Low-complexity optimal symmetric interpolation filters for SDR receivers

A modified Farrow structure for the second-order polynomial, symmetric interpolator suitable for low-complexity hardware implementation is presented. The significant reduction in complexity of the modified structure allows a faster and simpler implementation, and a better interpolation performance with longer filters. The optimum filter coefficients are derived by using a proposed cost function that takes into consideration the desired time and frequency responses as well as the symbol timing error, suitable for practical design objectives. A vector form of the cost function is derived to allow the use of fast optimization algorithm. Illustrative design examples for flexible digital receivers are presented. Simulation results show a superior performance of the proposed low-complexity interpolation filters.