create a SSB tracker that supports kSSB

[catkira]

The current design uses the PSS detector for initial cell search as well as SSB tracking, which is need for continuous CFO/STO estimation. This implies that the SSB is always centered in the ressource grid bandwidth. The 5G NR standard however allows the SSB to have a frequency offset from the center of the ressource grid. This frequency offset is specified inside the MIB (Master Information Block) by the kSSB parameter.

If full 5G NR compliance is required, this feature has to be added. I think the easiest way to achieve this would be to add a separate SSB tracker core which operates in frequency domain. The PSS detector will then only be used for initial cell search. After that the higher layers inform the lower phy about the SSB offset. The lower phy (or higher layers) will then adjust the rx frequency of the AD9361 to the center of the ressource grid.