There are a lot of different technologies that have been used effectively for indoor positioning. There are plenty more that were huge, embarrassing failures. The techniques in this article lie somewhere in between. They’ve got some pros, but no shortage of cons. Does this make them evil? No. But it does limit their effectiveness, and narrows the conditions where they can be thoughtfully implemented.
If you haven’t already, take a minute to read the previous posts in this series on indoor positioning and wayfinding in healthcare where we talked about
Many of the things discussed in those articles will be good to keep in mind as we discuss what really works with the practical application of these technologies.
We'll start with two fun but relatively flawed technologies: echolocation and infrared in this blog post and then dive deeper into another technology, geomagnetic positioning, in the next article.
So, both bats and dolphins are pretty good at this, but does it make sense for indoor location technology? Well, kind of. Less entertainingly described as ultrasonic positioning (UP), this approach has some interesting qualities.
Ultrasonic positioning leverages sound waves outside the human audible range. The core premise is to determine the Time-of-Flight between a transmitter and a receiver. Do enough of these and you can trilaterate the position of the receiving device with all the boons and banes of such an approach.
We know a lot about sound. Leveraging phenomena like the doppler effect for moving objects, or just better understanding how sound waves propagate through an environment allows for some real fancy algorithms which lead to a very precise solution. The infrastructure for UP is not insanely priced and the power consumption also isn’t anything crazy, which makes it fairly scalable. This balance of high accuracy and reasonable infrastructure make this a decent option for some use cases.
However, ultrasound is not a robust signal and is vulnerable to noise. Literal noise in this case, but it can also be disrupted or changed by various environmental conditions. While sound waves are good at bouncing around certain objects, they’re unable to pierce floors, ceilings, and walls. Combine this with the lack of suitability for infrastructure reducing techniques like fingerprinting and you’re going to be installing a lot of hardware. Last, and maybe least, while the tech needed to facilitate such a solution (speaker, microphone) are common in consumer devices, there’s a bit of a creep factor to having your phone constantly listening while you walk around.
In all, ultrasonic has some high potential with accuracy, but it’s a bit too delicate for dedicated use.
An old standby on the consumer technology front, infrared (IR) signal technology powers TV remotes, video game controllers, thermometers, and even virtual reality positioning systems. IR cameras are common for security to detect warm bodies, and thermal imaging in general can be quite useful to determine what’s hot or not. IR has also been used for indoor positioning systems, which is why we’re talking about it here.
Similar to ultrasonic, IR positioning relies on measuring the distance between an emitter up on a wall or ceiling and an IR sensor on the device you’re looking to track. Or reverse that depending on your approach. What’s important is that either the emitter or the sensor has its location known by whatever is doing the distance calculation.
Infrared is also capable of transmitting data with the signal, like when you select a channel with your TV remote. This can help with the configuration and calibration of a system, since it’s very important the receiver knows which emitter sent a signal.
Given its extensive proliferation, IR devices are cheap, plentiful, and reliable. Like ultrasonic, the level of accuracy under optimal conditions is quite good. IR is unaffected by activity in the RF spectrum, so can be a good solution if it’s a noisy space with a lot of wifi or bluetooth signals bouncing about.
It does require line of sight between sensors and emitters which can be very easily blocked. This rules out areas crowded with people, since the human body puts out some heat. In practice, many emitters will need to be placed in order to ensure redundancy, and they’ll need to be thoughtfully positioned. IR range is not very impressive, which also adds to the number of devices needed. Intense light, such as sunlight, can also interfere with the transmission, limiting the use to inside. IR cameras are not super common on phones either, which limits consumer positioning for use cases like wayfinding.
That said, IR could still be an ok solution for locations like warehouses, where the environment is highly structured and predictable, leading to an optimal layout for intentional positioning.
All in all, neither infrared or echilocation/ultrasound are the best candidates for complex indoor positioning and wayfinding in a healthcare setting where there is a lot of potential noise and other blockers. Watch for our next post in this series where we discuss the pros and cons of geomagnetic positioning.