CN117177256A - L1/L2 triggering mobility method and device - Google Patents

Abstract

Apparatus and methods are presented for inter-cell handover between different DUs using beam management. In one novel aspect, a UE receives a cell switch command, wherein the cell switch command indicates a layer 2 cell switch from a source cell to a target cell, and wherein the source cell and the target cell belong to two different DUs. The UE performs RLC re-establishment and MAC reset. A PDCP status report is sent by the PDCP entity of the UE to the target cell to indicate a DL or UL data transfer failure of one or more PDCP PDUs to the source cell for the unacknowledged mode or acknowledged mode radio bearer. The method includes performing a PDCP retransmission of the UE self-detection when the UE detects one or more source-failed UL PDCP PDUs not transmitted to the source cell, and wherein the one or more source-failed UL PDCP PDUs are retransmitted to the target cell when one or more conditions are satisfied.

Description

L1/L2 triggering mobility method and device

Technical Field

The disclosed embodiments relate generally to wireless communications and, more particularly, to improving UE experience during different inter-cell beam management between different DUs.

Background

In a traditional network of the third generation partnership project (the 3rd generation partnership project,3GPP) 5G new radio (nr), a serving cell change needs to be performed at some point when a User Equipment (UE) moves from the coverage area of one cell to the coverage area of another cell. Currently, the serving cell change is triggered by layer 3 (L3) measurements and is done by radio resource control (radio resource control, RRC) reconfiguration signaling with synchronization for primary cell (PCell) and primary secondary cell (primary and secondary cell, PSCell) change and release/addition of secondary cells (SCell) where applicable. The cell handover procedure involves a full layer 2 (L2) (and layer 1 (L1)) reset, which results in longer latency, greater overhead and longer interruption times than beam handover mobility. To reduce latency, overhead, and break times during UE movement, mobility mechanisms may be enhanced to allow the serving cell to shift via beam management using L1/L2 signaling. Different inter-cell mobility/L1/L2 triggered mobility (L1/L2-triggered Mobility, LTM) based on L1/L2 for different cells using beam management should support different scenarios including Distributed Unit (DU)/different inter-DU cell mobility transitions, FR1/FR2, intra-frequency/different inter-frequency, source cell and target cell may or may not be synchronized.

In a conventional Handover (HO) design controlled by a series of L3 procedures including radio resource management (radio resource management, RRM) measurements and RRC reconfiguration, in order to reduce the occurrence of HO, a relatively long time of stay (ToS) should be used to avoid ping-pong effects, accompanied by a reduction in signaling overhead and interruption throughout the life of the RRC connection. However, a disadvantage is that if the best beam does not belong to the serving cell, the UE cannot achieve an optimized instantaneous (instantaneous) throughput. With the development of different inter-cell mobility based on L1/L2 using beam management, the UE makes more decisions in preventing data loss during cell handover.

The cell handover between different DUs needs to be improved and enhanced to enhance the UE experience.

Disclosure of Invention

Apparatus and methods are presented for inter-cell handover between different DUs using beam management. In one novel aspect, a UE receives a cell handover command. Wherein the cell handover command indicates a layer 2 cell handover from a source cell to a target cell, and wherein the source cell and the target cell belong to two different DUs. RLC re-establishment is performed by the RLC entity of the UE. The MAC reset is performed by the MAC entity of the UE. A PDCP status report is sent by the PDCP entity of the UE to the target cell to indicate a DL or UL data transfer failure of one or more PDCP PDUs to the source cell for the unacknowledged mode or acknowledged mode radio bearer. When the UE detects one or more source failed UL PDCP PDUs that are not transmitted to the source cell, a UE self-detected PDCP retransmission is performed for UL data delivery. When one or more conditions are met, the UE self-detected PDCP retransmissions retransmit the one or more source failed UL PDCP PDUs to the target cell.

In one embodiment, the cell switch command is carried by the CE or PDCCH of the MAC. In one embodiment, the MAC entity sends a cell handover indication to the RRC entity of the UE. The RRC entity sends an RRC request to the PDCP entity and the RLC entity of the UE for cell switching. In one embodiment, when a cell handover command is received, the UE needs to identify PDCP PDUs that were not successfully transmitted to or to the source cell before performing RLC re-establishment. In one embodiment, the RLC entity identifies information of PDCP PDUs for which the source failed. In another embodiment, the UE sends RLC SDUs, RLC SDU segments, RLC data PDUs waiting for initial transmission back to the PDCP entity, and the PDCP entity identifies which PDCP PDUs were not successfully delivered or transmitted to the source cell. The PDCP entity performs PDCP retransmission to the target cell. In one embodiment, the UE triggers, compiles and sends a PDCP status report to the target cell.

In one embodiment, the MAC reset includes controlling a source TAG associated with the source cell and keeping a timealignment timer associated with the source cell running. In another embodiment, the MAC reset controls the operation of a beamfailuredecision timer associated with the source cell. In one embodiment, UE self-detected PDCP retransmissions involve determining whether to retransmit one or more source failed UL PDCP PDUs based on a comparison of the number of source failed UL PDCP PDUs to a pre-configured source failure threshold.

In another aspect, a user equipment for layer 1 or layer 2 triggered mobility is presented, the UE comprising an RF transceiver for transmitting and receiving RF signals in a wireless network. The UE comprises a command receiving module for receiving a cell handover command from a gNB in the wireless network, wherein the cell handover command indicates a layer 2 cell handover from a source cell to a target cell, and wherein the source cell and the target cell belong to two different distributed units. The UE further includes an RLC entity for performing RLC re-establishment. The UE further includes a MAC entity for performing a MAC reset. A PDCP entity for sending a PDCP status report in uplink to the target cell to indicate downlink or uplink data delivery failure of one or more PDCP PDUs to the source cell for a non-acknowledged mode or acknowledged mode radio bearer. The UE further includes a self-detection module to perform UE self-detected PDCP retransmissions for uplink data delivery when the UE detects one or more source failed uplink PDCP PDUs not transmitted to the source cell, and wherein the UE self-detected PDCP retransmissions retransmit the one or more source failed uplink PDCP PDUs to the target cell when one or more conditions are met.

