By virtue of its improving bandwidth efficiency along with user fairness, non-orthogonal multiple access (NOMA) technique is considered a promising method for next-generation wireless communication systems. Since fading effect of wireless channels in vehicle-to-vehicle (V2V) communication systems are more severe than those in traditional systems, in this study, we employ the power-domain downlink NOMA technique in cooperative V2V communication systems to enhance data transmission capacity and network efficiency. In the proposed system, the base station communicates with two vehicular nodes, namely near and far users, through a relay vehicle employing the fixed-gain amplify-and-forward scheme. In real-life scenarios, the relay and the users move in high velocities; hence, the corresponding fading channels between these nodes are exposed as having double-Rayleigh fading characteristic in which the fading coefficient of a wireless channel is modeled as the product of two Rayleigh distributed random variables. To analyze the system performance, we first investigate the outage probability and derive its exact closed-form expressions for the near and far users. Then, we make the exact ergodic capacity analysis and obtain the closed-form solution for the near user. Furthermore, outage and ergodic performances of the NOMA-enabled system are compared to the simulation results of the traditional orthogonal multiple access approach. We also give analytic and numerical results to evaluate the performance of the proposed system and show the consistency of Monte-Carlo simulations with analytical derivations. It is observed that even with the small power allocation, both performances of the near user mostly outperform the far user.
Vehicle-to-vehicle (V2V) communications is a part of next-generation wireless networks to create smart cities with the connectivity of intelligent transportation systems. Besides, green communications is considered in V2V communication systems for energy sustainability and carbon neutrality. In this scope, radiofrequency (RF) energy harvesting (EH) provides a battery-free energy source as a solution for the future of V2V communications. Herein, the employment of RF-EH in V2V communications is considered where the bit error probability (BEP) of a dual-hop decode-and-forward relaying system is obtained depending on the utilization of antennas at the relay. The multiple antenna powerconstraint relay harvests its power by applying dedicated antenna (DA)/power splitting (PS) EH modes and linear (L)/nonlinear (NL) EH models. Moreover, the links between nodes are exposed to double-Rayleigh fading. Finally, the performance of different system parameters is compared using theoretical derivations of BEP. The results provide a comprehensive analysis of the proposed system considering PS/DA-EH modes and L/NL-EH models, as well as deterministic/uniformly distributed placement of nodes. It is observed that PS-EH outperforms DA-EH assuming a placement of an equal number of antennas and distances. Moreover, optimal performance of PS/DA-EH is achieved by allocating more power and increasing the number of antennas for EH, respectively.
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