On ACIPR of π/4 shifted DQPSK for US digital land mobile radio systems

The adjacent channel interference characteristics of a system employing Nyquist-pulse, π/4-shifted differential quadrature phase (DQPSK) modulation were investigated for a US digital land mobile radio application. The effects of transmit pulse-shape windowing, power amplifier characteristics, and the performance reference defining minimum receiver sensitivity on the achievable adjacent channel interference protection ratio (ACIPR) were examined via computer simulation. Estimates of in-band to adjacent-band power are presented, and ACIPR data obtained from simulations of the proposed system based on a modification of the selectivity measurement defined in EIA Standard RS204-C are given. These results indicate that the proposed system provides from 40 dB to 70 dB of ACIPR with a two-fold increase in capacity, depending on the transmitter´s power and required average probability of bit error