Suo

Suo is a modem library. Suo can be also seen as a framework for implementing the physical layer of various communication systems.

Suo is designed to be modular and portable. Modules are divided into a few different categories. For each category, a common interface based on function calls and possibly callbacks is defined.

Signal processing code is mostly platform independent and kept separate from the platform-dependent parts related to interfacing SDR hardware, operating systems and other programs.

It may seem silly to do something like this in C these days, but it happened because:

• It started as something simpler and organically grew into something more complex
• Since I haven't really made programs this complex before, I hadn't seen the need to learn proper OOP languages
• The code uses liquid-dsp which is C-friendly
• The code was somewhat inspired by liquid-dsp in general
• One can always dream of making a version 2 in another language later

Using libsuo

To use libsuo as a part of your own application, link code under libsuo/ into your application and call the functions as needed. For some documentation of the different module categories and their interfaces, see the file libsuo/suo.h.

Compilation into a dynamic library is not implemented yet and not considered really necessary. By running make under libsuo/, libsuo-dsp.a and libsuo-io.a files for static linking are created. If that does not work for your usecase, use your preferred way to add the necessary source files into your application.

Note that there are dependencies on other libraries. Most of the modem code depends on liquid-dsp.

Using the Suo application

To run Suo modems on general-purpose operating systems, the program under suoapp/ can be used. In most cases, this is probably easier than using libsuo directly.

There is an ugly configuration file system, which might change to something better some day.

For some examples on running and interfacing Suo, see the files under examples/. Note that Suo is meant to be used as a part of other systems, so alone it doesn't do that much.

I/O interfaces implemented at the moment

With SoapySDR, Suo can be easily used with common SDR hardware. It has been tested on USRP, rtl-sdr, LimeSDR and xtrx.

File I/O is also supported, which is useful for testing with recorded or simulated signals read from a file, or for piping the signals from some other program.

Sound cards can be used through the ALSA I/O module.

Higher protocol layers should run in a separate process, and ZeroMQ sockets are used to transfer frames between processes. ZeroMQ messages are prefixed with a frame metadata struct.

Modems implemented at the moment

Currently, there is simple_receiver and simple_transmitter, which are primarily made for FSK packet waveforms similar to those used by typical small radio chips. It supports the common preamble-syncword-payload format with 2-GFSK modulation. It's not a very high performance modem, but it's already useful and also helps test other parts of the software.

There's also a PI/4 DQPSK burst modem primarily made for TETRA experimentation, but it could grow to a more general phase-shift keying modem as well.

Other, better modems are being developed.

Installation on Ubuntu or Debian

If you have a LimeSDR, I recommend using Ubuntu 18.04 and following instructions for MyriadRF PPA first.

For other devices, use your preferred distribution and install a SoapySDR module for your device. Sometimes it's convenient to use an Ubuntu-based Docker, nspawn or lxd container. Installation of these is outside of the scope of this document.

Next, install some dependencies:

sudo apt install git gcc make automake libsoapysdr-dev libzmq3-dev libasound2-dev python3 python3-zmq

cd
git clone https://github.com/jgaeddert/liquid-dsp
cd liquid-dsp
./bootstrap.sh
./configure
make -j4
sudo make install
sudo ldconfig

Compile Suo:

cd
git clone https://github.com/tejeez/suo  # Do this only if it wasn't cloned yet
cd suo/libsuo
make -j4
cd ../suoapp
make -j4

Run it:

cd ~/suo/example
../suoapp/build/suo example-config.txt

Installation on Windows

Install PothosSDR. This contains SoapySDR and liquid-dsp compiled for Windows. Install it at the default place, C:\Program Files\PothosSDR.

Install MSYS2. This contains a GCC toolchain for Windows.

Open the MSYS2 shell and install dependencies:

pacman -S git mingw-w64-x86_64-toolchain mingw-w64-x86_64-zeromq

To compile and run Suo, open the MSYS2 shell and use the same commands that were used on Ubuntu. Before running it, do this:

export PATH="/c/Program Files/PothosSDR/bin:/mingw64/bin:"$PATH

Tested with USRP B200 and LimeSDR on 64-bit Windows 10. LimeSDR driver has to be installed first.

Licensing

Code in this repository is under the MIT license.

Note that it's possible to have Suo modules and Suo based applications under different licenses as well.