Hello !
I am using USRP2953R to get LTE signal from commercial base station with LabVIEW LTE framework. Now I have a problem of acquiring GPS time stamp at USRP side, and wonder if anyone can help to solve it.
Here is a brief description about my plan, and please let me know if it is not clear.
I try to put a USRP2953R with LabVIEW into a car and drive it around, so that I can receive commercial base station signal from the USRP and export it into the laptop via DMA and PCI card . Based on this signal, I hope to get the multipath information, and use SLAM (Simultaneous Location and Mapping) algorithm to find the position of base station/ reflectors and estimate the vehicle trajectory. On the other hand, we also plan to put a High Definition GPS RTK into the car, and record the trajectory of vehicle in centimeter level accuracy, and use it as ground truth to compare with our estimation of vehicle trajectory based on LTE signal.
I need to align the data logged from USRP to the data recorded by GPS RTK. I think there are two ways to solve this problem.
One way is to insert the GPS time stamp periodically to the data stream. My think is that the USRP 2953R has an internal GPS, and maybe I can get this GPS’s time stamp at the FPGA side, and insert it to the data stream I logged periodically, but I don’t know how to implement it, and didn’t find any useful information from online/community.
On the other way, I found a module called niUSRP get time, but this model is at Host side. By using this module, I can get the timestamp of current FPGA time, but the data I get from DMA doesn’t align with that time, and I think the data is lagged behind that FPGA time because DMA needs to take time to transfer the FPGA data to the host, and I don’t know the exact time or approximate time of this delay. I think by this way, I call this module only once at the beginning of each time I start to log the data, thus save lots of overhead, since we know the relative time between logged data samples if we assume the oscillator in FPGA has high accuracy disciplined by GPS.
Does anyone have any ideas on how to utilize this module?
Thanks a lot.
Best regards
Junshi Chen
