Search

New Radio Unlicensed (NR-U) enables 5G networks to operate in unlicensed channels, including the sub-7 GHz bands where transmitters are required to adhere to a set of contention resolution rules known as listen before talk (LBT). NR-U derives from a scheduled radio access technology where transmissions are expected to begin at fixed slot boundaries. The end of an LBT procedure, however, may not coincide with such a boundary. One solution to this problem is to have the NR-U base station wait a gap period to align with the slot boundary. We design, implement, and validate a simulator of NR-U channel access and conduct a performance analysis to assess several important issues: slot boundary synchronization between NR-U base stations, gap placement methods, impact of transmission settings, and performance under dense deployments. We also propose a method for improving the fairness of contending NR-U base stations and conclude our research with guidelines for configuring NR-U networks operating under gap-based channel access.

To improve the capacity of cellular systems without additional expenses on licensed frequency bands, the 3GPP consortium has designed cellular technologies that use the unlicensed spectrum. The important peculiarity of the usage models of these technologies, the latest of which is New Radio Unlicensed (NR-U), is the coexistence with Wi-Fi networks deployed in the same frequency band. That is why NR-U uses channel access methods similar to those of Wi-Fi. However, the performance of Wi-Fi networks notably deteriorates in coexistence scenarios. One of the reasons is the slotted structure of transmissions of cellular base stations in the unlicensed spectrum, which may imply the use of a reservation signal. The paper proposes two novel channel access methods for NR-U, in which an NR-U base station randomly stops sending the reservation signal to listen to the channel to detect and resolve collisions. Analytical models are developed to validate the proposed methods and evaluate their efficiency, taking into account important features of NR-U networks, such as flexible numerology and mini-slot transmissions. The obtained numerical results show that the proposed methods significantly improve the performance of the Wi-Fi or NR-U network without degradation of the throughput of the other technology in coexistence scenarios.

A widely deployed cellular network, supported by direct connections, can offer a promising solution that supports new services with strict requirements on access availability, reliability, and end-to-end (E2E) latency. The communications between vehicles can be made using different radio interfaces: One for cellular communication (i.e., cellular communication over the cellular network based on uplink (UL)/downlink (DL) connections) and the other for direct communication (i.e., D2D-based direct communications between vehicles which allows vehicular users (V-UEs) to communicate directly with others). Common cellular systems with licensed spectrum backed by direct communication using unlicensed spectrum can ensure high quality of service requirements for new intelligent transportation systems (ITS) services, increase network capacity and reduce overall delays. However, selecting a convenient radio interface and allocating radio resources to users according to the quality of service (QoS) requirements becomes a challenge. In this regard, let’s introduce a new radio resource allocation strategy to determine when it’s appropriate to establish the communication between the vehicles over a cellular network using licensed spectrum resources or D2D-based direct connections over unlicensed spectrum sharing with Wi-Fi. The proposed strategy aims at meeting the quality of service requirements of users, including reducing the possibility of exceeding the maximum delay restrictions and enhancing network capacity utilization in order to avoid service interruption. The proposed solution is evaluated by highlighting different conditions for the considered scenario, and it is demonstrated that the proposed strategy improves network performance in terms of transmitted data rate, packet success rate, latency, and resource usage

This paper elaborates on the design challenges, opportunities, and solutions for New Radio-based access to Unlicensed spectrum (NR-U) by taking into account the beam-based transmissions and the worldwide regulatory requirements. NR-U intends to expand the applicability of 5th generation New Radio access technology to support operation in unlicensed bands by adhering to Listen-Before-Talk (LBT) requirements for accessing the channel. LBT was already adopted by different variants of 4th generation Long Term Evolution (LTE) in unlicensed spectrum, i.e., Licensed-Assisted Access and MulteFire, to guarantee fair coexistence among different radio access technologies. In the case of beam-based transmissions, the NR-U coexistence framework is significantly different as compared to LTE in unlicensed spectrum due to the use of directional antennas, which enhance the spatial reuse but also complicate the interference management. In particular, beam-based transmissions are needed in the unlicensed spectrum at millimeter-wave (mmWave) bands, which is an attractive candidate for NR-U due to its large amount of allocated spectrum. As a consequence, some major design principles need to be revisited to address coexistence for beam-based NR-U. In this paper, different problems and the potential solutions related to channel access procedures, frame structure, initial access procedures, re-transmission procedures, and scheduling schemes are discussed. A simulation evaluation of different LBT-based channel access procedures for NR-U/Wi-Fi indoor mmWave coexistence scenarios is also provided., Comment: accepted for publication in IEEE Commun. Surveys & Tutorials

3GPP cellular communications in unlicensed spectrum allow transmission only after completing listen-before-talk (LBT) operation. For downlink, the LBT operation helps cellular traffic to coexist well with Wi-Fi traffic. However, cellular uplink transmission is attempted only at the time specifically determined by the base station after having a successful LBT and the user equipment (UE) may suffer transmission failure and delayed transmission due to Wi-Fi interference. As a result, cellular uplink traffic does not coexist well with Wi-Fi traffic. This article mathematically analyzes the problem of unfairness between cellular and Wi-Fi for uplink channel access. To address the coexistence problem in unlicensed spectrum, we propose a standard-compliant approach, termed UpChance, which allows the UE to use a minimum length of uplink reservation signal and the base station to determine the optimal timing for the UE’s uplink transmission. Through ns-3 simulation, we verify that UpChance improves the performance of fairness and random access completion time by up to 88% and 99%, respectively.

