Understanding link-level characterization of long-distance 802.11g semi-urban links

WiFi-based Long Distance (WiLD) mesh networks have been widely deployed with the intention of bringing extremely low-cost Internet connectivity to the rural areas worldwide. Prior studies do not discuss performance degradation in outdoor 802.11g links caused by faulty driver/card-specific proprietary algorithms and have fewer investigations on the impact of external WiFi interferences in terms of burst loss on WiLD 802.11g links. To the best of our knowledge, this is the first study of long distance 802.11g links in a typical semi-urban environment, concerning the maximum achievable throughput as well as the bursty features of loss ratio. We found that the principle causes for poor link performance are the buggy ANI (Ambient Noise Immunity) algorithm implemented in Atheros chips and the inefficient 802.11 CSMA/CA mechanism for point-to-point links. The former results in massive undecodable frames due to PHY errors while the latter throttles the transmission rate of the sender. OFDM timing and CRC errors caused by external interference contribute most to the burst loss, which appears in the magnitude of several to tens of seconds. Besides, we also document some valuable experiences learned in our experiments.