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AD HOC NETWORKS
ALCATEL


This is a three years Industrial research project on Ad-Hoc Networks, realized in collaboration with ALCATEL. The project runs from 2001 till December 2003. Our works refer to a scenario with a multiplicity of nodes which form a multi-hop network used for coverage extension, rural networks, or mesh networks. The network is characterize by fixed nodes and/or mobile nodes, and the entire network is energy constrained. This kind of radio networks are distributed, and all the terminal are equal, so each nodes is also a router for the other nodes if it is required to delivery the data packets through the networks. The Ad-Hoc networks are \u201cnetworks available and utilizable everywhere and every time\u201d. With the purpose to simulate this kind of networks, the TLC group of the Engineer Department of the University of Ferrara, developed the Simple Ad-hoc siMulator (SAM). This simulator is based on the TCP/IP protocol, so we have worked at the MAC layer, at the Routing layer, and at the Transport layer with the aim to improve the network performance in terms of packet delivery, throughput, delay, and in particular energy spent by the network. In particular, we focus our attention on the Routing level because is in the routing activities that the nodes consume the biggest amount of energy because each node have to find the paths toward the destinations, route its packets, and route the packets of the other nodes if is required and if is possible. In fact, the energy is a hard constraint for an Ad-Hoc network, because the terminals have only a battery of limited energy capability, and excessive or not controlled energy consumption could cause a network partition and clustering. To avoid these problems and to obtain energy savings in to the network, the Distributed Power Control (DPC) mechanism has been developed; with this new mechanism the nodes choose the path toward the destination which minimize the total transmitted energy, allowing to save a remarkable amount of energy.

In order to evaluate the effectiveness of the SAM simulator and of the DPC mechanism, different unicast and multicast routing protocol have been implemented. Not only the Routing level is taken under consideration, but also the MAC layer, with the introduction of the IEEE 802.11 and the IEEE 802.11b protocols, and the Transport layer, with the introducing of the QoS mechanism to improve the network quality of the transmissions.

The technical work will focus mostly on the performance of the different routing protocols under different scenarios and work conditions, taking under consideration the energy spent by the network as a hard constraint.

The performance of unicast routing protocols (Dijkstra, DSR, AODV and OLSR) over IEEE 802.11b with multimedia traffic have been analysed, evaluating the performance of the unicast routing protocols while taking into account the link adaptation capability of IEEE 802.11b, and considering the native and DPC version of the protocols; the performance of multicast routing protocols (AMRIS and ODMRP) over IEEE 802.11b with multimedia traffic has been evaluated, implementing in the simulator the more representative protocols and considering them under different scenarios; parameter optimization for existing multicast routing schemes have been sought, with specific reference to interference reduction and energy efficiency, and the simulation results have been tested against the original version results; we had the goal to investigate efficient schemes at the Transport level for the support of streaming application (e.g. video distribution), and the QoS mechanism has been implemented.

Our contribution regards study and implementation of unicast and multicast routing protocols in its native and DPC versions at the Routing level, of IEEE 802.11b MAC protocol and of the QoS mechanism at the Transport level. The results obtained from the simulation made with the utilization of the SAM simulator, shows that different routing algorithm maximize different figure of merit (e.g. packet delivery fraction, energy consumption, average delay) and a trade-off as to be achieved. The introducing of the DPC mechanism allow a remarkable energy saving in the performance of all the routing protocols, but introducing the node mobility the DPC performance go down quickly with respect to the native versions of the protocols, so a trade-off between packet delivery fraction and energy consumption as to be achieved. Also, the routing protocols perform better with the IEEE 802.11b protocol with respect to the IEEE 802.11, but the energy consumption is slightly higher if the network traffic is low. The QoS mechanism introduced with multicast routing protocols and video trace traffic improve the network performance in terms of packet delivery and even in terms of energy consumption.

Our future works are directed to the reduction of the energy consumption, in particular to the reduction of the energy spent when the nodes are in receiving state, turning-off some the nodes of the network with particular criteria that avoid a reducing of the network performance in terms of packet delivery and connectivity of the nodes.


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