An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> A VLC (Visible Light Communication) system using fluorescent lights has been developed for indoor guidance of the visually impaired. While it is relatively straightforward to provide generalized location information for a blind user, precise location information is much more difficult to determine. We propose that the effective data reception range and the receiver's precise location can be calculated using measured sensor angles. A series of experiments have been performed in a practical platform with 22 fluorescent lights, 39 measuring points (MP). The average distance error could reach as low as 10 cm. This development will provide greater accuracy and therefore less stress for blind users. <s> BIB001 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> We report about a Line of Sight Optical Wireless Communication (LoS OWC) system aided by a simplified Visible Light localization algorithm for tracking purposes. We show experimentally that by combining the LoS OWC system with the localization algorithm it is possible to provide a gross data-rate exceeding 300 Mb/s over a 90° illumination angle by using a RGB visible-light LED at 90cm distance. <s> BIB002 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> An LED based 2-D indoor localization system is proposed. For evaluation purpose we also present computer simulations results that show for a normal room size, we can locate a target to within centimeters. <s> BIB003 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> LEDs (Light Emitting Diodes) are considered by many researcher to represent the next-generation lighting technology. Furthermore indoor LED lighting has a potential to converge with IT technology such as Visible Light Communication (VLC) based Location Awareness. In this paper, we suggest Angle of Arrival (AOA) estimation algorithm under VLC environment in order to find out the location of a light source (LED) using circular-PD-array. We propose truncated-weighting method in order to enhance the accuracy of estimated AOA. Through simulations, we confirm that the number of PDs in circular-PD-array affects the AOA estimation error performance of a light source. In addition, our proposed truncated-weighting scheme shows better AOA estimation performance than those of simple average and Maxs chemes. Based on AOA algorithms, we also investigate the performance indoor location estimation. As a consequence, we can final that our truncated scheme also shows better location awareness performance than other conventional ones. <s> BIB004 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> We propose optical wireless indoor localization using light emitting diodes (LEDs). In the proposed method, four LED lamps for illumination are employed and strength ratio between received LED light signals is utilized for location estimation. <s> BIB005 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> Indoor positioning has attracted a lot of attention in the literature. Positioning systems using the existing wireless network have low deployment cost but the position error can be up to several meters. Some proposed systems have low position error; however, they require extra hardware, thereby resulting in high deployment costs. In this work, we propose a positioning system that offers low position error at a low deployment cost. The proposed system uses visible light communications (VLC) together with the accelerometers in mobile devices. In contrast to existing works on VLC for positioning, our system neither requires the knowledge of the height of the receiver from the ground, nor does it require the receiver to be oriented such that the angle of irradiance of a transmitter equals the incidence angle at the receiver. The proposed system has low complexity, and simulation results show that it achieves position errors of less than 0.5 meter. <s> BIB006 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> We propose and demonstrate an indoor location awareness method for an autonomous robot vehicle using light-emitting diodes (LEDs). The location is estimated by measuring received signal strength ratio (RSSR), which is the relative ratio of optical powers detected between each LED and optical receiver. In this method, multiple LED lamps on the indoor ceiling are used, which can radiate light only during the individual time slot assigned to each of them. Using the RSSRs, circle or straight line equations are obtained and the crossing point among those equations determines the location of the object. In the experiment, four LED lamps are iden- tified by time-division multiplexing with room dimensions of 1.0 × 1.0 × 1.3 m 3 , and the results show that the mean of the location error is 3.24 cm in the entire floor area. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including <s> BIB007 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> Indoor positioning has become an attractive research topic within the past two decades. However, no satisfying solution has been found with consideration of both accuracy and system complexity. Recently, research on visible light communications (VLC) offer new opportunities in realizing accurate indoor positioning with relatively simple system configuration. An indoor positioning system based on VLC technology is intro- duced, with no synchronization requirement on the transmitters. Simulation results show that, with over 95% confidence, the target receiver can be located with an accuracy of 5.9 cm, assuming indirect sunlight exposure and proper installation of light-emitting diode bulbs. