Parameters Optimization of Quantization Schemes for Channel-Based Key Extraction

We propose a scheme which generates shared secret keys from the amplitude of frequency domain channel state information (CSI) of individual orthogonal frequency-division multiplexing (OFDM) subcarrier. A unique quantization scheme is proposed, with the use of two parameters, alpha and beta, to set the quantization threshold. Based on multivariate Rayleigh distribution, we derive the analytical expressions for key bit disagreement rate (BDR) and key length. The theoretical analysis of BDR and key length aligns with the simulation results. We also present a mathematical model to optimize the parameters of our proposed quantization scheme and a guideline to set alpha and beta. Our proposed method for iterative tuning of beta can balance the number of zeros and ones in the generated key sequences so that the randomness requirement is met.