Wireless Sensor Networks Outline Introduction to Wireless Sensor

Wireless Sensor Networks

Outline Introduction to Wireless Sensor Networks p Basic Features of WSNs p Applications p Factors Influencing WSN Design p Localization and Coverage Issues p Topology Control p Security of Sensor Networks p Data management p 7/2009 (L. Ni) 2

Introduction p Sensor Networks: n n n p Composed of a large number of low-cost, low-power, multifunctional sensor nodes, densely deployed either inside the phenomenon or very close to it. Sensor node consists of sensing, data processing, and communicating components The positions of sensor nodes need not be engineered or pre-determined Purpose: To monitor, combine, analyze and respond to the data collected by hundreds (thousands) sensors distributed 7/2009 (L. Ni)in the physical world in a timely manner. 3 n

Basic Features of WSNs Self-organizing capabilities p Short range broadcast communication and multihop routing p Dense deployment and cooperative effort of sensor nodes p Frequently changing topology due to fading and node failures p Limitation in energy, transmit power, memory and computing power p 7/2009 (L. Ni) 4

Applications（1）：Military p p p Monitoring friendly forces, equipment and ammunition Reconnaissance of opposing forces and terrain Battlefield surveillance Battle damage assessment Nuclear, biological and chemical attack detection Battlefield surveillance 7/2009 (L. Ni) 5 Urban warfare

Applications（2）：Environmental 7/2009 (L. Ni) Great Duck Island Ecosystem Monitoring 6

Applications（3）：Home Network Management Sensor Fusion Middleware Framework Speech Database Recognizer & Data Miner Wired Network WLAN Access Point High-speed Wireless LAN (WLAN) WLAN-Piconet Bridge Piconet WLAN-Piconet Bridge Sensors Modules Piconet Sensor Badge Networked Toys 7/2009 (L. Ni) Smart Kindergarten Project: Sensor-based Wireless Networks of Toys 7

Factors Influencing WSN Design Fault tolerance p Scalability p Production costs p Operating environment p Sensor network topology p Hardware constraints p Transmission media p Power consumption p 7/2009 (L. Ni) 8

Fault tolerance（1） p Failures: n n n lack of power physical damage in harsh environment Interference by other objects (e. g. radios) and other sensors. Fault tolerance: the ability to sustain sensor network functionalities without any interruption due to failures p The environment is important to the fault tolerance of algorithms and protocols p 7/2009 (L. Ni) 9

Scalability（2） p Number of sensors n p Good scalability n p hundreds, thousands, to millions, depending on the type of applications. Architecture and protocol design should have very good scalability Density also depends on the applications. 7/2009 (L. Ni) 10

Costs（3） p Per node cost is important for large sensor networks. n p Bluetooth radio system: n p It has to be kept low. $5 now, but still too expensive for sensors, targeted to be < 50 c. More challenging, with large amount of functionalities 7/2009 (L. Ni) 11

Unique Hardware Constrains（4） p Low computational power n n p p Limited memory Poor communication bandwidth n n n p Current mote processors run at < 10 MIPS No enough horsepower to do real signal processing Current radios achieve about 10 Kbps per mote 802. 15. 4 (Zigbee) radios now available at 250 Kbps But with small packets, real data rate is about 25 kbps Limited energy budget n n n 7/2009 (L. Ni) 2 AA motes provide about 2850 m. Ah Coin-cell Li-Ion batteries provide around 800 m. Ah Solar cells can generate around 5 m. A/cm 2 in direct sunlight 12

Sensor network topology（5） p Topology maintenance a challenging task n p Pre-deployment and deployment phase n p no careful planning: the installation cost, no need for any preorganization and pre-planning, the flexibility of arrangement, and better self-organization and fault tolerance. Post-deployment phase n n p # of nodes, failures, dynamics etc topology changes are due to change in position, reachability (due to jamming, noise, moving obstacles, etc. ), available energy, malfunctioning, etc How to maintain the topology change? Re-deployment of additional nodes phase n Adding new sensors 7/2009 (L. Ni) 13

Transmission media（6） p Diverse transmission media n Wireless communication, formed by radio, infrared or optical media 7/2009 (L. Ni) 14

Power Consumption（7） p Sensing, communication, and data processing n Communication p n A sensor node expends maximum energy in data communication, the active power + the start-up power consumption Data processing p 7/2009 (L. Ni) Much less, local data processing is crucial in minimizing power consumption in a multi-hop sensor network. 15

Localization and Coverage Issues Finding locations of sensors without GPS p One-hop or multi-hop time synchronization (important for scheduling of sensor nodes). p Placement of data-sinks for efficient data collection or network throughput. p Network connectivity (or area coverage) and node density. p 7/2009 (L. Ni) 16

Topology Control Qo. S topology control p Dynamic, distributed (localized), and efficient. p 7/2009 (L. Ni) 17

Security of Sensor Networks Light-weight cryptographic primitives p Light-weight security protocols for key distribution / key management / authentication p Intrusion detection / intrusion tolerance p Secured routing (lack of security infrastructure) p 7/2009 (L. Ni) 18

Data management Data Aggregation a key enabler for efficient networking p Other options – data storage, broadcasting aggregates – also well supportable p 7/2009 (L. Ni) 19