Mobile Radio Diversity Reception

Abstract

This paper examines a particular kind of diversity system, under conditions of multipath fading, when there is interference from either random noise or from an unwanted station. The transmitter sends a pilot wave along with the modulated signal. The receiver's mixer stage heterodynes the signal with the pilot (instead of with a locally generated tone). Doppler phase distortion, which affects the signal and pilot in nearly the same way, cancels out during mixing. The diversity system with N antennas adds the outputs from N such mixers. This kind of diversity tends to add the N signal outputs in phase, while random noise components as well as certain other interferences add powerwise. In the presence of an interfering station, diversity smooths out amplitude fluctuations. It thereby reduces the probability that the interference will override the desired station.