Research Of OFDM Based On Index Modulation Technique

With the rapid development of mobile communication technology,the high efficiency and high reliability of wireless communication technology has attracted more and more attention.Orthogonal Frequency Division Multiplexing,as a classic technology with high spectral efficiency and resistance to narrowband interference,is widely applied in various wireless communication scenarios.In 2012,OFDM-IM(OFDM with Index Modulation)technology was proposed to provide a frequency-selective fading channel to improve the system diversity gain,especially in the scenario of low spectral efficiency,which can effectively improve the system error performance.In OFDM-IM scheme,special index bit transmission and index structure design improve diversity gain,which has attracted extensive attention.How to achieve better error performance and higher spectrum utilization ratio than OFDM through index structure design has become a hot topic in the research direction of index modulation aided OFDM.In order to solve these two problems,this paper studies the spectral efficiency of index structure in order to further improve the spectral efficiency according to the characteristics of index structure.At the same time,how the index structure itself brings about additional diversity gain is the focus of this paper.The main contains of our work are as follows:(1)Aiming at the low spectral efficiency of Index Modulation in OFDM,this paper proposes a Modulation technique of OFDM-JS-IM(OFDM with Joint Subblock Index Modulation),which combines the discarded indexes in the mapping and uses them repeatedly in the joint subblock space.Simulation and theoretical analysis show that OFDM-JS-IM scheme can effectively improve the spectral efficiency of OFDM-IM at the cost of slight error performance loss.(2)The relationship between index structure and diversity performance is analyzed.Due to the special structure of OFDM-IM,the diversity order of index bit is higher than that of symbol bit,which results in better performance of OFDM-IM compared to that of OFDM.However,the index modulation structure in OFDM can only increase the diversity order to the degree of 2.This paper proposes an OFDM with all index modulation(OFDM-AIM),which transfers information in the form of index bits instead of using symbol bits with low diversity order,and proposes a search algorithm that improves diversity order,so as to construct a legal sub-block set with high diversity order.Simulation results show that the scheme can effectively improve the diversity gain of the system.(3)Based on OFDM-AIM,this paper further proposes a scheme of subblock design aided OFDM-AIM using adaptive subblock length.Since the subblock length of OFDM-AIM determines the highest diversity order of the system,the subblock length can be appropriately increased to find more subblocks with higher diversity order,so as to improve the diversity gain.According to the requirements of spectral efficiency and computational complexity,the scheme can achieve better performance tradeoff by adaptive subblock length in practical applications.(4)Diversity order is only used to evaluate the characteristics of the transmitting signa.However,the error performance of the system is not only related to diversity order,but also to Euclidean distance between different sub-block symbols and channel characteristics.To solve this problem,the genetic algorithm of heuristic algorithm is used to search the subblock look-up table with the best error performance.In this paper,the PEP(Pairwise Error Probability),which gives the theoretical upper bound of the look-up table was regarded as the fitness.The channel characteristics were taken as the biological environment.Finally,the look-up table with better error performance was obtained through iteration.Compared with the existing index modulation aided OFDM scheme,the error performance is improved obviously.The research content of this paper is the cutting-edge technology in OFDM,which provides valuable reference for OFDM transmission with high rate and high performance in frequency-selective fading channel,and has strong practical significance.