Following the successful use of sidelink in Long Term Evolution (LTE) for Proximity Services (ProSe) and Cellular Vehicular-to-everything (C-V2X), the 3rd Generation Partnership Project (3GPP) is working towards its evolution in New Radio (NR) systems in the context of the so-called NR V2X. This new technology is expected to complement LTE C-V2X for advanced services by offering low latency, high reliability, and high throughput V2X services for advanced driving use cases. To do this, NR V2X is equipped with new features, such as the support for groupcast and unicast communication, a novel feedback channel, and a new control channel design. In this paper, we provide a complete history of sidelink technology in 3GPP followed by a detailed overview of NR V2X technology, with special emphasis on Mode 2 for out of coverage operation and autonomous resource selection. Furthermore, this paper presents a system-level NR V2X standard-compliant simulator, as an extension of the popular and open-source NR network simulator 5G-LENA, based on ns-3. In particular, we focus on the design, implementation, and evaluation of the sensing-based resource selection in NR V2X Mode 2, in a highway scenario for a platooning use case. Through several and extensive simulation campaigns, we test the impact of different NR V2X parameters, such as the numerology, the resource selection window size, the number of retransmissions, the maximum number of resources per reservation, and the probability of keeping the same resources during reselection, in a sensing-based resource selection. Finally, we provide a comparison campaign that shows the gains attained by the sensing-based resource selection, proposed during 3GPP Release 16, over the random selection strategy, considered in 3GPP Release 17 for power saving purposes.
This paper presents a machine learning based handover management scheme for LTE to improve the Quality of Experience (QoE) of the user in the presence of obstacles. We show that, in this scenario, a state-of-the-art handover algorithm is unable to select the appropriate target cell for handover, since it always selects the target cell with the strongest signal without taking into account the perceived QoE of the user after the handover. In contrast, our scheme learns from past experience how the QoE of the user is affected when the handover was done to a certain eNB. Our performance evaluation shows that the proposed scheme substantially improves the number of completed downloads and the average download time compared to stateof-the-art. Furthermore, its performance is close to an optimal approach in the coverage region affected by an obstacle.
Recently, there has been much interest by the cellular network industry in utilizing unlicensed spectrum to expand potential capacity. In particular, two LTE unlicensed technologies gained much attention: licensed-assisted access (LAA) and LTE unlicensed (LTE-U). While these are rapidly entering the market, there are not many studies in the literature that are providing a complete evaluation and comparison of their performance. Available work usually focuses on single technology standalone evaluations. Also, despite the vast body of simulation results by industry and academia, the simulators are not publicly available, and the analytical models proposed in the literature do not offer complex enough frameworks for thorough performance evaluations. To carry out an evaluation study, we have built a comprehensive simulation platform, strictly complying with the standards and specifications of each technology. The models are built upon popular ns-3 simulator, have been designed in close consultation with industry experts, and have been validated through calibration processes and against analytical proposals and experimental platforms. In this paper, we provide a detailed overview, performance evaluation, and comparison of LAA and LTE-U in a wide variety of scenarios, following 3GPP and Wi-Fi Alliance (WFA) guidelines. We show that despite the market is confirming LAA as the leading unlicensed LTE technology, in certain setups, efficient implementations of LTE-U may prove unexpectedly better in coexisting with Wi-Fi. Similarly, the expected behaviors of the LAA LBT procedure can reveal untrue, depending on the traffic or interference patterns and specific implementation details, even in Wi-Fi. This paper also includes scenarios involving TCP, which is a rarely treated topic in the literature in the context of LTE and Wi-Fi coexistence. The end-to-end and full protocol stack simulation platform is openly available to foster results' reproducibility and collaborative development.
In this paper, we present our approach to simulate mobility management scenarios for LTE heterogeneous network deployments defined by challenging radio propagation scenarios, such as the presence of coverage holes. We focus on the LTE module of ns-3, which is also known as LENA. Our contribution is twofold. On one hand, we propose a set of new features for the LTE module, including a new model for simulating obstacles blocking the propagation of radio signals, and a handover model suitable for the offline evaluation of mobility management solutions. On the other hand, we describe in detail the setup of the simulation scenario, highlighting the challenges that we faced during the implementation and discussing the chosen configuration parameters. Finally, we present some simulation results that we obtained with the proposed approach.
In this paper, we propose a statistical framework to systematically evaluate the fairness offered by different LTE (Long Term Evaluation) technologies when they coexist with Wi-Fi in unlicensed band. In particular, we study the coexistence performance of both 3GPP LAA (Licensed Assisted Access) and LTE-U (LTE in unlicensed spectrum), as specified by LTE-U forum. We map the generally accepted 3GPP definition of fairness onto the stochastic dominance concept. We use the two-sample one-sided Kolmogorov-Smirnov test (KS-test) to test the specific hypothesis of fairness defined through throughput and latency performance, as proposed by 3GPP. We evaluate throughput and latency by means of the ns-3 simulator for LTE and Wi-Fi coexistence. According to both the simulation results and the statistical analysis, there is a need for proprietary solutions to operate on top of what has been standardized, which will able to improve the fairness in the coexistence scenario. On the other hand, through the comparative analysis of LAA and LTE-U coexistence performance, we confirm what could be expected, i.e., that LAA better performs in terms of fairness in both throughput and latency and LTE-U introduces more collisions.
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