The unlicensed spectrum has been utilized to make up the shortage on frequency spectrum in new radio (NR) systems. To fully exploit the advantages brought by the unlicensed bands, one of the key issues is to guarantee the fair coexistence with WiFi systems. To reach this goal, timely and accurate estimation on the WiFi traffic loads is an important prerequisite. In this paper, a machine learning (ML) based method is proposed to detect the number of WiFi users on the unlicensed bands. An unsupervised Neural Network (NN) structure is applied to filter the detected transmission collision probability on the unlicensed spectrum, which enables the NR users to precisely rectify the measurement error and estimate the number of active WiFi users. Moreover, NN is trained online and the related parameters and learning rate of NN are jointly optimized to estimate the number of WiFi users adaptively with high accuracy. Simulation results demonstrate that compared with the conventional Kalman Filter based detection mechanism, the proposed approach has lower complexity and can achieve a more stable and accurate estimation.

The rapid proliferation of user devices with access to mobile broadband has been a challenge from both the operation and deployment points of view. With the incorporation of new services with high demand for bandwidth such as video in 4K, it has been deemed necessary to expand the existing capacity by including new bands, among which the unlicensed 5-GHz band is a very promising candidate. The operation of future 3GPP (Third Generation Partnership Project) mobile network standards deployments in this band implies the coexistence with other technologies such as WiFi, which is widespread. In this context, the provision of Quality of Service (QoS) or Quality of Experience (QoE) becomes an essential asset and is a challenge that has yet to be overcome. In this sense, 3GPP has proposed a traffic prioritization method based on the Listen Before Talk access parameters, defining a series of priorities. However, it does not specify how to make use of them, and even less so in potentially conflicting situations. This paper assesses the end-to-end performance of downlink unlicensed channel priorities in dense scenarios via implementing a novel simulation setup in terms of both multi-service performance and coexistence.

This paper aims to unlock the unlicensed band potential in realizing the Industry 4.0 communication goals of the Fifth-Generation (5G) and beyond. New Radio in the Unlicensed band (NR-U) is a new NR Release 16 mode of operation that has the capability to offer the necessary technology for cellular operators to integrate the unlicensed spectrum into 5G networks. NR-U enables both uplink and downlink operation in unlicensed bands, supporting 5G advanced features of ultra-high-speed, high bandwidth, low latency, and improvement in the reliability of wireless communications, which is essential to address massive-scale and highly-diverse future industrial networks. This paper highlights NR-U as a next-generation communication technology for smart industrial network communication and discusses the technology trends adopted by 5G in support of the Industry 4.0 revolution. However, due to operation in the shared/unlicensed spectrum, NR-U possesses several regulatory and coexistence challenges, limiting its application for operationally intensive environments such as manufacturing, supply chain, transportation systems, and energy. Thus, we discuss the significant challenges and potential solution approaches such as shared maximum channel occupancy time (MCOT), handover skipping, the self-organized network (SON), the adaptive back-off mechanism, and the multi-domain coexistence approach to overcome the unlicensed/shared band challenges and boost the realization of NR-U technology in mission-critical industrial applications. Further, we highlight the role of machine learning in providing the necessary intelligence and adaptation mechanisms for the realization of industrial 5G communication goals.

Two channel access procedures are being considered for New Radio-based access to unlicensed spectrum (NR-U) in millimeter-wave (mmWave) bands: omnidirectional Listen-Before-Talk (omniLBT) and directional LBT (dirLBT), which differ on the type of physical carrier sense. Under beam-based transmissions, omniLBT is overprotective and reduces spatial reuse due to exposed node situations, while dirLBT enables spatial reuse, but may create hidden node problems. To address the omniLBTdirLBT trade-off, this paper proposes LBT switching procedures to dynamically adapt the type of physical carrier sense for LBT in NR-U devices. Switching from dirLBT to omniLBT can be implemented by exploiting already available control messages in NR. Differently, to switch from omniLBT to dirLBT, no information in NR specifications is still available at the time of writing. We define new procedures to measure the overprotection level of spatial reuse provided by omniLBT, and send the switching indication accordingly. Results demonstrate the effectiveness of LBT switching, which enables an independent and dynamic adaptation according to the density and activity of neighboring nodes., Grant numbers : This work was partially funded by Spanish MINECO grant TEC2017-88373-R (5G-REFINE).