Abstract
Wireless Sensor Networks (WSNs) is a group of spatially dispersed autonomous sensor devices, named motes. These motes have a microcontroller, sensors, are powered by AA or AAA batteries, and mainly have the ability to communicate using the IEEE 802.15.4 standard. The motes communicate between them inside the WSN exchanging packets using a multi-hop routing. They use a very low amount of power (below 100 mW). This limits the maximum communication distance between motes within the WSN. Usually, one mote acts as a gateway to other networks and this mote is also called sink or simply Base Station (BS), and the data collected by the sensors of each mote are sent to this mote. The maximum distance between the BS and the nearest mote is below 100 m because of the power limitations of the motes. If the WSN-BS distance is above this boundary, the communication will surely fail. We propose a new technique in order to achieve a long range communication from the WSN, for instance to communicate to a Low Earth Orbit (LEO) satellite. Many proposals in the literature based on Collaborative Beamforming (CB), also known as Distributed or Cooperative Beamforming, for these long range communications are found, however the synchronization of clocks is an almost impossible task given the simplicity and cheapness of the architecture of the motes. To overcome this problem, we propose a new technique, named Stochastic Collaborative Beamforming (SCB), in which we take advantage of the synchronization errors of the clocks. In SCB, it is possible to obtain the adequate time delay that permits the interference or sufficient gain in the direction of the receiver. This gain is obtained from interfering independent signals coming from each mote of the WSN, using a repetition scheme. Although it does not get all the nominal gain that could be obtained in case of a perfect synchronization, it does get a sufficient gain to reach the BS with limited power consumption.
Highlights
Wireless Sensor Networks (WSNs) is a group of small devices called nodes or motes
This improves the possibilities of Collaborative Beamforming (CB) transmission of a WSN, with a large number of motes, spread over a large area, especially considering the eventual cost of such a deployment compared to an antenna of such dimensions
We have demonstrated the the possibility of implementing communications from WSN to Base Station (BS), when it is at a great distance
Summary
Wireless Sensor Networks (WSNs) is a group of small devices called nodes or motes. These nodes or motes contain a microcontroller to which a multitude of sensors can be attached and which have the capacity to communicate mainly using the IEEE 802.15.4 [1] standard in the ISM In many applications the motes have been distributed by means of an aerial procedure in inaccessible spaces, or they have been hidden due to their small size and the difficulties of the terrain, or merely there has not been interest in recovering them after exhausting their batteries For those cases, the motes are designed to be self-destructible, biodegradable, and sometimes a new deployment is made to change or continue monitoring. Large antenna arrays have an extraordinary gain, which allows them to sweep the space with a “pencil beam” in radar systems This improves the possibilities of CB transmission of a WSN, with a large number of motes, spread over a large area, especially considering the eventual cost of such a deployment compared to an antenna of such dimensions.
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