Yuan Gao

Bio: Yuan Gao is an academic researcher from University of Sheffield. The author has contributed to research in topics: Throughput & Wireless network. The author has an hindex of 5, co-authored 12 publications receiving 254 citations.

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

Abstract: 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.

Performance Analysis of LAA and WiFi Coexistence in Unlicensed Spectrum Based on Markov Chain

Abstract: License-assisted access (LAA) is a candidate feature in 3GPP Rel-13 to meet the explosive growth of traffic demand. The main idea of LAA is to deploy LTE in the unlicensed band (mainly the 5GHz band), which is abundant with available spectrum. However, the major concern is the coexistence between WiFi and LAA in the same band. This paper presents a new framework to evaluate the downlink performance of coexisting LAA and WiFi networks. By using Markov chain, analytical models are established based on WiFi distributed coordination function (DCF) and two listen-before- talk (LBT) schemes. These two LBT schemes are Cat 3 and Cat 4 LBT, which mainly differ in medium access schemes in terms of backoff procedure. Unlike most existing works, which focus on the impact on WiFi performance posed by LAA, the performance of LAA is also evaluated. Our analysis shows that throughput of a WiFi network can be enhanced by adding or replacing WiFi access points (APs) with LAA E-UTRAN Node Bs (eNBs), at the expense of different levels of WiFi performance degradation. A trade-off between WiFi protection and LAA-WiFi system performance enhancement is observed. WiFi throughput and delay are less affected by Cat 4 LBT scheme, while Cat 3 LBT scheme provides higher LAA-WiFi system throughput. The choice of LBT schemes relies on the network planning priority, WiFi performance protection and LAA system performance requirements.

Resource Allocation in LTE-LAA and WiFi Coexistence: A Joint Contention Window Optimization Scheme

Abstract: Licensed-assisted access (LAA) is a promising technology to meet the exponential increase of traffic demand by exploiting the 5GHz unlicensed spectrum. However, without proper coexistence schemes, the performance of WiFi in coexistence with LAA will be degraded significantly. Equipped with listen-before-talk (LBT) schemes, LAA applies a channel access mechanism similar to distributed coordination function (DCF) in WiFi, which is not optimal in terms of spectrum efficiency. In this paper, we propose an joint optimization scheme to find the optimal combination of WiFi and LAA contention windows (CWs) that maximizes LAA throughput, while guarantees WiFi throughput above a predefined threshold. The accuracy and efficiency of the proposed scheme is evaluated by comparing with the exhaustive search: almost the same combination of CWs are achieved with much lower complexity by using the proposed scheme than the exhaustive search. Numeric results show that the proposed adaptive scheme is more effective in dense scenario, where high system (up to 40%) and LAA throughput gain (up to 100%) are achieved. The trade-off between LAA (system) throughput and WiFi throughput is also revealed.

Licensed and Unlicensed Bands Allocation for Cellular Users: A Matching-Based Approach

Abstract: Long term evolution-unlicensed (LTE-U) technologies allow cellular users (CUs) to be served in unlicensed bands. However, how a CU properly chooses between licensed and unlicensed bands and how a CU can utilize the unlicensed bands without jeopardizing other unlicensed-band users, e.g., Wi-Fi users (WUs), remain as open problems. In this letter, we aim to optimize the allocation of radio resources in both licensed and unlicensed bands in an LTE-U and Wi-Fi coexisting scenario, where a CU can be allocated either a licensed or unlicensed band. We formulate a multi-objective optimization problem to maximize every CU’s utility, while guaranteeing the throughput requirements of both CUs and WUs. We propose an algorithm based on one-to-one and many-to-one matching algorithms to solve it. The stability, Pareto optimality, and convergence of the proposed matching-based algorithm are proven. Simulation results show that the proposed algorithm can achieve near-optimal performance but with a low computational complexity.

Density Analysis of LTE-LAA Networks Coexisting With WiFi Sharing Multiple Unlicensed Channels

Abstract: With data traffic explosion, operating Long-Term Evolution (LTE) in the 5 GHz unlicensed band, which has already been used by WiFi networks, has been proposed. To harmoniously coexist with the incumbent WiFi networks, LTE-Licensed Assisted Access (LAA) has been proposed recently, advocating cellular networks to access the unlicensed band by employing listen-before-talk mechanism. However, the performance of LAA has not been analysed under multiple accessible unlicensed channels (UCs). In this work, we analyse the user throughput and spatial spectral efficiency (SSE) of the multi-UC coexisting LTE-LAA and WiFi networks versus the network density based on the Matern hard core process. The throughput and SSE are obtained as functions of the downlink successful transmission probability (STP), of which analytical expressions are derived and validated by Monte Carlo simulations. The results show that an optimal LTE access point (LAP) density exists to maximise the LTE-LAA user equipment (LUE) throughput, and our derived closed-form STP lower bound of LUE can be used to obtain a sufficiently accurate prediction of the optimal LAP density. Moreover, the SSE does not change much under relatively low LAP densities, and when the LAP density is larger than 1, 585 LAPs per km 2 , the SSE approaches the asymptotic SSE as the LAP density approaches infinity.

Deferred Acceptance Algorithms: History, Theory, Practice, and Open Questions

Abstract: The deferred acceptance algorithm proposed by Gale and Shapley (1962) has had a profound influence on market design, both directly, by being adapted into practical matching mechanisms, and, indirectly, by raising new theoretical questions. Deferred acceptance algorithms are at the basis of a number of labor market clearinghouses around the world, and have recently been implemented in school choice systems in Boston and New York City. In addition, the study of markets that have failed in ways that can be fixed with centralized mechanisms has led to a deeper understanding of some of the tasks a marketplace needs to accomplish to perform well. In particular, marketplaces work well when they provide thickness to the market, help it deal with the congestion that thickness can bring, and make it safe for participants to act effectively on their preferences. Centralized clearinghouses organized around the deferred acceptance algorithm can have these properties, and this has sometimes allowed failed markets to be reorganized.

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

Abstract: 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.

Dynamic Spectrum Sharing in 5G Wireless Networks With Full-Duplex Technology: Recent Advances and Research Challenges

Abstract: Full-duplex (FD) wireless technology enables a radio to transmit and receive on the same frequency band at the same time, and it is considered to be one of the candidate technologies for the fifth generation (5G) and beyond wireless communication systems due to its advantages, including potential doubling of the capacity and increased spectrum utilization efficiency. However, one of the main challenges of FD technology is the mitigation of strong self-interference (SI). Recent advances in different SI cancellation techniques, such as antenna cancellation, analog cancellation, and digital cancellation methods, have led to the feasibility of using FD technology in different wireless applications. Among potential applications, one important application area is dynamic spectrum sharing (DSS) in wireless systems particularly 5G networks, where FD can provide several benefits and possibilities such as concurrent sensing and transmission (CST), concurrent transmission and reception, improved sensing efficiency and secondary throughput, and the mitigation of the hidden terminal problem. In this direction, first, starting with a detailed overview of FD-enabled DSS, we provide a comprehensive survey of recent advances in this domain. We then highlight several potential techniques for enabling FD operation in DSS wireless systems. Subsequently, we propose a novel communication framework to enable CST in DSS systems by employing a power control-based SI mitigation scheme and carry out the throughput performance analysis of this proposed framework. Finally, we discuss some open research issues and future directions with the objective of stimulating future research efforts in the emerging FD-enabled DSS wireless systems.

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

Abstract: 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.

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

Abstract: 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.