Craig,

I agree that the test was not flawed. However, did you test different combinations of beacon interval and/or DTIM settings on the access point? If so, you might see your results improve (or worsen).

One of the main problems with 802.11 PSM is that it is statically set at the AP for all clients. It has been shown that, as you observed, PSM can have little effect, or even cause higher power consumption, depending on traffic patterns, the round-trip time of TCP traversals, and how packets "line up" in time with the beacon/DTIM intervals. Since the client has no ability to vary its individual power save profile settings, it is at the mercy of the AP settings as to what effect PSM has.

You are correct that in a laptop scenario, the WLAN power savings due to PSM are most likely relatively minor compared to the other subsytems' consumption. In an application such as wireless sensors, though, where the WLAN radio is usually the major system power draw, communications can be infrequent, and one has to deal with a very limited power budget, we have seen that properly tuned PSM settings can significantly reduce the average power consumption of the overall solution. Again, however, the same settings that minimize one client's consumption can have the exact opposite effect on another client.

Thanks. -Michael Blossom