Uninterrupted Connectivity Time in THz Systems Under User Micromobility and Blockage

Terahertz (THz) band is considered as the main candidate for new radio access technology in sixth-generation (6G) cellular systems. However, the performance of these systems will be severely affected by not only blockage but user equipment (UE) micromobility in hands of a user. The negative effects of these phenomena can be alleviated by utilizing the multi-connectivity functionality that allows UE to maintain two or more links to nearby base stations (BS) and use them when the currently active link is lost. By accounting for THz specific propagation, antenna and beamsearching design, the density of THz BS deployment, and multi-connectivity operation, we investigate the successful session completion probability under both types of impairments. Our results indicate that the gains of multi-connectivity are observed up to 5 simultaneously supported links and heavily depend on the application outage tolerance time and is mostly affected by micromobility. To improve it, one needs to ensure that the application may tolerate outage caused by beamsearching time which is on the order of milliseconds.acceptedVersionPeer reviewe

Coverage, Rate, and Last Hop Selection in Multi-Hop Communications in Highway Scenarios

The recent 3GPP initiative to extend IAB technology to mobile nodes in recently stated Release 18 opens up new opportunities for services operators in highway scenarios, where the extreme density of base stations (BS) is required to deliver uninterrupted coverage. The latter problem is specifically important for millimeter wave (mmWave) and future sub-terahertz (sub-THz) deployments. However, in such systems, there are inherent trade-offs between the rate provided over the multi-hop chain, the so-called “bridge”, and the inter-site distance. One of the critical factors involved in this trade-off is the choice of the last hop. In this paper, we utilize realistic channel measurements at 300 GHz to develop a framework characterizing the above-mentioned trade-off. Then, we proceed proposing a simple technique to maximize the latter by addressing the “last-hop problem” and compare its performance to the set of alternative solutions. Our numerical results illustrate that bumper location is better in terms of relaying communication distance. Furthermore, the proposed last hop selection strategies allow for extreme performance gains in terms of data rate as compared to the traditional approaches reaching 100% for large ISD and 400–500% for small ISDs. In absolute numbers, the proposed relying with the last hop selection strategy allows for reducing the required BS density along the highways by 15–30% depending on the vehicle density and required level of connectivity

Optimal Antenna Locations for Coverage Extension in Sub-Terahertz Vehicle-to-Vehicle Communications

Sub-terahertz (sub-THz, 100-300 GHz) communications promise to bring extraordinary rates in future 6G systems. High path loss and blockage effects will limit the coverage of base stations (BS) to a few hundred meters making deployment of such systems along the roads expensive. As a way to decrease the BS density, relaying has been proposed. However, vehicle-to-vehicle (V2V) propagation is characterized by different sets of communications paths depending on the antenna locations raising the question of their optimal positions. In this paper, by utilizing IEEE 802.15.3d parameters and 300 GHz propagation measurements, we develop a mathematical framework for comparison of multi-hop relaying systems with different antenna locations. We utilize coverage, BS availability, and the data rate over a multi-hop path as metrics of interest. Our results show that the windshield location is characterized by lower data rates and larger coverage while bumper and engine levels are similar in terms of these metrics. For the windshield location, the coverage is extended by 50% with BS availability 0.95. The windshield location is recommended as it is less sensitive to the technology penetration rate and is characterized by larger coverage. The proposed approach shows gains of up to 32% in terms of required BS density for the range of vehicles density (10-40 units/km).Peer reviewe

System-Level Analysis of Energy and Performance Trade-offs in mmWave 5G NR Systems

Energy efficiency and service reliability are two critical requirements for 5G New Radio cellular access. To address the latter, 3GPP has proposed multiconnectivity operation allowing user equipment (UE) to maintain active links to more than a single base station. However, the use of this technique compromises the energy efficiency of UE. In this paper, we develop a mathematical model capturing key energy and performance indicators as a function of system and environmental conditions. Then, we apply it to investigate the trade-offs between user performance and energy efficiency as well as the effect of scaling of discontinuous reception (DRX) timers. For a considered set of system parameters, our results reveal that for low micromobility speed ≤ 0.1° /s and blockers density, ≤ 0.1 bl./m2 two simultaneously supported links with minimal DRX timers lead to optimal performance. For higher blockers density more than two links are needed to optimize energy efficiency while for high micromobility speed multiconnectivity does not allow to improve energy efficiency at all. Thus, the optimal degree of multiconnectivity and DRX timer scaling coefficients depend on the environmental characteristics including both micromobility speed and density of blockers and need to be dynamically updated during UE operation.Peer reviewe

