Patent Publication Number: US-2022232514-A1

Title: Ue grouping for paging enhancement

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119 from U.S. Provisional Application No. 63/137,777 entitled “UE Grouping for Paging Enhancements UE Power Saving,” filed on Jan. 15, 2021, the subject matter of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosed embodiments relate generally to wireless communication systems, and, more particularly, to power efficient paging mechanism enhancement with paging early indication (PEI). 
     BACKGROUND 
     Third generation partnership project (3GPP) and 5G New Radio (NR) mobile telecommunication systems provide high data rate, lower latency and improved system performances. In 3GPP NR, 5G terrestrial New Radio (NR) access network (includes a plurality of base stations, e.g., Next Generation Node-Bs (gNBs), communicating with a plurality of mobile stations referred as user equipment (UEs). Orthogonal Frequency Division Multiple Access (OFDMA) has been selected for NR downlink (DL) radio access scheme due to its robustness to multipath fading, higher spectral efficiency, and bandwidth scalability. Multiple access in the downlink is achieved by assigning different sub-bands (i.e., groups of subcarriers, denoted as resource blocks (RBs)) of the system bandwidth to individual users based on their existing channel condition. In LTE and NR networks, Physical Downlink Control Channel (PDCCH) is used for downlink scheduling. Physical Downlink Shared Channel (PDSCH) is used for downlink data. Similarly, Physical Uplink Control Channel (PUCCH) is used for carrying uplink control information. Physical Uplink Shared Channel (PUSCH) is used for uplink data. In addition, physical random-access channel (PRACH) is used for non-contention-based RACH. 
     One important use of broadcast information in any cellular systems is to set up channels for communication between the UE and the gNB. This is generally referred to as paging. Paging is a procedure the wireless network uses to find out the location of a UE, before the actual connection establishment. Paging is used to alert the UE of an incoming session (call). In most cases, the paging process happens while UE is in radio resource control (RRC) idle mode. This means that UE has to monitor whether the networking is sending any paging message to it and it has to spend some energy to run this “monitoring” process. During idle mode, a UE gets into and stays in sleeping mode defined in discontinuous reception (DRX) cycle. UE periodically wakes up and monitors PDCCH to check for the presence of a paging message. If the PDCCH indicates that a paging message is transmitted in a subframe, then the UE demodulates the paging channel to see if the paging message is directed to it. 
     In NR, paging reception consumes less than 2.5% of the total power. However, due to synchronization signal block (SSB) transmission scheme in NR, LOOP operations (including AGC, FTL, and TTL) and measurements (MEAS) can only be performed in certain occasions. As a result, the gap between the SSBs for LOOP/MEAS and paging occasion (PO) is longer, and UE may enter light sleep mode in the gap. A paging early indication (PEI) is introduced for power consumption enhancements in a 5G/NR network. PEI is provided to UE before paging and UE monitors PO only if paging is indicated by the PEI. As a result, UE can save power consumption not only for paging reception, but also for the light sleep between the last SSB and PO gap. Furthermore, since the power consumption profile (PCP) and the paging probability of each UE can be very different, additional power saving enhancements can be achieved if the PEI can be provided to subgroups of UEs based on their PCP and paging probability. 
     SUMMARY 
     A method of providing paging early indication (PEI) for power consumption enhancements in a 5G/NR network is proposed. In accordance with one novel aspect, UE subgrouping is used to indicate whether some UEs (a subgroup) among those UEs monitoring the same paging occasion needs to read paging. The UE subgroup can be grouped based on different factors, e.g., power consumption profiled (PCP), or paging probability. Not every factor needs to be considered in each PEI group set, but more than two factors are allowed for UE subgrouping The UE subgroup has a reduced number of UEs, with a reduced false alarm rate for paging, at thus a reduced power consumption. In one preferred embodiment, the PEI contains a bitmap, each bit indicates if a subgroup of UEs monitoring the same PO needs to read paging. 
