Efficient symbol synchronization techniques using variable FIR or IIR interpolation filters

Maximum Likelihood estimation theory can be used to develop optimal timing recovery schemes for digital communication systems. Tunable 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 efficiently utilizing the tunable gathering filter structure for FIR filters and 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 for the IIR gathering structure with transient suppression, and the performance of FIR and IIR implementations and their computational complexity are compared in example simulations.