Professor Jean Armstrong



Abstract— Energy efficient white LEDs are increasingly being used for indoor lighting but unlike conventional lighting, the intensity of the light emitted by white LEDs can be modulated at high frequencies. This paper describes a novel positioning technique based on transmitting signals with known sinusoidal components from a number of LEDs. The receiver uses the resultant optical signal at the receiver photodiode to calculate the receiver position. Proof of concept experiments show that white LEDs designed for indoor lighting can be used as the transmitters. The modulation bandwidth of white LEDs is large enough to give a range of localisation that is compatible with typical indoor applications.

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Abstract— The widespread introduction of white LEDs for illumination provides a unique opportunity to create an indoor positioning system that is flexible, accurate, and ubiquitous. Signals transmitted by the LEDs are used to determine the position of a person or object within a room. To take full advantage of this new opportunity, it is essential that comprehensive and robust international standards are developed before a plethora of incompatible proprietary systems flood the market. In this article, we discuss the very diverse range of potential applications of these future systems and their implications for the design of a new standard. Another consideration is that the transmission of positioning signals must not compromise the primary function of the LEDs, which is energy-efficient illumination, so visible flicker must be avoided. Position information can be derived from a range of properties of the received signal, such as the power of the received signal or the angle at which the signal reaches the receiver. The suitability of different techniques for an indoor positioning system is considered.Finally, we discuss the implications each of these aspects has for the design of an effective standard.

J. Armstrong, Y. A. Sekercioglu and A. Neild, "Visible Light Positioning: A Roadmap for International Standardisation," IEEE Communications Magazine, December 2013.


K. Panta and J. Armstrong, "Indoor localisation using white LEDs," Electronics Letters, vol. 48, pp. 228-230, 2012


Abstract— This paper analyzes an indoor positioning system that uses white lighting LEDs. Modulated signals transmitted by the LEDs are used as the basis of time-of-arrival based distance estimation. The theoretical limits on the accuracy of estimation are calculated by deriving the Cramer-Rao bound for intensity modulated windowed sinusoidal signals. Calculations for a typical indoor scenario, assuming perfect synchronization between transmitter and receiver, but using realistic values for other parameters show that very accurate distance estimates are achievable, with typical errors being in the order of centimeters depending on the frequency and power of the sinusoidal signals, the distance from the LED and the properties of the LED and the photoreceiver.

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T. Q. Wang, Y. A. Sekercioglu, A. Neild, and J. Armstrong, "Position Accuracy of Time-of-Arrival Based Ranging Using Visible Light With Application in Indoor Localization Systems," Journal of Lightwave  Technology, vol. 31, pp. 3302-3308, 2013. Download


Recent Papers on Positioning and Localization