search

osqzss / gps-sdr-sim

Software-Defined GPS Signal Simulator
MIT License
2.61k stars 761 forks source link

Running GPS-SDR-SIM without adding noise #337

Closed fener1efes2 closed 1 year ago

fener1efes2 commented 1 year ago

GPS-SDR-SIM adds noise in band purposefully. I want to observe its BPSK signal. How can I turn off adding noise property?

image

osqzss commented 1 year ago

gps-sdr-sim generates pure baseband signals. No noise is added.

fener1efes2 commented 1 year ago

gps-sdr-sim generates pure baseband signals. No noise is added.

I shared output of the HackRF transmitting signal produced by the GPS-SDR-SIM. As you can see, the waveform is not as it is expected. I would expect a waveform as shown below. Therefore, I supposed that GPS-SDR-SIM adds noise deliberately. But since you said that it is not, then why do I view the waveform as it is shown above?

image

osqzss commented 1 year ago

Yes, that's exactly what you can expect to see. It seems that the HackRF did not transmit the baseband samples properly. You have to set the I/Q sample format to 8-bit with -b option for the HackRF.

aeaotst commented 1 year ago

I get similar results using the USRP B200 mini-i regardless of whether I use 16-bit or 8-bit. My receiver is reading the signal and getting a fix so perhaps not an issue, though I have to wonder if there's any implication for C/N.

osqzss commented 1 year ago

Here's a sample PSD plot of the L1 C/A signal with a 2.6MHz sampling rate and a 2.5MHz double-side bandwidth. You can see the main lobe on center and partial side lobes on both ends.

PXL_20210104_032442100

fener1efes2 commented 1 year ago

Here's a sample PSD plot of the L1 C/A signal with a 2.6MHz sampling rate and a 2.5MHz double-side bandwidth. You can see the main lobe on center and partial side lobes on both ends.

PXL_20210104_032442100 @osqzss Is the bandwidth of the signal 3.6MHz? If I see the span correctly which is 6MHz, then the BW must be 3.6MHz?

Imtiaz08 commented 1 year ago

I think the transmitter and the receiver component added noise can't be neglected. Have you checked probing the signal in the software without transmitting it?

IvanKor commented 1 year ago

I think ...

GPS uses pseudo-noise 1023-bit technology.

By connecting the output RF of the HackRF transmitter Real-time GPS signal simulator based on GPS-SDR-SIM via an attenuator to the NEO-M8T antenna input for 1.5 hours and turning on all corrections Solution: SINGLE RTKLIB make sure that during this time the total error (RMS) ~ 0.1 meters.

If use USRP B200 (16-bit) instead of HackRF (8-bit), then instead of RMS~0.1m get RMS<0.01m

If your simulator has RMS>0.1m (1m or more) then this simulator is not correct.