The invention realizes the beneficial effect of improving the user experience through the cell switching between different DUs based on the L2/L1.

This summary is not intended to limit the invention. The invention is defined by the claims.

Drawings

The accompanying drawings illustrate embodiments of the invention and in which like reference numerals refer to like elements throughout.

Fig. 1A is a schematic system diagram illustrating an exemplary wireless network for different inter-cell beam management between different DUs in accordance with an embodiment of the present invention.

Fig. 1B shows the HOF rates for a conventional HO and different inter-cell mobility based on L1/L2 using beam management.

Fig. 1C illustrates a conventional HO and ping-pong rates for different L1/L2 based inter-cell mobility using beam management.

Fig. 1D shows ToS based on conventional HO and L1/L2 inter-cell mobility using beam management.

Fig. 2 shows an exemplary NR wireless system with a centralized upper layer of the NR radio interface protocol stack according to an embodiment of the present invention.

Fig. 3 illustrates an exemplary deployment scenario for beam management between different cells within a DU according to an embodiment of the present invention.

Fig. 4 illustrates an exemplary deployment scenario for beam management between different cells between different DUs according to an embodiment of the present invention.

Fig. 5 shows an exemplary flow of UP processing for beam management between different cells between different DUs according to an embodiment of the present invention.

Fig. 6 shows an exemplary flow of beam management between different inter-DUs with mobility from the network and UE perspective, according to an embodiment of the invention.

Fig. 7A illustrates an exemplary interaction between different layers on the UE side when the MAC sends an indication to the RRC layer to initiate an UP flow upon receiving a cell handover command, according to an embodiment of the present invention.

Fig. 7B illustrates an exemplary interaction between different layers of the UE side when the MAC transmits an indication to the PDCP and RLC layers to initiate an UP flow upon receiving a cell handover command according to an embodiment of the present invention.

Fig. 8 shows an exemplary flow of DL data transfer from the corners of a network and a UE for different inter-DU different inter-cell beam management with mobility according to an embodiment of the present invention.

Fig. 9 shows an exemplary flow of UL data transmission for beam management between different cells between different DUs with mobility from the perspective of a network and a UE according to an embodiment of the present invention.

Fig. 10 shows an exemplary flow of processing an UP flow at the UE side for beam management between different cells between different DUs according to an embodiment of the present invention.

Fig. 11A shows an exemplary flow of network-side source DU initiated DL data transmission for beam management between different cells between different DUs according to an embodiment of the present invention.

Fig. 11B shows an exemplary flow of network-side CU initiated DL data transmission for beam management between different cells between different DUs with mobility according to an embodiment of the present invention.

Fig. 12 illustrates an exemplary flow chart of beam management between different cells between different DUs with UE PDCP status reporting and retransmission in accordance with an embodiment 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. 1A is a schematic system diagram illustrating an exemplary wireless network for different inter-cell beam management between different DUs in accordance with an embodiment of the present invention. The wireless system 100 includes one or more fixed infrastructure elements forming a network distributed over a geographic area. As an example, base stations/gnbs 101, 102, and 103 serve a plurality of mobile stations, e.g., UEs 111, 112, and 113, within a service area (e.g., cell) or cell sector. In some systems, one or more base stations are coupled to a controller forming an access network coupled to one or more core networks through a network entity, such as network entity 106. The gnbs 101, 102, and 103 are base stations in NR, whose service areas may or may not overlap each other. As an example, the UE or mobile station 112 is only in the service area of the gNB 101 and is connected with the gNB 101. UE 112 is connected only to gNB 101. UE 111 is in an overlapping service area of gNB 101 and gNB 102 and may switch back and forth between gNB 101 and gNB 102. UE 113 is in an overlapping service area of gNB 102 and gNB 103 and may switch back and forth between gnbs 102. The base stations (e.g., gnbs 101, 102, and 103) are connected to the network through network entities (e.g., network entity 106) through NG connections (e.g., NG connections 136, 137, and 138), respectively. Xn connections 131 and 132 connect non-co-located receiving base units. Xn connection 131 connects gNB 101 and gNB 102.Xn connection 132 connects gNB 102 and gNB 103. These Xn/NG connections may be the same or different.

When a UE such as UE 111 is in an overlapping area, L1/L2-based inter-cell mobility is performed. For L1/L2 based inter-cell mobility using beam management, the network may exploit the ping-pong effect (i.e., cell switching back and forth between the source and target cells) to select the best beam in a wider area including the source and target cells for improved throughput during UE mobility. The inter-cell mobility based on L1/L2 is more suitable for the scene of cell transformation in DU and among different DUs. The ping-pong effect is not important in these scenarios. No additional signaling/delay is required at the network side for intra-DU cell transformation. For cell transitions between different DUs, the F1 interface between DU and CU can support high data rates with short latency. Considering that the F1 interface delay is 5ms, the inter-cell mobility based on L1/L2 is supportable.

