Troubleshooting Wireless Networks
If you have been in and around the AV industry for any length of time, you probably realize that things don’t always work out of the box once you get to the site. Despite frustrations with manufacturers and products, most people realize that there are conditions onsite that vary widely and can’t be pre-engineered to compensate for. One of the biggest question marks with a given site is the wireless interference. Sometimes no matter where you put the transmitter or receiver, you just can’t get reliable communication and when that happens it can be painful to say the least.
When you do have wireless issues, one of the best ways to help diagnose these problems is using a laptop that has WiFi (which is pretty much any current laptop) and a WiFi scanning software. I like to use a tool called inSSIDer http://www.metageek.net/products/inssider/
Starting up inSSIDer, you will have to choose which interface to listen on, and press “start” to begin scanning. At the bottom of the screen, you can view the WiFi channels in use. Due to the number of wireless transmitters and receivers in the public 2.4GHz spectrum there can be a lot of different devices competing for a certain channel. So what exactly are you looking for? With inSSIDer running, you can see all the wireless networks in the area, their channel assignment, and signal strength. With this information, you can determine what channel your access point can be set on to obtain maximum performance in the space.
Although multiple devices can transmit and receive on the same channel with some degree of success, radio theory tells us that there will be interference between close frequencies, and this will cause drop outs and poor signal throughput. Even though WiFi has been designed to allow for occasional dropouts and does a great job of compensating for this, we can get a better quality link by moving to a frequency that is less congested.
Once you know what frequency is free, you can change the channel on your WiFi access point or router. Typically this is done from the web interface of the device, follow manufacturer directions if you are unsure of the procedure. Changing the channel does not require any reconfiguration on the other devices in the system – they listen on all frequencies in the WiFi band and will find the network based on it’s SSID (basically the name) regardless of what frequency/channel it happens to be on.
While we are discussing wireless technology, you should also be aware that not everything wireless is “WiFi”. Meaning that you could be using devices that fall outside of the 2.4GHz spectrum, and employ a totally different way of frequency allocation. For example, most Wireless microphones are not “WiFi” devices. Despite the different frequencies (and modulation techniques) the same philosophy of frequency allocation and interference applies to all wireless devices. Instead of a tool like inSSIDer, you would have to use a tool called a spectrum analyzer to see what devices are active at a given frequency range, and tune your transmitters to clear bands. Note that in most cases, a real spectrum analyzer will cost you 10’s of thousands of dollars and requires some knowledge to operate. That being said, there are some higher ends wireless microphone receivers that allow you to view interference within their channel range.
While this article has just touched on some basic wireless concepts, there is a wealth of knowledge on the internet on wireless theory. Keep in mind that this theory can get quite technical and complex – be warned!
