Measurement Based Link Level Investigation of IEEE 802.11g Channels

Abstract

Assessing channel conditions is critical to routing and MAC protocols. But, this task is challenging due to the highly dynamic nature of wireless channels and the characteristic differences between indoor and outdoor environments. This paper presents observations and analysis from extensive measurements on IEEE 802.11g channels indoor and outdoor. The experiments are designed to investigate the channel dynamics through metrics such as successful frame delivery rate, loss rate , and Signal- to-Noise Ratio on IEEE 802.11 networks. The objective of this work is to reveal the interaction between these metrics and their variations in time and space. This paper makes the following observations. Frame delivery rate for fixed stations fluctuates over time in most scenarios. Statistics over large time intervals get bursty and do not provide valuable information about channel conditions. Generally, Signal- to-Noise Ratio (SNR) varies widely over time even for fixed stations. However, the SNR remains stable for micro time scales. As a consequence, the frame delivery does not strongly correlate with S N R . Another o b s e r v a t i o n i s t h a t indoor and o u t d o o r require different sampling intervals to measure valuable frame loss rate. If sent at a favourable time, a set of frames is likely to be delivered successfully continuously. Although the intermediate distribution of the intervals between consecutive losses varies wildly for different transmission rates (modulations), most of these intervals are less than 5 ms regardless of the rate and location .