Energy Harvesting Communication - Why, How and Where?

This article is a part of the technical article board at SSET

Abstract

The recent trends in communication and signal processing looks for low energy circuits and algorithms. In this article we look into some of the practical schemes of implementing a network of sensors using renewable sources of energy. An effi cient computation between the sensor nodes is also presented.

Introduction

Hand held devices are battery operated and is often drained o frequently in day to day applications.
There is a provision to recharge these cells as and when needed, using power sockets. But in applications such as environment monitoring or deep space observation where there are multiple sensor nodes, this "scheme" is not possible. Li-ion batteries are being replaced with supercapacitors, which has the ability to store charges from renewable sources. The intermittent availability of the energy packets, makes the energy available at any point to be random according to some 'probability distribution'.

A Working Example

Consider a communication system having one transmitter and a receiver - called as a 'point to point'

channel. A transmitter requires energy to transmit bits to the receiver and needs to 'obey' the channel

rules for end to end reliability.

The Energy harvester block is a solar panel wind turbine, a piezo electric or bio-mechanical gear, which is capable of converting various energy sources to electrical energy. The charge gets stored in the supercapacitor, where it is available for usage while transmitting. The transmission is an adaptive scheme, where the power disbursed on each packet/bit is controlled with respect to the energy available within the storage device. The power also needs to be decided by the channel condition - i.e in low SNR regime send at a lower rate and at higher SNR send at a larger rate.

Make Your Own Harvester

• Solar : Easily available and can be applied to almost all sensors. But its e ciency is less than 10%
• Piezo : Useful in converting natural movements to storable form. Advantage that no other storage medium is required.
• Bio-Mechanical : Converts periodic regular movements to electricity using mechnical pronciples of gear.

Can we get energy for free?

Neodymium magnets when placed near the CPU fans can act as a dynamo to run an LED bulb!

Reference

[1] Shaviv, Dor, and Ayfer zgr. "Universally Near-Optimal Online Power Control for Energy Harvesting Nodes." arXiv preprint arXiv:1511.00353 (2015).

[2] Marjan Aslani, "Electrochemical Double Layer Capacitors (Supercapacitors)", 2012, Web link : http://large.stanford.edu/courses/2012/ph240/aslani1/