Encryption key establishment using space-time correlated MIMO channels

This paper investigates the establishment of secret encryption keys from temporally and spatially correlated MIMO channel matrices. The discussion first examines the influence of correlation on the secret key rate with the help of a simple SISO channel model that generates samples with correlation behavior that can be described in closed-form. This analysis reveals that an optimal sampling approach can be devised that minimizes the total time required to achieve a key with a specified length. The presentation also examines the decorrelation of measured channel samples, and demonstrates that independently removing spatial and temporal correlations fails to produce random variables that are truly decorrelated. Finally, attention turns to a method for quantizing the uncorrelated channel samples. Simulations using real channel measurements reconfirm the observations made using the simple channel model and demonstrate that while existing algorithms for channel quantization can be effective, their performance falls short of that predicted by the upper bound.