Study of Space Communications Spread Spectrum Systems. Part 1: Saw-Based JointGroup Demodulation of Frequency Shift Keyed and Differential Phase Shift Keyed Signals

摘要

A surface acoustic wave (SAW) device based processor, capable of the joint groupdemodulation of frequency shift keying (FSK) and differential phase shift keying (DPSK) signals, and intended for use in the Canadian extremely high frequency (EHF) Satcom system is proposed. The processor is based on the ability of SAW filters to implement wideband, real time, Fourier transforms with an observation interval corresponding to the hop period of the system. The background for such an implementation is given. The SAW-based transforms are simulated using digital Fourier transforms, and a quasi-analytical technique is applied to determine bit error rate performance of both binary and quaternary differential phase shift keying in the presence of narrow band Gaussian noise. Signal parameters such as windowing, carrier separation, user bandwidth allocations, and nonlinear characteristics of the SAW devices are also considered. Based on the results determined, the SAW-based processor is capable of performing group binary DPSK demodulation. The maximum number of DPSK users depends on the time-bandwidth (TB) product of the SAW devices used in the implementation, varying from 3 users for TB=512 to 12 users for TB=2048. It is also shown that binary DPSK consistently out-performs quaternary DPSK for this application.