Design of Circular Signal Constellations in the Presence of Phase Noise

In order to save the limited bandwidth resource, high-order M-ary amplitude and phase shift keying (APSK) signal constellation as quadrature amplitude modulation (QAM) is widely employed in modern bandwidth-limited communication and broadcasting systems. However, such dense constellation is very sensitive to the disturbance of noise, including not only white Gaussian noise but also phase noise which is caused by many nonideal factors in transmitter, receiver and channel. This paper proposed a design method of circular signal constellations which are extremely robust in the presence of phase noise. As for 64 points, the circular constellation we proposed performs at least 5 dB better than the square QAM at the error rate of 10^-3 under the phase noise of 0.1 rad. And compared with the existing patent constellation designed to mitigate phase noise´s effect, the proposed circular constellation not only performs 1 dB better in phase noise of 0.1 rad, but also sacrifices no error performance under white Gaussian noise only. And since the circular constellation is with small amplitude fluctuation, it can be further used to mitigate the requirement of power amplifier´s linear range in certain systems. Further, a reliable and easy-to-implement demodulation method is also presented.