Carrier Phase Recovery in Turbo Receivers: Cramer-Rao Bound and Synchronizer Performance

This contribution considers carrier phase recovery in turbo receivers. We point out that the resulting Cramer-Rao bound (CRB) is close to its high signal-to-noise ratio (SNR) asymptote, even at the typical low operating SNR of turbo systems. We show that ‘code-unaware’ phase estimators are unable to perform closely to the CRB at the normal operating SNR of powerful codes. The advantage of ‘codeaware’ carrier recovery is illustrated with examples of existing phase estimation techniques applied to a turbocoded 4-PSK system. Comparison with the CRB reveals that the ‘code-aware’ soft decision-directed phase estimator presented in [1] performs very close to the CRB.