Ever wondered how positioning during emergency calls is working? This article will give you all the basic information!
Everyday people around the globe use their mobile phones to contact the emergency services (police, fire department, first responders), for example the E911 in the United States, or the E112 in the European Union. The call is routed through the cellular network to the PSAP, who in turn sends the emergency responders in their way to help the person in distress. For that, the PSAP first need to obtain the location of the caller. In some cases, the caller may be able to tell his or her own location. Obviously this could be very innacurate information and cost emergency service time in tracking down the victime fast enough. However, how does positioning during emergency calls work? How can you be sure to get a location when the caller provides in-accurate information or does not know where he is.
In the European Union, with the eCall directive, cars are equipped with emergency call functionality. In case of a car accident, they can automatically dial the 112, without any interaction from the car driver. In this case, maybe the car driver is even unconscious and cannot communicate with the emergency responders. Thus, an automated way to calculate the car’s location and transmit the positioning information to the PSAP is needed. Thankfully, devices capable to perform calls through the cellular network (e.g. LTE or 5G), are also able to trigger a positioning session.
Positioning during emergency calls
So, what happens when a mobile device dials the emergency number? The PSAP, using the cellular network, triggers an emergency positioning session. The mobile phone is expected to discard all previously stored location information and start a fresh position calculation (the so-called “cold start”). This is necessary to make sure that the mobile device is not using outdated positioning data to calculate a location fix.
Imagine the caller is stranded in the mountains with bad network connectivity and the last location fix is from a couple of hours ago, when the mobile device was in a nearby town with good network coverage. In this case, without starting a fresh position calculation, the phone may send to the emergency services the latest valid position, which could be a few kilometers off. Of course, the side-effect of this is that the historical location data is also deleted in occasions where it is perfectly valid. Nonetheless, which side would you prefer to err on?
That’s also the reason why Android / iOS apps are often much faster obtaining location fixes, as pointed out in the famous Last Week Tonight video about positioning during E911 calls (clicking on the image will open embedded player).
A mobile phone app using location-based services takes full advantage of the historical location data, and can have a location fix available almost immediately. Of course, there could be a handful of cases when the historical data is not accurate, but the consequences are normally not dramatic.
On the other hand, for positioning during emergency calls, the location fix (due to the cold start) can take up to 30 seconds. 30 seconds can make a difference in emergency situations, but it’s the price to pay to avoid relaying on potentially outdated historial data. In some cases, the network can request an early fix to obtain a coarse location in a few seconds, and a more accurate one after the full 30 seconds are expired.
Positioning methods used for E911 / eCall
Ok, we have seen that during the E911 call, the cellular network has triggered a positioning session. Which technologies do the mobile phone use for calculating its location? The answer is simple: all available. Typically, the mobile phone will try to obtain a GNSS location fix, since GNSS is considered to be the most accurate positioning method. Failing to do that, it can rely on other cellular network technologies, Wi-Fi, Bluetooth or sensors.
Furthermore, the mobile phone can even override your privacy settings (e.g. can use Wi-Fi scanning, even if your Wi-Fi is deactivated) in order to obtain an emergency location fix. You have agreed to that when you accepted the terms and conditions of the OS of your mobile phone. Nonetheless, the mobile can only use that for positioning during emergency calls, which is probably a good idea. It is in your best interest that the emergency services can find you fast and without problems.
Further reading
We hope this small article has helped you understand a bit better how positioning during emergency calls is working. If you want to read more about it, you can check our book, which will be published in August 2020. There, you will find all the information about the emergency positioning regulatory requirements, the positioning methods and a lot of interesting information about cellular network positioning. Check it out!
Do check our news section for other interesting articles. If you have already read everything, be sure to come back in a few days!
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