gnss-sdr/docs/changelog.md

<!-- prettier-ignore-start -->
[comment]: # (
SPDX-License-Identifier: GPL-3.0-or-later
)

[comment]: # (
SPDX-FileCopyrightText: 2011-2020 Carles Fernandez-Prades <carles.fernandez@cttc.es>
)
<!-- prettier-ignore-end -->

## Unreleased

### Improvements in Efficiency:

- Faster internal handling of `Gnss_Synchro` objects by reducing the amount of
  copying via adding `noexcept` move constructor and move assignment operators,
  so the move semantics are also used in STL containers.
- Add building option `ENABLE_STRIP` to generate stripped binaries (that is,
  without debugging symbols), smaller in size and potentially providing better
  performance than non-stripped counterparts. Only for GCC in Release build
  mode. Set to `OFF` by default.

### Improvements in Maintainability:

- The software can now be built against the GNU Radio 3.9 API that uses C++11
  smart pointers instead of Boost smart pointers.
- The software can now be built against Boost <= 1.73 (minimum version: 1.53).
- Removed python six module as a dependency if using Python 3.x.
- Improved usage of smart pointers to better express ownership.
- Add definition of std::make_unique for buildings with C++11, and make use of
  it along the source code.
- Private members in headers have been sorted by type and size, minimizing
  padding space in the stack and making the files more readable for humans.
- Fixed building with GCC 10 (gcc-10 and above flipped a default from `-fcommon`
  to `-fno-common`, causing an error due to multiple defined lambda functions).
- Fixed warnings risen by GCC 10 and Clang 10.
- Various improvements in the CMake scripts: better decision on the C++ standard
  to use; simplifications for various API dependency and environment versions
  requirements, with more intuitive naming for variables; fixed the
  `ENABLE_CLANG_TIDY` option; better GFORTRAN module; and broader adoption of
  the modern per-target approach.
- Add a new building option `ENABLE_BENCHMARKS` which activates the building of
  benchmarks for some code snippets.

### Improvements in Portability:

- The software can now be cross-compiled on Petalinux environments.
- Make use of `std::span` if the compiler supports it, and use gsl-lite as a
  fallback. The latter has been updated to version
  [0.37.0](https://github.com/gsl-lite/gsl-lite/releases/tag/0.37.0).
- Improved finding of libgfortran in openSUSE and Fedora distributions.
- Allow a random name for the build type. If not recognized, it is set to
  `None`. This allows packaging in some distributions that pass an arbitrary
  name as the build type (e.g., Gentoo) to avoid unexpected compiler flags. The
  building option `ENABLE_PACKAGING` must set to `ON` when packaging.
- Do not stop the receiver if SysV message queues cannot be created.

### Improvements in Reliability:

- Fixed a bug in GLONASS GNAV CRC computation.
- Fixed a possible buffer overflow in the generation of RTCM messages.
- Fixed a bug that could cause a random crash on receiver stopping.

### Improvements in Reproducibility:

- Improved reproducibility of the volk_gnsssdr library: Drop compile-time CPU
  detection.

### Improvements in Usability:

- Do not pollute the source directory if the software is built from an
  out-of-source-tree directory. Downloaded external sources and test raw files
  are now stored in a `./thirdparty` folder under the building directory. In
  case of an out-of-source-tree build, the generated binaries are stored in an
  `./install` folder, also under the building directory. The old behavior for
  generated binaries is maintained if the building is done from any source tree
  subfolder (for instance, `gnss-sdr/build`): in that case, binaries are stored
  in the source tree (under `gnss-sdr/install`).
- Updated version of the Contributor Covenant to version 2.0.
- Added a Matlab script to quantize the input signal with a given number of bits
  per sample.

&nbsp;

## [GNSS-SDR v0.0.12](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.12)

### Improvements in Accuracy:

- Improved accuracy of the C/N0 estimator.

### Improvements in Availability:

- Fixed computation of acquisition threshold when using the `Acquisition_XX.pfa`
  configuration parameter, including non-coherent accumulation
  (`Acquisition_XX.max_dwells` > 1).

### Improvements in Efficiency:

- Faster implementation of the Viterbi decoder for Galileo navigation messages.
- The `-O3` flag is now passed to GCC in `Release` and `RelWithDebInfo` build
  types (instead of `-O2`), thus enabling tree vectorization. Disabled if
  building for Fedora or Gentoo.

### Improvements in Flexibility:

- New Tracking parameters allow the configuration of the C/N0 and lock detector
  smoothers, as well as the activation of the FLL in pull-in and steady state
  stages.
- Added new Tracking parameter `Tracking_XX.carrier_aiding`, allowing
  enabling/disabling of carrier aiding to the code tracking loop.
- New PVT parameter `PVT.enable_rx_clock_correction` allows to enable or disable
  the continuous application of the Time solution correction (clock steering) to
  the computation of Observables. By default is set to `false` (that is,
  disabled).
- New PVT parameter `PVT.max_clock_offset_ms`: if
  `PVT.enable_rx_clock_correction` is set to `false`, this parameter sets the
  maximum allowed local clock offset with respect to the Time solution. If the
  estimated offset exceeds this parameter, a clock correction is applied to the
  computation of Observables.
- Fixed L5 and E5a receiver chains when tracking the data component.
- Added new PVT configuration parameter `PVT.rinex_name` to specify a custom
  name of the generated RINEX files. A commandline flag `--RINEX_name` is also
  available, and overrides the configuration.

### Improvements in Interoperability:

- Fixed PVT solution in receivers processing L1 plus L2C and/or L5 signals.
- Fixed the initialization of the carrier phase accumulator. Carrier phase
  measurements are now usable to compute integer ambiguity resolution.
- Added carrier phase observable initialization to match the pseudorange length.
- Added RINEX files generation for triple-band configurations (L1 + L2C + L5 and
  L1 + E1 + L2C + L5 + E5a).
- Fixed bugs in the decoding of BeiDou navigation messages.
- Fixed bugs in the generation of RTCM messages.
- Fixed a bug in feeding Galileo channels' observations to RTKLIB, which was
  causing wrong date of PVT fixes in Galileo-only receivers and not considering
  Galileo observations in multi-constellation receivers when using signals after
  the GPS rollover on April 6, 2019.
- Improved management of devices with the AD9361 RF transceiver.
- Fixed bugs in FPGA off-loading.

