Effect of Non-Ergodic Channels on Wireless Fading-Based Key Generation

Physical layer key generation techniques based on wireless channel fading are widely considered to be secure as long as any eavesdroppers are separated from the terminals by a distance greater than the channel correlation length. This short paper discusses how this definition of the minimum secure distance is based on only a lower bound on the eavesdropper´s mutual information. The non-ergodic channel is a deterministic function of unknown channel parameters that can be estimated from multiple observations. The Cramér-Rao lower bound for the variance of an eavesdropper´s estimated channel is presented.