Interference immunity and spectral reuse in PCS systems

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 a QPSK modulated digital interferer by determining the interference spectral density at baseband as a function of the RF carrier-to-interference ratio. This density is then compared with that due to an equivalent analog interferer. Interfering signals with the same power but employing different modulation schemes and occupying different bandwidths are shown to cause vastly different performance degradation at baseband for the victim signal. This methodology is more accurate in determining the carrier-to-interference objective and serves as an improved design tool for optimizing bandwidth in various scenarios of spectral reuse involving dissimilar systems