Research On Multicarrier Systems With Index Modulation

By modulating symbols to the parallel multiple carriers,multi-carrier modulation technique can improve the spectral efficiency in the limited spectral resource and provide a stable and reli-able high-speed data transmission in the effective spectrum.As one of the multi-carrier modulation systems,OFDM has the advantages of robustness to the fading channel.However,the power effi-ciency and the spectral efficiency of OFDM system are not so high.Besides,OFDM is sensitive to carrier frequency offset and the rectangular shaping pulse leads to high out of band emission.To solve these problems of OFDM system,the researchers go on investigating the multi-carrier mod-ulation technique,then propose OFDM-IM system and the FBMC system.Compared with OFDM system,OFDM-IM system have higher complexity and higher power efficiency.By activating a subset of subcarriers to carry the modulated symbol and utilizing the active subcarrier indices as a source of information,OFDM-IM can provide a more flexible trade-off between the spectral ef-ficiency and the error performance.Apart from its main advantage of significantly reduced out of band emission,FBMC can achieve a higher spectral efficiency as it does not use any CP and is more robust to carrier frequency offset.As a result,OFDM-IM and FBMC have attracted much attention and are worth studying.Based on the analysis of basic principles of OFDM-IM and FBMC,the key research points of this two systems are pointed out.To improve the transmission rate of OFDM-IM,the MIMO transmission technique and OFDM-IM technique are combined.To improve the error performance,the index modulation technique is applied to FBMC system and C-FBMC system.Besides,the key problems after the application of the index modulation technique are solved.Firstly,the fundamentals of OFDM-IM and FBMC are introduced.For OFDM-IM,the basic system model is introduced and the basic principle is presented as well as the detection of the receiver.Then,the error performance bound of OFDM-IM is studied and its reachable spectral efficiency bound is also analyzed.Compare with OFDM,OFDM-IM have the advantages of better error performance and adjustable spectral efficiency.For FBMC,the system model and the basic principle are introduced.Then,the advantage of higher spectral efficiency of FBMC is analyzed.At last,the implementation method of FBMC based on FFT operation and the prototype filter used in FBMC are introduced.Then,to improve the transmission rate of OFDM-IM,the MIMO transmission technique and OFDM-IM technique are combined,then the MIMO-OFDM-IM system is proposed.Because of the introduction of the index modulation technique,MIMO-OFDM-IM system can achieve a better error performance than the traditional MIMO-OFDM system.However,the detection of the active subcarrier indices and the modulated symbols become a challenging problem as the complexity of the optimal detection algorithm is too high to implement.Besides,the other detection algorithms suffer from a significant error performance compared to optimal detection algorithm.To achieve near-optimal error performance while maintain low computational complexity,two low complexity K-best detectors are proposed.The K-best-1 detector retains K best nodes at each layer of the search tree by regarding each OFDM-IM subblock as a super symbol to reduce the complexity of optimal detector.To minimize the size of the subblock,the proposed K-best-2 detector selects the K best nodes at subcarrier level.Next,to cancel the interference,the application of the index modulation technique in FBMC system is investigated.FBMC system may encounter inter-symbol interference and inter-carrier interference caused by either imperfect prototype filter or dispersive channels that can not be elim-inated completely by simple ZF equalizer.The interference mainly comes from the neighbouring symbols in the frequency or time domain.Based on this view,the index modulation technique is introduced to FBMC system and FBMC-IM system is proposed.As some subcarriers carry noth-ing but zeros in the proposed FBMC-IM system,the interference power will be smaller compared with that of the conventional FBMC system and a better SIR will be achieved while the spectral efficiency is the same.However,the interference is not eliminated completely and the remaining interference still affect the performance of FBMC-IM system.In order to reduce the effect of the remaining interference,an optimal combination-selection algorithm and an optimal combination-mapping rule are proposed.By considering both the largest average HD principle and the fewest bad combinations principle,the combination-selection algorithm is proposed to select the optimal combinations.After selecting optimal combinations,these combinations are mapped into specified bits by following the optimal combination-mapping rule.By optimization,a better error perfor-mance of FBMC-IM system can be achieved.Finally,the application of index modulation technique in the C-FBMC system is investigated.Due to the fact that there exists the ramp-up and ramp-down problem at the beginning and end of the frame in FBMC system,the spectral efficiency of the FBMC system decreases in the applications with short messages.To improve the spectral efficiency of the conventional FBMC system,the truncation tails method and the circular FBMC method are proposed.However,for truncation tails method,the orthogonality of the edge symbols will be degraded due to emitting the signal tails.Besides,for circular FBMC method,there exists a performance loss in multi-path fading channel.To solve these problems,a C-FBMC-IM system model is built in matrix form.The signal processing method in the receiver is improved to eliminate the interference introduced by channel.As a result,the proposed C-FBMC-IM system outperforms the conventional C-FBMC system.The theoretical analysis and simulation results demonstrate that both BER and spectral efficiency improvement can be achieved when the index modulation technique is applied to C-FBMC system.