Securing 5G NR Networks: Innovative Artificial Noise Methods for Protecting Cell-Free Massive MIMO

This paper explores the vulnerability of downlink cell-free massive MIMO systems to passive and active eaves-dropping, focusing on a 5G New Radio framework. To enhance the security of downlink transmissions over the Physical Downlink Shared Channel (PDSCH) against eavesdropping threats, we propose two novel methods based on cooperative artificial noise (AN). The first approach, called cooperative artificial noise (CAN), involves all access points (APs) broadcasting AN in the null space of the users' channel matrix to confuse potential eavesdroppers. The second approach, named partial artificial noise (PAN), divides the APs into two groups: one group cooperatively transmits AN, while the other group serves the legitimate users. Additionally, we implement three different precoding schemes for legitimate users: maximum ratio transmission, zero-forcing, and minimum mean square error. We conduct link-level simulations of wiretap channels under various frequency-selective fading scenarios and noise conditions, using tapped delay line channel models as defined by the 3GPP TR 38.901 standard. The system's security performance is evaluated by analyzing the block error rate of legitimate users and the block success rate of eavesdroppers. Despite the limitation of having only one antenna per access point, our findings demonstrate that AN can be strategically designed through the cooperation of APs. By designing appropriate groups of APs specifically for generating AN, our second approach, PAN, significantly reduces the block successive rate of eavesdroppers, lowering it from 0.2 without AN to 0.1 with CAN and further down to 0.025 with PAN.