2.4.1 WSN Infrastructure and Constraints

A WSN is a collection of spatially distributed autonomous devices (nodes or motes) that collaborate to monitor environmental conditions.

2.4.2 The Anatomy of a WSN Node (The "Mote")

• Power Unit: The bottleneck. Usually AA batteries or Energy Harvesting (Solar/Vibration).
• Sensing Unit: Measures parameters (Temp, Light, Gas).
• Processing Unit: 8-bit/32-bit MCU (Atmel, ARM Cortex-M).
• Communication Unit: Low-power radio transceiver (IEEE 802.15.4 standard).

2.4.3 WSN Network Topologies: Comparative Analysis

1. Star Topology: Every node talks directly to the central gateway. Pro: Simplicity. Con: Limited range, single point of failure (Gateway).
2. Mesh Topology: Nodes talk to their neighbors. Data hops from node to node. Pro: Self-healing, long range. Con: High latency, complex routing (RPL).
3. Cluster-based Topology: Nodes organized into groups with a elected "Cluster Head" (CH). Pro: Saves energy by performing data aggregation at the CH before sending to the gateway.

2.4.4 Participatory Sensing Technology

Participatory sensing shifts the sensing burden from dedicated infrastructure to the Citizenry.

• Concept: Using smartphone sensors (GPS, Microphone, Accelerometer) to monitor city conditions.
• Examples: Using Waze for traffic mapping or the NoiseTube app for city noise mapping.
• Issues: Data privacy, incentive models, and handling heterogeneous data quality.