Fig. 1A further illustrates a simplified block diagram of a base station and mobile device/UE for beam management between different cells between different DUs. The gNB 102 has an antenna 156 that transmits and receives radio signals. A Radio Frequency (RF) transceiver circuit 153 coupled to antenna 156 receives RF signals from antenna 156, converts the RF signals to baseband signals, and sends the baseband signals to processor 152. The RF transceiver circuit 153 also converts baseband signals received from the processor 152, converts them to RF signals, and sends them to the antenna 156. The processor 152 processes the received baseband signals and invokes different functional modules to perform functions in the gNB 102. Memory 151 stores program instructions and data 154 to control the operation of gNB 102. The gNB 102 also includes a set of control modules 155 that perform functional tasks to communicate with the mobile station. The RRC state controller 181 performs access control to the UE. The data radio bearer (data radio bearer, DRB) controller 182 performs control functions to establish/add, reconfigure/modify and release/remove DRBs based on different sets of conditions for DRB establishment, reconfiguration and release. The protocol stack controller 183 manages a protocol stack to add, modify, or remove DRBs. The protocol stack includes a PHY layer 189 for a user plane, a MAC layer 188, an RLC layer 187, a PDCP layer 186, an SDAP layer 185a, and an RRC layer 185b for a control plane.

UE 111 has an antenna 165 that transmits and receives radio signals. Coupled to the RF transceiver circuit 163 receives RF signals from the antenna 165, converts them to baseband signals, and sends the baseband signals to the processor 162. In one embodiment, the RF transceiver circuit 163 may include two radio frequency modules (not shown) for different frequency bands. The RF transceiver circuit 163 also converts baseband signals received from the processor 162, converts them to RF signals, and sends them to the antenna 165. The processor 162 processes the received baseband signal and invokes different functional modules to perform functions in the UE 111. Memory 161 stores program instructions and data 164 to control the operation of UE 111. Antenna 165 transmits uplink transmissions to antenna 156 of gNB 102 and receives downlink transmissions from antenna 156 of gNB 102.

UE 111 also includes a set of control modules that perform functional tasks. These control modules may be implemented in circuitry, software, firmware, or a combination thereof. The RRC state controller 171 controls the RRC state of the UE according to the network command and the UE condition. The UE supports the following RRC states, rrc_idle, rrc_connected, and rrc_inactive. The DRB controller 172 controls establishment/addition, reconfiguration/modification and release/removal of DRBs for DRB establishment, reconfiguration and release based on different sets of conditions. The protocol stack controller 173 manages the protocol stack to add, modify, or remove DRBs. The protocol stack includes an SDAP layer 175a for the user plane, an RRC layer 175b for the control plane, a PDCP layer 176, an RLC layer 177, a MAC layer 178, and a PHY layer 179. The command receiving module 191 receives a cell handover command from a gNB in the wireless network, wherein the cell handover command indicates a layer 2 (L2) cell handover from a source cell to a target cell, and wherein the source cell and the target cell belong to two different DUs. The RLC entity 192 performs RLC re-establishment through the RLC entity of the UE. The MAC entity 193 performs MAC reset. The PDCP entity 194 sends PDCP status reports in the Uplink (UL) to the target cell indicating one or more PDCP protocol data units (protocol data unit, PDUs) for unacknowledged mode (unacknowledged mode, UM) or Acknowledged Mode (AM) radio bearers that failed DL or UL data transfer for the source cell. The self-detection module 195 performs UE self-detected PDCP retransmissions for UL data delivery when the UE detects one or more source failed UL PDCP PDUs that failed to be transmitted to the source cell, and wherein the UE self-detected PDCP retransmissions retransmit the one or more source failed UL PDCP PDUs to the target cell when one or more conditions are met.

For the scenario of handover between different DUs, the conventional handover procedure always triggers RLC re-establishment and MAC reset. All data packets in RLC and MAC that were not successfully delivered before the handover was performed are discarded. Since the AMDRB is to guarantee lossless (lossless) data transmission, those PDCP PDUs that have not been successfully delivered will be retransmitted after handover to the target cell. For UM DRBs, data loss is allowed during handover, PDCP PDUs that have not been successfully delivered are not retransmitted after handover and are considered lost. However, for beam management between different cells between different DUs with mobility, existing User Plane (UP) processing methods through RLC re-establishment and MAC reset will cause serious problems. Frequent User Plane (UP) resets result in frequent data retransmissions for AM DRBs and a large amount of data loss for UM DRBs due to high ping-pong rate and short time of stay (ToS), which ultimately compromises the user experience. Fig. 1B, 1C, and 1D provide performance data to illustrate ping-pong effects and ToS at different settings.

We run system level simulations to compare mobility performance in terms of handover failure (HOF) rate, radio link failure (radio link failure, RLF) rate, handover interruption time (handover interruption time, HIT), ping-pong rate, and/or ToS. Fig. 1B shows the HOF rates for a conventional HO and different inter-cell mobility based on L1/L2 using beam management. HOFs may include measurement reports (measurement report, MR) TX failure, random access response (random access response, RAR) RX failure, HO complete TX failure, and RLF. Options #1, #2, #3 are different options for L1/L2 based different inter-cell mobility using beam management, with different delays to perform handover or cell handover from a source cell to a target cell. Cell switch delays for options #1, #2, and #3 are 45 ms, 25 ms, and 5ms, respectively. The baseline represents a normal handover procedure performed by a series of L3 procedures with a trigger time of 0ms (TTT 0) or 160ms (TTT 160). In the usual case of FR2, the switching delay is 75ms. In fig. 1B, it can be observed that different inter-cell mobility based on L1/L2 using beam management can significantly reduce the HOF rate at TTT0 or TTT80 (i.e., ttt=80 ms). The shorter the delay, the better the HOF rate.

