristics of the signal propagation environment. Because the projected required voice communication services are most influential in sizing of the satellite and shipboard terminal, emphasis is given to the analysis of various analog and digital forms of voice signal modulation and processing for their power and bandwidth efficiency, wherein it is concluded that a form of NBFM is most suitable. Following a similar comparative evaluation of data link modulation techniques, system access schemes were analyzed for their practicality and efficiency in implementing the ordered sharing of a few channels by thousands of shipboard users and also in the sharing of a common critically power limited satellite transmitter output amplifier. The major results of the analyses and technique selections are presented in terms of two primary system characteristics - RF bandwidth and shipboard antenna gain, each for example configurations at VHF (160 MHz) and UHF (1600 MHz). (Author)