Nonreciprocal Radio System Calibration for Propagation-Based Key Generation

Propagation-based secret key generation (SKG) is a physical layer method for establishing encryption keys based on two radios observing a reciprocal propagation channel. However, nonreciprocal contributions to the channel introduced by the radio circuitry significantly degrade the ability to reliably generate keys using such methods, necessitating the development of calibration methods for removing the impact of channel nonreciprocity. This paper uses a total least squares (TLS) algorithm coupled with a detailed model of the multiple-input multiple-output radio frequency circuitry and propagation for the radio system to achieve such a calibration. Simulations show that the method is highly effective in removing the impact of nonreciprocal circuit contributions over a range of operational parameters.