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EP-4132204-B1 - METHOD EXECUTED BY USER EQUIPMENT, AND USER EQUIPMENT

EP4132204B1EP 4132204 B1EP4132204 B1EP 4132204B1EP-4132204-B1

Inventors

  • LIU, RENMAO
  • XIAO, Fangying
  • ZHANG, CHONGMING

Dates

Publication Date
20260513
Application Date
20210315

Claims (2)

  1. A method performed by user equipment (30), comprising: receiving a Radio Resource Control, RRC, message which includes data radio bearer, DRB, identities for DRBs configured for small data transmission, SDT, wherein one of the DRB identities identifies a DRB used for data transmission in an RRC connected state, initiating RRC resumption procedure for SDT with a condition that data provided by upper layer for transmission is from the DRBs configured for SDT, in a case that the RRC connection resumption procedure for SDT is triggered, restoring configurations for the DRBs configured for SDT, re-establishing Packet Data Convergence Protocol, PDCP, entities for the DRBs configured for SDT, resuming the DRBs configured for SDT, and submitting an RRC Resume Request message for transmission to lower layers.
  2. User equipment (30), comprising: a processor (301); and a memory (302) in electronic communication with the processor, wherein instructions stored in the memory are executable to: receive a Radio Resource Control, RRC, message which includes data radio bearer, DRB, identities for DRBs configured for small data transmission, SDT, wherein one of the DRB identities identifies a DRB used for data transmission in an RRC connected state, initiate RRC resumption procedure for SDT with a condition that data provided by upper layer for transmission is from the DRBs configured for SDT, in a case that the RRC resumption procedure for SDT is triggered, restore configurations for the DRBs configured for SDT, re-establish Packet Data Convergence Protocol, PDCP, entities for the DRBs configured for SDT, resume the DRBs configured for SDT, and submit an RRC Resume Request message for transmission to lower layers.

Description

TECHNICAL FIELD The present invention relates to the technical field of wireless communications. More specifically, the present invention relates to a method performed by user equipment, and a corresponding user equipment. BACKGROUND To shorten a transmission latency and to reduce signaling overhead, UE entering an RRC inactive state may transmit, on a preconfigured uplink resource (PUR), a transport block having a predetermined size and carrying data. Such a transmission manner may be referred to as PUR transmission. A transport block carrying user data may also be transmitted in a message three or a message A during a random access procedure. Both of the two manners may be referred to as small data transmission. In order to enable UE to perform data transmission in an inactive state, the UE first needs to resume a DRB. The UE restores the RRC configuration from the stored UE access stratum (AS) context, restores a PDCP state, and then reestablishes a PDCP entity, thereby resuming a DRB. With the preparation described above, the UE may then perform small data transmission in a currently resident cell. Such a cell may be referred to as a cell that provides a small data transmission service. In such a cell, the UE may obtain a preconfigured uplink resource, or may obtain a random access resource on the basis of system information broadcast in the cell, so as to perform small data transmission. However, the following situation may occur during preparation of small data transmission: Before entering the inactive state, the UE is configured with an allowed serving cell list (allowedServingCells), and in allowedServingCells, information of a serving cell, such as an index number, is recorded. When a logical channel is configured with allowedServingCells, data from the logical channel can only be transmitted via a serving cell recorded in allowedServingCells. Similarly, the UE may also be configured with an allowed subcarrier spacing list (allowedSCS-List), and in allowedSCS-List, allowed subcarrier spacings are recorded. When a logical channel is configured with allowedSCS-List, data from the logical channel can only be transmitted via a physical resource satisfying a subcarrier spacing recorded in allowedSCS-List. Each DRB is associated with at least one logical channel. To resume the DRB, the UE restores the previous RRC configurations, but the resource configurations of a cell currently providing the small data transmission service may not match those in the previous RRC configurations. For example, the cell currently providing the service is not a cell in allowedServingCells. As another example, a subcarrier spacing of the current cell is not in allowedSCS-List. As a result, although the UE resumes transmission of the DRB, the physical resource of the lower layer cannot satisfy the existing RRC configuration, so that data arriving from the DRB cannot be transmitted on the cell currently providing the small data transmission. In order to transmit data, the UE has to enter a connected state again, thus causing additional signaling overhead and increasing power consumption. Therefore, this is a problem that needs to be solved in performing small data transmission. WO 2014/182338 A1 describes a user equipment (UE) operable to communicate small data to an evolved node B (eNB), the UE having computer circuitry configured to: communicate with the eNB to establish a small data radio bearer (SDRB) for communicating the small data to the eNB; enter a power saving mode according to a power saving configuration; maintain UE context information for the SDRB, at the UE, while the UE is in the power saving mode; and reestablish the SDRB using the UE context information when the UE awakes from the power saving mode to enable the UE to communicate the small data on the SDRB to the eNB. The computer circuitry may further be configured to communicate with the eNB to establish the SDRB is further configured to: send a radio resource control (RRC) connection request message to the eNB with an establishment cause of small data; and receive an RRC connection setup message from the eNB for an SDRB configuration. Post-published application EP 4 165 900 A1 describes methods and apparatuses handling robust header compression (ROHC), power headroom report (PHR), and buffer status report (BSR) for data transmission in a radio resoure control (RRC) inactive state in a wireless communication system. Post-published application EP 4 165 939 A1 describes a method and apparatus for small data transmission. Post-published application EP 4 201 141 A1 describes a method and apparatus for small data transmission. SUMMARY In order to solve the above problems in the prior art, provided in the present invention are a method performed by user equipment and user equipment, as defined in the claims. The method performed by the user equipment and the user equipment can avoid additional signaling overhead and reduce power consumption in the case that use