Spread spectrum multi-h modulation

Applying direct random spreading to a digital information sequence prior to multi-h modulation creates a novel class of signals, called spread-spectrum multi-h (SSMH) signaling. The spectral efficiency allows control of the power spectral density, while the power-efficient modulation allows transmission at lower signal-to-noise ratios when the receiver knows a priori the spreading sequence and modulation index sequence. An optimal receiver structure is derived and numerically evaluated in an additive white Gaussian noise environment where correlated noise samples are added to noise-free correlation filter outputs. It is shown that performance depends on the spreading sequence, the modulation indices, and the possible phase states and that it can exceed that of direct-sequence binary-phase-shift keying (DS/BPSK) by 1-2 db at bit-error rates of 10/sup -5/. Composite likelihood ratio analysis reveals a reduction by 50-70% in detectability of completely known SSMH signals namely DS/BPSK at error rates of 10/sup -4/. The spectral control, power efficiency, and reduced detectability make SSMH a viable low-probability-of-intercept signaling technique. >