We investigate whether adapting the transmit power optimally to the time-varying channel compares favorably, in terms of total energy consumption, to using a fixed link margin in wireless networks over short transmission distances. Over short distances, the circuit energy consumption dominates the transmission energy. For that reason, feeding back channel state information -a requirement for power control -may not be a power efficient strategy. We investigate both slow and fast power control and conclude, somewhat surprisingly, that using a fixed margin is typically more power-efficient than using power control.
A common technique in wireless sensor networks (WSN) is to use multihopping, that is, relaying messages via intermediate nodes. In this work we compare the energy efficiency of single-hop and multihop taking into account circuit energy consumption as well as transmission energy. We consider a simple two-hop case as well as a multihop case for a uniform two-dimensional network of arbitrary size. Contrary to common beliefs, we find that single-hop is superior for all realistic cases covered by our model. Even in comparison to the simple two-hop case single-hop is preferable. Only at very large path losses would multihop be a serious alternative. At present there are however very few WSN radios available that can operate under such conditions. In spite of the relatively simple networks considered we argue that our findings have quite general applicability with strong implications for the choice of routing protocols.
We present Sensei-UU, a testbed that supports mobile sensor nodes. The design objectives are to provide wireless sensor network (WSN) experiments with repeatable mobility and to be able to use the same testbed at different locations, including the target location. The testbed is inexpensive, expandable, relocatable and it is possible to reproduce it by other researchers.Mobile sensor nodes are carried by robots that use floor markings for navigation and localization. The testbed is typically used to evaluate WSN applications when sensor nodes move in meters rather than millimeters, eg. when human carries a mobile data sink (mobile phone) collecting data while passing fixed sensor nodes. To investigate the repeatability of robot movements, we have measured the achieved precision and timing of the robots. This precision is of importance to ensure the same radio link characteristics from one protocol experiment to another.We find that our robot localization is accurate to ±1 cm and variations in link characteristics are acceptably low to capture fading phenomena in IEEE 802.15.4. In the paper we show repeatable experiment results from three environments, two university corridors and from an anechoic chamber. We conclude that the testbed is relocatable between different environments and that the precision is good enough to capture fading effects in a repeatable way.
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