     In one embodiment, a UE performs registration in a wireless communication network. The UE belongs to a paging subgroup. The UE receives system information that comprises a paging early indication (PEI) configuration associated with a corresponding paging frame (PF). The UE monitors a PEI on a PEI-carrying radio frame based on the PEI configuration. The PEI indicates whether there is a paging opportunity (PO) in the corresponding PF for paging subgroups. The UE determines whether the PEI indicates positive paging for the paging subgroup that the UE belongs to. The UE monitors the PO in the corresponding PF when the PEI indicates positive paging. 
     Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
         FIG. 1  illustrates paging reception with paging early indication (PEI) and UE grouping for power saving enhancement in a 5G New Radio (NR) network in accordance with one novel aspect. 
         FIG. 2  is a simplified block diagram of a UE and a base station in accordance with various embodiments of the present invention. 
         FIG. 3  illustrates the concept of providing PEI for UE paging subgrouping for idle-mode power saving in accordance with one novel aspect. 
         FIG. 4  illustrates a preferred embodiment of providing PEI for UE paging subgrouping for idle-mode power saving in accordance with one novel aspect. 
         FIG. 5  illustrates a sequence flow between a UE and network entities supporting a first embodiment of UE paging subgrouping using PEI. 
         FIG. 6  illustrates a sequence flow between a UE and network entities supporting a second embodiment of UE paging subgrouping using PEI. 
         FIG. 7  is a flow chart of a method of UE paging subgrouping for power consumption enhancements in a 5G/NR network in accordance with one novel aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 1  illustrates paging reception with paging early indication (PEI) and UE grouping for power saving enhancement in a 5G New Radio (NR) network  100  in accordance with one novel aspect. In 3GPP NR, 5G NR access network (a plurality of base stations, e.g., Next Generation Node-Bs (gNBs), communicating with a plurality of mobile stations referred as user equipment (UEs). Orthogonal Frequency Division Multiple Access (OFDMA) has been selected for NR downlink (DL) radio access scheme due to its robustness to multipath fading, higher spectral efficiency, and bandwidth scalability. In both LTE and NR networks, Physical Downlink Control Channel (PDCCH) is used for downlink scheduling. Physical Downlink Shared Channel (PDSCH) is used for downlink data. Similarly, Physical Uplink Control Channel (PUCCH) is used for carrying uplink control information. Physical Uplink Shared Channel (PUSCH) is used for uplink data. In addition, physical random-access channel (PRACH) is used for non-contention-based RACH. 
     One important use of broadcast information in any cellular systems is to set up channels for communication between the UE and the gNB. This is generally referred to as paging. Paging is a procedure the wireless network uses to find out the location of a UE, before the actual connection establishment. Paging is used to alert the UE of an incoming session (call). In most cases, the paging process happens while UE is in radio resource control (RRC) idle mode. This means that UE has to monitor whether the networking is sending any paging message to it and it has to spend some energy to run this “monitoring” process. During RRC idle mode, a UE gets into and stays in sleeping mode defined in discontinuous reception (DRX) cycle. UE periodically wakes up and monitors PDCCH to check for the presence of a paging message. If the PDCCH indicates that a paging message is transmitted in a subframe, then the UE demodulates the paging channel to see if the paging message is directed to it. 
     In NR, paging reception consumes less than 2.5% of the total power. However, due to synchronization signal block (SSB) transmission scheme in NR, LOOP operations (including AGC, FTL, and TTL) and measurements (MEAS) can only be performed in certain occasions. As a result, there is some gap between the SSBs for LOOP/MEAS and paging occasion (PO), and UE may enter light sleep mode in the gap. A paging early indication (PEI) is introduced for power consumption enhancements in a 5G/NR network. PEI is provided to UE before paging and UE monitors PO only if paging is indicated by the PEI. As a result, UE can save power consumption not only for paging reception, but also for the light sleep between the last SSB and PO gap. Note that in light sleep mode, UE does not fully turn of its receiver, and thus the power consumption is higher than that in deep sleep mode, but lower than normal mode. Compared to deep sleep mode, light sleep mode requires less transition power to/from normal mode. 
