| Optical wireless communication,also known as free-space optical communication(FSO),is considered a feasible method to realize wireless access in the future due to large bandwidth,license-free spectrum and other advantages.However,due to the existence of atmospheric turbulence effect,the transmission rate and reliability of the system are reduced.Faster-than-Nyquist(FTN)technology improves spectral efficiency via compressing the interval between adjacent signals.FTN technology is introduced to improve the transmission rate in the FSO system.However,due to inter-symbol interference is introduced by FTN and the existence of atmospheric turbulence effect in the FSO system,the system performance is seriously deteriorated,and the communication quality and reliability of the system are reduced.As a new type of hard decision forward error correction technology,staircase code(SCC)has the advantages of high code rate and high decoding performance,while multi-input multi-output(MIMO)technology is an effective measure to suppress atmospheric turbulence.Therefore,in order to reduce the influence of the inter-symbol interference and channel turbulence interference in the FTN-FSO system,in this thesis,SCC coding combined with FTN technology and MIMO technology is applied to the FSO system,two system schemes of SCC-FTN-FSO and SCC-FTN-MIMO-FSO are proposed,and focuses on the bit error performance of the two systems and the factors affecting the bit error performance.The specific work is as follows:(1)In order to effectively eliminate and suppress the inter-symbol interference of FTN and channel turbulence interference,and improve the bit error rate performance of system,this thesis first proposes a FTN-FSO system scheme based on staircase code and deeply analyzes the whole process of staircase code encoding,decoding and system signal transmission.On this basis,the system is analyzed theoretically and Monte Carlo simulation method is used to verify the bit error rate performance of the system scheme.The results show that the bit error rate performance of FTN-FSO system is improved significantly after the introduction of staircase code.Compared with the uncoded FTN-FSO system,the bit error rate performance gain reaches 11.053 d B at a code rate of 0.5,and compared with the code rate of 0.75,the bit error rate performance improves 3.56 d B at a code rate of0.5.In addition,the introduction of SCC can eliminate the inter-symbol interference of FTN and channel turbulence interference,but these interferences can’t be completely eliminated.Meanwhile,the bit error rate performance of SCC-FTN-FSO system improves with the decrease of turbulence intensity,with the increase of receiving aperture,roll-off factor and acceleration factor.(2)In order to further resist the influence of atmospheric turbulence and improve the bit error rate performance of system,in this thesis,on the basis of SCC-FTN-FSO single-input single-output system scheme,the SCC-FTN-MIMOFSO system scheme is proposed in combination with the MIMO technology.The FTN signal is loaded on multiple antennas for transmission after encoding,and effectively improves the communication quality of the system by receiving multiple antennas.Meanwhile,the bit error rate performance of the system under different conditions is analyzed via Monte Carlo simulation.The results show that SCC-FTN-MIMO-FSO system can effectively eliminate the influence of turbulence on the bit error rate performance of system,compared with the SISO system,the bit error rate performance gain reaches 14.075 d B under the strong turbulence intensity.Meanwhile,appropriately increasing the number of antennas can effectively improve the bit error rate performance of system,and the performance gain from increasing the number of receiving antennas is significantly better than increasing the number of transmitting antennas.In addition,the bit error rate performance of SCC-FTNMIMO-FSO system also improves with the increase of receiving aperture,roll-off factor,and acceleration factor. |
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