A Simplified Approach to Direct Sequence Carrier Modulation and its Selection

Direct sequence modulated spread spectrum systems are quite similar in many ways to more conventional digital communications systems. They employ some form of phase shift amplitude shift frequency shift keying to modulate their carriers and provide the desired spread bandwidth. A key consideration, however, is the choice of carrier modulation to provide maximum antijamming margin while operating in nonlinear processing, plus minimizing impact on synchronization and cost/complexity of the modulators, demodulators, and synchronizers required. This paper examines the relationships that exist between the various candidate waveforms and shows their common roots. Also defined are the criteria that affect the choice of a waveforms, where various implementations are possible.