Software GNSS receiver
A GNSS receiver is an electronic device that receives and digitally processes the signals from a GNSS 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.
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 exists 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).
- Real-Time Software Receivers, GPS World, September 1, 2009 by Pierre-André Farine, Marcel Baracchi-Frei, Grégoire Waelchli, Cyril Botteron
- Software GPS has many advantages
- Springer Press A Software-Defined GPS and Galileo Receiver. Borre, K., Akos, D.M., Bertelsen, N., Rinder, P., Jensen, S.H.
- GNSS-SDR An open source GNSS software receiver.
- A starting point for learning about GPS with Open Source Software
- NAMURU Software Defined GNSS Receiver