       FIG. 1  depicts the SSB transmission scheme in NR, where LOOP operations (including AGC, FTL, and TTL) and measurements (MEAS) can only be performed in certain occasions, e.g., during SSB bursts. UE wakes up for SSBs, e.g., every 20 ms (every 2 radio frames). UE may enter light sleep mode in the gap between the SSBs for LOOP/MEAS and paging occasion (PO). Note that Low-SINR UEs need to wake up earlier, i.e., monitor more SSB bursts (larger NssB) before being able to decode paging message. High-SINR UEs may wake up later before PO monitoring. Therefore, if there is only one PEI for each PO, PEI needs to be relatively early in order to cover a wide range of SINR values since a PEI serves many UEs. 
     When PEI is introduced, UE can skip PO monitoring if PEI indicates negative, e.g., entering deep sleep in the gap between PEI and PO. The UE main receiver is turned on in every paging cycle, for LOOP, MEAS, and PEI reception. If PEI indicates no paging, then after performing required measurements, UE can turn off its main receiver and go to deep sleep until the next PEI. Note that UE is required to perform intra- or inter-frequency measurements when the serving cell is below certain threshold. Usually UE performs the required measurements when it wakes up for paging monitoring (i.e., every paging cycle), then UE will stay in deep sleep until next PEI. Since PEIs are always transmitted and are located near SSB bursts, power saving can be achieved not only for PO monitoring but also for light sleep between the last SSB/PEI and the PO monitoring gap and state transitions (e.g., the power mode transition from/to normal mode to/from light sleep mode), when no UE in the UE group is paged. 
     In accordance with one novel aspect, UE subgrouping is used to indicate whether some UEs (a subgroup) among those UEs monitoring the same paging occasion needs to read paging. The UE subgroup can be grouped based on different criteria, e.g., power consumption profiled (PCP), or paging probability. The UE subgroup has a reduced number of UEs, with a reduced false alarm rate for paging, at thus a reduced power consumption. In one preferred embodiment, the PEI contains a bitmap, each bit indicates if a subgroup of UEs monitoring the same PO needs to read paging. In the example of  FIG. 1, 110  represents a group of UEs monitoring the same PO, and  120  represents a subgroup of UEs within UE group  110 . PEI  130  is located next to the SSB burst  131 , and PEI  130  contains a bitmap, e.g., a bit “0” indicates a corresponding UE subgroup has no paging, those UEs can enter deep sleep in  132 ; and a bit “1” indicates a corresponding UE subgroup needs to read paging in the upcoming PO. 
       FIG. 2  is a simplified block diagram of wireless devices  201  and  211  in accordance with embodiments of the present invention. For wireless device  201  (e.g., a base station), antennae  207  and  208  transmit and receive radio signal. RF transceiver module  206 , coupled with the antennae, receives RF signals from the antennae, converts them to baseband signals and sends them to processor  203 . RF transceiver  206  also converts received baseband signals from the processor, converts them to RF signals, and sends out to antennae  207  and  208 . Processor  203  processes the received baseband signals and invokes different functional modules and circuits to perform features in wireless device  201 . Memory  202  stores program instructions and data  210  to control the operations of device  201 . 
     Similarly, for wireless device  211  (e.g., a user equipment), antennae  217  and  218  transmit and receive RF signals. RF transceiver module  216 , coupled with the antennae, receives RF signals from the antennae, converts them to baseband signals and sends them to processor  213 . The RF transceiver  216  also converts received baseband signals from the processor, converts them to RF signals, and sends out to antennae  217  and  218 . Processor  213  processes the received baseband signals and invokes different functional modules and circuits to perform features in wireless device  211 . Memory  212  stores program instructions and data  220  to control the operations of the wireless device  211 . 
