Spread-spectrum multi-h modulation

Applying a direct random spreading sequence to a digital information sequence prior to multi-h modulation creates a new class of signals called spread-spectrum multi-h (SSMH) signaling. By spreading a known bandwidth efficient modulation scheme, the power spectral density is controlled so that the transmitted spectrum will have a wide, flat mainlobe and rapid sidelobe rolloff. Coincidentally, 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. Optimal receiver structures are derived and numerically evaluated in an additive white Gaussian noise environment. It is shown that performance is dependent on the spreading sequence, the modulation indexes, and the possible phase states and can exceed direct sequence binary phase-shift keying by 1-2 dB at bit error rates of 10^-5. Composite likelihood ratio analysis reveals a reduction of 50-70% in detectability of completely known SSMH signals vis-a-vis direct-sequence binary phase shift keying (DS/BPSK) at error rates of 10^-4