Patent Application
20250106708
The teachings in accordance with the exemplary embodiments of this invention relate generally to RACH-less handover operations and, more specifically, relate to RACH-less handover operations including where a serving distributed unit informs target distributed unit via a central unit about a target reference signal index X/indices X1 . . . Xn that shall be used for PDCCH transmission or PUSCH reception.
This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Certain abbreviations that may be found in the description and/or in the Figures are herewith defined as follows:
Fifth generation mobile networks must address substantial growth of traffic load, connected devices, and provide reliability and also reduce latency. Particularly, mobility such as via handovers is essential for achieving low handover latency. However, current networks can require synchronous base stations for handovers based on random access which can add latency. To try to address this RACH-less handover operations have been introduced.
The RACH-less handover operations offer significant reductions in the data connectivity interruption time at each handover, no need for random access in the target cell, and reduced overall handover execution time.
Example embodiments of the invention work to improve handover mechanisms with new operations for RACH-less handover schemes.
The above and other aspects, features, and benefits of various embodiments of the present disclosure will become more fully apparent from the following detailed description with reference to the accompanying drawings, in which like reference signs are used to designate like or equivalent elements. The drawings are illustrated for facilitating better understanding of the embodiments of the disclosure and are not necessarily drawn to scale, in which:
In this invention, there is proposed for a RACH-less handover operations including where a serving distributed unit informs target distributed unit via a central unit about a target reference signal index X/indices X1 . . . Xn that shall be used for PDCCH transmissions or PUSCH receptions.
Example embodiments of the invention as disclosed herein relates to L1/2 inter-cell mobility, which is one of the upcoming objectives for mobility enhancement at the time of this application. In contrast to L3 mobility procedures where the handover between two cells is decided by RRC layer, L1/2 inter-cell mobility is performed by the MAC layer terminated in the Distributed Unit.
In the example embodiments of the invention there is a focus on executing the cell change for L1/2 inter-cell mobility in a RACH-less manner. RACH-less handover was designed with LTE Rel-14. Its main goal was to decrease the interruption encountered by the UE during handover by skipping the first two steps of the Random-Access procedure.
In this application there is provided first an overview of L1/2 inter-cell mobility. Then, there is review RACH-less handover procedure which is specified in LTE and discussed for NR in Rel. 16 and TCI states that are used in beam management (beam switching).
L1/2 inter-cell mobility is one of the upcoming objectives for mobility enhancement in Rel. 18. In contrast to L3 mobility procedures where the handover between two cells is decided by RRC layer, L1/2 inter-cell mobility is performed by the MAC layer terminated in the Distributed Unit (DU).
There are two options for RACH-less HO to obtain an UL grant when applied to L1/2 inter-cell mobility:
Both options have shortcomings when applied to L1/2 inter-cell mobility.
Some main steps of L1/2 inter-cell mobility are summarized in the following:
Further, it is noted that 3GPP definitions for components pertaining to this application can include:
RACH-less HO has been discussed for NR beamformed system at the time of this application but was not specified. Now at the time of this application mobility enhancement is re-considered for L1/2 inter-cell mobility.
It is noted that the term en-gNB is for a node providing NR user plane and control plane protocol terminations towards the UE, and acting as Secondary Node in EN-DC. In addition, that a gNB is a node or base station providing NR user plane and control plane protocol terminations towards the UE, and connected via the NG interface to the 5GC.
RACH-less handover (HO) was designed as a part of LTE Rel-14 [TS 36.300]. Its main goal was to decrease the interruption encountered by the UE during handover by skipping the first two steps of the Random-Access procedure (transmission of RACH preamble and receiving RACH Response (RAR)) and sending RRC Reconfiguration Complete directly after the reception of the handover command from the network. In order to make it possible, the following challenges had to be addressed (all applicable for the target cell):
The LTE Rel-14 RACH-less HO solution addressed these issues as follows:
RACH-less HO has been discussed for NR beamformed system in Rel. 16 but was not specified. Herein, Quasi-co Location (QCL) information of the PUSCH grant has been discussed for Option 1. For instance, a PUSCH grant is QCL with a specific RS index (SSB or CSI-RS) if the transmission of RS index (from network side) shares the same channel properties (doppler shift, doppler spread, average delay, delay spread, spatial RX parameter) as the received signal (payload) on PUSCH grant. Similarly, for Option 2, a PDCCH transmission from a (target) cell is QCL with a specific RS (SSB or CSI-RS) if the reception of RS index (from UE side) shares the same channel properties as the reception of PDCCH signal.
