Design Guide for the Alcatel
OmniPCX
Enterprise – Mobile IP Touch
3.2.
Predictive Environment Solution Options (Responding to RFx)
When answering an RFP or RFI, normally, there is little possibility of scheduling a Site Survey for various
reasons: Building under construction or not yet built, short delay to answer the RFP, fair competition clause,
etc. In these cases we can make a compromise between absolute accuracy of design and ease of offer
presentation by trying to evaluate the user environment and theorize the required quantity of Access Points. It
is essential to never forget to clearly indicate on the RFP, or unsolicited bid, that a compulsory Site Survey is
required to verify the correct quantity of AP and their related locations.
3.2.1.
Manual Calculation of Predictive Coverage
The following predictive method can be used to produce a budgetary design. Many environment variables
like wave propagation, type of building, wall structure, interferences, etc. may, unexpectedly- affect the size
quality, and complexity of the RF (Radio Frequency) coverage plan.
Figure 9 User Throughput (type of Wall) for 802.11g
In the above chart:
R=”The coverage radius provided by an AP and is used to define a perimeter or radial-footprint.”
Z=”The coverage square contained within the perimeter(R).”
A=”The area of (Z
2
) covered in square meters.”
For the following example (Drywall construction office building), use of the above defined calculation table
results in an estimated bandwidth average of roughly 18 Mbps for data 802.11g Wi-Fi traffic. We can apply
the same calculation strategy to VoWLAN simply by focusing on the performance of 802.11b at an estimated
signal strength of -65dBm (target limit for voice.)
Calculating Access Point Quantity
•
Drywall building with a theoretical bandwidth of 18 Mbps for 802.11a (-65dBm)
•
Determine Radius & Z factors: R=~11.5m Z=~16.5m Z²=~250m² (approximated with margin
of error)
•
Divide the building floor in rectangles and calculate the number of AP by dividing the area of
each rectangle by Z²:
ESD/ Central Pre Sales / DF/ JM
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June 2005 – Ed 01
