Packet Loss Characterization in WiFi-Based Long Distance Networks

Despite the increasing number of WiFi-based Long Distance (WiLD) network deployments, there is a lack of understanding of how WiLD networks perform in practice. In this paper, we perform a systematic study to investigate the commonly cited sources of packet loss induced by the wireless channel and by the 802.11 MAC protocol. The channel induced losses that we study are external WiFi, non-WiFi and multipath interference. The protocol induced losses that we study are protocol timeouts and the breakdown of CSMA over WiLD links. Our results are based on measurements performed on two real-world WiLD deployments and a wireless channel emulator. The two deployments allow us to compare measurements across rural and urban settings. The channel emulator allows us to study each source of packet loss in isolation in a controlled environment. Based on our experiments we observe that the presence of external WiFi interference leads to significant amount of packet loss in WiLD links. In addition to identifying the sources of packet loss, we analyze the loss variability across time. We also explore the solution space and propose a range of MAC and network layer adaptation algorithms to mitigate the channel and protocol induced losses. The key lessons from this study were also used in the design of a TDMA based MAC protocol for high performance long distance multihop wireless networks [12].