     The wireless devices  201  and  211  also include several functional modules and circuits that can be implemented and configured to perform embodiments of the present invention. In the example of  FIG. 2 , wireless device  201  is a base station that includes an RRC connection handling module  205 , a scheduler  204 , a paging and mobility management module  209 , and a control and configuration circuit  221 . Wireless device  211  is a UE that includes a connection handling module  215 , a registration module  214 , a paging and mobility handling module  219 , and a control and configuration circuit  231 . Note that a wireless device may be both a transmitting device and a receiving device. The different functional modules and circuits can be implemented and configured by software, firmware, hardware, and any combination thereof. The function modules and circuits, when executed by the processors  203  and  213  (e.g., via executing program codes  210  and  220 ), allow base station  201  and UE  211  to perform embodiments of the present invention. 
     In one example, the base station  201  establishes an RRC connection with the UE  211  via RRC connection handling circuit  205 , schedules downlink and uplink transmission for UEs via scheduler  204 , performs paging, mobility, and handover management via mobility management module  209 , and provides PEI, paging, measurement, and measurement reporting configuration information to UEs via configuration circuit  221 . The UE  211  performs registration with the network via registration module  214 , handles RRC connection via RRC connection handling circuit  215 , performs PEI and paging monitoring and mobility via paging and mobility handling module  219 , and obtains configuration information via control and configuration circuit  231 . In one novel aspect, UE  211  receives paging configuration for PEI and monitors PEI, which indicates whether UE subgroups have paging. UE  211  can skip PO monitoring if PEI indicates negative to achieve power saving for PO monitoring and between the PEI and the PO monitoring gap. 
       FIG. 3  illustrates the concept of providing PEI for UE paging subgrouping for idle-mode power saving in accordance with one novel aspect. A two-step approach is adopted for UE paging subgrouping. In a first step, the network assigns PEI group sets to PEI groups, each PEI group set contains a selected number of PEI groups, which are also referred to as paging subgroups. In a second step, UE-ID (hashing) based subgroup selection is applied. A number of subgrouping factors, e.g., power consumption profile and paging probability, can be used for assigning PEI group sets. Multiple factors can be considered for subgrouping, and different factors can be considered in different PEI group sets. 
     In the example of  FIG. 3 , there are twelve (12) PEI groups monitoring the same PO. In the first step, the twelve PEI groups are divided into three PEI group sets. PEI groups  0 - 2  belong to PEI group set # 0  (power-critical, paging probability level # 0 ), PEI groups  3 - 4  belong to PEI group set # 1  power-critical, paging probability level # 1 ), and PEI groups  6 - 11  belong to PEI group set # 3  (non-power-critical). Note that not every factor needs to be considered in each PEI group set, but more than two factors are allowed for UE subgrouping. In one example, for power-critical UEs, UE grouping is based on two levels of paging probability. For non-power-critical UEs, UE grouping based on paging probability is not considered. In the second step, UE-ID is then used for PEI group selection, e.g., UE selects its paging subgroup from the assigned PEI group set# using UE-ID (hashing). The parameters need to be configured include: 1) total number of PEI groups; 2) the number of PEI groups for each PEI group set; 3) the thresholds for paging probability levels; 4) the list of factors considered; and 5) the factors for a PEI group set, in the format of tuples, the size depends on the number of factors for UE paging subgrouping. 
       FIG. 4  illustrates a preferred embodiment of providing PEI for UE paging subgrouping for idle-mode power saving in accordance with one novel aspect. In the embodiment of  FIG. 4 , UE paging subgrouping can be assigned by the core network (CN) directly, or selected based on UE-ID (hashing) based subgrouping. If both methods can co-exist in a cell, a UE may  1 ) be assigned with a paging subgroup ID directly from CN  401 ; and 2) calculate its paging subgroup ID based on its UE-ID assigned by its serving base station gNB  402 . For example, there are total eight (8) PEI groups monitoring the same PO. CN  401  assigns paging subgroups with PEI group IDs # 0 -# 3  to some UEs (e.g., power-critical UEs). This is equivalent to having four “PEI group sets”, each PEI group set having only one PEI group/paging subgroup. For UEs without CN-assigned paging subgroup ID (e.g., non-power-critical UEs), then each UE selects its paging subgroup from PEI groups # 4 -# 7  based on UE-ID. 
