30(48)
Date
Rev
Documentnumber
Prepared
Doc respons/Approved Checked
Reference
1999-07-15 A
1531-BDV BS 101 05 Uen
INSTALLATION INSTRUCTION
Subject responsible
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 differ be-
tween 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 orders a system with 24 portable telephones and estimates that each portable generates 150 mE in av-
erage (that is 9 minutes off-hook time per portable per hour). With an accepted GOS of 2.0% the system has a traf-
fic capacity of 3,6 Erl. (0,15x24=3,6).
7.2.1 Traffic Capacity of Base Stations
A Base Station with 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 that 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 which means that 20 portables
generate together 20 x 0.150 = 3 E. Every Base Station has a traffic capacity of 2.7 Erlang. To offer sufficient cover-
age two Base Stations covering the busiest area of the company are needed.
Generally the total capacity offered by the cordless network is more than sufficient. However in certain places, traffic
demands may vary to such extent that the network is often blocked locally, or has a lower GOS than required. For in-
stance a purchase department may easily generate 300 mE per Portable during busy hour, thus, when e.g. with a
number 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 Erl. 3.2 Erl. 2.7 Erl. 2.1Erl.
circuits
IC-CU2
mErlangMinutes
per hour
503
1006
mErlangMinutes
per hour
1509
20012
mErlangMinutes
per hour
25015
30018
mErlangMinutes
per hour
50030
75045
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