A method of estimating the quality of a communication channel from a differential phase angle between a received signal and the corresponding transmitted phase angle employs determining a signal to impairment ratio (SIR) as an indicator of channel state information (CSI). A maximum likelihood estimation...http://www.google.de/patents/US5351274?utm_source=gb-gplus-sharePatent US5351274 - Post detection selection combining diversity receivers for mobile and indoor radio channels
