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EP-4289217-B1 - MANAGING DATA COMMUNICATION BEFORE AND AFTER A STATE TRANSITION

EP4289217B1EP 4289217 B1EP4289217 B1EP 4289217B1EP-4289217-B1

Inventors

  • WU, CHIH-HSIANG

Dates

Publication Date
20260506
Application Date
20220311

Claims (10)

  1. A method in a central unit, CU, (172) of a base station for managing communications from a user equipment, UE, (102) during a state transition, the method comprising: performing, by the CU (172) with the UE (102) in an inactive state, an early data transmission procedure, including communicating at least one data packet of a sequence of data packets via a distributed unit, DU, (174) of the base station using a packet data convergence protocol, PDCP, entity; determining, by the CU (172), to transition the UE (102) from the inactive state to a connected state; and in response to the determining to transition the UE (102) to the connected state: refraining from reestablishing the PDCP entity; and communicating, by the CU (172), a next data packet in the sequence of data packets with the UE (102) using the PDCP entity, or retransmitting, by the CU (172), the at least one data packet to the UE (102) via the DU (174) using the PDCP entity in response to failing to determine the at least one data packet has been received.
  2. The method of claim 1, wherein performing an early data transmission procedure with the UE (102) includes: receiving, by the CU (172), a radio resource control, RRC, message without an initial data packet from the UE (102) via the DU (174); and receiving, by the CU (172), data packets from the UE (102) via the DU (174) having sequence numbers including an initial sequence number.
  3. The method of any of the preceding claims, further comprising: in response to determining to transition the UE (102) from the inactive state to the connected state, transmitting, by the CU (172), a UE context request message to a DU (174) of the base station to obtain a radio configuration for the UE (102); receiving, by the CU (172) from the DU (174), a UE context response including the radio configuration for the UE (102); and at least one of: transmitting, by the CU (172), a radio resource control, RRC, resume message to the UE (102) via the DU (174); or transmitting, by the CU (172), a radio resource control, RRC, setup message to the UE (102) via the DU (174); and optionally: wherein the UE context request message is a first UE context request message that causes the DU (174) to release a UE context, and further comprising: transmitting, by the CU (172), a second UE context request message to establish a new UE context for the UE.
  4. The method of claim 1, wherein: performing an early data transmission procedure with the UE (102) includes: receiving, by the CU (172), an initial data packet from the UE (102) via the DU (174) having an initial sequence number; and receiving, by the CU, subsequent data packets from the UE via the DU having subsequent sequence numbers.
  5. The method of claim 4, further comprising: assigning, by the CU (172), at least one sequence number for the at least one data packet from an initial downlink sequence number to M, and/or wherein the initial and subsequent data packets from the UE have sequence numbers from the initial sequence number to K.
  6. The method of claim 4, wherein refraining from reestablishing the PDCP entity includes: assigning a sequence number for the next data packet of M+1 based on not reestablishing the PDCP entity; and/or receiving, by the CU (172), additional data packets from the UE (102) via the DU having sequence numbers starting at K+1 based on not reestablishing the PDCP entity.
  7. The method of claim 1, wherein performing the early data transmission procedure includes: transmitting, by the CU (172), a hybrid automatic repeat request,HARQ, transmission of the at least one data packet to the UE (102) using a HARQ process number, and optionally further comprising at least one of: in response to transitioning the UE (102) to the connected state, (i) flushing, by the CU (172), a HARQ buffer associated with the HARQ process number; and generating, by the CU (172), a next HARQ transmission associated with the HARQ process number as a transmission to the UE (102); or (ii) refraining from using the HARQ process number for HARQ transmissions to the UE in the connected state; and transmitting, by the CU (172), a next HARQ transmission using a different HARQ process number that was not used in the inactive state; or (iii) wherein the at least one data packet is a first data packet, and further comprising determining, by the CU (172), whether a HARQ acknowledgement for the HARQ transmission was received from the UE (102); in a first instance in response to determining that the HARQ acknowledgement was received, transmitting, by the CU (172) to the UE (102), a new HARQ transmission of a second data packet using the HARQ process number; and in a second instance in response to determining that the HARQ acknowledgement was not received, transmitting, by the CU (172) to the UE (102), a new HARQ transmission of the first data packet using the HARQ process number; or (iv) transmitting, by the CU (172), a HARQ retransmission of the at least one data packet to the UE using the HARQ process number; or (v) wherein the HARQ transmission is associated with a new data indicator and further comprising, toggling, by the CU (172), the new data indicator for a next HARQ transmission; and transmitting, by the CU, the next HARQ transmission to the UE using the HARQ process number.
