Simulating LTE and Wi-Fi Coexistence in Unlicensed Spectrum with ns-3

The use of unlicensed spectrum for future LTE systems raises concerns about its impact on co-located Wi-Fi networks. As specifications are being developed, simulation has been widely employed for assessing the performance of coexistence mechanisms for LTE on unlicensed bands. We report herein on extensions to a popular network simulator, known as ns-3, to model such coexistence. To our knowledge, this simulator is novel in two important ways. First, it is presently the only freely available simulator for coexistence studies, and as open source software, it offers new opportunities for reproducible research and collaborative model development. Second, we are not aware of other simulators with similar wireless models that allow full system studies to be conducted, such as performance evaluation of upper-layer protocols in a coexistence environment. We illustrate the value of a system simulator by describing a simulation campaign for an indoor scenario using new ns-3 models for LTE Listen Before Talk (LBT) techniques, intended for fair coexistence with Wi-Fi. LBT models have been widely simulated at the link and physical layer by many companies. We first show that we are able to tune the scenario to reproduce similar performance metrics as reported in the literature. We then extend the simulations by adding TCP to the file transfers and explore the different behaviour observed. Our initial study reveals that there remain many open questions about how LTE should be implemented to achieve good coexistence properties, and that a broader scope of implementation issues, traffic models, and fuller system models should be studied further before drawing final conclusions on the performance of LBT mechanisms. Keywords— LAA, LBT, network simulation, ns-3