Here are some interesting stats from Vodafone they have published earlier this year on the number of base stations they have in Germany. In the press release they mention that they have more than 20.000 GSM base station covering 99% of the population and 13.000 UMTS base stations covering 80% of the population.
Taking into account their current customer base (or more precise the number of SIM ards) of around 34 million let’s do some maths with the numbers:
For GSM: 34 million customers divided by 20.000 base stations means that each base station on average serves around 1700 customers. Most base stations have three sectors, so each sector covers on average 1700 / 3 = 566 customers.
Number of voice minutes on average per user per month: 111 minutes. So each sector of a base station would on average serve 111 minutes per month * 566 customers = 62900 voice minutes. To count in effects such as busy hour, let’s say those minutes are handled in 15 hours (a gross simplification…) of the day. 62900 / 30 days / 15 hours = 139 voice minutes per sector per hour. Given that most sectors are equipped with 2-3 Transceivers which can each serve between 6 and 8 voice calls would result in more than enough average capacity and still leave ample room for GPRS/EDGE services. Actually, I think the number looks rather low compared to what should be possible. Not sure why that is…
Note that in big cities, the base stations are probably much higher loaded due to the higher population density. That’s easily missed when working with averages.
Concerning the UMTS numbers, it’s a bit difficult to make meaningful similar calculations here. Vodafone says they have 5+ million UMTS customers. That probably means they have that many customers with a 3G phone. However, it says nothing about how many people have locked their phone to 2G for various reasons and also gives no indication on how many people use data intensive 3G Internet access. So I'll leave those numbers as they are for the moment.
BS are planned to support busy hours so, averaging wouldn’t let you have a clear picture of the network configuration. Most minutes per month/user are consumed during the busy hour. If you assume that 50% of the monthly traffic is consumed during busy hours then the per-sector requirement will raise to a more logical number.
Maybe 139 minutes per sector seems low because… a more common rule-of-thumb reckons a busy hour contains 1/250 of the month’s traffic. Also Vodafone might be counting sectors (not sites) as the ’20K base stations’ – so it would be 1700 * 111 / 250 = 755 minutes of calls in the busy hour, or about 12.5 calls in progress at a time. Then 2-3 transceivers is just enough capacity to avoid blocking new calls… which is to be expected after a decade of adding in-fill sites whenever any sector gets too busy.
City sectors would have more capacity, but mainly they are closer together.
Hi Chris,
The 1/250 of traffic for a busy hour is interesting. I’ve had a look if they could mean sectors instead of base stations but I think the 20k number is really base stations and not sectors for two reasons:
-The press release in German says “base station” and not sectors.
-A press release from Ericsson from some years ago states that they will replace 10.000 of T-Mobile’s old GSM base stations with new equipment which at the time was about half of T-Mobile’s installed base. Here again, base stations instead of sectors are used. Here’s the link: http://www.ericsson.com/ericsson/press/releases/20050117-976111.shtml
-If you divide the size of Germany (in km2) by the number of base stations to see how much territory each base station covers a total count of 20.000 seems more realistic than just a third of that.
No final proof here but very strong evidence 🙂
If I use the 1/250 rule with the 20.000 base stations it would amount to 251 voice minutes in the busy hour. Still a bit low so the mystery remains for the moment.
Cheers,
Martin
Update: Another suggestion I received was that the minutes quoted are actually only outgoing minutes which the subscriber pays for. The number doesn’t take into account the incoming minutes. Depending on where the outgoing calls terminate (fixed or mobile) and how many fixed calls are terminated on mobile the total number of voice minutes per user (paid and incoming) could be much higher, maybe double the number used in the calculations above. This would result in twice the utilization and would be much more realistic.