Furthermore, transmission performance of CO-OFDM system is investigated with and without equalizer at 10Gbps data rate for single channel and the results is presented in the form of simulations. Then we present the principle of Maximum likelihood sequence estimation technique to compensate the distortion produced by chromatic dispersion in the optical fiber link. The article is organized as follows: First, we give a brief state-of-the-art review of OFDM technique. In cases that are most computationally straight-forward, root mean square deviation can be used as the decision criterion for the lowest error probability. The receiver compares the time response with the actual received signal and determines the most likely signal. All possible transmitted data streams are fed into this distorted channel model. The receiver emulates the distorted channel. For an optimized detector for digital signals the priority is not to reconstruct the transmitter signal, but it should do a best estimation of the transmitted data with the least possible number of errors. MLSE is a mathematical algorithm to extract useful data out of a noisy data stream. The Maximum likelihood sequence estimation (MLSE) is a widely used nonlinear signal processing tool. It comes under the post dispersion compensation methods. As intra-channel nonlinearity distortion of the CO-OFDM system is generally caused by SPM and FWM among subcarriers so a nonlinear signal processing schemes to compensate for intra-channel nonlinearity is also included in the paper.Įqualization is the process of correcting or estimating received information that is corrupted due to the chromatic dispersion in the optical link and the output of the equalizer is the estimate of the transmitted signal. As a result, nonlinearity compensation is a crucial component of the CO-OFDM system. Because OFDM is a multi-carrier modulation scheme, the four-wave mixing (FMW) among subcarriers within one channel also causes concerns among researchers.
Since the OFDM system has a high peak to average power ratio (PAPR), a CO-OFDM system has more severe SPM and XPM compared with traditional optical communication systems. Both of SPM and XPM are caused by the optical signal intensity fluctuation. One major concern about the CO-OFDM system is its vulnerability to fiber nonlinear effects such as self-phase modulation (SPM) and cross-phase modulation (XPM).
PMD COMPENSATION IN OPTISYSTEM CODE
Moreover, the cyclic prefix code of the COOFDM system makes the system more resistant to inter-symbol interference caused by chromatic dispersion and polarization mode dispersion (PMD). The OFDM modulation scheme also leads to a high spectral efficiency because of its partially overlapping subcarriers. OFDM is a multicarrier transmission technique where a data stream is carried with many lower rate subcarrier tones that is high bit rate data stream is divided into several low bit rates streams that are simultaneously modulated onto orthogonal subcarriers. Optical frequency division multiplexing (OFDM) is an attractive modulation scheme that recently received a lot of attention in the fiber optic community.
PMD COMPENSATION IN OPTISYSTEM FULL
The coherent optical communication system makes full compensation of chromatic dispersion, after optical/electrical conversion, possible. As a coherent system, the CO-OFDM system maintains both signal amplitude and phase, thus increasing bandwidth utilization. OFDM, QAM, equalizer, Coherent detection, Modulation.Ĭoherent Optical OFDM (CO-OFDM) is considered an enabling technology of the next generation optical communication system. The simulation results reveal that the system with equalizer has better transmission performance in comparison to the system without equalizer. The transmission performance for single channel 16-QAM CO-OFDM system is demonstrated through simulation at 10Gbps data rate with and without equalizer. The advantage of using equalizer for system at 10 Gbps data rate is discussed at the receiver side. An overview of COOFDM for high speed, long haul optical transmission link for single channel is presented in this paper. Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) has attracted significant attention in research and development during the last several years as it combines the advantages of „Coherent Detection‟ and OFDM Modulation‟ and possess many merits that are critical for future high speed fiber transmission systems.
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