Improved Map Decoders For Turbo Codes With Nonperfect Timing And Phase Synchronization

This paper presents the behaviour of a turbo coding scheme when the synchronization parameters are not perfectly estimated. The paper proposes improved MAP decoding algorithms for the situations when the timing and phase error are given by the Gaussian probability distribution. It is shown that relatively simple operations can improve the bit error probability without the need of reconstructing the classical decoding algorithm. I. INTRODUCTION The behaviour of turbo codes is usually tested under the assumption of perfect channel knowledge and perfect synchronization. This assumption is, however, rather unrealistic, since the low signal-to-noise region, where such codes operate, causes a great deal of difficulties when it comes to estimation of the phase and timing of the incoming signal. Unfortunately, turbo codes are rather sensitive to timing and phase mismatch and new techniques of synchronization are needed in order to preserve their exceptional performance. II. TURBO CODES AND ..