Connected Mode Discontinuous Reception for Narrow Band Internet of Things
A novel and efficient DRX operation mechanism is proposed to maintain the reliability and energy efficiency for NB-IOT systems. In NB-IOT systems, the length of a NB-PDCCH (with repetition) and the interval between two NB-PDCCHs are extended and can be reconfigured by eNB for each UE. The eNB can also adaptively adjusts the DRX parameters accordingly. NB-IOT UE monitors the NB-PDCCH in DRX ON duration, which is configured in number of NB-PDCCHs. Specifically, if a DRX timer duration is configured by the eNB in units of a PDCCH period, the UE should calculate the timer in terms of number of PDCCH user-specific search spaces (USSs), or in terms of PDCCH subframes by multiplying the number of PDCCH periods with the PDCCH repetition level.
1 . A method comprising:
receiving a control signal by a user equipment (UE) for configuring a number of narrowband physical downlink control channel (NB-PDCCH) periods that carry downlink control information (DCI), wherein each NB-PDCCH period refers to an interval between the start of two consecutive NB-PDCCH occasions;
configuring discontinuous reception (DRX) parameters by the UE for DRX operation in radio resource control (RRC) connected mode;
determining a NB-PDCCH user-specific search space (USS) for each NB-PDCCH period, wherein each NB-PDCCH USS comprises a repetition level of NB-PDCCH subframes for NB-PDCCH transmission; and
monitoring the DCI for a monitoring time such that the UE monitors a total number of NB-PDCCH USSs during an On Duration of each DRX cycle.
2 . The method of claim 1 , wherein the total number of NB-PDCCH subframes equals to the number of configured PDCCH periods multiplied by the repetition level.
3 . The method of claim 1 , wherein the monitoring time equals to the number of configured PDCCH periods multiplied by a time duration for each PDCCH period.
4 . The method of claim 3 , wherein the UE extends the monitoring time when some subframes within a NB-PDCCH USS are reserved for non-PDCCH transmission.
5 . The method of claim 3 , wherein the UE extends the monitoring time when a NB-PDCCH USS is located at the end of a hyper frame.
6 . The method of claim 1 , wherein the UE enters light sleep between two consecutive NB-PDCCHs when no grant is received in the former PDCCH.
7 . The method of claim 1 , wherein the UE periodically monitors the NB-PDCCHs by calculating wakeup time in each DRX cycle using a modulo formula.
8 . The method of claim 7 , wherein the UE enters idle mode when the total number of NB-PDCCH subframes are monitored and no grant is received.
9 . The method of claim 1 , wherein the UE monitors the NB-PDCCHs after each media access control (MAC) protocol data unit (PDU) transmission or retransmission.
10 . The method of claim 1 , wherein the UE monitors the NB-PDCCHs for retransmission in a hybrid automatic retransmission (HARQ) process.
11 . A user equipment (UE) comprising:
a receiver that receives a control signal for configuring a number of narrowband physical downlink control channel (NB-PDCCH) periods that carry downlink control information (DCI), wherein each NB-PDCCH period refers to an interval between the start of two consecutive NB-PDCCH occasions;
a configuration circuit that configures discontinuous reception (DRX) parameters by the UE for DRX operation in radio resource control (RRC) connected mode; and
a monitoring circuit that determines a NB-PDCCH user-specific search space (USS) for each NB-PDCCH period, wherein each NB-PDCCH USS comprises a repetition number of NB-PDCCH subframes for NB-PDCCH transmission, and wherein the UE monitors the DCI for a monitoring time such that the UE monitors a total number of NB-PDCCH USSs during an On Duration of each DRX cycle.
12 . The UE of claim 11 , wherein the total number of NB-PDCCH subframes equals to the number of configured PDCCH periods multiplied by the repetition number.
13 . The UE of claim 11 , wherein the monitoring time equals to the number of configured PDCCH periods multiplied by a time duration for each PDCCH period.
14 . The UE of claim 13 , wherein the UE extends the monitoring time when some subframes within a NB-PDCCH USS are reserved for non-PDCCH transmission.
15 . The UE of claim 13 , wherein the UE extends the monitoring time when a NB-PDCCH USS is located at the end of a hyper frame.
16 . The UE of claim 11 , wherein the UE enters light sleep between two consecutive NB-PDCCHs when no grant is received in the former PDCCH.
17 . The UE of claim 11 , wherein the UE periodically monitors the NB-PDCCHs by calculating wakeup time in each DRX cycle using a modulo formula.
18 . The UE of claim 17 , wherein the UE enters idle mode when the total number of NB-PDCCH subframes are monitored and no grant is received.
19 . The UE of claim 11 , wherein the UE monitors the NB-PDCCHs after each media access control (MAC) protocol data unit (PDU) transmission or retransmission.
20 . The UE of claim 11 , wherein the UE monitors the NB-PDCCHs for retransmission in a hybrid automatic retransmission (HARQ) process.