Polynomial-based maximum-likelihood technique for synchronization in digital receivers

Maximum-likelihood estimation theory provides a general framework for developing near-optimum (with respect to the Cramer-Rao bound) synchronization schemes for digital communication systems. A new technique for jointly estimating the symbol timing and carrier phase in digital receivers for linear digital modulations with nonsynchronized sampling is established for both data-aided and nondata-aided systems using a block-based feedforward architecture. This technique is a practical, fully digitally implemented synchronization concept based on a low-order polynomial approximation of the likelihood functions using the Farrow-based interpolator. It is shown that low oversampling, like two samples per symbol, can be used in timing recovery without compromising the system performance. This results in efficient overall receiver implementation. It is also demonstrated that the quality of the interpolator design has a big effect on the performance of the synchronization scheme. Frequency-domain optimized polynomial interpolator designs provide significantly better performance than the well-known Lagrange interpolators.