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 little progress to date. Accordingly, in one of the first work of its kind, we develop a new framework for estimating the throughput of Wi-Fi and LTE-LAA in coexistence scenarios via suitable modifications to the celebrated Bianchi Bianchi model. The impact of various network parameters such as energy detection (ED) threshold on Wi-Fi and LTE-LAA coexistence is explored as a byproduct and corroborated via a National Instrument (NI) experimental testbed that validates the results for LTE-LAA access priority class 1 and 3.
In summary, industry driven research has produced mixed results: some results predict largely negative consequences for Wi-Fi with the proposed LTE-LAA coexistence mechanisms, and others that claim that fair coexistence is feasible with necessary tweaks or enhancements. There is a great need to cohere these opposing conclusions and characterize scenarios in which different conclusions are (legitimately) possible; progress on this requires a careful and transparent approach such as ours using model-based analysis of the problem. We next summarize some of the pertinent academic literature - that while undertaking exploration of aspects of network performance in coexistence scenarios, have largely not focused on 3GPP prescriptions for 'fair' sharing. For example, @cite_29 explores design aspects of LBT schemes for LTE-LAA as a means of providing equal opportunity channel access in the presence of Wi-Fi. Similarly @cite_17 proposed an enhanced LBT algorithm with contention window size adaptation for LTE-LAA in order to achieve fair channel access as well as Quality of Service (QoS) fairness. In @cite_12 , authors designed the MAC protocol for LTE-LAA for fair coexistence - the LTE transmission time is optimized for maximizing the overall normalized channel rate contributed by both LTE-LAA and Wi-Fi while protecting Wi-Fi.
@cite_29 @cite_12 @cite_17
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With licensed spectrum at a premium, recent interest has shifted to investigating the possibility of utilizing unlicensed bands as a means of providing additional bandwidth. License assisted access (LAA) and Long Term Evolution-Unlicensed (LTE-U) are radio access technologies (RATs) aimed at providing carrier-grade wireless service in the 5 GHz unlicensed spectrum. Since Wi-Fi devices are widespread in the unlicensed space, it is important to ensure that any new technology deployed coexists fairly with Wi-Fi and other preexisting technologies that already occupy this space. At the heart of the Wi-Fi-LAA coexistence problem is the difference in channel access mechanisms for these two technologies; Wi-Fi is a contention based channel access scheme, while Long Term Evolution (LTE) is schedule-based. As a result, introducing an LTE system as is into the Wi-Fi space would likely result in LAA gradually taking over the channel and starving Wi-Fi of access. In this paper we focus on schemes to address this very issue. In particular, we will focus on various design aspects of Listen Before Talk (LBT) schemes for LAA that aim to emulate the contention based scheme in Wi-Fi as a means of providing equal opportunity channel access for both of these technologies. We consider and evaluate the impact of various design aspects on fairness through several key performance metrics. Our simulation results demonstrate that LBT when applied to LTE can ensure good Wi-Fi-LAA coexistence. Licensed-assisted access (LAA), which conveys data information via both licensed and unlicensed bands through spectrum aggregation, becomes a promising solution to enhance the capacity of wireless systems. In view of the potential impact on the incumbent system operating in unlicensed bands, the medium access control (MAC) protocol design for LAA system to harmonically coexist with its neighboring incumbent users is one of the most critical and challenging issues. In this paper, we consider a long-term evolution-based LAA (LAA-LTE) system operating in the WiFi unlicensed spectrum, for which the listen-before-talk-based MAC protocol is carefully designed. By quantifying the WiFi throughput and packet delay in the coexisting system, we formulate the constraints of LAA-LTE transmission time to fairly maintain WiFi services. The conditions of known and unknown network size of incumbent WiFi system are each considered separately. Then, the feasible region of LAA-LTE transmission time is determined, and the LAA-LTE protocol is optimized for maximizing the LAA-LTE throughput or the overall throughput contributed by both LAA-LTE and WiFi system. The theoretical analysis is validated via simulation, which also illustrates important observations when LAA-LTE and WiFi systems coexist. This paper offers guidelines to design the LAA-LTE system, paving the way to a controllable, not only harmonious, coexistence of LAA-LTE and WiFi systems in the unlicensed spectrum. In this paper, we focus on the deployment of LTE technologies coexisting with Wi-Fi technologies in the unlicensed spectrum 5 GHz. Listen before talk (LBT) functionality is required in unlicensed band in order to ensure the fair coexistence among different operators. We propose a LBT enhancement algorithm with contention window size adaptation for LTE with Licensed-Assisted Access (LTE-LAA) in order to achieve not only channel access fairness but also the QoS fairness. Simulation results show that LTE-LAA with LBT mechanism does not impact Wi-Fi services more than an additional Wi-Fi network. Compared with the fixed LBT mechanism, our proposed LBT algorithm could achieve around 4 and 6 LTE-LAA performance gain in user perceived throughput (UPT) and transmission latency, respectively. And, more than 25 Wi-Fi transmission latency gain can be also achieved. Furthermore, the simulation result shows the advantage of proposed LBT algorithm over original LBT procedure in the case of two LTE operators coexistence.