# Does GSCN reflect offsettopointa and KSSB?

GSCN is not only for 5G SA.

Yes for both.

So if UE know SSB based on GSCN why to use offesttopointA?

UE doesn’t know the location of SSB in the channel bandwidth.

It needs to know the exact location in the channel bandwidth.

So this will be known through offsettopointA.

This GSCN should do it right?

As it’s giving the centre of SSB.

Center of SSB.

But still he dont where the SSB located in the channel bandwidth.

Channel bandwidth for example.

N78 100 Mhz.

GSCN if the center freq of ssb which is 20 MHz.

If UE knows the centre it can detect it easily.

No.

There is a big difference between SSB and channel bandwidth.

SSB is just 20 PRBs in frequency and 4 symbols in time.

Oh so offsettopointa to know where carrier start?

Exactly.

Look to the picture and you might figure out what I mean:

Thank you all.

One last question: In which message UE received GSCN?

In no message.

This is mapped on every UE by firmware.

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It blindly detect SSB position,

So GSCN is just theoretical meaning?

GSCN is used when UE is powered ON.

It scans all possible locations to find an SSB.

All possible locations are all possible GSCNs.

If is the center of SSB the GSCN.

For me It was a complicated subject, it takes time with me to understand it → 5G SSB Detailed Explanation (Theory + Practical + Configuration recommendation)

GSCN is a list of frequency points that can be used to transmit synchronisation signals.

Think about as a different unit of measurement

The analogy of Arfcn and GSCN relation could be like centimeters and meters

The steps on every unit is different so for example in FR1 > 3 Ghz, 1 step on GSCN is equal to 96 steps on ARFCN

For NSA, the center of SSB in this range can be on any even ARFCN but to support SA it has to be on GSCN (i.e. possible once every 96 ARFCN). This help SA UE to blindly scan the band faster

GSCN is to get the SSB location that can be anywhere in the band if it is a valid GSCN.

“KSSB + offsetToPointA*12” tells how far your SSB’s starting point is from point A in terms of subcarriers.

If kSSB is zero then your SSB start is align to PRB boundary otherwise not.