Fig. 1C illustrates a conventional HO and ping-pong rates for different L1/L2 based inter-cell mobility using beam management. Different inter-cell mobility based on L1/L2 using beam management can lead to high ping-pong rates. The baseline represents normal handoff procedures at TTT0 or TTT 160. As shown, the result of the ping-pong rate increasing from 55.77% in conventional handover to 74% high ping-pong rate in different L1/L2 based inter-cell mobility using beam management is a short ToS.

Fig. 1D shows ToS based on conventional HO and L1/L2 inter-cell mobility using beam management. The baseline represents normal handoff procedures at TTT0 or TTT 160. In different L1/L2 based inter-cell mobility using beam management, the average ToS can be reduced to about 200 milliseconds. For different inter-cell mobility based on L1/L2 mechanisms using beam management, the network may exploit the ping-pong effect (i.e. cell switching back and forth between the source and target cells) to select the best beam in a wider area including the source and target cells for improving throughput during UE mobility. The inter-cell mobility based on L1/L2 is more suitable for the scene of cell transformation in DU and among different DUs. The ping-pong effect is not important in these scenarios. No additional signaling/delay is required at the network side for intra-DU cell transformation. For cell transitions between different DUs, the F1 interface between DU and CU can support high data rates with short latency. Considering that the F1 interface delay is 5ms, the inter-cell mobility based on L1/L2 is supportable.

With the new characteristics of cell handover shown, the conventional way of triggering RLC re-establishment and MAC reset needs to be improved, especially for the case between different DUs using beam management (as shown in fig. 1B, 1C and 1D). In one novel aspect, RLC re-establishment and MAC reset are controlled by the PDCP entity. Triggering a UE-initiated PDCP status report indicating PDCP PDU failure for DL or UL data delivery during a cell handover. PDCP status reports from the UE trigger PDCP retransmissions. In another novel aspect, when the UE detects one or more source failed UL PDCP PDUs that have not been transmitted to the source cell, the UE self-detected PDCP retransmission is triggered for UL data delivery during the cell handover, and wherein when one or more conditions are met, the UE self-detected PDCP retransmission retransmits the one or more source failed UL PDCP PDUs to the target cell. When the PDCP PDU has not been successfully transmitted or has not been transmitted to the source cell, the UE detects a source failed UL PDCP PDU.

Fig. 2 shows an exemplary NR wireless system with a centralized upper layer of the NR radio interface protocol stack according to an embodiment of the present invention. Different protocol split options may exist between Central Units (CUs) and Distributed Units (DUs) of the gNB. The functional partitioning between CUs and DUs of the gNB may depend on the transport layer. The low performance transmission between the CU and the DU of the gNB may enable the higher protocol layers of the NR radio stack to be supported in the CU, since the higher protocol layers have lower performance requirements on the transmission layer in terms of bandwidth, latency, synchronization and jitter. In one embodiment, the SDAP and PDCP layers are located in the CU, while the RLC, MAC and PHY layers are located in the DU. The core unit 201 is connected to a CU 211 having a gNB upper layer 252. In one embodiment 250, the gNB upper layer 252 includes a PDCP layer and an optional SDAP layer. CU 211 is connected to DUs 221, 222, and 221. DUs 221, 222, and 223 correspond to cells 231, 232, and 233, respectively. DUs, such as 221, 222, and 223, include gNB lower layer 251. In one embodiment 250, the gNB lower layer 251 includes PHY, MAC, and RLC layers.

Fig. 3 illustrates an exemplary deployment scenario for beam management between different cells within a DU according to an embodiment of the present invention. CU 302 is connected to two DUs 303 and 304 through an F1 interface. CU 302 includes a protocol stack PDCP layer 321. The DU 303 includes a protocol stack RLC layer 331 and a MAC layer 332. The DU 304 includes a protocol stack RLC layer 341 and a MAC layer 342.DU 303 and DU 304 are respectively connected to a plurality of Radio Units (RUs). A cell may consist of a range covered by one or more RUs under the same DU. RU/gNB 381, 382, 383, 384 and 385 are connected to DU 303. RU/gnbs 391, 392, 393, 394 and 395 connect with DU 304. In this scenario, UE 301 moves from the edge of one cell served by the gNB 382 to another cell served by the gNB 381, both belonging to the same DU 303 and sharing a common protocol stack. Beam management between different cells within the DU can be used in this scenario to replace the traditional handover procedure, thereby reducing outage and improving UE throughput. In one embodiment, a single protocol stack (common RLC/MAC) on the UE side is used to handle L1/L2 based beam management with mobility between unused cells.

Fig. 4 illustrates an exemplary deployment scenario for beam management between different cells between different DUs according to an embodiment of the present invention. CU 402 is connected to two DUs, DU 403 and DU 404, respectively, through an F1 interface. CU 402 includes a protocol stack PDCP layer 421. The DU 403 includes a protocol stack RLC layer 431 and a MAC layer 432. The DU 404 includes a protocol stack RLC layer 441 and a MAC layer 442.DU 403 and DU 404 are connected to the plurality of RUs, respectively. A cell may consist of a range covered by one or more RUs under the same DU. RU/gNB 481, 482, 483, 484 and 485 are connected to DU 403. RU/gNB 491, 492, 493, 494 and 495 are connected to DU 404. In this scenario, UE 401 moves from the edge of one cell served by the gNB 481 to another cell served by the gNB 491, which belong to different DUs, DUs 403 and DUs 404, respectively, and share a common CU 402. The lower layer user plane (RLC, MAC) is different and the higher layer (PDCP) remains the same in both DUs. Beam management between different cells between different DUs can be used in this scenario to replace the traditional handover procedure, thereby reducing the interruption and improving the throughput of the UE. In one embodiment, a single protocol stack (common RLC/MAC) on the UE side is used to handle beam management between different L1/L2 based cells with mobility. In one embodiment, a dual protocol stack (separate RLC/MAC) on the UE side is used to handle beam management between different L1/L2 based cells with mobility.

