Demodulation/Remodulation Performance for a Class of Digitally Phase Modulated Signals

Abstract

Demodulation/remodulation in a multi-link (e.g., satellite) communication system may take on a variety of forms and may satisfy one or more system requirements, such as anti-jam protection. The focus of this paper is on a specific signal structure that has broad applicability and a specific demod/remod scheme employed by the Space Shuttle. The signal is characterized by a residual carrier with binary data PSK modulated onto a subcarrier and additional data phase modulated onto the carrier. The signal is demodulated to baseband in a broad bandwidth, hard-limited and suppressed carrier/BPSK remodulated for final transmission. This paper analytically determines the spectral density of the hard-limited baseband signal and applies the result to bit error rate (BER) evaluation. Computed results display illustrative spectra and BER results, which are functions of: carrier and subcarrier data rate, modulation indices and signal-to-noise ratio (SNR). Hard-limiter suppression and enhancement factors are also explicitly treated; the relationships of these factors to modulation indices - especially for high SNR values - are particularly noted.