Slide153Introduction-Definition Sensor: measures a physical phenomenon (motion, heat, light …) and converts it into an electrical signal.
Slide154Introduction-Definition Ø A wireless sensor network is a special network with large numbers of nodes. Ø The nodes are equipped with embedded processors, sensors and radios. Ø These nodes collaborate to accomplish a common task such as environment monitoring or asset tracking. Wireless Sensor Networks (WSN):
Slide159Sensor network topology •The sensor nodes are usually scattered in a sensor field. •Nodes collect data and route data back to the end users by a multi-hop infrastructure-less architecture through the sink. •The sink may communicate with the task manager node via Internet or Satellite.
Slide160Ø Environmental monitoring Ø Seismic activity detection; Ø Industrial monitoring and control Ø High-precision agriculture Ø Structural health monitoring Ø healthcare and medical research Ø Homeland security. Ø military applications. Smart Buildings to improve living conditions and reduce energy consumption Inventory Management Fire Monitoring Applications
Slide161Generic Node Architecture A sensor node is made up of four basic components 1. Sensing Unit. 2) Processing Unit. 3) Transceiver Unit 4) Power Unit. Additional units location finding system--power generator--mobilizer.
Slide162Constraints for Sensor Nodes Required small size: ØCan be placed in more locations and used in more scenarios (applications) more flexibility. ØCollect more data deployed densely.
Slide163Constraints for Sensor Nodes q Consume extremely low power (µAmps.): Øuse low-power hardware components . ØTransmit and receive only if necessary. q Power consumption in each node: Ø sensing, data processing and communication. q Radio communication will consume a significant fraction of total energy.
Slide164Constraints for Sens or Nodes qStrategies to reduce the average supply current of the radio: ØReduce the amount of data transmitted through data compression and reduction. ØReduce the frame overhead. ØImplement strict power management mechanisms (power-down and sleep modes). Ø only transmit data when a sensor event occurs
Slide167Protocol Stack q The protocol stack used by the sink and all sensor nodes: Ø Combines power and routing awareness, Ø integrates data with networking protocols, Ø communicates power efficiently through the wireless medium. Ø promotes cooperative efforts of nodes.
Slide168•The power, mobility, and task managem ent planes: monitor the power, mobility, and task distribution among the sensor nodes.
Slide169Physical Layer (1/3) •Responsible of: –Frequency selection : 916 MHz, 2.4 GHz –carrier frequency generation, –signal detection, –modulation and data encryption.
Slide170Physical Layer (2/3) q Energy minimization has significant importance more than: scattering, shadowing, reflection, diffraction, multi-path and fading effects. q Multi-hop communication can effectively overcome shadowing and path-loss effects, if the node density is high enough.
Slide171Physical Layer (3/3) ØM-ary scheme increased radio power consumption. ØBinary modulation scheme is more energy efficient BFSK used.
Slide172Responsible for: –the multiplexing of data streams, –data frame detection, –medium access and error control. Data Link Layer
Slide173Data Link Layer-MAC Protocol Sources of energy inefficiency: ØCollision. ØOverhearing. ØControl packet overhead. ØIdle listening. So, there is a need for a MAC protocol that solve these problems.
Slide174Data Link Layer-MAC Protocol Several Protocols used in the Link Layer: Self-Organizing Medium Access Control for Sensor Networks (S-MACS) CSMA. Hybrid TDMA/FDMA based.
Slide175Data Link Layer-MAC Protocol qS-MAC: –MAC protocol specifically designed for WSN. –Building on random access - based protocols. qS-MAC solve the problem of all the major sources of energy waste: –idle listening, collision, overhearing and control overhead. qNot suitable for time-critical applications because latency in end-to-end communication.
Slide176Data Link Layer/S-MAC Uses a sleep/wakeup cycle to allow nodes to spend most of their time sleep: qListen period: Øfor nodes that have data to send to coordinate. qA sleep period : Ønodes sleep if they have no data to send or receive, and nodes remain awake and exchange data if they are involved in communication. qIn a sleep mode when the radio is switched off, the node sets a timer to a wake later. qWhen the timer expires, it wakes up. qSelection of sleep and listen duration is based on the application scenarios.
Slide177Data Link Layer/S-MAC •Nodes a and b follow different schedules. •If a wants to send to b, it just wait until b is listening.
Slide178Data Link Layer/S-MAC ØNeighboring nodes are synchronized together. ØMaintaining Synchronization: –Needed to prevent clock drift –Periodic updating using a SYNC packet –Receivers adjust their timer counters
Slide179Data Link Layer/S-MAC q Collision avoidance: ØPerform virtual and physical carrier sense before transmission. ØRTS/CTS solves the hidden terminal problem. ØInterfering nodes go to sleep after they hear the RTS or CTS packet qOverhearing Avoidance: ØNAV. indicates how long the remaining transmission will be. ØThe medium is busy when the NAV value is not zero ØAll immediate neighbors of sender and receiver should go to sleep avoiding energy waste on overhearing.
Slide181Network Layer (1/6) •Special multi-hop wireless routing protocols between sink node and se nsors are needed. –Traditional ad hoc routing techniques do not usually fit. •When we design network layer protocols for sensor networks, we nee d to consider: –Power efficiency. –Sensor networks are data-centric. –addressing and location awareness.
Slide182Network Layer (1/3) Routing Techniques: •Maximum PA route: ØMax. total PA without including routes that add extra hops. •Minimum Energy route: ØRoute that consumes min. energy. •Energy-efficient routes: –can be found based on the available power (PA) and the energy required α for transmission in the links. •Minimum hop route: ØMin. hop to reach the sink. •Maximum minimum PA node route: ØUse the route in which the min. PA is larger than the min. PAs of the other routes. ØThis scheme prevents the risk of using up a sensor node with low PA m uch earlier than the others just because it is on the route with nodes tha t have very high PAs.
Slide183Network Layer (2/3) •Flooding is an old technique for routing. ØDuplicate messages. ØOverlap. ØResource blindness. •Sensor Protocols for Information via Negotiations (SPIN): ØSend sensor data instead of all the data. Ø3 types of messages: Advertise, Request & Data.
Slide184Network Layer (3/3) The characteristics of LEACH: • Randomly rotating the cluster-head among sensors. • Low energy consumption.
Slide185Transport Layer Transport layer is especially needed when the system is planned to be acce ssed through the Internet or other external networks. TCP: transmission window mechanisms is not suitable, TCP splitting will be used: Between User Sink (TCP or UDP) Between Sink nodes (UDP)
Slide186Application Layer Sensor Management protocol: ØExchanging the data. ØTime synchronization ØMoving the nodes, turning them on and off etc. •Sensor Query and Data distribution protocol. ØUser applications with interfaces to issue queries, respond to queries and collect incoming replies.