Paging Frame and Paging Occasion
- The paging cycle defines the interval between consecutive paging occasions, and it can range from 16 to 2560 radio frames, with the default value being 256 radio frames (i.e., 5.12 seconds). The value of the paging cycle is chosen based on the trade-off between the paging latency and the paging overhead. Commonly used value for Paging cycles is 128. It means 128 radio frames. (128 radio frames=1280 msec=1.28 seconds)
- It means UE will wake up after every 1.28 seconds even in Idle Mode to see if there is Paging information for the UE or not.
Paging Frame and Paging Occasion
In LTE networks, paging frames and paging occasions are used to optimize the paging procedure and reduce the impact on network resources.
A paging frame is a radio frame in which the UE (User Equipment) monitors the paging channel (PCH) for paging messages. The paging frame is specified in the System Information Block Type 2 (SIB2) and is typically set to a value that aligns with the radio frame boundary of the UE’s cell.
A paging occasion is a specific subframe within a paging frame in which the network searches for an idle UE to deliver data to. Instead, it wakes up in a specific subframe either subframe 0, 4, 5 or 9 within a radio frame. These specific subframes within a Paging Frame when UE wakes up are called as Pagi.ng Occasions (POs).
The paging occasion is determined by the combination of the paging cycle and the radio frame number (RFN) of the cell. The paging occasion is used to minimize the signaling overhead by limiting the number of subframes that the network searches for idle UEs.
The paging cycle determines the interval between consecutive paging occasions, as I explained in my previous answer. The RFN of the cell is a counter that increments with every radio frame, and it is used to determine the subframes that correspond to the paging occasion.
picture reference – http://www.techtrained.com
The paging occasion is calculated using the following formula:
SFN mod T = (T/N) x (UE_ID mod N)
Where,
T = DRX cycle length in radio frames
N = Min(T,nB)
nB is broadcast within SIB2 and can have values of {4T,2T,T,T/2,T/4,T/8,T/16,T/32} N can have values of {T,T/2,T/4,T/8,T/16,T/32}
UE_ID = IMSI mod 1024
The formula to compute paging occasion is extracted from a look-up table which is indexed using:
Ns = Max (1, nB/T )
i_s = Floor(UE_ID / N) mod Ns
