Symbol error rate comparisons of star MQAM schemes based on equal cubic metric

In this paper, we present several schemes of N rings star M-ary quadrature amplitude modulation (NR-MQAM) with independent bit mapping. The theoretical expression of symbol error rate (SER) for NR-MQAM is derived and compared with that of cross or square MQAM. For NR-MQAM, the ring ratio is selected based on the principle that its cubic metric (CM) value is equal to that of cross or square MQAM. The theoretical SER curves and numerical simulation results show that 4R-32QAM, 8R-64QAM and 8R-256QAM have a lower SER and stronger ability to resist the phase errors than other 32QAMs, 64QAMs and 256QAMs. The validity of simulated results is demonstrated by the minimum Euclidean distance.