64APSK constellation scheme for short-reach DMT with ISDD enabled SFO compensation

Abstract

Sampling frequency offset between digital-to-analog converter (DAC) and analog-to-digital converter (ADC) always exists in asynchronous optical discrete multi-tone (DMT) systems. The overall bit error rate (BER) performance may be seriously deteriorated due to SFO-induced phase rotation. Inter-symbol differential encoding/detection (ISDE/ISDD) with decision-aided residual phase compensation (RPC) has been employed to compensate SFO. No extra training sequences or pilot subcarriers are required for SFO compensation. However, the increased phase noise induced by ISDD is still a problem and may degrade the BER performance of the DMT receiver, especially for high-order modulation formats. In this work, we propose the use of amplitude and phase shift keying (APSK) constellation scheme to against the ISDD-induced phase noise and then improve the BER performance. In our simulations, the 64QAM and two types of 64APSK modulation formats for DMT are studied in both additive white Gaussian noise (AWGN) channel and intensity-modulation/direct-detection optical fiber transmission system. The simulated results exhibit that the employed two 64APSK constellation schemes outperform the conventional 64QAM modulation format in the presence of ISDD-induced phase noise. By using the proposed 64APSK constellation scheme, the SNR performance can be improved by up to 3dB when the BER is 1E-3 in AWGN channel. Besides, up to 2dB improvement in the receiver sensitivity in terms of the received optical power can be also achieved, compared to the conventional 64QAM modulation format.