### Improvements in Maintainability:

- Rewriting of acquisition and tracking adapters, thus avoiding a lot of code
  duplication.
- New CMake option `-DENABLE_ARMA_NO_DEBUG` defines the macro `ARMA_NO_DEBUG`,
  which disables all run-time checks, such as bounds checking, in the Armadillo
  library. This will result in faster code. This option is disabled by default
  during development, but automatically set to `ON` if the option
  `ENABLE_PACKAGING` is set to `ON`.
- All shadowed variables detected by passing `-Wshadow` to the compiler have
  been fixed (see https://rules.sonarsource.com/cpp/RSPEC-1117?search=shadow and
  MISRA C++:2008, 2-10-2 - Identifiers declared in an inner scope shall not hide
  an identifier declared in an outer scope).
- Apply more clang-tidy checks related to readability:
  `readability-avoid-const-params-in-decls`,
  `readability-braces-around-statements`, `readability-isolate-declaration`,
  `readability-redundant-control-flow`, `readability-uppercase-literal-suffix`.
  Fixed raised warnings.
- Fixed a number of defects detected by `cpplint.py`. Filters applied:
  `+build/class`, `+build/c++14`, `+build/deprecated`,
  `+build/explicit_make_pair`, `+build/include_what_you_use`,
  `+build/printf_format`, `+build/storage_class`, `+readability/constructors`,
  `+readability/namespace`, `+readability/newline`, `+readability/utf8`,
  `+runtime/casting`, `+runtime/explicit`, `+runtime/indentation_namespace`,
  `+runtime/init`, `+runtime/invalid_increment`,
  `+runtime/member_string_references`, `+runtime/memset`, `+runtime/operator`,
  `+runtime/printf`, `+runtime/printf_format`, `+whitespace/blank_line`.
- `clang-format` can now be applied to the whole code tree without breaking
  compilation.
- Added more check options to `.clang-tidy` file.
- Default Python version is now >= 3.4. Python 2.7 still can be used in systems
  where Python 3 is not available (e.g., CentOS 7, Debian 8, Ubuntu 10.04).
- CMake now passes the `-DCMAKE_BUILD_TYPE` (or configuration in
  multi-configuration generators like Xcode) to modules built along gnss-sdr
  (e.g, the volk_gnsssdr library and googletest). Build types available: `None`,
  `Release` (by default), `Debug`, `RelWithDebInfo`, `MinSizeRel`, `Coverage`,
  `NoOptWithASM`, `O2WithASM`, `O3WithASM`, `ASAN`.
- Fix runtime errors when compiling in `Debug` mode on macOS.
- Updated links in comments along the source code and in CMake scripts.
- Update GSL implementation to 0.36.0. See
  https://github.com/gsl-lite/gsl-lite/releases/tag/v0.36.0
- Create a CI job on GitHub to ensure that `clang-tidy` has been applied in most
  of the source code (some optional blocks and tests are left apart).
- Create a CI job on GitHub to ensure that `clang-format` has been applied.
- Create a CI job on GitHub to ensure that `cpplint` filters have been applied.
- Create a CI job on GitHub to ensure compliance with REUSE Specification (see
  https://reuse.software)
- Create a CI job on GitHub using `prettier` (https://prettier.io/) to check
  markdown files formatting.
- Create a CI job on GitHub to check the formatting of CMake scripts using
  `cmakelint` (see https://github.com/richq/cmake-lint).

### Improvements in Openness:

- Make software compliant with REUSE Specification – Version 3.0 (see
  https://reuse.software/spec/).

### Improvements in Portability:

- The CMake scripts now find dependencies in Debian's riscv64 architecture.
- Enable AVX2 kernels of the volk_gnsssdr library when using the Clang compiler.
- Fixed building in some ARM-based devices. Now Clang and ARMClang can be used
  for native building.
- Added toolchain files for building gnss-sdr and the volk_gnsssdr library in
  several ARM processor architectures, including those in Raspberry Pi 3 and 4.
- The software can now be built using Xcode (passing `-GXcode` to CMake) without
  previous manual installation of volk_gnsssdr.
- The software can now be built using Xcode (passing `-GXcode` to CMake) without
  gflags, glog, matio, PugiXML, Protocol Buffers or googletest previously
  installed.
- Now the volk_gnsssdr library can be built on Microsoft Windows.
- Now the volk_gnsssdr library makes use of C11 `aligned_alloc` where available.
- Improved CMake script for cross-compilation and for the detection of AVX, AVX2
  and NEON (v7 and v8) instructions.
- Fixed warnings raised by CMake 3.17.
- Fixed warnings raised by `cmake --warn-uninitialized ..`
- Fixed the receiver's availability in systems in which the Sys V message queue
  mechanism is not available.

### Improvements in Reliability:

- Decoding of navigation messages no longer rely on implementation defined
  behavior for shifting left a signed integer.
- Removed usage of functions with insecure API (e.g., `strcpy`, `sprintf`).
- New type alias `volk_gnsssdr::vector` allows both aligned memory allocation
  and automatic deallocation.
- Fixed a memory leak in the generation of Galileo PRN codes.
- Added clang-tidy checks `clang-analyzer-security.*`,
  `clang-analyzer-optin.portability.UnixAPI` clang-tidy checks. Fixed raised
  warnings.
- Fixed `cpplint.py` `runtime/printf` and `runtime/explicit` errors.
- All constructors callable with one argument are marked with the keyword
  explicit. See MISRA C++:2008, 12-1-3 - All constructors that are callable with
  a single argument of fundamental type shall be declared explicit.

### Improvements in Repeatability:

- Added the option to apply carrier smoothing of code pseudoranges with new
  Observables parameter `Observables.enable_carrier_smoothing`.
- Fixed normalization of DLL discriminator in BPSK modulations when the spacing
  between correlators was not 0.5.

### Improvements in Testability:

- Add receiver runtime to `position_test` report.
- Improvements in FPGA unit tests.
- Add new utility tool `obsdiff` to perform single and double differences
  computations from observation RINEX files. Requires GPSTk and Armadillo >=
  9.800.

