4. The Challenge Of Throughput Vs. Range Testing

Wireless LAN product manufacturers make speed and range claims for their products that always come with "your mileage may vary" disclaimers. The disclaimers attempt to protect the makers from false advertising claims and reflect the harsh reality that the nature of the wireless beast is that performance is highly dependent on the environment in which the products are used.

So most manufacturers test just as reviewers do: by parking the AP in a location, then moving a notebook containing a STA (or client) to multiple locations and running a throughput measurement using a steady traffic stream. There are variations on this theme, such as slowly spinning tables for the STA that attempt to cancel out antenna positioning effects. Manufacturers usually perform tests in multiple locations, some in employee's homes, others in rented houses.

But in the end, comparing the results of any two tests in different environments is a crapshoot. Even with the most careful test setup and data recording methodology, all that can be said of the results is that they represent what happened under a very specific set of conditions.

To measure the ideal performance of WLAN products, you would want:

An environment free of interfering signals The ability to attenuate the signal between AP (or wireless router) and client (also referred to as the Station or STA) in small, repeatable increments.

The first point would ensure that only the product under test is being measured, while the second provides the ability to simulate the effect of distance between AP and STA.

Ideally, what we're after is to produce a throughput (or rate) vs. range plot that would look something like Figure 8, which is from Buffalo's AirStation Turbo G High Power Wireless Smart Router marketing material.

Figure 8: Buffalo Rate vs. Range Plot Example

The Y-axis represents throughput (or rate) in Mbps, which the X-axis represents distance in feet. Buffalo is actually pretty brave in publishing this curve, since most other manufacturers opt for squishier representations of performance. Figure 9 is from Linksys' Wireless-N marketing collateral, in which there is no mention of actual throughput performance in Mbps.

Figure 9: Nice picture, but no useful information (from Linksys)