On Architectures of Transmit-Only, UWBased Wireless Sensor Networks

We are interested in designing a pulse-based Ultra-Wide-Band (UWB) sensor network. This network consists of a large number (in the order of 100) of wireless sensor nodes (SNs) that sense the environment and transmit the resulting data, and several (1-10) cluster heads (CHs), that collect the data packets sent by the SNs and forward them to a central server (CS) for further processing. The goal is to have a network with simple and low-cost SNs that can support low data traffic rate (10 kbps on average). An UWB wireless receiver circuit in this case is much more complex than a transmitter one, and it is prohibitively expensive to integrate a receiver in a simple SN. We thus focus on sensor networks in which the SNs can only transmit data to CHs (transmit-only SNs), and we are interested in the optimal architectures of the SNs, CHs and CS such that the number of packets sent by the SNs and received successfully by the CS is maximized.
At the physical layer we decide to use a non-coherent receiver with an energy detector because of its implementation simplicity and low-power consumption. Furthermore we prefer a robust modulation scheme over those with high data rates and select 2-PPM as modulation scheme. At the MAC layer we propose a novel power-aware multi-access scheme that allows both the SNs and the CHs to turn off their radio transceivers and save energy during idle periods.
We find that the system performance can be drastically increased by introducing a detection threshold at the CHs: only packets whose received power is larger than a certain detection threshold are to be captured. By using an adaptive scheme that varies the detection threshold proportionally to the total traffic load generated by the SNs, we show that the system performance can be doubled during high traffic bursts without additional cost at the receiver. We also show that an additional improvement can be made by introducing an extra detection circuit, which detects packets with stronger power and switches the main receiver to that packet when it happens. We also find that combining data received from several CHs at the central server improves the coverage range without decreasing the
throughput. Finally, we find that FEC coding of packets does not improve performance.

By: Bozidar Radunovic; Hong Linh Truong; Martin Weisenhorn

Published in: RZ3596 in 2005


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