29(46)
Date
Rev
Documentnumber
Prepared
Doc respons/Approved Checked
Reference
1998-05-29 L
1531-BDV BS 101 01 Uen
INSTALLATION INSTRUCTION
Subject responsible
Practically, this table is used to calculate from a given GOS and Erlang value the number of portable users.
For the calculation it is necessary to estimate the time the portables actually make calls. The table below shows the
Erlang value depending on the estimated mean call-minutes for a portable telephone. These values may be different
between departments depending on their activities. These values multiplied by the number of portables result in a
traffic capacity that has to be provided.
Example:
A customer ordering a system with 24 portable telephones. He estimates that each portable generates 200 mE
each in average. These values require a system with a traffic capacity of 3,6 E (0,15x24). With an accepted GOS of
2.0% the traffic capacity can be met.
7.2.1 Traffic Capacity of Base Stations
A Base Station, having 8 channels available, has an Erlang value of 2.7 with a GOS of 0.5%. This means that each
Base Station can serve 18 portables, assuming each portable generates 150 mE during busy hour or 13.5 portables
generating 200 mE each.
Example:
Assuming a full coverage in a building can be achieved with 2 Base Stations means that 20 portables generate
together 20 x 0.150 = 3 E. Every Base Station has a traffic capacity of 2.7 Erlang. To have a sufficient
coverage two Base Stations covering the area of the busiest part of the company are needed.
Practically, the total capacity offered by the cordless network is generally more than sufficient, but this is from an av-
erage point of view. In certain places, traffic demands may vary such that locally the network is often blocked, or has
a lower GOS than required. For instance a purchase department may easily generate 300 mE per Portable during
busy hour, thus, when e.g. with 6 persons giving a very high load on the Base Station close by. It may be necessary
to add a Base Station in this area to have enough capacity for others to call as well. Also think of e.g. canteens during
lunch time etc.
Speech Grade of service (GOS)
2% 1% 0.5% 0.1%
1
8 3.6 3.2 2.7 2.1
circuits
IC-CU2
mErlangMinutes
per hour
503
1006
1509
20012
mErlangMinutes
per hour
25015
30018
50030
75045
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