In 5G systems, a predefined codebook with a limited number of beams is used during the initial access and beam management procedures to establish and maintain the connection between the users and the network. At 5G mmimeter wave (mmWave) frequencies, due to the very narrow and directional beams obtained by beamforming, intelligently designing a codebook with a limited number of beams is crucial to avoid coverage holes. We formulate an optimization problem for the beam-codebook design to maximize the coverage probability, which is a quadratically-constrained mixed-integer problem. We propose a set of data-driven codebook design algorithms to solve the optimization problem, which, for a given codebook size constraint, adapts the codebook to the deployment scenario using the provided input channel data. For a sample deployment scenario, we show that as the codebook size increases, the proposed algorithms converge to the upper bound in terms of the coverage probability much faster than several benchmark algorithms. Hence, the proposed algorithms can achieve the coverage levels of benchmark algorithms with a much smaller codebook size. This can significantly reduce the initial access, beam management, and handover delays, which in turn provide higher data rates, lower latency, and lower interruption times.

We consider vehicle-to-infrastructure (V2I) type communication over millimeter wave (mmWave) frequencies and evaluate its performance limitations in terms of coverage. Specifically, we analyze the outage probability and average outage duration for a communicating vehicle exchanging data with roadside units (RSUs), where the system performance is limited by the path-loss that the intermediate links experience. The path-loss depends on the length of the link, as well as the number of vehicles blocking the line-of-sight (LOS) path. By using a Markov chain formulation and its steady-state solution, we obtain analytical expressions for the outage probability and average outage duration. After demonstrating that the durations of outage events constitute a greater limitation on the system performance than outage probability, we examine two approaches to mitigate this limitation: increasing the RSU density and increasing the path-loss threshold for communication.

Millimeter-wave (mmWave) is a promising network access technology to enable reliable communications in future vehicular networks, which is expected to be dominated by autonomous vehicles. In this study, we consider line-of- sight (LOS) communications between mmWave-enabled vehicles and roadside units (RSUs) in a highway scenario where the LOS links can potentially get blocked by blocking vehicles. We focus on two performance metrics, namely the blockage probability and the average blockage duration. We establish a continuous-time Markov chain formulation of the problem in which transition rates depend on the speed, length and intervehicle distance of blocking vehicles. By using the steady-state solution of this model, we explicitly derive the blockage probability and average blockage duration. After validating the accuracy of the analytical results by comparing with simulations, we demonstrate that the main performance limitation of mmWave systems is due to the blockage duration, not the probability of blockage events. We also discuss the implications of our results in terms of the deployment of RSUs to provide ultra-reliable and low-latency connectivity.

A transmission profile refers to a transmission power and a modulation and coding scheme to be used for packet transmissions over a wireless link. The goal of this paper is to develop transmission profile selection policies so as to minimize the average power consumption on a wireless link while satisfying a certain delay constraint given in terms of a delay violation probability. Toward the assessment of profile selection policies, a multi-regime Markov fluid queue model is proposed to obtain the average power consumption and the queue waiting time distribution which allows one to analyze the energy-delay tradeoff in queuing systems for which the packet transmission duration is allowed to depend on the delay experienced by the packet until the beginning of service. Numerical examples are presented with transmission profiles obtained from realistic LTE simulations. Several transmission profile selection policies are proposed and subsequently compared using the analytical model.