Visible light communication (VLC) using light-emitting diodes has been gaining increasing attention in recent years as it is appealing for a wide range of applications such as indoor positioning. Orthogonal frequency division multiplexing (OFDM) has been applied to indoor wireless optical communications in order to mitigate the effect of multipath distortion of the optical channel as well as increasing the data rate. An OFDM VLC system is proposed, which can be utilized for both communications and indoor positioning. A positioning algorithm based on power attenuation is used to estimate the receiver coordinates. We further calculate the positioning errors in all the locations of a room and compare them with those using single-carrier modulation schemes, i.e., on–off keying modulation. We demonstrate that our proposed OFDM positioning system outperforms by 74% its conventional counterpart. Finally, we investigate the impact of different system parameters on the positioning accuracy of the proposed OFDM VLC system.
KEYWORDS: Free space optics, Receivers, Turbulence, Atmospheric turbulence, Error analysis, Signal to noise ratio, Systems modeling, Atmospheric modeling, Free space optical communications, Statistical analysis
Free space optical (FSO) communication has been receiving increasing attention in recent years with its ability to achieve ultra-high data rates over unlicensed optical spectrum. A major performance limiting factor in FSO systems is atmospheric turbulence which severely degrades the system performance. To address this issue, multiple transmit and/or receive apertures can be employed, and the performance can be improved via diversity gain. In this paper, we investigate the bit error rate (BER) performance of FSO systems with transmit diversity or receive diversity with equal gain combining (EGC) over atmospheric turbulence channels described by the Double Generalized Gamma (Double GG) distribution. The Double GG distribution, recently proposed, generalizes many existing turbulence models in a closed-form expression and covers all turbulence conditions. Since the distribution function of a sum of Double GG random variables (RVs) appears in BER expression, we first derive a closed-form upper bound for the distribution of the sum of Double GG distributed RVs. A novel union upper bound for the average BER as well as corresponding asymptotic expression is then derived and evaluated in terms of Meijers G-functions.
With the development of location based services (LBS), indoor positioning has been a popular research topic in recent years. Since global positioning system (GPS) signal suffers from severe attenuation when penetrating through solid walls, other alternatives are proposed to realize indoor positioning. Visible light communication (VLC) systems offer a practical solution. Light emitting diode (LED) is able to be modulated in high speed as a transmitter, and a photodiode (PD) is commonly a receiver to detect the optical signal strength. In VLC based indoor positioning system, LEDs are applied for both positioning and illumination purposes so that infrastructure cost and power consumption are decreased. In addition, light positioning system provides other advantages such as no electromagnetic interference and better immunity against multipath reflections. Several methods are proposed to realize indoor positioning, such as triangulation, scene analysis and proximity, which are also applicable for a VLC based system. In prior works, the height of receiver is known so that the coordinates on the horizontal plane can be calculated. In this paper, the proposed method includes two stages: the height is presumed in the prediction stage and nonlinear estimation is applied in the correction stage to realize three dimensional coordinate estimation.
Over the past decade, location based services (LBS) have found their wide applications in indoor environments, such as large shopping malls, hospitals, warehouses, airports, etc. Current technologies provide wide choices of available solutions, which include Radio-frequency identification (RFID), Ultra wideband (UWB), wireless local area network (WLAN) and Bluetooth. With the rapid development of light-emitting-diodes (LED) technology, visible light communications (VLC) also bring a practical approach to LBS. As visible light has a better immunity against multipath effect than radio waves, higher positioning accuracy is achieved. LEDs are utilized both for illumination and positioning purpose to realize relatively lower infrastructure cost. In this paper, an indoor positioning system using VLC is proposed, with LEDs as transmitters and photo diodes as receivers. The algorithm for estimation is based on received-signalstrength (RSS) information collected from photo diodes and trilateration technique. By appropriately making use of the characteristics of receiver movements and the property of trilateration, estimation on three-dimensional (3-D) coordinates is attained. Filtering technique is applied to enable tracking capability of the algorithm, and a higher accuracy is reached compare to raw estimates. Gaussian mixture Sigma-point particle filter (GM-SPPF) is proposed for this 3-D system, which introduces the notion of Gaussian Mixture Model (GMM). The number of particles in the filter is reduced by approximating the probability distribution with Gaussian components.
This paper introduces an indoor positioning system based on visible light communication technology with three-dimensional positioning capability. Light-emitting diodes are employed as transmitters, with photodiodes as receivers to obtain the received signal strength (RSS) information. Based on the trilateration technique, the proposed algorithm is able to calculate horizontal coordinates of the receiver with RSS information, after which the height of the receiver is estimated. The system does not require other measurements such as time-of-arrival or angle-of-arrival, thus system design and costs are simplified and minimized. Basic framed slotted ALOHA is applied as the channel access method to enable asynchronous transmissions. In addition, Kalman and particle filters are used in order to realize target tracking. Results show that both filters help to increase the positioning accuracy and the particle filter exhibits a better performance than the Kalman filter, with a higher computational complexity.
With the fast growing and popularization of smart computing devices, there is a rise in demand for accurate and reliable indoor positioning. Recently, systems using visible light communications (VLC) technology have been considered as candidates for indoor positioning applications. A number of researchers have reported that VLC-based positioning systems could achieve position estimation accuracy in the order of centimeter. This paper proposes an Indoors navigation environment, based on visible light communications (VLC) technology. Light-emitting-diodes (LEDs), which are essentially semiconductor devices, can be easily modulated and used as transmitters within the proposed system. Positioning is realized by collecting received-signal-strength (RSS) information on the receiver side, following which least square estimation is performed to obtain the receiver position. To enable tracking of user’s trajectory and reduce the effect of wild values in raw measurements, different filters are employed. In this paper, by computer simulations we have shown that Gaussian mixture Sigma-point particle filter (GM-SPPF) outperforms other filters such as basic Kalman filter and sequential importance-resampling particle filter (SIR-PF), at a reasonable computational cost.
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