Access Point Placement – Part 1

Designing a Wireless network is not just engineering and configuring hardware, but I feel there is lots of creativity and art that is involved in it. That is why if you are studying for a CWDP or reading any Wi-Fi Design best practices white paper, blog etc you will find that walking the site is always encouraged. While onsite it is very imperative to gather as much information as possible, but in this post I’m going to just discuss something that I feel gets overlooked at times, “Access Point Placement”. Over the years of doing site surveys in multiple buildings and working on so many predictive models etc I believe access point placement is a very important factor when designing a good wireless. And for that having good understanding of few things mentioned below is important (Note: Depending on the experience of all the other engineers working in different industries and verticals I’m certain more can be added to this list and discussed, these are just a few):

  • Antenna radiation patterns
  • Building construction, walls, windows etc
  • FSPL (Free Space Path Loss)
  • Access point mounting restrictions/challenges
  • User density (I’m talking the physical bodies)
  • User orientation

I remember one day at work I received a phone call from an internal customer asking me the following, “Is there any science to put these AP’s up or can I just throw them up in the ceiling anywhere since we will be moving things around”. For a few seconds I was speechless. Anyways, point being this is something that get over looked at times for multiple reasons (which aren’t really a topic of discussion here so I won’t get into them).

I really encourage all new wireless engineers or if someone who hasn’t already read and study CWNP material, CWNA and CWDP has some good information in there. If you can find the older CWDP book study that. For CWNA book written by David A. Westcott and David D. Coleman is excellent. Additionally studying antenna radiation pattern from manufacturer website as well as other sources is invaluable. I also encourage everyone to read the following article by Nigel Bowden on Wi-Fi Planning.

First example I have seen and I’d like to show is 3 rooms in line, middle room is smaller than the two other rooms on the side. Access points are placed in the two side rooms centered, with no access point in the middle room. RSSI requirement is -65 dBm, walls are Cinder block with approximate 8 dB attenuation.

With access pointed centered in the two rooms we can see that the middle room RSSI requirements are not met in this scenario and these numbers can go down even further depending on the client device being used, if there are shelves, white board and/or additional stuff on the walls on each side.
Looking at the same image I can see that the FSPL from the access point to the wall is little over 16 dBm, then it is the wall that is further attenuating that signal and the edge of -65 dBm is showing as well as additional FSPL is shown towards the top at -67 dBm.
After I re-arrange the two access points, room coverage looks much better, by moving the access points closer to the wall I reduced the FSPL and by moving them in two different sections each section of the middle room is being covered by one of the access point within the required RSSI of -65 dBm
Here is a quick example showing 4 Room with re-arranged access pints.

By simply rearranging the access point placement I was able to reduce the FSPL from access point to Room#2. This helped me achieve better RSSI values in the middle room. NOTE: This is just one of many examples and all the different variables such as wall attenuation, RSSI values shown, access point models, radiation pattern of an access point antenna, distance, FSPL may vary depending on the environment and other factors. Goal here is to just show that access point placement is a critical part of any wireless design.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

WordPress SEO