| Orthogonal Time Frequency Space(OTFS)modulation is considered to be one of the popular technologies suitable for high mobility scenarios,and Index Modulation(IM)also attracts attention due to it’s advantages.In order to solve signal detection in OTFS with index modulation,this paper proposes two different ideas based on the message passing algorithm,one is the message passing(MP)algorithm based on probabilistic sorting,and the other is based on j oint detection.In the message passing algorithm,these two algorithms can detect activation index combinations and constellation symbols without increasing the complexity of the algorithm.In order to obtain spatial diversity,this paper firstly introduces index modulation technology into the Multiple Input Multiple Output(MIMO)orthogonal time-frequency space system,and presents MIMO-OTFS with index modulation(MIMOOTFS-IM)system model and low-complexity signal detection method,and also simulation verification of system bit error rate performance.The main contents of this paper is organized as follows:Firstly,this article briefly introduces the basic realization of the wireless channel delayDoppler domain representation and OTFS modulation,and then focuses on the analysis of the 1CP and NCP system models and signal detection algorithms of OTFS.Secondly,this paper proposes two improved ideas from message passing algorithms for signal detection in index modulation OTFS systems.One is a message passing algorithm based on probabilistic sorting.The realization idea is to first use traditional message passing algorithms to get each data symbol at the time of decision.Then,the activation index combination and the constellation symbol are obtained through the probabilistic ranking of the data symbols in the sub-block;the other is a message passing algorithm based on joint detection,and the realization idea is to model the variable node and the observation node as a sub-block in index modulation,message transmission is carried out in units of sub-blocks to realize joint detection of activation index and constellation symbols,effectively avoiding the interference of invalid activation index combination during detection.In term of larger parameters and SNR of 20dB,system’s BER can reach 10-3.Compared with the MMSE equalization scheme,the message passing algorithm based on joint detection has slightly better performance and lower complexity,the message passing algorithm based on probability ranking perform slightly worse but it’s complexity is linear.Finally,OTFS with index modulation is combined with MIMO transmission to take advantage of the benefits of these two techniques.MIMO-OTFS-IM system model is proposed and this paper derives the input and output relationship of the system.And then a message passing algorithm based on joint detection is proposed for signal detection and simulation result shows that MIMO-OTFS with index modulation has a lower bit error rate than MIMO-OTFS. |
