Performance of Frequency-Hopping Multiple-Access Multilevel FSK Systems with Hard-Limited and Linear Combining

In comparing two proposed frequency-hopping mobile radio systems for digitized speech, Goodman et al. have observed that the system employing multiple-frequency-shift-keying (MFSK) can accommodate many more users than the ones with differential-phaseshift-keying (DPSK). Besides the difference in modulation methods, the MFSK system uses hard-limited combining while the DPSK one uses linear combining. In this paper, we show that using linear combining in the MFSK system causes the performance to degrade considerably.