## Pinpointing Cell Phone Users using Emergency9

Expected Accuracy of Triangulation.

In urban areas the accuracy can be down to 50 meters.  Accuracy can vary between 25-100 meters.

In rural areas, coverage of the cell tower can vary from about a quarter of a kilometer to several kilometers depending upon how many obstacles could be blocking the tower’s signal.

There are two methods for pinpointing the location of cell phone users.

1. The less-accurate method is often called “Cell Tower Triangulation”, referring to how the cell towers which receive a phone’s signal is used to calculate its geophysical location - this is what E9 currently uses.
2. The second, and more accurate is Global Positioning System (GPS), which uses signals from satellites to pinpoint location very accurately - next generation E9 solution.

According to some industry research estimates, only about 11% of phones manufactured have the GPS capability, so the remaining 89% of phones without GPS would have to depend upon “Cell Tower Triangulation” in order to disclose geolocation data for applications.

Just what is Cell Tower Triangulation?

In a best-case-scenario, a cell phone’s signal may be picked up by three or more cell towers, enabling the “triangulation” to work. From a geometric/mathematical standpoint, if you have the distance to an item from each of three distinct points, you can compute the approximate location of that cell phone in relation to the three reference points. This geometric calculation applies in the case of cell phones, since we know the locations of the cell towers which receive the phone’s signal, and we can estimate the distance of the phone from each of those antennae towers. The distance is based upon the lag time between when the tower sends a ping to the phone and receives the answering ping back.

The cell phone is detected within a certain radius of 3 cell towers - that is the area where each cell tower circles overlap, see above.

In many cases, there may actually be more than three cell towers receiving a phone’s signal, allowing for even greater degrees of accuracy. In densely developed, urban areas, the accuracy of cell phone pinpointing is considered to be very high because there are typically more cell towers with their signal coverage areas overlapping. In cases where a cell user is inside large structures or underground, cell tower triangulation may be the only location pinpointing method since GPS signal may not be available.

For many cell tower networks, the pinpointing accuracy may be even greater, since directional antennae may be used on the tower, and thus the direction of the cell phone’s signal might be identifiable. With the signal direction plus the distance of the phone from the cell tower, accuracy might be pretty good, even with only two towers.

However, there are many places where there are fewer cell towers available, such as in the fringes of the cities and out in the country. If you have fewer than three cell towers available, pinpointing a mobile device can become a lot less precise. In cities where there are a lot more vertical structures which can be barriers to cell phone broadcasting and receiving, there have to be many more cell towers distributed in order to have good service. In the countryside, there are relatively fewer cell towers and a phone’s signal may be picked up only by a single one at much greater distance.

Those areas where a phone is only getting picked up by a single tower, and if it’s equipped with only omnidirectional antennae, the accuracy becomes even less.

Interestingly, Google’s Maps for mobile with My Location apparently is not using any form of calculated triangulation at all — they’re strictly using only a single cell tower. Google displays a vague circle area representing the zone covered by the primary cell tower that’s in contact with the phone. Rural areas with fewer cell towers display larger locational circles while the urban areas show much smaller areas.

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