WO2023184476A1

WO2023184476A1 - Methods and apparatus of ta maintenance and acquisition for mobility with inter-cell beam management

Info

Publication number: WO2023184476A1
Application number: PCT/CN2022/084793
Authority: WO
Inventors: Xiaonan Zhang; Yuanyuan Zhang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2022-04-01
Filing date: 2022-04-01
Publication date: 2023-10-05
Also published as: CN116896780A

Abstract

This disclosure describes methods and apparatus to perform inter-cell beam management and switching between a first cell and a second cell, further comprising the step of pre-configuration before cell switch, dynamic cell switch by cell switch MAC CE, keeping the TAG from source cell so as to skip the RA procedure in the following cell switch procedure.

Description

METHODS AND APPARATUS OF TA MAINTENANCE AND ACQUISITION FOR MOBILITY WITH INTER-CELL BEAM MANAGEMENT

TECHNICAL FIELD

The present disclosure relates generally to communication systems, and more particularly, the method of TA maintenance and acquisition for mobility with inter-cell beam management.

BACKGROUND

In conventional network of 3rd generation partnership project (3GPP) 5G new radio (NR) , when the UE moves from the coverage area of one cell to another cell, at some point a serving cell change needs to be performed. Currently serving cell change is triggered by L3 measurements and is done by RRC signaling triggered by Reconfiguration with Synchronization for change of PCell and PSCell, as well as release/add for SCells when applicable. All cases involve complete L2 (and L1) resets, leading to longer latency, larger overhead and longer interruption time than beam switch mobility. In order to reduce the latency, overhead and interruption time during UE mobility, the mobility mechanism can be enhanced to enable a serving cell to change via beam management with L1/L2 signaling. The L1/L2 based inter-cell mobility with beam management should support the different scenarios, including intra-DU/inter-DU inter-cell cell change, FR1/FR2, intra-frequency/inter-frequency, and source and target cells may be synchronized or non-synchronized.

In legacy HO design controlled by a series of L3 procedures including RRM measurement and RRC Reconfiguration, ping-pong effects should be avoided with relatively long ToS (time of stay) in order to reduce the occurrences of HOs, accompanied with which is the reduce of signaling overhead and interruption during the overall lifetime of RRC connection. However, the drawback is that UE can’t achieve the optimized instantaneous throughput if the best beam is not belonging to the serving cell. For L1/L2 based inter-cell mobility with beam management, the network can take advantage of ping-pong effects, i.e., cell switch back and forth between the source and target cells, to select the best beams among a wider area including both the source cell and target cell for throughput boosting during UE mobility. L1/L2 based inter-cell mobility is more proper for the scenarios of intra-DU and inter-DU cell change. Ping-pong effect is not concerned in those scenarios. For intra-DU cell change, there is no additional signaling/latency needed at the network side; for inter-DU cell change, the F1 interface between DU and CU can support high data rate with short latency (inter-DU) . L1/L2 based inter-cell mobility is supportable considering the F1 latency is 5ms.

During L1/L2 based inter-cell mobility, UL time alignment is required with the corresponding serving cell. By default, UE needs to perform random access (RA) procedure towards the cell, to which UE accesses. Considering that UE may be switched back-and-forth between different cells, it’s complicated and power-consumed if UE always performs RA procedure towards the cell to which UE is switched. A method to control TA maintenance and acquisition should be introduced to enable L1/L2 based inter-cell mobility with beam management.

In this invention, apparatus and mechanisms are sought to control TA maintenance and acquisition for L1/L2 based inter-cell mobility with beam management.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE.

In the preparation for inter-cell beam management, UE receives dedicated RRC signaling indicated by network, which contains the pre-configuration for the upcoming cell switch. In one embodiment, the pre-configuration is for intra-DU inter-cell beam management. In one embodiment, the pre-configuration is for inter-DU inter-cell beam management. When UE receive the cell switch MAC CE from the network, UE keep the TAG for source cell and maintain the associate TAT, then perform cell switch to the target cell. In one embodiment, the inter-cell beam management is realized by single protocol stack. In one embodiment, the inter-cell beam management is realized by dual protocol stack.