### Improvements in Usability:

- A new global parameter `GNSS-SDR.pre_2009_file` allows to process raw sample
  files containing GPS L1 C/A signals dated before July 14, 2009.
- Improved DLL-PLL binary dump MATLAB/Octave plot script. Old versions removed.
- Simplified RTKLIB error log.
- Added a Python 3 plotting script to show relative performance of generic
  volk_gnsssdr kernels wrt SIMD fastest versions.
- Added reporting of velocity in the terminal.
- Added reporting of user clock drift estimation, in ppm, in the Pvt_Monitor and
  in internal logging (`Debug` mode).
- Updated documentation generated by Doxygen, now the `pdfmanual` target works
  when using ninja.
- CMake now generates an improved summary of required/optional dependency
  packages found and enabled/disabled features, including the building system
  and GNSS-SDR, CMake and compiler versions. This info is also stored in a file
  called `features.log` in the building directory.
- Markdown files have been wrapped to 80 characters line length to make it
  easier to read them from the terminal.

See the definitions of concepts and metrics at
https://gnss-sdr.org/design-forces/

&nbsp;

## [GNSS-SDR v0.0.11](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.11)

This release has several improvements in different dimensions, addition of new
features and bug fixes:

### Improvements in Accuracy:

- Local clock correction based on PVT solution, allowing the delivery of
  continuous observables.
- Fix a bug in broadcast ionospheric parameters usage.

### Improvements in Availability:

- Improved mechanism for false lock detection in the Tracking loops.
- Fixed bug in Galileo INAV/FNAV message decoding when PLL is locked at 180
  degrees, which prevented from correct navigation message decoding in some
  situations.
- Fixed bug that caused a random deadlock in the Observables block, preventing
  the computation of PVT fixes.
- Fixed PVT computation continuity through the TOW rollover.
- Improved signal acquisition and tracking mechanisms in high dynamic scenarios.

### Improvements in Efficiency:

- Added mechanism for assisted acquisition of signals on a secondary band when
  the primary has already been acquired. This allows a great reduction of the
  computational load in multi-frequency configurations.
- Tracking loops now perform bit synchronization, simplifying the decoding
  process in Telemetry blocks and FPGA-offloading.
- Improved preamble detection implementation in the decoding of navigation
  messages (acceleration by x1.6 on average per channel).
- Shortened Acquisition to Tracking transition time.
- Applied clang-tidy checks and fixes related to performance:
  performance-faster-string-find, performance-for-range-copy,
  performance-implicit-conversion-in-loop, performance-inefficient-algorithm,
  performance-inefficient-string-concatenation,
  performance-inefficient-vector-operation, performance-move-const-arg,
  performance-move-constructor-init, performance-noexcept-move-constructor,
  performance-type-promotion-in-math-fn,
  performance-unnecessary-copy-initialization,
  performance-unnecessary-value-param, readability-string-compare.

### Improvements in Flexibility:

- Rewritten Control Thread and GNSS flow graph for increased control of
  channels' status and smarter assignation of satellites in multi-band
  configurations.
- New Tracking parameters allow the configuration of PLL and DLL filters order.
- Added parameter to enable FLL during pull-in time.
- Configurable pull-in time in the Tracking loops.

### Improvements in Interoperability:

- Added the BeiDou B1I and B3I receiver chains.
- Fix bug in GLONASS dual frequency receiver.
- Added a custom UDP/IP output for PVT data streaming.
- Improved Monitor block with UDP/IP output for internal receiver's data
  streaming.
- Custom output formats described with .proto files, making easier to other
  applications reading them in a forward and backward-compatible fashion upon
  future format changes. New dependency: Protocol Buffers >= 3.0.0
- Fixes in RINEX generation: week rollover, annotations are not repeated anymore
  in navigation files. Parameter rinexnav_rate_ms has been removed, annotations
  are made as new ephemeris arrive.
- Fixes in RTCM messages generation: week rollover.

### Improvements in Maintainability:

- The internal communication mechanism based on gr::msg_queue has been replaced
  by a thread-safe, built-in asynchronous message passing system based on GNU
  Radio's Polymorphic Types. This change is backwards-compatible and prevents
  from a failure in case of a possible future deprecation or removal of the
  gr::msg_queue API.
- Deprecated boost::asio::io_service replaced by boost::asio::io_context if
  Boost > 1.65
- CMake turns all policies to ON according to the running version up to version
  3.15.
- Usage of clang-tidy integrated into CMake scripts. New option
  -DENABLE_CLANG_TIDY=ON executes clang-tidy along with compilation. Requires
  clang compiler.
- Applied clang-tidy checks and fixes related to readability:
  readability-container-size-empty, readability-identifier-naming,
  readability-inconsistent-declaration-parameter-name,
  readability-named-parameter, readability-non-const-parameter,
  readability-string-compare.
- Improved includes selection following suggestions by include-what-you-use (see
  https://include-what-you-use.org/), allowing faster compiles, fewer recompiles
  and making refactoring easier.
- Massive reduction of warnings triggered by clang-tidy checks.
- Throughout code cleaning and formatting performed with automated tools in
  order to reduce future commit noise.

### Improvements in Portability:

- Added interfaces for FPGA off-loading in GPS L1 C/A, Galileo E1b/c, GPS L2C,
  GPS L5 and Galileo E5a receiver chains.
- CMake scripts now follow a modern approach (targets and properties) but still
  work with 2.8.12.
- Improvements for macOS users using Homebrew.
- The software builds against GNU Radio >= 3.7.3, including 3.8.0. Automatically
  detected, no user intervention is required.
- The volk_gnsssdr library can now be built without requiring Boost if the
  compiler supports C++17 or higher.
- The Boost Filesystem library is not anymore a required dependency in cases
  where it can be replaced by std::filesystem. Automatically detected, no user
  intervention is required.
- CMake scripts automatically select among C++11, C++14, C++17 or C++20
  standards, the most recent as possible, depending on compiler and dependencies
  versions.
- Drawback in portability: Protocol Buffers >= 3.0.0 is a new required
  dependency.

