Research And Design Of Permutation Mode Based On Orthogonal Frequency Division Multiplexing Index Modulation

Orthogonal frequency division multiplexing with index modulation(OFDM-IM)technology makes use of subcarriers index modulation to achieve better transmission performance in frequency selective fading channels,thus becoming one of the competitive technologies for future wireless transmission systems.However,the transmission mode of OFDM-IM,which only activates part of the subcarriers,produces a large number of silent subcarriers.Therefore,the subcarrier utilization of the OFDMIM system is not high enough.This thesis mainly worked on a modified OFDM-IM system model to improve the subcarrier utilization.The contents and results are as follows:1.This thesis proposes a novel index system named permutation mode OFDM-IM(PM-OFDM-IM).The system introduces subcarrier permutation information by using different constellation mapping on the data of sub-blocks at the transmitter to implement transmission of additional data information.This thesis analyzes the performance of PMOFDM-IM system by derived the bit error rate(BER),the anti-frequency offset ability and the achievable rate.The simulation results of achievable bit rate(ABR)show that PM-OFDM-IM can effectively improve the utilization of subcarriers.Meanwhile compared with other index optimization models,PM-OFDM-IM not only remains the good anti-frequency offset ability but also achieves better BER performance in Gaussian channel and Rayleigh channel respectively under the similar subcarrier utilization.2.In order to cooperate with the PM-OFDM-IM system and improve the BER performance,two constellation mapping schemes based on amplitude phase shift keying(APSK)are proposed.The first one is to determine the number of concentric circles according to the activated subcarriers in the sub-block and each concentric circle represents a transmission mode.The second scheme adopts two concentric circles,and all the mapping points are evenly distributed on each circle.The first mapping scheme is simple and suitable for PM-OFDM-IM with lower BER performance requirements.On the other hand,the second mapping scheme guarantees better BER performance at the cost of complexity.Furthermore,maximum likelihood detection algorithm based on soft demodulation(Sd-ML)is proposed for these two constellation mapping schemes.After soft demodulating,the results of each subcarrier will be detected based on ML criterion according to channel conditions.ML detection complexity is related to two factors including the number of search blocks and search length factor.The simulation results show that PM-OFDM-IM system cooperating with proposed APSK has a lower peak to average power ratio(PAPR)than with quadrature amplitude modulation(QAM)and it has better BER performance under Rayleigh channel.The proposed detection algorithm loses BER performance compared to the ML detector at low signal-to-noise ratio(SNR),but it effectively reduces the exponential order complexity of the ML detection.Finally,BER performance of the proposed ML detection algorithm is tested by simulating the number of search blocks and search length factor.The detection complexity and BER performance of the scheme requires a compromise between the number of search blocks and the size of the search length factor.