2015.06.28 00:00 | Kurt Tomlinson
My desktop recently died on me, so I'm looking to build a new computer. Part of the build includes a USB Wi-Fi adapter. The last Wi-Fi adapter I bought was 802.11g. Since then, 802.11n and 802.11ac have come out and wireless networking has gotten a lot more complicated.
A user reported a connection speed of only 65 Mbps between his laptop and router even though both were advertised to operate at up to 150 Mbps. Why? His laptop can operate a pair of simultaneous 20 MHz streams at 72.2 Mbps each. His router, on the other hand, supports only one stream but with a 40 MHz bandwidth.
This combination is limited to one stream by his router and a maximum channel width of 20 MHz by his laptop. The fastest speed possible with a single 20 MHz channel is 72.2 Mbps when using a short guard interval. Since his setup is running with a long guard interval, the speed is reduced to 65 Mbps.
The take-away is to make sure that you match the number of streams and channel widths between your devices for optimal speed. That doesn't sound too hard, but it is. Manufacturers don't readily advertise that information. Instead they use wonky class designations that are ambiguous and sometimes misleading.
I've bolded the class designations below that I recommend. Products with these class designations are most likely to be 100% compatible with your existing devices and are the least likely to feature proprietary extensions to the 802.11 standards that won't work with devices from other manufacturers. Specifically, these class designations are N600, N900, AC1200, and AC1750. (The N300 designation is generally also free of proprietary extensions, but higher performing N600 routers can be purchased for approximately the same price.)
Decoding the wireless N class designation is pretty simple. See the table below for how D-Link explains wireless N class designations.
Basically, take the number after N, divide by 300, and round down to get the minimum number of streams you have on a given frequency band. (For N750 we have 750/300 = 2.5 → at least 2 streams on the 2.4 GHz and 5 GHz bands.)
If your device is not dual-band, it only operates at 2.4 GHZ or 5 GHz but not both. In this case, use 150 instead of 300 in the calculations above. (For single-band N450 we have 450/150 = 3 → 3 streams.)
These calculations are assuming a 40 MHz channel. This is not always the case as evidenced by the issue at the beginning of this post. For more information, see the chart of 802.11n data rates.
Decoding the meaning of the wireless AC class designations is a bit more difficult. The table below gives my best guess for each term using the standard 802.11ac data rates. Beware that different combinations could be used by manufacturers to get to the same class designation. Always read your device's specifications carefully.
*Proprietary extensions to the 802.11n specification.
**Not widely available as of September, 2014.
Photo by Sean MacEntee