Method and apparatus for performing initial beam alignment during a random access procedure

Abstract

The present disclosure relates to a communication method and system for merging a 5th generation (5G) communication system for supporting higher data rates beyond the 4th generation (4G) system with a technology for the Internet of Things (IoT). The present disclosure can be applied to smart services based on 5G communication technology and technology related to IoT, such as smart homes, smart buildings, smart cities, smart cars, connected cars, health care, digital education, smart retail, security and safety services. Embodiments herein disclose a method and system for performing initial beam alignment by a user equipment (UE) during a random access (RACH) procedure.

Description

[0001] This application is a divisional application of a patent application with an application date of March 22, 2018, application number 201880019763.7, and invention name “Method and user equipment for performing initial beam alignment during a random access (RACH) process”. Technical Field

[0002] The present invention relates to a wireless communication system, and more particularly to a method and a user equipment (UE) for performing initial beam alignment during a random access (RACH) procedure. Background Art

[0003] In order to meet the needs of wireless data services that have increased due to the deployment of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also called 'super 4G networks' or 'post-LTE systems'. 5G communication systems are considered to be implemented in higher frequency bands (millimeter waves), such as 60GHz bands, to achieve higher data rates. In order to reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple input multiple output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna technology are discussed in 5G communication systems. In addition, in 5G communication systems, the development of system network improvements is being carried out based on advanced small cells, cloud radio access networks (RAN), ultra-dense networks, device-to-device (D2D) communications, wireless backhaul, mobile networks, cooperative communications, coordinated multi-point (CoMP), receiving-end interference elimination, etc. In 5G systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coding modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) have been developed as advanced access technologies.

[0004] The Internet, as a human-centered connectivity network where humans generate and consume information, has now developed into the Internet of Things (IoT), in which distributed entities such as objects exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of IoT technology and big data processing technology through connection with a cloud server, has emerged. Since technical elements such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology" and "security technology" are already required for IoT implementation, sensor networks, machine-to-machine (M2M) communication, machine type communication (MTC), etc. have been studied recently. This IoT environment can provide intelligent Internet technology services that create new value for human life by collecting and analyzing data generated among connected objects. IoT can be applied to various fields, including smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, health care, smart instruments and advanced medical services through aggregation and combination between existing information technology (IT) and various industrial applications.

[0005] In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine type communications (MTC), and machine-to-machine (M2M) communications can be implemented through beamforming, MIMO, and array antennas. It can also be considered that the application of a cloud radio access network (RAN) as the above-mentioned big data processing technology is an example of the convergence between 5G technology and IoT technology.

[0006] In recent years, several broadband wireless technologies have been developed to meet the increasing number of broadband users and to provide more and better applications and services. The second generation wireless communication system has been developed to provide voice services while ensuring the mobility of users. The third generation wireless communication system supports not only voice services but also data services. In recent years, the fourth generation wireless communication system has been developed to provide high-speed data services. However, at present, the fourth generation wireless communication system is subject to the lack of resources to meet the needs of the growing high-speed data services. In addition, the fourth generation wireless communication system does not have the native support for the emerging applications and services (such as industrial automation) that support very low latency and very high reliability of transmission. Therefore, the fifth generation wireless communication system is being developed to meet the needs of the growing high-speed data services and to support ultra-reliability and low-latency applications.

[0007] The fifth generation wireless communication system will be adopted not only in lower frequency bands but also in higher frequency bands (millimeter waves), for example, in the 10 GHz to 100 GHz band, thereby achieving higher data rates. In order to reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple input multiple output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna technology are being considered in the design of the fifth generation wireless communication system. In addition, the fifth generation wireless communication system is expected to solve different use cases with quite different requirements in terms of data rate, delay, reliability, mobility, etc. However, it is expected that the design of the air interface of the fifth generation wireless communication system will be flexible enough to serve UEs with quite different performance depending on the use cases and market segments of the services provided by the UE to the terminal customers. Example use cases that the fifth generation wireless communication system wireless system is expected to solve are enhanced mobile broadband (eMBB), massive machine type communication (m-MTC), ultra-reliable low latency communication (URLL), etc. eMBB requirements such as data rates of tens of Gbps, low latency, high mobility, etc. address the market segment of traditional wireless broadband users who need Internet connectivity anywhere, anytime, and on the move. m-MTC requirements such as very high connection density, infrequent data transmission, very long battery life, low mobility, etc. address the market segment of Internet of Things (IoT) / Internet of Everything (IoE) connectivity envisioning hundreds of millions of devices. URLL requirements such as very low latency, very high reliability, and variable mobility address the market segment of industrial automation applications, vehicle-to-vehicle / vehicle-to-infrastructure communications envisioned as one of the enablers for autonomous vehicles.

[0008] In the fourth generation wireless communication system, an enhanced Node B (eNB) or base station serves one or more cells on the same frequency or different frequencies. During mobility when a UE moves from one cell to another cell served by the same eNB or a different eNB, the UE reports the signal strength measured for the reference signal of the cell detected by the UE (e.g., a cell-specific reference signal, i.e., CRS in LTE). The serving cell on which the UE is currently serving is called the source cell, and its signal strength becomes weaker when the UE moves toward the border or cell edge of the source cell. One or more neighboring cells to which the UE has reported signal strength measurements, i.e., CRS measurements, are called potential target cells. When the UE moves toward the target cell, the signal strength of one or more potential target cells becomes better than that of the serving cell, and therefore, for service continuity, it is necessary to switch the radio link serving the UE from the source cell to the target cell. The serving eNB based on the CRS measurements reported by the UE for the potential target cell prepares the target eNB so that resources are available in the target eNB when the radio link is switched. This process for handling mobility in which the radio link is switched from the serving cell to the target cell and the target cell becomes the new serving cell of the UE is called a handover process.

[0009] The above information is presented as background information only to help readers understand the present invention. Applicants make no determination or assertion as to whether any of the above may be applied as prior art with respect to the present application. Summary of the invention

[0010] Technical issues

[0011] A method is needed to perform initial beam alignment by a user equipment (UE) during a random access (RACH) procedure.

[0012] Technical Solution

[0013] Therefore, embodiments herein provide a method for performing initial beam alignment by a user equipment (UE) during a random access (RACH) process. The method includes sending a measurement report associated with a target cell to a serving cell in response to a handover event triggered at the UE. The method includes receiving, by the serving cell, a handover command that includes at least a channel state information reference signal (CSI-RS) configuration of the target cell. In addition, the method includes performing downlink (DL) synchronization with the target cell with respect to a synchronization signal (SS) block. In addition, the method includes indicating the best CSI-RS resource identifier to the target cell by measuring a subset of the CSI-RS resources received in the handover command.

[0014] In an embodiment, the measurement report includes at least one of: a measurement of the best SS block, one or more corresponding SS block identifiers associated with the measurement of the target cell and the best CSI-RS resource, and one or more corresponding CSI-RS resource identifiers associated with the target cell, wherein the reported measurement and the associated identifiers are above a preconfigured threshold.

[0015] In an embodiment, indicating the best CSI-RS resource identifier to the target cell by measuring a subset of CSI-RS resources received in a handover command during a RACH process includes identifying a subset of the best SS blocks from measurements of SS blocks associated with the target cell while performing DL synchronization. The method includes determining a subset of CSI-RS resources among the CSI-RS resources received in the handover command based on the identified subset of the best SS blocks. The method includes measuring the determined subset of CSI-RS resources to identify the best CSI-RS resource identifier. In addition, the method includes indicating the best CSI-RS resource identifier to the target cell.

[0016] In an embodiment, measuring the determined subset of CSI-RS resources to identify the best CSI-RS resource identifier includes one of the following: receiving an indication called a CSI request bit and a CSI-RS configuration in response to a preamble transmission on the target cell, wherein, if the CSI request bit is enabled or if the CSI-RS configuration is present, the UE performs measurements on the determined subset of CSI-RS resources to identify at least one best CSI-RS resource identifier, and reports one or more best CSI-RS measurements and one or more associated CSI-RS resource identifiers.

[0017] In an embodiment, the best CSI-RS resource identifier for the target cell is indicated in MSG 3 of the RACH procedure.

[0018] In an embodiment, one or more best CSI-RS measurements and one or more associated CSI-RS resource identifiers are reported to the target cell in a corresponding PUSCH transmission after completion of the RACH procedure.

[0019] Therefore, embodiments herein provide a user equipment (UE) for performing initial beam alignment during a random access (RACH) procedure. The UE is configured to send a measurement report associated with a target cell to a serving cell in response to a handover event triggered at the UE. The UE is configured to receive a handover command including at least a channel state information reference signal (CSI-RS) configuration of the target cell via the serving cell. In addition, the UE is configured to perform downlink (DL) synchronization with the target cell with respect to a synchronization signal (SS) block. In addition, the UE is configured to indicate the best CSI-RS resource identifier to the target cell by measuring a subset of the CSI-RS resources received in the handover command.

