Research On Low-Complexity Detector Design For OFDM With Index Modulation

With the development of the internet,Internet of Things and Intelligent Transportation System,the increases demand for higher quality of service and data speed in wireless communications.How to improve the spectrum efficiency,energy efficiency and reliability requirements of the next generation wireless communications has attracted many attentions.Orthogonal frequency division multiplexing(OFDM)has been regarded as the core technology of 4G wireless communications,and can effectively combat the inter-symbol interference caused by the multipath interference of the wireless channel.OFDM with Index Modulation(OFDM-IM)is a recently proposed improved multicarrier transmission technique of OFDM,which is the application of the index modulation in the frequency domain.In OFDM-IM,the indices of the activated subcarriers act as an information-carrying mechanism besides the ordinarily modulated symbols.OFDM-IM keeps the merits of classical OFDM and can achieve superior spectral efficiency and bit error rate(BER)by choosing appropriate index modulation schemes.Due to the dependence of the active states of the subcarriers in the OFDM-IM subblock,we need to detect the activated index combinations of the subblock and the modulated symbols carried on the activated subcarriers jointly,which makes the detection of OFDM-IM more complicated.In this paper,we study the detector design of OFDM-IM and propose a low-complexity subcarrier-wise detector for OFDM-IM,which can achieve near-optimal BER performance and has an approximate computational complexity of classical OFDM.In coded OFDM-IM,we study the calculation algorithm of the Log-Likelihood Ratio(LLR)of each bit and propose a sphere decoding-like LLR calculation algorithm to calculate the LLR value of each bit,which can achieve near-optimal coded BER performance with considerably low computational complexity.Multiple-input multiple-output(MIMO)can improve the capacity and achieves better BER performance compared with classical single antenna system.Combine MIMO-OFDM with the index modulation(MIMO-OFDM-IM),the new transmission technique has potential to achieve better BER performance than classical MIMO-OFDM,however,its computational complexity becomes more complicated due to the index modulation.In this paper,we studythe characteristic of the MIMO-OFDM-IM subblock,and then propose a subcarrier-wise Maximum Likelihood(ML)detector for MIMO-OFDM-IM,which achieves the optimal BER performance with considerably low computational complexity.Then we propose a hierarchical search based sequential Monte Carlo(SMC)detector and a tree search based SMC detector for MIMO-OFDM-IM.Computer simulation and numerical results in terms of BER performance and number of floating-point operations(FLOPs)corroborate the superiority of the proposed detectors.In OFDM-IM,the inactive subcarriers themselves do not carry any information.To increases the spectral efficiency of OFDM-IM,we replace the zero symbol with another distinguishable symbol mode.To fully exploit the potential of index modulation,a new transmission technique called multiple-mode OFDM-IM(MM-OFDM-IM)is proposed,which transmits symbols from different symbol modes on different subcarriers in the OFDM-IM subblock.In MM-OFDM-IM,both the permutations of the symbol modes(PSMs)and the transmitted symbols in the subblock need to be detected jointly,which makes the detection in MM-OFDM-IM more complicated.In this paper,we study the characteristic of the PSMs and propose a low-complexity tree search based detector for MM-OFDM-IM.Finally,numerical simulation results demonstrate the superior BER performance and low computational complexity of the proposed detector.