5G (NR) DRX (Discontinuous Reception) Definition

I. DRX (Discontinuous Reception) is a technology used in mobile communication designed to save battery power for user equipment (UE). Specifically, the mobile terminal (UE) and the network (RAN) negotiate so that the terminal's (UE) receiver only operates during data transmission and is switched off and enters a low-power state at other times.

II. DRX Framework: The 5G system supports the DRX architecture, allowing negotiation of idle mode DRX cycles between the UE and the AMF; the idle mode DRX cycle applies to:

• UEs in CM-IDLE state;
• UEs in CM-CONNECTED state that enter RRC Inactive state.

III. DRX Application: In 5G, if the UE wishes to use specific DRX parameters, it should include its preferred values during each initial registration and mobility registration process, respectively for NR/WB-EUTRA and NB-IoT;

• the registration and mobility registration processes performed on NB-IoT cells follow standard 5G procedures. For NB-IoT cells, the cell broadcasts an indication of support for UE-specific DRX for NB-IoT, and the UE can request UE-specific DRX for NB-IoT during the registration process regardless of whether the cell broadcasts this support indication.
• The AMF should determine the accepted DRX parameters based on the received UE-specific DRX parameters, and the AMF should accept the values requested by the UE, but the AMF may change the values ​​requested by the UE based on operator policy. The AMF should reply to the UE with the accepted DRX parameters for NR/WB-EUTRA and NB-IoT, respectively.

---- For detailed information on DRX parameters, please refer to TS 38.331 [28] and TS 36.331 [51].

Unless the UE has received the accepted DRX parameters for that RAT from the AMF, and for NB-IoT, the cell supports UE-specific DRX for NB-IoT; otherwise, the UE should apply the DRX cycle broadcast by the RAN in the cell. If the above parameters have been received, the UE shall apply the DRX cycle of the cell broadcast or the DRX parameters of the accepted RAT (as defined in TS 38.304 [50] and TS 36.304 [52]).

IV. The TAU and DRX periodic registration procedures do not change the UE's DRX settings. A terminal (UE) in CM-CONNECTED state and entering RRC Inactive mode will apply the DRX cycle negotiated with the AMF, the DRX cycle broadcast by the RAN, or the UE-specific DRX cycle configured by the RAN (as defined in TS 38.300 [27] and TS 38.304 [50]).