Physical Layer Security for MmWave Communications:Challenges and Solutions

The mmWave communication is a promising technique to enable human commutation and a large number of machine-type commu⁃nications of massive data from various non-cellphone devices like Internet of Things(IoT)devices,autonomous vehicles and remotely con⁃trolled robots.For this reason,information security,in terms of the confidentiality,integrity and availability(CIA),becomes more important in the mmWave communication than ever since.The physical layer security(PLS),which is based on the information theory and focuses on the secrecy capacity of the wiretap channel model,is a cost effective and scalable technique to protect the CIA,compared with the traditional cryptographic techniques.In this paper,the theory foundation of PLS is briefly introduced together with the typical PLS performance metrics secrecy rate and outage probability.Then,the most typical PLS techniques for mmWave are introduced,analyzed and compared,which are classified into three major categories of directional modulation(DM),artificial noise(AN),and directional precoding(DPC).Finally,several mmWave PLS research problems are briefly discussed,including the low-complexity DM weight vector codebook construction,impact of phase shifter(PS)with finite precision on PLS,and DM-based communications for multiple target receivers.

Joint User Association and Resource Allocation for mmWave Communication:A Neural Network Approach

With the rapid growth of wireless data demand and the shortage of global bandwidth,the use of millimeter-wave(mmWave)frequency band for wireless cellular networks has become the core content of the fifth generation cellular network.Because mmWave communication has different characteristics from microwave communication,using traditional optimization techniques to manage the resource of mmWave communication networks is inappropriate.In this paper,we propose a neural network-based algorithm to solve the joint user association and resource allocation for mmWave communication system with multi-connectivity(MC)and integrated access backhaul(IAB).The resource allocation problem is formulated as a mixed-integer quadratically constrained quadratic programming(MIQCQP),which is very difficult to solve.First,we decompose the MIQCQP into two sub-problems,i.e.,binary associated matrix sub-problem and continuous IAB ratio sub-problem.Then we propose a neural network to solve the binary associated matrix inference problem and a resource allocation algorithm to find the sub-optimal IAB ratio.Simulation results show that the proposed algorithm can achieve good performance with a fast inference speed.

Low complexity asymptotically unitary algorithm for hybrid beamforming in mmWave communication systems

In millimeter wave （mmWave） massive multiple-input multiple-output （MIMO） systems, because of the high hardware cost and high power consumption, the traditional fully digital beamforming （DBF） cannot be implemented easily. Meanwhile, analog beamforming which is implemented with phase shifters has high availability but suffers poor performance. Considering the advantages of above two, a potential solution is to design an appropriate hybrid analog and digital beamforming structure, where the available iterative optimization algorithm can get performance close to fully digital processing, but solving this sparse optimization problem faces with a high computational complexity. The key challenge of seeking out hybrid beamforming （HBF） matrices lies in leveraging the trade-off between the spectral efficiency performance and the computational complexity. In this paper, we propose an asymptotically unitary hybrid precoding （AUHP） algorithm based on antenna array response （AAR） properties to solve the HBF optimization problem. Firstly, we get the optimal orthogonal analog and digital beamforming matrices relying on the channel＇s path gain in absolute value by taking into account that the AAR matrices are asymptotically unitary. Then, an improved simultaneously orthogonal matching pursuit （SOMP） algorithm based on recursion is adopted to refine the hybrid combining. Numerical results demonstrate that our proposed AUHP algorithm enables a lower computational complexity with negligible spectral efficiency performance degradation.

Multi-User MmWave Beam Tracking via Multi-Agent Deep Q-Learning

Beamforming is significant for millimeter wave multi-user massive multi-input multi-output systems.In the meanwhile,the overhead cost of channel state information and beam training is considerable,especially in dynamic environments.To reduce the overhead cost,we propose a multi-user beam tracking algorithm using a distributed deep Q-learning method.With online learning of users’moving trajectories,the proposed algorithm learns to scan a beam subspace to maximize the average effective sum rate.Considering practical implementation,we model the continuous beam tracking problem as a non-Markov decision process and thus develop a simplified training scheme of deep Q-learning to reduce the training complexity.Furthermore,we propose a scalable state-action-reward design for scenarios with different users and antenna numbers.Simulation results verify the effectiveness of the designed method.

