Long term evolution (LTE) carrier aggregation with 5 GHz unlicensed national informational infrastructure band has been pointed out by the industry as a good solution to handle the rapidly increasing amounts of data traffic. To provide fair coexistence of LTE-licensed assisted access (LTE-LAA) and Wi-Fi on 5 GHz, several coexistence mechanisms have already been proposed. This paper provides a comprehensive survey of the coexistence of LTE-LAA and Wi-Fi on 5 GHz with corresponding deployment scenarios. We first analyze coexistence-related features of those two technologies, including motivation, LTE carrier aggregation with unlicensed band, LTE and Wi-Fi medium access control protocols comparison, coexistence challenges and enablers, performance difference between LTE-LAA and Wi-Fi, as well as co-channel interference. Second, we further extensively discuss current considerations about the coexistence of LTE-LAA and Wi-Fi. Third, influential factors for the classification of small cell scenarios, as well as four representative scenarios are investigated in detail. Then we explore a relatively smooth technical route for solving coexistence-related problems, which practically takes features of a specific scenario as the base for designing deployment mode of LTE-LAA and/or Wi-Fi. A scenario-oriented decision making procedure for the coexistence issue and the analysis on an example deployment scenario, including design and performance evaluation metrics focusing on the concept of the scenario-oriented coexistence are presented. We finally forecast further research trends on the basis of our conclusion.

Coexistence of LTE-LAA and Wi-Fi on 5 GHz With Corresponding Deployment Scenarios: A Survey

Future 5th generation networks are expected to enable three key services—enhanced mobile broadband, massive machine type communications and ultra-reliable and low latency communications (URLLC). As per the 3rd generation partnership project URLLC requirements, it is expected that the reliability of one transmission of a 32 byte packet will be at least 99.999% and the latency will be at most 1 ms. This unprecedented level of reliability and latency will yield various new applications, such as smart grids, industrial automation and intelligent transport systems. In this survey we present potential future URLLC applications, and summarize the corresponding reliability and latency requirements. We provide a comprehensive discussion on physical (PHY) and medium access control (MAC) layer techniques that enable URLLC, addressing both licensed and unlicensed bands. This paper evaluates the relevant PHY and MAC techniques for their ability to improve the reliability and reduce the latency. We identify that enabling long-term evolution to coexist in the unlicensed spectrum is also a potential enabler of URLLC in the unlicensed band, and provide numerical evaluations. Lastly, this paper discusses the potential future research directions and challenges in achieving the URLLC requirements.

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Enabling Technologies for Ultra-Reliable and Low Latency Communications: From PHY and MAC Layer Perspectives

In this letter, we analyze the coexistence performance of Wi-Fi and cellular networks with different listen-before-talk (LBT) procedures in the unlicensed spectrum. For this analysis, the behavior of a cellular base station is modeled as a Markov chain that is combined with Bianchi’s Markov model depicting the behavior of a Wi-Fi access point. The proposed mathematical framework finds the optimal contention window size of cellular base stations, which maximizes the total throughput of both networks while satisfying the required throughput of each network. Numerical results show the validity of adjustment in the parameter of LBT.

Coexistence of Wi-Fi and Cellular With Listen-Before-Talk in Unlicensed Spectrum

As the 2.4 GHz spectrum band has become significantly congested, there is growing interest from the Wi-Fi proponents, cellular operators, and other stakeholders to use the spectrum in the 5 GHz bands. The 5 GHz bands have emerged as the most coveted bands for launching new wireless applications and services, because of their relatively favorable propagation characteristics and the relative abundance of spectrum therein. To meet the exploding demand for more unlicensed spectrum, regulators across the world such as the United States Federal Communications Commission and the European Electronic Communications Committee have recently started considerations for opening up additional spectrum in the 5 GHz bands for use by unlicensed devices. Moreover, to boost cellular network capacity, wireless service providers are considering the deployment of unlicensed long term evaluation (LTE) in the 5 GHz bands. This and other emerging wireless technologies and applications have resulted in likely deployment scenarios where multiple licensed and unlicensed networks operate in overlapping spectrum. This paper provides a comprehensive overview of the various coexistence scenarios in the 5 GHz bands. In this paper, we discuss coexistence issues between a number of important wireless technologies—viz., LTE and Wi-Fi, radar and Wi-Fi, dedicated short range communication (DSRC) and Wi-Fi, and coexistence among various 802.11 protocols operating in the 5 GHz bands. Additionally, we identify and provide brief discussions on an impending coexistence issue—one between Cellular V2X and DSRC/Wi-Fi. We summarize relevant standardization initiatives, explain existing coexistence solutions, and discuss open research problems.

Coexistence of Wireless Technologies in the 5 GHz Bands: A Survey of Existing Solutions and a Roadmap for Future Research

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.