Quantifying the Density of mmWave NR Deployments for Provisioning Multi-Layer VR Services

The 5G New Radio (NR) technology operating in millimeter wave (mmWave) frequency band is designed for support bandwidth-greedy applications requiring extraordinary rates at the access interface. However, the use of directional antenna radiation patterns, as well as extremely large path losses and blockage phenomenon, requires efficient algorithms to support these services. In this study, we consider the multi-layer virtual reality (VR) service that utilizes multicast capabilities for baseline layer and unicast transmissions for delivering an enhanced experience. By utilizing the tools of stochastic geometry and queuing theory we develop a simple algorithm allowing to estimate the deployment density of mmWave NR base stations (BS) supporting prescribed delivery guarantees. Our numerical results show that the highest gains of utilizing multicast service for distributing base layer is observed for high UE densities. Despite of its simplicity, the proposed multicast group formation scheme operates close to the state-of-the-art algorithms utilizing the widest beams with longest coverage distance in approximately 50-70% of cases when UE density is lambda >= 0.3. Among other parameters, QoS profile and UE density have a profound impact on the required density of NR BSs while the effect of blockers density is non-linear having the greatest impact on strict QoS profiles. Depending on the system and service parameters the required density of NR BSs may vary in the range of 20-250 BS/km(2).publishedVersionPeer reviewe

Balancing Latency and Energy Efficiency in mmWave 5G NR Systems with Multiconnectivity

Multiconnectivity is a vital option in 5G New Radio (NR) systems allowing user equipment (UE) to maintain multiple links to nearby base stations (BS) improving service reliability. However, this functionality is very power-hungry prohibiting its application in practice. To alleviate this shortcoming discontinuous reception (DRX) mechanism can be utilized. The latter requires careful parameterization as it may drastically increase latency at the air interface. In this paper, we develop a mathematical model to characterize the trade-off between energy efficiency and latency in millimeter wave (mmWave) 5G NR systems under micromobility and blockage impairments. We then utilize it to determine the optimal type of DRX timers scaling. We show that micromobility has a positive impact on energy efficiency. For low micromobility speeds (< 0.2°/s) proportional DRX scaling scheme with the scaling coefficient k < 1.0, provides the best performance in terms of considered metrics while for higher speeds it leads to a compromise between them. The optimal value of k depends on design preferences.acceptedVersionPeer reviewe

Modeling Coexistence of Unicast and Multicast Communications in 5G New Radio Systems

Multicasting is widely used in conventional wired and wireless networks as it allows to significantly improve resource utilization in presence of users interested in the same content. However, the support of this type of service in prospective 5G New Radio (NR) systems has received only little attention so far. In this paper, merging the tools of queuing theory and stochastic geometry we develop a model of 5G NR base station (BS) serving a mixture of unicast and multicast traffic. We validate our model against computer simulations using multicast/unicast session drop probabilities and system resource utilization as metrics of interest. Our numerical results illustrate that the presence of multicast type of traffic severely compromises performance of unicast sessions. Furthermore, this effect is amplified when the inter-site distance (ISD) between BSs increases. Thus, in order to satisfy prescribed performance guarantees in terms of unicast and multicast session drop probabilities, explicit resource reservation mechanism at NR BS might be required.acceptedVersionPeer reviewe

Ergodic Outage and Capacity of Terahertz Systems Under Micromobility and Blockage Impairments

Terahertz (THz) communications systems are expected to become a major enabling technology at the air interface in sixth-generation (6G) cellular systems. However, utilizing extremely narrow antenna radiation patterns at both base station (BS) and user equipment (UE) sides, these systems are affected by not only dynamic blockage but micromobility of UEs. To alleviate the impact of both factors one may utilize the multiconnectivity mechanism allowing for UE to remain connected to several BSs simultaneously and switch between them in case the active connection is lost. In this work, we develop a mathematical framework to characterize the outage probability and spectral efficiency associated with different degrees of multiconnectivity in dynamic blockage and micromobility environment for different beamsearching design options. Our results demonstrate that the presence of UE micromobility may have a positive impact on system performance. Particularly, multiconnectivity allows improving outage and spectral efficiency for small and medium blockers density (up to 0.5 bl./m2) up to that of an ideal system with zero beamsearching times. Furthermore, higher gains are observed for higher degrees of multiconnectivity (e.g., greater than two) as compared to the system with only blockage impairments. For higher blockers densities, however, the reverse effect is observed.acceptedVersionPeer reviewe