A software GNSS receiver is a Global Navigation Satellite System (GNSS) receiver that has been designed and implemented using software-defined radio.
A GNSS receiver, in general, is an electronic device that receives and digitally processes the signals from a navigation satellite constellation in order to provide position, velocity and time (of the receiver).
GNSS receivers have been traditionally implemented in hardware: a hardware GNSS receiver is conceived as a dedicated chip that have been designed and built (from the very beginning) with the only purpose of being a GNSS receiver.
In a software GNSS receiver, all digital processing is performed by a general purpose microprocessor. In this approach, a small amount of inexpensive hardware is still needed, known as the frontend, that digitizes the signal from the satellites. The microprocessor can then work on this raw digital stream to implement the GNSS functionality.
Hardware vs. software GNSS receivers
When comparing hardware vs software GNSS receivers, a number of pros and cons can be found for each approach:
Hardware GNSS receivers are in general more efficient from the point of view of both computational load and power consumption since they have been designed in a highly specialized way with the only purpose of implementing the GNSS processing.
Software GNSS receivers allow a huge flexibility: many features of the receiver can be modified just through software. This provides the receiver with adaptive capabilities, depending on the user's needs and working conditions. In addition, the receiver can be easily upgraded via software.
Under some assumptions, Software GNSS receivers can be more profitable for some applications, as long as sufficient computational power is available (and can be shared among multiple applications). For example, the microprocessor of a smartphone can be used to provide GNSS navigation with the only need of including a frontend (instead of a full, more expensive, hardware receiver).
Currently, most of the GNSS receiver market is still hardware. However, there already exist operational solutions based on the software approach able to run on low-cost microprocessors. Software GNSS receivers are expected to increase their market share or even take over in the near future, following the development of the computational capabilities of the microprocessors (Moore's law).
Comparison of GNSS SDR implementations
This comparison is strictly about GNSS SDR; please do not include general GNSS positioning and mapping software.
Galileo Satellite Navigation LTD.- GSN:
Business Model - IP core license + royalties
Development
Programming language: C
User interface - NMEA
Hardware support:
Platforms
PC - windows
PC - Linux
CEVA - XC family
CEVA - TL3/4
Cadence (Tensilica) - BBE16/32
RF FE
MAXIM
NEC
GNSS/SBAS signals support:
GPS: L1/CA,
GLONASS: G1
Galileo: E1,
BeiDou: B1
SBAS
QZSS: L1/CA
Features:
Acquisition: yes
Tracking: yes
Generating pseudo-range observable: yes
Decoding navigation data: yes
Position estimation: yes
Maximum number of real-time channels demonstrated: 16/system
Non real-time (post-processing) GNSS software receiver
Development:
Programming language: MATLAB
User interface (none, CLI, GUI): CLI and GUI
Number of developers: 4 (along the project)
Under active development (as-of date): public version - no, non-public versions - yes (2013-Sep-30)
Hardware support:
Front-ends: SiGe GN3S Sampler v1 (in the original SDR and driver release). Signal records originating from other Sampler versions or other front-ends require configuration changes and in some cases also minor code changes.
Host computer special hardware supported: no
Multicore supported?: no
GNSS/SBAS signals support (separate version for each band of each GNSS):
GPS: L1CA
Features:
Acquisition: yes
Tracking: yes
Generating pseudo-range observable: yes
Generating carrier-phase observable: no
Decoding navigation data: yes
Position estimation: yes
GNSS-SDR, An open source GNSS Software Defined Receiver
General information:
Software licence: GPL v3
Development:
Programming language: C++
User interface (none, CLI, GUI): CLI.
Number of developers: 26 (along the project)
Under active development (as-of date): yes (2021-Jan-08)
Creator/sponsor organization: Centre Tecnològic de Telecomunicacions de Catalunya
Latest release (version and date): 0.0.14 (as Jan 2021)
First release (version and date): 2011-Mar-11 first svn commit
Host computer special hardware supported: SIMD (via VOLK and VOLK_GNSSSDR), CUDA
Multicore supported?: Yes
GNSS/SBAS signals support:
GPS: L1CA, L2C, L5
GLONASS: L1SP, L2SP
Galileo: E1b, E1c, E5a
BeiDou: B1I, B3I
SBAS: EGNOS
Features:
Acquisition: yes (several algorithms)
Tracking: yes (several algorithms)
Generating pseudo-range observable: yes
Generating carrier-phase observable: yes
Decoding navigation data: yes
Position estimation: yes
Maximum number of real-time channels demonstrated: > 100
Output formats: RINEX, KML, GPX, GeoJSON, NMEA, RTCM, intermediate results stored in binary .mat files readable from MATLAB and Octave, and from Python via h5py.
Publication: Software-Defined GNSS is Ready for Launch
Contact: Radionavigation Laboratory, Locus Lock
Development:
Programming language: C++
Platforms: Linux, Windows, MacOS
User interface (none, CLI, GUI): CLI.
Number of developers: 15 (along the project)
Under active development (as-of date): yes (2023-Apr-28)
Creator/sponsor organization: University of Texas at Austin
Latest release (version and date): 2022 annual release
First release (version and date): 2008-Jul-01
Hardware support:
Front-ends: Several and, practically speaking, any.
Host computer special hardware supported: Intel SIMD (SSE2 through AVX-512), ARM NEON (64-bit and 128-bit)
Multicore supported?: Yes
GNSS/SBAS signals support:
GPS: L1CA, L2C, L5
Galileo: E1b, E1c, E5a
QZSS: L1CA
SBAS: WAAS L1
Features:
Acquisition: yes (several algorithms)
Tracking: yes (several algorithms)
Generating pseudo-range observable: yes
Generating carrier-phase observable: yes
Decoding navigation data: yes
Position estimation: yes
Multiple antennas: yes
Real-time Kinematic: yes, GRID can function as an RTK-base station or rover with integrated network support, RTK estimation when integrated with PpEngine (available through separate license)
Differential corrections: yes, CNAV and SBAS
Maximum number of real-time channels: Hardware-dependent, 30 on a Raspberry Pi 1, >100 on most desktop computers.
Current applications: experimental FOTON receiver, several GNSS-RO commercial applications, commercial LEO satellite on-board navigation, RTK-based rocket navigation (launch-to-orbit), RTK-based vehicle navigation in urban environments, RTK-based drone, several fixed reference stations, signal abnormality monitoring
References
Further reading
Borre, K; Akos, D; Bertelsen, N; Rinder, P; Jensen, S H (2007). A software-defined GPS and Galileo receiver: a single-frequency approach. Birkhauser. ISBN 978-0-8176-4390-4.
Pany, Thomas (2010). Navigation Signal Processing for GNSS Software Receivers. Artech House. ISBN 9781608070282.
Petrovski, Ivan; Tsujii, Toshiaki (2012). Digital satellite navigation and geophysics a practical guide with GNSS signal simulator and receiver laboratory. Cambridge University Press. ISBN 9780521760546.
External links
Software GPS has many advantages
A starting point for learning about GPS with Open Source Software Archived 2012-08-30 at the Wayback Machine
Mitigation of ionospheric effects on GNSS positioning