Jose, During my talk at the last GNU Radio Conference (September 2022), I was asked by an audience member about how to handle Doppler for spacecraft links so I later developed Transmit/Receive Flowgraphs with Doppler that are located at:
https://github.com/DavidToddMiller/gr-HighDataRate_Modem You can find the flowgraphs that include Doppler in the following folder on the repository site: “examples/Doppler_And_CCSDS_TTC_Flowgraphs_LowRate” When running one of the flowgraphs, you will see the Transmit carrier (PM modulation with a subcarrier) slowly drifting across the Frequency Sink display in the GUI (about 200-300 Hz per second to simulate typical S-band link Doppler in Low Earth Orbit). On the receive end of the flowgraph, a continuous FFT is used to acquire and track the carrier. Generating the Doppler portion of the flowgraph is done with just standard In-Tree GNU Radio blocks. Since the GNU Radio Conference, I have added a lot more to this repository including Doppler and a lot of codes: CCSDS Reed Solomon, CCSDS Convolutional, and CCSDS DVB-S2 to test them at high data rates with CPU multicores. However, the Doppler flowgraphs to which I am pointing you is low data rate. Support for a CCSDS rate ½ LDPC Encoder/Decoder is at my other repository, but it does not include Doppler yet in the flowgraphs (maybe later this year): https://github.com/DavidToddMiller/gr-aff3ct_codes Regards, Dave Miller On Thu, Jul 27, 2023 at 4:19 PM Jose Ruvalcaba wrote: > Hello, > > I am trying to simulate an accurate representation of Doppler Shift in a > channel and I was told that to do this I would have to multiply a complex > signal with a cosine and implement a resampler block to simulate the signal > samples that are coming closer or farther away from each other. > > My question is this, can I use either the rational resampler or fractional > resampler block in GNU Radio to dynamically simulate samples moving closer > or farther than each other? Or would I need to make my own OOT block to do > this? > > I tried using a QT GUI Range block to change the resampling ratio of a > fractional resampler but my flowgraph froze. > > Any suggestions? > > Thanks, > Jose >
