3G/UMTS

Paging

The UE may use Discontinuous Reception (DRX) in idle mode in order to reduce power consumption. When DRX is used the UE needs only to monitor one Page Indicator, PI, in one Paging Occasion per DRX cycle.

< Factors affecting Paging Cycle >

• DRX Cycle : to be calculated
• DRX Index : to be calculated
• PI (Paging Indicator): to be calculated, a short indicator that is transmitted on the PICH to tell the UE that there is a paging message on an associated paging channel carried by the SCCPCH. If the PI bits are set in the paging occasion (SFN), the UE reads the paging message on the PCH transmitted on the associated SCCPCH.
• Np (18,36,72,144) : pi-CountPerFrame in SIB5, number of paging indicators per radio frame
• IMSI : from USIM
• K (Number of SCCPCH) : sCCPCH-SystemInformationList value in SIB5, Equal to the number of listed SCCPCHs which carry a PCH
• DRX Cycle Length : to be calculated
• k (DRX cycle length coefficient)
• SCCPCH Number : to be calculated

< Structure of Paging Channel (PICH) >

If every bits in a PI is '1', it means there is a paging for you

< How these Params are interrelated ? >

SCCPCH Number = Index of selected SCCPCH = IMSI mod K

DRX Index = MISI div 8192

PI = DRX Index mod Np

DRX Cycle Length = 2^k frames (for FDD)

Paging Occasion (SFN) = (IMSI div K) mod (DRX Cycle Length) + n * DRX cycle length

                                        , where n = 0,1,2,…

< Example >

IMSI = 23415123456789

K = 4 (4 SCCPCH each carrying PCH)

DRX length coefficient (k) = 6

IMSI mod k = 23415123456789 mod K = 1 (SCCPCH1 is selected)

DRX Cycle Length = 2^6 = 64 frames

Paging Occasion (SFN) = (IMSI div K) mod (DRX Cycle Length)  + n * DRX cycle length

                                         = (23415123456789 div 4) mod 64 + n * 64

                                         = 5853780864197 mod 64 + n * 64

                                         = 5 + n*64

                                         = 5, 69,133,197,…