Frequency-Hopping, Multiple-Access, Phase-Shift-Keying System Performancein a Rayleigh Fading Environment

T w o major impairments of mobile radio communication systems are interference from other users and multipath fading. T h e frequencydivision, multiple-access (FDMA) technique uses guard bands between frequency channels to minimize interference and increased signal power to combat fading. Recently, various frequency-hopping (FH) techniques have been proposed for transmitting digitized speech in 861 mobile radio, including a differential phase-shift-keyed (DPSK) system1 and a multilevel frequency-shift-keyed (MFSK) system.2 The FHMA approach uses frequency diversity against fading and keeps the interference down to an acceptable level by properly designing the set of frequency-hopping patterns (addresses) assigned to the users. While the effectiveness of diversity schemes in a fading environment with no interference is well known, the system degradation of the frame asynchronous FHMA-PSK scheme due to other user interference has not been analyzed, except by modeling the interference as additive white Gaussian noise (AWGN). 1 In this paper, we study the performance of FHMA-PSK systems with orthogonal coding (Ref. 3, p. 232) in a Rayleigh fading environment using both coherent and differentially coherent detection. (Empirical evidence shows that the Rayleigh model is accurate for urban mobile radio situtations.4) The approach of using coding and soft-decision decoding on multiple access channels is similar to that studied in Ref. 5, although the modulation technique is different.