Research On The Age Of Information Optimization Policy In SWIPT-Enabled Cooperative NOMA Systems

In recent years,with 5G technology grows mature gradually and uses widely,the demand for spectrum resources of widely deployed wireless nodes has increased dramatically.Non-orthogonal multiple access(NOMA)technology is expected to increase spectral efficiency(SE)while realizing massive connections of node,however the problem of energy holes in a large number of nodes remains to be solved.As an emerging technology,simultaneous wireless information and power transfer(SWIPT)can provide energy for wireless devices while interacting with them,prolong the lifetime of network,and usually combine with relay cooperation technology to ensure timely and reliable communication.On the other hand,real-time applications such as driverless driving,telemedicine,and health monitoring have developed rapidly.In these real-time applications,only fresh and timely data has practical application value,and outdated information loses its value because it cannot accurately reflect the current state.Therefore,in energy constrained network that is sensitive to the freshness of information,it is critical to ensure the timeliness and freshness of data transmission.In this paper,the following analysis and study are carried out on the age of information(AoI)in SWIPT-Enabled cooperative NOMA systems:(1)In the relay cooperative network,firstly in order to solve the problem of limited energy of relay nodes,SWIPT technology is applied to the downlink two-user NOMA decode-and-forward(DF)relay system.Then,according to the dynamic energy level and energy-harvesting status of the relay node,the average peak AoI optimization problem based on the PS-DF protocol is established under the constraints of the energy and data causality,and by solving the approximate convex optimization problem,a heuristic dynamic online update transmission policy is proposed.Finally,the simulation results show that the proposed policy can significantly reduce the system's average peak AoI and achieve a better balance between energy-rate-AoI.(2)Based on(1),the concept of relaying decision threshold is introduced in the SWIPT-Enabled Cooperative NOMA systems.Unlike the traditional wireless cooperative network where the decoding threshold is reused as a condition for relay activation.In this paper,relaying decision threshold is taken as the condition for relay start-up,and decoding threshold is taken as the condition of successful information decoding.Then,the influence of the introduction of relaying decision threshold in the SWIPT-Enabled cooperative NOMA system is analyzed,the mathematical expression of the system's average peak AoI is derived,and the optimization problem aiming at minimizing the average peak AoI value is established.The relaying decision threshold which is at least the local optimal solution is obtained by the gradient iteration method.The simulation results show that,combined with the heuristic dynamic online update transmission policy,the introduction of relaying decision threshold can balance the transmission relationship between direct link and relay link,and there is an optimal relaying decision threshold,which further reduce the system's average peak AoI.Finally,the relationship between the average peak AoI performance and the base station transmitting power and the energy conversion coefficient is simulates and analyzed in this paper.Meanwhile,the NOMA scheme is compared with the OMA scheme.