Research And Application Of Two-Dimensional Spreading Technique In Orthogonal Time Frequency Spreading

In recent years,with the rapid development of mobile communications,the demand of mobile communications becomes more urgent.The new communication technology must be able to meet the demands under various scenarios.Therefore,the spreading scheme which can utilize the multi-path fading property of the channel and obtain the diversity both in time-domain and frequency-domain is very worth to research.Based on the traditional spreading methods,this paper analyzes the two-dimensional sine wave complex spreading and concludes the two-dimensional spreading method that can achieve the time-domain and frequency-domain diversity.Meanwhile,a new pilot multiplexing scheme that can multiplex multiple antenna ports in new coordinate system is proposed.And the performance at high speed is improved when combined with channel estimation algorithms for high-speed scenarios.The paper first outlines the current communication technologies which apply the spreading mode:one is the binary square wave orthogonal spreading,the related application is Code Division Multiple Access technology using one-dimensional spreading and Variable Spreading Factor-orthogonal Frequency and Code Division Multiplexing technology using two-dimensional spreading;the other is sine wave complex spreading,the relevant application is the Single-carrier Frequency-Division Multiple Access technology.The paper mainly focuses on the Single-carrier Frequency-Division Multiple Access system which applies one-dimensional sine wave complex spreading.Relevant preparations for the coming two-dimensional sine wave complex spreading is made.The second thesis of the paper mainly studies the two-dimensional sine wave complex spreading and its system structure.First of all,under the circumstance of time-varying channel,the two-dimensional sine wave complex is theoretically deduced.The traditional time-frequency domain is transformed into delay-Doppler domain through two-dimensional spreading,then we can achieve the Orthogonal Time Frequency Spreading system structure.Afterwards,the Orthogonal Time Frequency Spreading special uplink resource allocation structure is analyzed.In the delay-Doppler domain,the disjoint resource blocks is allocated to different user equipment.Then they can be extended to the whole time and frequency domain by Orthogonal Time Frequency Spreading.Therefore,the uplink system also has the ability to obtain diversity in time and frequency domain.The simulation results show that Orthogonal Time Frequency Spreading can achieve diversity in both time domain and frequency domain,and has a relatively high ability to suppress Doppler effect of the channel.This is very helpful to improve the performance of high-speed scenario communication system.And the uplink resource allocation scheme has lower Peak to Average Power Ratio than Single-carrier Frequency-Division Multiple Access system.The main work of the paper is the research of channel estimation in the delay-Doppler domain.The first is to design the pilot scheme under the delay-Doppler domain.The influence of delay-Doppler channel on pilot is localized,which provides guidance for the design of pilot scheme.And the number of antenna ports in the delay-Doppler domain also meets the corresponding rules,which provides a theoretical basis for multiplexing a large number of antenna ports.The simulation results show that our pilot scheme has a lower pilot overhead and does no harm to the system's information rate.Then the channel estimation algorithm in high-speed scenes is discussed.Through the formula deduction,we can conclude that the traditional channel algorithm is not suitable for the high-speed scenarios.The introduced Enhanced Least Minimum Mean Square Error algorithms based on multipath Doppler Frequency Offset solves the problems.It reduces the complexity of the algorithm and improves the accuracy of the channel estimation.The simulation results show that the performance of Orthogonal Time Frequency Spreading combined with Enhanced-Least Mean Minimum Square Error channel estimation algorithm has better performance,and can be chosen as a communication scheme for high-speed scenarios.