tworking: The network is of networked sensing are in improved robustness and peer-to-peer, with a mesh topology and dynamic, scalability. A decentralized sensing system is inherently mobile, and unreliable connectivity. There are no more robust against individual sensor node or link fail- universal routing protocols or central registry ser- ures, because of redundancy in the network. Decentral- vices. Each node acts both as a router and as an ized algorithms are also far more scalable in practical application host. deployment and may be the only way to achieve the large Limited support for software development: The tasks scales needed for some applications. are typically real-time and massively distributed, involve dynamic collaboration among nodes, and 3.7.2.1 Energy advantage must handle multiple competing events. Global properties can be specified only via local instructions. Because of the unique attenuation characteristics of Because of the coupling between applications and radio-frequency (RF) signals, a multihop RF network system layers, the software architecture must be provides a significant energy saving over a single-hop codesigned with the information processing network for the same distance. Consider the following architecture. simple example of an N-hop network. Assume the overall distance for transmission is Nr, where r is the one- hop distance. The minimum receiving power at a node 3.7.2 Advantages of sensor for a given transmission error rate is Preceive, and the networks power at a transmission node is Psend- Then, the RF attenuation model near the ground is given by Networked sensing offers unique advantages over traditional centralized approaches. Dense networks Preceive Psend , of distributed communicating sensors can improve signal-to-noise ratio (SNR) by reducing average distances where r is the transmission distance and a is the RF at- from sensor to source of signal, or target. Increased tenuation exponent. Due to multipath and other Wireless sensor networks CHAPTER 3.7 interference effec