Research Of Carrier Recovery Algorithms For High-order QAM And Implementation Of QAM Tester

The carrier recovery is a necessary part in the digital communication system. It is used to compensate frequency offset and phase jitter brought by transmission and demodulation. Firstly, this paper introduces the maximum likelihood (ML) algorithm, the decision directed (DD) algorithm and the reduced constellation (RC) algorithm. Although ML algorithm is one of the best in the theory, it is too complex to implement. DD algorithm reduces the complexity of ML algorithm and gets widely used in reality. But in the case of constant loop bandwidth, it is impossible to harmonize the conflict of convergence speed and steady-state variance. To solve the problem, this paper proposes a new DD algorithm with adaptive loop bandwidth. And proved by simulation, the new algorithm can solve the problem well. Then this paper introduces the polarity decision algorithm for high-order QAM, which has many states. It uses RC algorithm with wider acquisition range at the beginning, and uses DD algorithm in the tracking status. Based on the research of the polarity decision algorithm, this paper proposes a new status transform method, and a new algorithm of "polarity decision and scan frequency algorithm". In this method we can get wider acquisition range. Finally, this paper gives the scheme of QAM tester's design and implementation.