The Gaussian Mixture Probability Hypothesis Density (GM-PHD) recursion is a closed-form solution to the probability hypothesis density (PHD) recursion, which was proposed for jointly estimating the time-varying number of targets and their states from a sequence of noisy measurement sets in the presence of data association uncertainty, clutter and miss-detection. However the GM-PHD filter does not provide identities of individual target state estimates, that are needed to construct tracks of individual targets. In this paper, we propose a new multi-target tracker based on the GM-PHD filter, which gives the association amongst state estimates of targets over time and provides track labels. Various issues regarding initiating, propagating and terminating tracks are discussed. Furthermore, we also propose a technique for resolving identities of targets in close proximity, which the PHD filter is unable to do on its own.

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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.