Bounds on secret key rates in fading channels under practical channel estimation schemes

Secret key generation algorithms based on radio channel measurements have been proposed to support private communications. This paper presents methods for calculating upper bounds on the secret key generation rate for realistic channel measurement techniques. Bounds are shown for secret key generation using non-simultaneous channel measurements from each communicating party. Since short measurement periods with frequent transmit/receive mode switching is inefficient, the bound calculations are extended for long measurement periods for each user. It is shown for the wireless system parameters of standard IEEE 802.11 networks, excellent secret key generation rates are available for practical secret key generation methods. The bounds demonstrate that even when one party measures the channel for a larger proportion of the time than the other, excellent secret key rates are still available.