Research On Wireless Communication Technology Based On Spatial/Frequency Index Modulation

In recent years,the global popularity of the Fifth Generation(5G)has continuously stimulated the development of mobile Internet.More and more wireless mobile devices and service demands have caused unprecedented growth in the amount of mobile data,which puts forward new requirements for the research of the future wireless communication technology.On the one hand,the future wireless communication technology needs to satisfy the high data rate and adapt to the mobility of the wireless devices in order to achieve high spectrum efficiency.On the other hand,it is necessary to consider some potential challenges currently faced,such as spectrum resource crisis and energy crisis.Therefore,the development of the future wireless communications must take into account both spectrum efficiency and energy efficiency.As two key technologies that have been successfully applied in the Fourth Generation(4G)mobile communication system,multiple-input multiple-output(MIMO)and orthogonal frequency division multiplexing(OFDM)will undoubtedly become the supporting technology of wireless communication for a long time in the future due to the high spectrum efficiency.However,multiple antennas used in MIMO at the transceiver will introduce some problems such as inter-antenna interference and the energy consumption,and OFDM also faces the disadvantages of inter-subcarrier interference and peak-to-average ratio.In order to deal with these problems,index modulation(IM)technology that has emerged in recent years can be used as a solution.IM is a new wireless communication technology that can use the active state of the communication resource to carry additional information.It has been applied in various fields of wireless communication.There are two most typical IM technologies at present,namely spatial modulation(SM)and OFDM with IM(OFDM-IM).SM is the application of IM in MIMO and OFDM-IM technology is a combination of IM and OFDM.This paper will focus on these two IM technologies.In SM,antenna selection technology is regarded as an effective mean to improve the system performance.However,the main idea of the current antenna selection technology is to select a part of the original antennas configured in SM according to certain criteria,which requires that the number of original antennas is greater than the number of antennas actually used,resulting in the waste of antenna resources.In order to solve this problem,in this paper,we consider the antenna selection methods in which the number of active antennas is not fixed and propose an enhanced spatial modulation with generalized antenna selection(ESM-GAS)for multiple input single output(MISO)systems.In ESM-GAS,all possible antenna combinations are regarded as equivalent antennas and the corresponding channels are defined as equivalent channels.Two equivalent channel selection schemes are proposed.One is first to arrange the equivalent channels according to their corresponding channel power gains,and then a proportion of equivalent channels with larger channel power gains are selected as candidate equivalent channels.The other is to combine ESM-GAS with the conventional EDAS(ESM-GAS-EDAS),which use the minimum Euclidean distance criterion to select the candidate equivalent channels.After the selection,the index of the final active equivalent channel is determined from these candidate equivalent channels by additional information bits.In this way,these two ESM-GAS systems only need to activate antennas within the physical antennas used,without occupying additional antenna resources.Finally,simulation results indicate that the BER performance of ESM-GAS and ESM-GAS-EDAS are better than that of conventional SM and EDAS systems respectively.Multi-Mode OFDM-IM(MM-OFDM-IM)is a new multi-carrier IM technology.Unlike OFDM-IM,MM-OFDM-IM allows all subcarriers to be activated to carry constellation symbols.In order to achieve IM,MM-OFDM-IM assigns a unique constellation mode to each subcarrier and uses the spermutation of these constellation mode to carry additional information.The simulation results show that MM-OFDM-IM has superior error performance and spectral efficiency than the existing OFDM-IM schemes.In this paper,we propose a new detector based on Expectation Maximization(EM)algorithm for MM-OFDM-IM.The EM detector can recover MM-OFDM-IM symbols with unknown channel state information in two stages.The first stage is to locate the possible signal constellation points iteratively according to the EM algorithm for a given mode permutation.Then,all located signal constellation points for all mode permutations trials are included in a candidate set as the input of the second stage,which acts as a filter and outputs the most-likely correct signal constellation points with the minimum Euclidean distance to the received signal.Monte Carlo simulation results verify the effectiveness of the proposed EM detector from the perspective of BER performance.In addition,the proposed EM demodulation algorithm is also suitable for dual-mode OFDM-IM(DM-OFDM-IM).At present,the relay systems based on OFDM-IM mainly focus on the communication between the source and the destination,which means that the relay is only used to improve the communication quality between the source and the destination.In this paper,we propose a totally different relay system,namely space frequency index modulation system based on distributed relays,which uses the index bits of the source OFDM-IM signal to determine the activation status of the distributed relays to achieve index modulation of the relays.Specifically,in the proposed system,both the source and the relays need to communicate with the destination.In the first time slot,the source broadcasts its signal to the relays that employ DF protocol.The relay that has the same identity index as the subcarrier active patten is activated to forward signal to the destination in the second time slot,which is a superposition of the decoded OFDM-IM signal and its own signal over the inactive subcarriers.We derive closed-form upper bounds on the BERs of both the source and the active relay,and verify our analysis via Monte Carlo simulations.