A Tutorial on Mathematical Modeling of 5G/6G Millimeter Wave and Terahertz Cellular Systems

Millimeter wave (mmWave) and terahertz (THz) radio access technologies (RAT) are expected to become a critical part of the future cellular ecosystem providing an abundant amount of bandwidth in areas with high traffic demands. However, extremely directional antenna radiation patterns that need to be utilized at both transmit and receive sides of a link to overcome severe path losses, dynamic blockage of propagation paths by large static and small dynamic objects, macro-and micromobility of user equipment (UE) makes provisioning of reliable service over THz/mmWave RATs an extremely complex task. This challenge is further complicated by the type of applications envisioned for these systems inherently requiring guaranteed bitrates at the air interface. This tutorial aims to introduce a versatile mathematical methodology for assessing performance reliability improvement algorithms for mmWave and THz systems. Our methodology accounts for both radio interface specifics as well as service process of sessions at mmWave/THz base stations (BS) and is capable of evaluating the performance of systems with multiconnectivity operation, resource reservation mechanisms, priorities between multiple traffic types having different service requirements. The framework is logically separated into two parts: (i) parameterization part that abstracts the specifics of deployment and radio mechanisms, and (ii) queuing part, accounting for details of the service process at mmWave/THz BSs. The modular decoupled structure of the framework allows for further extensions to advanced service mechanisms in prospective mmWave/THz cellular deployments while keeping the complexity manageable and thus making it attractive for system analysts.publishedVersionPeer reviewe

A Tutorial on Mathematical Modeling of 5G/6G Millimeter Wave and Terahertz Cellular Systems

Millimeter wave (mmWave) and terahertz (THz) radio access technologies (RAT) are expected to become a critical part of the future cellular ecosystem providing an abundant amount of bandwidth in areas with high traffic demands. However, extremely directional antenna radiation patterns that need to be utilized at both transmit and receive sides of a link to overcome severe path losses, dynamic blockage of propagation paths by large static and small dynamic objects, macro-and micromobility of user equipment (UE) makes provisioning of reliable service over THz/mmWave RATs an extremely complex task. This challenge is further complicated by the type of applications envisioned for these systems inherently requiring guaranteed bitrates at the air interface. This tutorial aims to introduce a versatile mathematical methodology for assessing performance reliability improvement algorithms for mmWave and THz systems. Our methodology accounts for both radio interface specifics as well as service process of sessions at mmWave/THz base stations (BS) and is capable of evaluating the performance of systems with multiconnectivity operation, resource reservation mechanisms, priorities between multiple traffic types having different service requirements. The framework is logically separated into two parts: (i) parameterization part that abstracts the specifics of deployment and radio mechanisms, and (ii) queuing part, accounting for details of the service process at mmWave/THz BSs. The modular decoupled structure of the framework allows for further extensions to advanced service mechanisms in prospective mmWave/THz cellular deployments while keeping the complexity manageable and thus making it attractive for system analysts.publishedVersionPeer reviewe

Optimal Multicasting in Dual mmWave/ μ Wave 5G NR Deployments With Multi-Beam Directional Antennas

The design of multicast services in the fifth-generation (5G) New Radio (NR) deployments is hampered by the directional nature of antenna radiation patterns. This complexity is further compounded by the emergence of new deployment options, such as dual millimeter wave (mmWave) and microwave (μ Wave) base station (BS) deployments, as well as new antenna design solutions. In this paper, the resource allocation task for multicast services in dual mmWave/ μ Wave deployments with multi-beam directional antennas is addressed as a multi-period variable cost and size bin packing problem. We solve this problem and characterize the globally optimal solution. To decrease complexity, we then propose and test the simulated annealing approximation and relaxation techniques, i.e., local branching and relaxation-induced neighborhood search heuristic. Our results show that for the considered system parameters, the properties of the optimal solution depend on the density of dual-mode BS deployment and BS deployment type. We observe a transition point at which the system shifts from primarily utilizing mmWave resources to exclusively using μ Wave BS. Furthermore, the optimal number of beams is upper limited by 3 for mmWave and by 2 for μ Wave BSs. The efficiency of resource utilization is also affected by the utilized numerology and technology selection priority. Finally, we show that the simulated annealing technique allows for decreasing the solution complexity at the expense of slightly overestimating the amount of resources.Peer reviewe

