ASYNCHRONOUS MULTIPLE-ACCESS PERFORMANCES OF FREQUENCY-TIME-HOPPED MULTILEVEL FREQUENCY-TIME SHIFT KEYING COMMUNICATION-SYSTEMS

Assuming application to the mobile multiple-access communication, chip -asynchronous mobile-to-base perfor mances of FH/FTH (Frequency-Time-H opped) -MFTSK (Multi-level Frequency-Time Shift Keying) systems are in vestigated. Analytical expressions are obtained for the probabilities of false detection and missed detection of signal elements, assuming i ndependent and asynchronous arrival of each of the signal elements wit h Rayleigh fading and optional AWG noise. Using the result or by simul ation and employing dual-k coding, parameter optimization was carried out to obtain the maximum spectrum efficiency. The results of the nois y case analysis and simulation show high noise-robustness of the FTH s ystems. For a given value of information transmission rate the optimiz ed FTH-MFTSK gives an effectively constant spectrum efficiency for a w ide range of the number K(f) of frequency chips. As a result, FTH-MFTS K well outperforms FTH-MFSK at any, especially small value of K(f). Re lative to the overall optimum FH-MFSK, FTH-MFSK systems show typically around 20% of degradation in spectrum efficiency even with one-eighth of K(f). Compared with FH-MFSK, accordingly, FTH-MFTSK systems allow the designer to reduce, without any degradation in multiple-access per formances, the number of frequency chips to the minimum value tolerate d by the frequency selective fading characteristics and the time chip duration requirement imposed by the signal-to-noise ratio margin and t he transmitter peak power rating.