How does gNB know nature of data in UL

Hello dear experts,

Questions or Scheduling Request SR and uplink transmissions in general. I realize this is a MAC concept. The UE sends SR requesting uplink resources. Question what does SR look like at the PHY layer? I know it should be series of 0s and 1s at PHY layer but how is it different than say HARQ acks. When the gnb decodes information how does UE know this is SR versus this is ACK or PUSCH?
Thank you very much

SR has 0 bits and it is not decoded
Any strong signal detected by eNB on the PUCCH resource dedicated for SR is considered as SR and will trigger the transmission of UL grant


Thank you @O.B.
So what does the UE populate the subcarriers of this PUCCH resource? Does the gnb have a threshold detector to detect the SR?
What do you mean by SR being 0 bit?
Thank you for any insights

There is no information sent for SR. For HARQ for example 1 means ACH and 0 means NACK but for SR no bits. And yes, gNB has a threshold which is usually too low to avoid missing SR but can result in false detection

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