[0020] In addition, the embodiments herein provide a method and system in which millimeter wave / centimeter wave bands are considered common scenarios for the deployment of 5G or new radio (NR) systems and therefore the processes are described using the radio characteristics within those bands. However, in actual deployments, the air interface and beamforming techniques of NR can be applied even below the 6 GHz band, so the applicability and processes of the next generation RAT disclosed in this disclosure should not be considered to be strictly limited to millimeter wave / centimeter wave bands. Because the radio characteristics of frequencies in the millimeter wave / centimeter wave bands are different compared to frequencies in the sub-6 GHz bands, it is also expected that the NR system will have native support for beamforming techniques for both broadcast and unicast transmissions to the UE to overcome the short propagation distance of radio signals at millimeter wave / centimeter wave frequencies.

[0021] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and accompanying drawings. However, it should be understood that the following description, while indicating the preferred embodiments and many of their specific details, is given by way of illustration and not limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

[0022] Technical Effects

[0023] A primary object of embodiments herein is to provide a method for performing initial beam alignment during a random access (RACH) procedure by a user equipment (UE).

[0024] Another object of embodiments herein is to provide a method for sending a measurement report associated with a target cell to a serving cell in response to a handover event triggered at a UE.

[0025] Another object of embodiments herein is to provide a method for receiving, by a serving cell, a handover command including at least a channel state information reference signal (CSI-RS) configuration of a target cell.

[0026] Another object of embodiments herein is to provide a method for performing downlink (DL) synchronization with a target cell with respect to a synchronization signal (SS) block.

[0027] It is another object of embodiments herein to provide a method for indicating the best CSI-RS resource identifier to a target cell by measuring a subset of CSI-RS resources received in a handover command.

[0028] Another object of embodiments herein is to measure a subset of CSI-RS resources received in a handover command during a RACH procedure.

[0029] It is another object of embodiments herein to identify a subset of best SS blocks from measurements of SS blocks associated with a target cell while performing DL synchronization.

[0030] Another object of embodiments herein is to determine a subset of CSI-RS resources among the CSI-RS resources received in a handover command based on an identified subset of best SS blocks.

[0031] Another object of embodiments herein is to measure a subset of the determined CSI-RS resources to identify the best CSI-RS resource identifier.

[0032] It is another object of embodiments herein to report one or more best CSI-RS measurements and one or more associated CSI-RS resource identifiers to the target cell in a corresponding PUSCH transmission after completion of a RACH procedure.

[0033] Another object of the embodiments herein is to provide a method and system for handling initial beam alignment during RRC connection establishment so that the Gbps data rate available on the NR physical layer can be achieved by the UE immediately after the RACH procedure for RRC connection establishment is completed.

[0034] Another object of the embodiments herein is to provide a method for handover (HO) based on CSI-RS set 2 configuration.

[0035] Another object of embodiments herein is to provide a method for handover (HO) based on conditional triggering.

[0036] Another object of embodiments herein is to provide a method for CSI-RS set 2 configuration in a handover (HO) command.

[0037] Another object of embodiments herein is to provide a method for CSI-RS set 2 activation in a random access response (RAR) message.

[0038] Another object of embodiments herein is to provide a method for indicating a subset in a RAR from a configured CSI-RS set 2.

[0039] Another object of the embodiments herein is to provide a method for CSI-RS set 2 configuration in RAR.

[0040] Another object of the embodiments herein is to provide a method for CSI-RS set 2 configuration in system information.

[0041] Another object of embodiments herein is to provide a method for CSI-RS set 2 activation with preamble transmission.

[0042] It is another object of embodiments herein to provide a method for CSI-RS set 2 configuration during connection establishment. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention is illustrated in the accompanying drawings, in which the same reference numerals indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the accompanying drawings, in which:

[0044] Figure 1 is an example illustration of a radio access network (RAN) deployment for a next generation wireless system according to embodiments as disclosed herein;

[0045] Figure 2A illustrates a secondary cell mobility scenario for a UE operating in a beamformed 5G system according to an embodiment as disclosed herein;

[0046] Figure 2B is a flow chart illustrating a method for performing initial beam alignment during a random access (RACH) procedure by a user equipment (UE) according to an embodiment as disclosed herein;

[0047] Figure 2C is a flow chart illustrating a method for indicating a best CSI-RS resource identifier to a target cell according to an embodiment as disclosed herein;

[0048] Figure 3 is a sequence diagram depicting a HO procedure in a New Radio (NR) system according to an embodiment as disclosed herein;

[0049] Figure 4 is another sequence diagram depicting a HO procedure in a NR system based on conditional triggering according to an embodiment as disclosed herein;

[0050] Figure 5 is a sequence diagram depicting process messages for CSI-RS based initial beam alignment according to embodiments as disclosed herein;

[0051] Figure 6 is another sequence diagram depicting a process for CSI-RS based initial beam alignment according to embodiments as disclosed herein;

[0052] Figure 7 is yet another sequence diagram depicting a process for CSI-RS based initial beam alignment according to embodiments as disclosed herein;

[0053] Figure 8 is another sequence diagram depicting an initial beam alignment procedure based on CSI-RS configuration in a random access response (RAR) according to embodiments as disclosed herein;

[0054] Fig. 9 is another sequence diagram depicting a process for initial beam alignment based on CSI-RS configuration in system information according to embodiments as disclosed herein;

[0055] Fig.10 is another sequence diagram depicting a process for an initial beam alignment process based on CSI-RS configuration in system information according to an embodiment as disclosed herein;

[0056] Fig.11 is another sequence diagram depicting a process for initial beam alignment during connection setup / establishment according to embodiments as disclosed herein; and

[0057] Fig.12 is a block diagram illustrating various modules of a UE according to embodiments as disclosed herein. DETAILED DESCRIPTION

[0058] The embodiments herein and their various features and beneficial details will be explained more fully with reference to the non-limiting embodiments illustrated in the accompanying drawings and described in detail in the following description. The description of known components and processing techniques is omitted so as not to unnecessarily obscure the embodiments herein. In addition, the various embodiments described herein do not necessarily exclude each other, because certain embodiments can be combined with one or more other embodiments to form new embodiments. The term "or" used herein refers to non-exclusive or, unless otherwise specified. The examples used herein are intended only to promote understanding in a manner that the embodiments herein can be implemented and to further enable those skilled in the art to implement the embodiments herein. Therefore, the examples should not be viewed as limiting the scope of the embodiments herein.

[0059] Embodiments herein implement a method for performing initial beam alignment during a random access (RACH) procedure by a user equipment (UE). The method includes sending a measurement report associated with a target cell to a serving cell in response to a handover event triggered at the UE. The method includes receiving, by the serving cell, a handover command that includes at least a channel state information reference signal (CSI-RS) configuration of the target cell. In addition, the method includes performing downlink (DL) synchronization with the target cell with respect to a synchronization signal (SS) block. In addition, the method includes indicating the best CSI-RS resource identifier to the target cell by measuring a subset of the CSI-RS resources received in the handover command.

[0060] The embodiments for implementing the initial beam alignment during the RACH process herein are explained based on CSI-RS set 2 as a cell-specific RS. This should not be considered as a limiting case of the applicability of the present invention. In fact, CSI-RS set 1 and CSI-RS set 2 may be a single set, in which case the different methods disclosed in the present invention may be applied to a single CSI-RS set. Throughout this specification, the terms source cell and serving cell are used interchangeably.

[0061] The embodiments for implementing initial beam alignment during the RACH procedure herein are explained in terms of a contention-based random access procedure. This should not be considered as a limiting case of the applicability of the present invention. In fact, the RACH procedure may also be contention-free, in which case the different methods disclosed in the present invention may be applied to both contention-free and contention-based random access (RACH) procedures.