New Radio Beam-Based Access to Unlicensed Spectrum: Design Challenges and Solutions

Deployment of LTE in unlicensed bands is being considered in Rel-13 of LTE. This feature is called Licensed-Assisted Access (LAA) using LTE. Unlicensed band is attractive due to the large amount of available spectrum. However, in shared spectrum the coexistence between LAA and WiFi systems becomes a primary challenge. This paper presents an analytical framework to investigate the downlink coexistence performance between two systems with a simple listen-before-talk (LBT) mechanism enforced on LAA. Using this framework, theoretical models based on Markov chains are established for both systems and downlink throughput can be calculated. Numerical results from the models show that the simple listen-before-talk scheme is very effective in LAA and LAA coexistence scenario (i.e. two LAA systems sharing the same spectrum). In LAA and WiFi coexistence scenario, it can improve WiFi performance substantially.

Downlink Performance Analysis of LTE and WiFi Coexistence in Unlicensed Bands with a Simple Listen-Before-Talk Scheme

IEEE 802.11ay defines new PHY and MAC specifications that enable 100 Gb/s communications in the 60 GHz millimeter-wave (mmWave) band. Among the various use cases supported by IEEE 802.11ay, fixed wireless access, a cost-efficient high-performance alternative and/ or complement to conventional fixed access, differentiates itself due to its unique requirements and characteristics. In this article, our goal is to identify and describe key elements incorporated into IEEE 802.11ay, including scheduling, beamforming, and link maintenance, that efficiently support fixed wireless access. IEEE 802.11ay is thus a viable and strong candidate to form the basis of future generations of standards-compliant (i.e., non-proprietary) mmWave fixed wireless access networks.

Millimeter-Wave Fixed Wireless Access Using IEEE 802.11ay

IEEE 802.11ay is a standard that enables enhanced throughput for IEEE 802.11 systems operating in the license-exempt 60 GHz band. By specifying advanced physical layer (PHY) features, improved channel access, and enhanced beamforming training, IEEE 802.11ay supports a maximum data rate of 100 Gb/s, making it a standard of great interest for applications as diverse as virtual reality, high density/throughput networking, and backhaul. In this paper, we provide a description and discussion of two important beamforming training procedures defined in IEEE 802.11ay, namely beam refinement protocol (BRP) transmit sector sweep (TXSS) and asymmetric beamforming training. Because these procedures build upon concepts defined in IEEE 802.11ad, we also examine two legacy beamforming training procedures: Sector-level sweep (SLS) and BRP. PHY definitions relevant to beamforming training are also reviewed.

Beamforming Training for IEEE 802.11 ay Millimeter Wave Systems

We consider a wireless network in which multiple Service Providers (SPs) compete to provide both macrocell and femtocell services in different bands. There are two types of users: mobile users that can only connect to macrocells, and fixed users that can be served by both macrocells and femtocells. For a given allocation of bandwidths across SPs, we characterize for each SP the optimal bandwidth split across the macro- and femtocells along with the equilibrium prices. We show that there exists a unique Nash equilibrium wherein for each SP, macrocells only serve mobile users while femtocells only serve fixed users. All possible Nash equilibria for different system parameters are sorted into four categories corresponding to whether or not different SPs assign bandwidth to the macro- and/or femtocells. In addition, we characterize properties of each category. The equilibrium prices and macro/femto bandwidths can be computed via a series of best response updates, which is proven to converge. Conditions are also given that guarantee optimal social welfare as the number of SPs tends to infinity. Numerical results are presented to illustrate how the Nash equilibrium can change as a function of SP bandwidths.

Bandwidth optimization in hetnets with competing service providers

IEEE 802.11ay is an amendment that enables enhanced throughput for IEEE 802.11 systems operating in the license-exempt 60 GHz band. By specifying advanced physical layer (PHY) features such as channel bonding and aggregation, multiple input multiple output (MIMO) transmission, and non-uniform modulation constellation, IEEE 802.11ay supports a maximum data rate of 100 Gb/s, making it an amendment of great interest for applications as diverse as wireless virtual reality (VR) and backhauling. In this paper, we provide a description and analysis of certain fundamental elements of the single-carrier (SC) PHY defined by IEEE 802.11ay. Among the topics that are discussed are the new frame format, modulation and coding schemes (MCSs), and beamforming training field defined in the amendment. Simulation results of key aspects for the topics covered are presented.

Cheng Chen

Papers

Downlink Performance Analysis of LTE and WiFi Coexistence in Unlicensed Bands with a Simple Listen-Before-Talk Scheme

Millimeter-Wave Fixed Wireless Access Using IEEE 802.11ay

Beamforming Training for IEEE 802.11 ay Millimeter Wave Systems

Bandwidth optimization in hetnets with competing service providers

Analysis and Simulation of the IEEE 802.11ay Single-Carrier PHY