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/ 1.OE.53.4.045105) <s> BIB008 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> Indoor positioning system is a critical part in location-based services. Highly precise positioning systems can support different mobile applications in future wireless systems. Positioning systems using existing wireless networks have low deployment costs, but the position error can be up to several meters. While there are positioning systems proposed in the literature that have low position error, they require extra hardware and are therefore costly to deploy. In this paper, we propose an indoor positioning system based on visible light communications (VLC). In contrast to existing works on VLC for positioning, our system estimates the location of the receiver in three dimensions even without: 1) the knowledge of the height of the receiver from ground; and 2) requiring the alignment of the receiver’s normal with the LED’s normal. Our system has low installation cost as it uses existing lighting sources as transmitters. Light sensor and accelerometer, which can be found in most smartphones, are used at the receiver’s side. They are used to measure the received light intensity and the orientation of the smartphone. A low-complexity algorithm is then used to find out the receiver’s position. Our system does not require the knowledge of the LED transmitters’ physical parameters. Experimental results show that our system achieves average position errors of less than 0.25 m. <s> BIB009 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> Visible light LEDs, due to their numerous advantages, are expected to become the dominant indoor lighting technology. These lights can also be switched ON/OFF at high frequency, enabling their additional use for wireless communication and indoor positioning. In this article, visible LED light--based indoor positioning systems are surveyed and classified into two broad categories based on the receiver structure. The basic principle and architecture of each design category, along with various position computation algorithms, are discussed and compared. Finally, several new research, implementation, commercialization, and standardization challenges are identified and highlighted for this relatively novel and interesting indoor localization technology. <s> BIB010 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> An optical wireless location (OWL) system is introduced for indoor positioning. The OWL system makes use of a mobile photoreceiver that facilitates triangulation by measuring angle-of-arrival (AOA) bearings from LEDs in an optical beacon grid. The photoreceiver has three photodiodes (PDs), arranged in a corner-cube, to facilitate differential photocurrent sensing of the incident light AOA, by way of azimuthal ϕ and polar θ angles. The AOA error for indoor positioning is characterized empirically. Optical AOA positioning is shown to have a fundamental advantage over known optical received signal strength (RSS) positioning, as AOA estimation is insensitive to power and alignment imbalances of the optical beacon grid. The OWL system is built, and a performance comparison is carried out between optical AOA and RSS positioning. It is shown that optical AOA positioning can achieve a mean 3-D positioning error of only 5 cm. Experimental design and future prospects of optical AOA positioning are discussed. <s> BIB011 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Received Signal Strength Ratio and Received Signal Strength Difference <s> An indoor positioning system is a key component in enabling location-based services in future wireless networks. The need for a highly accurate indoor positioning system is rapidly increasing. In the past couple of years, several positioning systems based on visible light communications that achieve good positioning accuracy have been proposed. Some of these systems are based on assumptions such as complete knowledge of the height of the receiver, and exact alignment of the transmitter and receiver normals to the normal of the ceiling. Some other systems do not support user mobility because they require a user to vary the receiver orientation at a fixed location. Another common assumption is that the transmitters are at the same height from the ground. In order to support user mobility, this paper proposes a novel positioning system using multiple optical receivers that provides coordinates and an orientation of the mobile receiver. The remarkable features of the system are as follows: 1) the receiver can be mobile; 2) the positioning is done within 2.5 ms in our experimental setup; 3) the heights of the transmitters need not be the same; 4) the receiver's height need not be known; and 5) the receiver's normal need not be aligned with those of the transmitters. Experimental results show that mean position errors of less than 0.06 m is achievable even when the average receiver speed is 1.3 m/s. <s> BIB012
Instead of directly translating the received power to the distance, the received signal strength ratio (RSSR) technique translates the ratio of the received power from multiple base stations to the ratio of distance and determines the position based on the distance ratio. The advantage of RSSR compared to RSS is that the ratio of received power would cancel the error caused by the non-zero irradiance angle of the light. Therefore, the ratio of received power can be translated into the distance ratio with less error than the distance directly translated from the power, thus achieving higher accuracy. The limitation of this technique is that the surface of the receiver must be parallel to the LED, which would be impractical for some applications. RSSR indoor positioning systems based VLC were proposed in BIB005  BIB007 . In the proposed systems, the receiver was assumed to be parallel to the LED and thus the incidence angle and the irradiance angle are equal. Also, the incidence angle was assumed to be smaller than the FOV at all measured points. Recalling Figure 8 and Equation (13), the received power in this case can be rewritten as: Where K is a value independent of the receiver position. From Equation BIB010 , the distance ratio can be calculated easily from the RSSR: Supposing that (x 1 , y 1 , h) and (x 2 , y 2 , h) are the coordinates of the two LED base stations, the following equation is given: Therefore, given an RSSR, a circle or a perpendicular bisector (in case is defined. The position of the receiver then is determined as the intersection of these circles of bisectors. In BIB005  BIB007 , time division multiplexing was used to distinguish signals from different LEDs. The experiment was conducted in an area measuring 1 × 1 m 2 and distance error ranging from 3.89 to 1.68 cm were reported. Another derivation of RSS is the received signal strength difference technique, which was proposed in BIB003 BIB008 . The distance was not derived directly from the received power but from the difference in the received power between logical 0s and 1s. The IDs of base stations were transmitted to the receiver through visible LED light modulated in OOK format. To lessen the demand of perfect synchronization between base stations, the framed slotted ALOHA (FSA) protocol was used for the LED base stations to transmit their IDs without collisions. The difference in the received power of the logical 0 and 1 was calculated and translated to the distance using a proposed model. After that, the linear least square method was used to solve trilateration equations to obtain the position. The simulation reported a distance error of 11 cm (no direct sunlight exposure assumed) and 17 cm (direct sunlight exposure assumed) in an area measuring 6 m × 6 m, achieved by this method. 