### Improvements in Reliability:

- Included the Guidelines Support Library. General improvement of memory
  management, replacement of raw pointers by containers or smart pointers.
- Applied clang-tidy checks and fixes related to High Integrity C++:
  performance-move-const-arg, modernize-use-auto, modernize-use-equals-default,
  modernize-use-equals-delete, modernize-use-noexcept, modernize-use-nullptr,
  cert-dcl21-cpp, misc-new-delete-overloads, cert-dcl58-cpp, cert-err52-cpp,
  cert-err60-cpp, hicpp-exception-baseclass, hicpp-explicit-conversions.
- Fixed a number of defects detected by Coverity Scan (version June 2019).

### Improvements in Usability:

- The receiver now admits FPGA off-loading, allowing for real time operation in
  embedded systems at high sampling rates and high number of signals and
  channels per signal in multiple bands.
- Fixed program termination (avoiding hangs and segfaults in some
  platforms/configurations).
- The Labsat_Signal_Source now terminates the receiver's execution when the end
  of file(s) is reached. It now accepts LabSat 2 filenames and series of LabSat
  3 files.
- Added configuration parameters to set the annotation rate in KML, GPX, GeoJSON
  and NMEA outputs, set by default to 1 s.
- New parameter PVT.show_local_time_zone displays time in the local time zone.
  Subject to the proper system configuration of the machine running the software
  receiver. This feature is not available in old compilers.
- CMake now generates a summary of required/optional dependency packages found
  and enabled/disabled features. This info is also stored in a file called
  features.log in the building directory.
- Improved information provided to the user in case of building configuration
  and runtime failures.

See the definitions of concepts and metrics at
https://gnss-sdr.org/design-forces/

&nbsp;

## [GNSS-SDR v0.0.10](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.10)

This release has several improvements in different dimensions, addition of new
features and bug fixes:

### Improvements in Accuracy:

- Part of the RTKLIB core library has been integrated into GNSS-SDR. There is
  now a single PVT block implementation which makes use of RTKLIB to deliver PVT
  solutions, including Single and PPP navigation modes.
- Fixed CN0 estimation for other correlation times than 1 ms.
- Improved computation of tracking parameters and GNSS observables.
- Other minor bug fixes.

### Improvements in Availability:

- Internal Finite State Machines rewritten for improved continuity in delivering
  position fixes. This fixes a bug that was stalling the receiver after about
  six hours of continuous operation.
- Redesign of the time counter for enhanced continuity.
- Improved flow graph in multi-system configurations: the receiver does not get
  stalled anymore if no signal is found from the first system.
- Improved acquisition and tracking sensitivity.
- Added mechanisms for Assisted GNSS, thus shortening the Time-To-First-Fix.
  Provision of data via XML files or via SUPL v1.0. Documented at
  https://gnss-sdr.org/docs/sp-blocks/global-parameters/
- Other minor bug fixes.

### Improvements in Efficiency:

- Added the possibility of non-blocking acquisition, which works well when using
  real-time data from an RF front-end.
- Improved flow graph in multi-band configurations: satellites acquired in one
  band are immediately searched in others.
- Complex local codes have been replaced by real codes, alleviating the
  computational burden.
- New volk_gnsssdr kernels: volk_gnsssdr_16i_xn_resampler_16i_xn.h,
  volk_gnsssdr_16ic_16i_rotator_dot_prod_16ic_xn.h,
  volk_gnsssdr_32f_xn_resampler_32f_xn.h,
  volk_gnsssdr_32fc_32f_rotator_dot_prod_32fc_xn.h
- Some AVX2 implementations added to the volk_gnsssdr library.
- Improvement in C++ usage: Use of const container calls when result is
  immediately converted to a const iterator. Using these members removes an
  implicit conversion from iterator to const_iterator.
- Output printers can be shut down, with some savings in memory and storage
  requirements.
- A number of code optimizations here and there.

### Improvements in Flexibility:

- A number of new parameters have been exposed to the configuration system.
- Possibility to choose Pilot or Data component for tracking of GPS L5 and
  Galileo E5a signals.
- Enabled extended coherent integration times for signal tracking.
- Configurable coherent and/or non-coherent signal acquisition.
- Some configuration parameters can now be overridden by commandline flags for
  easier use in scripts.

### Improvements in Interoperability:

- Added the GPS L5 receiver chain.
- Added the GLONASS L1 SP receiver chain.
- Added the GLONASS L2 SP receiver chain.
- Improvements in the Galileo E5a and GPS L2C receiver chains.
- Updated list of available GNSS satellites.
- Added five more signal sources: "Fmcomms2_Signal_Source" (requires gr-iio),
  "Plutosdr_Signal Source" (requires gr-iio), "Spir_GSS6450_File_Signal_Source",
  "Labsat_Signal_Source" and "Custom_UDP_Signal_Source" (requires libpcap).
  Documented in https://gnss-sdr.org/docs/sp-blocks/signal-source/
- Improved support for BladeRF, HackRF and RTL-SDR front-ends.
- Added tools for the interaction with front-ends based on the AD9361 chipset.
- Intermediate results are now saved in MAT-file format (.mat), readable from
  Matlab/Octave and from Python via h5py.
- Added the GPX output format.
- Improvements in the generation of KML files.
- Improvements in the NMEA output. The receiver can produce GPGGA, GPRMC, GPGSA,
  GPGSV, GAGSA and GAGSV sentences.
- Improvements in the RTCM server stability.
- Improvements in the correctness of generated RINEX files.
- The receiver can read and make use of Galileo almanac XML files published by
  the European GNSS Service Centre at
  https://www.gsc-europa.eu/system-status/almanac-data
- Own-defined XML schemas for navigation data published at
  https://github.com/gnss-sdr/gnss-sdr/tree/next/docs/xml-schemas
- Added program rinex2assist to convert RINEX navigation files into XML files
  usable for Assisted GNSS. Only available building from source. See
  https://github.com/gnss-sdr/gnss-sdr/tree/next/src/utils/rinex2assist

