SSB location: Frequency and Time domain

As part of cell search process finding SSB is mandatory as it carriers all important information like PSS, SSS and PBCH along with its reference signals PBCH DMRS.lets see where and how its location can be traced in both time and frequency domain.

Time Domain:

In time domain device gets SSB from number of beams it depends on the operating band.

if the operating band:

<= 3GHz =>> 4 beams possible

< 6GHz ==>> 8 beams possible

>=6 GHz ==>> 64 beams possible

and each beam will carry one SSB. and each SSB will have SSB index and these SSB indexes are always transmitted in 5msec window as below shown below and 2nd important parameter is its SSB periodicity generally in the ranges of 5, 10,20,40,80 and 160msec and most commonly used is 20msec.

lets say 10msec is the periodicity and 4 SSB index will be transmitted and repeated every 10msec.

here the beams shown below are maximum and it is upto network gNB to transmit the number of beams and it cant be 4 all the time. the symbol locations of these SSB beams are fixed and predifined.

for Case 15KHz scs symbol locations are 2,8,16 and 22. i.e if SSB starts at 2nd symbol and as we know SSB takes 4 symbols from there so the its symbols are 2,3,4 and 5.

similarly it starts at symbol 8 again and from there it takes 4 symbols which is 8,9,10 and 11 and goes on.

for case B > 30KHz SCS symbol locations are 4,8,16 and 20…

for case C > 30KHz SCS symbols locations are 2,8,16 and 22…

for case D > 120KHz SCS symbol locations are 4,8,16 and 20…

difference between B and C are depends not the usage of PDCCH, DL/UL switch and Ack/Nack.

Frequency Domain Location:

SSB in frequency domain can be transmitted mainly controlled by 2 parameters.

offset to point A: this is the offset from point A(where lowest prb and lowest subcarrier to the pub where SSB located in actual.

Kssb : this helps to move in terms of subcarriers and note that each prb combinedly called as 12 subcarriers.

i.e Ex: lets take  offsettopointA is 20PRBs and Kssb is 10 subcarriers, so total subcarriers 20*12+10 = 250 subcarriers. each subcarrier is 15KHz

250*15KHz = 3750KHz or 3.75MHz

this is where SSB location in frequency domain.

in FR1 both these parameters taken for 15Khz where as in FR2 case offsettopointA is 60KHz and Kssb as either 60KHz or 120Khz.

ref: 3gpp 38.211