GNU Radio LTE Receiver

The gr-lte project is an Open Source Software Package which aims to provide a GNU Radio LTE Receiver to receive, synchronize and decode LTE signals. Its development was focused on modularity. This makes the project easy to extend and reuse its blocks.

This project was initiated as a Bachelor thesis at the Communication Engineering Lab (CEL) at the Karlsruhe Institute of Technology (KIT), Germany, http://www.cel.kit.edu.

The Idea

This project aims to provide a modular environment for an LTE downlink receiver. All blocks should be replacable. e.g. introduce a new channel estimator block with more advanced algorithms. On the other hand it should be fairly easy to add new blocks to decode additional physical channels.
The block design aims to be modular and reusable. Where possible GR blocks are used.
Furthermore message ports are used for configuration on runtime. This is supposed to make the control flow visible to users and thus better understandable.

Publications

This is a list of related publications for further reference.

J. Demel, S. Koslowski, and F. Jondral, A LTE Receiver Framework Implementation in GNU Radio, SDR-WInnComm-Europe-2013, June 2013.

Johannes Demel, Sebastian Koslowski, and Friedrich K. Jondral, A LTE Receiver Framework Using GNU Radio, Journal of Signal Processing Systems, 78(3):313–320, 2015.

Capabilities

gr-lte provides blocks to synchronize to a LTE downlink signal. It performs OFDM operation to operate in the frequency domain and provides a channel estimator. At this point physical LTE downlink channels can be extracted from the symbols and be processed. PBCH is fully implemented and decodes MIB. PCFICH is available too. Almost all code for PHICH is implemented and there is lots of code to bring PDCCH support. It is not yet possible to just plug it in, though. Eventually all channels shall be supported.

Flowgraphs

A lot of example flowgraphs are located in the examples folder. These include some hierarchical flowgraphs and the corresponding top-level flowgraphs. Two different algorithms for synchronization are available.

• step-by-step synchronization
  • starts with symbol sync, PSS, SSS
  • for single RX antenna
• direct PSS sync
  • Syncs directly to PSS half-frames
  • may use multiple RX antennas
  • 2RX and 4RX flowgraphs available

Requirements

• GNU Radio 3.7.6 or newer

  • some bugs just got fixed in this new version and we take advantage of them.
  • all code was moved to GR 3.7 API.

• GR 3.6.5.1 (deprecated)

  • use commit tagged with 'gnuradio-v3.6.5.1'
  • message passing API is necessary
  • all the latest bug fixes
  • project used to use GR 3.6 API

• MATLAB (deprecated)

  • R2011b tested
  • m-files are replaced by Python/Numpy/Scipy code which offers greater flexibility and connectivity to GNU Radio.
  • for .m-files
  • If you want, have a look at the m-files

Build/Install instructions for Linux

You can use PyBOMBS to install GNU Radio and gr-lte or use the instructions below.

1. Get, build and install GNU Radio from http://www.gnuradio.org

2. Get gr-lte from github

3. Configure it using CMake
   Assuming you are already in the project folder
   mkdir build
cp cmake_command.sh build/
cd build
./cmake_command.sh
   
   This will just run a little script to aid with project setup for Code::Blocks
   Otherwise run cmake ..

4. Compile and Install
   make -jX where X is a number of choice (Often the number of cores available)
   sudo make install (make it available in GRC)

5. compile hierarchical GRC blocks
   These blocks are located in the 'examples' directory.
   hierarchical GRC blocks must be generated by opening them in GRC and clicking Generate. Afterwards reload blocks or restart GRC. This makes the hier blocks available in GRC just as all the other blocks.
   An alternative is to use the python script examples/hier_block_install_helper.py, which calls 'grcc' for all grc files in the current directory and installs them.

6. Have fun
   If everything runs without errors the gr-lte blocks should be available in GRC.
   The flowgraph 'LTE_flowgraph_top_level.grc' is meant as a reference. It is supposed to contain a working flowgraph with all available blocks. Only the source must be updated. Specify the path to your recorded samples and update the resampler parameters.
   By changing the variable 'fftlen' you update a whole bunch of other variables which basically configure the expected bandwidth and the maximum subcarriers the flowgraph can handle.

7. Troubleshooting
   In case you have trouble with parts of the flowgraph etc. write an email preferably to the GNU Radio mailinglist. This way others with the same problem can find hints in the mailinglist archives.