[0062] Figure 1 is an example illustration of a radio access network (RAN) deployment for a next generation wireless system according to embodiments as disclosed herein. Figure 1Describes a RAN-level network architecture consisting of multiple 5G Node Bs (gNBs) or centralized units (CUs), etc., serving multiple coverage areas or cells or transmit receive point (TRP) groups or distributed unit (DU) groups of a NR system. A data gateway (GW) can be connected to 1…r 5G nodes of NR, i.e., gNB / CU for handling one or more frequency carriers in a coverage area. One gNB / CU of NR can be connected to more than one GW. Within the coverage of gNB1 / CU1 and gNB2 / CU2, multiple UEs, etc. supporting next generation RAT functions (i.e., 5G or NR functions) are served in one or more cells. The 5G or NR system hierarchical architecture consists of 1…k CU / gNB nodes, such that each gNB / CU node serves 1…m coverage areas or cells or DU groups. In addition, one 5G cell or coverage area or DU consists of 1…n, i.e., TRP groups, etc.; wherein the fronthaul between the gNB / CU node and the DU / TRP group can be ideal or non-ideal. The TRP / DU of one 5G cell or coverage area controlled by a 5G CU / gNB operates to provide 1...p "DL coverage beams". In addition, it seems reasonable to assume that all TRP / DUs belonging to the same cell or coverage area are "time synchronized", i.e., the same radio frame and system frame sequence number (SFN) timing. However, in some implementations, the TRP / DU may not be time synchronized. The radio frame duration of the NR system is assumed to be 10 milliseconds and the SFN range is 0-1023. In some implementations, super SFN, i.e., H-SFN is possible and therefore the SFN range is used for illustration purposes. The maximum number of DL coverage beams 'p' typically depends on the network implementation and the operating frequency band, i.e., it may be larger at higher rates due to the smaller antenna spacing at the TRP / DU of the 5G CU / gNB where large antenna arrays are practical. The cells of the next generation wireless system are identified by a "physical cell identifier" (PCI) based on the DL NR synchronization signal (NR-SS) broadcast in the cell. There may also be a coverage area Id or TRP group ID or DU group ID encoded in the NR-SS. The UE can obtain the PCI / coverage area ID / TRP group ID / DU group ID from the NR-SS sent by the 5G cell of the next generation RAT. It is assumed that the TRPs operate together to provide beams to the UE, and the intention of individual TRPs is transparent to the UE. Therefore, at least the PCI is detected by the UE through the NR radio. The UE should detect and decode the NR synchronization signal (NR-SS) and the physical broadcast channel (PBCH) to determine the PCI and the global cell identity, respectively. The global cell identity is a unique identifier for cells within an operator network (PLMN), however the PCI has a limited range and is repeated in non-overlapping coverage areas of the operator network. TRP groups or DUs operate together to provide two sets of beams, namely, 1) coverage beams and 2) dedicated beams.There may be an explicit beam index sequence that determines the "beam identifier (beamId)", or the beamId may be implicitly encoded on the radio (e.g., like a time index).

[0063] A coverage beam is a wide beam transmitted by a TRP group or DU under the control of a 5G CU / gNB. A coverage beam provides cell coverage with a fixed set of direct coverage beams, also referred to as a "grid of beams". A coverage beam covers a relatively wide area and may therefore only support relatively low data rates. For example, in a cell, NR-SS may be transmitted on a DL coverage beam. In addition to NR-SS, a gNB may transmit a cell-specific reference signal called a channel state information reference signal (CSI-RS) on a DL coverage beam. CSI-RS is a cell-specific reference signal that may be turned on / off depending on the presence of an RRC_CONNECTED UE in the cell. In addition to the cell-specific CSI-RS, there may be a UE-specific CSI-RS transmitted using a narrow dedicated beam. Therefore, there are two sets of CSI-RS, namely, CSI-RS set 1 as UE-specific and CSI-RS set 2 as cell-specific. The two CSI-RS set reference signals are not always-on signals like NR-SS. As an example, each DL coverage beam from each TRP / DU can cover a 30-60 degree sector angle so that the grid of coverage beams covers a circular area of ​​the cell radius. Each coverage beam is implicitly or explicitly identified by a "beam Id" so that the UE can identify the NR-SS block RSRP or CSI-RS RSRP of set 2. The coverage beam sends synchronization signal (SS) blocks and PBCH in a time division multiplexing manner or a frequency division multiplexing manner. The cell-specific reference signal, i.e., CSI-RS set 2, can be used for beam signal strength measurements for a process called "initial beam alignment". In addition, the beam quality of CSI-RS set 2 can be combined to derive the cell quality, and can therefore be used for the HO process or the so-called RRC driven L3 mobility. These reference signals are collectively referred to as channel state information reference signals (CSI-RS set 2) and can be used for radio resource management (RRM) measurements for cell-level mobility. The characteristics of the DL coverage beam that transmits NR-SS / PBCH and the DL coverage beam that transmits CSI-RS set 2, i.e., beam width, beam gain, etc., may be the same or different depending on the network implementation. In addition, the coverage beam may also be used to send DL common channel signaling, such as RACH responses. The coverage beam may carry control channel transmissions like the enhanced Physical Downlink Control Channel (ePDCCH), and the user data Physical Downlink Shared Channel (PDSCH) may also be sent on the coverage beam when the dedicated beam to the UE has been lost.

[0064] Dedicated transmissions to the UE (ePDCCH / PDSCH) can potentially use even more direct and sharp beams (e.g., UE-specific precoding) on ​​so-called "dedicated beams". The coverage area of ​​a dedicated beam is much smaller than that of a coverage beam in terms of beamwidth (e.g., 1 / 2, 1 / 4, or 1 / 8 of the coverage beam area). The dedicated beam is managed based on UE measurements of UE-specific channel state information reference signals (CSI-RS set 1), and the UE provides CSI feedback at the PHY or MAC layer. This is called beam switching or beam management, which may occur across beams of the serving DU / TRP group of the control cell. Beam switching or beam management within the same cell is managed at the PHY or MAC layer based on CSI feedback from the UE derived from UE-specific CSI-RS set 1. CSI feedback is sent on an uplink control channel like PUCCH or can also be sent on a shared data channel like PUSCH. To demodulate the ePDCCH / PDSCH carried on the dedicated beam, a demodulation reference signal (DMRS) is also sent on the dedicated beam. Because the UE only sees the DMRS species of the reference signal from the cell of the NR system, the intention of the coverage beam and the dedicated beam is transparent to the UE from the PDSCH reception perspective. However, the intention of the coverage beam for reception of NR-SS is known to the UE. Therefore, when the TRP / DU of the 5G gNB / CU detects that the UE has lost the dedicated beam based on the CSI-RS set 1 measurement feedback and the UE schedules data on the coverage beam, the UE will not know that the transmission is from the coverage beam. To the UE, this looks like any other transmission from the dedicated beam. The cell edge bit rate on the coverage beam will be much lower than the cell edge bit rate achievable by the dedicated beam.

[0065] Beam switching within the same cell does not have any impact on the user plane functions / layers. For beam switching or beam management from a serving DU / TRP group across a different DU / TRP group of another cell, the UE first needs to go through a HO process. During the HO process, initial beam alignment in the target cell served by a DU / TRP group different from the DU / TRP group serving the source cell is required. If the initial beam alignment is not performed as early as possible, i.e., when the RACH is completed in the target cell, there is a possibility of data rate degradation. When the UE is served by the source cell, the dedicated beam is used for data scheduling with very high data rates, for example, several Gbps data rates, and when the HO process is triggered for the target cell, it is hoped that the UE is served by the dedicated beam of the target cell as early as possible to maintain the Gbps data rate. Otherwise, at the HO to the target cell, the UE may be served by the coverage beam of the target cell, but with temporary data rate degradation, which is recovered after receiving feedback of CSI-RS set 1. This temporary degradation of the Gbps data rate has an impact on the TCP performance climbing up after a slow start. Therefore, it is necessary to handle mobility so that the initial beam alignment is performed as early as possible during the HO process in order to avoid Gbps data rate degradation. The RACH in the target cell during the HO process can be a contention-free or contention-based random access. In another scenario, when the UE transitions from the idle state to the connected state (i.e., during RRC connection establishment), it is desirable to schedule the UE on a dedicated beam as early as possible so that the slow start of the TCP mechanism is completed as soon as possible. Therefore, it is necessary to handle the initial beam alignment during the RRC connection establishment so that the Gbps data rate available on the NR physical layer can be achieved by the UE immediately after completing the RACH process for RRC connection establishment.

[0066] Referring now to the drawings, and more particularly to FIGS. Fig.12 , wherein like reference numerals indicate corresponding features consistently throughout the drawings, there is shown a preferred embodiment.

[0067] Figure 2AA secondary cell mobility scenario for a user equipment operating in a beamformed 5G system is shown according to an embodiment as disclosed herein. UE 102 is configured to operate in beamforming mode, served by Cell#1 of gNB#1 from a 5G or NR system. The first level of UE 102 mobility involves a change of primary cell (PCell), where UE 102 switches from PCell#1 of gNB#1 to PCell#2 of gNB#2. PCell mobility can be understood as coverage layer mobility handled by a handover process involving the triggering of measurement events based on handover events similar to Event A1, Event A2, Event A3, Event A4, etc. as specified in TS36.331. At the boundary or cell edge, which is the overlapping area of ​​PCell#1 (i.e., source cell) and PCell#2 (i.e., potential target cell), a measurement event configured for UE 102 is triggered in order to support such coverage layer mobility. This measurement event is based on signal strength measurements (e.g., RSRP / RSRQ) performed by UE 102 for synchronization signals (NR-SS) and / or RSRP / RSRQ measurements for cell-specific reference signals similar to CSI-RS (referred to as CSI-RS set 2) transmitted by PCell#1 and PCell#2.