### Improvements in Maintainability:

- Setup of a Continuous Integration system that checks building and runs QA code
  in a wide range of GNU/Linux distributions (Arch Linux, CentOS, Debian,
  Fedora, OpenSUSE, Ubuntu) and releases. See
  https://gitlab.com/gnss-sdr/gnss-sdr
- Creation of multi-system processing blocks, drastically reducing code
  duplication and maintainability time.
- Automated code formatting with clang-format. This tool is widely available and
  easy to integrate into many code editors, and it also can be used from the
  command line. It cuts time spent on adhering to the project's code formatting
  style.
- Improvement in C++ usage: C-style casts have been replaced by C++ casts.
  C-style casts are difficult to search for. C++ casts provide compile time
  checking ability and express programmers' intent better, so they are safer and
  clearer.
- Improvement in C++ usage: The override special identifier is now used when
  overriding a virtual function. This helps the compiler to check for type
  changes in the base class, making the detection of errors easier.
- Improvement in C++ usage: A number of unused includes have been removed. Order
  of includes set to: local (in-source) headers, then library headers, then
  system headers. This helps to detect missing includes.
- Improvement in C++ usage: Enhanced const correctness. Misuses of those
  variables are detected by the compiler.
- Improved code with clang-tidy and generation of a compile_commands.json file
  containing the exact compiler calls for all translation units of the project
  in machine-readable form if clang-tidy is detected.
- Applied some style rules to CMake scripts.
- Minimal versions of dependencies identified and detected.

### Improvements in Portability:

- Several CMake scripts improvements, more verbose outputs in case of errors.
  Building configuration has been documented in
  https://gnss-sdr.org/docs/tutorials/configuration-options-building-time/
- Improved SDK for cross-compilation in embedded devices. Documented in
  https://gnss-sdr.org/docs/tutorials/cross-compiling/
- Improved control over minimum required versions for core dependencies.
- The software builds with C++11, C++14 and C++17 standards.
- The software can now be built using GCC >= 4.7.2 or LLVM/Clang >= 3.4.0
  compilers on GNU/Linux, and with Clang/AppleClang on macOS.
- The Ninja build system can be used in replacement of make.
- The volk_gnsssdr library can be built using Python 2.7+ or Python 3.6+.
- The volk_gnsssdr library is now ready for AArch64 NEON instructions.
- Improved detection of required and optional dependencies in many GNU/Linux
  distributions and processor architectures.
- Improvement in C++ usage: The <ctime> library has been replaced by the more
  modern and portable <chrono> (except for the interaction with RTKLIB).
- Improvement in C++ usage: The <stdio.h> library has been replaced by the more
  modern and portable <fstream> for file handling.
- Improvement in C++ usage: C++ libraries preferred over C libraries (e.g.,
  <cctype> instead of <ctype.h>, <cmath> instead of <math.h>).
- Fix compatibility with Boost 1.67 (closes Debian bug #911882
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=911882)
- Fixes required by Debian packaging.
- Fixes required by Macports packaging.
- A downside in portability: BLAS and LAPACK libraries are now required even in
  ARM devices.
- A downside in portability: the matio library >= 1.5.3 is a new required
  dependency. If not found, it is downloaded and built automatically at building
  time, but this requires libtool, automake and hdf5 already installed in the
  system.
- A downside in portability: the PugiXML library is a new required dependency.
  If not found, it is downloaded and built automatically at building time.

### Improvements in Reliability:

- Introduced 3 new Input Filter implementations for pulsed and narrowband
  interference mitigation: `Pulse_Blanking_Filter`, `Notch_Filter` and
  `Notch_Filter_Lite`. Documented in
  https://gnss-sdr.org/docs/sp-blocks/input-filter/
- Improved flow graph stability.
- Introduction of high-integrity C++ practices into the source code and included
  in the coding style guide. See https://gnss-sdr.org/coding-style/
- Fixed a number of defects detected by Coverity Scan.
- Improvement of QA code and addition of a number of new tests. Documented at
  https://gnss-sdr.org/docs/tutorials/testing-software-receiver-2/
- Improvement in C++ usage: rand() function replaced by <random> library.
- Improvement in C++ usage: strlen and strncpy have been replaced by safer C++
  counterparts.
- Improvement in C++ usage: Some destructors have been fixed, avoiding
  segmentation faults when exiting the program.
- Website switched from http to https. Links in the source tree switched when
  available.

### Improvements in Reproducibility:

- Setup of a Continuous Reproducibility system at GitLab for the automatic
  reproduction of experiments. The concept was introduced in
  https://ieeexplore.ieee.org/document/8331069/ Example added in the
  src/utils/reproducibility/ieee-access18/ folder.
- Fixes of Lintian warnings related to build reproducibility.

### Improvements in Scalability:

- Improvements in multi-system, multi-band receiver configurations. The receiver
  now accepts any number of channels and systems in the three available bands.
- All possible combinations of signals and integration times are now accepted by
  the Observables block.

### Improvements in Testability:

- Several Unit Tests added. Documentation of testing concepts and available
  tests at https://gnss-sdr.org/docs/tutorials/testing-software-receiver/
- New extra unit test AcquisitionPerformanceTest checks the performance of
  Acquisition blocks.
- New extra unit test TrackingPullInTest checks acquisition to tracking
  transition.
- New extra unit test HybridObservablesTest checks the generation of
  observables.
- Improved system testing: position_test accepts a wide list of parameters and
  can be used with external files.
- Receiver channels can now be fixed to a given satellite.
- Testing integrated in a Continuous Reproducibility system (see above).
- Improved CTest support in volk_gnsssdr.

### Improvements in Usability:

- All Observables block implementations have been merged into a single
  implementation for all kinds of GNSS signals, making it easier to configure.
- All PVT block implementations have been merged into a single implementation
  for all kinds of GNSS signals, making it easier to configure.
- Misleading parameter name GNSS-SDR.internal_fs_hz has been replaced by
  GNSS-SDR.internal_fs_sps. The old parameter name is still read. If found, a
  warning is provided to the user. The old name will be removed in future
  releases.
- Updated and improved online documentation of processing blocks at
  https://gnss-sdr.org/docs/sp-blocks/
- Improved documentation of required dependency packages in several GNU/Linux
  distributions.
- Dump and output files can now be stored anywhere.
- Parameter names with the same role have been harmonized within different block
  implementations.
- Added a changelog, a code of conduct, a contributing guide and a pull-request
  template in the source tree.
- Added colors to the commandline user interface.
- Updated manfiles.
- Updated examples of configuration files under the conf/ folder.

