Embedded Systems for Wireless Sensor NetworkRabi MahapatraMahapatra-Texas A&M-Spring'07 2Background• Advancement of integration between “tiny embedded processors, wireless interfaces, and “micro-sensors” based on MEMS led to emergence of wireless sensor network.• Characterized by their ability to monitor the physical environment through ad-hoc deployment of numerous tiny, intelligent, wirelessly networked sensor nodes.Mahapatra-Texas A&M-Spring'07 3• Large number of heterogeneous sensor devices– Ad Hoc Network• complex sensor nodes with– communication, processing, storage capabilitiesWhat is Wireless Sensor NetworksMahapatra-Texas A&M-Spring'07 4Emerging applications• Indoor Settings: condition based maintenance of equipment in factory• Outdoor environment:– Monitor natural habitats– Remote ecosystems– Forest fires– Disaster sites– Defense armaments– Spy microsatsMahapatra-Texas A&M-Spring'07 5Challenges of WSN• Requirements: small size, large number, tetherless and low cost. Hence constrained by– Energy, computation and communication• Small form factors => prohibits large long lasting batteries• Cost & energy => low power processors, small radios with minimum bandwidth & small transmission ranges.• Ad-hoc deployment => no maintenance and battery replacement• Increase NW lifetime => No raw data to gateway for computationMahapatra-Texas A&M-Spring'07 6Topics to be discussed• Simulation tools on WSN• A simulation architecture overview• Sensor node model & framework of SN• Battery model• Case studies• Bonus pointsMahapatra-Texas A&M-Spring'07 7Existing SimulatorsJavaSim:• Pros – Very modular– Easy to use• Cons– Geared for wired inter-networks– No wireless support, not efficient due to overheadSSFNet: a parallel simulator for wirelessGlomoSim:• Specific for mobile wireless networks. • Built as a set of libraries. The libraries are built in Parsec( a C-based discrete event simulation language).• Layered architecture with easy plug-in capability.SSFNet and Glomosim are not better than NS-2 in terms of design and extensibility.Mahapatra-Texas A&M-Spring'07 8Existing Simulators • NS-2: De facto standard for network simulations– Does support wireless simulations– A primitive energy model is present.– Object oriented design and Lots of documentation.– Uses Tcl to specify the Components, and Otcl to glue them together.Cons:– Difficult to use and learn – Interdependency among modules pose difficult to implement new protocols.– Originally built for wired networks, later extended for wireless.– Supposedly, does not work well for large topologies.Mahapatra-Texas A&M-Spring'07 9More Sensor Network Simulator• WSNS – Based on Low Energy Adaptive Clustering Hierarchy (LEACH) protocol developed by Dr. Wendi Heinzelman– Has included Network Preserving Protocol (NPP) for better performance along with LEACH– Not completed for robustnessMahapatra-Texas A&M-Spring'07 10Sensor Network SimulatorSENSE (www.cs.rpi.edu/~cheng3/sense/)• Component Features: (2004)– Battery Model: Linear Battery, Discharge Rate Dependent and/or Relaxation Battery – Application Layer : Random Neighbor; Constant Bit Rate – Network Layer: Simple Flooding; a simplified verion of ADOV without route repairing, a simplified version of DSR without route repairing – MAC Layer: NullMAC; IEEE 802.11 – Physical Layer: Duplex Transceiver; Wireless Channel – Simulation Engine: CostSimEng (sequential)Mahapatra-Texas A&M-Spring'07 11Status of simulators• Other simulator: OpNET• All these tools are not equipped to capture all the aspects of interests in sensor networks.Mahapatra-Texas A&M-Spring'07 12Simulator: SensorSim from UCLA• Extension to NS - 2.• Provides battery models, radio propagation models and sensor channel models.• Provides a lightweight protocol stack.• Has support for hybrid simulation.• Must be integrated with NS - 2.Mahapatra-Texas A&M-Spring'07 13SensorSim Architecturemonitor and controlhybrid network(local or remote)Simulation MachineGateway Machinensmodified event schedulerVRVVVGUIappappRreal sensor apps onvirtual sensor nodesgatewaysocketcommserialcommHS InterfaceEthernetRS232Proxies for realsensor nodesGUI InterfaceappMahapatra-Texas A&M-Spring'07 14SensorSim Architecture Overview• Sensor NW has three types of nodes:– Sensor nodes: monitor immediate environment, with many transducers– Target nodes: generates various stimuli for sensor nodes– User nodes: client and administration of sensor network • Separate channels: – Sensor channels: communication among sensor nodes and target– Network channels: to user node or gateways and onward transmission to other network.– Concurrent transmission possible– Easier to model complex behavior of sensor nodes, reaction to multiple sensor signals.Mahapatra-Texas A&M-Spring'07 15Sensor Network Model architectureSensor channelWireless channelsensorsensorsensorTargetuserMahapatra-Texas A&M-Spring'07 16SensorSim Model• Sensor node => one wireless NW protocol stack, one or more sensor stack corresponds to as many transducers– Sensor stack detects stimuli, process it and forward them to application layer, which in turn process and send them to user node through wireless channel– A power model corresponding to energy producing-consuming hardware components is also provided. These component can stay at different power saving and performance states.– The algorithm in both the stacks control the mode of power states of hardware components. Also, performance of the algorithm depends on the mode.Mahapatra-Texas A&M-Spring'07 17Sensor Node Model in SensorSimNode Function ModelNetwork LayerSensor NodeApplicationsPower Model(Energy Consumers and Providers)Battery ModelRadio ModelCPU ModelSensor #1 ModelSensor #2 ModelMAC LayerPhysical LayerSensor LayerWireless ChannelSensor Channel 1NetworkProtocol StackSensorProtocol StackMiddlewarePhysical LayerState ChangeStatusCheckSensor Stack 1Sensor LayerPhysical LayerSensor Channel 2Mahapatra-Texas A&M-Spring'07 18NetworkProtocol StackNetwork LayerMAC LayerPhysical LayerWireless ChannelUser ApplicationUser NodeSensor Stack Sensor LayerPhysical LayerTarget ApplicationSensor channelTarget NodeMahapatra-Texas A&M-Spring'07 19Framework of Sensor Network Simulation• Node Placement & traffic generation– Performance of WSN is affected when topology of node distribution changes– Application requires a