Timing and automatic frequency control of digital receiver using the

Abstract

A technique for correcting the sampling time and carrier frequency error in a receiver for digitally modulated signals. Discrete-time, complex-valued samples of the incoming signal are fed to a pair of non-linear operators such as correlators. The first correlator provides a signal having a first phase component related to the symbol timing error and a second phase component related to the carrier frequency error. The second correlator provides a signal having a first phase component related to the symbol timing error and a second phase component related to the negative of the carrier frequency error. The phase components are then separated and detected to extract an estimate of the symbol timing error and the carrier frequency error. In the preferred embodiment, the complex-valued samples are frequency-shifted, before being fed to the correlators, so that the phase components of interest appear at zero frequency. The invention satisfactorily demodulates transmitted digital signals in applications, such as cellular time-division multiple access (TDMA), where they are susceptible to multipath fading.