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I am conducting research into the accuracy of smartphone positional fixing accuracy. I have come to understand that smartphones use software-defined receivers rather than hardware-defined receivers. Is this correct?

Furthermore, would it be correct to make the following statement:

"Traditionally, GNSS receivers are implemented in hardware in comparison to modern software-defined receivers where processing of the satellite signals are performed by a low-cost microprocessor. The latter, common in smartphone devices, has the added benefit of flexibility with easily modified and updated features."

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What exactly is a software-defined-radio in context of GPS? All receivers include CPUs for navigation message decoding, orbit determination, position fix and so on. The question is, how much of the processing is done in special purpose DSP-hardware and how much in the CPU.

It is quite common to have hardware for baseband processing (several millions of realtime complex multiplications/accumulations per second) but do the control loop filtering (several thousand realtime trigonometric operations per second) in the interrupt routine. Designs with weak microcontrollers (high interrupt latency, no hardware multipliers) may have coprocessor support for the filtering. Bit-boundary-detection, deframing, decoding, etc are low-rate threads without realtime constraints, so thats where software takes over.

Without any insight in a real world smartphone GPS design, I would expect that cellular baseband hardware is reused for GNSS reception. Realtime software processing may just eat up too much battery.

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Traditionally refers back to the late 1980ies when GPS was a military thing and receivers filled a height unit in the radio rack inside the tank.

Everyone uses SDR since about 20 years. That alone made GPS receivers affordable to anyone.

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  • \$\begingroup\$ im still quite confused about what a software defined reciever is. is this something that all modern gnss units use? i am mainly comparing smartphone recievers with recreaitonal grade recievers and the difference between the two \$\endgroup\$ – Tom Haywood Apr 24 at 19:24
  • \$\begingroup\$ Someone else knows it better. Let that person answer. \$\endgroup\$ – Janka Apr 24 at 19:34
  • \$\begingroup\$ Software defined receivers, in short, take in raw radio waves via an antenna, convert them to digital quantities (via an ADC), and then perform filtering/demodulating/etc. via DSP, rather than relying on hardware implementations. \$\endgroup\$ – esilk Apr 24 at 20:38
  • \$\begingroup\$ @Janka I am not the one to downvote you. But yeah, not everything is SDR. \$\endgroup\$ – Andreas Apr 24 at 20:54
  • \$\begingroup\$ It's about where you draw the line. Which kind of input stage is enough to make it none-SDR? – I have a deja-vu. \$\endgroup\$ – Janka Apr 24 at 20:56

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