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GSM / GPRS Calculations

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• #35065
Daniel betelu
Guest

I am making an “air interface” calculation for a GSM/GPRS cellular network
with the following conditions:

* Both busy hours are the same (VOICE Busy Hour + GPRS DATA Busy Hour)
* There is a city with 0.025 Erl per subscriber
* There is 5500 subscribers in that city. All of them talked during the
VOICE Busy Hour.
* Some of them are sending data simultaneously, so take 3 TCH free per
sector for GPRS DATA. Use sites with 3 sectors.

If it is used a cell with a configuration of 8/8/8 (3 sectors with 8
carriers each), this cell can handle 151,8 Erl (50,6 Erl each sector –
considering 59 lines with a GoS of 3%). My questions are:
* Is it enough one cell with 8/8/8?
* 5500 x 0.025 = 137.5 Erl, but how can I transform 3 TCH in Erl?
* If it takes 3 TCH off, how much Erl can handle the cell? Maybe I have to
consider 56 lines with a GoS of 3% that is equal to 47.7?
* What if I take 4 TCH free per sector for GPRS DATA? Still is it possible
to be complied?

Daniel Betelu
Cellular System Engineer

#35066
Mike Hartley
Guest

* Is it enough one cell with 8/8/8?

In theory yes- you already worked out the site’s capacity correctly. In practice probably not, since this assumes that you have the site in the centre of an ‘ideal’ flat, circular city with uniform traffic density. You are far more likely to find that traffic is concentrated on one or two sectors, and that the topography may mean you need more than one site to provide coverage.

* 5500 x 0.025 = 137.5 Erl, but how can I transform 3 TCH in Erl?
Easiest way is to treat the 3TCH you want to be available as either 3E more traffic or 3 less TCH for circuit switched- this depenmds on whether or not you plan to dedicate the channels for GPRS.

* If it takes 3 TCH off, how much Erl can handle the cell? Maybe I have to
consider 56 lines with a GoS of 3% that is equal to 47.7?
See above.

* What if I take 4 TCH free per sector for GPRS DATA? Still is it possible
to be complied?
See above.

#35067
emmanuel offiong
Guest

how to convert erlang traffic to cash

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