Wireless Ad Hoc and Sensor Networks

Background on Networking 33was supported by DARPA through the VINT project at LBL, Xerox PARC,UCB, and USC/ISI. Currently, NS development is supported throughDARPA with SAMAN and through NSF with CONSER, both in collaborationwith other researchers, including ACIRI. NS has always included substantialcontributions from other researchers, including wireless code fromthe UCB Daedelus and CMU Monarch projects and Sun Microsystems.NS-2 provides a split-programming model. OTcl is interpreted and isused to define the composition of the objects in the simulation (nodes,links, etc.) to allow changing scenarios without having to recompile. C++focuses on the mechanisms and internals of the objects and protocols toallow packet simulation to be efficient. This split-programming approachcan benefit research productivity. Also, NS-2 can produce a detailed tracefile and an animation file for each network simulation, which is veryconvenient for analyzing the behavior. It is open source and can be downloadedfrom the Internet. For additional functionality, existing protocolscan be extended and new protocols can also be implemented. Complextraffic patterns, topologies, and dynamic events can be automatically generatedto test the created network topologies. There are several relatedprotocols for both wired and wireless communications that have beenalready implemented. Thus, NS-2 simulator was normally chosen toimplement the computer network and ad hoc and sensor networkingschemes and protocols.1.4.8 Power Control Implementation in MAC 802.11 Using NSEfficient control of transmission power would combat interference andincrease channel reuse. At present, in IEEE 802.11 protocol, a transmitteris allowed to transmit only at a single power level. But, incorporation ofthe power control scheme requires the users in the network to transmitat different power levels. Hence, modifications are to be made in the 802.11protocol to incorporate power control.Modifications to the IEEE 802.11 protocol can be made such that whena receiver receives an RTS message, it will encode the ratio of the receivedsignal strength of the RTS message to the interference felt by the receiverin the header of the CTS reply message. Similarly, when transmitting theDATA message, the transmitter will encode onto it the ratio with respectto the received CTS. Thus, during one RTS-CTS-DATA-ACK exchange,both the transmitter and the receiver inform each other about the qualityof their transmitted signals. Both nodes can now alter their transmit powerlevels according to the power control algorithms for further communicationbetween each other. The sequence of events that usually take placebetween a transmitter and receiver in a network is shown in the Figure 1.5.The performance of a power control scheme is measured by its abilityto preserve the accuracy of the encoded data. In mobile wireless networks,