Like typical GNSS receivers, the MuSNAT software receiver undergoes signal processing steps such as acquisition, tracking, navigation message decoding, and Position, Velocity, and Time (PVT) computation. It carries out signal processing exclusively through software on a conventional CPU. The receiver can handle IF samples from prerecorded data streams retrieved from a Front-End and real-time sample input for subsequent post-processing.
The software architecture and data flow are depicted in Figure below. As previously mentioned, the software receiver receives digital IF sample data in real-time or retrieved from preexisting data files. Upon receiving IF sample data from an external source, the GNSS signal processing is internally managed by a central entity known as the "Master Receiver." This "Master Receiver" contains multiple units (receivers), each tasked with tracking signals associated with specific GNSS services, for example, GPS L1 C/A.
Each individual "Receiver" unit consists of a "Master Channel" for each SV and various "Channels," each dedicated to tracking a particular GNSS satellite signal. These "Receivers" employ a versatile tracking scheme that can be customized for each unit. Among the "Receiver" units , one notable distinction is their navigation message decoders.
To enhance signal acquisition control, dedicated units have been established. These units are structured as follows:
- An overarching entity referred to as the "Acquisition". Before performing an FFT acquisition, the receiver tries to acquire the signals by computing the signal's code phase and Doppler from the last position fix (so-called vector acquisition). The estimates are treated as input to the tracking loops, which are in charge of improving the estimates to reduce measurement errors. If the accuracy of those measurements is precise enough, the values are used to start tracking.
- Should acquisition remain unattainable through this methodology, the receiver proceeds with the optimized FFT acquisition technique referring to the "FFTAcquisitionLevel*", where * represents the acquisition unit described in Section FFTAcquisitionLevel*.
Continuing with the workflow, the "Navigation Processor" retrieves measurements from the "Master Receiver" and then forwards them to one or more designated "Navigation Modules." These modules execute a spectrum of tasks, including single-point positioning, generating RINEX output, and monitoring signal quality. The user defines the activation or deactivation of particular navigation modules through a configuration (.musnat) file. A more in-depth understanding of the functions and features of this module shall be given in the dedicated section.