Frequency-hopped spread-spectrum transmission with band-efficient modulations and simplified noncoherent sequence estimation

Frequency-hopped spread-spectrum transmission using band-efficient modulations that are phase-continuous during each hop, is presented. A range of system parameters is considered, including signaling spectrum, reception, system complexity, and performance in the presence of noise and jamming. The particular cases where the hopped modulation is minimum-shift-keying (MSK), duobinary minimum-shift-keying (DMSK), or tamed-FM (TFM), are studied in detail. Results are presented for various modulation indexes, rectangular and raised cosine pulse shapings, and a range of hop interval lengths. Sequence estimation on a hop-by-hop basis is considered. The noncoherent likelihood sequence receiver must keep all possible paths, and so the computation and complexity becomes large for system transmitting many bits per hop. Therefore, a simplified noncoherent Viterbi-like sequence estimation algorithm with reduced complexity is introduced. System performance has been evaluated in Gaussian noise, partial-band jamming and multiple-tone jamming, using bounds and a system simulation. The compact nature of the hopped spectrum, when a number of bits are transmitted per hop, offers greater spectrum utilization and the prospect of improved performance in the presence of multiple-tone jamming or interference.<
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