TCI states defines the Quasi Co-Location (QCL) information for receiving the PDCCH or PDSCH signal. In particular, TCI state indicates for the UE the RS index (SSB index or CSI-RS index) for which the channel information(s) (doppler shift, doppler spread, average delay, delay spread, spatial RX parameter) apply for receiving PDCCH or PDSCH signals. The TCI states are configured to the UE by CU using an RRC Reconfiguration message. For triggering a beam switch within the same cell, the MAC layer of the serving base station updates the TCI-state ID (which is associated with a particular RS index). For instance, if the UE was using the QCL information of SSB index 1 (associated with TCI state ID 1) to receive/transmit (to the serving cell), the UE needs to start using QCL information of for example SSB index 2 (associated with TCI state 2) if the MAC CE sent by the DU contains TCI State ID 2.
In standards at the time of this application for mobility enhancement RACH-less execution of cell change is re-considered for L1/2 inter-cell mobility. Example embodiments of the invention focus on executing the cell change for L1/2 inter-cell mobility (step 11 of
Here, there are explained issues that are associated with the two LTE options for obtaining an UL grant when applied to L1/2 inter-cell mobility.
The signaling diagram for Option 1 is shown in
The relevant steps of
The disadvantages of this approach are summarized in the following:
The signaling diagram for Option 2 is shown in
In this option 2, the UE needs to monitor the PDCCH transmission from the target cell in step 13 to receive the UL grant for sending RRC Reconfiguration Complete message in step 14.
The issues with this approach are the following:
As such, both options 1 and 2 for RACH-less HO have shortcomings when applied to L1/2 inter-cell mobility.
To improve the handling example embodiments of this invention proposes two new methods:
One target for example embodiments of the invention is for standards at the time of this application when L1/2 centric mobility will be defined.
A main novel step of example embodiments of the invention is that serving DU informs target DU via the CU about the target RS index X/indices X1 . . . Xn that shall be used for PDCCH transmission or PUSCH reception.
Before describing the example embodiments of the invention in detail, reference is made to
The UE 10 includes one or more processors DP 10A, one or more memories MEM 10B, and one or more transceivers TRANS 10D interconnected through one or more buses. Each of the one or more transceivers TRANS 10D includes a receiver and a transmitter. The one or more buses may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, and the like. The one or more transceivers TRANS 10D which can be optionally connected to one or more antennas for communication to NN 12 and NN 13, respectively. The one or more memories MEM 10B include computer program code PROG 10C. The UE 10 communicates with NN 12 and/or NN 13 via a wireless link 11.
The NN 12 (NR/5G Node B, an evolved NB, or LTE device) is a network node such as a master or secondary node base station (e.g., for NR or LTE long term evolution) that communicates with devices such as NN 13 and UE 10 of
The NN 13 can be associated with a mobility function device such as an AMF or SMF, further the NN 13 may comprise a NR/5G Node B or possibly an evolved NB a base station such as a master or secondary node base station (e.g., for NR or LTE long term evolution) that communicates with devices such as the NN 12 and/or UE 10 and/or the wireless network 1. The NN 13 includes one or more processors DP 13A, one or more memories MEM 13B, one or more network interfaces, and one or more transceivers TRANS 13D interconnected through one or more buses. In accordance with the example embodiments these network interfaces of NN 13 can include X2 and/or Xn interfaces for use to perform the example embodiments of the invention. Each of the one or more transceivers TRANS 13D includes a receiver and a transmitter that can optionally be connected to one or more antennas. The one or more memories MEM 13B include computer program code PROG 13C. For instance, the one or more memories MEM 13B and the computer program code PROG 13C are configured to cause, with the one or more processors DP 13A, the NN 13 to perform one or more of the operations as described herein. The NN 13 may communicate with another mobility function device and/or eNB such as the NN 12 and the UE 10 or any other device using, e.g., link 11 or another link. The Link 14 as shown in
The one or more buses of the device of
It is noted that although
Also, it is noted that description herein indicates that “cells” perform functions, but it should be clear that the gNB that forms the cell and/or a user equipment and/or mobility management function device that will perform the functions. In addition, the cell makes up part of a gNB, and there can be multiple cells per gNB.