In one embodiment, UE access to the target cell at the first time, and UE perform random access (RA) to get the TAG from the target cell. In one embodiment, UE has switched to the target cell before so UE switch to target cell without RA procedure. After cell switch, network may indicate UE to switch back to the first cell by cell switch MAC CE according to the L1 measurement reported by UE.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a schematic system diagram illustrating an exemplary 5G new radio network in accordance with embodiments of the current invention.

Figure 2 illustrates an exemplary NR wireless system with centralization of the upper layers of the NR radio stacks in accordance with embodiments of the current invention.

Figure 3 illustrates an exemplary deployment scenario for intra-DU inter-cell beam management in accordance with embodiments of the current invention.

Figure 4 illustrates an exemplary deployment scenario for inter-DU inter-cell beam management in accordance with embodiments of the current invention.

Figure 5 illustrate an exemplary process for UE to partial reset MAC entity and maintain the TAG from the source cell for the single-stack based inter-cell beam management in accordance with embodiments of the current invention.

Figure 6 illustrate an exemplary process for UE to establish a new MAC entity and maintain the source MAC entity for the dual-stack based inter-cell beam management in accordance with embodiments of the current invention.

Figure 7A-7C illustrate exemplary processes of UE to keep the TAG for source cell and perform random access (RA) at the first access to target cell and skip the RA procedure when switch back to source cell and switch again to target cell in accordance with embodiments of the current invention.

Figure 8 illustrate an exemplary overall flow of inter-cell beam management in accordance with embodiments of the current invention.

Figure 9 illustrates an exemplary flowchart for UE to perform inter-cell beam management in accordance with embodiments of the current invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

Aspects of the present disclosure provide methods, apparatus, processing systems, and computer readable mediums for NR (new radio access technology, or 5G technology) or other radio access technology. NR may support various wireless communication services. These services may have different quality of service (QoS) requirements e.g. latency and reliability requirements.

Figure 1 illustrates a schematic system diagram illustrating an exemplary wireless network in accordance with embodiments of the current invention. Wireless system includes one or more fixed base infrastructure units forming a network distributed over a geographical region. The base unit may also be referred to as an access point, an access terminal, a base station, a Node-B, an eNode-B, a gNB, or by other terminology used in the art. As an example, base stations serve a number of mobile stations within a serving area, for example, a cell, or within a cell sector. In some systems, one or more base stations are coupled to a controller forming an access network that is coupled to one or more core networks. gNB 1and gNB 2 are base stations in NR, the serving area of which may or may not overlap with each other. As an example, UE1 or mobile station is only in the service area of gNB 1 and connected with gNB1. UE1 is connected with gNB1 only, gNB1 is connected with gNB 1 and 2 via Xn interface. UE2 is in the overlapping service area of gNB1 and gNB2.

Figure 1 further illustrates simplified block diagrams for UE2 and gNB2, respectively. UE has an antenna, which transmits and receives radio signals. A RF transceiver, coupled with the antenna, receives RF signals from antenna, converts them to baseband signal, and sends them to processor. In one embodiment, the RF transceiver may comprise two RF modules (not shown) . A first RF module is used for transmitting and receiving on one frequency band, and the other RF module is used for different frequency bands transmitting and receiving which is different from the first transmitting and receiving. RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functional modules to perform features in UE. Memory stores program instructions and data to control the operations of mobile station. UE also includes multiple function modules that carry out different tasks in accordance with embodiments of the current invention.

A RRC State controller, which controls UE RRC state according to network’s command and UE conditions. RRC supports the following states, RRC_IDLE, RRC_CONNECTED and RRC_INACTIVE.

A DRB controller, which controls to establish/add, reconfigure/modify and release/remove a DRB based on different sets of conditions for DRB establishment, reconfiguration and release. A protocol stack controller, which manage to add, modify or remove the protocol stack for the DRB. The protocol Stack includes SDAP, PDCP, RLC, MAC and PHY layers.

In one embodiment, the SDAP layer supports the functions of transfer of data, mapping between a QoS flow and a DRB, marking QoS flow ID, reflective QoS flow to DRB mapping for the UL SDAP data PDUs, etc.

In one embodiment, the PDCP layer supports the functions of transfer of data, maintenance of PDCP SN, header compression and decompression using the ROHC protocol, ciphering and deciphering, integrity protection and integrity verification, timer based SDU discard, routing for split bearer, duplication, re-ordering and in-order delivery; out of order delivery and duplication discarding.