[0068] In an embodiment, the configuration of the handling of PCell mobility for NR is for measurement events for UE 102 to be based on RSRP / RSRQ measurements performed by the UE for NR-SS and / or cell-specific reference signals such as CSI-RS (CSI-RS set 2) transmitted on DL coverage beams by PCell #1, PCell #2, PCell #3, etc., respectively. The cell quality definition of a cell of an NR system that needs to be considered for comparing relative or absolute signal strength is based on measurement metrics of NR-SS and / or CSI-RS set 2.

[0069] Depending on the measurement report based on NR-SS and / or CSI-RS set 2 sent by UE 102 to gNB#1 on PCell#1 (e.g., through RRC signaling), at least the following events are possible: a) performing a PCell#2 preparation procedure to prepare PCell#2 of gNB#2, b) triggering a PCell change procedure based on the HO command prepared by the target gNB#2 after a response from gNB#2. The current serving cell of the UE, i.e., PCell#1 of gNB#1, is changed to PCell#2 of gNB#2 based on the NR-SS and / or CSI-RS set 2 measurements of PCell#1 and PCell#2.

[0070] Upon receiving the RRC reconfiguration message containing the HO command that essentially includes the PCell#2 configuration, the UE 102 will initiate a RACH process toward PCell#2 to reestablish the user plane protocol stack including at least MAC, RLC, and PDCP entities. In this case, the UE 102 reestablishes the data radio bearer on PCell#2 to continue the DL / UL data transmission on PCell#2 for service continuity. The RACH process can be contention-free or contention-based. During the first level of mobility, i.e., the HO process driven by RRC, the second level of UE mobility, known as beam-level mobility or beam management, also needs to be handled. Beam management involves two stages, namely, a) a first stage known as initial beam alignment, in which the serving DL beam of the UE 102 in the source cell is switched to another serving DL beam in the target cell, and b) a second stage known as beam refinement, in which the serving DL beam of the UE 102 in the new source cell (i.e., the target cell) is switched to another serving DL beam in the new source cell. There are several methods for handling the first stage of beam management (i.e., initial beam alignment). The initial beam alignment may be processed at the physical (PHY) layer, the MAC layer, or the RRC layer depending on the selected method. Such initial beam alignment may be based on measurement feedback for NR-SS and / or CSI-RS set 2. The beam level measurement configuration, i.e., the CSI-RS set 2 configuration, may be provided to the UE in the system information and / or during the PCell change process, i.e., the HO command. In an embodiment, the beam mobility measurement configuration, i.e., the CSI-RS set 2 configuration, includes at least CSI-RS resources or CSI-RS processing, the PCI of the cell sending the CSI-RS set 2, the beam index or resource identifier, the mapping of the beam index or resource identifier to the CSI-RS resource, and the like. The UE should monitor the CSI-RS set 2 to perform CSI measurements including at least CSI-RS RSRP measurements for the CSI-RS set 2 resources configured for the UE 102. These CSI set 2 measurements are reported by the UE 102 to the concerned PCell in a measurement report triggered at the RRC level or directly to the concerned PCell at the MAC / PHY layer so that the concerned PCell performs an initial beam alignment decision. The CSI-RS measurements associated with the target cell performed by the UE may be reported as one of a channel quality indicator (CQI), a rank indicator (RI), a precoding matrix indicator (PMI), and an associated resource identifier.

[0071] Figure 2B is a flow chart 200b illustrating a method for performing initial beam alignment during a random access (RACH) procedure by a user equipment (UE) according to embodiments as disclosed herein.

[0072] At step 202b, the method includes sending a measurement report associated with the target cell 104b to the serving cell 104a in response to a handover event triggered at the UE 102. The UE 102 is configured to send a measurement report associated with the target cell 104b to the serving cell 104a in response to a handover event triggered at the UE 102.

[0073] In an embodiment, the measurement report includes at least one of the following: a measurement of the best SS block, one or more corresponding SS block identifiers associated with the measurement of the target cell and the best CSI-RS resource (i.e., CSI-RS RSRP or CSI-RSRQ), and one or more corresponding CSI-RS resource identifiers associated with the target cell. The reported measurement and the associated identifier are above a preconfigured threshold. In step 204b, the method includes receiving a handover command including at least the CSI-RS configuration of the target cell 104b through the serving cell 104a. The UE 102 is configured to receive a handover command including at least the CSI-RS configuration of the target cell 104b through the serving cell 104a. The CSI-RS configuration includes at least a cell-specific signal time window (period, offset, duration) called a CSI-RS measurement timing configuration, a list of configurations, the list of configurations including a CSI-RS resource identifier, a PCI, a scrambling identifier, a resource configuration, a subframe offset, and a Qoffset, the resource configuration including a non-zero power (NZP) resource, a zero power (ZP) resource, and an interference measurement (IM) resource.

[0074] At step 206b, the method includes performing downlink (DL) synchronization with the target cell with respect to the SS block.The UE 102 is configured to perform DL synchronization with the target cell 104b with respect to the SS block.

[0075] At step 208b, the method includes indicating the best CSI-RS resource identifier to the target cell by measuring a subset of the CSI-RS resources received in the handover command. The UE 102 is configured to indicate the best CSI-RS resource identifier to the target cell by measuring a subset of the CSI-RS resources received in the handover command. In an embodiment, at least the best CSI-RS resource identifier and CQI, PMI, RI for the target cell are indicated in MSG 3 of the RACH procedure. In an alternative embodiment, the best / appropriate CSI-RS resource identifier is indicated in MSG1, wherein the UE sends MSG1 (PRACH preamble) using a dedicated preamble and / or resources corresponding to the CSI-RS resource identifier.

[0076] The best NR-SS and the associated beam index or the best CSI-RS resource and the associated resource identifier represent a qualified measurement or a suitable measurement above a pre-configured threshold, where the threshold may be a relative threshold or an absolute threshold.

[0077] The various actions, actions, blocks, steps, etc. in flow chart 200b can be performed in the order presented, in a different order, or simultaneously. In addition, in some embodiments, some actions, actions, blocks, steps, etc. can be omitted, added, modified, or skipped without departing from the scope of the present invention.

[0078] Figure 2C is a flow chart 200c illustrating a method for indicating a best CSI-RS resource identifier to a target cell according to embodiments disclosed herein.

[0079] At step 202c, the method includes identifying a subset of best SS blocks from measurements of SS blocks associated with the target cell while performing DL synchronization. The UE 102 is configured to identify a subset of best SS blocks from measurements of SS blocks associated with the target cell while performing DL synchronization.

[0080] At step 204c, the method includes determining a subset of CSI-RS resources among the CSI-RS resources received in the handover command based on the identified subset of best SS blocks. The UE 102 is configured to determine a subset of CSI-RS resources among the CSI-RS resources received in the handover command based on the identified subset of best SS blocks.

[0081] At step 206c, the method includes measuring the determined subset of CSI-RS resources to identify the best CSI-RS resource identifier. The UE 102 is configured to measure the determined subset of CSI-RS resources to identify the best CSI-RS resource identifier.

[0082] In an embodiment, the UE is configured to measure a subset of the determined CSI-RS resources in response to a preamble transmission on the target cell 104b by receiving an indication called a CSI request bit. If the CSI request bit is enabled, the UE 102 performs measurements on the determined subset of CSI-RS resources to identify at least one best CSI-RS resource identifier and report corresponding CQI, PMI, RI. The UE may report one or more best CSI-RS measurements and one or more associated CSI-RS resource identifiers.

[0083] At step 208c, the method includes indicating the best CSI-RS resource identifier and the corresponding CQI, PMI, RI to the target cell. The UE is configured to indicate the best CSI-RS resource identifier and the corresponding CQI, PMI, RI to the target cell 104b. In an embodiment, the best CSI-RS resource identifier and the corresponding CQI, PMI, RI for the target cell are indicated in MSG 3 of the RACH procedure. In an embodiment, the best CSI-RS resource identifier and the corresponding CQI, PMI, RI for the target cell are sent to the target cell in an UL grant received in a random access response of the RACH procedure.

[0084] The various actions, actions, blocks, steps, etc. in flow chart 200c may be performed in the order presented, in a different order, or simultaneously. In addition, in some embodiments, some actions, actions, blocks, steps, etc. may be omitted, added, modified, or skipped without departing from the scope of the present invention.

