Link Quality and Signal-to-Noise Ratio in 802.11 WLAN with Fading: A Time-Series Analysis

It is known that for multipath fading channels individual points or average signal-to-noise ratio (SNR) alone do not adequately describe the wireless channel quality. This paper uses time-series modeling to investigate the relationship between SNR and 802.11 link bandwidth which we use to define the link quality. Two models, one linear and another nonlinear, are constructed and fitted to time-series of SNR as input and link bandwidth as output. Their performance is measured in terms of the accuracy of prediction of the link bandwidth. By the linear Auto- Regressive Moving Average exogenous variables (ARMAX) model, we show the existence of nonlinearity in the input data series, which results in high prediction error. The prediction performance is significantly improved by the nonlinear Echo State Network (ESN) model due to its ability of nonlinear re-expression of the SNR time-series and associating them with the correct link bandwidth.