       FIG. 5  illustrates a sequence flow between a UE and network entities supporting a first embodiment of UE paging subgrouping using PEI. The first embodiment of  FIG. 5  corresponds to the two-step approach illustrated in  FIG. 3 . In step  511 , UE  501  sends a registration request message to AMF  504 . The registration request message comprises PEI assistance information, which further comprises UE capability such as the minimum required gap between PO and corresponding PEI. In step  512 , UE  501  receives a registration accept message from AMF  504 . The registration accept message comprises PEI group set ID# assigned to the UE. In step  513 , AMF  504  sends a UE context modification request message to serving base station gNB  502 , with PEI group set assignments. In step  514 , gNB  502  sends a UE context modification response message to AMF  504 . In step  515 , UE  501  sends a registration complete message to AMF  504 . 
     UE  501  may enter RRC idle state at a later time. In step  521 , UE  501  receives system information containing UE-group PEI configuration from gNB  502  and gNB  503 , e.g., via broadcasting. The PEI configuration indicates whether and where the network sends PEI and paging messages. For example, the paging configuration indicates a PEI offset value associated with a corresponding paging frame (PF). In step  522 , UE  501  calculates its PEI group/paging subgroup. For example, UE  501  can derive its paging subgroup based on the assigned PEI group set ID# and its UE-ID. In step  531 , AMF  504  sends out paging notification to gNB  502  and gNB  503 . The paging notification includes UE-ID and PEI group set ID# to be paged. In step  532 , gNB  502  and gNB  503  calculate the PEI group/paging subgroup to be paged. In step  533 , gNB  502  and gNB  503  provide PEI for UE paging subgroups in a PEI-carrying radio frame. UE  501  determines the radio frame that carries PEI, and determines the starting point and duration of PEI monitoring based on PEI configuration. Upon PEI monitoring, UE  501  also determines whether the PEI indicates positive paging for the paging subgroup that UE  501  belongs to. In step  534 , gNB  502  and gNB  503  forwards the paging notification in a paging frame to a group of UEs including UE  501 . UE  501  goes to deep sleep during the gap from PEI to PO, if the PEI indicates negative paging. UE  501  monitors PO and decodes the paging message inside, if the PEI indicates positive paging. Steps  541 - 543  are RAN paging for RRC inactive state. 
       FIG. 6  illustrates a sequence flow between a UE and network entities supporting a second embodiment of UE paging subgrouping using PEI. The second embodiment of  FIG. 6  corresponds to the embodiment illustrated in  FIG. 4 . Steps  611 - 643  are similar to steps  511 - 543  of the first embodiment in  FIG. 5 . However, in step  612 , in the registration accept message, instead of providing PEI group set assignment to UE, the network optionally provides PEI group#, e.g., paging subgroup assignment directly. In this way, in step  622 , UE  601  may  1 ) be assigned with a paging subgroup ID directly from AMF  604  (e.g., for power-critical UEs); and 2) calculate its paging subgroup ID based on its UE-ID (if PEI group# is not provided, e.g., for non-power-critical UEs). The second embodiment of  FIG. 6  can also be viewed as a special case of the first embodiment of  FIG. 5 . In other words, each assigned PEI group can be viewed as an assigned PEI group set, having only one PEI group member. 
       FIG. 7  is a flow chart of a method of UE paging subgrouping for power consumption enhancements in a 5G/NR network in accordance with one novel aspect of the present invention. In step  701 , a UE performs registration in a wireless communication network. The UE belongs to a paging subgroup. In step  702 , the UE receives system information that comprises a paging early indication (PEI) configuration associated with a corresponding paging frame (PF). In step  703 , the UE monitors a PEI on a PEI-carrying radio frame based on the PEI configuration. The PEI indicates whether there is a paging opportunity (PO) in the corresponding PF for paging subgroups. In step  704 , the UE determines whether the PEI indicates positive paging for the paging subgroup that the UE belongs to. The UE monitors the PO in the corresponding PF when the PEI indicates positive paging. 
     Although the present invention is described above in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.