You are outside walking and are looking for a certain shop or perhaps a friend’s house. To help you find the way you use the GPS on your phone. But when you are inside a building the GPS can’t find you. Nor if you are underground. An indoor positioning system solves this problem. It does the same thing inside as the GPS does for you outside – for people or things!
INDOOR POSITIONING IS MORE COMPLEX THAN OUTDOOR POSITIONING
So why are we used to outdoor positioning systems but not indoor? The answer is simply that indoor positioning is far more complex. Inside there are a lot of obstacles such as walls and furniture that blocks or reflects signals and creates delays. Outdoor positioning relies on line-of-sight but that is not possible indoors.
TECHNOLOGIES FOR INDOOR POSITIONING
There are several methods for finding the position used in indoor positioning used in different technologies.
WIFI: WiFi is the most commonly used technology so far. The main reason for this is the technology utilizes standard hardware and can, therefore, be deployed over existing WiFi networks. By far the most commonly used positioning method with WiFi is “fingerprinting” with RSSI (Received Signal Strength Indication) which uses the signal strength received at each tag to determine position.
The signal range of up to 30-40m for WiFi can perhaps be considered as the medium, from an indoor perspective. A clear upside is that existing WiFi infrastructure can be used, thus lowering the initial investment.
Unfortunately, there are many uncontrollable factors which greatly affect the accuracy of “fingerprinting” and it is difficult to achieve good results unless a lot of access points are used (a VoIP grade network). Generally, achievable accuracy in real-world applications varies between 8 – 15 meters. Plus with a lot of access points, there are more points of failure, and higher configuration and maintenance costs.
BLUETOOTH: Like WiFi, Bluetooth was originally not intended for positioning applications. And it still isn’t. Bluetooth solutions are about proximity (again using signal strength). To map a large indoor area you, therefore, need many nodes and complex configuration. The signals are short range (up to 15 meters) and do not penetrate walls as well. However, proximity beacons have been used to implement indoor positioning systems in the past.
The hardware is standard and cost-effective with a low energy consumption. It also has a better accuracy compared to WiFi (down to 1m) due to the shorter ranges involved and generally high beacon density.
The downside is the short range. This means you also need a large number of beacons to cover a large area, leading to complex configuration and a lot of items that can fail. Because most beacons are battery powered, the system becomes very expensive over time.
RADIO FREQUENCY IDENTIFICATION (RFID): Indoor positioning systems can also be built using passive RFID chips. The technology indexes location of tags using checkpoints. To achieve accurate positioning, either narrow passages must be used, or very expensive, time-synchronized RFID readers.
The technology is easy to use and the hardware is cheap and easy to maintain, but expensive to install due to extensive cabling requirements. The range is either very short (passive tags) or medium (active battery-powered tags) with fairly high building penetration capabilities due to the sub-GHz frequencies used.
On the downside, the passive tag technology is too short range to be really useful as a positioning system, and the long-range tags are difficult to position accurately.
ULTRA WIDEBAND (UWB): Unlike most other radio technologies, UWB was designed for positioning, and its performance is very good at shorter ranges. It is extremely accurate (sub-meter accuracy) and uses little battery power.
The downsides are very complex and sensitive antennas on the tag. Penetration through structures is poor due to the extremely high-frequency bands used – the radio energy bounces off surfaces rather than penetrating. As an indoor positioning solution, it has a niche market in applications where penetration of structures is not required.
WITTRA: The Wittra network uses sub-GHz, license-free radio frequencies. The position is derived using patented ToA (Time of Arrival) and AoA (Angle of Arrival) signal measuring methods. Requiring only a few base stations, large indoor (and outdoor!) areas are covered due to superior signal penetration and transmission range.
The system is easy and cheap to deploy. It doesn’t require complex configuration or calibration and the hardware is low cost. Signal penetration and range (up to 2,000 meters line-of-sight) keep the number of base stations low, which lowers overall cost even further. It also enables the system to position tags outside the building, with the same base stations used for indoor positioning. The coverage is thus fully indoor and outdoor.
The downside is the tag cost - the tags are slightly more expensive than WiFi or Bluetooth tags.
There are many technologies used to build indoor positioning systems, but few that give satisfying results. Solutions using sub-GHz radio frequencies seem to be the most promising due to cost, signal range and ability to penetrate structures, providing reliability in coverage. A system like Wittra is thus scalable. It provides an indoor positioning system that actually works.