Samuel Montejo-Sanchez

Dynamic control of beacon transmission rate and power with position error constraint in cooperative vehicular networks

Cooperative vehicular networks require the continuous exchange of beacon messages between neighboring vehicles to support cooperative awareness applications. The position error computed by surrounding vehicles impacts on applications capability to detect and mitigate potentially dangerous traffic situations in real-time. A challenge in cooperative safety systems is to maintain a high position accuracy, while controlling the communication channel load. In this paper, we propose a novel joint power/rate control distributed algorithm to meet the position accuracy requirements of cooperative safety applications. The beacon transmission rate is adjusted dynamically as a function of the vehicle movement status, to constrain position error computed by surrounding vehicles. Then, the transmit power is adjusted according to the channel load and the preset beacon transmission rate, to decrease packet collisions. This algorithm has been evaluated in a realistic simulation framework, considering different traffic densities for an urban scenario. The simulation results show that the proposed algorithm outperforms other basic beaconing algorithms addressed in this paper, in terms of trade-off between position accuracy, packet collisions, and warning range.

Dynamic Beaconing using Probability Density Functions in Cooperative Vehicular Networks.

Vehicular networks comprise vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications based on wireless radio access technologies. These network s require the periodic exchange of beacon messages between neighboring vehicles, to support cooperativ road safety applications. The regular broadcast of beacon in the common control channel (CCH) using the IEEE 802 .11p standard can lead to interference and recurrent packet collisions. This issue impacts negativel y in the quality and freshness of the beaconing information which is essential to detect and mitigate potentiall y dangerous traffic situations on time. In this paper, we evaluate the performance of a dynamic beaconing strategy where both beacon rate and transmit power are assigned by means of probability density functions (PDFs). The idea is to know which PDF is more convenient to increase the system’s performance according to vehicula r scenario characteristics. We investigate four types of PDFs, attending to four different performance metrics, i n four distinct vehicular scenarios, using the well established Veins (Vehicles in network simulation) framew ork. The simulation results show that a beaconing strategy based on uniform PDF is convenient in scenarios wit h high vehicle density and low relative speed, whereas a beaconing strategy based on normal PDF is suitable in sc narios with high relative speed and low vehicle density.

Towards Intelligent Tuning of Frequency and Transmission Power Adjustment in Beacon-based Ad-Hoc Networks.

This paper presents a genetic-based approach to determine optimal values of frequency and transmission power in beacon-based ad-hoc networks. The approach has been evaluated through simulations, and it has demonstrated to be more efficient than a dynamic control of frequency and transmission power, with reduction of up to 73% in packet collisions and with reduction of packet losses of up to 63% in an urban scenario. The approach and the results presented in this paper represent our initial efforts towards a more efficient control of beacon frequency and transmission power, which can exploit the benefits of a geneticbased approach but that can be applied in runtime in practical scenarios.

Energy Efficient Cooperation Based on Relay Switching ON–OFF Probability for WSNs

Cooperative communications can substantially improve the performance in fading channels. However, in energy-constrained wireless sensor networks, the benefits of cooperation only go until certain limits, beyond which the energy cost of cooperation can be significant and unprofitable. We propose a cooperative scheme in which the relays activate the receiving circuitry based on a switching ON–OFF probability. We derive analytic expressions for the amount of effective information transmitted through the network and the associated outage probability under Nakagami-m fading channels. Based on the developed analysis, we formulate an optimization problem in which the switching ON–OFF probabilities are adjusted to reduce the energy consumption, subject to an outage probability constraint. We evaluate the performance of the proposed scheme under fixed and random network topologies. Our results indicate that the proposed scheme substantially outperforms the standard cooperative reception approach in terms of the amount of effective information transmitted through the network.