Wireless Sensor Networks

1. Wireless Sensor Networks

2. Outline • Introduction to Wireless Sensor Networks • Basic Features of WSNs • Applications • Factors Influencing WSN Design • Localization and Coverage Issues • Topology Control • Security of Sensor Networks • Data management

3. Introduction • Sensor Networks: • Composed of a large number of low-cost, low-power, multifunctionalsensor 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 in the physical world in a timely manner.

4. Basic Features of WSNs • Self-organizing capabilities • Short range broadcast communication and multi-hop routing • Dense deployment and cooperative effort of sensor nodes • Frequently changing topology due to fading and node failures • Limitation in energy, transmit power, memory and computing power

5. Applications（1）：Military • 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 Urban warfare

6. Applications（2）：Environmental Great Duck Island Ecosystem Monitoring

7. Middleware Framework NetworkManagement SensorManagement SensorFusion Speech Recognizer Database & Data Miner Wired Network WLAN Access Point High-speed Wireless LAN (WLAN) WLAN-Piconet Bridge WLAN-Piconet Bridge Piconet Piconet SensorsModules Sensor Badge Networked Toys Applications（3）：Home Smart Kindergarten Project: Sensor-based Wireless Networks of Toys

8. Factors Influencing WSN Design • Fault tolerance • Scalability • Production costs • Operating environment • Sensor network topology • Hardware constraints • Transmission media • Power consumption

9. Fault tolerance（1） • Failures: • 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 • The environment is important to the fault tolerance of algorithms and protocols

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

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

12. Unique Hardware Constrains（4） Low computational power Current mote processors run at < 10 MIPS No enough horsepower to do real signal processing Limited memory Poor communication bandwidth 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 2 AA motes provide about 2850 mAh Coin-cell Li-Ion batteries provide around 800 mAh Solar cells can generate around 5 mA/cm2 in direct sunlight

13. Sensor network topology（5） • Topology maintenance a challenging task • # of nodes, failures, dynamics etc • Pre-deployment and deployment phase • no careful planning: the installation cost, no need for any pre-organization and pre-planning, the flexibility of arrangement, and better self-organization and fault tolerance. • Post-deployment phase • 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 • Adding new sensors

14. Transmission media（6） • Diverse transmission media • Wireless communication, formed by radio, infrared or optical media

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

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

17. Topology Control • QoS topology control • Dynamic, distributed (localized), and efficient.

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

19. Data management • Data Aggregation a key enabler for efficient networking • Other options – data storage, broadcasting aggregates – also well supportable