Introduction to Wireless Sensor Networks (WSNs) GholamHossein Ekbatanifard Assistant Professor ekbatanifard@ieee.org

What is WSN? Wireless Sensor Network WSN Wireless Network Computational Power Sensor Technology Wireless Network WSN

Network In general, the term network can refer to any interconnected group or system. A network is any method of sharing information between two systems.

Deployment Challenges - Network How scalable is the network? How fault tolerant is the network? How is the network affected by node failure? What is the network latency? What is the packet loss behavior?

Wireless The term wireless is normally used to refer to any type of electrical operation which is accomplished without the use of a "hard wired" connection. Wireless communication is the transfer of information over a distance without the use of electrical conductors

Deployment Challenges - Wireless Transmission Medium Vegetation vs desert High vs low humidity etc Coverage What is the range of the mote? Connectivity How stable is the connection? How is it affected by the change in battery voltage? Power consumption How much power does the radio use? What happens when the voltage drops?

Size reduction of cellular telephones Wireless Revolution Size reduction of cellular telephones

Wireless Networking

Threats Disclosure of sensitive/confidential data Denial of Service (DoS) Unauthorized access to wireless-enabled resources Potential weakening of existing security measures on connected wired networks and systems

Infrastructure-based Wireless Networks Typical wireless network: Based on infrastructure E.g., GSM, UMTS, … Base stations connected to a wired backbone network Mobile entities communicate wirelessly to these base stations Traffic between different mobile entities is relayed by base stations and wired backbone Mobility is supported by switching from one base station to another Backbone infrastructure required for administrative tasks IP backbone Further networks Gateways Server Router

Infrastructure-based Wireless Networks – Limits? What if … No infrastructure is available? E.g., in disaster areas, under-developed countries It is too expensive/inconvenient to set up? E.g., in remote, large construction sites There is no time to set it up? E.g. in military operations

Solution: (Wireless) Ad hoc Networks Try to construct a network without infrastructure, using networking abilities of the participants This is an ad hoc network – a network constructed “for a special purpose” Simplest example: Laptops in a conference room – a single-hop ad hoc network

Possible Applications for Infrastructure-free Networks Factory floor automation Disaster recovery Car-to-car communication Military networking Search-and-rescue Personal area networking (watch, glasses, PDA, medical appliance, …) …

Problems & Challenges for Ad hoc Networks Without a central infrastructure, things become much more difficult Problems are due to Lack of central entity for organization available Limited range of wireless communication Mobility of participants Battery-operated entities

No Central Entity ! Self-Organization Without a central entity (like a base station), participants must organize themselves into a network. Pertains to (among others): Medium access control (MAC) no base station can assign transmission resources, must be decided in a distributed fashion Finding a route from one participant to another (Routing)

Limited Range ! Multi-Hopping For many scenarios, communication with peers outside immediate communication range is required Direct communication limited because of distance, obstacles, … Solution: multi-hop network ?

Mobility  Suitable, Adaptive Protocols In many ad hoc network applications, participants move around In cellular network: simply hand over to another base station In mobile ad hoc networks (MANET): Mobility changes neighborhood relationship Must be compensated Routes in the network have to be changed Complicated by scale Large number of such nodes difficult to support

Battery-Operated Devices  Energy-Efficient Operation Often participants in an ad hoc network draw energy from batteries Desirable: long run time for Individual devices Network as a whole  Energy-efficient networking protocols E.g., use multi-hop routes with low energy consumption (energy/bit) E.g., take available battery capacity of devices into account How to resolve conflicts between different optimizations?

Advantages of wireless networks Easy to Install: hard-to-networking environment: river, highway, historic cites fast installation: festival, assembly, Q-&-A in congress reliability: (wired cables might be cut, get rusty, …) in a company: re-organization, change office, etc.

Features of Wireless Communication One global bandwidth shared by all users Fortunately channels, such as (frequency, time-slot) pairs, can be reused Radio-based Low bandwidth High latency radio communication links Higher bit error rate (BER) Fading Short-term multipath fading (Rayleigh effect) Due to same signal taking different paths and arriving at the receiver shifted in phase Long-term fading (radio shadow) Topology of the terrain (like mountains) can cause signal dropouts Solution: deploying multiple antenna sites

Sensor A SENSOR is a device which measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. Technological progress allows more and more sensors to be manufactured on a microscopic scale as microsensors using MEMS (Micro-Electro-Mechanical Systems) technology.

Types of Sensor Thermal Electromagnetic Mechanical Chemical Optical radiation Ionizing radiation Acoustic

Types of Sensor-Actuator Hardware Platforms RFID equipped sensors Smart-dust tags typically act as data-collectors or “trip-wires” limited processing and communications Mote/Stargate-scale nodes more flexible processing and communications More powerful gateway nodes, potentially using wall power

Deployment Challenges - Sensor What kind of sensor modality should be used? – acoustic, magnetic, seismic… What is the range of the sensor? How reliable is the sensor? What is the resolution of the sensor? How much power does the sensor use? What is the cost of the sensor?

