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.Index Terms-Cramer-Rao bound, indoor localization, intensity modulation and direct detection, ranging, time-of-arrival, visible light communication, windowed sinusoid.

White lighting LEDs offer great potential for high speed communications, especially for indoor applications. However, for their widespread adoption, two important issues need to be addressed: the lack of diversity in multiple-input multiple output (MIMO) systems, and the small field of view of receivers. In this paper, we describe a design using a hemispherical lens in the receiver that solves these problems. By using classical optics, we derive exact expressions for the channel gain and the optical power density of the projected images. Simulation results of a typical indoor scenario show that the new system has a wide field of view, and provides adequate channel gain for angles of incidence as large as 70 degrees. We present the distribution of optical power on the imaging plane for various receiving positions and tilted receivers over a number of representative indoor scenarios. They show that the images of LEDs are clearly distinguishable. The results demonstrate the presence of low channel correlations between individual transmitters and receivers. Consequently, this confirms that the new technique is capable of providing significant diversity order for MIMO optical wireless applications.

Indoor visible light positioning (VLP) using signals transmitted by lighting LEDs is a topic attracting increasing interest within the research community. In recent years, VLP techniques using a range of receiver structures and positioning algorithms have been described. In this paper we analyze the performance of a VLP system which uses an aperture-based receiver and measurements of received signal strength. An aperture-based receiver has a number of receiving elements each consisting of a photodiode and an associated aperture. It has been shown that receivers of this form can be designed which are compact and provide both a wide overall field-of-view and good angular diversity. As a result they can efficiently extract positionrelated information from light transmitted by non-directional LEDs. In our approach, we correlate the signals at the outputs of the photodiodes with a set of reference signals. The resulting observations include information on the received signal strength as well as the angle-of-arrival, and are used to directly estimate the receiver's position. In order to assess the performance of positioning algorithms based on this approach, we derive the Cramer-Rao lower bound on the position estimate. We show that the Cramer-Rao bound depends on the selected reference signal, and that sub-centimetre to centimetre accuracy can be obtained, using only a limited number of non-directional LEDs.

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