UAV Communications with Millimeter-Wave Beamforming:Potentials,Scenarios,and Challenges

Unmanned aerial vehicle(UAV)has been widely used in many fields and is arousing global attention.As the resolution of the equipped sensors in the UAV becomes higher and the tasks become more complicated,much higher data rate and longer communication range are required in the foreseeable future.As the millimeter-wave(mm Wave)band can provide more abundant frequency resources than the microwave band,much higher achievable rate can be guaranteed to support UAV services such as video surveillance,hotspot coverage,and emergency communications,etc.The flexible mm Wave beamforming can be used to overcome the high path loss caused by the long propagation distance.In this paper,we study three typical application scenarios for mm Wave-UAV communications,namely communication terminal,access point,and backbone link.We present several key enabling techniques for UAV communications,including beam tracking,multi-beam forming,joint Tx/Rx beam alignment,and full-duplex relay techniques.We show the coupling relation between mm Wave beamforming and UAV positioning for mm Wave-UAV communications.Lastly,we summarize the challenges and research directions of mm Wave-UAV communications in detail.

Joint User Association and Resource Allocation for Self-Backhaul Ultra-Dense Networks

In order to meet the exponentially increasing demand on mobile data traffic, self-backhaul ultra-dense networks(UDNs) combined with millimeter wave(mm Wave) communications are expected to provide high spatial multiplexing gain and wide bandwidths for multi-gigabit peak data rates. In selfbackhaul UDNs, how to make the radio access rates of small cells match their backhaul rates by user association and how to dynamically allocate bandwidth for the access links and backhaul links to balance two-hop link resources are two key problems on improving the overall throughputs. Based on this, a joint scheme of user association and resource allocation is proposed in self-backhaul ultra-dense networks. Because of the combinatorial and nonconvex features of the original optimization problem, it has been divided into two subproblems. Firstly, to make the radio access rates of small base stations match their backhaul rates and maximize sum access rates per Hz of all small cells, a proportional constraint is introduced, and immune optimization algorithm(IOA) is adopted to optimize the association indicator variables and the boresight angles of between users and base stations. Then, the optimal backhaul and access bandwidths are calculated by differentiating the general expression of overall throughput. Simulation results indicatethat the proposed scheme increases the overall throughputs significantly compared to the traditional minimum-distance based association scheme.

A robust beam tracking scheme for millimeter wave HetNets

Millimeter Wave(mmWave)communication has been widely acknowledged as an attractive solution to address high-speed transmission of massive data in 5G and beyond 5G systems due to the promising spectrum availability.However,mmWave signals are highly susceptible to blockage and may suffer from rapidly changing channels.Thus,directional/beam tracking becomes imperative yet essential for robust mmWave communications.To address this challenge,we propose a robust beam tracking scheme for mmWave Heterogeneous Networks(HetNets)with multi-connectivity.Different from most existing schemes,the proposed beam tracking scheme is effective for outage events.We first discuss theμWave-assisted beam tracking procedure with and without candidate beams,and then analyze the inherent correlation between mmWave link quality and the operating beamwidth and occlusion range to derive the optimal beamwidth.Theoretical and numerical results show that the proposed beam tracking scheme can improve the robustness of mmWave communications while guaranteeing the rate performance.

Forward link outage performance of aeronautical broadband satellite communications

High-throughput satellites(HTSs) play an important role in future millimeter-wave(mm Wave) aeronautical communication to meet high speed and broad bandwidth requirements. This paper investigates the outage performance of an aeronautical broadband satellite communication system’s forward link, where the feeder link from the gateway to the HTS uses free-space optical(FSO) transmission and the user link from the HTS to aircraft operates at the mm Wave band. In the user link, spot beam technology is exploited at the HTS and a massive antenna array is deployed at the aircraft. We first present a location-based beamforming(BF) scheme to maximize the expected output signal-to-noise ratio(SNR) of the forward link with the amplify-and-forward(AF) protocol,which turns out to be a phased array. Then, by supposing that the FSO feeder link follows Gamma-Gamma fading whereas the mm Wave user link experiences shadowed Rician fading, we take the influence of the phase error into account, and derive the closed-form expression of the outage probability(OP) for the considered system. To gain further insight, a simple asymptotic OP expression at a high SNR is provided to show the diversity order and coding gain. Finally, numerical simulations are conducted to confirm the validity of the theoretical analysis and reveal the effects of phase errors on the system outage performance.

Internet of radio and light:5G building network radio and edge architecture

The Internet of Radio-Light(IoRL)is a cutting-edge system paradigm to enable seamless 5G service provision in indoor environments,such as homes,hospitals,and museums.The system draws on innovative architectural structure that sits on the synergy between the Radio Access Network(RAN)technologies of millimeter Wave communications(mmWave)and Visible Light Communications(VLC)for improving network throughput,latency,and coverage compared to existing efforts.The aim of this paper is to introduce the IoRL system architecture and present the key technologies and techniques utilised at each layer of the system.Special emphasis is given in detailing the IoRL physical layer(Layer 1)and Medium Access Control layer(MAC,Layer 2)by means of describing their unique design characteristics and interfaces as well as the robust IoRL methods of improving the estimation accuracy of user positioning relying on uplink mmWave and downlink VLC measurements.