Wi-Fi Coexistence with Duty Cycled LTE-U

Coexistence of Wi-Fi and LTE-Unlicensed (LTE-U) technologies has drawn significant concern in industry. In this paper, we investigate the Wi-Fi performance in the presence of duty cycle based LTE-U transmission on the same channel. More specifically, one LTE-U cell and one Wi-Fi basic service set (BSS) coexist by allowing LTE-U devices transmit their signals only in predetermined duty cycles. Wi-Fi stations, on the other hand, simply contend the shared channel using the distributed coordination function (DCF) protocol without cooperation with the LTE-U system or prior knowledge about the duty cycle period or duty cycle of LTE-U transmission. We define the fairness of the above scheme as the difference between Wi-Fi performance loss ratio (considering a defined reference performance) and the LTE-U duty cycle (or function of LTE-U duty cycle). Depending on the interference to noise ratio (INR) being above or below -62dbm, we classify the LTE-U interference as strong or weak and establish mathematical models accordingly. The average throughput and average service time of Wi-Fi are both formulated as functions of Wi-Fi and LTE-U system parameters using probability theory. Lastly, we use the Monte Carlo analysis to demonstrate the fairness of Wi-Fi and LTE-U air time sharing

LTE-U and Wi-Fi hidden terminal problem: How serious is it for deployment consideration?

The deployment of LTE in unlicensed spectrum is a plausible solution to meet explosive traffic demand from mobile users. However, fair coexistence with the existing unlicensed technologies, mainly Wi-Fi, needs to be ensured before any such deployment. Duty cycled LTE (LTE-U) is a simple and an easily adaptable scheme which helps in fair coexistence with the Wi-Fi. Nonetheless, the immense deployment of Wi-Fi necessitates a user-oriented study to find the effects of LTE-U operation, primarily in scenarios where the LTE-U eNB remains hidden from Wi-Fi Access Point. To comprehend these effects, we perform a user-level throughput study of Wi-Fi in the presence of LTE-U using a testbed and observe a clear unfairness in throughput distribution among Wi-Fi users. Furthermore, we also notice inability among the disadvantaged users to receive the periodic Wi-Fi beacon frames successfully. The reasons and the subsequent consequences, of throughput unfairness and beacon losses, are carefully elaborated. Also, to validate the beacon loss results, we present a beacon loss analysis which provides a mathematical expression to find the beacon loss percentage. Finally, we examine the results and highlight a need for incorporating additional functionalities in either LTE-U or Wi-Fi to overcome the present challenges

On the Impact of Duty Cycled LTE-U on Wi-Fi Users: An Experimental Study

The deployment of LTE in unlicensed spectrum is a plausible solution to meet explosive traffic demand from mobile users. However, fair coexistence with the existing unlicensed technologies, mainly Wi-Fi, needs to be ensured before any such deployment. Duty cycled LTE (LTE-U) is a simple and an easily adaptable scheme which helps in fair coexistence with the Wi-Fi. Nonetheless, the immense deployment of Wi-Fi necessitates a user-oriented study to find the effects of LTE-U operation, primarily in scenarios where the LTE-U eNB remains hidden from Wi-Fi Access Point. To delineate these effects, we perform a user-level Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) throughputs study of Wi-Fi in the presence of LTE-U using a testbed. Since, TCP is a more complicated protocol, we analyzed the Congestion Window and Round Trip Time data to comprehend the throughput results. This further explains the unfairness in throughput distribution among Wi-Fi users. Furthermore, we also notice inability among the disadvantaged users to receive the periodic Wi-Fi beacon frames successfully. The reasons and the subsequent consequences of throughput unfairness and beacon losses, are carefully elaborated. Also, to validate the beacon loss results, we present a beacon loss analysis which provides a mathematical expression to find the beacon loss percentage. Finally, we examine the results and highlight a need for incorporating additional functionalities in either LTE-U or Wi-Fi to overcome the present challenges

A novel coexistence scheme for IEEE 802.11 for user fairness and efficient spectrum utilization in the presence of LTE-U

A promising solution satisfying the industry’s demand to have minimum modification in LTE for its operation in unlicensed spectrum is duty cycled LTE-U scheme, which adopts discontinuous transmission to ensure fair coexistence with 802.11 (Wi-Fi) WLANs. Even though the scheme guarantees to maintain Wi-Fi network performance, the fairness among Wi-Fi users still remains arcane. In this work, we present a practical scenario where LTE-U, despite being discontinuous (by following an ON/OFF cycle), results in not only unfair throughput distribution among Wi-Fi users but also causes degradation in Wi-Fi AP’s downlink performance. This is due to the domination of few Wi-Fi users who harness channel in both ON and OFF durations of LTE-U, namely non-victim users over those who get access only in OFF duration, called victim users. In this paper, we studied the performance of victim and non-victim Wi-Fi users, and Wi-Fi AP while varying LTE-U ON fraction (i.e., duty cycle). A propitious scheme is proposed for WLANs, with regard to ease of implementation, employing Point/Hybrid Coordination Function (PCF/HCF) mode of 802.11, promising fairness among Wi-Fi users with improvement in the channel utilization of Wi-Fi network. The key idea is that the victim users, who can only be served during the LTE-U OFF period should be served in Contention Free Period (CFP)—so as to improve their throughputs and make them equally competitive with non-victim users. Also, we present an analytical model to demonstrate guaranteed improvement and to validate our simulation results

