On the Fairness of Wi-Fi and LTE-LAA Coexistence (original) (raw)
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Delivering Fairness and QoS Guarantees for LTE/Wi-Fi Coexistence Under LAA Operation
IEEE Access, 2018
Licensed assisted access (LAA) enables the coexistence of long-term evolution (LTE) and Wi-Fi in unlicensed bands, while potentially offering improved coverage and data rates. However, cooperation with the conventional random-access protocols that employ listen-before-talk (LBT) considerations makes meeting the LTE performance requirements difficult, since delay and throughput guarantees should be delivered. In this paper, we propose a novel channel sharing mechanism for the LAA system that is capable of simultaneously providing the fairness of resource allocation across the competing LTE and Wi-Fi sessions as well as satisfying the quality-of-service guarantees of the LTE sessions in terms of their upper delay bound and throughput. Our proposal is based on two key mechanisms: 1) LAA connection admission control for the LTE sessions and 2) adaptive duty cycle resource division. The only external information necessary for the intended operation is the current number of active Wi-Fi sessions inferred by monitoring the shared channel. In the proposed scheme, LAA-enabled LTE base station fully controls the shared environment by dynamically adjusting the time allocations for both Wi-Fi and LTE technologies, while only admitting those LTE connections that should not interfere with Wi-Fi more than another Wi-Fi access point operating on the same channel would. To characterize the key performance trade-offs pertaining to the proposed operation, we develop a new analytical model. We then comprehensively investigate the performance of the developed channel sharing mechanism by confirming that it allows to achieve a high degree of fairness between the LTE and Wi-Fi connections as well as provides guarantees in terms of upper delay bound and throughput for the admitted LTE sessions. We also demonstrate that our scheme outperforms a typical LBT-based LAA implementation. INDEX TERMS LAA, long-term evolution (LTE), IEEE 802.11, QoS, fairness.
A Game-Theoretic Approach for Fair Coexistence Between LTE-U and Wi-Fi Systems
IEEE Transactions on Vehicular Technology, 2018
LTE over unlicensed band (LTE-U) has emerged as an effective technique to overcome the challenge of spectrum scarcity. Using LTE-U along with advanced techniques such as carrier aggregation, one can boost the performance of existing cellular networks. However, if not properly managed, the use of LTE-U can potentially degrade the performance of co-existing Wi-Fi access points, which operate over the unlicensed frequency bands. Moreover, most of the existing works consider single operator in their proposals. In this paper, an effective coexistence mechanism between LTE-U and Wi-Fi systems is studied. The goal is to enable the cellular network to use LTE-U with CA to meet the quality-ofservice (QoS) needs of its users while protecting Wi-Fi access points (WAPs) for a network with multiple operators. In particular, the problem of LTE-U sum-rate maximization is addressed under user QoS and WAP-LTE-U coexistence constraints. To solve this problem, a cooperative Nash bargaining game (NBG) and a one-sided matching game are proposed. Here, the NBG solves the coexistence issue between LTE-U and Wi-Fi system, while the matching game solves the resources allocation problem in the LTE-U system. These two games repeat until convergence. Simulation results show the quality of the proposed approach over other comparing methods in terms of the per-user achieved rate, percentage of unsatisfied users, and fairness. The result also shows that the proposed approach can better protect the performance of Wi-Fi users, compared to the conventional listen-before-talk scheme.
Static Contention Window Method for Improved LTE-LAA/Wi-Fi Coexistence in Unlicensed Bands
2019 International Conference on Wireless Networks and Mobile Communications (WINCOM), 2019
The 3rd Generation Partnership Project (3GPP) has recently defined a Licensed Assisted Access (LAA) scheme to enable Long Term Evolution (LTE) networks to use unlicensed frequency bands. However, the unlicensed bands are mainly occupied by the Wi-Fi technology. Hence, achieving fairness between LAA using LTE (LTE-LAA) and Wi-Fi in the unlicensed bands is a primary challenge. The 3GPP has recently standardised in Release 13 a Listen Before Talk (LBT) algorithm to ensure the fairness among these two technologies (LTE and Wi-Fi) over the unlicensed bands. In this paper, we focus on the downlink performance of LTE-LAA and Wi-Fi with different traffic loads. To achieve not only better fairness but also higher total aggregated throughputs for the coexisting networks, a static Contention Window (CW) selection method based on the fairness definition is proposed. The main novelty of this work is that the knowledge of Wi-Fi activity statistics is exploited effectively to select the CW of LAA. We show that the fairness between LAA and Wi-Fi networks depends on the LAA CW size adaptation criterion. Simulation results validate that the proposed method is effective in LAA/Wi-Fi coexistence scenario, can improve fairness performance and provide higher total aggregated throughputs for both coexisting networks compared with the current Category 4 LBT (Cat 4 LBT) algorithm defined in the 3GPP standard.
Computer Networks
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 APs 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.
Revisiting 802.11 for User Fairness and Efficient Channel Utilization in Presence of LTE-U
ArXiv, 2016
A promising solution satisfying the industry's demand to have minimum alterations 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 APs 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 duration (i.e., duty cycle). A propitious sche...
