I'm starting up on another R&D project using GnuRadio.
The project is a transponder, used by NASA for ranging. It uses DSSS on both the uplink and the downlink. The transponder has to be coherent, and it synchronizes the PN epochs of the received uplink and the transmitted downlink. This allows the groundstation to compute the round-trip time, (and hence the range), by comparing the offset of the received epoch to that of the one originally transmitted to the transponder. My plan is to use stream tags to accomplish the synchronization. This will require getting a time tag for each received sample, identifying the time of the first sample associated with the epoch of the received uplink, and using that time to start the transmission of the first sample of the downlink epoch a small integer number of epochs later (to allow for GnuRadio latency). I have not yet used stream tags, and have a number of questions: 1. Is it possible to get timetags for every sample? My readings on time tags seemed to imply that only one is created at the beginning of a stream. 2. What is the accuracy/precision of the time tags? Jitter is going to be the make-or-break factor on this project. 3. It looks like the Start-Of-Burst (SOB) tag is the only way to control the time of transmission. Is there any limitation on the length of a burst? In my case, I would want to start the transmitter in response to receiving the uplink, and not stop it until the uplink ceases, about 4 minutes later. 4. Is there any good tutorial or example information on the use of stream tags? (I'm using GR 3.6.1) 5. Does all this sound like I'm headed in the right direction, or is there something fundamental that I'm missing? Thanks in advance for any help! @(^.^)@ Ed _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
