Are All Bits Equal? – Experimental Study of IEEE 802.11 Communication Bit Errors

In IEEE 802.11 Wireless LAN (WLAN) systems, techniques such as acknowledgement, retransmission and transmission rate adaptation are frame-level mechanisms designed for combating transmission errors. Recently practical sub-frame level schemes, such as frame combining and partial packet recovery, have been proposed by the research community. In this paper, we present experimental results obtained from our bit error study for identifying sub-frame error patterns, because we believe that identifiable bit error patterns can potentially introduce new opportunities in channel coding, network coding, forward error correction (FEC) and frame combining mechanisms. We have constructed a number of IEEE 802.11 WLAN testbeds and conducted extensive experiments to study the characteristics of bit errors and their location distribution. Our measurement results identify three bit error patterns: the slope-line, saw-line and finger patterns. Conventional wisdom dictates that bit error probability is the result of channel conditions and ought to follow corresponding distribution. However, our experimental results show that the slope-line and finger patterns are not induced by channel conditions. Among these three patterns, we have verified that the slope-line and saw-line patterns are present in WLAN transmissions in different physical environments and across different WLAN hardware platforms. We also discuss our current hypotheses for the reasons behind these bit error probability patterns and how identifying these patterns may help improve the robustness of WLAN transmission.