On the orthogonality of signal tones in SFH/MFSK systems over multipath fading channels

In this paper, the effect of multipath fading on orthogonality of signal tones in slow frequency-hopping communication system using M-ary frequency-shift keying modulation with non-coherent demodulation (SFH/MFSK) is analyzed. A general expression of orthogonality loss factor Djnl is derived, which is determined not only by multipath delays, signal strength fading and synchronization time error, but also by phase variation caused by multipath delays. The results obtained here are also more general than that of traditional FH system which transmits only one symbol per hop. Numerical results demonstrate that the effects vary greatly with different phase variations.