Fig. 5 shows an exemplary flow of UP processing for beam management between different cells between different DUs according to an embodiment of the present invention. In step 501, the UE receives a cell handover command from the network during a movement. In one embodiment, the cell switch command is sent through a MAC CE. In one embodiment, the cell switch command is sent with the beam management indication through the MAC CE. In one embodiment, the cell handover command is sent by an RRC message. In one embodiment, the cell switch command is sent through the PDCCH. After receiving the cell handover command, the UE re-establishes an RLC entity for each RB in step 502. In step 503, the UE resets the MAC and in step 504, the UE performs PDCP processing. In one embodiment, RLC re-establishment is triggered by an RRC request from an RRC entity of the UE. When receiving the cell switch instruction from the MAC entity, triggering the RRC request from the RRC entity. Optionally, the MAC reset is also triggered by an RRC request. In another embodiment, RLC re-establishment and/or MAC reset is triggered by a cell handover indication directly from the MAC entity. In one embodiment, PDCP status reports are sent by the UE in UM or AM mode for DL and UL data transfer during cell handover. In another embodiment, the UE performs a self-detected PDCP retransmission to the target cell upon detecting one or more source failed ul PDCP PDUs. When the PDCP PDU has not been successfully transmitted or has not been transmitted to the source cell, the UE detects a source failed UL PDCP PDU. The source failed UL PDCP PDU is retransmitted by the UE to the target cell. In some embodiments, the cell handover command includes an indication to enable or disable PDCP retransmissions by the UE from detection.

Fig. 6 shows an exemplary flow of beam management between different inter-DUs with mobility from the network and UE perspective, according to an embodiment of the invention. UE 600a at the source cell (601) is configured with a source protocol stack including MAC 611, RLC 612, and PDCP 613. The source cell has a DU 606 including a protocol stack of MAC 661 and RLC 662. The UE 600a with the target protocol stack including MAC 621, RLC 622, and PDCP 623 is handed over to the target cell (602). The target cell has a DU 607 of the protocol stack including MAC 671 and RLC 672. DU 606 and DU 607 are connected to CU 605. CU 605 has PDCP 651 protocol stack. Initially, the UE is connected to the source cell 601. When the UE moves to the target cell 602, a pre-configuration of a candidate cell or target cell list is provided, including at least a cell identity, a physical resource configuration (e.g., PRACH resources), a MAC configuration, and so on. When the UE moves to the edge of the source cell, the network decides to perform a cell handover and transitions the serving cell from the source cell to the target cell. The network then sends a cell switch command to the UE. The UE performs RLC re-establishment and MAC reset for cell handover. PDCP processing is enhanced to avoid loss of data during L1/L2 triggered mobility for cell handover between different DUs.

In one embodiment, there is one MAC entity to support different L1/L2 based inter-cell mobility using beam management. In one embodiment, the MAC entity controls two timing advance groups (timing advance group, TAG) associated with the first cell and the second cell, respectively. In one embodiment, the two TAGs are the master timing advance group (primary timing advance group, pTAG). In one embodiment, a MAC entity controls two beam failure detection (beamfailure detection) timers associated with a first cell and a second cell, respectively. In one embodiment, the first cell is a source cell and the second cell is a target cell. In one embodiment, the UE switches back and forth between the first and second cells. If the UE switches back from the second cell to the first cell, the second cell is considered the source cell and the first cell is considered the target cell. The UL time alignment status of the first and second cells is controlled by an associated time alignment timer (time alignment timer, TAT) of the TAG. In one embodiment, the UE performs a MAC reset upon receiving a cell handover command from the network. In one embodiment, a specific MAC reset procedure is performed for a cell handover. In the MAC reset procedure, the UE keeps the time alignment timer of the TAG associated with the source cell running, i.e. stops all timers except the time alignment timer of the TAG associated with the source cell (if running). In one embodiment, the UE further keeps a beam fault detection timer associated with the source cell running. In one embodiment, the UE stops (if running) all timers except the beam fault detection timer and the time alignment timer associated with the source cell. In one embodiment, the UE skips a Random Access (RA) procedure for the target cell when the UE performs a cell handover with a TAG associated with the target cell valid and a time alignment timer for the TAG running.

Fig. 7A illustrates an exemplary interaction between different layers on the UE side when the MAC sends an indication to the RRC layer to initiate an UP flow upon receiving a cell handover command, according to an embodiment of the present invention. The UE has a MAC entity 710, an RLC entity 711, a PDCP entity 712, and an RRC entity 713. In one embodiment, the cell switch command is received through a MAC CE or PDCCH. Upon receiving the cell switch command, the MAC entity 710 sends an indication of the cell switch to the RRC layer in step 715. The RRC entity 713 transmits a cell handover request to the RLC entity 711 to perform RLC re-establishment in step 717, so that the RLC entity performs RLC re-establishment at the time of the RRC request. The RRC entity 713 transmits a cell handover indication to the PDCP entity 712 to trigger PDCP processing in step 716, so that the PDCP entity 712 initiates PDCP processing when the RRC requests cell handover. In one embodiment, the PDCP entity 712 sends PDCP status reports and/or performs PDCP data recovery. In another embodiment, the PDCP entity 712 performs PDCP data recovery for RLC UM DRBs. In one embodiment, in step 718, RRC entity 713 further sends a request to MAC entity 710, MAC entity 710 performing a MAC reset for the cell handover.

