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The physical layer (PHY) rate is the speed at which client devices communicate with the AP. When you move a computer connected to the AP within the WLAN coverage area, the adapter properties dialog in Windows displays the varying connection speed, which may be as high as 450 or 300 Mbps when you are close to the AP or as low as 1 Mbps when you are 50 meters away from it. The displayed speed is the PHY rate.
The PHY rate directly affects the throughput rate, which is the average speed at which the client and AP can exchange application-level data, such as files. The throughput rate is always lower than the PHY rate, typically by more than 50%, due to a number of factors, such as protocol overheads and retransmissions. A low PHY rate always means low data throughput and therefore poor WLAN performance.
The PHY rate is shown for the AP that has the strongest signal in the given map area among the APs selected for analysis. This mimics the roaming behavior of client adapters that connected to the strongest AP. While other audible APs may offer higher PHY rates, a typical adapter will connect to the AP with the strongest signal. You can deselect one or several of the selected APs to see PHY rate values for less strong APs.
Expected PHY rate calculations are based on signal strength and use a table that maps signal levels to PHY data rates. The table uses average values for common adapter types. The actual PHY rate that you observe may be lower or higher than the expected rate, depending on the specific adapter and AP equipment being used.
Double-clicking on the Expected PHY rate legend on the status bar allows you to configure the color scheme.
Suggested Solutions
When low expected PHY rate areas are discovered, the following solutions are suggested:
| § | Increase the signal level, as it is directly related to the PHY rate. See the suggested solutions for increasing signal level in the Signal Level chapter. |
| § | Check your AP capabilities. If you are using newer 802.11n equipment, make sure that the maximum MCS indices, Short GI, and 40 MHz channel bandwidth are allowed in the device configuration. |
| § | If you are using legacy 802.11 a/b/g equipment, consider upgrading to 802.11n. |
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