[0085] Figure 3 is a sequence diagram depicting a HO procedure in a NR system according to an embodiment as disclosed herein. Figure 3Depicted is a configuration of cell-specific reference signals, i.e., channel state information reference signals (CSI-RS), for radio resource management (RRM) measurements to be performed by a UE 102 for cells of interest involved in HO, i.e., RRC-driven L3 mobility. The UE 102 receives (302) a measurement configuration from a serving cell 104a, i.e., Cell#1 served by a serving gNB. The measurement configuration from the serving cell 104a configures the UE 102 to report measurements. The measurement configuration may include a list of measurements, each including the following elements: a) a measurement identifier that identifies a measurement object linking the measurement object to a reporting configuration; b) a measurement object that specifies a carrier frequency of a certain RAT type (e.g., MeasObject#1 for all cells on NR frequencies, MeasObject#2 for all cells on LTE frequencies, etc.), etc., and c) a measurement report configuration that specifies when the UE 102 should trigger a measurement report and what information the UE 102 should include in the measurement report. The trigger for sending the measurement report is specified as a specific "event condition", for example, a neighbor cell becomes a better offset than the current serving cell, i.e., event A3. The measurement report can also be triggered at regular intervals, i.e., periodically, possibly up to a configurable number of times. The report configuration also specifies which measurement quantities should be reported and the maximum number of cells that can be included (in the order of the measurement results, i.e., the best cell first). The report configuration can be the same for NR-SS measurement reports and CSI-RS measurement reports. In addition, for beam quality reports, the report configuration either includes only the beam index of the best beam or includes both the beam index and the corresponding NR-SS block RSRP or CSI-RS RSRP value. The report configuration can also configure UE 102 to report the N best beams, where the value of N is configured in the report configuration, or the N best beams depend on the number of good beams or qualified / appropriate beams within the XdB offset of the best beam. A qualified / appropriate beam can also be determined if the signal strength of the beam is above an absolute threshold, i.e., greater than or equal to Y dBm. Because NR-SS signals are always-on signals that are self-discoverable by UE 102, these NR-SS signals can be sent as NR-SS bursts including NR-SS blocks. NR-SS blocks include at least a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a primary broadcast channel. A beam index sequence or SS block ID may also be sent in the SS block. The NR-SS burst may be sent via a DL coverage beam so that a set of NR-SS bursts are repeated in an NR-SS burst period. After decoding the NR-SS, the UE 102 may measure the NR-SS block signal strength, i.e., the NR-SS block RSRP, which may correspond to the beam quality of the DL coverage beam on which the NR-SS block is sent.During the NR-SS burst periodicity, the UE 102 may detect one or more NR-SS blocks, i.e., one or more beam qualities, which may be combined based on some method such as averaging the detected beam qualities or some other method such as weighted averaging of the detected beam qualities to derive the cell quality. Based on a configured event, if an event for reporting the cell quality of the source cell 104a and the target cell 104b is triggered (304), the UE 102 sends (306) a measurement report #1 (i.e., the UE 102 reports the NR-SS RSRP and / or RSRQ of the source cell 104a and the target cell 104b). The measurement report includes at least one of the following: a measurement of the best SS block and one or more corresponding SS block identifiers, i.e., a beam index associated with the target cell. The reported NR-SS beam measurement and the associated identifier are above a pre-configured threshold, which may be a relative or absolute threshold. Based on the measurement report #1, the serving cell 104a initiates (308) a process towards the target cell 104b to activate CSI-RS set 2 transmission.

[0086] Because the CSI-RS set 2 signal is not a constantly on signal like NR-SS, it can be turned on and off based on certain triggers. The target cell 104b regards the activation message from the serving cell 104a as a trigger for activating the target cell 104b, i.e., the transmission of CSI-RS set 2 in cell #2 indicated in the activation message. The target cell 104b also provides (310) CSI-RS set 2 to the serving cell 104a, the CSI-RS configuration including at least a cell-specific signal time window (period, offset, duration) called CSI-RS measurement timing configuration and a list of CSI-RS configurations, the list of CSI-RS configurations including CSI-RS resource identifier, PCI, scrambling identifier, resource configuration, subframe offset and Qoffset, the resource configuration including non-zero power (NZP) resources, zero power (ZP) resources and interference measurement (IM) resources. The serving cell 104a (i.e., cell #1) includes its own CSI-RS set 2 configuration in the RRC message sent (312) to the UE 102 in addition to the CSI-RS set 2 configuration of the target cell 104b (i.e., cell #2). The serving cell 104a (i.e., cell #1) and the target cell (i.e., cell #2) begin (314) sending each cell-specific CSI-RS set 2 to enable the UE to measure the corresponding signal strength for the CSI-RS resource for mobility (i.e., PCell change) decision evaluation. Assuming that cell #1 and cell #2 are on the same frequency, the UE 102 begins (316) measuring the CSI-RS set 2 of the cell involved according to the configuration in the received RRC message. If cell #1 and cell #2 are on different frequencies, the process remains the same. Similar to NR-SS, even if CSI-RS set 2 is sent on multiple DL coverage beams, the characteristics of the DL coverage beams for NR-SS and CSI-RS set 2 may or may not be the same. However, UE 102 derives the cell quality of the source cell and the target cell based on the beam quality of CSI-RS set 2 in a manner similar to the cell quality based on NR-SS. The event for triggering a report based on NR-SS and the event for triggering a report based on CSI-RS set 2 are independent events. UE 102 sends (318) measurement report #2, which includes the cell quality based on CSI-RS set 2 (CSI-RS RSRP) of the cell involved and also includes the best beam quality of CSI-RS set 2, i.e., the CSI feedback of the target cell. The measurement report includes at least one of the following: a measurement of the best CSI-RS resource and one or more corresponding resource identifiers, i.e., a beam index associated with the target cell. The reported CSI-RS beam measurement and the associated identifier are qualified or appropriate measurements above a pre-configured threshold, which can be a relative or absolute threshold.Upon receiving measurement report #2, serving cell 104a initiates (320) a HO preparation procedure toward the target cell so that radio resources are available in target cell 104b, i.e., cell #2, when UE 102 radio link switches to cell #2. During the HO preparation procedure, serving cell 104a forwards CSI feedback corresponding to the best beam of the target cell provided by UE 102. The CSI feedback may include CQI, PMI, RI, and associated resource identifiers. After a RACH procedure in the target cell, such information may be useful in the target cell to start scheduling data transmission with the best beam reported by UE 102. Figure 3 In the process depicted in FIG. 1 , HO is based on the MR including the RSRP of the NR-SS of the involved cells (i.e., measurement report #1) and the CSI-RS RSRP of the involved cells (i.e., measurement report #2). Moreover, the identification of the best beam of the target cell 104b for initial beam alignment is based on the CSI-RS set 2 of the target cell 104b reported in MR #2. Therefore, the HO for both L3 mobility and initial beam alignment is based on the MR including the RSRP of the NR-SS of the involved cells (i.e., measurement report #1). Figure 3 The procedure is based on the cell-specific CSI-RS.

[0087] The measurement report includes the best CSI-RS resource identifier, i.e., the best beam of the target cell 104b, then it is possible that when the UE 102 completes the RACH with the target cell 104b, the reported best beam is no longer the best beam. The RACH process on the target cell 104b can be contention-free or contention-based. There is a considerable delay after sending the measurement report #2, i.e., the serving cell 104a has to prepare the target cell 104b on an X2-like interface and then forward (322) the HO command to the UE 102. After receiving the HO command, the UE 102 performs (324) DL synchronization with the target cell 104b and performs (326) RACH. Therefore, in certain implementations where the latency is high, the best beam of the target cell 104b reported in the measurement report may no longer be the best beam. Instead, the initial beam alignment measurement should start after the UE 102 receives the HO command and when the UE 102 performs DL synchronization with the target cell 104b. During this operation, UE 102 may know CSI-RS set 2 of target cell 104b (e.g., CSI-RS set 2 of target cell 104b may be received from serving cell 104a; or CSI-RS set 2 of target cell 104b may be obtained by UE 102 from system information of target cell 104b; or CSI-RS set 2 of target cell 104b may also be received from target cell 104b in RAR during random access procedure (328)), and start measuring CSI-RS resources while UE 102 initiates RACH in parallel. If N best CSI-RSs, i.e., one or more bundles, are determined, they should be reported in the RACH procedure (330), i.e., may be reported in MSG3. In an embodiment, the best / appropriate CSI-RS resource identifier may be indicated in MSG1, where the UE sends MSG1 (PRACH preamble) using a dedicated preamble and / or resources corresponding to the CSI-RS resource identifier. Because this is the latest measurement, this helps with initial beam alignment compared to the older measurement sent in measurement report #2. During the RACH procedure in the target cell 104b, it is possible that the RAR may include a 1-bit indication, called a CSI request bit, for the UE 102 to start measuring the CSI-RS resources of the target cell, or the RAR may indicate (332) a subset of CSI-RS resources from a previous CSI-RS Set 2 configuration to be measured by the UE 102.

