Performance of DS/SFH-SSMA system with overlapping BFSK in the presence of both MTJ and MAI

The performance of a direct-sequence (DS)/SFH-SSMA communication system using overlapping binary frequency-shift keying (BFSK) modulation is analyzed in additive white Gaussian noise (AWGN), multiple-access interference (MAI), and multitone jamming (MTJ) channels. An SSMA system is considered where the DS spread spectra are overlapped and the maximum overlapping limitation is 1/T, which is the minimum spacing for noncoherent FSK signaling. As the amount of overlapping increases, the multiple-access interference as well as the processing gain becomes larger. Thus, the bit error rate (BER) can be improved by optimizing the overlap ratio. The phase angles and time delays of the received signals, and the phase angles of tone jamming signals, are assumed to be mutually independent random variables. A BER equation is derived for the overlapping BFSK DS/SFH-SSMA communication system in the AWGN, MAI, and MTJ channels. From the numerical analyses and the simulation results, the BER performance is improved by about 3 dB at a BER of 10^-3 in the optimized overlapping system over the nonoverlapping system under the condition that the total processing gain is 39 dB, the number of total user is 100, jammer-to-signal ratio is 20 dB, and the number of jamming tones is ten.