The wireless network 1 or any network it can represent may or may not include a NCE/MME/SGW/UDM/PCF/AMF/SMF 14 that may include (NCE) network control element functionality, MME (Mobility Management Entity)/SGW (Serving Gateway) functionality, and/or serving gateway (SGW), and/or MME (Mobility Management Entity) and/or SGW (Serving Gateway) functionality, and/or user data management functionality (UDM), and/or PCF (Policy Control) functionality, and/or Access and Mobility Management Function (AMF) functionality, and/or Session Management (SMF) functionality, and/or Authentication Server (AUSF) functionality and which provides connectivity with a further network, such as a telephone network and/or a data communications network (e.g., the Internet), and which is configured to perform any 5G and/or NR operations in addition to or instead of other standard operations at the time of this application. The NCE/MME/SGW/UDM/PCF/AMF/SMF 14 is configurable to perform operations in accordance with example embodiments of the invention in any of an LTE, NR, 5G and/or any standards based communication technologies being performed or discussed at the time of this application. In addition, it is noted that the operations in accordance with example embodiments of the invention, as performed by the NN 12 and/or NN 13, may also be performed at the NCE/MME/SGW/UDM/PCF/AMF/SMF 14.
The NCE/MME/SGW/UDM/PCF/AMF/SMF 14 includes one or more processors DP 14A, one or more memories MEM 14B, and one or more network interfaces (N/W I/F(s)), interconnected through one or more buses coupled with the link 13 and/or 14. In accordance with the example embodiments these network interfaces can include X2 and/or Xn interfaces for use to perform the example embodiments of the invention. The one or more memories MEM 14B include computer program code PROG 14C. The one or more memories MEM 14B and the computer program code PROG 14C are configured to, with the one or more processors DP 14A, cause the NCE/MME/SGW/UDM/PCF/AMF/SMF 14 to perform one or more operations which may be needed to support the operations in accordance with the example embodiments of the invention.
The wireless Network 1 may implement network virtualization, which is the process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Network virtualization involves platform virtualization, often combined with resource virtualization. Network virtualization is categorized as either external, combining many networks, or parts of networks, into a virtual unit, or internal, providing network-like functionality to software containers on a single system. Note that the virtualized entities that result from the network virtualization are still implemented, at some level, using hardware such as processors DP10, DP12A, DP13A, and/or DP14A and memories MEM 10B, MEM 12B, MEM 13B, and/or MEM 14B, and also such virtualized entities create technical effects.
The computer readable memories MEM 12B, MEM 13B, and MEM 14B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The computer readable memories MEM 12B, MEM 13B, and MEM 14B may be means for performing storage functions. The processors DP10, DP12A, DP13A, and DP14A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples. The processors DP10, DP12A, DP13A, and DP14A may be means for performing functions, such as controlling the UE 10, NN 12, NN 13, and other functions as described herein.
In accordance with an example embodiment of the invention as described above there is an apparatus comprising: means for receiving (TRANS 12D and/or TRANS 13D, MEM 12B and/or MEM 13B, PROG 12C and/or PROG 13C, and DP 12A and/or DP 13A as in
As similarly stated above one main novel step of example embodiments of the invention is that serving DU informs target DU via the CU about the target RS index X/indices X1 . . . Xn that shall be used for PDCCH transmission or PUCCH reception.
In example embodiments of this invention, there is proposed a first method in accordance with example embodiments of the invention (Method 1, building enhancements on top of Option 2,
To improve the reliability of PDCCH reception at the UE side, Method 1 can be enhanced with the following embodiments/aspects in accordance with example embodiments of the invention:
In addition, another method 2 (building on top of Option 1,
When receiving a request to prepare a UE configuration in a candidate target cell, the DU provides the configuration of the periodic UL grants, where each UL is QCL with a RS index, but does not reserve radio resources for these UL grants until a notification is received from the serving cell:
An advantage of this approach compared to Method 1 is that the network saves the signalling of PDCCH transmission at the expense of either 1) additional complexity for configuring the timer T in case the notification is sent at the time of cell change or 2) higher radio resource reservation if the notification is sent before the handover.
In addition, it is noted that an approximate value of 8-10 ms can be considered as the average RTT (Round trip time) over the F1 interface.
In one embodiment, the notification from DU 1 to DU 2 (step 12/13) may be also delivered using a control PDU which is faster than normal F1 messages as it avoids encoding/decoding at CU.
In another embodiment, step 12 and 13 might be performed earlier than or at the same time with step 11 depending on the F1 interface RTT.
