Design of improved GMSK quadrature modulator

Abstract

We propose an improved Gaussian baseband filtered minimum shift keying (GMSK) quadrature modulator using a finite impulse response (FIR) filter whose coefficients are given by the difference of the phase response to remove the coefficient noise resulting from the conventional method. The modulator is designed by considering the effects resulting from the difference between the ideal analog signal and its digitized version in terms of the sampling noise, quantization noise, truncation noise, and coefficient noise. It is also confirmed by an experiment that it can be used for a digital cellular system.