Changes between Version 11 and Version 12 of 802.11/Usage/BestPractices

Timestamp:

Dec 19, 2014, 4:28:54 PM (9 years ago)

Author:

chunter

Comment:

--

802.11/Usage/BestPractices

@@ -16 +16 @@
 === Make your receivers "intentionally deaf" to very weak signals ===
 
-Before running an experiment, you should consider what would happen if your design is exposed to weak, but frequent, interference. The 802.11 Rx PHY can only process one packet in any given instant in time. If the PHY starts attempting to decode weak interference, it may be unable to decode your own stronger traffic if it occurs immediately during and after the interference event. Instead, it may make sense to use the "Minimum Packet Detection Power" feature of the design ([wiki:802.11/Benchmarks/Pkt_Det_Min_Power_Char characterized here]). This parameter lets you prevent the PHY from beginning to start processing a packet unless it is sufficient strong to meet a power requirement that you specify.
+Before running an experiment, you should consider what would happen if your design is exposed to weak, but frequent, interference. The 802.11 Rx PHY can only process one packet in any given instant in time. If the PHY starts attempting to decode weak interference, it may be unable to decode your own stronger traffic if it occurs immediately during and after the interference event. Instead, it may make sense to use the "Minimum Packet Detection Power" feature of the design ([wiki:802.11/Benchmarks/Pkt_Det_Min_Power_Char characterized here]). This parameter lets you prevent the PHY from beginning to start processing a packet unless it is sufficient strong to meet a power requirement that you specify. In effect, this is a way to at least partially isolate your test setup from other interferers.
 
 To provide a concrete example of where this function can be useful, consider the [wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows DCF with Multiple Flows Application Note]. This experiment was to show the interaction of DCF behaviors on a few nodes in a very small tabletop topology. In this experiment, the Tx power was intentionally lowered to a minimum value (-10dBm), resulting in received powers between [https://warpproject.org/trac/raw-attachment/wiki/802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs/v1_0_cs_pow_vs_time.png -75 dBm and -70 dBm] for the duration of the experiment. At the same time, in the active scan figure above, we can see that there are other Wi-Fi channels near the scanner that packets as low as -90 dBm. If we set the minimum detection power to, say, -80dBm, we can keep the PHY from being "distracted" by the low-level interference and yet still be able to detect our -75 dBm to -70 dBm traffic with high probability. If we hadn't lowered the Tx power so much, we could potentially raise this threshold much more.