An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Time of Arrival-TOA <s> Wireless indoor positioning systems have become very popular in recent years. These systems have been successfully used in many applications such as asset tracking and inventory management. This paper provides an overview of the existing wireless indoor positioning solutions and attempts to classify different techniques and systems. Three typical location estimation schemes of triangulation, scene analysis, and proximity are analyzed. We also discuss location fingerprinting in detail since it is used in most current system or solutions. We then examine a set of properties by which location systems are evaluated, and apply this evaluation method to survey a number of existing systems. Comprehensive performance comparisons including accuracy, precision, complexity, scalability, robustness, and cost are presented. <s> BIB001 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Time of Arrival-TOA <s> 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. <s> BIB002
TOA, which is the basis of the GPS system, calculates the distances between LEDs and mobile devices from the arrival time of signals and then uses these estimated distances to derive the position of the mobile device. For visible light, the distance is calculated by directly multiplying the propagation delay of the signal by the speed of light. To estimate a 2-D location, distances to at least three base stations must be obtained. In Figure 5 , R 1 , R 2 , and R 3 are the distances to three base stations A, B, and C. The position of the mobile device is determined as the intersection of the three circles with radii of R 1 , R 2 , and R 3 and centers at A, B, and C. In practice, the position of the mobile device can be determined using least-squares algorithm. Suppose that (x, y) is the coordinate of the mobile device, (x 1 , y 1 ), (x 2 , y 2 ), ..., (x n , y n ) are the coordinates of n base stations, and ∆t 1 , ∆t 2 , ..., ∆t n are the measured propagation delays of light signals from n base stations. The values of x and y are chosen to minimize the cost function BIB001 : where the residual r 2 i (x, y) is given as: where c is the speed of light. In BIB002 , the accuracy of a VLC based positioning system using TOA was analyzed. Orthogonal frequency division multiplexing (OFDM) was used to separate the signals from the different LEDs. The LEDs and the PD receiver were assumed to be perfectly synchronized to a common clock. The theoretical limits on the estimation accuracy calculated by using the Cramer-Rao bound showed that the error ranged from 2 to 6 cm.