Adaptive rate selection in Wi-Fi networks

* Managing Wi-Fi data rates

While it is usually desirable to set all your Wi-Fi nodes at the maximum possible data rate (11Mbps for 802.11b and 54Mbps for 802.11g and 802.11a), there are a few exceptions to every rule. Let’s look at a few of the pros and cons of doing so:

PRO: Theoretically, higher speeds should result in higher throughput and performance, and thus a better user experience.

PRO: Transmitting at maximum speed saves battery life because faster transmissions take less time.

PRO: Dropping data rates back to their adaptive speeds can cause interference on its own in other parts of the network. Transmissions can go farther at slower speeds. Let’s say you’ve built a “honeycomb” or “checkerboard” of non-overlapping 2.4GHz channels 1, 6, 11, for your 802.11b/g networks and set the data rate of all devices for their maximum speed of 11Mbps. Then, interference enters the picture, causing the data rate to adapt, or fall back, to a lower speed, sending the signals farther distances. Those signals could cross over into other “1-6-11 cells” of the honeycomb and interfere with the corresponding channels there, slowing those data rates.

CON: The lower data rates use less complex and more redundant methods of encoding the data, making them less susceptible to interference and signal attenuation.

CON: There might be clients performing suboptimally because of the quality of the client software driver. If you discover lots of retransmissions from a particular client, your monitoring analysis might indicate that the particular client should be set back to one of the adaptive rates at all times - such as to 5.5Mbps in an 802.11b network – and account for the potentially increased reach of that client in the design scheme.

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