Adaptive Wireless Channel Probing for Shared Key Generation Based on PID Controller

Generating a shared key between two parties from the wireless channel is an increasingly interesting topic. The process of obtaining information from the wireless channel is called channel probing. Previous key generation schemes probe the channel at a preset and constant rate without any consideration of channel variation or probing efficiency. To satisfy the users' requirements for key generation rate (KGR) and to use the wireless channel efficiently, we propose an adaptive channel probing scheme based on the proportional-integral-derivative controller, which is used to tune the probing rate. Moreover, we use the Lempel-Ziv complexity to estimate the entropy rate of channel statistics (received signal strength), which is considered as an indicator of probing efficiency. The experimental results show that the controller can dynamically tune the probing rate and, meanwhile, to achieve a user desired KGR. It stabilizes the KGR at the desired value with error below 1 bit/s. Besides, channel probing process is efficient under different user velocities, motion types, and sites.