WSN Node Components Low-power processor. Limited processing. Memory. Limited storage. Radio. Low-power. Low data rate. Limited range. Sensors. Scalar sensors: temperature, light, etc. Cameras, microphones. Power. Sensors P O W E R Storage Processor Radio WSN device schematics

Block Diagram – Mote

Picture- Mote

WSN: “Motes”

Mote Evolution

Challenges Challenges Limited battery power Limited storage and computation Lower bandwidth and high error rates Scalability to 1000s of nodes Network Protocol Design Goals Operate in self-configured mode (no infrastructure network support) Limit memory footprint of protocols Limit computation needs of protocols -> simple, yet efficient protocols Conserve battery power in all ways possible

Typical Features of WSN A very large number of nodes, often in the order of thousands Asymmetric flow of information, from the observers or sensor nodes to a command node Communications are triggered by queries or events At each node there is a limited amount of energy which in many applications is impossible to replace or recharge Almost static topology

Typical Features of WSN (cont.) Low cost, size, and weight per node Prone to failures More use of broadcast communications instead of point-to-point Nodes do not have a global ID such as an IP number! The security, both physical and at the communication level, is more limited than conventional wireless networks

Design Considerations Fault tolerance – The failure of nodes should not severely degrade the overall performance of the network Scalability – The mechanism employed should be able to adapt to a wide range of network sizes (number of nodes) Cost – The cost of a single node should be kept very low Power consumption – Should be kept to a minimum to extend the useful life of network

Design Considerations (cont.) Hardware and software constraints – Sensors, location finding system, antenna, power amplifier, modulation, coding, CPU, RAM, operating system Topology maintenance – In particular to cope with the expected high rate of node failure Deployment – Pre-deployment mechanisms and plans for node replacement and/or maintenance Transmission media – ISM bands, infrared, etc.

Design Considerations (cont.) Environment Busy intersections Interior of a large machinery Bottom of an ocean Inside a twister Surface of an ocean during a tornado Biologically or chemically contaminated field Battlefield beyond the enemy lines Home or a large building Large warehouse Animals Fast moving vehicles Drain or river moving with current.

Application Spectrum

Some Problems Calibration = correcting systematic errors in sensor data Causes: manufacturing, environment, age, crud Localization = establish spatial coordinates for sensors and target objects Power-aware Networking low-power media access; power-aware routing of data packets Macro-programming= high-level program for a sensor network; not low-level programs for individual sensors

WSN Communications Architecture Sensing node Sensor nodes can be data originators and data routers Internet Sink Manager Node Sensor nodes Sensor field

Objective

Network Architectures Clustered Architecture Layered Architecture Base Station Larger Nodes denote Cluster Heads Base Station Layer 1 Layer 2 Layer 3

Clustered Network Architecture Sensor nodes autonomously form a group called clusters. The clustering process is applied recursively to form a hierarchy of clusters.

LEACH (Low Energy Adaptive Clustering Hierarchy) It uses two-tier hierarchy clustering architecture. It uses distributed algorithm to organize the sensor nodes into clusters. The cluster-head nodes create TDMA schedules. Nodes transmit data during their assigned slots. The energy efficiency of the LEACH is mainly due to data fusion.

Sensor Network Protocol Stack Power Management – How the sensor uses its power, e.g. turns off its circuitry after receiving a message. Application Task Management Transport Mobility Management Mobility Management – Detects and registers the movements of the sensor nodes Network Power Management Data Link Task Management – Balances and schedules the sensing tasks given to a specific region Physical

Application Layer Makes the hardware and software of the lower layers transparent to the sensor network management applications. Different management protocols: Sensor Management Protocol (SMP) Task assignment and data advertisement protocol (TADAP) Sensor Query and Data Dissemination Protocol (SQDDP)

Transport Layer This layer is especially needed when the system is planned to be accessed through Internet or other external networks. End to end delivery Reliability Congestion control

Network Layer Power efficiency is always an important consideration. Sensor networks are mostly data centric. Data aggregation is useful only when it does not hinder the collaborative effort of the sensor nodes. An ideal sensor network has attribute-based addressing and location awareness.

Routing Problem – How to efficiently route: Data from the sensors to the sink and, Queries and control packets from the sink to the sensor nodes

Routing Multihop routing is common due to limited transmission range Phenomenon being sensed Data aggregation takes place here Sink Multihop routing is common due to limited transmission range Low node mobility Power aware Irregular topology MAC aware Limited buffer space Some routing issues in WSNs

Communication architecture of sensor networks Maximum available power (PA) route: Route 2 Minimum energy (ME) route: Route 1 Minimum hop (MH) route: Route 3 Maximum minimum PA node route: Route 3 Minimum longest edge route: Route 1

Data Aggregation Data coming from multiple sensor nodes are aggregated, if they have about the same attributes of the phenomenon being sensed Phenomenon being sensed

Data Link Layer (MAC Layer) The data link layer is responsible for : Medium access Creation of the network infrastructure Fairly and efficiently share communication resources between sensor nodes Power saving modes of operation Error control. Forward Error Correction (FEC) Automatic Repeat Request (ARQ). Reliable point-to-point Point-to-multipoint connections

Physical Layer The physical layer is responsible for: Frequency selection Frequency generation Signal detection Modulation Data encryption Open research issues Modulation schemes Strategies to overcome signal propagation effects Hardware design

WSN: Open Source Tools Simulators Programming Languages TOSSIM Avrora NCTUns OMNET++ J-Sim Ptolemy Programming Languages Assembly C Giotto Esterel Lustre Signal E-FRP nesC Operating Systems TinyOS YATOS Contiki MANTIS SOS Application Tools Localization Tools TinyDB Surge TOSBase