  8. The method of claim 1, further comprising: in response to transitioning the UE (102) to the connected state, receiving, by the CU (172) information from the UE indicating that the UE did not receive the at least one data packet; and retransmitting, by the CU (172), the at least one data packet in accordance with the information.
  9. The method of claim 8, further comprising: in response to transitioning the UE (102) to the connected state, transmitting, by the CU (172), a request to the UE to transmit information indicating a received status of the at least one data packet; and receiving, by the CU, information from the UE indicating the received status of the at least one data packet.
  10. A central unit, CU (172) of a base station comprising processing hardware and configured to perform a method according to any of the preceding claims.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of the filing date of U.S. Provisional Patent Application No. 63/200,898 entitled "Managing Data Communication Before and After a State Transition," filed on April 1, 2021. FIELD OF THE DISCLOSURE This disclosure relates generally to wireless communications and, more particularly, to communication of data at a user equipment (UE) and a radio access network (RAN) when the UE operates in an inactive or idle state associated with a protocol for controlling radio resources and after the UE transitions to a connected state associated with the protocol for controlling radio resources. BACKGROUND This background description is provided for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. Generally speaking, a base station operating a cellular radio access network (RAN) communicates with a user equipment (UE) using a certain radio access technology (RAT) and multiple layers of a protocol stack. For example, the physical layer (PHY) of a RAT provides transport channels to the Medium Access Control (MAC) sublayer, which in turn provides logical channels to the Radio Link Control (RLC) sublayer, and the RLC sublayer in turn provides data transfer services to the Packet Data Convergence Protocol (PDCP) sublayer. The Radio Resource Control (RRC) sublayer is disposed above the PDCP sublayer. The RRC sublayer specifies the RRC_IDLE state, in which a UE does not have an active radio connection with a base station; the RRC_CONNECTED state, in which the UE has an active radio connection with the base station; and the RRC_INACTIVE to allow a UE to more quickly transition back to the RRC_CONNECTED state due to Radio Access Network (RAN)-level base station coordination and RAN-paging procedures. In some cases, the UE in the RRC_IDLE or RRC_INACTIVE state has only one, relatively small packet to transmit. In these cases, the UE is in the RRC_IDLE or RRC_INACTIVE state can perform an early data transmission (also referred to herein as small data transmission) without transitioning to the RRC_CONNECTED state, e.g., by using techniques as specified in section 7.3 in 3GPP specification 36.300 v16.54.0. In some scenarios, during early data communication between a RAN and a UE operating in an inactive or idle state, the RAN transitions the UE to a connected state, e.g., because the RAN needs to communicate a data packet associated to particular quality of service (QoS) requirements, or link quality between the UE and RAN becomes worse. It is not clear how to proceed with data communication after the UE transitions to the connected state. Publication 'Ericsson: "Email discussion report on [NB-IoT-AH#3] PDCP handling at resume", 3GPP DRAFT; R2-164042 - Email discussion report on [NB-IoT-AH#3] PDCP handling at resume, 3GPP, Mobile Competence Centre 650, Route des Lucioles; F-06921 Sophia, vol. RAN WG2, no. Nanjing, China; 20160523-20160527 26 May 2016' discloses the handling of the RLC and PDCP contexts at RRC suspend/resume procedures. WO 2018/126449 discloses a method for modifying a data transmission window and a device thereof, and a communication system. SUMMARY The invention provides methods as set out in the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a block diagram of an example wireless communication system in which a user device and a base station of this disclosure can implement the techniques of this disclosure for reducing latency in data communication;Fig. 1B is a block diagram of an example base station in which a centralized unit (CU) and a distributed unit (DU) can operate in the system of Fig. 1A;Fig. 2A is a block diagram of an example protocol stack according to which the UE of Fig. 1A communicates with base stations;Fig. 2B is a block diagram of an example protocol stack according to which the UE of Fig. 1A can communicate with a DU and a CU;Fig. 3A is a messaging diagram of an example procedure for managing communications from a UE during a state transition from an inactive state to a connected state with the base station;Fig. 3B is a messaging diagram of another example procedure for managing communications from a UE during a state transition from an inactive state to a connected state with the base station, where the UE or the CU reestablishes a packet data convergence protocol (PDCP) entity;Fig. 3C is a messaging diagram of yet another example procedure for managing communications from a UE during a state transition from an inactive state to a connected state with the base station, where an initial radio resource control (RRC) message does not include an initial data packet;Fig. 3D is a messaging