Carrier phase recovery for turbo-coded systems with pre-coded GMSK modulation

摘要

A carrier phase recovery scheme suited for turbo-coded systems with pre-coded Gaussian minimum shift keying (GMSK) modulation is proposed and evaluated in terms of bit-error-rate (BER) performance. This scheme involves utilizing the extrinsic information obtained from the turbo-decoder to aid an iterative carrier phase estimation process, based on a maximum-likelihood (ML) strategy. The phase estimator works jointly with the turbo-decoder, using the updated extrinsic information from the turbo-decoder in every iterative decoding. A pre-coder is used to remove the inherent differential encoding of the GMSK modulation. Two bandwidths of GMSK signals are considered: BT = 0.5 and 0.25, which are recommended by the European Cooperation for Space Standardization (ECSS). It is shown that the performance of this technique is quite close to the perfect synchronized system within a wide range of phase errors. This technique is further developed to recover nearly any phase error in [-π,+π] by increasing the number of phase estimators and joint decoding units. This, however, will increase the complexity of the system.