Research On Channel Estimation Technology Of OFDM Transmission In Reversely Single Sideband Radio-over-fiber System

In recent years,data flow of mobile Internet has increased quickly.Wireless and broadband communications have been the interests of information industry.Radio-over-Fiber technology(ROF)can achieve high frequency signal transmission and broadband wireless access,which integrates advantages of both optical and wireless systems.Today China's 4G network has been developing very fast.As the core technology of 4G network,orthogonal frequency division multiplexing(OFDM)technology has got a lot of attentions and actively studied due to high spectrum efficiency and anti-interference ability.Utilizing the OFDM technology in ROF system will not only improve the tolerance to dispersion impairments in the fiber link but also enhance the transmission reliability in wireless delivery.Therefore,OFDM-ROF system has considered as a promising method in the future broadband access networks.Reversely single sideband(RSSB)ROF system which is energy efficient,walk-off effect free and data format compatible has been proposed.This system has got more and more attentions and been widely investigated since it was proposed.Channels of different systems have their own characteristics,channel estimation of RSSB ROF system is very important,while there is no research on channel estimation in this system.This article focuses on the optim ization of pilots structure and the choice of interpolation algorithms in the channel estimation technology based on pilots for RSSB-OFDM system.The main work of this paper include:1.The knowledge about RSSB-OFDM systems is detailed.We give the structure and working principle of RSSB-OFDM system,then a mathematical model of this system are derived and analyzed.The impairment of the system and the channel estimation process are introduced.2.The pilots based channel estimation technology is studied in RSSB-OFDM system and some pilots optimization scheme which improved the performance of system by 2dB receiving sensitivity are proposed.According to the main impairment of this system,we placed more pilots data in the area where channel conditions are relatively good,the increased interval allocation scheme can obtain the best performance and improve the performance by nearly 2dB receiving sensitivity comparing with the poor pilots interval scheme.For anti-interference,we improved the power of pilots in the area where channel conditions are relatively poor,the increased power allocation scheme can obtain the best performance and improve the performance by 2dB receiving sensitivity comparing with the poor pilots power scheme.3.Four common interpolation algorithms in the channel estimation are analyzed and the conclusion is given that the best algorithm for RSSB-OFDM system is cubic spline interpolation.Four algorithms are linear interpolation,cubic spline interpolation,low pass interpolation and time domain interpolation.The theoretical analysis and simulation results both show that the channel estimation based on cubic spline interpolation has the best performance due to no requirement in pilots structure and improves the performance by 3dB receiving sensitivity comparing with other algorithms.