Wireless Performance - more
Let's first look at IxChariot plots of wireless runs made with the Intel 5300 AGN set to draft 11n mode. Figure 9 shows the runs made in 20 MHz mode, downlink. The curious thing here is that best case throughput of 41.1 Mbps was obtained in Location C, not in-room Location A.
Figure 9: Wireless throughput - N client, 20 MHz mode, downlink
The 20 MHz mode uplink runs shown in Figure 10 also show odd behavior in Location A, with periods of low throughput below 10 Mbps alternating with speeds in the 40 Mbps range. This was not a one-time anomaly;I saw this behavior frequently during my testing.
Note that for both up and downlink, the Intel client was able to associate with the 120N and complete the test runs at lowest signal level Locations E and F, although at speeds too low to be practically useful.
Figure 10: Wireless throughput - N client, 20 MHz mode, uplink
The 120N and Intel 5300 seemed somewhat better behaved in Location A when I forced the router to 40 MHz mode as shown in Figure 11. But the Location D trace still shows the high / low throughput cycling shown in Figure 10. Note the best case throughput of 66.857 Mbps in Location A.
Figure 11: Wireless throughput - N client, 40 MHz mode, downlink
This is also seen to a lesser extent for Location D in the 40 MHz mode uplink plot.
It's perfectly possible that the wonkyness is due to something in the Intel 5300 adapter's driver vs. the 120N. So I tried another notebook that has an Intel Wi-Fi Link 5100 AGN mini-PCIe card in it. It didn't seem to do much better, as shown in the simultaneous up / downlink plot shown in Figure 12.