In one embodiment, the RLC layer supports the functions of error correction through ARQ, segmentation and reassembly, re-segmentation, duplication detection, re-establishment, etc. In one embodiment, a new procedure for RLC reconfiguration is performed, which can reconfigure the RLC entity to associated to one or two logical channels.

In one embodiment, the MAC layer supports the following functions: mapping between logical channels and transport channels, multiplexing/demultiplexing, HARQ, radio resource selection, etc. In one embodiment, there is one MAC entity to support L1/L2 inter-cell mobility with beam management. In one embodiment, the MAC entity controls two TAGs associated to the first cell and the second cell respectively. In one embodiment, the two TAGs are pTAGs. In one embodiment, there is two MAC entities to support L1/L2 inter-cell mobility with beam management. The MAC entities are associated to the first and the second cell respectively. Two TAGs of the MAC entities are associated to the first cell and the second cell respectively. In one embodiment, the two TAGs are pTAGs, belonging to two different cell group (CG) . In one embodiment, the first cell is the source cell and the second cell is the target cell. In one embodiment, UE is switched back-and-forth between the first and second cell. If UE is switched back from the second cell to the first cell, the second cell is considered as source cell and the first cell is considered as the target cell. The UL time alignment status of the first and the second cell is controlled by the TAT of the associated TAG. In one embodiment, multiple candidate cells belonging to multiple TAGs are configured for the UE. UE maintains the UL time alignment of the TAGs for the candidate cells configured.

Similarly, gNB2 has an antenna, which transmits and receives radio signals. A RF transceiver, coupled with the antenna, receives RF signals from antenna, converts them to baseband signals, and sends them to processor. RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functional modules to perform features in gNB2. Memory stores program instructions and data to control the operations of gNB2. gNB2 also includes multiple function modules that carry out different tasks in accordance with embodiments of the current invention.

A RRC State controller, which performs access control for the UE.

A DRB controller, which controls to establish/add, reconfigure/modify and release/remove a DRB based on different sets of conditions for DRB establishment, reconfiguration and release. A protocol stack controller, which manage to add, modify or remove the protocol stack for the DRB. The protocol Stack includes RLC, MAC and PHY layers In one embodiment, the MAC entity controls two TAGs associated to the first cell and the second cell respectively. In one embodiment, the MAC entity control one TAG associated to the first or the second cell. In one embodiment the MAC entity controls multiple TAGs associated to multiple candidate cells. In one embodiment, the TAGs are pTAGs.

Figure 2 illustrates an exemplary NR wireless system with centralization of the upper layers of the NR radio stacks in accordance with embodiments of the current invention. Different protocol split options between Central Unit and lower layers of gNB nodes may be possible. The functional split between the Central Unit and lower layers of gNB nodes may depend on the transport layer. Low performance transport between the Central Unit and lower layers of gNB nodes can enable the higher protocol layers of the NR radio stacks to be supported in the Central Unit, since the higher protocol layers have lower performance requirements on the transport layer in terms of bandwidth, delay, synchronization and jitter. In one embodiment, SDAP and PDCP layer are located in the central unit, while RLC, MAC and PHY layers are located in the distributed unit.

Figure 3 illustrates an exemplary deployment scenario for intra-DU inter-cell beam management in accordance with embodiments of the current invention. A CU (Central Unit) is connected to two DUs (Distributed Unit) through the F1 interface, and two DUs are connected to multiple RUs respectively. A cell may consist of a range covered by one or more RUs under the same DU. In this scenario, a UE is moving from the edge of one cell to another cell, which two belong to the same DU and share a common protocol stack. Intra-DU inter-cell beam management can be used in this scenario to replace the legacy handover process to reduce the interruption and improve the throughput of UE. In one embodiment, single protocol stack at the UE side (common RLC/MAC) is used to handle L1/L2 inter-cell beam management with mobility.