In one embodiment, the PDCCH transmissions of step 17 and 19 of
In another embodiment, the location of UL grants (in terms of time/frequency radio resources) may depend on the RS index that is QCL with the PDCCH transmission. The offset locations for each RS index may be pre-configured by the target cell as part of step 6 and 8 messages. Herein, the PDCCH transmissions providing UL grant in step 17 and 19 point to the same reference location of the UL grant. The final location of the UL grant is obtained by the UE by adding the corresponding offset location to the reference location.
The signaling diagram for Method 2 in accordance with example embodiments of the invention is shown in
In operations of the method 2, when receiving a request to prepare a UE configuration in a candidate target cell, the target DU provides the configuration of the periodic UL grants, where each UL is QCL with a RS index, but does not reserve radio resources for these UL grants until a notification is received from the serving cell. For this a new timer is introduced at the UE, which guarantees, that the UE uses the UL grant to send RRC Reconfiguration Complete not before this time duration has elapsed.
The time duration T must be long enough to ensure that the target node receives the notification from the serving cell over F1 interfaces and reserve the radio resources for the UL grants.
In accordance with the example embodiments as described in the paragraph above, wherein the serving cell controlled by the distributed unit of the serving cell sends a medium access control-control element or layer 1 message to the user equipment to trigger a cell change indicating to the user equipment a transmission configuration indication state change to at least one target reference signal index X for reception of the at least one physical downlink control channel transmission or transmission on the at least one physical uplink shared channel.
In accordance with the example embodiments as described in the paragraphs above, wherein the serving cell indicates to the user equipment using the medium access control-control element or layer 1 message, the transmission configuration indication state change to multiple target reference signal indices X1, X2, . . . , XN for reception of the at least one physical downlink control channel transmissions or transmission on the at least one physical uplink shared channel.
In accordance with the example embodiments as described in the paragraphs above, wherein the serving cell informs the target distributed unit via the central unit about the at least one target reference signal index X that shall be used for at least one physical downlink control channel transmission or at least one physical uplink shared channel reception.
In accordance with the example embodiments as described in the paragraphs above, wherein the central unit is associated with a distributed unit of the target cell.
In accordance with the example embodiments as described in the paragraphs above, wherein the layer 1 serving cell change command comprises at least one of a medium access control-control element or a layer 1 message.
In accordance with the example embodiments as described in the paragraphs above, wherein the at least one memory and computer program code is configured with the at least one processor to cause the apparatus to: receive from the central unit information comprising at least one configuration of periodic uplink grants for the physical uplink shared channel transmissions, where each uplink grant is quasi co-located with the at least one target reference signal index, wherein the target cell preparation does not involve reserving radio resources for the uplink grants.
A non-transitory computer-readable medium (MEM 12B and/or MEM 13B as in
In accordance with an example embodiment of the invention as described above there is an apparatus comprising: means for sending (TRANS 12D and/or TRANS 13D, MEM 12B and/or MEM 13B, PROG 12C and/or PROG 13C, and DP 12A and/or DP 13A as in
In the example aspect of the invention according to the paragraph above, wherein at least the means for sending comprises a non-transitory computer readable medium [MEM 12B and/or MEM 13B] encoded with a computer program [PROG 12C and/or PROG 13C] executable by at least one processor [DP 12A and/or 13A].
In accordance with the example embodiments as described in the paragraph above, wherein the configuration information comprises the at least one target reference signal index that shall be used for the physical downlink control channel transmissions or the physical uplink shared channel reception.
In accordance with the example embodiments as described in the paragraphs above, wherein the at least one non-transitory memory including the computer program code is configured with the at least one processor to cause the apparatus to: based on the received signaling one of: set a transmit beam according to the at least one target reference signal index and perform the physical downlink control channel transmissions, or set a receive beam according to the at least one target reference signal index and perform the physical uplink shared channel reception.
In accordance with the example embodiments as described in the paragraphs above, wherein based on receiving the signaling comprising configuration information the distributed unit of a target cell sets a transmit beam according to the at least one target reference signal index and performs the physical downlink control channel transmissions correspondingly.
In accordance with the example embodiments as described in the paragraphs above, wherein the target cell selects a beam based on a physical uplink shared channel location where the radio resource control reconfiguration complete message is received.
In accordance with the example embodiments as described in the paragraphs above, wherein the at least one non-transitory memory including the computer program code is configured with the at least one processor to cause the distributed unit of the target cell to: based on receiving a request from the central unit to prepare a user equipment configuration in a candidate target cell, provide configuration of periodic uplink grants to the user equipment.
