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Sustainable development

Laure Guion - 21/03/2013

Sustainable development as a by-product

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The chosen topic for the second Semaine des mathématiques (Maths Week) , 18th - 24th March 2013, is "Mathematics for planet Earth".
Certain mathematics and digital sciences projects are focussing on the key challenge of sustainable development. However, this concern with respect for our planet may also have a shared effect, without being the stated aim, as illustrated by a number of examples.

Redundancy for improved transmission

Whether you are calling from your mobile phone, connecting via wifi in your home or using any other type of wireless communication, the message transmitted may be disrupted by different kinds of bad weather and contain errors . There are actually two possible solutions for dealing with this problem. The first solution is to increase the transmission power and the amplitude of the signal, from a relay antenna, for example, based on the principle that if you shout louder you will definitely be heard, but this requires more energy to be used. The second solution is known as coding  and plays a part in almost all the communication processes around you . Coding, which should not be confused with cryptography, which is designed to protect messages from malicious individuals, is used to correct minor errors that may occur in messages during "transmission", in order to guarantee their integrity on arrival. In order to do so, coding adds a message… to the message, i.e. redundancy  in order to be able to subsequently  correct errors that have slipped into the content, based on a suitable decoding protocol. "By adding redundancy, it is thought that a longer message is transmitted and that, as a result, this uses more energy," explains Alain Couvreur, Research Scientist within the Grace team. "But because you can transmit less powerfully with an equally effective result, you can significantly reduce the quantity of energy needed for transmission . "

The challenge for batteries in sensor networks

Wireless communication is also used by sensor networks . In this kind of network, which is made up of very small communicating objects, the batteries cannot be very large, battery life is therefore an extremely problematic factor . It is difficult to regularly change the batteries in temperature sensors placed in a forest, whose job is to raise the alarm in the event of a fire, or in movement sensors on a sensitive site, which are designed to detect possible intrusion. "What uses the most energy", explains Aline Carneiro Viana, Research Scientist, "is not gathering information on the environment, or even the act of working together, but communication. Therefore, communication protocols must minimise the message exchanged , with the aim of reducing energy expenditure. "

And in the future?

These smart networks  are only a premise. We will have more and more objects around us that will gather information and communicate with each other, while also being very small and unobtrusive, and thereby be easily spread around our environment. These objects may have access to the internet (the famous "internet of things"), and have independent roles designed to make our lives easier: sensing our presence on the doorstep in order to unlock the door, play ambient music and have pre-heated our living room… These machine-to-machine  relationships will, therefore, require a great deal of work in order to use the least possible energy.

 "Smart Grids" , i.e. grids that will communicate with each other in order to distribute electricity in a balanced manner  within a city or over a larger area, are another subject for the future. They will allow consumption by small companies and private individuals to be regulated. This will make it possible, for example, to automatically instruct all laptops to cease being powered for 30 minutes, in order to release a quantity of available energy in the event of exceptionally high demand, or even to intelligently choose when you should recharge your electric car; the user will no longer be able to use power immediately, but the grid will choose the most efficient way of doing so. In order to consume energy in a smarter way, together .

Keywords: Alain Couvreur Aline Carneiro Viana Energy Sensor networks Inria Saclay - Île-de-France Smart grids Coding

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