GRCon23 - Time of flight measurement with sub sampling period resolution using SDR - by JM Friedt

https://github.com/oscimp/amaranth_tw...

The RADAR equation states that the range resolution is inverse of the bandwidth. This generic time of flight assessment resolution under general conditions is greatly improved under the assumption of a single isolated target illuminated by a known noise sequence with a delay resolution improved by the signal to noise ratio brought by the correlation during the pulse compression.

Using pseudo-random sequence spectrum spreading over less than typical Commercial Off The Shelf (COTS) Software Defined Radio (SDR) hardware (2.5 Mchips/s BPSK modulation of a 70 MHz carrier spreading over less than 5 MHz bandwidth), we qualify the fine time delay with a resolution much lower than the sampling period. Each individual channel of dual channel receivers is observed to exhibit time delays randomly distributed within the sampling period despite the external PPS and clock being synchronized in the B210 and X310 SDR receivers, with standard deviations within each continuous acquisition in the sub-ps range. We demonstrate however that the differential delay of the X310 between both channels exhibits a reproducibility from one run to another in the sub-100 ps range whereas the complex ADi AD936x frontend of the B210 introduces fluctuations of the differential delay in the ns range. A basic experimental setup is demonstrated for reproducing the experiment on any SDR RF frontend.