Abstract-Vehicular networks that require additional spectrum for communication may leverage cognitive radio technology. Towards this aim, the vehicle must select one among several candidate channels for data transmission, with the possibility that other surrounding vehicles may also identify the same spectrum for their use. Such networks are distinguished from their classical, stationary counterparts by high mobility, timevarying and heterogeneous environment leading to dynamic channel availability. Owing to this changing environment, the history of spectrum usage information may be unavailable to the vehicles at all points on their journey, necessitating blind decisionmaking. In this paper, we propose a method of spectrum selection without a priori channel information. The main contributions of our work are: (i) we provide a framework to determine, through a Hidden Markov Model, whether a channel is occupied by a licensed user, another cognitive radio enabled vehicle, or if the observed signal fluctuations are due to noise; and (ii) we devise a prediction algorithm to determine which channels are likely to be available within the shortest amount of time. Our approach is verified through a simulation study, and we demonstrate equivalent performance to schemes that use prior history of the channel usage at specific vehicle locations.

The performance of cooperative communications is highly dependent on careful resource allocation such as relay selection. Considering individual QoS requirements in a multi user system, traditional cross-layer relay selection schemes, failed to achieve an acceptable level of fairness considering limited buffer capacity of relays. To address this problem, in this paper, we propose a buffer management-based best relay selection algorithm considering both physical and MAC layer parameters. Our simulation results show that the proposed algorithm outperforms traditional ones significantly in terms of fairness, system spectrum efficiency, and average transmission time delay. Moreover, the proposed algorithm can be implemented in a distributed fashion with no need to a central processor and with minimum required signaling among the nodes.

Recently, cross-layer relay selection methods are proposed in favor of providing QoS requirements of users in multi-user cooperative networks as a way to achieve a better performance. However, most of them have failed to achieve an acceptable level of fairness in satisfying diverse QoS requirements in a multi-media service. On the other hand, reducing consumed power is essential today in cooperative networks. In this paper, we aim to improve fairness and reduce consumed power in a multi-user cooperative network with multimedia service. For this purpose, we propose a novel algorithm based on management of relay nodes' buffer space and the priority concept during relay selection. Simulation results certify that our algorithm outperforms previous ones in terms of system spectrum efficiency, fairness, and average consumed power.

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