Abstract-In wireless ad hoc networks, nodes communicate with far off destinations using intermediate nodes as relays. Since wireless nodes are energy constrained, it may not be in the best interest of a node to always accept relay requests. On the other hand, if all nodes decide not to expend energy in relaying, then network throughput will drop dramatically. Both these extreme scenarios (complete cooperation and complete noncooperation) are inimical to the interests of a user. In this paper we address the issue of user cooperation in ad hoc networks. We assume that nodes are rational, i.e., their actions are strictly determined by self interest, and that each node is associated with a minimum lifetime constraint. Given these lifetime constraints and the assumption of rational behavior, we are able to determine the optimal throughput that each node should receive. We define this to be the rational Pareto optimal operating point. We then propose a distributed and scalable acceptance algorithm called Generous TIT-FOR-TAT (GTFT). The acceptance algorithm is used by the nodes to decide whether to accept or reject a relay request. We show that GTFT results in a Nash equilibrium and prove that the system converges to the rational and optimal operating point.
and surveillance. Although sensors may be mobile. they can be considered to be stationary after deployment. A typical network configuration c n n s i s~~ of sensors working unattended and transmitting their observation values to some processing or control center. the so-called sink node. which serves as a user interhce. Due to the limited transmission range. sensors that are Par away from the sink deliver their data through mrdtihop communications. i.e.. using intermediate nodes as relays. In this case a sensor may he both a data source and a data router.Most application scenarios for sensnr networks involve battery-powered nodes with limited energy resources. Recharging or replacing the sensors battery may he inconvenient. or even impossible i n harsh working environments.Thus. when a node exhausts its energy. it cannot help hut ceases sensing and routing data. possibly degrading the coverage and connectivity level of the entire network. This implies that making good use of energy resources is a must in sensor networks.Various nevertheless they consume a significant amount of power. In sleep mode. instead, some parts of the sensor circuitry (e.g.. microprocessor, memory. radio frequency (RF) components) are turned off. As more circuitry components are switched off.the power consumption as well as the operational capabilities of the sensor decrease. Clearly. a trade-off exists between the node energy saving and the network performance in terms of throughput and data delivery delay.In this work. we develop an analytical model which enables us to explore this trade-off and to investigate the network performance as the sensor dynamics in sleeplactive mode vary.We consider a sensor network with stationary nodes. all of them conveying the gathered information to the sink node through multihop communications. Each sensor is characterized by two operational states: active and sleep. In active state the node is fully working and is able to transmitireceive data_ while in sleep state i t cannot take part i n the network activity: thus. the network topology changes as nodcs cntcrlcxit thc sleep state. Through standard Markovian techniques. we construct a system model rcprescnting: (i) the bchavior of a single sensor. (ii) the dynamics of thc entire nctwork. and (iii) the channel contention among interfering sensors. The solution of the system model is then obtained by means of a Fixed Point Approximation (ITA) procedure. and the model is Validated via simulation.By using our analytical model. we study the network performance in terms of capacity. data delivery delay and energy consumption. as the sensor dynamics in sleeplactive mode change. Furthermore. we are able to derive the performance of the single sensor nodes as their distance from the sink vary.Although our work mainly focuses on energy consumption and data delay. the level of abstraction of the proposed model is such that it can he applied to investipate various aspects in the design of sensor networks.To the best of ow knowledge. this is the tirst analytical mo...
Abstract. We analyze the performance of 802.11 WLANs that employ the Distributed Coordination Function (DCF). We consider contending stations within radio proximity, and investigate the case in which stations operate under nonsaturated conditions. Our modelling technique can be used to study several important issues in 802.11 networks, such as the impact of bursty traffic and the system performance in a multirate environment. The accuracy of the analytical results is verified by simulation with ns-2.
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