Fig. 7B illustrates an exemplary interaction between different layers of the UE side when the MAC transmits an indication to the PDCP and RLC layers to initiate an UP flow upon receiving a cell handover command according to an embodiment of the present invention. The UE has a MAC entity 720, an RLC entity 721, a PDCP entity 722, and an RRC entity 723. Upon receiving the cell switch command, the MAC entity 720 sends an indication of the cell switch to the RLC entity 721 in step 728, thereby causing the RLC entity 721 to perform RLC re-establishment upon a MAC request. The MAC entity 720 also transmits an indication of the cell handover to the PDCP entity 722 in step 727, so that the PDCP entity 722 initiates PDCP processing when the MAC requests the cell handover. In one embodiment, the PDCP entity 722 sends PDCP status reports and/or performs PDCP data recovery. In another embodiment, PDCP entity 722 performs PDCP data recovery for RLC UM DRBs. In one embodiment, MAC entity 720 initiates and performs a MAC reset for a cell handover.

Fig. 8 shows an exemplary flow of DL data transfer from the corners of a network and a UE for different inter-DU different inter-cell beam management with mobility according to an embodiment of the present invention. UE800a at the source cell (801) is configured with a source protocol stack including MAC 811, RLC 812 and PDCP 813. Source cell 801 has a DU 806 including the protocol stack of MAC 861 and RLC 862. UE800a with a target protocol stack including MAC 821, RLC 822, and PDCP 823 switches to a target cell (802). The target cell 802 has a DU 807 including the protocol stack of MAC 871 and RLC 872. DU 806 and DU 807 are connected 805 with the CU. CU 805 has the protocol stack of PDCP 851. PDCP PDUs with sn#7, #8, #9, #10 are not successfully delivered or transmitted to the UE when the network decides to perform a cell handover from a source DU to a target DU. After the cell handover, those PDCP PDUs with sn#7, #8, #9, #10 are retransmitted by the target cell to the UE. For AM RBs, successful delivery means that RLC ACKs for those PDCP PDUs have been received. For UM RBs, in one embodiment, if those RLC SDUs or RLC SDU segments have not been included in RLC data PDUs, or RLC data PDUs wait for initial transmission, then the associated PDCP PDUs are deemed as not yet transmitted. In another embodiment for UM RBs, if HARQ ACK feedback is not received for those RLC data PDUs that have been transmitted by a lower layer, the associated PDCP PDU is deemed to be unsuccessfully transmitted. In one embodiment, upon receiving the cell handover command in step 881, the PDCP entity of the UE triggers, compiles and sends a PDCP status report in step 882 to inform the target DUs which PDCP PDUs are deemed to be failed. The target DU retransmits the PDCP PDU reported as failed in the PDCP status report.

Fig. 9 shows an exemplary flow of UL data transmission for beam management between different cells between different DUs with mobility from the perspective of a network and a UE according to an embodiment of the present invention. UE900a at source cell (901) is configured with the source protocol stacks of MAC 911, RLC 812, and PDCP 913. Source cell 901 has a DU 906 of the protocol stack including MAC 961 and RLC 962. UE900a with a target protocol stack including MAC 921, RLC 922, and PDCP 923 switches to the target cell (902). The target cell has a DU 907 of the protocol stack including MAC 971 and RLC 972. DU 906 and DU 907 are connected to CU 905. CU 905 has the protocol stack of PDCP 951. PDCP PDUs with sn#7, #8, #9, #10 are also delegated to be successfully transmitted to or to the source DU when the UE receives a cell handover command to perform a cell handover from the source DU to the target DU. After the cell handover, the UE retransmits PDCP PDUs of sn#7, #8, #9, #10 to the target cell. In one embodiment, the target DU sends PDCP status reports to the UE, providing information of which PDCP PDUs are deemed to have failed. In one embodiment, the UE finds itself which PDCP PDUs were not successfully transmitted or not successfully transmitted to the source cell. For AM RBs, successful delivery means that RLC ACKs for those PDCP PDUs have been received. For UM RBs, in one embodiment, if those RLC SDUs or RLC SDU segments have not been included in RLC data PDUs, or RLC data PDUs wait for initial transmission, then the associated PDCP PDUs are deemed as not yet transmitted. In another embodiment for UM RBs, if HARQ ACK feedback is not received for those RLC data PDUs that have been transmitted by a lower layer, the associated PDCP PDU is deemed to be unsuccessfully transmitted.

Fig. 10 shows an exemplary flow of processing an UP flow at the UE side for beam management between different cells between different DUs according to an embodiment of the present invention. When the UE receives the cell handover command, the UE performs RLC re-establishment and UL/DL data transfer. In one embodiment, upon receiving the cell handover command, RLC entity 1020 receives a request for RLC re-establishment in step 1021. Before performing RLC re-establishment, RLC entity 1020 performs additional procedures to help identify PDCP PDUs that were not successfully delivered or transmitted to lower layers. The RLC entity 1020 finds out which PDCP PDUs were not successfully delivered or transmitted. In some embodiments, RLC entity 1020 finds out which PDCP PDUs were not successfully delivered or transmitted to lower layers.

In one embodiment, the RLC entity 1020 sends back to the PDCP entity 1010 those PDCP PDUs (RLC SDUs) that were not successfully delivered in step 1022. In another embodiment, the RLC entity sends an indication of those PDCP PDUs (RLC SDUs) that were not successfully delivered to the PDCP entity 1010 in step 1022. In step 1023, the RLC entity performs RLC re-establishment. The PDCP entity 1010 then finds out which PDCP PDUs were not successfully transmitted or delivered. In step 1013, the PDCP entity retransmits to the target cell the PDCP PDU that was not successfully transmitted or transmitted to the source DU side before the cell handover. In one embodiment, after receiving the cell handover command in step 1011, the PDCP entity 1010 of the UE receives PDCP status reports from the target cell after the cell handover (step 1012), based on which the UE knows which PDCP PDUs are considered to be failed. The PDCP entity 1010 retransmits the PDCP PDU reported as failed in the PDCP status report to the target cell in step 1013.

