A robust co-channel interference rejection technique for current mobile phone system

Technologies such as new digital modulation techniques, antenna sectoring, and microcells have been developed to accommodate the large increase in mobile phone users. DSP interference rejection techniques offer another alternative for increasing system capacity. For the current advanced mobile phone system (AMPS), frequency reuse produces co-channel interference. Co-channel interference, in fact, limits the system capacity. DSP interference rejection techniques that exploit cyclostationarity have been developed for mitigating AMPS interference. An AMPS signal exhibits spectral correlation because of the supervisory audio tone (SAT). The effect of the SAT is to replicate the modulated voice spectrum at multiples of the SAT frequency, thus the signal exhibits spectral correlation. A blind time-dependent adaptive filter (TDAF) is designed as a pre-processor to the AMPS receiver to exploit the cyclostationary characteristic of the AMPS signal and to suppress co-channel interference. The theoretical performance for this blind adaptive filter is computed numerically, which provides a bound on performance. A new adaptive algorithm, similar to Griffith's beamforming algorithm, is applied to blindly adapt this time-dependent adaptive filter. This new technique is especially effective for fading signals.