Browsing by Subject "routing"

Now showing 1 - 5 of 5

Open Access
An analytical model of IEEE 80211 DCF for multi-hop wireless networks and its application to goodput and energy analysis
(2010) Aydoğdu, Canan
In this thesis, we present an analytical model for the IEEE 802.11 DCF in multihop networks that considers hidden terminals and works for a large range of traffic loads. A goodput model which considers rate reduction due to collisions, retransmissions and hidden terminals, and an energy model, which considers energy consumption due to collisions, retransmissions, exponential backoff and freezing mechanisms, and overhearing of nodes, are proposed and used to analyze the goodput and energy performance of various routing strategies in IEEE 802.11 DCF based multi-hop wireless networks. Moreover, an adaptive routing algorithm which determines the optimum routing strategy adaptively according to the network and traffic conditions is suggested. Viewed from goodput aspect the results are as follows: Under light traf- fic, arrival rate of packets is dominant, making any routing strategy equivalently optimum. Under moderate traffic, concurrent transmissions dominate and multihop transmissions become more advantageous. At heavy traffic, multi-hoppingbecomes unstable due to increased packet collisions and excessive traffic congestion, and direct transmission increases goodput. From a throughput aspect, it is shown that throughput is topology dependent rather than traffic load dependent, and multi-hopping is optimum for large networks whereas direct transmissions may increase the throughput for small networks. Viewed from energy aspect similar results are obtained: Under light traf- fic, energy spent during idle mode dominates in the energy model, making any routing strategy nearly optimum. Under moderate traffic, energy spent during idle and receive modes dominates and multi-hop transmissions become more advantageous as the optimum hop number varies with processing power consumed at intermediate nodes. At the very heavy traffic conditions, multi-hopping becomes unstable due to increased collisions and direct transmission becomes more energy-efficient.The choice of hop-count in routing strategy is observed to affect energyefficiency and goodput more for large and homogeneous networks where it is possible to use shorter hops each covering similar distances. The results indicate that a cross-layer routing approach, which takes energy expenditure due to MAC contentions into account and dynamically changes the routing strategy according to the network traffic load, can increase goodput by at least 18% and save energy by at least 21% in a realistic wireless network where the network traffic load changes in time. The goodput gain increases up to 222% and energy saving up to 68% for denser networks where multi-hopping with much shorter hops becomes possible.
Open Access
Joint topology design with routing and power control in ad hoc networks
(2003) Önal, Aydoğan
We discuss the problem of designing an ad hoc network topology by jointly using power control and routing. A well-designed topology in ad hoc networks provides several advantages: increasing the capacity, decreasing the complexity and reducing the power consumption. We formulate the topology design problem as an Integer Linear Programming (ILP) model. An optimal topology is designed subject to interference and connectivity constraints with three different objective functions and two power control approaches. Common transmit power (COMPOW) and the adaptive power (ADPOW) are the two different power control techniques used in this thesis. The objectives of the models that are used in the topology design are maximizing the number of established links, using shortest path routing strategy and minimizing the maximum traffic load over the most congested link by load balancing. Performance comparisons between two power control approaches with three different objectives in the topology design are achieved using numerical results on a sample network. Minimum end-to-end throughput, total throughput, total power consumption and the number of established links are used as the performance metrics. The numerical results show that selecting the optimal power for both power control approaches provides similar performance results. Therefore, simplicity of the COMPOW makes it more attractive than ADPOW in the topology design.
