Tx Protection; Guard Interval - HP MSM3xx Management And Configuration Manual

Tx protection

Supported on: E-MSM430, E-MSM460, E-MSM466
Not available in Monitor or Sensor modes.
When an AP is operating in an 802.11n mode, and legacy (a/b/g) traffic is present on the same
channel as 802.11n traffic, this feature can be used to ensure maximum 802.11n throughput.
The following options are available:
 CTS-to-self: 802.11n transmissions from the AP are protected by sending a Clear To
Send (CTS) frame that blocks other wireless clients from accessing the wireless network.
 RTS/CTS: 802.11n transmissions from the AP are protected by first sending a Request To
Send (RTS) frame to the intended recipient and then waiting for a Clear to Send (CTS)
frame to be sent back. This is a more robust, but slower, solution than CTS-to-self.
However, this method resolves the hidden station problem (where certain legacy stations
may not see only a CTS frame).
 No MAC protection: This setting gives the best performance for 802.11n clients in the
presence of 802.11g or 802.11a legacy clients or APs. No protection frames (CTS-to-self or
RTS/CTS) are sent at the MAC layer by the AP. PHY-based protection remains active,
which alerts legacy clients to stay off the air while the AP is transmitting data to 802.11n
clients. This method of protection is supported by most 802.11g or 802.11a clients, but is
not supported for 802.11b-only clients and should not be used if such clients are expected
on the network.

Guard interval

Supported on: MSM410, MSM422 (radio 1), E-MSM430, E-MSM460, E-MSM466
Not available in Monitor or Sensor modes.
This parameter is only configurable when Wireless mode is set to support an 802.11n option.
On the MSM410 and MSM422, Guard interval is automatically set to Long when Channel
width is set to 20 MHz.
To enhance performance in 802.11n modes, the guard interval can be reduced from its default
of 800 nanoseconds to 400.
The guard interval is the intersymbol time period that is used to prevent symbol interference
when multiple data streams are used (MIMO). However, symbol interference reduces the
effective SNR of the link, so reducing the guard interval may not improve performance under
all conditions.
The following settings are available:
 Short: Sets the guard interval to 400 nanoseconds which can provide improved
throughput (up to 10%) in some environments. The AP remains compatible with clients
that only support a long guard interval. Use this setting when Channel width is set to
Auto 20/40 MHz to get the best throughput.
 Long: Sets the guard interval to the standard of 800 nanoseconds.
Wireless configuration
Radio configuration
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