Digital portable transceiver using GMSK modem and ADM codec

Digital mobile radio transmission techniques and integrated circuit devices have been developed for application to a digital portable transceiver utilizing narrow-band GMSK modulation and ADM voice coding. Design and performance of a quadrature type GMSK modulator and a single-chip coherent demodulator as the GMSK modem are described. To overcome slow fading, encountered in portable applications, switching diversity using a jitter detection type sensor is proposed and shown to be effective. An experimental portable transceiver, developed to demonstrate hardware feasibility, is also described.