The performance of penalty compensation in 40G bit/s Non-Return-to-Zero (NRZ) systems that use nonlinear adaptive decision-feedback equalizer (ADFE) based on least mean squares (LMS) arithmetic is demonstrated in this paper. There is remarkable performance improvement of dispersion tolerance in single channel 40G bit/s NRZ systems by comparing the 1dB eye-opening penalty (EOP) after the ADFE is introduced. The PMD tolerance limit is improved from 0.17/bit slot of before equalization to 0.22/bit slots, when the system outage probability of tolerant (@BER>10-9) is 10-3.
Numerical simulations have been conducted to investigate the performance of a transmission system in which high spectral-efficiency duobinary modulation format is combined with adaptive electrical equalizer. The conventional filter parameters and the optimum filter parameters are used for comparison of system performance with and without adaptive linear equalizer (ALE). Numerical simulation results show that the dispersion tolerance and nonlinear tolerance (@1 dB EOP penalty) are effectively improved by ALE for duobinary NRZ (DNRZ) with conventional filter parameters, but it is not obvious for DNRZ with optimum filter parameters.
The work presented in this paper gives performance comparisons of Carrier Suppressed Return-to-Zero Differential Phase-Shift Keying (CSRZ-DPSK) with Return-to-Zero Differential Phase-Shift Keying (RZ-DPSK) against both the effects of Intra-Channel Four-Wave Mixing (IFWM) and inter-channel Four Wave Mixing (FWM) in 16×40 Gb/s WDM systems with symmetrical fiber link schemes. IFWM gives smaller phase perturbation to CSRZ-DPSK signal than to RZ33-DPSK, although BER performance of CSRZ-DPSK is worse than that of RZ33-DPSK. The numerical comparison indicates that RZ33-DPSK is a better candidate for 40 Gb/s WDM systems than CSRZ-DPSK.
The performance of 10Gb/s or above optical single channel transmission system is mainly limited by the chromatic dispersion (CD) and polarization mode dispersion (PMD) effect, and hence, different modulation formats and equalization methods are required to increase transmission distance, and mitigate transmission impairment. In this paper, we numerically evaluate the performance of 10G bit/s optical single channel transmission systems, which combine with varied kinds of modulation formats, which includes non-return-to-zero (NRZ), return-to-zero (RZ), carrier suppressed return-to-zero (CSRZ), and two kinds of electrical signal process (ESP) techniques which includes linear equalizer (LE) and decision feedback equalizer (DFE). Numerical simulation results show that the combined use of varied modulation formats and equalizer, we can obtain complete different performance improvement.
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