Indoor localisation using white LEDs

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.Described is 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.Introduction: White light emitting diodes (LEDs) are increasingly replacing incandescent and fluorescent lighting because of their energy efficiency. Although designed for lighting, unlike conventional forms of lighting, white LEDs can be modulated at frequencies up to 20 MHz [1] and as a result are forming the basis of a range of novel localisation and data communication systems. A number of papers have described the use of LEDs for localisation [2, 3] and for high speed data transmission [1, 4 -6].This Letter describes a novel technique for measuring time difference of arrival (TDOA) using sinusoidal signals transmitted by two LEDs. This technique depends on the fact that in intensity modulated direct detection (IM/DD) systems, frequency selective fading is a baseband, not a passband, phenomenon [7]. This means that when intensity modulation is used at the transmitters and direct detection using a photodiode is used at the receiver, the interference pattern created by the two sinusoids either adding or subtracting depends on the baseband modulating frequency not on the optical carrier frequency and therefore has dimensions suitable for indoor localisation applications. Many recently proposed optical wireless systems use orthogonal frequency division multiplexing (OFDM) for data transmission [1]. In this case one or more of the subcarriers can be reserved for localisation and data transmission and localisation can be simultaneously achieved.

Maximum likelihood estimation of vehicle position for outdoor image sensor-based visible light positioning system

“…Therefore, most of the PD-based VLPs proposed belong to indoor positioning. [11][12][13][14][15][16][17] For the IS-based VLP, 9,[18][19][20] IS is used as an optical reception device. IS can detect not only the intensity but also the angle of arrival (AOA) of incoming light.…”

Development of a Localization System Based on VLC Technique for an Indoor Environment

“…Over the past few decades, many indoor localization systems (ILSs) based on IR, Ultrasound, RFID, WLAN, Bluetooth, and UWB have been proposed, but these systems have limitations such as the necessity of additional infrastructure, low accuracy, noises, electromagnetic interference, multi-path effects, low security, and etc [5,6]. Naturally, much research has been conducted recently on using these indoor LED lighting and VLC techniques as an alternative indoor localization signal for places where satellite globalpositioning-system (GPS) signals are not available [6][7][8][9][10][11][12][13][14][15]. The biggest advantage of using VLC techniques for indoor localization is that no additional infrastructure is required for the installation since the system uses existing infrastructure of LED ceiling lamps, which reduces the cost of the ILS.…”

“…AOA [9], ToA, TDoA [7,10] approaches have disadvantage such as deployment of an array of image sensors, synchronization problem of all transmitters and receivers, precise delay control, and sensitivity to the phase noise [8], [11]. These in turn bring cost and complexity problems when implementing the actual system.…”

Indoor location awareness based on received signal strength ratio and time division multiplexing using light-emitting diode light

“…Moreover, because the LEDs can easily switch and modulate electrical signals into lightwave signals at high speed, they can be used for visible light communication 1,2 and head-tracking techniques. 3 Numerous LED-based positioning systems have been reported by using image sensors, 4 fingerprinting, 5 correlation, 6 and time difference of arrival (TDOA) 7,8 so far. However, the image-sensorbased systems require LEDs of different colors in order to distinguish each one among all of them.…”