LTE and Wi-Fi Coexistence in Unlicensed Spectrum with Application to Smart Grid: A Review

Long Term Evolution (LTE) is expanding its utilization in unlicensed band by deploying LTE Unlicensed (LTEU) and Licensed Assisted Access LTE (LTE-LAA) technology. Smart Grid can take the advantages of unlicensed bands for achieving two-way communication between smart meters and utility data centers by using LTE-U/LTE-LAA. However, both schemes must co-exist with the incumbent Wi-Fi system. In this paper, several co-existence schemes of Wi-Fi and LTE technology is comprehensively reviewed. The challenges of deploying LTE and Wi-Fi in the same band are clearly addressed based on the papers reviewed. Solution procedures and techniques to resolve the challenging issues are discussed in a short manner. The performance of various network architectures such as listenbefore- talk (LBT) based LTE, carrier sense multiple access with collision avoidance (CSMA/CA) based Wi-Fi is briefly compared. Finally, an attempt is made to implement these proposed LTEWi- Fi models in smart grid technology.Comment: submitted in 2018 IEEE PES T&

LTE-U와 공존하는 적응적인 Wi-Fi 절전 모드

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2019. 2. 최성현.LTE-Unlicensed (LTE-U) supports LTE downlink operation in 5~GHz unlicensed bands, where Wi-Fi has been a traditional incumbent for a long time. To achieve a fair coexistence with Wi-Fi, LTE-U employs carrier sense adaptive transmission (CSAT), but it does not guarantee a perfectly fair coexistence. Therefore, many studies have dealt with unfair coexistence problems of Wi-Fi and LTE-U. In this paper, our experiment results show that a Wi-Fi station not only suffers from unfair coexistence but also wastes energy and air time when it coexists with LTE-U. To cope with this problem, we propose AWARE, a station-driven adaptive Wi-Fi power save operation coexisting with LTE-U, which does not require any hardware modification. We implement AWARE on a commercial 802.11n device, and our evaluation shows that AWARE enhances throughput of Wi-Fi by up to 50% while reducing the power consumption of Wi-Fi station by up to 33% by effectively adapting Wi-Fi power state.LTE-Unlicensed(LTE-U)는 Wi-Fi가 오랫동안 사용하던 5~GHz 비면허 대역에서 LTE 하향링크 동작을 지원한다. 비면허 대역을 사용하는 Wi-Fi와의 공평한 공존을 하기 위해 LTE-U는 carrirer sense adaptive transmission(CSAT)을 이용하지만, 이는 공평한 공존을 완벽하게 보장하지 않는다. 따라서 많은 연구들은 Wi-Fi와 LTE-U의 불공평한 공존 문제를 다룬다. 본 논문에서, 우리는 실험을 통해 LTE-U와 공존하는 경우에 Wi-Fi 단말이 불공평한 공존 문제뿐만 아니라 에너지 낭비와 매체 점유 시간 낭비문제를 겪는다는 것을 확인했다. 이러한 문제를 해결하기 위해 우리는 AWARE를 제안한다. AWARE는 하드웨어의 수정없이 단말기에서 동작하는 적응적인 Wi-Fi 절전 동작이다. 우리는 상용 802.11n 장비에 AWARE를 구현하여 기존의 Wi-Fi와 성능을 비교하였다. AWARE를 통해 효과적으로 Wi-Fi 단말기의 파워 상태를 조절하여 Wi-Fi 단말기의 에너지가 약 33% 절약되었고 동시에 Wi-Fi 단말기의 수율이 약 50% 증가하였다.1. INTRODUCTION 2. RELATED WORK 3. PRELIMINARIES 3.1 LTE-Unlicensed (LTE-U) 3.2 Wi-Fi Power Save Mode (PSM) 3.2.1 Static PSM 3.2.2 Dynamic PSM 3.3 Automatic power save delivery (APSD) 4. MOTIVATION 4.1 Performance of Wi-Fi Coexisting with LTE-U 4.1.1 Scenario 1 4.1.2 Scenario 2 4.2 Energy and Air Time Waste Problem 5. AWARE: Proposed Algorithm 5.1 LTE-U Detection 5.1.1 Processing 5.1.2 Calibrating 5.2 Enhanced Power Save Operation (EPSO) 6. PERFORMANCE EVALUATION 6.1 LTE-U Detection 6.2 AWARE 6.2.1 Scenario 1 6.2.2 Scenario 2 6.2.3 Scenario 3 6.2.4 Scenario 4 7. CONCLUSIONMaste