Delay-Constrained Data Transmission with Minimal Energy Consumption in Cognitive Radio/WiFi Vehicular Networks

Cognitive radio benefits vehicular users to access massive and broadband services in a radio environment of limited spectrum. Reducing energy consumption is critical for energy-limited users and is also helpful to reduce greenhouse gas emission. This paper first proposes an energy-efficient transmission scheme in cognitive radio/WiFi vehicular networks, in which traffic is optimally distributed to cognitive radio and WiFi interfaces such that traffic is transmitted in an energy-efficient and timely manner. The traffic distribution problem is formulated as an optimization problem in which the amount of the energy of spectrum sensing and data transmission is minimized such that (1) data transmission is completed within a delay constraint and (2) the interference constraint of primary users and the power limitation of transmitters are satisfied. We prove that the optimization problem is a convex problem and does not always have a general solution. Due to the computation cost of the optimization problem, we propose a heuristic algorithm, namely, relay-weighted transmission, to solve the traffic distribution problem. Extensive numerical results show that the optimal transmission and the relay-weighted transmission schemes appropriately distribute data into the two radio interfaces such that the power consumption is significantly reduced.