Noise-tolerant spiral 16-QAM system based on cascaded Kalman filters

We proposed a spiral 16-QAM system based on cascaded Kalman filters. The spiral 16-QAM signal has larger Euclidean distance and minimum angular distance than that of the traditional square 16-QAM signal. The cascaded Kalman filters enable us to suppress the phase noise caused by the laser linewidth to a great degree. These advantages enhance the noise tolerance of the proposed system. Simulation are performed on the spiral 16-QAM signal and the traditional square 16-QAM signal to evaluate the system's robustness of the laser linewidth and the signal and noise ratio.