Evaluating SIR in 3D mmWave Deployments: Direct Modeling and Feasible Approximations

Recently, new opportunities for utilizing the extremely high frequencies have become instrumental to design the fifthgeneration (5G) mobile technology. The use of highly directional antennas in millimeter-wave (mmWave) bands poses an important question of whether 2D modeling suffices to capture the resulting system performance accurately. In this work, we develop a novel mathematical framework for performance assessment of the emerging 3D mmWave communication scenarios, which takes into account vertical and planar directivities at both ends of a radio link, blockage effects in three dimensions, and random heights of communicating entities. We also formulate models having different levels of details and verify their accuracy for a wide range of system parameters. We show that capturing the randomness of both Tx and Rx heights as well as the vertical antenna directivities becomes crucial for accurate system characterization. The conventional planar models provide overly optimistic results that overestimate performance. For instance, the model with fixed heights that disregards the effect of vertical exposure is utterly pessimistic. Other two models, one having random heights and neglecting vertical exposure and another one characterized by fixed heights and capturing vertical exposure are less computationally expensive and can be used as feasible approximations for certain ranges of input parameters.acceptedVersionPeer reviewe

Quantifying the Impact of Guard Capacity on Session Continuity in 3GPP New Radio Systems

Dynamic blockage of millimeter-wave (mmWave) radio propagation paths by dense moving crowds calls for advanced techniques to preserve session continuity in the emerging New Radio (NR) systems. To further improve user performance by balancing the new and ongoing session drop probabilities, we investigate the concept of guard capacity – reserving a fraction of radio resources at the NR base stations exclusively for the sessions already accepted for service. To this aim, we develop a detailed mathematical framework that takes into account the key effects in mmWave systems, including the heights of communicating entities, blocker geometry and mobility, modulation and coding schemes and antenna array geometry, as well as radio propagation and queuing specifics. Using our framework, which enables sessions to change their resource requirements during service, we demonstrate that reserving even a small fraction of bandwidth (less than 10%) exclusively for the sessions already accepted by the system allows to enhance session continuity at the expense of a slight growth in the new session drop probability as well as a small decrease in the resource utilization (approximately 5–7%). Furthermore, guard capacity is shown to perform better in overloaded conditions and with sessions having high data rate requirements, thus making it particularly useful for the NR systems. Our results indicate that guard capacity is a viable option for improving session continuity that can be used by the network operators in combination with other techniques, such as multi-connectivity, to maintain user experience.acceptedVersionPeer reviewe

Modeling Three-Dimensional Interference and SIR in Highly Directional mmWave Communications

Recently, new opportunities for utilizing extremely high frequencies have become instrumental in developing fifth-generation(5G) mobile technology. The use of highly directional antennas in millimeter-wave (mmWave) bands poses an important question of whether two- dimensional modeling suffices to capture the resulting system performance. Accounting for the effects of human body blockage by mmWave transmissions, in this work we compare the performance of the conventional two-dimensional and the proposed three- dimensional modeling. With our stochastic geometry based approach, we consider the aggregate interference and signal-to- interference ratio (SIR) to be the main metrics of interest. Both counterpart models attempt to capture the inherent behavior of 5G mmWave systems by incorporating the effects of human body blockage and antenna directivity. We thus deliver a realistic numerical assessment by comparing the three-dimensional modeling with its two-dimensional projection to reveal the resulting discrepancy.acceptedVersionPeer reviewe

Analyzing Effects of Directionality and Random Heights in Drone-based mmWave Communication

Utilization of drones as aerial access points (AAPs) is a promising concept to enhance network coverage and area capacity promptly and on demand. The emerging millimeter-wave (mmWave) communication technology may in principle deliver higher data rates, thus making the use of AAPs more effective. By extending the conventional (planar) stochastic geometry considerations, we construct a novel three-dimensional model for drone-based mmWave communication that captures the high directionality of transmissions as well as the random heights of the communicating entities. Choosing signal-to-interference ratio (SIR) as our primary parameter of interest, we assess system performance with an emphasis on the impact of the ‘vertical’ dimension in aerial mmWave connectivity. We also demonstrate that accurate performance assessment is only possible with simplified models for certain ranges of input parameters.acceptedVersionPeer reviewe

