Wireless LAN product testing has always been plagued by the inability to perform repeatable, consistent testing among products. This is primarily caused by the lack of consistent test environments that are free of RF interference.
While we're fortunate at SmallNetBuilder to have a quiet RF environment, we have used the same walk-around test method used by most every other reviewer. We haven't bothered to use the rotating table that some publications use to achieve more "consistent" results because, with so many other uncontrolled factors, we didn't think the effort produced results any more useful than our stationary client method.
On the plus side, however, through the continuing generosity of first NetIQ and now Ixia, we have been able to use IxChariot for our throughput measurements. This has allowed us to present detailed measurements and analysis unmatched by other publications for not only wireless products, but routers and other networking products as well.
Now through the generosity of another company, we are able to once more raise the standard for wireless product reviews.
New Range Test Method
Starting in March 2007 with the review of the draft 11n Buffalo nFiniti Dual-Band router, we switched over to using Azimuth's ACE 400NB Channel Emulator, Director and Radio Proof enclosures for wireless LAN product range testing. The Azimuth system provides a controlled, interference-free RF environment with programmable attenuation that can be used to repeatably simulate varying distance between AP (access point or wireless router) and STA (client) devices. This allows us to present a complete throughput vs. range profile for devices over their entire operating range.
The ACE is internally a very complex box, performing bi-directional emulation of up to 32-channel 4x4 MIMO systems. You can choose from six standard usage models as well as two special modes: Bypass and Butler. Figure 1 shows a block diagram of the ACE, so that you can get an idea of what's inside.
Figure 1 : Azimuth ACE NB Block Diagram
We can't begin to scratch the surface of what the ACE can do and how it does it, but the basic idea is that the ACE digitizes the incoming signal from up to four channels and applies some pretty hefty digital signal processing to it to simulate multipath, delay, fading and the other stuff that happens to the RF signals in the real world. After all the crunching, the signal is converted back to analog and sent out the second set of ports.