Optimized Design Of Optical Wireless Communication System Based On Flip-OFDM

In recent years,the visible light communication(VLC)has attracted more and more attention as a novel wireless optical communication technology.Since the transmitted signal only can be represented by the intensity of light sources,the transmitted signal must be real and positive.Then the transmission mode can be referred to intensity modulation and direct detection(IM/DD).Flipped orthogonal frequency division multiplexing(Flip-OFDM),as a unipolar OFDM technique which is suitable for IM/DD transmission mode,receives much attention due to its low hardware complexity and high power efficiency.Therefore,this thesis will do some research and improvement based on the technology which is related to Flip-OFDM system.First of all,an overview of the VLC system is introduced,and the reason why the Flip-OFDM system is studied in this paper is explained.Secondly,the fundamental theory of the diversity combining technology is introduced.Then,this paper proposes a novel Flip-OFDM receiver based on the temporal or spectral diversity combining,which can take full advantage of the received power by extracting effective information from both the sum and the difference of the two received subframes,in order to improve the performance of the Flip-OFDM system.Compared with the current Flip-OFDM receivers such as the conventional Flip-OFDM receiver and the threshold-based receiver by simulation,the novel receiver,especially the spectral diversity combining receiver,has the better BER performance in both the additive white Gaussian noise(AWGN)channel and the not-line-of-sight(NLOS)channel.In addition,the proposed spectral receiver also has lower computational complexity compared with the existing iterative receiver.Then,a novel precoding Flip-OFDM system which is based on the adaptive joint optimization of precoder and equalizer is proposed.In the system,the energy of the transmitted signals is constrained to reduce the probability of the maximum peak to average power ratio(PAPR).Moreover,the novel precoding system can be combined with the proposed Flip-OFDM receivers to make full use of the information of the received subframes and further enhance the bit error ratio(BER)performance of the Flip-OFDM system.The result of simulation shows that both in AWGN channel and NLOS channel,the novel precoding Flip-OFDM systems,especially those combined with the proposed receivers,have better BER performance compared with other systems.In addition,the proposed PE-Scale precoding Flip-OFDM system which is combined with the proposed spectral receiver has the best performance in NLOS channel.Finally,in order to further reduce the adverse impact of the high PAPR,a new joint optimization design which is based on the double-sided clipping technology and the PE-Scale precoding Flip-OFDM system is proposed,which is called the clipping PE precoding Flip-OFDM system.Since using the clipping technology will adversely affect the BER performance of the communication system,the precoder design takes the information of the clipping signal into account to reduce the losses.The result of simulation shows that,compared with other systems,the effect caused by the clipping technology has the least impact on the proposed clipping PE precoding Flip-OFDM system in the NLOS channel.In addition,compared with other systems which combine the clipping precoding systems with the proposed receivers,the proposed clipping PE precoding system combined with the proposed spectral receiver has the best performance in NLOS channel.