Combined interpolation and maximum likelihood symbol timing recovery in digital receivers

Abstract

Maximum likelihood (ML) estimation theory provides a general framework for developing optimum timing recovery schemes for digital communication systems. Feedforward schemes based on ML-theory have been shown to have rapid acquisition characteristics. Another important trend is to use digital interpolation for symbol timing adjustment. The so-called Farrow (1988) structure has become popular in this context because it offers an efficient and flexible realization structure for such an interpolation task. We propose a new feedforward timing estimation scheme which utilizes the Farrow structure efficiently. The scheme is based on a low-order polynomial approximation for the log-likelihood function and also the derivative of this function is available with a small additional computational cost. The performance of the new timing recovery technique is found to be close to ideal even with short symbol block-lengths which is very important in mobile systems.