Research On High-order QAM Carrier Recovery Technology

With the development of modern digital communication,people’s demand for information transmission is increasing,and the frequency resources are becoming more and more tense.A stable and reliable high-speed data transmission mode is very important.Multiple quadrature amplitude modulation(MQAM)is a modulation method that carries data both in amplitude and phase.It has high spectrum utilization and strong anti-noise performance,so it is widely used in digital communication system and VDES system.However,in MQAM communication system,due to the influence of channel and receiver,MQAM signal will produce frequency offset and phase offset at the receiving end,which will affect the demodulation process and cause performance loss.The higher the order,the more serious the loss.Carrier recovery technology can estimate and compensate the frequency offset and phase offset,so the carrier recovery module is indispensable in the receiver.Based on the analysis of the research status at home and abroad,this paper mainly analyzes the carrier recovery of MQAM signal from two aspects of data-assisted algorithm and non-data-assisted algorithm.In the non-data-assisted aided algorithm,aiming at the problem that the acquisition range of closed-loop structure is not ideal,a joint IFOE algorithm is proposed to improve the acquisition range,and a multithreshold method is introduced to reduce the acquisition time without increasing the lock phase error.Aiming at the problem that the maximum likelihood estimation(ML)algorithm in the open-loop structure algorithm has too much computation.A multi-level estimation algorithm is proposed,which can simplify the calculation effectively,and set the power detector to remove the interference constellation points,which can improve the estimation accuracy.In the data-assisted algorithm,this paper introduces three autocorrelation data aided algorithms: L&R,L&W,and Fitz.The performance characteristics of each algorithm are analyzed by simulation,and a new interpolation estimation algorithm is proposed.Compared with the traditional interpolation algorithm,the proposed algorithm has higher accuracy.