Proc. SPIE. 8645, Broadband Access Communication Technologies VII
KEYWORDS: Digital signal processing, Quadrature amplitude modulation, Stars, Modulation, Signal attenuation, Phase shift keying, Modulators, Semiconductor lasers, Systems modeling, Thick film dielectric electroluminescent technology
In this paper, we study the performance of star quadrature amplitude modulation (QAM) signals with various
constellations for hierarchically-modulated PON systems that overlay an over 20-Gbps PSK signal on a 10-Gbps on-off
keying (OOK) signal; previous work examined only the performance of an 8-star QAM signal. A star QAM signal
consists of a PSK signal with lower amplitude (inner-PSK signal) and a PSK signal with higher amplitude (outer-PSK
signal). We propose to decrease the modulation level of the inner-PSK signal and increase that of the outer-PSK signal
with the goal of improving the bit error rate performance in some conditions. Simulations indicate the minimum required
received power for the various constellations examined: it is shown that effective design depends on the extinction ratio.
For example, 10-star QAM improves the minimum required received power by 3 dB compared to 8-star QAM when the
extinction ratio is 12 dB.