| With the rapid development of optical communication network,high speed,optical orthogonal frequency division multiplexing(OOFDM)technology has become the key technology for the development of high speed optical communication system.The direct detection optical orthogonal frequency division multiplexing(DD-OOFDM)system has the characteristics of simple structure,low cost and insensitivity to frequency and phase noise,which can be used in optical network for medium-haul and short-haul transmission.However,the limited receiver sensitivity,dispersion tolerance and baseband noise caused by the signal beat frequency interference(SSBI)reduce the performance of the system to a certain extent.In order to effectively overcome the fading effect caused by optical fiber dispersion in the double side-band(DSB)DD-OOFDM system,the single side-band(SSB)modulation technology is applied to the DD-OOFDM system.Using the beat frequency interference cancellation receiver based on balance detection(ICRBD),consisting of an interleaver(IL),a 2×2 optical coupler(OC),two photodiodes(PD)and a subtracter,can eliminate SSBI and reduce the GB,which can effectively improve the spectrum efficiency.Polarization multiplexing(PDM))technology realizes double transmission of signals by carrying two polarized orthogonal signals on two polarization states of the light wave,which further improves the channel capacity and spectral efficiency,but the polarization mode dispersion in the fiber link needs to be solved.This paper mainly studies the PDM-DD-SSB-OOFDM system,uses 2×2 MIMO to model the PMD channel,and proposes the channel estimation based on LS and ISFA algorithm to compensate the polarization mode dispersion(PMD).In this paper,the history and significance of OFDM technology and PDM-OFDM technology in optical communication systems at home and abroad are introduced.Then the principle of OFDM and SSB-OFDM signal generation are discussed in detail,and the principle of SSBI elimination based on ICRBD structure is introduced.Based on these researches,the MIMO demultiplexing is realized based on LS algorithm and ISFA algorithm.The PDM-SSB-OOFDM system is analyzed and simulated.The work of the paper mainly includes the following contents:(1)MIMO polarization demultiplexing technology for RGB-PDM-SSB-OOFDM system based on LS algorithm.Based on the characteristics of the PDM-SSB-OOFDM system,the 2×2 MIMO channel estimation scheme based on LS algorithm is proposed.The theoretical analysis shows that the channel evaluation scheme can be used effectively for the PMD.By building a 2×40Gbit/s 16QAM PDM-SSB-OOFDM system link,the constellation diagram and error vector amplitude(EVM)curves are obtained,and the comparative study shows that PDM-MIMO technology has good adaptability in the ICRBD-based SSB-OFDM system,which can double the spectrum efficiency and channel capacity of the system.(2)Improvement of channel estimation based on ISFA algorithm in MIMO PDM-SSB-OOFDM link.Based on the LS algorithm,the channel estimation based on the ISFA algorithm is further studied.Based on the LS algorithm,the algorithm is to evaluate and average the adjacent matrix of each subcarrier as independent transmission channel matrix,which is equivalent to smoothing the channel to improve the system channel estimation accuracy.The simulation link of the 2×40Gbit/s 16QAM based on the ISFA algorithm is built.According to the constellation and the EVM versus the transmission distance,the optical signal to noise ratio,the guard band and the optical power,the contrastive study between the estimation of LS algorithm and ISFA algorithm shows that ISFA algorithm is more effective than LS algorithm for the PDM-SSB-OFDM system. |
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