# Welcome to VOLK_GNSSSDR, the Vector-Optimized Library of Kernels for GNSS-SDR

VOLK_GNSSSDR is a sub-project of GNSS-SDR. This library provides a set
of extra kernels that can be used stand-alone or in combination with
VOLK's. Please see http://libvolk.org for documentation, source code,
and contact information about the original VOLK library.

The boilerplate of this code was initially generated with
```volk_modtool```, an application provided by VOLK that creates the
skeleton than can then be filled with custom kernels. Some modifications
were added to accomodate the specificities of Global Navigation
Satellite Systems (GNSS) signal processing. Those changes are clearly
indicated in the source code, and do not break compatibility.

This library contains kernels of hand-written SIMD code for different
mathematical operations, mainly with 8-bit and 16-bit real and complex
data types, offering a platform/architecture agnostic version that will
run in all machines, plus other versions for different SIMD instruction
sets. Then, the application ```volk_gnsssdr_profile``` runs some
iterations of all versions that your machine can execute and annotates
which is the fastest, which will then be selected at runtime when
executing GNSS-SDR. In this way, we can address at the same time
[portability](http://gnss-sdr.org/design-forces/portability/) (by
creating executables that will run in nearly all processor
architectures) and
[efficiency](http://gnss-sdr.org/design-forces/efficiency/) (by
providing custom implementations specially designed to take advantage of
the specific processor that is running the code).

These kernels have some specific features (e.g. saturation arithmetics)
that are aimed to GNSS signal processing, but could make them not
suitable for its general use in other applications. Check out the
documentation generated by Doxygen and the *generic* (that is, plain C)
implementation to see what each kernel is actually doing.

## How to use VOLK_GNSSSDR:

This library is automatically built and installed along with GNSS-SDR if
it is not found by CMake on your system at configure time.

However, you can install and use VOLK_GNSSSDR kernels as you use VOLK's,
independently from GNSS-SDR.

First, make sure that the required dependencies are installed in your
machine:

~~~~~~ 
$ sudo apt-get install cmake python-mako python-six libboost-dev \
  libboost-filesystem-dev libboost-system-dev
~~~~~~ 

In order to build and install the library, go to the base folder of the
source code and do:

~~~~~~ 
$ mkdir build
$ cd build
$ cmake ..
$ make
$ sudo make install
~~~~~~ 

That's it!

Before its first use, please execute ```volk_gnsssdr_profile``` to let
your system know which is the fastest available implementation. This
only has to be done once:

~~~~~~ 
$ volk_gnsssdr_profile
~~~~~~

From now on, GNSS-SDR (and any other program of your own that makes use
of VOLK_GNSSSDR) will benefit from the acceleration provided by SIMD
instructions available in your processor.

The execution of ```volk_gnsssdr_profile``` can be set automatically
after building, leaving your system ready to use:

~~~~~~
$ cmake -DENABLE_PROFILING=ON ../
$ make
$ sudo make install
~~~~~~


This figure shows the role of some VOLK_GNSSSDR kernels in the context
of a GNSS baseband processor:

![Example of VOLK_GNSSSDR
usage.](./docs/images/VOLK_GNSSSDR_Usage_Example.png)



If you use VOLK_GNSSSDR in your research and/or software, please cite
the following paper:

 * C. Fernández-Prades, J. Arribas, P. Closas, [*Accelerating
GNSS Software Receivers*](https://zenodo.org/record/266493), in Proc. of
the ION GNSS+ 2016 Conference, pp. 44-61, Portland, Oregon, Sept. 12-16, 2016.

Citations are useful for the continued development and maintenance of
the library.



___

VOLK_GNSSSDR was originally created by Andres Cecilia Luque in the
framework of the [Summer Of Code In Space (SOCIS
2014)](http://sophia.estec.esa.int/socis2014/?q=about "SOCIS 2014
webpage") program organized by the European Space Agency, and then
evolved and maintained by Carles Fernández-Prades and Javier
Arribas. This software is released under the GNU General Public License
version 3, see the file COPYING.

This project is managed by [Centre Tecnologic de Telecomunicacions de
Catalunya](http://www.cttc.es "CTTC webpage").