In another embodiment 1050, the UE self-detected PDCP retransmission involves determining whether to retransmit one or more source failed UL PDCP PDUs based on one or more conditions. In one embodiment, the condition is a comparison of the number of UL PDCP PDUs source failed to a preconfigured source failure threshold. When the UE receives a cell handover command, it calculates the data amount of PDCP PDUs that have not been successfully transmitted or transferred. If the data amount is less than the threshold, the UE does not perform PDCP PDU retransmission after cell handover to the target cell. The threshold may be configured by RRC signaling from the network or pre-configured by UE/network/operator/rules. In one embodiment, whether PDCP retransmissions are performed for the target cell is configured by RRC signaling. In one embodiment, whether PDCP retransmissions are performed for the target cell is indicated along with a cell handover command.

Fig. 11A shows an exemplary flow of network-side source DU initiated DL data transmission for beam management between different cells between different DUs according to an embodiment of the present invention. The UE is connected to a source DU 1101. The cell switch is determined to switch to the target DU 1102.DU 1101 and DU 1102 are connected to CU 1103. In one embodiment, source DU 1101 makes a cell handover decision. In step 1111, the source DU 1101 sends a cell handover command to the UE. When the network sends a cell switch command to the UE, the source DU 1101 sends a DL data transfer status to the CU 1103 in step 1112. In one embodiment, the source DU 1101 informs the CU 1103 which PDCP PDUs were not successfully transmitted. In one embodiment for UM DRBs, the source DU 1101 informs the CU 1103 of the highest PDCP PDU SN successfully delivered to the UE in sequence among those PDCP PDUs received from the CU 1103. In one embodiment for UM DRBS, DU 1101 informs CU 1103 of the highest PDCP PDU SN transmitted to the lower layer among those PDCP PDUs received from CU 1103. In step 1113, the CU 1103 retransmits the PDCP PDU that was not successfully transmitted or transferred on the source DU 1101 side to the target DU 1102. The target DU 1102 retransmits these PDCP PDUs to the UE after the UE is handed over to the target cell.

Fig. 11B shows an exemplary flow of network-side CU initiated DL data transmission for beam management between different cells between different DUs with mobility according to an embodiment of the present invention. The UE is connected to a source DU 1101. The cell switch is determined to switch to the target DU 1102.DU 1101 and DU 1102 are connected to CU 1103. In one embodiment, CU 1103 makes a cell switch decision. In step 1121, source CU 1103 sends a cell handover command to source DU 1101, and source DU 1101 sends a cell handover command to the UE. As with the source DU initiated cell handover, in step 1122, the source DU 1101 sends a DL data transfer status to the CU 1103. The DL data transfer state follows the same rules as described in fig. 11A for DU initiated cell handover. In step 1123, the CU 1103 retransmits the PDCP PDU that was not successfully transmitted or sent on the source DU 1101 side to the target DU 1102. The target DU 1102 retransmits these PDCP PDUs to the UE after the UE is handed over to the target cell.

Fig. 12 illustrates an exemplary flow chart of beam management between different cells between different DUs with UE PDCP status reporting and retransmission in accordance with an embodiment of the present invention. In step 1201, the UE receives a cell handover command from a gNB in the wireless network, wherein the cell handover command indicates a layer 2 (L2) cell handover from a source cell to a target cell, and wherein the source cell and the target cell belong to two different DUs. In step 1202, the UE performs RLC re-establishment through the RLC entity of the UE. In step 1203, the UE performs a MAC reset by the MAC entity of the UE. In step 1204, the UE sends a Packet Data Convergence Protocol (PDCP) status report to the target cell in an Uplink (UL) through a PDCP entity of the UE to indicate DL or UL data transfer failure of one or more PDCP Protocol Data Units (PDUs) to the source cell for a non-acknowledged mode (UM) or Acknowledged Mode (AM) radio bearer. In step 1205, when the UE detects one or more source failed UL PDCP PDUs that are not sent to the source cell, the UE performs a UE self-detected PDCP retransmission for UL data delivery, and wherein when one or more conditions are met, the UE self-detected PDCP retransmission retransmits the one or more source failed UL PDCP PDUs to the target cell.

Although the invention has been described in connection with certain specific embodiments for purposes of illustration, the invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of the various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.

Claims (20)

1. A layer 1 or layer 2 triggered mobility method comprising:

the user equipment receiving a cell handover command from a next generation node B in the wireless network, wherein the cell handover command indicates a layer 2 cell handover from a source cell to a target cell, and wherein the source cell and the target cell belong to two different distributed units;

performing radio link control re-establishment by a radio link control entity of the user equipment;

performing medium access control reset by a medium access control entity of the user equipment;

transmitting, by the packet data convergence protocol entity of the user equipment, a packet data convergence protocol status report in an uplink to the target cell to indicate a downlink or uplink data transfer failure of one or more protocol data units of the packet data convergence protocol to the source cell for a non-acknowledged mode or acknowledged mode radio bearer;

When the user equipment detects a protocol data unit of an uplink packet data convergence protocol that failed one or more sources not sent to the source cell, performing a user equipment self-detected packet data convergence protocol retransmission for uplink data transfer, and wherein when one or more conditions are met, the user equipment self-detected packet data convergence protocol retransmission retransmits the protocol data unit of the uplink packet data convergence protocol that failed the one or more sources to the target cell.

2. The layer 1 or layer 2 triggered mobility method of claim 1, wherein the cell handover command is carried by a control element of medium access control or a physical downlink control channel.

