Coexistence of TDMA and AMPS: performance degradation of analog AMPS-type signals due to QPSK/MSK modulated TDMA-type interference in fading channels

The advent of PCS has necessitated systems employing different bandwidths, modulation techniques and access schemes to coexist. In this scenario, the conventional method for analyzing intersystem interference, considering only the relative power levels of the carrier and the interferer, is insufficient to determine the performance degradation. This paper analyzes the interference effects on analog phase modulated systems due to QPSK and MSK modulated digital interferers by determining the spectral density of the interference at the baseband as a function of the RF carrier-to-interference ratio. Interfering signals with the same power but employing different modulation schemes and occupying different bandwidths are shown to cause different performance degradation at the baseband of the victim signal. This methodology is more accurate in determining the reuse characteristics of the spectrum and serves as an improved design tool for optimizing bandwidth.