Backscatter-enabled CR-NOMA based cooperative V2X communication with imperfect CSI

Abstract

Non orthogonal multiple access (NOMA) and backscatter communications are considered to be promising technology due to their applications in large scale communications and spectral efficiency. Cognitive radio (CR) also has distinct advantage in terms of allowing secondary users to share spectrum with the primary users. Thus CR and NOMA provides a new way to enable vehicle to everything (V2X) communication through cooperation, in terms of the achievable rate (throughput), which is further enhanced with use of backscatter devices. Moreover, in V2X it is critical to inspect imperfect channel state information (CSI) because, mobility of vehicles leads to more channel estimation uncertainties. Therefore, CR based approach which is supported by NOMA with imperfect CSI, called as B-CR-NOMA is proposed in which several vehicles connect with the base stations (BSs) through different road side units (RSUs) and backscatter devices. To optimize the performance of the proposed approach, a problem of optimal (maximization) of throughput has been formulated. Moreover, the non-convexity associated with the signal to interference plus noise ratio (SINR) is removed by the use of Lagrangian dual transformation by introducing auxiliary variables, which is further solved under Karush–Kuhn–Tucker (KKT) conditions along with using sub-gradient techniques. The exceptional attainment of the throughput for the proposed approach in comparison to the contemporary algorithms in terms of: power as well as number of RSU, number of vehicle users and channel estimation error, accentuate the capability of the proposed approach. The fortitude of B-CR-NOMA is further substantiated in terms of fairness (fairness index), which is measured and compared based on the channel CSI: perfect and imperfect. Also, the effect of the auxiliary variables and iterations on the throughput for the proposed approach is also analyzed. Along with this, two key metrics: average outage probability and average fairness index, which measures the cooperative V2X communication, are also considered for in depth analysis of the proposed approach.