Research On Detection Algorithm Based On Orthogonal Time Frequency Space Wireless Transmission System

At present,OFDM technology has been widely used in 4G,5G and various Wi Fi wireless networks.However,in the scenario of high mobility,when there is a high relative speed between the mobile terminal and the communication base station,it will have a serious Doppler effect on the subcarrier of OFDM signal and offset the frequency of the signal.Due to the Doppler effect,the degree of frequency offset between subcarriers is different,which destroys the orthogonality between carriers,leads to the introduction of serious inter carrier interference in OFDM system,and affects the performance of OFDM communication system.Therefore,in the high mobility scenario,a new modulation scheme orthogonal time frequency space(OTFS)system is proposed,which can be used to provide reliable communication in the high mobility scenario.At present,one of the main problems of OTFS is that the complexity of existing detection algorithms is high,so it is necessary to design low complexity detection algorithms for OTFS system.According to the characteristics of OTFS,this thesis studies the low complexity detection algorithm of OTFS system.Firstly,this thesis proposes a low complexity signal detection algorithm for OTFS system based on orthogonalization and blocking.In this scheme,the OTFS received frame is divided into multiple orthogonal blocks,and then the existing detection algorithms are used to detect the symbols of the orthogonal blocks.This thesis reveals the attribute that the OTFS received frame can be divided into multiple orthogonal blocks.The orthogonal blocks are independent of each other,and the received symbols between blocks do not have a common transmission symbol component.In this thesis,the blocking work of the received frame is modeled as a search work based on graph theory,the bipartite graph of sending symbols and receiving symbols is established,and a fast OTFS system blocking algorithm is proposed based on the classical depth first search algorithm(DFS).The algorithm can quickly output the orthogonal blocks after blocking the OTFS received symbols.Then the existing detector is selected to complete the detection of symbols in orthogonal blocks.Through the relevant complexity analysis,it is further expressed that the blocking algorithm is a linear complexity algorithm,and then the scheme of blocking algorithm combined with MMSE detection algorithm is simulated.The simulation results show that this scheme can greatly reduce the overall complexity of detection while ensuring the performance of symbol detection.Secondly,this thesis proposes a linear complexity signal detection algorithm of OTFS system based on embedded pilot scheme.This thesis uses serial interference cancellation algorithm to detect the symbol of OTFS received frame.OTFS system based on embedded pilot scheme can estimate the channel simply and efficiently,classify the received symbols according to the degree of interference between symbols,implement different symbol detection strategies according to the interference of different received symbols,and detect the received symbols by introducing low complexity serial interference cancellation technology.Firstly,the received symbols without inter symbol interference are decided,and the signal is reconstructed with the decided symbols,then the interference elimination process is executed,and finally the iterative process of "decision-reconstruction signal-interference elimination" is executed according to the results of interference elimination.Through simulation,it is found that the performance of the proposed serial interference cancellation detection algorithm is poor.In order to further improve the performance of using serial interference cancellation in OTFS system,the unreliable decision-making of weak path is avoided through unidirectional interference cancellation strategy,and then a unidirectional serial interference cancellation algorithm is proposed.The performance of the detection algorithm is improved by formulating unidirectional interference cancellation rules,Finally,the low complexity and effectiveness of the detection algorithm are proved by complexity analysis and simulation.