Dropping calls on outdoor Mesh Deployments

     This is a topic that I have dealt with for about 4 years during a government project deployment. Dealing with outdoor mesh deployments for the most part are relatively simple and hassle free, but there are some issues you will encounter and problems with VoIP is a hot topic.

    Problem Encountered

     When doing post installation testing of your outdoor mesh, you would typically want to use the VoIP phone and walk around the covered area, roaming from AP to AP, doing a "Can you hear me now?" commercial. By grabbing a couple of the phones (remember... designing for the devices to be used on the network is the best way) and placing a call between them, one person can walk the coverage area while the other monitors the call from an office somewhere. The non-mobile person will monitor the clarity of the call and pay attention to any moments where one side or the other cannot hear the other, and also take note of any dropped calls and where the call was dropped.

     Lightweight AP design Glitch

     When deploying mesh networks in a lightweight scenario, the controller sets the channels and the power just as it does for indoor deployments. Here is where the glitch is:

     Indoors- the access points typically see each other in a relatively familiar pattern as the devices would pick up on them such as walls between them, high shelving, etc..

     Outdoors- the access points mostly have a clear line of sight to each other because of the deployment model, while the devices themselves dwell at ground level between the buildings and other obstacles.

Why does this matter? Roaming.

   Unless you are in a single channel architecture model, wireless devices will not roam across identical channels. Each access point that the device roams to has to be on a different channel than the one it is roaming from in order to hand off the connection without dropping it. This presents a problem with outdoor mesh deployments sometimes because the actual walk Path of the user varies significantly from actual coverage that the access points monitor from the roof tops.

     There will come a time that calls will be dropped because your device is traveling from (scenario) say a channel 1 to a channel 1, or a channel 36 to a channel 36.

     As an engineer, you will have to use something like Google maps and place all of your outdoor access points on the map, then view and even physically walk the area, locating all of the most common walk paths within the deployment coverage. This will help you identify how to manually set channels to avoid any of your walk paths containing a same channel roaming issue.

     I have had to do this several times over the past few years to avoid dropped calls due to same channel roaming. I have attempted to tweak the sensitivity on the Auto channel option but it still had issues, and the best way to ensure the problem stayed away was to manually configure the channels and leave the power settings to my RF profile within the AP Group.

Note***

     If you performed your survey correctly, ran a spec an of the area to identify and remove any interferers, and your power levels along with proper cell overlap is all correct, take a look at the channel situation because a controller does not take "Walk paths" into consideration when setting channels automatically.

Brett Hill, CWNE #147