Side Effects of Ambient Noise Immunity Techniques on Outdoor IEEE 802.11 Deployments

A very common conclusion of many experimental studies about IEEE 802.11 outdoor network deployments is that their poor performance results derive from the unfavorable interference and multi-path signals in which the WLAN-cards are required to operate. Goal of this paper is to show that this condition does not always hold, and unexpected and inaccurated PHY layer implementations can be a primary cause of packet losses. With the support of extensive measurement campaigns led in our campus, we provide the performance evidence that IEEE 802.11 outdoor performance impairments are strongly affected by proprietary interference mitigation techniques that adaptively adjust the WLAN-card receiver sensitivity thresholds on the basis of the perceived noise levels. Because of the immediate relationship between these receiver sensitivity parameters with the carrier sense functions, we show how, in highly interfered outdoor scenarios, interference mitigation algorithms may cause tremendous amplifications of either the hidden or the exposed terminal phenomena, thus determining dramatic wireless link failures. Surprisingly, deactivating such mechanisms allows to achieve high link quality performance.