In accordance with the example embodiments as described in the paragraphs above, wherein each uplink grant is quasi co-located with a reference signal index.
In accordance with the example embodiments as described in the paragraphs above, wherein the at least one memory and computer program code is configured with the at least one processor to cause the apparatus to: configure a timer value controlling the validity of uplink grant after triggering of the layer 1 based serving cell change.
In accordance with the example embodiments as described in the paragraphs above, wherein the configuration of periodic uplink grants is not reserving radio resources for these uplink grants until a notification is received from the serving cell.
In accordance with the example embodiments as described in the paragraphs above, including sending towards the central unit of the network node, information comprising at least one configuration of periodic uplink grants for the physical uplink shared channel transmissions, where each uplink grant is quasi co-located with the at least one target reference signal index, wherein the target cell preparation does not involve reserving radio resources for the uplink grants.
A non-transitory computer-readable medium (MEM 12B and/or MEM 13B as in
In accordance with an example embodiment of the invention as described above there is an apparatus comprising: means for receiving (TRANS 12D and/or TRANS 13D, MEM 12B and/or MEM 13B, PROG 12C and/or PROG 13C, and DP 12A and/or DP 13A as in
In the example aspect of the invention according to the paragraph above, wherein at least the means for receiving comprises a non-transitory computer readable medium [MEM 12B and/or MEM 13B] encoded with a computer program [PROG 12C and/or PROG 13C] executable by at least one processor [DP 12A and/or 13A].
In accordance with the example embodiments as described in the paragraph above, wherein the layer 1 serving cell change command comprises at least one of a medium access control-control element or a layer 1 message.
In accordance with the example embodiments as described in the paragraphs above, wherein the layer 1 serving cell change command comprises at least one least one target reference signal index that shall be used for physical downlink control channel reception or physical uplink shared channel transmission.
In accordance with the example embodiments as described in the paragraphs above, wherein the configuration of periodic uplink grants for the physical uplink shared channel transmissions is quasi co-located with reference signal indexes that are indicated by one of the source or target distributed unit.
In accordance with the example embodiments as described in the paragraphs above, wherein after receiving the at least one of a medium access control-control element or a layer 1 message the user equipment uses the quasi co-located reference signal index with a strongest layer 1 beam measurement for physical downlink control channel reception or physical uplink shared channel transmission.
A non-transitory computer-readable medium (MEM 10B as in
In accordance with an example embodiment of the invention as described above there is an apparatus comprising: means for receiving (TRANS 10D, MEM 10B, PROG 10C, DP 10A) by a user equipment (UE 10 as in
In the example aspect of the invention according to the paragraph above, wherein at least the means for receiving and selecting comprises a non-transitory computer readable medium [MEM 10B] encoded with a computer program [PROG 10C] executable by at least one processor [DP 10A].
Further, in accordance with example embodiments of the invention there is circuitry for performing operations in accordance with example embodiments of the invention as disclosed herein. This circuitry can include any type of circuitry including content coding circuitry, content decoding circuitry, processing circuitry, image generation circuitry, data analysis circuitry, etc.). Further, this circuitry can include discrete circuitry, application-specific integrated circuitry (ASIC), and/or field-programmable gate array circuitry (FPGA), etc. as well as a processor specifically configured by software to perform the respective function, or dual-core processors with software and corresponding digital signal processors, etc.).
Additionally, there are provided necessary inputs to and outputs from the circuitry, the function performed by the circuitry and the interconnection (perhaps via the inputs and outputs) of the circuitry with other components that may include other circuitry in order to perform example embodiments of the invention as described herein.
In accordance with example embodiments of the invention as disclosed in this application this application, the “circuitry” provided can include at least one or more or all of the following:
In accordance with example embodiments of the invention, there is adequate circuitry for performing at least novel operations as disclosed in this application, this ‘circuitry’ as may be used herein refers to at least the following:
This definition of ‘circuitry’ applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term “circuitry” would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term “circuitry” would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or other network device.
In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described in this Detailed Description are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims.
The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the best method and apparatus presently contemplated by the inventors for carrying out the invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention.
It should be noted that the terms “connected,” “coupled,” or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are “connected” or “coupled” together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be “connected” or “coupled” together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non-limiting and non-exhaustive examples.
Furthermore, some of the features of the preferred embodiments of this invention could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the invention, and not in limitation thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202141059410 | Dec 2021 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/086417 | 12/16/2022 | WO |