[0088] Figure 4 is a sequence diagram depicting a HO procedure in a NR system based on conditional triggering according to an embodiment as disclosed herein. Figure 4 The solution depicted in Figure 3The solution in , which assumes that there are independent events for NR-SS based measurement report triggering and CSI-RS based measurement report (MR) triggering. Figure 4 In the MR, the UE 102 triggers (402) an MR based on an event comparing the NR-SS of the serving cell and the RSRP of the NR-SS of the target cell 104b. In the MR, the UE 102 indicates (404) the PCI and the corresponding cell quality, i.e., the NR-SS RSRP, of the target cell 104b. The measurement report includes at least one of the following: a measurement of the best SS block and one or more corresponding SS block identifiers, i.e., a beam index associated with the target cell. The reported NR-SS beam measurement and the associated identifier are qualified or appropriate measurements above a pre-configured threshold, which can be a relative or absolute threshold. Upon receiving the MR, the serving cell 104a initiates (406) a HO preparation process towards the target gNB so that radio resources are available in at least one target cell 104b, i.e., cell #2, when the UE 102 radio link is switched to cell #2.

[0089] During the HO preparation process, the serving cell 104a may forward the NR-SS RSRP provided by the UE 102 corresponding to the PCI of the target cell 104b processed by the target gNB. The serving cell 104a provides (408) the CSI-RS set 2 configuration of the target cell 104b through UE-specific signaling (i.e., an RRC reconfiguration message corresponding to the HO command), and there may be a conditional HO command executed by the UE 102 at a later time. The CSI-RS configuration includes at least a cell-specific signal time window (period, offset, duration) called a CSI-RS measurement timing configuration, a list of configurations including a CSI-RS resource identifier, a PCI, a cipher identifier, a resource configuration, a subframe offset, and a Qoffset, the resource configuration including non-zero power (NZP) resources, zero power (ZP) resources, and interference measurement (IM) resources. The conditions for executing the HO command may be based on, for example, a CSI-RS event estimate. The serving cell 104a (i.e., cell #1) and the target cell (i.e., cell #2) begin (410) transmitting each cell-specific CSI-RS set 2 to enable the UE 102 to measure the corresponding signal strength for the CSI-RS resources for mobility (i.e., PCell change) decision estimation. The UE 102 measures (412) the CSI-RS of the serving cell 104a and the CSI-RS of the target cell 104b. Figure 3 In , since there is no conditional HO command, MR#2 is triggered based on the event configured for CSI-RS. Figure 4, because the CSI-RS based event trigger is the condition, MR#2 does not need to be sent. UE 102 makes a HO decision autonomously based on the RSRP of the CSI-RS of the cells involved. UE 102 executes the HO command received earlier. In addition, UE 102 performs (414) DL synchronization with the target cell 104b and measures the NR-SS of the target cell 104b. Because the CSI-RS set 2 configuration of the target cell 104b is known, UE 102 identifies the N best beams based on the measurement of the CSI-RS set 2 of the target cell 104b while attempting RACH (416) on the target cell 104b. The RACH process towards the target cell 104b can be contention-free or contention-based. In MSG3, UE 102 indicates the N best beams (i.e., CSI feedback) based on the N best CSI-RS used for initial beam alignment. The CSI feedback may include a CQI, PMI, RI, and an associated resource identifier corresponding to the target cell 104b.

[0090] In an embodiment, during the RACH procedure in the target cell 104b, it is possible that the random access response (RAR) (418) may include a 1-bit indication, called a CSI request bit, for the UE 102 to start measuring the CSI-RS resources of the target cell 104b. In this case, the UE 102 may measure (420) all CSI resources in the CSI-RS set 2 received in the HO command.

[0091] Alternatively, UE 102 may measure a subset of resources in CSI-RS set 2 corresponding to the best SS block of target cell 104b. In an alternative embodiment, the RAR may indicate a subset of CSI-RS resources to be measured by UE 102 from the previously configured CSI-RS set 2 configuration in the HO command. Figure 4 In the process depicted in , the HO is based on the MR including the RSRP of the NR-SS of the involved cells (ie, the measurement report) and the CSI-RS RSRP of the involved cells (ie, conditional HO without measurement report #2).

[0092] Additionally, identification of the N best beams for the target cell 104b for initial beam alignment is based on measurements of the CSI-RS set 2 of the target cell 104b reported (422) in the UL grant received in MSG3 or in the RAR, and the target cell 104b provides (424) a beam indication to the UE 102. Thus, the N best beams for both L3 mobility and initial beam alignment are identified based on measurements of the CSI-RS set 2 of the target cell 104b reported (422) in the UL grant received in the RAR. Figure 4 The process is based on the cell-specific CSI-RS.

[0093] Figure 5is a sequence diagram depicting NR-SS based HO and CSI-RS based initial beam alignment according to embodiments as disclosed herein. Figure 5 In the process depicted in , the HO is based only on the MR including the RSRP (i.e., measurement report) of the NR-SS of the cell involved, and for the purpose of simplification of the method, the CSI-RS RSRP of the cell involved is not used for the HO decision. This is not a limitation, and the HO decision may depend on the network configuration based on the signal strength of the NR-SS measurement or the signal strength of the CSI-RS measurement. In addition, the identification of the N best beams of the target cell 104b for initial beam alignment is based on the measurement of the CSI-RS set 2 configuration of the target cell 104b provided in the HO command. In an embodiment, the UE 102 may measure all CSI resources in the CSI-RS set 2 received in the HO command to identify the N best beams. In another embodiment, the UE 102 may measure a subset of the resources in the CSI-RS set 2 corresponding to the best SS block of the target cell 104b.

[0094] Therefore, in Figure 5 In the process, for explanation, L3 mobility is based on NR-SS signal quality, i.e., cell quality based on NR-SS RSRP, and initial beam alignment is based on cell-specific CSI-RS, i.e., beam quality based on CSI-RS RSRP.

[0095] The UE triggers (502) a handover event based on NR-SS measurements of the serving cell 104a and the target cell 104b. The UE 102 triggers (504) an MR based on the handover event of comparing the RSRP of the NR-SS of the serving cell 104a and the NR-SS of the target cell 104b. In the MR, the UE 102 indicates the PCI and the corresponding cell quality, i.e., the NR-SS RSRP, of the target cell 104b. The measurement report includes at least one of the following: a measurement of the best SS block and one or more corresponding SS block identifiers, i.e., a beam index associated with the target cell. The reported NR-SS beam measurement and the associated identifier are above a pre-configured threshold, which can be a relative or absolute threshold. Upon receiving the MR, the serving cell 104a initiates (506) a HO preparation process towards the target cell 104b to make radio resources available in at least one target cell 104b.

[0096] After HO preparation with the target gNB, the serving cell 104a (i.e., cell #1) forwards the CSI-RS set 2 configuration of the target cell 104b received from the target gNB to the UE 102 (508). The CSI-RS configuration includes at least a cell-specific signal time window (period, offset, duration) called a CSI-RS measurement timing configuration, a list of configurations including a CSI-RS resource identifier, a PCI, a cipher identifier, a resource configuration, a subframe offset, and a Qoffset, the resource configuration including non-zero power (NZP) resources, zero power (ZP) resources, and interference measurement (IM) resources. After receiving the HO command, the UE 102 measures (512) the NR-SS of the target cell 104b. The UE 102 measures the NR-SS block RSRP corresponding to the beam level quality. The UE 102 determines the best beam quality of the NR-SS block. Even though the DL coverage beam characteristics of the NR-SS transmission and the CSI-RS set 2 transmission may or may not be the same, the UE 102 may implicitly identify a subset set of CSI-RS resources to be measured (514) from the CSI-RS configuration of the target cell 104b based on the best beam quality corresponding to the NR-SS block of the target cell 104b. In addition, the UE 102 initiates (516) a RACH and receives (518) a RAR message from the target cell 104b. The RACH process toward the target cell 104b may be contention-free or contention-based. The CSI-RS RSRP of the best CSI-RS resource and the associated CSI-RS resource identifier from the subset of resources may be indicated (520) by the UE 102 to the target cell 104b in MSG3 of the RACH process or in the UL grant received in the RAR along with the HO confirmation as CSI feedback. The CSI feedback may include a CQI, PMI, RI, and an associated resource identifier corresponding to the target cell 104b. Alternatively, the CSI feedback may correspond to the N best beams measured based on CSI-RS resources from a subset of set 2 resources. In an alternative embodiment, the best / appropriate CSI-RS resource identifier is indicated in MSG1, wherein the UE sends MSG1 (PRACH preamble) using a dedicated preamble and / or resources corresponding to the CSI-RS resource identifier. The target cell 104b can make an informed decision about data scheduling for the UE 102 based on the CSI feedback, thereby avoiding data degradation and avoiding degradation of TCP performance. The target cell 104b indicates (522) the best beam to the UE 102 based on the CSI feedback.

