A Lightweight Preprocessing Scheme for Secret Key Generation from MmWave Massive MIMO Channel Measurements

Abstract

Due to the new channel characteristics, previous preprocessing methods for physical layer key generation cannot be directly applied in mmWave massive MIMO systems. Actually, due to the intolerable high computation complexity and time consumption caused by large dimension of massive MIMO channel, even the previous optimal preprocessing method principal component analysis (PCA) is not suitable. To address the problem, in this paper, we propose a lightweight preprocessing approach called beamspace refinement, which is suitable for mmWave massive MIMO channel by exploiting its channel characteristics namely sparsity. The proposed scheme brings the following advantages. 1) It is lightweight. The computational complexity is quiet low. Unlike the PCA scheme, the proposed scheme does not involve the exponential calculation of the number of antennas, which makes it very suitable for mmWave massive MIMO channel. 2) It is robust against noise. Thus, it can be used to generate secret key with quiet high-entropy and high bit agreement ratio even in low SNR regimes. Numerical results show that the proposed approach outperforms the previous method DCT, WT and PCA in terms of bit agreement ratio, and is on par with PCA in terms of key capacity. Besides, the increase of the antennas number can improve key agreement ratio in our scheme, which is beneficial for massive MIMO system.