Monday, October 8, 2012

Programmable Attenuator: Rate v/s Attenuation

I spent some time over the weekend integrating the Attenuator with the LANforge hunt script logic.  The hunt script iterates through packet sizes and attenuation settings.  At each iteration, it runs tests and adjusts the transmit rate to find the highest rate that meets constraints (latency, packet-loss, etc).  The best run for each iteration is saved for reporting.

Here's the Hunt Script configuration for this run:

The graphs below are two views of the 3D graph that shows the relationship between UDP payload size, WiFi RX-Signal level, and RX-BPS.  The test case is an AP connected through the attenuator to a WiFi station system.  The test shows that at very low attenuation (less that you would see in over-the-air testing), throughput suffers, and it starts suffering again at around -55 signal quality.  Larger PDU sizes help throughput as well, but at least some of that is because the AP system has a fairly weak CPU and was running lots of other processes when this test was running.  I still need to work on better RF shielding, so the signal does not go below about -75 dBm.

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