[0097] Figure 6 is a sequence diagram depicting an alternative process for CSI-RS based initial beam alignment according to embodiments as disclosed herein. Figure 6 In the process described in Figure 5 In the solution shown, the HO is based only on the MR including the RSRP (i.e., measurement report) of the NR-SS of the cell involved. For simplicity of the method, the CSI-RS RSRP of the cell involved is not used for the HO decision. This is not a limitation, and the HO decision may depend on the network configuration based on the signal strength of NR-SS measurements or the signal strength of CSI-RS measurements. The measurement report includes at least one of the following: a measurement of the best SS block and one or more corresponding SS block identifiers, i.e., a beam index associated with the target cell. The reported NR-SS beam measurement and the associated identifier are above a pre-configured threshold, which may be a relative or absolute threshold. In addition, the identification of the N best beams of the target cell 104b for initial beam alignment is based on the CSI-RS set 2 configuration of the target cell 104b provided in the HO command. However, unlike Figure 5 The difference compared to the solution depicted in is that the UE 102 does not autonomously perform CSI-RS measurements of the target cell 104b after receiving the HO command. In the RAR of the RACH procedure on the target cell 104b, the UE 102 is indicated (614) with a bit indication called the CSI request bit to start measuring the CSI-RS resources of set 2. This indication is useful because CSI-RS set 2 transmissions are on / off transmissions, so the 1-bit indication indicates the activation of CSI-RS set 2 transmissions in the target cell. In addition, during the HO in the target cell 104b, there is no dedicated PUCCH in the UL for the UE. In order to support CSI-RS based beam selection in the target cell at the earliest, the RAR includes a CSI request so that the UE can report CSI feedback, i.e., CQI, PMI, RI, on the PUSCH in the UL (i.e., MSG3 of the RACH procedure). After the dedicated PUCCH is configured upon successful completion of the RACH procedure in the target cell 104b, the UE continues with periodic CSI feedback reporting on the dedicated PUCCH resources. In an embodiment, UE 102 may measure all CSI resources in CSI-RS set 2 received in the HO command to identify the N best beams. In another embodiment, UE 102 may measure (618) a subset of resources in CSI-RS set 2 corresponding to the best SS block of target cell 104b.

[0098] Even though the DL coverage beam characteristics of the NR-SS transmission and the CSI-RS set 2 transmission may or may not be the same, the UE 102 may implicitly identify a subset set of CSI-RS resources to be measured from the CSI-RS configuration of the target cell 104b based on the best beam quality corresponding to the NR-SS block of the target cell 104b. The CSI feedback (620) may include a CQI, PMI, RI, and an associated resource identifier corresponding to the target cell 104b.

[0099] Figure 7 is a sequence diagram depicting another alternative process for CSI-RS based initial beam alignment according to embodiments as disclosed herein. Figure 7 In the process described in Figure 5 In the solution shown, the HO is based only on the MR including the RSRP (i.e., measurement report) of the NR-SS of the cell involved. For simplicity of the method, the CSI-RS RSRP of the cell involved is not used for the HO decision. This is not a limitation, and the HO decision may depend on the network configuration based on the signal strength of NR-SS measurements or the signal strength of CSI-RS measurements. The measurement report includes at least one of the following: a measurement of the best SS block and one or more corresponding SS block identifiers, i.e., a beam index associated with the target cell. The reported NR-SS beam measurement and the associated identifier are above a pre-configured threshold, which may be a relative or absolute threshold. In addition, the identification of the N best beams of the target cell 104b for initial beam alignment is based on the CSI-RS set 2 configuration of the target cell 104b provided in the HO command. However, unlike Figure 5 The difference compared to the solution shown in is that the UE 102 does not autonomously perform CSI-RS measurements of the target cell 104b after receiving the HO command. Figure 6 In the RACH procedure, the RAR includes a bit called the CSI request bit to indicate the CSI-RS resources to start measuring set 2, but in Figure 7 In the RAR, the 1-bit indication (i.e., CSI request bit) is replaced with an indication of a subset of CSI-RS resources that the UE 102 should measure (714). The indication of the subset in the RAR can be based on the CSI-RS resource identifier / index indicated in the CSI-RS set 2 configuration previously provided in the HO command. The DL coverage beam characteristics of the NR-SS transmission and the CSI-RS set 2 transmission may or may not be the same. The UE 102 is explicitly notified to identify a subset set of CSI-RS resources to be measured (718) from the CSI-RS configuration of the target cell 104b previously provided in the HO command based on the indication / information in the RAR. The CSI feedback (720) may include a CQI, PMI, RI, and an associated resource identifier corresponding to the target cell 104b.

[0100] Figure 8 is a sequence diagram depicting an initial beam alignment process based on CSI-RS configuration in RAR according to an embodiment as disclosed herein. Figure 8 In the process described in Figure 5In the solution shown, HO is based only on the MR including the RSRP (i.e. measurement report) of the NR-SS of the involved cell. For the simplicity of the method, the CSI-RS RSRP of the involved cell is not used for the HO decision. This is not a limitation, and the HO decision may depend on the network configuration based on the signal strength of NR-SS measurements or the signal strength of CSI-RS measurements. The measurement report includes at least one of the following: a measurement of the best SS block and one or more corresponding SS block identifiers, i.e. a beam index associated with the target cell. The reported NR-SS beam measurement and the associated identifier are above a preconfigured threshold, which may be a relative or absolute threshold. In addition, Figure 5 , Figure 6 and Figure 7 In the HO command, the identification of the best beam of the target cell 104b for initial beam alignment is based on the CSI-RS set 2 configuration of the target cell 104b provided in the HO command. Figure 8 In the solution depicted in , the identification of the N best beams of the target cell for initial beam alignment is based on the CSI-RS set 2 configuration of the target cell provided in the RAR (814) during a RACH process initiated on the target cell 104b. The RACH process towards the target cell 104b can be contention-free or contention-based. The UE 102 is explicitly notified to measure a subset set of CSI-RS resources (814) based on the CSI-RS configuration of the target cell 104b provided in the RAR. In an embodiment, the UE 102 may measure a subset of resources in the CSI-RS set 2 corresponding to the best SS block of the target cell 104b. In an alternative embodiment, the UE 102 may measure all CSI resources in the CSI-RS set 2 received in the RAR to identify the N best beams. The CSI feedback (818) may include a CQI, PMI, RI, and an associated resource identifier corresponding to the target cell 104b.

[0101] Fig. 9 is a sequence diagram depicting an initial beam alignment process based on CSI-RS configuration in system information according to an embodiment as disclosed herein. Fig. 9 In the process described in Figure 5 In the solution shown, HO is based only on the MR including the RSRP (i.e. measurement report) of the NR-SS of the involved cells. For the simplicity of the method, the CSI-RSRSRP of the involved cells is not used for the HO decision. This is not a limitation, and the HO decision may be based on the signal strength measured by NR-SS or the signal strength measured by CSI-RS depending on the network configuration. In addition, Figure 5 , Figure 6 and Figure 7In the HO command, the identification of the N best beams of the target cell 104b for initial beam alignment is based on the CSI-RS set 2 configuration of the target cell 104b provided in the HO command. Fig. 9 In the solution depicted in , the identification of the N best beams of the target cell 104b for initial beam alignment is based on the CSI-RS set 2 configuration of the target cell 104b obtained by the UE 102 by reading (912) the system information of the target cell 104b. The UE 102 is required to obtain a system information block (SIB) from a cell broadcast including the CSI-RS set 2 configuration. The CSI-RS configuration includes at least a cell-specific signal time window (period, offset, duration) called a CSI-RS measurement timing configuration, a list of configurations including a CSI-RS resource identifier, a PCI, an encryption identifier, a resource configuration, a subframe offset, and a Qoffset, the resource configuration including non-zero power (NZP) resources, zero power (ZP) resources, and interference measurement (IM) resources. In Fig. 9 In the process depicted in , the UE 102 assumes that after receiving the HO command, the target cell 104b should periodically broadcast a SIB including the CSI-RS set 2 configuration. There are several options for measuring CSI-RS resources. In one option, based on a 1-bit indication in the RAR called a CSI request, the UE 102 then measures all CSI-RS resources of the CSI-RS set 2 obtained from the system information. In another embodiment, based on a subset indication in the RAR, the UE 102 only measures a subset of the CSI-RS resources of the CSI-RS set 2 obtained from the system information. The UE 102 is explicitly notified to identify a subset set of CSI-RS resources to be measured (918) from the CSI-RS configuration of the target cell 104b obtained from the system information based on the indication / information in the RAR. In yet another embodiment, based on a 1-bit indication in the RAR (i.e., a CSI request), the UE 102 only measures a subset of the CSI-RS resources of the CSI-RS set 2 obtained from the system information based on the best NR-SS block. UE 102 measures the CSI-RS resources of CSI-RS set 2 obtained from system information autonomously or based on the indication in RAR (918). CSI feedback (920) sent on MSG3 in UL, i.e., PUSCH transmission, may include CQI, PMI, RI and associated resource identifier corresponding to target cell 104b. In an embodiment, the best / appropriate CSI-RS resource identifier is indicated in MSG1, where the UE sends MSG1 (PRACH preamble) using a dedicated preamble and / or resources corresponding to the CSI-RS resource identifier.