Figure 4 illustrates an exemplary deployment scenario for inter-DU inter-cell beam management in accordance with embodiments of the current invention. A CU (Central Unit) is connected to two DUs (Distributed Unit) through the F1 interface, and two DUs are connected to multiple RUs respectively. A cell may consist of a range covered by one or more RUs under the same DU. In this scenario, a UE is moving from the edge of one cell to another cell, which two belong to different DUs and share a common CU. The low layer user plane (RLC, MAC) is different in two DUs while high layer (PDCP) remains the same. Inter-DU inter-cell beam management can be used in this scenario to replace the legacy handover process to reduce the interruption and improve the throughput of UE. In one embodiment, single protocol stack at the UE side (common RLC/MAC) is used to handle L1/L2 inter-cell beam management with mobility. In one embodiment, dual protocol stack at the UE side (separate RLC/MAC) are used to handleL1/L2 inter-cell beam management with mobility.

Figure 5 illustrate an exemplary process for UE to partial reset MAC entity and maintain the TAG from the source cell if single stack is used at the UE side in accordance with embodiments of the current invention. In one embodiment, the cell switch is performed within the same DU. In one embodiment, the cell switch is performed across different DUs. UE may receive the inter-cell beam management indication when approaching a neighbor cell. In one embodiment, the UE is configured to use inter-cell beam management single-stack for inter-cell beam management. In one embodiment, the inter-cell beam management indication is a MAC Control Element (MAC CE) . When receiving the inter-cell beam management indication, UE creates one TAG for the target cell , resets MAC entity except keeping the TAG and maintain the associated TAT of the source cell, , and re-establishes the RLC entity and switch to the target cell. The TAG of the source cell will be maintained and the TAT keeps running until it expires.

Figure 6 illustrate an exemplary process for UE to create a new MAC entity and maintain the source MAC entity if dual stack is used in accordance with embodiments of the current invention. In one embodiment, the cell switch is performed across different DUs. UE may receive the inter-cell beam management indication when approaching a neighbor cell. In one embodiment, the UE is configured to use dual-stack for inter-cell beam management. In one embodiment, the inter-cell beam management indication is a MAC Control Element (MAC CE) . In one embodiment, UE create a new MAC entity for the target cell in the pre-configuration before the inter-cell beam management indication. When receiving the inter-cell beam management indication, UE switches to the target cell with the new MAC entity for data transmission/reception. The TAG of the source cell will be maintained and the TAT keeps running until the it expires.

Figure 7A-7C illustrate exemplary processes of UE to keep the TAG for source cell and perform random access (RA) at the first access to target cell and skip the RA procedure when switch back to source cell and switch again to target cell in accordance with embodiments of the current invention. In one embodiment, the cell switches are intra-DU cell switch. In one embodiment, the cell switches are inter-DU cell switch. In one embodiment, the cell switches are based on single-stack based inter-cell beam management. In one embodiment, the cell switches are based on dual-stack based inter-cell beam management.

Figure 7A illustrates an exemplary process of UE to switch to the target cell at the first time and perform random access to the target cell while keep the TAG of source cell in accordance with embodiments of the current invention. When receiving the inter-cell beam management indication, UE performs RA procedure towards the second cell. Meanwhile, the TAG of the source (first) cell is maintained, and TAT of the TAG keeps running. The second cell is considered as the source cell after RA procedure is successfully completed.

Figure 7B illustrates an exemplary process of UE to switch back to the first cell and skip the RA procedure while keep the TAG of the second cell in accordance with embodiments of the current invention. UE may receive the inter-cell beam management indication from the network to switch back to the first cell according to the L1 measurement report. The second cell is considered as the source cell and the first cell is considered as the target cell, since UE relies on the second cell for communication with the network. When receiving the inter-cell beam management indication to switch back to the first cell, UE keep the TAG for the source (second) cell and check the TAG of the target (second) cell. In one embodiment, UE skips the RA procedure towards the target (first) cell when the associated TAT is running. Then UE switches to the target (first) cell. Meanwhile, the TAG of the source (second) cell is maintained, and TAT of the TAG keeps running.