See the definitions of concepts and metrics at
https://gnss-sdr.org/design-forces/

&nbsp;

## [GNSS-SDR v0.0.9](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.9)

DOI: https://doi.org/10.5281/zenodo.291371

This release has several improvements, addition of new features and bug fixes in
many dimensions:

### Improvements in Accuracy:

- Major rewriting in the generation of pseudoranges.
- Fixed bug in Galileo E5a/I codes.
- Fixed bug in Galileo E1 correlator spacing.
- Fixed bug that was causing errors in receivers above the troposphere.
- Fixed 16-bit complex resampler.
- Improved time tracking algorithm.
- Added Bancroft's algorithm implementation for PVT initialization.

### Improvements in Availability:

- Improved numerical stability of the PVT solution. The infamous bug that was
  causing apparently random error peaks has finally been fixed.

### Improvements in Efficiency:

- VOLK_GNSSSDR: Added NEON,AVX and unaligned protokernels for
  volk_gnsssdr_32f_index_max_32 kernel.
- VOLK_GNSSSDR: Added volk_gnsssdr-config-info to the list of generated
  executables.

### Improvements in Flexibility:

- Added maximum number of dwells in the Tong algorithm.

### Improvements in Interoperability:

- Added six new Galileo satellites: FM7, FM10, FM11, FM12, FM13, FM14.
- The Hybrid_Observables and Hybrid_PVT implementations can now handle more
  types of GNSS signals.
- The RINEX printer can now print L2C and E5a observables and navigation files,
  including multiband configurations.
- Added RTCM 3.2 output to more receiver configurations.

### Improvements in Maintainability:

- The VOLK_GNSSSDR library can now be built with Python 3. Switched dependencies
  for VOLK_GNSSDR: from (old, python2.7-only) python-cheetah templates to
  Python3 friendly python-mako and python-six. So, Python-cheetah dependency has
  been dropped, and python-mako and python-six have been added.
- If suitable versions of gflags, glog, armadillo or googletest are not found in
  the system, they will be downloaded and built at compile time (versions 2.2.0,
  0.3.4, 7.600.2 and 1.8.0, respectively).
- Fixed more than 30 defects detected by Coverity Scan.
- Added CMake Python finder and module checker.
- Deleted files related to CPack.
- Fixes, updates and improvements in the documentation.
- Improvements in CMake scripts: General code cleaning and addition of comments.
  Improved user information in case of failure. Improved detection of
  dependencies in more processor architectures (e.g. aarch64).

### Improvements in Marketability:

- Reduced time from a commit to deployment (see virtualization mechanisms in
  Portability).

### Improvements in Portability:

- Now GNSS-SDR can be run in virtual environments through snap packages (see
  https://github.com/carlesfernandez/snapcraft-sandbox) and docker images (see
  https://github.com/carlesfernandez/docker-gnsssdr).
- Now GNSS-SDR is adapted to cross-compiling environments for embedded devices
  (see https://github.com/carlesfernandez/oe-gnss-sdr-manifest).
- BLAS and LAPACK libraries are no longer mandatory on ARM devices.

### Improvements in Scalability:

- Fixed bug in acquisition with rata rates higher than 16 Msps in 4ms code
  periods.

### Improvements in Testability:

- Major QA source code refactoring: they has been split into
  src/tests/unit-tests and src/tests/system-tests folders. They are optionally
  built with the ENABLE_UNIT_TESTING=ON (unit testing QA code),
  ENABLE_UNIT_TESTING_EXTRA=ON (unit tests that require extra files downloaded
  at configure time), ENABLE_SYSTEM_TESTING=ON (system tests, such as
  measurement of Time-To-First-Fix) and ENABLE_SYSTEM_TESTING_EXTRA=ON (extra
  system test requiring external tools, automatically downloaded and built at
  building time) configuration flags. The EXTRA options also download and build
  a custom software-defined signal generator and version 2.9 of GPSTk, if not
  already found on the system. Download and local link of version 2.9 can be
  forced by ENABLE_OWN_GPSTK=ON building configuration flag. Only
  ENABLE_UNIT_TESTING is set to ON by default.
- Unit tests added: CPU_multicorrelator_test and GPU_multicorrelator_test
  measure computer performance in multicorrelator setups.
- Unit tests added: GpsL1CADllPllTracking and GpsL1CATelemetryDecoderTest.
- System test added: ttff_gps_l1 performs a set of cold / assisted runs of the
  software receiver and computes statistics about the obtained Time To First
  Fix.
- System test added: obs_gps_l1_system_test uses an external software-defined
  signal generator to produce raw digital GNSS signal from a RINEX navigation
  file and a position (static or dynamic), processes it with GNSS-SDR, and then
  compares the RINEX observation file produced by the software receiver to that
  produced by the signal generator.
- Software Development Kit provided for embedded devices (see
  https://gnss-sdr.org/docs/tutorials/cross-compiling/).

### Improvements in Usability:

- Now the block factory automatically detects Channel input data type, so it is
  no longer required to specify Channel.input_type in the configuration. An
  error raises if Acquisition and Tracking Blocks are not configured with the
  same input data type.
- Block names changed from L2_M to L2C.
- Documentation available at https://gnss-sdr.org/docs/
- Improved tools for compilation, execution and testing in embedded devices.

See the definitions of concepts and metrics at
https://gnss-sdr.org/design-forces/

&nbsp;

## [GNSS-SDR v0.0.8](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.8)

DOI: https://doi.org/10.5281/zenodo.57022

This is a maintenance and bug fix release with no relevant new features with
respect to v0.0.7. The main changes are:

- Fixed a bug that broke building when using latest VOLK release
- Updated PYBOMBS instructions
- Added Tests for FFT length
- Added Tests for CUDA-based tracking
- Added Tests for SIMD-based tracking
- Improved CUDA-based correlation.
- Updated documentation
- Fixed building in mips and powerpc architectures.
- gr-gn3s and gr-dbfcttc moved to its own repository.
- Improved package reproducibility
- VOLK_GNSSSDR: Fixed a bug in AVX2 puppet
- VOLK_GNSSSDR: can now be built using the C98 standard
- VOLK_GNSSSDR: Fixed a bug that broke building when linking to Boost in some
  configurations.
- VOLK_GNSSSDR: Added an option to trigger profiling at building time.
- VOLK_GNSSSDR: Fix the CMake-based check for posix_memalign.