3. The layer 1 or layer 2 triggered mobility method of claim 2, further comprising:

when receiving the cell switching command, transmitting a cell switching instruction to a radio resource control entity of the user equipment through the medium access control entity of the user equipment; and

the radio resource control entity sends a radio resource control request to the packet data convergence protocol entity and the radio link control entity when receiving the cell switch indication.

4. A layer 1 or layer 2 triggered mobility method as claimed in claim 3, characterized in that the radio link control re-establishment, the packet data convergence protocol status report and the user equipment self-detected packet data convergence protocol retransmission are triggered by the radio resource control request from the radio link control entity of the user equipment.

5. A layer 1 or layer 2 triggered mobility method as claimed in claim 3, wherein the radio resource control request is sent to the medium access control entity, and wherein the radio resource control request triggers the medium access control reset.

6. The layer 1 or layer 2 triggered mobility method of claim 2, wherein a cell switch indication is sent by the medium access control entity of the user equipment to the packet data convergence protocol entity and the radio link control entity, respectively, and wherein the radio link control re-establishment, the packet data convergence protocol status report and the user equipment self-detected packet data convergence protocol retransmission are triggered by the cell switch indication from the medium access control entity of the user equipment.

7. The layer 1 or layer 2 triggered mobility method of claim 1, wherein performing the medium access control reset further comprises:

controlling a source timing advance group associated with the source cell; and

a time alignment timer associated with the source cell is maintained running.

8. The layer 1 or layer 2 triggered mobility method of claim 7, wherein performing the medium access control reset comprises further maintaining a beam fault timer associated with the source cell running.

9. The layer 1 or layer 2 triggered mobility method of claim 1, wherein the user equipment self-detected packet data convergence protocol retransmission comprises protocol data units of an uplink packet data convergence protocol that the lower layer of the user equipment identified the one or more sources as failed.

10. The layer 1 or layer 2 triggered mobility method of claim 9, wherein the radio link control entity identifies protocol data units of the uplink packet data convergence protocol that failed by the one or more sources and sends a protocol data unit failure indication of the packet data convergence protocol to the packet data convergence protocol entity.

11. The layer 1 or layer 2 triggered mobility method of claim 9, wherein the radio link control entity identifies protocol data units of the one or more source failed uplink packet data convergence protocols and sends the protocol data units of the one or more source failed uplink packet data convergence protocols to the packet data convergence protocol entity.

12. The layer 1 or layer 2 triggered mobility method of claim 1, wherein the one or more conditions comprise at least one of:

the data amount of protocol data units of the one or more source failed uplink packet data convergence protocols is equal to or greater than a pre-configured threshold;

receiving radio resource control signaling; and

an indication in the cell switch command is received.

13. The layer 1 or layer 2 triggered mobility method of claim 1, wherein the cell switch command further comprises an indication to enable or disable the user equipment to self-detect a packet data convergence protocol retransmission.

14. A user equipment for layer 1 or layer 2 triggered mobility, comprising:

a radio frequency transceiver for transmitting and receiving radio frequency signals in a wireless network;

A command receiving module for receiving a cell handover command from a next generation node B in the wireless network, wherein the cell handover command indicates a layer 2 cell handover from a source cell to a target cell, and wherein the source cell and the target cell belong to two different distributed units;

a radio link control entity for performing radio link control re-establishment;

a medium access control entity for performing a medium access control reset;

a packet data convergence protocol entity for sending a packet data convergence protocol status report in an uplink to the target cell to indicate a downlink or uplink data transfer failure of one or more protocol data units of the packet data convergence protocol to the source cell for a non-acknowledged mode or acknowledged mode radio bearer;

a self-detection module for performing a user equipment self-detected packet data convergence protocol retransmission for uplink data transfer when the user equipment detects a protocol data unit of an uplink packet data convergence protocol failed by one or more sources not transmitted to the source cell, and wherein the user equipment self-detected packet data convergence protocol retransmission retransmits the protocol data unit of the uplink packet data convergence protocol failed by the one or more sources to the target cell when one or more conditions are satisfied.

15. The user equipment for layer 1 or layer 2 triggered mobility according to claim 14, characterized in that the cell handover command is carried by a control element of medium access control or a physical downlink control channel.

16. The user equipment for layer 1 or layer 2 triggered mobility of claim 15, further comprising a radio resource control entity,

wherein upon receiving the cell switch command, the medium access control entity sends a cell switch indication to the radio resource control entity, and

and the radio resource control entity sends a radio resource control request to the packet data convergence protocol entity and the radio link control entity when receiving the cell switching instruction.

17. The user equipment for layer 1 or layer 2 triggered mobility of claim 16, wherein the radio link control re-establishment, the packet data convergence protocol status report and the user equipment self-detected packet data convergence protocol retransmission are triggered by the radio resource control request from the radio link control entity of the user equipment.

18. The ue of claim 15, wherein the medium access control entity sends a cell switch indication to the pdu and the rlc entity, respectively, and wherein the rlc re-establishment, the pdu status report and the pdu self-detection by the ue are triggered by the cell switch indication from the medium access control entity.

19. The user equipment for layer 1 or layer 2 triggered mobility of claim 14, wherein the medium access control reset comprises: the medium access control entity controlling a source timing advance group associated with the source cell; and keep the time alignment timer and/or beam fault timer associated with the source cell running.

20. The user equipment for layer 1 or layer 2 triggered mobility of claim 14, wherein the one or more conditions comprise at least one of:

the data amount of protocol data units of the one or more source failed uplink packet data convergence protocols is equal to or greater than a pre-configured threshold;

receiving radio resource control signaling; and

an indication in the cell switch command is received.