Asymmetrically Clipped Optical OFDM With Index Modulation For Wireless Optical Communication

Optical orthogonal frequency division multiplexing(O-OFDM)can improve transmission rate of wireless optical communication(WOC)system by higher spectrum utilization.And it adopts orthogonal subcarriers to effectively restrain the interference of atmospheric turbulence and atmospheric attenuation.Unfortunately,some disadvantages of O-OFDM are high peak-toaverage power ratio(PAPR)and low energy efficiency(EE).The key idea of index modulation(IM)is to add the frequency-domain dimension by employing the subcarrier-indices to convey extra information.It can achieve trade off in EE,PAPR and transmission rate,etc.So it provides a new direction for the development of O-OFDM technology.Therefore,according to the characteristics of WOC system,asymmetrically clipped optical OFDM with index modulation(ACO-OFDM-IM)by combining ACO-OFDM and the combination of subcarrier indices is studied in this paper.At the same time,two subcarrier algorithms are studied,which are used to improve system error performance.The details are as follows:(1)The problem of the conventional optical OFDM with index modulation technonlogy is that the error performance gets worsen as the number of the activated subcarriers increases.In this paper,a new ACO-OFDM-IM scheme is proposed by combining ACO-OFDM and combination of subcarrier indices.The upper bound of theoretical bit error rate of the improved ACO-OFDM-IM is derived by using union bound technique.And the performance of the proposed scheme is analyzed,meanwhile,making the comparison with the conventional ACOOFDM system in the different system performance.The results show that ACO-OFDM-IM scheme can effectively improve the error performance of the system as well as ensuring high transmission rate.Then,according to the characteristics of ACO-OFDM-IM system.the subcarrier selection algorithm(SSA)is adopted to make full use of the redundancy of the combination of subcarrier indices.By maximizating the number of channel norm,the more reasonable subcarrier indices are achieved,which can achieve the improvement of system error performance.In addition,For the problem of multiple subcarriers are activated simultaneously to cause intersymbol interference(ISI)within one sub-block.Subcarrier allocation algorithm(SAA)is introduced to eliminate ISI by maximum the minimum Euclidean distance between symbols.(2)Due to a part of subcarriers transmits information in ACO-OFDM-IM scheme,the EE is effectively improved.But its transmission rate is still not perfect enough.So a generalized ACO-OFDM-IM(ACO-OFDM-GIM)scheme is further presented by activating different number subcarriers in each sub-block.The principle of ACO-OFDM-GIM modulation mapping is introduced in detail,and the theoretical bit error rate of ACO-OFDM-GIM in turbulent channel is derived.The results show that not only does ACO-OFDM-GIM ensure good error performance,but also greatly improves the transmission rate of the system.At the same time,it is found that ACO-OFDM-GIM has similar problems to ACO-OFDM-IM system.Subsequently,the SSA and SAA are also applied to ACO-OFDM-GIM system that can greatly improve the error performance.