Code-aided synchronization with QPSK, 8-PSK and 16-QAM modulations

The wireless transmission results in phase and frequency offset which degrades the communication performance of a system significantly. Estimation of the unknown parameters of phase and frequency offset is called synchronization. The synchronization is typically performed once prior to the channel decoding by utilizing pilot symbols. Nowadays, turbo decoder can operate at low signal-to-noise ratio (SNR). In low SNR region, the parameters estimation suffers from increased noise. Therefore, the conventional synchronizers can not synchronize receivers perfectly. The synchronization quality can be improved by combining the parameter estimation step with the iterations of turbo decoder which is known as code-aided turbo synchronization. However, if the synchronization is performed after each iteration of turbo decoder then it increases its latency which is not affordable due to tight latency budget. Moreover, as typical wireless communication standards support multiple modulations soit is desirable to design a single synchronization algorithm flexible for them. Due to the tight latency constraints, efficient hardware implementations are mandatory. Hardware implementations require fixed-point representation resulting in quantization losses. We present in this paper an efficient fixed-point realization of a code-aided synchronization algorithm well suited for hardware implementation. The synchronization can run in parallel to turbo decoder to keep its latency unaffected. Moreover, it provides flexibility for following multiple modulations: QPSK, 8-PSK and 16-QAM. We show simulation results to demonstrate the communication performance of the algorithm.