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This page describes a project originally sponsored by Wi-Fi Alliance to improve ns-3 models to facilitate studies about the coexistence, on the same channel, of Wi-Fi and unlicensed variants of LTE (see this brief description), with a special emphasis on aligning to methodologies defined by the 3GPP RAN1 and IEEE 802.11ax standards development organizations. The term License-Assisted Access (LAA) is frequently used to refer to these extensions, and refers to the fact that the use of unlicensed spectrum is complementary to the use of licensed spectrum for LTE, with the unlicensed spectrum providing complementary or secondary carriers that can be aggregated with carriers on licensed frequencies. The project has been conducted by CTTC and the University of Washington from 2015-16. The project seeks additional industrial sponsors to continue development; please contact Tom Henderson if interested in funding additional development or obtaining training or support.


Phase 1

This phase has produced a new Wi-Fi Spectrum-based physical layer, enabling Wi-Fi devices and LTE devices to coexist on the same ns-3 channel. Beyond this enabling capability, several enhancements to the ns-3 models have been made:

  • Enhancements to Wi-Fi clear-channel access (CCA) and frame synchronization models
  • A Wi-Fi roaming model for AP selection based on received signal strength
  • LTE interference model enhancements
  • New indoor and outdoor propagation models
  • Wi-Fi MIMO and interference models for fading model D
  • Duty-cycled LTE transmission model
  • Scenarios corresponding to the indoor and outdoor scenarios defined in 3GPP TR36.889
  • A framework for executing simulation campaigns and quickly plotting the results

Phase 2

Phase 2 was focused on developing models related to the standardization process for Release 13 which concluded in December 2015. In particular, a "Listen-Before-Talk" (LBT) mode was developed for LTE, and scenarios were constructed to evaluate technical topics such as the sensitivity on performance on the Energy Detection threshold used for the LBT CCA mechanism.

Phase 2 resulted in a Wi-Fi Alliance contribution to 3GPP RAN1 in November 2015 (see below).

Phase 3

Phase 3 further developed the models to include a voice application model, efficiency updates to the interaction between the LAA scheduler and channel access manager, and the ITU InH indoor channel model, among other enhancements.

Phase 3 resulted in a Wi-Fi Alliance liaison response to 3GPP RAN1 in August 2016 (see below).


The software is available in a repository at ns-3's main code server,

The software will eventually be migrated to ns-3 releases, but as of the latest ns-3 release, the LAA extensions are not available in the main release.

The extensions reside in four main directories:

  • Scripts, tests, and documentation to construct simulations involving these new models are in 'src/laa-wifi-coexistence'
  • Extensions to LTE to enable unlicensed variants are in 'src/lte'
  • Extensions to the Wi-Fi module to enable the SpectrumWifiPhy and new error models are in 'src/wifi'
  • Propagation model extensions are in 'src/propagation'


  • A contribution to the November 2015 3GPP RAN1 meeting (R1-156621) has been produced. The implementation has evolved since the November 3GPP RAN1 meeting and more current results are documented in the links below, and in the liaison response R1-167881 below.
  • A publication preprint, based on code from the June 2016 timeframe, is available here.
  • A liaison response to the August 2016 3GPP RAN1 meeting (R1-167881) has been produced.
  • A recent presentation about the models and scenario support (May 2016) is available here.

Getting started

All figures and data in the 3GPP RAN1 meeting contribution can be generated by following the steps in the above ns-3-lbt Phase 2 archive by consulting the README.txt in the software directory under 'src/laa-wifi-coexistence/experiments/README.txt'.

Specifically, the following versions of the ns-3-lbt repository are aligned with results shown in the following documents:

Additional documentation (updated as of February 2016, and consistent with Phase 2) is available at the following URLs:


If you wish to cite this work in your publication, please cite our arXiv paper "Simulating LTE and Wi-Fi Coexistence in Unlicensed Spectrum with ns-3" at


Contact Tom Henderson ( for more information.