Why Does My Wi-Fi Data Rate Keep Changing?

Question: Why Does My Wi-Fi Data Rate Keep Changing?

Wi-Fi networking standards including 802.11b and 802.11g advertise a maximum data rate (connection speed) like 11 Mbps or 54 Mbps. However, sometimes the data rate of a live Wi-Fi connection (as displayed in the configuration utilities) differs from these values.

Answer: This behavior is called dynamic rate scaling, a design feature of WiFi networks. When a computer is connected via Wi-Fi, the network data rate is set and changes automatically as the quality of the wireless signal changes.

Dynamic rate scaling extends the range at which wireless devices can connect to each other.

For example, an 802.11b WiFi computer in close proximity to a router will often connect at 11 Mbps as shown on the computer's wireless configuration screens. If the computer is moved further away from the router, the connection speed will automatically reduce from 11 Mbps to 5.5 Mbps, and sometimes lower.

Were this device to maintain a 11 Mbps connection across too far of a distance, the connection would fail and drop.

WiFi devices scale their data rate in defined increments. On 802.11b, the possible choices for data rate are:

• 11 Mbps
• 5.5 Mbps
• 2 Mbps
• 1 Mbps

Similarly, the possible data rates for 802.11g devices are:

• 54 Mbps
• 48 Mbps
• 36 Mbps
• 24 Mbps
• 18 Mbps
• 12 Mbps
• 9 Mbps
• 6 Mbps

Factors that determine which dynamic data rate is chosen for a WiFi device at any given time are:

• distance between the device and other WiFi communication endpoints
• radio interference in the path of the WiFi device
• physical obstructions in the path of the WiFi device, that also interfere with signal quality
• the power of the device's WiFi radio transmitter/receiver

Home WiFi equipment always uses the dynamic data rate scaling feature; a network administrator cannot disable it.