An adaptive maximum-likelihood receiver for colored noise and interference

A receiver that adapts to the second-order statistics of the disturbance (interference or noise) is presented. By adapting to the statistics of the disturbance, this receiver produces the maximum-likelihood (ML) estimate of the transmitted sequence for any type of disturbance, in contrast to a conventional receiver that only produces the ML estimate when the discrete-time disturbance is white. This disturbance signal could result from (1) cochannel interference, (2) adjacent-channel interference or (3) thermal noise. The proposed receiver consists of a Nyquist analog receive filter and an adaptive maximum-likelihood sequence estimator for colored noise. We show that the samples of the output of this analog receive filter, at one sample per symbol, are sufficient statistics for finding the most likely transmitted sequence regardless of the type of disturbance present at the input to the receiver. An important feature of this adaptive receiver is that the analog part of the this receiver is fixed, i.e. adaption to the statistics of the disturbance is accomplished by processing in the digital domain only (at one sample per symbol). Using the EGPRS air interface as an example, we show that this adaptive receiver performs substantially better than a conventional non-adaptive receiver: (1) cochannel dominated case: 4.0 dB of gain, (2) adjacent-channel dominated case: 3.5 dB of gain, (3) thermal-noise dominated case: 1.2 dB of gain.