[srsran-users] 5G NR "Phase compensation"

[Sylvain Munaut]

Hi Xavier,

Thank you very much for your reply.

> If the phase compensation was not in place, the UE would see a different phase in each OFDM symbol. The phase shift is relative to the difference of center frequencies between the gNb and itself and it would be difficult to detect.

Oh, yeah, I think I see.
And the f0 in that equation would be the center frequency that you
tuned to (i.e. the center of the grid you're decoding / FFT you're
doing ) which doesn't necessarily match the center of the cell or
whatever the gNB used in its RF chain.


> To conclude, as TS38.211 Section 5.4 says, the phase compensation is applied relative to the beginning of the subframe. This makes each of the OFDM symbol phases within a subframe coherent for transmission and reception, independently of the resource grid center frequencies.

Ah yeah, you're not supposed to make any assumption about the phase of
things across subframes anyway right.

Although I'm a bit curious when you say "TS38.211 Section 5.4 says"
because maybe I'm not looking at the right PDF but my copy of section
5.4 is really just one sentence and 3 equations with like no
explanation whatsoever, is there some more detailled spec I'm missing
? :)   Or did you mean "they say" as in "through those equations
they're telling us that" ?

Cheers,

    Sylvain