&nbsp;

## [GNSS-SDR v0.0.7](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.7)

DOI: https://doi.org/10.5281/zenodo.51521

This release has several improvements, addition of new features and bug fixes:

- Improvements in receiver design: Internal block communication has been
  redesigned to accommodate the addition of new signals, and now upstream and
  downstream communication within blocks is implemented through the GNU Radio
  block’s asynchronous message passing system, leading to a more scalable, more
  robust and cleaner design.
- Improvements in receiver design: Correlators have been rewritten to take full
  advantage of VOLK and VOLK_GNSSSDR, and they are of general use for any
  tracking block. Their API now admit an arbitrary number of correlators, spaced
  in an arbitrary manner, in 16ic and 32fc versions.
- Improvements in receiver design: Block adapters are now all managed by smart
  pointers, ensuring better memory management.
- Improvements in processing speed: The VOLK_GNSSSDR library has been rewritten,
  following current VOLK standards and adding a number of new kernels. This
  approach addresses both efficiency and portability. Now the library provides
  the key kernels for GNSS signal processing in 16ic and 32fc versions,
  including SSE2, SSE3, SSE4.1, AVX, AV2 and NEON implementations. Please
  execute volk_gnsssdr_profile and volk_profile to use the fastest
  implementation for your host machine.
- New source block: Two_Bit_Packed_File_Signal_Source. This block takes 2 bit
  samples that have been packed into bytes or shorts as input and generates a
  byte for each sample.
- Fixes in SUPL assistance (supl.nokia.com removed).
- Improvements in acquisition: Added a non CFAR PCPS acquisition algorithm based
  on the estimation of the post correlation noise floor. If enabled as an option
  in the acquisition configuration, it allows setting more stable thresholds in
  the presence of non-gaussian front-end noise (which is the usual behavior of
  front-ends.)
- Fixes in acquisition: Fixed mismatch between the config files and the
  acquisition code in the specification of the IF. Fixed a bug in the length of
  the FFT of local codes.
- Improvements in tracking sensitivity: Added configuration option to customize
  the extension of the GPS L1 CA correlation length after bit synchronization
  (options are: [1,2,4,5,10,20] ms). Only available in the
  GPS_L1_CA_DLL_PLL_C_Aid_Tracking implementation.
- New tracking block introduced: GPS_L1_CA_DLL_PLL_C_Aid_Tracking is a GPS L1
  C/A carrier PLL and code DLL with optional carrier-aid feedback. It is
  available in both 32 bits gr_complex input samples and in 16 bits short int
  complex samples. The gr_complex version has also the capability to extend the
  coherent correlation period from 1ms to 20ms using telemetry symbol
  synchronization.
- Increased resolution in CN0 estimator internal variables.
- Fixed a bug in computation of GPS L1 C/A carrier phase observable.
- Fixed a bug in the internal state machine that was blocking the receiver after
  a few hours of usage. Now the receiver can work continually (tested for more
  than one week, no known limit).
- New tracking block introduced: GPS_L1_CA_DLL_PLL_Tracking_GPU is a GPS L1 C/A
  carrier PLL and code DLL that uses the CUDA-compatible GPU to compute carrier
  wipe off and correlation operations, alleviating the CPU load.
- Obsolete/buggy blocks removed: GPS_L1_CA_DLL_FLL_PLL_Tracking,
  GPS_L1_CA_DLL_PLL_Optim_Tracking.
- Added a RTCM printer and TCP server in PVT blocks (still experimental). The
  receiver is now able to stream data in real time, serving RTCM 3.2 messages to
  multiple clients. For instance, it can act as a Ntrip Source feeding a Ntrip
  Server, or to be used as data input in RTKLIB, obtaining Precise Point
  Positioning fixes in real-time. The TCP port, Station ID, and rate of
  MT1019/MT1045 and MSM can be configured. GPS_L1_CA_PVT serves MT1019 (GPS
  Ephemeris) and MSM7 (MT1077, full GPS pseudoranges, phase ranges, phase range
  rates and CNR - high resolution) messages, while GALILEO_E1_PVT serves MT1045
  (Galileo ephemeris) and MSM7 (MT1097, full Galileo pseudoranges, phase ranges,
  phase range rates and CNR - high resolution).
- Added a GeoJSON printer. Basic (least-squares) position fixes can be now also
  stored in this format, in addition to KML.
- Obsolete block removed: output filter.
- QA code migrated to the new asynchronous message passing system.
- Improvements in documentation: update of README.md file, addition of
  documentation for the VOLK_GNSSSDR library, updated links to new ICDs.
- Improvements in documentation: Satellite identification updated to current
  constellation status.
- Updated and cleaner console output. Now Galileo satellites have the ‘E’
  identifier in their PRN number.
- Several improvements in CMake scripts allow to build GNSS-SDR in Linux Debian
  (Jessie, Stretch and Sid), Ubuntu (from 12.04 to 16.04), including amd64,
  i386, armhf and arm64 architectures, and possibly in other GNU/Linux
  distributions, as well as in Mac OS X 10.9 to 10.11. It also works well with
  CMake 3.5 (some problems solved with VOLK_GNSSSDR as a sub-project).
- The software can link either against OpenSSL or against GnuTLS with openssl
  extensions, whatever it is available. This allows buildings in distributions
  such as Fedora or ArchLinux, while being compatible with binary distribution
  through Debian packages.
- Fixed a number of defects detected by Coverity Scan.
- Some fixes required by Debian licensing and packaging system.
- Added a CGRAN (https://www.cgran.org/) manifest
- Lots of code cleaning and fixes of typos and small bugs.

