Research On Performance Of OFDM Based On Hartley Transform In Visible Light Communication System

Visible light communication has the advantages of rich spectrum resources,green environmental protection and energy saving,and high transmission rate.Aiming at the problems of high peak-to-average power ratio existed in orthogonal frequency division multiplex(OFDM)and OFDM signals using the traditional mapping are affected by LED nonlinearity in visible light communication system,which can cause spectral efficiency low and inter-carrier interference.In this thesis,the performance of OFDM modulation based on Hartley transform in visible light communication system was studied.The main works included:1.Aiming at the problems of computational complexity high and frequency band utilization low in OFDM based on Fourier transform,OFDM based on Hartley transform was established in visible light communication system.The characteristics of signal sequences transformed by Hartley inverse transform after PSK mapping were analyzed.And the nonlinearity effect of LED and its influence on system error performance were also analyzed.2.In order to improve the suppression scheme of peak-to-average power ratio in OFDM system,precoding and iterative clipping and filtering techniques were applied to the OFDM based on Hartley transform in visible light communication system.The suppression capability of Hadamard transform precoding,discrete cosine transform precoding on the peak signal were studied respectively.The computational complexity,spectral efficiency,peak-to-average power ratio and bit error rate of this system were compared with OFDM system based on traditional iterative clipping and filtering.3.In order to reduce the influence of LED nonlinear effects,improve the spectral efficiency of the system and suppress the inter-carrier interference,the Minimum Frequency Shift Keying(MSK)coding mapping was introduced,OFDM based on Hartley transform with MSK coding mapping in visible light communication system was established.The differences between this system and the OFDM modulation system with binary phase-shift keying in constellation,power spectral density,carrier interference ratio and anti-interference performance in carrier frequency offset environment were compared and analyzed.The results show that:(1)Compared with the OFDM system based on Fourier transform,OFDM system based on Hartley transform has the advantages of low computational complexity and high frequency band utilization.(2)Compared with OFDM system with traditional iterative clipping and filtering,the improved system can suppress signal peak-to-average power ratio and improve the bit error rate performance effectively,and discrete cosine transform precoding is better than Hadamard transform precoding in improving system performance.(3)Compared with binary phase-shift keying,OFDM system based on Hartley transform with MSK coding mapping has faster power spectrum sidelobe attenuation,more concentrated spectrum and better anti-interference in carrier frequency offset environment.