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.
Finally, while the imperative of much of the coexistence investigations are driven by progression to fair sharing as defined by 3GPP , we do not explore that issue in any depth in this work. This very important aspect deserves a much deeper investigation and is left for separate future work. Nonetheless, we quote a few relevant important prior art that has contributed to our understanding of the overall problem. In @cite_6 @cite_3 , the authors derive the proportional fair rate allocation Proportional fairness is well-known to achieve airtime fairness in rate-heterogeneous Wi-Fi networks. for Wi-Fi LTE-LAA (as well as Wi-Fi LTE-U) coexistence. Also in @cite_30 , the fairness in the coexistence of Wi-Fi LTE-LAA LBT based on the 3GPP criteria is investigated through a custom-built event-based system simulator. Their results suggest that LBT (and correct choice of LBT parameters) is essential to achieving proportional fairness.
@cite_30 @cite_3 @cite_6
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Continued growth in wireless data demands has driven the need for more spectrum. Both licensed and unlicensed spectrum solutions are being deployed and viewed as complementary in dealing with the wireless traffic explosion. For example, Wi-Fi is being used successfully to assist in offloading the more spectrally constrained licensed band systems. At the heart of Wi-Fi's success is the premise of fair co-existence so that multiple Wi-Fi system owners can deploy Wi-Fi access points in the same unlicensed spectrum in an unmanaged fashion. Given Wi-Fi's success, the idea of leveraging unlicensed spectrum with LTE is being proposed through a feature called Licensed Assisted Access (LAA-LTE). This paper reports our findings in designing LBT mechanisms for LAA-LTE to ensure that it operates at least as fairly as Wi-Fi in unlicensed spectrum. These findings are based on our simulation results of co-existence performance between LAA-LTE and Wi-Fi for different candidate LBT schemes as reported in this paper. It concludes that for fair co-existence LBT is essential for LAA-LTE, but also that the choice of LBT scheme and settings of that scheme matter, with those proposed in current European regulations likely to result in Wi-Fi being disadvantaged. Ensuring fair co-existence between unlicensed LTE and WiFi networks is currently of major concern to both cellular operators and WiFi providers. Two main unlicensed LTE approaches currently being discussed, namely Carrier Sense Adaptive Transmission (CSAT) and Listen Before Talk (LBT). While these mechanisms differ in their compatibility with existing LTE specifications and regulatory compliance in different countries, they also use fundamentally different approaches to access the channel. Nevertheless, we show in this article that when optimally configured both approaches are capable of providing the same level of fairness to WiFi and that the choice between CSAT and LBT is solely driven by the LTE operator's interests.