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GSMRULES

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.

David Boettger

Perhaps you could have started with 80% of the subscribers (27.2M subs) on 13k sites, yielding ~700 subscribers per cell (sector). Rather than 111 minutes/month, we can assume ~50 milliErlangs per sub during the busy hour, or about 35 Erlangs per cell. With a 3/9 frequency plan in 10 MHz, there are 5-6 frequencies available per cell, which could support 6 + 4or5x8 = 38to46 simultaneous calls (EFR codec, no FH). It would seem that Voda could handle the traffic in the 900 MHz band alone. And then there's probably another 10 MHz at 1800 MHz plus the half-rate codec plus FH. They've got lots of room (on average).

Chris Horton

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.

Martin

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

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.

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