UEs in idle mode monitor the PDCCH channel for P-RNTI used for paging to receive paging message from eNB. The UE needs to monitor the PDCCH only at certain UE specific paging occasion, i.e. only at specific subframe in specific radio frame. At other times, the UE may go to sleep mode to save battery power. The DRX parameters and the significance of each DRX parameter is discussed in first part of this blog. One of the DRX parameters ‘nB’ is the deciding factor for paging capacity in a cell. Let us discuss different scenarios by considering different values of nB in this blog and understand impact of this parameter on paging capacity.

Scenario 1: nB = T/2

  

Observations:

  • The UE needs to wake up every 32 ms and look for paging message (UE’s DRX cycle of 32 radio frames)
  • One out of every 2 radio frames (nB=16) available for paging within UE’ s DRX cycle. That is total of 16 paging frames are configured in the cell
  • One paging subframe (Ns=1) per paging frame available for paging
  • According to the pre-defined pattern for FDD, for Ns=1 ,i_s=0, sub frame 9 is used for paging in a paging frame
  • Total of 16 paging occasions (nB=16) per UE’s DRX cycle across which UEs are distributed based on the UE identity.

  

Scenario 2: nB = 2T

  

Observation:

  • Every radio frame is Paging Frame
  • 2 sub frames per PF (Ns = 2) are used for paging within UE’s DRX cycle
  • According to the pre-defined pattern for FDD, for Ns=2 and i_s=0, sub frames 0 and 4 are used for paging in a paging frame and Paging opportunity for the UE in discussion, is subframe 4
  • 32 Paging Frames and 64 Paging occasions (nB=64) are available within UE’s DRX cycle across which UEs are distributed based on the UE identity.

 

Scenario 3: nB = 4T

  

Observations:

  1. Every radio frame is Paging Frame
  2. 4 sub frames per PF (Ns = 4) are used for paging within UE’s DRX cycle
  3. According to the pre-defined pattern for FDD for Ns=4, sub frames 0,4,5 and 9 used for paging in a paging frame and paging opportunity for the UE in discussion is sub frame 5
  4. 32 Paging Frames and 128 Paging occasions(nB=128) are available within UE’s DRX cycle across which UEs are distributed based on the UE identity