LBT Enhancement for LTE-LAA Fair Coexistence
International Journal of Future Generation Communication and Networking, 2017
A common approach to increase wireless network capacity is to use additional spectrum. LTE in the unlicensed spectrum band has been introduced in the release 13 of 3GPP as Licensed Assisted Access (LAA). The LTE technology in the unlicensed band is enabled by Listen Before Talk (LBT) procedure for fair coexistence with other wireless technologies (i.e., Wi-Fi) operating in the same spectrum. LBT based on binary exponential back-off known as LBT category 4 can achieve a fair coexistence in low buffer but presents some limitations under full buffer evaluation. In this paper we propose different LBT mechanisms and evaluate their performances based on 3GPP coexistence scenarios (LAA/Wi-Fi, LAA/LAA). The simulation results show that the LBT category 4 with Optimal Constant Contention Window (OCCW) and the proposed fixed periodic LBT (P-LBT) can achieve better performance under saturation state even better than Wi-Fi only coexistence.
Enabling Fair Spectrum Sharing between Wi-Fi and LTE-Unlicensed
2018 IEEE International Conference on Communications (ICC), 2018
Due to the fast increase of mobile traffic, most mobile network operators face the congestion issue in licensed spectrum bands. Several telecommunication vendors and operators propose to expand LTE service to the unlicensed spectrum bands to relieve the traffic congestion. However, LTE in unlicensed spectrum may interfere with Wi-Fi communications in the same bands and cause significant decrease in the quality of service of Wi-Fi. In this paper, we propose a novel mechanism that enables negotiations between two different wireless technologies (Wi-Fi and LTE), which ensures fair spectrum sharing between Wi-Fi and LTE-Unlicensed (LTE-U) in the same bands. We formulate the co-existence of Wi-Fi and LTE-U as a constrained optimization problem, and we solve the problem. We evaluate the performance of the proposed scheme via NS-3 simulations. The simulation results show that our approach can effectively improve the overall channel utilization and reduce the interference between Wi-Fi and ...
Association fairness in Wi-Fi and LTE-U coexistence
2018 IEEE Wireless Communications and Networking Conference (WCNC), 2018
In this paper we address the issue of association fairness when Wi-Fi and LTE unlicensed (LTE-U) coexist on the same channel in the unlicensed 5 GHz band. Since beacon transmission is the first step in starting the association process in Wi-Fi, we define association fairness as how fair LTE-U is in allowing Wi-Fi to start transmitting beacons on a channel that it occupies with a very large duty cycle. According to the LTE-U specification, if a LTE-U base station determines that a channel is vacant, it can transmit for up to 20 ms and turn OFF for only 1 ms, resulting in a duty cycle of 95%. In an area with heavy spectrum usage, there will be cases when a Wi-Fi access point wishes to share the same channel, as it does today with Wi-Fi. We study, both theoretically and experimentally, the effect that such a large LTE-U duty cycle can have on the association process, specifically Wi-Fi beacon transmission and reception. We demonstrate via an experimental setup using National Instrument (NI) USRPs that a significant percentage of Wi-Fi beacons will either not be transmitted in a timely fashion or will not be received at the LTE-U BS thus making it difficult for the LTE-U BS to adapt its duty cycle in response to the Wi-Fi usage. Our experimental results corroborate our theoretical analysis. We compare the results with Wi-Fi/Wi-Fi coexistence and demonstrate that LTE-U/Wi-Fi coexistence is not fair when it comes to initial association since there is a much larger percentage of beacon errors in the latter case. Hence, the results in the paper indicate that in order to maintain association fairness, a LTE-U BS should not transmit at such high duty cycles, even if it deems the channel to be vacant.
Dynamic Contention Window Methods for Improved Coexistence Between LTE and Wi-Fi in Unlicensed Bands
2019 IEEE Wireless Communications and Networking Conference Workshop (WCNCW)
Recently, the 3rd Generation Partnership Project (3GPP) announced standards that permit the Licensed-Assisted Access (LAA) of Long Term Evolution (LTE) to operate over unlicensed spectrum bands. This permission, which is a part of the 5G specifications, is due to the scarcity of the licensed spectrum and the increased use of wireless networks and services. However, these unlicensed bands are mainly occupied by 802.11 based WLAN devices. Thus, challenges arise for the efficient coexistence mechanism to share the same unlicensed band by LAA and Wi-Fi to maintain the quality of service and manage the interference among users. In this work, we propose new variable contention window (CW) methods for LAA to enable the coexistence of LTE and Wi-Fi in a fair manner based on the Wi-Fi statistics. The main novelty of this work is that the knowledge of Wi-Fi activity statistics is exploited to adapt the CW of LAA more effectively. These methods are evaluated based on the 3GPP fairness definition for such coexistence mechanisms under various traffic loads. We show that the fairness depends on the LAA CW size. Further, through simulation results, we show that the proposed schemes are more friendly to the existing Wi-Fi network, in particular for the higher traffic loads, compared with the existing Category 4 Listen-Before-Talk (Cat 4 LBT) algorithm defined in the 3GPP standard and provide higher total throughputs for both coexisting networks, improving the overall network performance.
With both small-cell LTE and Wi-Fi networks available as alternatives for deployment in unlicensed bands (notably 5 GHz), the investigation into their coexistence is a topic of active interest, primarily driven by industry groups. 3GPP has recently standardized LTE licensed assisted access (LTE-LAA) that seeks to make LTE more co-existence friendly with Wi-Fi by incorporating similar sensing and back-off features. Nonetheless, the results presented by industry groups offer little consensus on important issues like respective network parameter settings that promote "fair access" as required by 3GPP. Answers to such key system deployment aspects, in turn, require credible analytical models, on which there has been a little progress to date. Accordingly, in one of the first works of its kind,