ns-3 is well-known for providing high fidelity, packet-level models of Wi-Fi and LTE, but simulation studies to date have not tried to combine the technologies on the same channel. In industry, 3GPP is defining standards for using LTE in unlicensed spectrum. 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.
This page describes a project sponsored by the Wi-Fi Alliance to improve ns-3 models to facilitate studies about the coexistence of Wi-Fi and unlicensed variants of LTE on the same channel. The project is being conducted by CTTC and the University of Washington.
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
Current work is focused on developing models related to the current standardization process for Release 13. In particular, a "Listen-Before-Talk" (LBT) mode is being developed for LTE, and scenarios are being constructed to evaluate technical topics such as the sensitivity on performance on the Energy Detection threshold used for the LBT CCA mechanism.
The software is available in a repository at ns-3's main code server, http://code.nsnam.org:
- The phase 1 code is available with Mercurial, can be browsed on the web, or by download in a zip or tar.bz2 format.
- The phase 2 code (under current development as of this September 2015 writing) is available with Mercurial, can be browsed on the web, or by download in a zip or tar.bz2 format.
The software will eventually be migrated to ns-3 releases, but as of the latest ns-3.24 release, none of the above extensions are 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 phase 1 technical report is available, and can be built using Python-Sphinx tools (similar to the ns-3 Sphinx documentation) based on files found in the directory src/laa-wifi-coexistence/doc.