Fast frequency shift keying using binary transversal filter

Abstract

Fast frequency shift keying signal has the following properties; 1) it has a continuous phase; 2) it has a low modulation index, h=0.5; 3) it has no discrete frequency components and nearly all the signal energy is contained within a narrow frequency region equal to 3/2 times the bit rate even without any bandlimiting; 4) when the observation interval is two bit periods, its error performance is about 3db better than that of conventional frequency shift keying. Since frequency shift keying is a nonlinear process, an analytical description of frequency shift keying signals in general is difficult. In this paper it is shown that by decomposing fast frequency shift keying signals, it is possible to describe time-and frequency-domain properties and to calculate the power spectral density and to find the optimum observation interval. Binary transversal filter performs as a modulator, the basic idea is very simple; a staircase approximation of the desired signal can be obtained with a single binary transversal filter, of which clocking rate is controlled by the frequency and polarity of the desired signal. An overall fast FSK system is implemented, and the merits of the system, such as 3 db gain over the conventional FSK and the narrow bandwidth among others, are experimentally verified.