&nbsp;

## [GNSS-SDR v0.0.6](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.6)

This release has several improvements and bug fixes:

- Added initial support to multi-band, multi-source configurations (multiple
  signal sources and signal conditioners).
- Updated configuration files to new notation. Old and new configuration
  notations still compatible.
- Added skeleton for mixed (multi-frequency and multi-system) observables block.
- Faster local carrier update (25% of improvement).
- Added initial support to GPS L2C real time tracking and decoding of CNAV
  message with NSL STEREO v2, Fraunhofer’s Flexiband, and USRPx front-ends (the
  latter requiring external clock).
- Added initial support to select the frontend clock reference source in UHD
  signal source (i.e. internal or external clock reference).
- Added 2 bits complex file source for GNSS-SDR GSoC 2015 signal sampler
  designed by Ajith Peter.
- Added a new rtl_tcp signal source, remote access to RTL2832U-based dongles via
  TCP.
- Always build front-end-cal, a calibration tool for some DVB-T receivers based
  on the Realtek's RTL2832U chipset.
- Fixed bug in UTC time computation for GPS signals.
- Updated satellite identification for GPS and Galileo.
- Defined ‘cbyte’ as a new input data type (std::complex<unsigned char>)
- Adding a new data_type_adapter, from interleaved short to std::complex<short>
- Adding a filter for complex short streams.
- Adding a fir_filter for std::complex<signed char> (aka cbyte). It converts the
  data type to floats, filters, and converts back to cbyte.
- Added a resampler for cbytes and cshorts.
- First working version of a GPS tracking block implementation using CUDA with
  multi-GPU device support.
- Updating RINEX obs header when leap second is available.
- Updating RINEX nav file when IONO and UTC data are available.
- Include Signal Strength Indicator in RINEX observable files.
- Tests fixed.
- Fixed more than 200 code defects detected by Coverity Scan.
- Updated documentation.
- Updated documentation and CMake scripts for the GN3S v2 driver (Linux-only)
- Armadillo version automatically downloaded and built if it is not present in
  the system is now 5.400.3.
- Updated old links from googlecode to new links at GitHub for Google Test,
  gflags, glog and gperftools.
- gfortran is no longer a required package, but it is used if available.
- Added an option to remove logging.
- Enabled cross-compilation for ARM devices.
- Lots of code cleaning.

&nbsp;

## [GNSS-SDR v0.0.5](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.5)

This release has several improvements and bug fixes:

- Now GNSS-SDR can be installed on the system with the usual ‘cmake ../ && make
  && sudo make install’.
- Added volk_gnsssdr library, a volk-like library implementing some specific
  kernels and ensuring portable executables. It comes with a
  ‘volk_gnsssdr_profile’ executable, in the fashion of volk_profile. Volk and
  volk_gnsssdr are compatible and can be mixed together. This is expected to
  enable faster execution of the software receiver in upcoming versions.
- The former ‘rtlsdr_signal_source’ has been replaced by a more general
  ‘osmosdr_signal_source’ compatible with all those front-ends accessible by the
  OsmoSDR driver (bladeRF, hackRF, etc.) in addition to RTL-based dongles.
- Added manpages when binaries gnss-sdr, volk_gnsssdr_profile and front-end-cal
  are installed.
- Now GNSS-SDR can be built on i386, amd64, armhf, armel and arm64
  architectures.
- Now GNSS-SDR builds on Ubuntu 14.04 and 14.10, Debian jessie/sid and Mac OS X
  10.9 and 10.10.
- Improved detection of dependencies, specially when installed as .deb packages.
- Added a ‘check' target with some minimal tests.
- Added support for interleaved I/Q byte-size sample files.
- Minor bug fixes, updated documentation and code cleaning.

&nbsp;

## [GNSS-SDR v0.0.4](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.4)

This release has several improvements and bug fixes:

- Added hybrid processing GPS L1 C/A and Galileo E1B, providing position fixes
  make use of observables for both constellations.
- Added implementations of the QuickSync algorithm for GPS L1 C/A and Galileo E1
  acquisition.
- Added processing blocks for Galileo E5a: Acquisition, Tracking,
  Telemetry_Decoder (experimental)
- New configuration files allow to configure GPS and Galileo channels in the
  same receiver.
- Added tropospheric corrections to GPS and Galileo PVT solution.
- Improved precision obtained by changing some variables from float to double.
- New building options: ENABLE_GN3S, ENABLE_RTLSDR and ENABLE_ARRAY and
  ENABLE_OPENCL.
- Improved documentation on how to enable optional drivers.
- Fixed bug in memory alignment that caused problems with high data rates.
- Added ENABLE_GENERIC_ARCH, an option to build the binary without detecting the
  SIMD instruction set present in the compiling machine, so it can be executed
  in other machines without those specific sets.
- Added ENABLE_GPERFTOOLS, which links the executable to tcmalloc and profiler
  if Gperftools is available on the system.
- Added carrier phase, Doppler shift and signal strength observables to the
  RINEX files. Static PPP solutions are available for GPS with RTKLIB via RINEX
  files.
- The executable now produces RINEX files version 3.02 of Galileo Observables,
  Navigation data, and mixed (GPS/Galileo) observables and nav data. RINEX 3.02
  is the default version of RINEX files.
- Armadillo version updated to 4.400.2
- Armadillo now uses OpenBLAS instead of BLAS if the former is available on the
  system.
- Some raw pointers have been changed to smart pointers.
- Minor bug fixes and code cleaning.

&nbsp;

## [GNSS-SDR v0.0.3](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.3)

This release has several improvements and bug fixes, completing the transition
from Subversion to Git. The main changes are:

- Created some missing directories lost in the SVN to Git transition.
- New C++11-ized block factory, flow graph and tests, resulting in better memory
  management and fewer segmentation faults. Several raw pointers converted to
  smart pointers.
- Reorganization of assistance data input and output.
- Fixed memory leak when talking to SUPL servers.
- Improved retrieval of assistance data.
- Fixing an error in a constant value related to Galileo.
- Inform users if the temporal folder is not /tmp.
- Fixes and additions to the documentation.
- README in markdown language so it looks better in Git repositories.
- Fixed a bug that prevented the update of all shared map structures (ephemeris,
  iono parameters, etc…).
- The configuration script now throws error if GCC is older than 4.7 or Boost is
  older than 1.45
- Improved detection / downloading & building if missing of Gflags and Glog.
- Improved detection / downloading & building if missing of Armadillo and
  related dependencies.
- Fixes many warnings that appeared when using CMake 3.0.
- Improved detection of GTEST_DIR variable.
- Include header files in libraries so IDEs such as Xcode can display them.

Enjoy it!