Star-QAM Constellation Design for Hierarchically Modulated PON Systems With 20-Gbps PSK and 10-Gbps OOK Signals

In this paper, we show an effective star-QAM constellation in terms of the allowable range of the extinction ratio for hierarchically modulated PON systems that overlay a 20-Gbps PSK signal on a 10-Gbps OOK signal. In ten-star and 17-star QAM signals, the modulation level of the PSK signal is dynamically changed based on the amplitude of the OOK signal while the modulation level of the PSK signal is constant in the fundamental eight-star QAM signal. Numerical results studied the performance of these constellations, and indicated the effective constellation to achieve the lowest power penalty depends on the extinction ratio. Simulation results showed that by using eight-star QAM or ten-star QAM signals, new ONUs satisfied the required receiver sensitivity in 10G-EPON and XG-PON. Experimental results showed that, compared to the eight-star QAM signal, the ten-star QAM signal enhanced the range of the extinction ratio wherein ONUs of legacy and new systems satisfied the required sensitivity for 10G-EPON and XG-PON. The range was from 7.4 -9.7 dB. The ten-star QAM signal also improved the required received power by 7.7 dB compared to the required sensitivity in 10G-EPON when the extinction ratio was 8.2 dB.