# Physical Layer Security for Military IoT Links Using MIMO-Beamforming at 60 GHz
## 1 Introduction  
Fifth-generation (5G) cellular networks were recently rolled out with performance metrics that are highly desirable in military communications, such as low latency and ultra-high data rates. The department of defense (DoD) is currently testing 5G cellular networks for logistics, smart warehousing, spectrum sharing, training exercises, battlefield commands and control (C2), and security [1; 2; 3]. Support for specialized military equipment, such as unmanned ground vehicles (UGVs) and battlefield C2, can be provided via the IoT and cutting-edge protocols in the cellular architecture. However, these are not currently designed for military-grade communications regarding either physical layer (PHY) access or the core network. Therefore, future cellular standards must incorporate military-specific communication protocols that will enable military-grade security and privacy to enable the military to take full advantage of Next-G cellular networks [4]. This paper focuses on MIMO-beamforming techniques, which can be used to enhance the security of cellular IoT links for military application. We discuss the use of reconfigurable beams from MIMO-beamforming arrays at 60 GHz as a means of realizing secure and covert wireless links for military IoT systems. This discussion will focus on the lossy 60-GHz mmWave bands, due to its unique lossy characteristics.  
PHY security has gained significant attention lately, both in the contexts of the terrestrial 5G cellular networks and the satellite systems. In [5], a comprehensive survey of PHY security techniques for satellite communications was presented. In [6], the security-reliability tradeoff that exists when using cooperative non-orthogonal multiple access (NOMA) techniques in terrestrial mobile communication networks was considered. Large-scale MIMO and beamforming techniques have also been studied extensively in the context of 5G cellular systems [7; 8]. The 60 GHz millimeter (mmWave) band has been characterized fairly well in studies we have examined [9; 10; 11]. However, the idea of exploring the lossy nature of the 60 GHz band to realize secure and covert military communication links is novel [4]. In such systems, the limited range of 60 GHz links, due to severe loss, will be turned into an advantage to realize secure radio communications over a short range. Severalchallenges are to be addressed, however, in order to enable the wireless communications community to develop appropriate techniques that can be used to engineer such a system. Adaptive tuning of radio beams to different angles during an ongoing communication between a transmitter (TX) and receiver (RX) is well-established in [7]. It has also been shown recently, in 5G cellular networks, that radio capacity is significantly enhanced when directional beams from massive MIMO systems are utilized. In this paper, we demonstrate how PHY secrecy and privacy is achievable when MIMO-beamforming is employed over a 60 GHz radio band. This will help address a vital requirement in the design specifications for military IoT systems that current cellular IoT links lack--secrecy and privacy [12; 13; 14].