Research On The Mitigation Of Ssbi/Ssmi And Other Impairments In DD-OOFDM Metro Transmission Systems

With the development of cloud computing, video on demand, large-scale data traffics in recent years, the requirements of the metro network’s capacity and flexibility increase dramatically. The direct detection OFDM system has the advantages of high spectral efficiency, strong resistance for the dispersion and the flexibility for bandwidth’s scheduling. Therefore, it is valuable and prominent for the practical application in the metro network. This paper mainly researches on the mitigation of SSBI/SSMI and other impairments in the direct detection OFDM transmission systems combined with the different modulation type (field modulation or intensity modulation), and gains a number of innovative research achievements. The main work and innovative contributions are listed as follows.1. For the I/Q imbalance problem in the field modulation RF-Assisted Gapped SSB-DD-OFDM system, a pre-compensation scheme for I/Q imbalance at the lower cost of computational complexity is proposed. This pre-compensation scheme intentionally distorts the original symbols according to the deviations of I/Q imbalance’s parameters, which can ensure the baseband signals of I/Q channels to pre-generate the amplitude, phase and time deviations matched to the actual deviations of the optical I/Q modulator. Thus, the pre-generated deviations based on the pre-compensation scheme can effectively offset the corresponding deviations of this imbalanced I/Q modulator, and mitigate I/Q imbalance-induced image interference. The40Gbps-100km field modulation RF-Assisted Gapped SSB-DD-OFDM system’s simulation result shows that the pre-compensation scheme improves about0.9dB receiver sensitivity compared with the system without the I/Q imbalance compensation technique under the typical I/Q imbalance configuration. 2. For the character of SSBI in the field modulation SSB-DD-OFDM system, a novel time diversity reception OFDM scheme is proposed. In this scheme, for every single OFDM symbol, the transmitter intentionally generates two consecutive OFDM symbols, and the phase of these two symbols is opposite to each other, which ensures the two consecutive received OFDM symbols after the direct detection at receiver produce the useful signal with opposite phase, and the in-phase SSBI, Thus, the SSBI impairment could be cancelled by jointing the two successive received symbols. The40Gbps-100km field modulation conventional SSB-DD-OFDM system’s simulation result shows that the proposed time diversity reception OFDM scheme improves about4.5dB receiver sensitivity compared with baseband OFDM scheme. Meanwhile, the result of the5Gbps-100km field modulation conventional SSB-DD-OOFDM offline experiment for the functional verification shows that the proposed scheme improves about3.4dB-sensitivity compared with baseband OFDM scheme.3. The SSMI model with the EAM’s dynamic chirp in the EAM-based IMDD-OFDM multi-band system is analyzed and the corresponding SSMI mitigation scheme based on frequency-domain pre-distortion is proposed. This SSMI mitigation scheme distorted the original symbols employing the nonlinear numerical iterative method, which ensures received symbols after the direct detection at receiver excluding the impairment of SSMI. The simulation result shows that, with the propose SSMI mitigation scheme, the40Gbps EAM-based IMDD-OFDM multi-band system is successfully obtained over100-km SSMF transmission. And the result of the30Gbps-100km EAM-based IMDD-OFDM offline experiment shows that the proposed pre-distortion technique could reaps about2.9dB sensitivity improvement compared with the system without SSMI mitigation.