I’ve been meaning to this post for a while – it’s inspried by a similar analysis of Vodafone coverage in Germany via WirelessMoves. Note, I’m definitely not an expert when it comes to carrier infrastructure especially since I’ve spent my whole career on the software side of the mobile biz :)

Anyways, I recently read that it’s estimated that ATT has approximately 50K cell sites in the US. I’m not sure what’s the split between GSM and UMTS base-stations but from a subscriber standpoint, I have read that approximately 30% of US subscribers are 3G subscribers meaning they have a 3G handset and are connected over 3G. In any case, let’s do some simple math assuming all 80M ATT subscribers were connected over the 50K cell sites. This means each cell site is serving 80M / 50K = 1600 customers. Base stations are usually split into three sectors meaning each sector covers 1600 / 3 = 533 customers. Now, the average ATT subscriber uses 760 voice minutes each month so now multiply 766 min * 533 customers and you have 408,278 voice minutes per sector. Now obviously, most of the calls are within a certain set of hours each day, I will assume 16 so you then have 408,278 minutes / 30 days / 16 hours = 850 minutes per sector per hour. A sector is typically equipped with 2-3 transcievers which can each server between 6 and 8 voice calls meaning the potential maximum would be 60 minutes * 3 transceivers * 8 voice calls = 1440 minutes per sector per hour – I have no idea if that is reasonable or not :)

Lots of assumptions here and I’d love to get some more accurate data. It’d be interesting to look at data consumption per sector and see if we are really under-capacity. Obviously, it’s not as simple as 50K cell sites since there is quite a bit of tower leasing meaning only partial capacity as well as a significant number of subscribers being prepaid and/or part of an ATT MVNO (ie Tracfone estimated at 14M prepaid subscribers). We also assuming an even distribution across the country which definitely doesn’t hold, you’d expect a higher density within urban centers.

In any case, interesting as it is – let me know if you have better data.

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