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.

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Evaluating unlicensed LTE technologies: LAA vs LTE-U

LTE-Licensed Assisted Access (LAA) networks are beginning to be deployed widely in major metropolitan areas in the U.S. in the unlicensed 5 GHz bands, which have existing dense deployments of Wi-Fi as well. Various aspects of the coexistence scenarios such deployments give rise to have been considered in a vast body of academic and industry research. However, there is very little data and research on how these coexisting networks will behave in practice. The question of “fair coexistence” between Wi-Fi and LAA has moved from a theoretical question to reality. The recent roll-out of LAA deployments provides an opportunity to collect data on the operation of these networks as well as studying coexistence issues on the ground. In this article we describe the first results of a measurement campaign conducted over many months, using custom apps as well as off-the-shelf tools, in several areas of Chicago where the major carriers have been expanding LAA deployments. The measurements reveal that coexistence between LAA and Wi-Fi in dense urban environments where both systems aggregate multiple channels continues to be a challenging problem that requires further research.

Measurement-Based Coexistence Studies of LAA & Wi-Fi Deployments in Chicago

6G communication research is currently in the early stage. A consensus on 6G has been achieved that ultra-reliable low latency communication (URLLC) is still an important application as it is in 5G. The spectrum resources are scarce to support the massive throughput demands, leading to unbearable latency. Also, the collisions in the shared spectrum make the channels unreliable. The problems in unlicensed bands are more severe due to interference among multiple communication technologies. Therefore, it is urgent to design efficient spectrum sharing algorithms to support URLLC in 5G and the emerging 6G. In this article, we explore the related 3GPP standards, recall the recent advances in spectrum sharing algorithms, and analyze the challenges of spectrum sharing in 5G/6G. We also provide potential research fields in future 5G/6G applications.

Spectrum Sharing for 5G/6G URLLC: Research Frontiers and Standards

Wireless mesh networks are being deployed all around the world both to provide ubiquitous connection to the Internet and to carry data generated by several services (video surveillance, smart grids, earthquake early warning systems, etc.). In those cases where fixed power connections are not available, mesh nodes operate by harvesting ambient energy (e.g., solar or wind power) and hence they can count on a limited and time-varying amount of power to accomplish their functions. Since we consider mesh nodes equipped with multiple radios, power savings and network performance can be maximized by properly routing flows, assigning channels to radios and identifying nodes/radios that can be turned off . Thus, the problem we address is a joint channel assignment and routing problem with additional constraints on the node power consumption, which is NP-complete. In this paper, we propose a heuristic, named minimum power channel assignment and routing algorithm (MP-CARA), which is guaranteed to return a local optimum for this problem. Based on a theoretical analysis that we present in the paper, which gives an upper bound on the outage probability as a function of the constraint on power consumption, we can guarantee that the probability that a node runs out of power with MP-CARA falls below a desired threshold. The performance of MP-CARA is assessed by means of an extensive simulation study aiming to compare the solutions returned by MP-CARA to those found by other heuristics proposed in the literature.

A Channel Assignment and Routing Algorithm for Energy Harvesting Multiradio Wireless Mesh Networks

Unlike the conventional device-to-device (D2D) networks, the unlicensed D2D (D2D-U) pairs can not only reuse the licensed channels with the base station (BS) but also share the unlicensed channels with the WiFi stations. One challenge arises from the fact that the co-channel interference on licensed channels and the collision probability on unlicensed channels may cause extra power consumption at the terminals. Accordingly, we first propose a channel access method for the D2D-U pairs on unlicensed channels. Then, a decentralized joint spectrum and power allocation scheme is designed to minimize the power consumption at D2D-U pairs. Different from the existing distributed schemes, the proposed scheme can guarantee the global minimization of power consumption across the D2D-U pairs. Simulation results validate the theoretical analysis and verify the performance from the proposed scheme.

Decentralized Radio Resource Adaptation in D2D-U Networks

On a fair coexistence of LTE and Wi-Fi in the unlicensed spectrum: A Survey

Routing in multi-radio wireless mesh networks is a very challenging problem. In this paper, we propose a forwarding paradigm based on MPLS (Multi Protocol Label Switching) which makes use of a novel mechanism, denoted as MPLS splitting policy. Such mechanism allows to configure multiple next hops at an intermediate node, so that the incoming traffic is partitioned among the next hops according to predefined coefficients named split ratios. The MPLS splitting policy has been designed to allow for load balancing and fast local restoration. With such a mechanism, it is crucial to properly determine the set of split ratios, as they determine how the traffic is routed across the network. We present an approach to compute a set of split ratios that guarantee high performance under different traffic loads. To this end, we adopt the hose traffic model, according to which we only have knowledge of the maximum amount of traffic entering or leaving the network at each edge node. A thorough simulation study is conducted to show that our approach outperforms other routing protocols in terms of throughput and robustness against traffic load variations and single node failures.

G. Di Stasi

Papers

On a fair coexistence of LTE and Wi-Fi in the unlicensed spectrum: A Survey

A New MPLS-Based Forwarding Paradigm for Multi-Radio Wireless Mesh Networks

Design and implementation of WiMesh