Q&A: Cell Tower Capacity
Dear Mark van der Hoek:
Q. Do you know how much capacity cell towers have? I'm on our local school board for a small rural district of about 2,000 students. There was discussion last night about in case of an emergency the students should not be able to use their cell phones because it would overload the cell towers and interfere with emergency personnel.
A. I can't give you an absolute answer because there are numerous variables. Perhaps the biggest is, how many cellular companies (carriers) provide service to your location? Obviously, the more the merrier as far as capacity. Assuming they have a fairly equal market share, of course.
However, the rural nature of your location and your (relatively) small population make it safe to make a few assumptions. It's not likely that any cellular carrier is going to serve your town with more than one, or at the MOST, two cell sites. Then, assuming you have, let's say, 5 wireless providers, that gives us a MAXIMUM of 10 sites to serve your town. Of course, that will be 5 sites that are likely to be dominant at the school, with 5 sites that could possibly take some overload. Realistically, it's probably 5 sites period, and those sites are probably going to be a mix of single and three sectored sites. Let's be generous and assume that 3 of the 5 carriers have three sectored sites, and all three are configured such that 2 of their 3 sectors are able to serve the school. That gives us (2*1) + (3*2) = 8 sectors to provide service at your school. Given that a single sector can carry anywhere from 7 (GSM) to 20-something (CDMA) calls at one time, that gives a capacity at your school of somewhere between (7*8 = 56) and (25*8 = 200) calls at one time.
While this is very much a "back of the napkin" exercise, oversimplified and with a lot of room for error, I do think your concern is well founded. I've probably been overly generous with the number of carriers and sites, and of course, if you have fewer carriers and fewer sites, the picture is even worse.
The sad thing is that even back in the analog days, we had the technology to deal with this. The engineers at Bell Labs who developed the technology foresaw this kind of thing, and built in a mechanism to prioritize traffic. Each phone was to be assigned an "Access Overload Class", and phones owned by bona fide emergency agencies would have a special ACCOC assigned. In an emergency, the cellular operator would simply deny channels to everyone BUT the emergency personnel. However, the FCC in a mistaken egalitarian zeal, decreed that such discrimination was unfair, and could not be implemented. So, a good idea died at the hands of a bureaucracy. The technology is STILL there, but cannot be used.
Mark van der Hoek
Front Royal, Virginia