Multitone frequency-hopped MFSK system for mobile radio

A digital spread spectrum technique employing frequency hopping and multilevel frequency-shift keying has recently been examined for possible application in mobile radiotelephony. Two system parameters, the number of bits per message and the number of tones in the frequency-hopping sequence, are determined by the available bandwidth and the data rate of each user. These parameters in turn determine the tone duration, which strongly influences the vulnerability of the system to transmission distortions. In this paper we describe a generalization of the MFSK scheme that allows users to transmit more than one tone simultaneously. Multitone transmission makes it possible for designers to increase the duration of each tone by increasing the total number of system frequencies. This flexibility slightly increases maximum efficiency and makes the system less vulnerable to multipath delay spread. It could also have implementation advantages.