Efficient symbol synchronization techniques using variable FIR or IIR interpolation filters

TL;DR: A feedforward timing estimation scheme which uses the efficient variable gathering filter structure for FIR filters leveraging an algorithm previously developed for the so-called Farrow structure, based on a low-order polynomial approximation of the log likelihood function.

Abstract: Maximum likelihood estimation theory can be used to develop optimal timing recovery schemes for digital communication systems. Variable digital interpolation filters are commonly used for symbol timing adjustment. The so-called gathering structure offers an efficient and flexible realization structure for such an interpolation task. In this paper we propose a feedforward timing estimation scheme which uses the efficient variable gathering filter structure for FIR filters leveraging an algorithm previously developed for the so-called Farrow structure. The scheme is based on a low-order polynomial approximation of the log likelihood function. Furthermore, the scheme is extended to an IIR gathering structure with transient suppression. The performance of IIR and FIR implementations and their computational complexity are compared in example simulations, showing that polynomially approximated low-order Thiran IIR fractional-delay filters offer more efficient implementation than their Lagrange FIR counterparts with similar performance.