Wireless Surveys - A how too guide

Version 2

    I'm not going to put myself out there as an expert, but in my time working with Wireless I've found a number of ways that people prepare for the installation of their Access Points.

     

    Preface: There are basically 3 types of radio signal management for wireless omni-directional - most common, Fixed directional antennas - used a lot in outdoor equipment or unique locations, Active directional signal management - only 1 vendor does this to my knowledge. That said the most common installations will use omni-directional signaling.

    • While in our minds we picture a roughly round projection (and reception) area - the zones will vary greatly by manufacturer, AP type, physical construction of the AP, location, physical make up of the location (interior, construction, furniture, people, equipment, etc.)
    • With the fixed directional antennas the signal can be managed better for very specific situations in that the signal can be "pointed" at the targets and thus reducing interference and increasing signal, both send and receive. The down side is the the pattern is fixed and therefore less flexible than omni-directional. This generally is not a good solution for indoor locations where most wireless is located
    • Active directional signal management allows the AP to actively re-configure the antenna array within the AP - basically the AP talks to client A and "points" directly at that client (increasing signal strength, reducing noise and increasing bandwidth - and gets the clients on and off the wireless much quicker) when the AP talks to the next client it re-configures the antenna array to point to that specific client.

     

    Keep in mind that 2.4 GHz and 5.0 GHz signals will have very different characteristics, so you survey should take this into account.

     

    Picture this:

    • Omni-directional - you are sitting in a room of 100 people all taking at the same time - you have to really strain to hear that person across the room to whom you are talking, noise level, interference, the speakers voice level, etc. all add to the difficulty.
    • Fixed directional - (pardon the illustration) you are in the same room but this time you have one of those dog cones on your head and it is tacked to the table. Now you don't hear all the side noise and you can hear directly in front much better - if the person to whom you are talking across the room is directly in front of you you have a better chance of having a reasonable conversation (if they can get past the laughing at you in that cone)
    • Active directional - now you are in that same room, with the cone on your head, but now it isn't tacked to the table. As you speak with different people you are able to look directly at them - each conversion is clearer as the signal is amplified by the attractive cone, noise is reduced and focus is increased.

     

    1.) Guess and Tell - like kiss and tell, Just Don't

    2.) Magic Projection - with this method the designer has a basic knowledge of the radiation pattern of the APs and, generally very confidently, lays out the AP locations on a floor plan based upon the "projected" coverage." Better than Guess and Tell but only marginally.

    3.) The GTMP shuffle - this is where the installer uses a combination of the above two methods and then spends the next days, weeks, months and generally years "re-adjusting" the locations, number and type of APs to "fill in the gaps." It's a nice gig if you can get it as you are sure to have plenty to do and your scope will be limited - keep playing with the APs. (You'll find a lot of Wireless Experts in this space)

    4.) Where Is We - this is when you have existing APs installed and you're trying to get a better handle on what needs to happen (we - before changing to our new vendor - had one of these "surveys" done at a very high cost) using a floor plan and a laptop and some signaling software (something that will give you a relative signal strength - there are many, some even for phones) you walk around the building(s) and take "signal strength" measurements. That information is then taken back to the office and analyzed - either manually or via software - to "map out" what the existing coverage looks like and then make best guess estimates of where APs need to be added (the most common answer that the vendor will provide), removed or just relocated. While we are getting closer to reality there will still be a lot of "tweaking" once the APs are in their new locations - again the signals are not clear circles and the interaction of devices, walls, equipment, microwave ovens, granite counter tops (yes they have a resonate frequency that interferes with 2.4 GHz signals) This method is helpful, but not great.

    5.) The Right Way - if you have no wireless currently this will work Much, Much better than options 1, 2 or 3. If you have existing wireless this will work to give you a True picture of what each location will look like. For this method in addition to the floor plans and laptop you will need a "Portable Wireless Survey Provisioning Station - Described below" Basically an AP on a stick - not to be confused with Jose Jalapeno on a stick. Configure that AP with an SSID not on your network and obvious for your testing. Now you have the ability to place that AP at the approximate location and height of the final installation and you are free to move it around during testing. Place the AP about where you think it should go - take some measurements, tweak the location a bit until you get the coverage areas that you are looking for. Add that to the floor plan for the final analysis back in the office (again either manually or via software) If you want to be even more accurate you could invest in several of the PWSPS and set them up simultaneously. For best results you can either turn off your existing wireless (not recommended during production hours, but you knew that) or select the vendor with the active directional antenna system, just sayin!

     

    Now, none of these methods are 100% but you can see that method 5 will get you the closest and leave the least amount of "tweaking."

     

    PWSPS - Portable Wireless Survey Provisioning Station

    While you can power an AP via PoE or a power adapter the best option is battery power on the station. So, you can either purchase commercially built units that will consist of a rolling cart with an extendable pole to which you can mount your AP, a built in battery and possibly a UPS system. You can make one very simply by gathering a simple shop cart and mounting an extendable (fixed if you must, but more difficult) pole. I've seen people just take a pole, mount an AP and have an assistant hold it up at the location - works, but not very efficient - I mean if you have an assistant they should be getting coffee, pizza, etc, not holding APs in place. Be sure to select a battery of sufficient capacity - while a UPS can be used I prefer a deep cycle 12 volt battery. If you use a UPS you can either power your AP with a power adapter if that is supported by your AP or a PoE injector.