Multicarrier spread spectrum system with constant envelope: antijamming, jamming estimation, multiuser access

A special complex sequence called a complex quadratic sequence is proposed as the frequency-spreading sequence for the multicarrier spread-spectrum (MC-SS) modulation scheme. The resulting MC-SS signal has constant envelope in both time and frequency domains. This feature provides flexibility for the MC-SS system to mitigate the effects of both partial-band and pulse jamming. For partial-band jamming, the MC-SS system with frequency domain detection and combining can outperform direct sequence spread spectrum. For pulse jamming, the MC-SS system with time-domain detection and combining can outperform other MC-SS systems. The proposed MC-SS signal has a constant envelope, thus, reducing linearity requirements on the power amplifier. A simple jammer state estimation scheme for both partial-band and pulse-jamming channels is also proposed. Furthermore, multiaccess with the MC-SS system is possible by assigning users different cyclic-shifts of the complex quadratic sequence.