Performance analysis of CDRT based cognitive NOMA vehicular networks with ambient backscatter relays

In order to improve the increasing spectrum requirements and the unguaranteed quality of service (QoS) for edge users in the internet of vehicles (IoV), many techniques such as cognitive radio (CR), non-orthogonal multiple access (NOMA) and coordinated direct and relay transmission (CDRT) have been proposed. To further enhance the spectrum utilization, this paper combines the above techniques with ambient backscatter communications (AmBC), which replaces the traditional relay in the network with a backscatter device (BD). When BD meets certain energy constraints (EC), an optimal dynamic reflect coefficient (RC) is enabled to promote the reflection effect. In this work, firstly, establish a CDRT-based CR-NOMA vehicular network with an ambient backscatter relay. Secondly, the closed expression for the outage probability of each secondary user is obtained with the help of Gauss Laguerre quadrature and Gauss Chebyshev quadrature. Then the system throughput analysis and the asymptotic analysis of each user when the maximum transmitting power as well as the interference temperature constrains (ITC) tends to infinity are performed. Finally, we performed simulations to reveal the impact of AmBC and ITC on edge users. Comparisons are also made with the system using fixed RC, the conventional system and its orthogonal multiple access (OMA) counterpart, demonstrating the superiority of our proposed system in improving the performance of edge users.