2016 Volume E99.B Issue 2 Pages 337-346
In modern communication systems, it is a critical and challenging issue for existing carrier tracking techniques to achieve near-ideal carrier synchronization without the help of pilot signals in the case of symbol rate sampling and low signal-to-noise ratio (SNR). To overcome this issue, this paper proposes an effective carrier frequency and phase offset tracking scheme which has a robust confluent synchronization architecture whose main components are a digital frequency-locked loop (FLL), a digital phase-locked loop (PLL), a modified symbol hard decision block and some sampling rate conversion blocks. As received signals are sampled at symbol baud rate, this carrier tracking scheme is still able to obtain precise estimated values of carrier synchronization parameters under the condition of very low SNRs. The performance of the proposed carrier synchronization scheme is also evaluated by using Monte-Carlo method. Simulation results confirm the feasibility of this carrier tracking scheme and demonstrate that it ensures that both the rate-3/4 irregular low-density parity-code (LDPC) coded system and the military voice transmission system utilizing the direct sequence spread spectrum (DSSS) technique achieve satisfactory bit-error rate (BER) performance at correspondingly low SNRs.