Figure 7C illustrates an exemplary process of UE to switch again to the second cell and skip the RA procedure while keep the TAG of the first cell in accordance with embodiments of the current invention. UE may receive the inter-cell beam management indication from the network to switch again to the second cell according to the L1 measurement report. The second cell is considered as the target cell and the first cell is considered as the source cell, since UE relies on the first cell for communication with the network. When receiving the inter-cell beam management indication to switch again, UE keep the TAG for the source (first) cell and check the TAG for the target (second) cell. In one embodiment, UE skip the RA procedure towards the target (second) cell when the associated TAT is running. Then UE switches to the target (second) cell. Meanwhile, the TAG of the source (first) cell is maintained, and TAT of the TAG keeps running as it is.

Figure 8 illustrate an exemplary overall flow of inter-cell beam management in accordance with embodiments of the current invention. Pre-configuration is provided first by network before the inter-cell beam management is executed. Network provides the pre-configuration and prepares the target/candidate cell according to UE measurement. In one embodiment, the pre-configuration is performed by RRC reconfiguration message. In one embodiment, UE creates a TAG for the target cell when receiving the RRC configuration for the second cell. In one embodiment, UE creates a TAG for the target cell upon reception of the inter-cell beam management indication. In one embodiment, UE creates a new MAC entity for the target cell when receiving the RRC configuration for the second cell. After the pre-configuration, UE sends L1 measurement report to the network. If an inter-cell beam management indication is received, UE keeps the TAG for the source cell and check the TAT for the TAG associated to the target cell. In one embodiment, if TAT of the TAG associated to the target cell is not running, UE performs random access procedure toward the target cell. If TAT of the TAG associated to the target cell is running, UE skips RA procedure and switched to the target cell upon reception of the inter-cell beam management indication.

Figure 9 illustrates an exemplary flowchart for UE to perform inter-cell beam management in accordance with embodiments of the current invention. In one embodiment, the cell switch is performed within the same DU. In one embodiment, the cell switch is performed across different DUs. Before the cell switch, UE receive the RRC reconfiguration for the pre-configuration of the cell switch and creates a TAG for the target cell. UE report L1 measurement to the network after the pre-configuration. When UE receive the inter-cell beam management indication, UE perform partial MAC reset while keep the TAG of source cell and maintain the associated TAT. Then UE check the TAT of the TAG associated to the target cell. In one embodiment, UE access the target cell at the first time, or the TAT of the TAG associated to the target cell is not running. Then UE perform random access toward the target cell. UE switch to the target cell after the RA success. If TAT of the TAG of the target cell is running, UE skips the RA procedure and switch to the target cell directly.

It is understood that the specific order or hierarchy of blocks in the processes /flowcharts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes /flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.

Claims

A method to control TA acquisition through random access for a UE when performing inter-cell beam management and switching between a first cell and a second cell, comprising the steps of:

Creating a TAG for the second cell when receiving the RRC configuration for the second cell;

Keeping the TAG and maintaining the associated TAT of the first cell;

Receiving an inter-cell beam management indication to switch the cell from the first cell to the second, or vice versa;

Determining whether to perform random access procedure to acquire TA of the switched cell.
The method of claim 1, wherein the first cell is the source cell and the second cell is the target cell.
The method of claim 1, wherein the TAG of the first cell is created when the RRC configuration for the first cell is received.
The method of claim 1, wherein the UE performs RA procedure towards the second cell when the very first inter-cell beam management indication to switch to the second cell is received.
The method of claim 1, wherein the first cell and the second cell belong to the same cell group.
The method of claim 5, further comprising performing partial MAC reset and stopping all timers except the TAT associated to the TAG of the first cell upon reception of the beam management indication.
The method of claim 1, wherein the first cell and the second cell belong to different cell group.
The method of claim 7, further comprising creating a MAC entity for the second cell upon receiving the RRC configuration.
The method of claim 1, wherein the inter-cell beam management indication indicating whether the UE is switched to the first or the second cell.
The method of claim 7, wherein UE performs RA procedure towards the indicated cell if the TAT of the associated TAG is not running.
The method of claim 7, wherein UE skips RA procedure and resumes UL transmission towards the indicated cell if the TAT of the associated TAG is running.
The method of claim 1, wherein the UL TAs for the TAGs of the first cell and the second cell are maintained independently.
The method of claim 10, wherein the TAT of the TAG of the first cell keeps running as it is if the TAT of the TAG of the second cell expires.
The method of claim 10, wherein the TAT of the TAG of the second cell keeps running as it is if the TAT of the TAG of the first cell expires.