Open Access
Multimodal multicommodity routing problem with scheduled services
(2008) Ayar, Burak
We study a multicommodity network flow problem faced by a third party logistics company that has the possibility of using ground and maritime transportation. We are given a set of commodities which should be picked up from their origins at given release times and should be delivered to their destinations no later than their duedates. The commodities may be carried directly from their origins to their destinations on trucks, or they may be carried on trucks to a seaport, may visit several seaports using maritime services, and then to be carried to their destinations on trucks. There is no capacity and time limitation on the use of ground transportation. However, the maritime services are scheduled in advance and the company has limitations on the amounts of volume that it can use on each service. The aim is to determine routes for commodities in order to minimize the sum of transportation cost and stocking costs at seaports, respecting the capacity and time related constraints. We call this problem the “Multimodal Multicommodity Routing Problem with Scheduled Services (MMR-S)”. We first prove that the problem is NP-hard. Next, we propose a first mixed integer programming formulation and strengthen it using variable fixing and valid inequalities. We relax the capacity constraints in a Lagrangian manner and show that the relaxed problems decompose into a series of shortest path problems defined on networks augmented by time for each commodity. The corresponding Lagrangian dual yields a lower bound, which may be stronger than that of the linear programming relaxation of our first formulation. Then, we provide an extended formulation whose linear programming relaxation gives the same bound as the Lagrangian dual. Finally, we use the Lagrangian relaxation to devise heuristic methods and report the results of our computational study.
Open Access
Power-source-aware adaptive routing in wireless sensor networks
(2013) Tekkalmaz, Metin
A wireless sensor network (WSN) is a collection of sensor nodes distributed over an area of interest to accomplish a certain task by monitoring environmental and physical conditions and sending the collected data to a special node called sink. Most studies on WSNs consider nodes to be powered with irreplaceable batteries, which limits network lifetime. There are, however, perpetual power source alternatives as well, including mains electricity and energy harvesting mechanisms, which can be utilized by at least some portion of the sensor nodes to further prolong the network lifetime. Our aim here is to increase the lifetime of such WSNs with heterogeneous power sources by centralized or distributed routing algorithms that distinguish battery- and mains-powered nodes in routing, so that energy consuming tasks are carried out mostly by mains-powered nodes. We first propose a framework for a class of routing algorithms, which forms and uses a backbone topology consisting of all mains-powered nodes, including the sinks, and possibly some battery-powered nodes, to route data packets. We propose and evaluate a set of centralized algorithms based on this framework, and our simulation results show that our algorithms can increase network lifetime by up to more than a factor of two. We also propose a fully distributed power-source-aware backbone-based routing algorithm (PSABR) that favors mains-powered nodes as relay nodes. We validate and evaluate our distributed algorithm with extensive ns-2 simulations and our results show that the proposed distributed algorithm can enhance network lifetime significantly with a low control messaging overhead. Besides wireless technology independent routing solutions, we also propose a technology specific power-source-aware routing solution (PSAR) for sensor and ad hoc networks which use 802.15.4/ZigBee as the wireless technology. Our solution is fully distributed, tree-based, and traffic-adaptive. It utilizes some protocol specific properties of ZigBee, such as distributed and hierarchical address assignment, to eliminate battery-powered nodes on the routing paths as much as possible. To validate and evaluate our ZigBee-specific algorithm, we first implemented ZigBee extensions to ns-2 simulator and then implemented and simulated our protocol in this extended ns-2 environment. Our results show that the proposed algorithm operates efficiently and can increase network lifetime without increasing the path lengths significantly, compared to the default ZigBee routing algorithm.
Open Access
A routing algorithm for low earth orbit satellite networks
(1995) Dinçerler, Cantekin
In this study, we consider the geometric aspects of low earth orbit (LEO) satellite constellations and investigate the performance of a satellite network that uses our proposed routing algorithm. The optimum inclination and harmonic factor of rosette constellations are obtained by considering the minimum coverage radius of a satellite. Actual altitude is determined by this radius and the specified elevation angle. The algorithm uses the uniformity of the geometric structure to form a continuously connected group of nodes in the network which renders global intersatellite connectivity information insignificant. Each group, consisting of a node and its four neighbours, does not change with time and a stationary network structure is obtained by allowing each node to communicate only with its neighbours. Queuing analysis of the network is made for both packet and voice traffic. Simulation results are then compared to analytical results derived from uniform ciricl equal traffic distribution. The proposed algorithm is simulated in a scenario in which sources, destinations, and gateways on the earth form the global traffic. We examine the effects of such a distribution on the performance of the network.