Cognio Spectrum Expert for Wi-Fi
April 28, 2006
This pricey tool could be invaluable in helping find the items interfering with the radio waves around your wireless LAN.
Pros: Identifies RF interference caused by non- 802.11 devices.
Cons: Doesn't provide detailed protocol-related WLAN data.
If you're in charge of maintaining a company's wireless network, you'd probably agree that few things are as frustrating as spending lot of time and money installing a WLAN only to have it plagued by things like slow performance and intermittent connectivity issues. When this happens, a spectrum analyzer can come in very handy as a way to help identify and correct (or at least compensate for) these sorts of WLAN problems. One such tool that may be useful for the task is Cognio's Spectrum Expert for Wi-Fi Mobile Edition, a spectrum analyzer that's particularly adept at exposing the litany of non-WLAN devices that may be wreaking havoc with your wireless network.
Most spectrum analyzers work by monitoring an 802.11 network and its various devices, providing information necessary to optimize facets of the WLAN. This can include things like optimizing the location of access points, minimizing co-channel interference caused by AP overlap, sniffing out unauthorized WLAN devices like rogue APs, and measuring the network traffic load to pinpoint overloaded (or underutilized) segments. Spectrum Expert takes a somewhat different approach, because instead of providing data about 802.11's protocol layer, it concentrates primarily on the underlying physical layer. This means it can detect not just WLAN devices, but any device that is using RF spectrum, which gives it the ability to expose almost any interference-causing device that may be causing network problems.
Be forewarned that Spectrum Expert isn't necessarily the type of program you can throw onto any old notebook you have lying around. The software -- which will run on either Windows XP or 2000 -- has relatively hefty minimum system requirements, needing at least a 1 GHz CPU and 512 MB of RAM, specs you may not always be able to take for granted on the type of lightweight notebook you might prefer to lug around the office for this kind of testing.
I used the software with a 3 lb. ultra-portable Dell Inspiron 300m, which barely qualified with its 1.2 GHz Pentium M and 640 MB of RAM. While running, the software consumed about 30 percent of the CPU cycles, so running Spectrum Expert alongside other applications is probably not recommended.
Spectrum Expert works with both 2.4 GHz and 5 GHz networks, and comes with its own CardBus-based probe with internal antenna. Also included is a more sensitive external antenna, along with a clip to attach it to a notebook lid.
Before running the software, you need to make sure that any built-in Wi-Fi adapter or CardBus card is set to receive-only mode (or at least not associated with any WLAN) to prevent it from causing interference. You can also choose to disable the Wi-Fi adapter entirely, but that will prevent Spectrum Expert from using it to gather any protocol-related network data like the presence of 802.11 devices.
Spectrum Expert can coexist on the same system with protocol-oriented analyzers like WildPackets AiroPeek or AirMagnet Surveyor two products it is actually re-branded and sold with so long as those products are configured for passive mode. That way, they're not transmitting packets while Spectrum Expert is in use.
Using the Software
An RF expert will undoubtedly feel at home with Spectrum Expert's numerous charts, graphs and spectrograms, but even those less well-versed in RF technology should find the software easy to use. While it certainly helps to have at least a basic familiarity with RF concepts, prospective RF sleuths will benefit from an extremely thorough and well-written manual that outlines in considerable detail the program's features and how best to exploit them. By default, Spectrum Expert displays a lot of information on the screen at once, but the interface is highly customizable, so you can add or remove individual elements. In addition to a real-time display, you can also use Spectrum Expert to record data for later playback.
Particularly useful to non-engineers is Spectrum Expert's Channel Summary, which provides an easy-to-read table of all monitored channels/frequencies and reports how many devices are present, plus the power being radiated on each. I set up a phalanx of potential interference-causing devices, including a microwave oven, Bluetooth mobile phone and headset, and several cordless phones. While operating, all were present on Spectrum Expert's Devices tab, which lists all of the active RF devices present. The software usually recognized each device by category, though a couple of them were simply identified as generic devices. The software contains a database of device signatures, so in some cases it may be able to ID a device by the manufacturer and model number.
Knowing what type of device is giving a network fits is a good start, but of course it doesn't do any good unless you can actually find it. That isn't always easy -- you might trace your problem to a microwave or a Bluetooth headset, but which one? To find out, Spectrum Expert's Device Finder acts as a sort of wireless Geiger counter. Highlight a device and then select Find It, and as you walk around, its signal strength and proximity is measured and plotted on a green/yellow/red bar graph. I successfully used Device Finder to sniff out several cordless phones of both the 2.4 and 5.8 GHz variety. (Cognio also offers an optional directional antenna for improved device detection.)
While Cognio Spectrum Expert isn't necessarily the tool to turn to if you're trying to fine-tune your wireless network throughput, it can be enormously helpful in helping you identify the underlying RF interference problems that may be keeping your network from operating at its full potential. Its nearly $4,000 price tag will be beyond the budget of some firms, but if a well-functioning WLAN is crucial to your operation, it will be money well spent.