Paging is indication to
UE to establish NAS Procedure basically happens at two occasions
1)
Incoming Call Alert: Means Mobile Terminated
Call.
2)
Broadcast Change : EUTRAN notifies the UEs by means of a Paging message
including a SystemInfoModification flag
Paging message will be
associated with PF and PO at RE  Grid Level.
Where PF is associated
with Corresponding SystemFrame and PO is associated with SubFrame where Paging
Message is Broadcasted.
Then how to Caliculate
Paging Frame and Paging Occasion for particular UE:
In caliculation the below
factors plays role
· SFN – System Frame Number
· DefaultPagingCycle is
from SIB2
· PagingDrx Cycle from
S1Paging Message
· Ue Id : Received from
S1Paging Message
· nB : From
SIB2
Now Let us Take Example
to caliculate Paging Occasion :
In
SIB2:
nB  T /
4
DefaultPagingCycle : 64
From S1Paging Message:
PagingDRX
: 128
UeIndex from S1 Paging
: UE_ID = 0x0115 = (0000 0001
0001 0101 ) after Removing 6 LSBs which makes (0000 0001 00 =
4)
The above
UeIndex is in general UeIdentity % 1024 which means, results only occupies 10
Bits Only. So, above we Removed 6 LSbits.
T = Min (PagingDRXCycle,
DefaultPagingDrxCycle) = Min ( 128,64) = 64
nB = T/4 = 64/4 =
16
N = min(T,nB) = Min(64,
16) = 16
UE_ID = 4 (From above
Steps derived from S1 Paging Message)
SFN mod T= (T div
N)*(UE_ID mod N)
RHS => (T Div N) *
(UE_ID mod N) = ( 64 Div 16) * ( 4 % 16) = 4 * 4 = 16
LHS => SFN Mod T = SFN
Mod 64 = 16
So,
PF values could be any
thing where SFN = (64 * i ) + 16 (I = 0 to N But SFN <=
1024)
i.e Values PF can be any
of 80, 144, 208, 272, 336, 400, 464, 528, 592, 656, 720, 784, 848, 912, 976,
1040, 1104, 1168.
Now Comes To Paging
Ocassion:
Ns: max(1,nB/T) = max (1,
16/64) = 1
i_s
= floor(UE_ID/N) mod Ns
ð i_s
= floot(4 / 16) mod 1 = 0
From
the below table when i_s == 0 and Ns = 1 => P0 = 9
FDD:
Ns

PO
when i_s=0

PO
when i_s=1

PO
when i_s=2

PO
when i_s=3

1

9

N/A

N/A

N/A

2

4

9

N/A

N/A

4

0

4

5

9

So
considering current SFN is 100 : for the above UE PF which is mentioned in the
series is 144. i.e Paging message can go in SF=144 and SFN=9
Ref
: 3GPP 36.304 UE Procedures in Idle Mode. Section 7.1 and
7.2