On the side-effects of proprietary solutions for fading and interference mitigations in IEEE 802.11b/g outdoor links

Experimental results are typically envisioned as the ultimate validation reference for any theoretical and/or simulation modelling assumptions. However, in the case of Wireless LANs, the situation is not as straightforward as it might seem. In this paper, we discuss to what (large) extent measurement results may depend on proprietary undocumented algorithms implemented in the vendor-specific card/driver employed. Specifically, we focus on the experimental study of IEEE 802.11b/g outdoor links based on the widely used Atheros/MadWiFi card/driver pair. We show that unexpected performance degradation appear to be mostly caused by some Atheros' proprietary algorithms (which we try to dissect in the paper), rather than by physical reasons such as interference, multipath, PHY/MAC settings, etc. Our findings appear quite critical for two reasons. First, the performance degradation induced by these proprietary mechanisms may be not only significant, but even dramatic in some outdoor link cases. Second, it seems that most of the WLAN research community is unaware of the existence of such proprietary mechanisms: this is crucial because, in most cases, lack of awareness about these mechanisms may lead to biased experimental trials and/or (mis)lead to erroneous interpretation of experimental results.