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./m ² ) 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.

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).

Presently, we observe an unprecedented growth of traffic volumes in modern cellular networks. Consequently, to effectively meet the impeding capacity crunch, current spectrum bands can be extended by using LSA (Licensed Shared Access) - the promising technology that allows an operator to lease additional frequency bands in order to satisfy the increasing data rate requirements. This technology is naturally suitable for the state-of-the-art 3GPP LTE cellular networks, since it allows to flexibly control resource allocation across the network users. Owing to that, the operator can employ the LSA band whenever desired to improve area capacity and increase data rate. However, due to the fact that the LSA band may be unexpectedly revoked by its original owner, there exists a certain chance of degradation in system performance and user service quality. This paper focuses on studying a one-cell 3GPP LTE system over the LSA technology, with both analysis and simulations, by proposing a baseline methodology to model the unreliable operation of an LSA frequency band.

As it is predicted that mobile traffic demand will reach an astonishing 190 exabytes by 2018, current methods of spectrum allocation and management need to be rethought towards more advanced sharing of frequency bands. To this end, a novel regulatory framework has recently emerged, named Licensed Shared Access (LSA), which enables guaranteed spectrum access for a limited number of sharers. However, realistic LSA band operation may result in its abrupt unavailability, causing traffic delays and even network access failures in case of unsuccessful “evacuation” of a user back to conventional cellular bands. In this paper, we formulate an adequate queuing-theoretical model for evaluating such service failure and interruption probability for users that attempt to operate within a cell of a network with the LSA capability.

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.

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./m ² 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.