3.3.5. Angle of Arrival-AoA AOA algorithms base on the estimated angles of arrival of signals from multiple LEDs to determine the position of the mobile device. The mechanism of AOA is described in Figure 9 . After obtaining the angle of arrival, the position of the mobile device is determined as the intersection of multiple bearings. Usually, to obtain the angle of arrival, a PD array can be used. Since the light radiated from a LED follows the Lambert cosine law, the changes in the angle of arrival will lead to changes in the received power at predictable manners. Therefore, the angle of the light can be inferred from the difference between the received power at a known angle and the received power at the current angle. In BIB004 , a circular PD array was used to estimate the AOA. This PD array is illustrated in Figure 10 . As expressed by Equation (13), the light signal power received by each PD in the PD array is affected by the distance d, radiance angle φ, and the incidence angle ψ. The distance d and the radiance angle φ can be assumed to be the same for all PDs since the size of the PD is very small compared to the distance. Therefore, the received power is determined only by the incidence angle ψ, which is different at each PD due to the circular placement as shown in Figure 10 . The irradiance angle of the light was determined using a proposed truncated-weighting algorithm, which is a weighted sum of angles of PDs in the PD array. The weight for each PD angle was determined by comparing the received power at different PDs. The simulation result showed that the distance error ranged from 5 to 30 cm. Using an accelerometer, BIB006 BIB009 could determine the AOA with only one PD. To do that, the PD was rotated to different orientations and the received power corresponding to these orientations was measure. Note that the position of PD must be the same while being rotated. By using an accelerometer, the orientation of the PD is always known. For each LED base station, two measurements corresponding to two orientations of the PD were made. Based on the two received powers measured at two orientations, the irradiance of the light was obtained. The locations of the LED base stations were transmitted through the VLC signal. Multiple signals were separated using TDM. After three irradiance angles corresponding to three LEDs were obtained, the position of the mobile device was determined. The simulation showed that the average position error was less than 25 cm, given that the receiver is static. A subsequent paper BIB012 improved upon the work of BIB006 BIB009 by using multiple tilted PDs combined with an accelerometer to estimate the AOA without the need for rotating the mobile device. The AOA estimation can be performed faster and thus user mobility is supported in this system. To improve the accuracy, a power correction method was proposed to mitigate the error which is caused by the non-zero distances between multiple PDs. The experiment was conducted with three LEDs mounted on the ceiling and 4 PDs grouped into a pyramid structure. The TDM was used to separate the signals from multiple LEDs. The result showed that the mean position error was less than 6 cm even when the receiver moved at the average speed of 1.3 m/s. One of the first studies on VLC based positioning BIB001 did not use LEDs, but fluorescent lights to determine the position. A single PD was used to estimate the vertical and horizontal angles between the PD and the fluorescent lamps. This was possible since the angle of view of the PD is small, 10 • . Therefore, when the PD was directed toward the fluorescent lamps, by considering the height of the ceiling where the lamps were installed and the size of the lamps, the angles and the position of the receiver could be estimated. The experiment was conducted in a wide area with 22 fluorescent lights and an average distance error of tens of cm was reported. A more sophisticated method for estimating the AOA was presented in BIB011 . A group of three orthogonal PDs was used to receive light signals from multiple LED base stations. The signals were modulated with distinct frequency channels, between 2 kHz and 3 kHz, so that they can be separated in the mixed received signal. Since the angles of the PDs are different, they were preferentially sensitive to light incident along different directions. The difference in the received power at these PDs was expressed as functions of the PD angles and light incidence angles. These functions were difficult to solve algebraically since they were piecewise. However, least-angle regression could be used to solve these equations to obtain the incident angle. Simulation results showed that the positioning error of this method was 5 cm. Then BIB002 presented a realistic application for VLC based positioning with which the position information was used to align the VLC transmitter and receiver to achieve higher communication SNR. In this system, a single PD was used to obtain AOA information. The PD was assumed to be perpendicular to the floor, which meant that the irradiance and incidence angles were equal. Then the received power at a certain position was expressed as a function of the maximum received power and the irradiance angle. The multiple reflections were also taken into account by adding a path loss exponent to the equation for the received power. The maximum received power of an LED base station was measured beforehand and assumed to be known by the receiver. Therefore, the irradiance angle of an LED can be determined from the received power. The signals from multiple LED base stations were separated by using OFDM. Upon receiving signals from three or more LED base stations, the position can be determined.