Cochannel interference rejection for AMPS signals using spectral correlation properties and an adaptive array

Cochannel interference is a major problem that limits the cell capacity in AMPS systems. Adaptive beamforming can significantly reduce co-channel interference by forming a beam in the direction of the signal-of-interest (SOI). This paper shows how the supervisory audio tone (SAT) feature can be exploited by the adaptive array to distinguish the SOI from the interferers. The presence of the SAT produces a cyclostationary feature in the AMPS signals. Using this feature, a SCORE-like beamformer (spectral correlation discriminator array-SCDA) provides 15 dB improvement in the demodulated voice SNR for low SIR received signals. The performance of SCDA is compared with a least-squares CMA (LSCMA) beamformer.