Using LED visible light communication to improve indoor positioning accuracy

Throughout history, people have always worried about getting lost. Early explorers used stars to navigate, and specialized instruments were later developed to help them pinpoint their exact location on Earth's surface. Today, people use electronic positioning technologies such as the Global Positioning System (GPS) to navigate their daily travels. While this technology is great for outdoor applications, it has significant limitations when used indoors. In this article, we explore the benefits of accurately locating people within a building and discuss the applicability of different techniques to indoor positioning systems (IPS). We then explain the concept of visible light communication (VLC) and show how this technique can be used to meet the accuracy requirements for indoor positioning.

Indoor location tracking

Shopping malls, airports, large business parks, and health care facilities often host large numbers of people, and the ability to understand where, when, and how people are moving in real-time presents numerous opportunities for companies managing these buildings. The indoor location tracking benefits offered by IPS mean that the technology is fast becoming a must-have solution for large indoor venues, enabling smarter, more optimized environments and enhancing the overall visitor experience. For example, in a busy retail store, knowing where customers are staying can be of great benefit when strategizing product placement. Customer targeting information can also be used to optimize store design, making shopper traffic more efficient. In an office environment, IPS can save time by guiding visitors to meeting rooms smoothly. In hospitals, it can help save lives by providing real-time information about emergency hospital admissions, allowing more space for patient care and enabling hospital management to ensure adequate staffing is available to respond to impending needs. Indoor location tracking can also improve the management and safety of people and assets. For example, it can provide instant information on the location of important equipment (laptops, tablets, or other connected devices) in a building and be used to trigger alerts when high-value assets are shipped out without authorization. Similarly, it can be used for access control to restrict individuals from entering certain areas within a building, depending on their authorization level. It can also be used to dynamically alert people to the location of the nearest fire escape route as they move around a building, and guide them to safety using the quickest route in the event of a fire. While the benefits of these real-time ap`plications are obvious, the data collected by indoor location tracking systems is just as valuable, if not more valuable, in the long run. By gathering information on the movement of large numbers of people over time, it is possible to create dynamic maps of how different areas of a building are used and over time to better understand seasonal foot traffic patterns. This information may also be used to provide location-based services and marketing.

visible light communication

GPS is the most widely used positioning technology in the world, but it is ineffective or inaccurate in indoor spaces. This is because radio frequency (RF) signals transmitted from satellites are blocked by indoor obstacles such as walls or ceilings of buildings. This shortcoming of GPS has led the industry to adopt other techniques for indoor location tracking, with varying degrees of success. IPS typically consists of two distinct elements - beacons and tags, where beacons are placed at different points in the building, and tags are carried by individuals or placed on objects that are being tracked by location. Some technologies used for location tracking include:

Inertial Measurement Units: These units use multiple sensors such as accelerometers, magnetometers, and gyroscopes to provide information about the relative movement of the tags. An advantage of this technique is that it does not require the use of beacons, but the overall accuracy is poor (a few meters) because position errors accumulate rapidly over time.

Ultrasonics: They use sound as a communication medium, operate on time-of-flight (the time it takes for sound to travel from a beacon to a tag, and vice versa), and can resolve position to less than 1 meter, but suffer from interference from solid objects. This means that measurements are not always reliable.

Other RF technologies: The widespread availability of Bluetooth and Wi-Fi makes them well suited for use with IPS, but the main difficulty is that these signals behave very differently in the presence of obstacles and people walking around (due to reflections and multipath propagation). Ultra-Wideband (UWB) can penetrate materials such as concrete, glass, and wood, making it suitable for in-building applications (where the beacon's line of sight is often obstructed as the tag moves around), but this technology not yet widely used, and the power levels of some signal frequencies are limited by regulations on the use of the radio spectrum.

The methods mentioned above have certain limitations in usage and accuracy, meaning they are not ideal for IPS applications, while visible light communication (VLC) is emerging as a very promising solution to the accuracy problem. Visible light is the part of the electromagnetic spectrum (375-780nm) that the human eye can perceive, and VLC uses this bandwidth to wirelessly transmit data while illuminating indoor spaces. In a VLC system, a microcontroller modulates data onto an LED (beacon), which is received by a photodiode in a tag (eg, a phone's front-facing camera). Using light as a medium to transmit data requires little extra power than LED lighting requires, and installation costs are low because lighting is already present in almost all interior spaces. While the modulated data inevitably causes the LEDs to flicker at frequencies that are imperceptible to the human eye, they are easily detected by the receiving device. By embedding a unique identifier in each LED and modulating it onto the LED driver, each light fixture (often called a light source) within a building can transmit a unique code related to its exact location. Using the identifiers received from the three luminaires, a triangulation algorithm can determine the location of the tag with an accuracy of 30 centimeters - an order of magnitude better than the best performing radio frequency-based positioning systems.