Improved Session Continuity in 5G NR with Joint Use of Multi-Connectivity and Guard Bandwidth

The intermittent millimeter-wave radio links as a result of human-body blockage are an inherent feature of the 5G New Radio (NR) technology by 3GPP. To improve session continuity in these emerging systems, two mechanisms have recently been proposed, namely, multi-connectivity and guard bandwidth. The former allows to establish multiple spatially-diverse connections and switch between them dynamically, while the latter reserves a fraction of system bandwidth for sessions changing their state from non-blocked to blocked, which ensures that the ongoing sessions have priority over the new ones. In this paper, we assess the joint performance of these two schemes for the user- and system-centric metrics of interest. Our numerical results reveal that the multi-connectivity operation alone may not suffice to increase the ongoing session drop probability considerably. On the other hand, the use of guard bandwidth significantly improves session continuity by somewhat compromising new session drop probability and system resource utilization. Surprisingly, the 5G NR system implementing both these techniques inherits their drawbacks. However, complementing it with an initial AP selection procedure effectively alleviates these limitations by maximizing the system resource utilization, while still providing sufficient flexibility to enable the desired trade-off between new and ongoing session drop probabilities.acceptedVersionPeer reviewe

Secure and Reliable IoT Networks Using Fog Computing with Software-Defined Networking and Blockchain

Designing Internet of Things (IoT) applications faces many challenges including security, massive traffic, high availability, high reliability and energy constraints. Recent distributed computing paradigms, such as Fog and multi-access edge computing (MEC), software-defined networking (SDN), network virtualization and blockchain can be exploited in IoT networks, either combined or individually, to overcome the aforementioned challenges while maintaining system performance. In this paper, we present a framework for IoT that employs an edge computing layer of Fog nodes controlled and managed by an SDN network to achieve high reliability and availability for latency-sensitive IoT applications. The SDN network is equipped with distributed controllers and distributed resource constrained OpenFlow switches. Blockchain is used to ensure decentralization in a trustful manner. Additionally, a data offloading algorithm is developed to allocate various processing and computing tasks to the OpenFlow switches based on their current workload. Moreover, a traffic model is proposed to model and analyze the traffic indifferent parts of the network. The proposed algorithm is evaluated in simulation and in a testbed. Experimental results show that the proposed framework achieves higher efficiency in terms of latency and resource utilization

Characterizing Resource Allocation Trade-Offs in 5G NR Serving Multicast and Unicast Traffic

The use of highly directional antenna radiation patterns for both the access point (AP) and the user equipment (UE) in the emerging millimeter-wave (mmWave)-based New Radio (NR) systems is inherently beneficial for unicast transmissions by providing an extension of the coverage range and eventually resulting in lower required NR AP densities. On the other hand, efficient resource utilization for serving multicast sessions demands narrower antenna directivities, which yields a trade-off between these two types of traffic that eventually affects the system deployment choices. In this work, with the tools from queuing theory and stochastic geometry, we develop an analytical framework capturing both the distance- and traffic-related aspects of the NR AP serving a mixture of multicast and unicast traffic. Our numerical results indicate that the service process of unicast sessions is severely compromised when (i) the fraction of unicast sessions is significant, (ii) the spatial session arrival intensity is high, or (iii) the service time of the multicast sessions is longer than that of the unicast sessions. To balance the multicast and unicast session drop probabilities, an explicit prioritization is required. Furthermore, for a given fraction of multicast sessions, lower antenna directivity at the NR AP characterized by a smaller NR AP inter-site distance (ISD) leads to a better performance in terms of multicast and unicast session drop probabilities. Aiming to increase the ISD, while also maintaining the drop probability at the target level, the serving of multicast sessions is possible over the unicast mechanisms, but it results in worse performance for the practical NR AP antenna configurations. However, this approach may become feasible as arrays with higher numbers of antenna elements begin to be available. Our developed mathematical framework can be employed to estimate the parameters of the NR AP when handling a mixture of multicast and unicast sessions as well as drive a lower bound on the density of the NR APs, which is needed to serve a certain mixture of multicast and unicast traffic types with their target performance requirements.acceptedVersionPeer reviewe