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.

A new Kalman carrier synchronization algorithm is developed for high-order QAM transmission to reduce complexity compared to the conventional Kalman approach. The state model in the proposed algorithm employs only phase, instead of both phase and frequency, as in the conventional method. A reduced-observation model is also introduced to eliminate matrix operations in the Kalman recursions. Simulations results show that the one-state Kalman algorithm has better performance and lower complexity than the two-state Kalman algorithm. The cable modem downstream system is applied to demonstrate the effectiveness of the proposed algorithm.

This paper considers a wireless coherent system that enables high-speed-data transmission in the presence of carrier phase error over an additive white Gaussian noise (AWGN) channel. Carrier phase noise is caused by imperfect carrier tracking of the coherent demodulation. The channel characteristics of the system were modeled using phase noise whose stochastic process followed the Tikhonov distribution. For this model, we first propose an optimum detector that produces the most suitable decoding metric for a soft-input/soft-output (SISO) decoder, and then develop some simpler forms of the optimum detector to obtain efficient implementation at close to optimal performance. Those simple detectors that have a wide range of performance/complexity tradeoffs are promising in various applications. To evaluate the effectiveness of the proposed detectors, we have applied them to a bandwidth-efficient turbo-coded modulation scheme in which a component decoder based on SISO principles necessitates more exact channel measurement than is possible with a conventional decoder based on Viterbi decoding. Simulation results have demonstrated that the optimum detector enables excellent bit error rate (BER) performance that exceeds that with a normal detector designed for AWGN channels by more than 1 dB at a BER of 10-6 under a severe phase noise environment.