Measured and predicted correlation between local average power and small scale fading in indoor wireless communication channels

A large data set of wireless indoor propagation measurements collected in several office buildings is analyzed to study the correlation between local average propagation loss and small scale fading statistics. We compare the correlation observed in measurements against the correlation found while simulating the measurements using a 3-D ray-tracing propagation prediction tool for Wireless System Engineering (WiSE). Each measured or predicted location is characterized by 1000 individual data points corresponding to an area several wavelength across, centered in the corresponding location. For each location we have computed measured and predicted average propagation loss and the Rician K-factor for the fluctuations about this mean. We have quantified the correlation between the K-factor and absolute, as well as excess propagation loss. Excess propagation loss is defined as the loss in excess of the loss estimated by a power-law relationship between propagation loss and distance. We show that the excess propagation loss and the small-scale fluctuation level are correlated, so that, when the receiver is not in a shadow, the small-scale signal level fluctuations are Rician with a small standard deviation. We also show that that when the receiver is in a shadow, or obstructed, the small scale signal level may approach a Rayleigh distribution with a large spread of signal levels about the mean. Quantifying this correlation allows greater accuracy and confidence in prediction of wireless channel capacity.