Research On Non-Orthogonal Multiple Access System Based On Time Reversal In Indoor Environment

With the rapid development of the Internet of Things,the surge in terminal access has made spectrum resources scarce.The new generation of wireless networks has put forward higher requirements for transmission rate,system delay,wireless coverage,and user experience.Non-orthogonal multiple access(NOMA)technology breaks the traditional orthogonal idea and effectively solves the problem of insufficient spectrum resources in the future by increasing the complexity of the receiving end in exchange for greater spectrum utilization.However,when NOMA is used indoors,the multipath effect will increase the interference between users,and cause problems such as channel gain attenuation and rapid signal amplitude fading.Time reversal(TR)is a special signal processing technology that can focus the signal energy on a specific location in an indoor multipath environment.This thesis uses the feature of TR to combine NOMA technology with TR technology in indoor communication scenarios.The main research content is divided into the following two parts:First,according to future development trend data,most of the traffic will be generated indoors,and indoor short-distance communication scenarios have become a new research hotspot.When applying NOMA technology in an indoor environment,the signal is affected by multipath effects,resulting in weaker received signal strength and much more interference between users.In order to solve this problem,this thesis proposes a NOMA system model based on Time reversal.First,the introduction of TR technology enables the signal energy in the system to be focused on the base station side,and the successive interference cancellation algorithm is executed on the base station side.Secondly,Analytical expressions of TR-NOMA system ergodic sum rate and average bit error rate are derived.Finally,through simulation analysis and comparison with traditional nonorthogonal multiple access schemes,the proposed scheme has better performance advantages in terms of system throughput and bit error rate.Second,based on the system model mentioned above,in-depth study proves that the system transmission efficiency is low in a multipath environment.To solve this problem,this thesis proposes an uplink NOMA network resource allocation algorithm based on TR.First,considering the user's minimum transmission rate constraint and the user's maximum transmission power constraint,a resource allocation model for maximizing system energy efficiency is established.Secondly,the fractional programming theory is used to transform the proposed problem into component subtraction form.Due to the coupling problem in the system rate expression,the continuous convex approximation method is utilized to solve the parameter coupling,and the proposed non-convex optimization problem is transformed into a solvable convex optimization problem,and the global optimal solution will be obtained by Lagrangian duality theory.The simulation results show that compared with the traditional algorithm,the proposed algorithm has better system energy efficiency.