[0102] Fig.10is another sequence diagram depicting an initial beam alignment process based on CSI-RS configuration in system information according to an embodiment as disclosed herein. Fig.10 In the process described in Figure 5 In the solution shown, HO is based only on the MR including the RSRP (i.e., measurement report) of the NR-SS of the involved cells. The CSI-RS RSRP of the involved cells is not used for the HO decision. Figure 5 , Figure 6 and Figure 7 In the HO command, the identification of the N best beams of the target cell 104b for initial beam alignment is based on the CSI-RS set 2 configuration of the target cell 104b provided in the HO command. Fig. 9 Compared to the solution depicted in Fig.10 In the solution in, the identification of the N best beams of the target cell 104b for initial beam alignment is based on the CSI-RS set 2 configuration of the target cell 104b obtained by the UE 102 by requesting the SIB from the target cell in an on-demand manner. Typically, the RACH during the HO procedure is a contention-free RACH, where PRACH resources and preambles are reserved. Because the target cell 104b provides PRACH resource reservation information, it identifies that the UE 102 is requesting a CSI-RS set 2 configuration with respect to decoding the reserved preamble. The target cell 104b starts broadcasting the SIB including the CSI-RS set 2 configuration. The UE 102 is required to obtain the system information block (SIB) from the cell broadcast including the CSI-RS set 2 configuration after sending the PRACH preamble. In Fig.10 In the process depicted in , the UE 102 does not assume that the target cell 104b should periodically broadcast the SIB including the CSI-RS set 2 configuration after receiving the HO command. In addition, the UE 102 can receive a 1-bit indication in the RAR (1018) for measuring CSI-RS resources or an indication of a subset of CSI-RS resources to be measured. In an embodiment, based on the 1-bit indication in the RAR, the UE 102 then measures all CSI-RS resources of the CSI-RS set 2 obtained from the system information. In another embodiment, based on the subset indication in the RAR, the UE 102 only measures a subset of the CSI-RS resources of the CSI-RS set 2 obtained from the system information. In yet another embodiment, based on the 1-bit indication in the RAR, the UE 102 only measures (1022) a subset of the CSI-RS resources of the CSI-RS set 2 obtained from the system information based on the best NR-SS block.

[0103] Fig.11 is another sequence diagram depicting the initial beam alignment process during connection setup / establishment according to embodiments as disclosed herein. Fig.11In the process depicted in FIG, an initial beam alignment process is shown for the transition of UE 102 from idle / inactive state to connected state, i.e., during connection setup / establishment. UE 102 may only assume the presence of NR-SS during idle / inactive state, so UE 102 may measure NR-SS block RSRP, i.e., beam quality of several NR-SS blocks belonging to a NR-SS burst. UE 102 may derive cell quality RSRP by combining the beam qualities, and the cell quality metric may be used to rank detected cells during the cell reselection process. When UE 102 decides to transition to connected state, e.g., data packets arrive in UE buffer or UE 102 is paged by the network, it would be desirable to schedule the UE with the best beam as early as possible to achieve high data rate, i.e., Gbps data rate achievable on NR PHY layer. One possible solution is that initial beam alignment may be implemented based on NR-SS block level measurements corresponding to DL gNB beam quality. Based on indexing the NR-SS blocks implicitly (e.g., time index) or explicitly (e.g., beam index sequence detection), the NR-SS block measurement can be considered as a beam measurement associated with a beam ID. The UE 102 can indicate the best beam for NR-SS reception by sending a preamble on the beam ID mapped by the PRACH resource. There is a mapping of preamble to beam ID or a mapping of PRACH resources to beam ID. Assuming channel reciprocity, the UE 102 sends the preamble with the UE 102Tx beam in the same direction of the detected DL gNB best beam. Under the assumption of channel reciprocity, initial beam alignment is possible based on the RACH process with mapping of PRACH resources to beam ID. However, if channel reciprocity is not maintained, the beam characteristics of the NR-SS block transmission may not be correlated with the beam characteristics of the dedicated beam used for data scheduling.

[0104] An alternative solution is for the UE 102 to obtain the CSI-RS configuration from the system information. Since the system information can be broadcast periodically or provided in an on-demand manner based on UE request, the UE 102 can take appropriate actions to obtain the CSI-RS configuration.

[0105] exist Fig.11, UE 102 sends (1106) a preamble reserved for the system information request. If CSI-RS set 2 has been sent in the cell for other connected UEs, then based on the UE system information request, the serving cell 104a starts (1108) broadcasting the CSI-RS configuration in each system information block. The UE reads (1110) the CSI-RS configuration from the cell broadcast based on the scheduling information of the system information. In the RAR (1112), the serving cell 104a can indicate the UE 102 to start measuring the CSI-RS set 2 resources. Optionally, the RAR can also indicate a subset of the CSI-RS resources to be measured. There are several options for measuring CSI-RS resources. In an embodiment, based on the 1-bit indication in the RAR, the UE 102 then measures all CSI-RS resources of the CSI-RS set 2 obtained from the system information. In another embodiment, based on the subset indication in the RAR, the UE 102 only measures a subset of the CSI-RS resources of the CSI-RS set 2 obtained from the system information. In yet another embodiment, based on a 1-bit indication in the RAR, the UE 102 measures (1114) only a subset of CSI-RS resources of CSI-RS set 2 obtained from system information based on the best NR-SS block. The UE 102 measures the CSI-RS resources of CSI-RS set 2 obtained from system information autonomously or based on the indication in the RAR. After measuring the CSI-RS RSRP of the corresponding CSI-RS resource subset, the best CSI-RS resource index is indicated to the serving cell in MSG3 (1116) as CSI feedback. Based on the UE CSI feedback, the serving cell 104a takes this information into account for initial beam alignment for data scheduling.

[0106] Fig.121 is a block diagram depicting various modules of a UE according to an embodiment as disclosed herein. The main blocks presented for communication include a communication module 1202, a control signaling module 1204, a processor module 1206, a memory module 1208, a radio resource management module 1210, and a display module 1212. In an embodiment, the communication module 1202 is configured to decode synchronization signals, beam index sequences, PBCH, and SBCH broadcast by a 5G eNB. In an embodiment, the communication module 1202 is configured to pass RRC signaling to and from the 5G eNB 103. For example, the wireless communication module 1202 in the UE 102 can be configured to pass measurement reports and RRC reconfiguration complete messages to the 5G eNB 103. In addition, the communication module 1202 in the UE 102 can perform initial beam alignment during a random access procedure for a cell of a next generation RAT served by the 5G eNB 103. In addition, the communication module 1202 in the UE 102 can be configured to send and receive data from the 5G eNB 103 according to the physical layer waveform and the coding assumed for the next generation wireless system. The control signaling module 1204 in the UE 102 can be configured to prepare the relevant RRC message to be sent to the 5G eNB 103 and can also be configured to parse the relevant RRC message received from the 5G eNB 103. The processor module 1206 depicts the computing environment in the UE 102 for implementing the method of performing initial beam alignment during the random access process in the next generation wireless system 100. The computing environment of 1206 includes at least one processing unit equipped with a control unit and an arithmetic logic unit (ALU), a clock chip, multiple networking devices, and multiple input and output (I / O) devices. The processor module 1206 is responsible for processing the instructions of the algorithm. The processing unit receives commands from the control unit to perform its processing. In addition, any logical and arithmetic operations involved in the execution of the instructions are calculated with the help of the ALU. The overall computing environment can be composed of multiple cores of the same or different types, multiple CPUs of different types, specific media and other accelerators. The processing unit is responsible for processing the instructions of the algorithm. The algorithm including the instructions and codes required for implementation is stored in the memory module 1208 or the storage device, or in both. When executed, the instructions can be taken out from the corresponding memory module 1208 or the storage unit and executed by the processing unit. The processing unit synchronizes operations and executes instructions based on the timing signal generated by the clock chip. The embodiments of the present disclosure disclosed herein can be implemented by at least one software program running on at least one hardware device and performing network management functions to control elements. In addition, the memory module 1208 is also configured to store information related to UE operation. The radio resource management module 1210 in the UE 102 is responsible for various aspects such as cell-level mobility and beam-level mobility.The radio resource management module 1210 in the UE 102 may be configured to evaluate cell selection / reselection switching events and perform CSI-RS RSRP measurements based on CSI-RS measurements, respectively. A display module 1212 in the UE 102 may be configured so that a user may input information or information may be output on a display for the user to understand some UE 102 operations when the UE 102 operates in a dual connectivity mode of operation. Most UE 102 operations are transparent to the user and may not require user input or output on a display.

[0107] The embodiments disclosed herein may be implemented by at least one software program running on at least one hardware device and performing network management functions to control the elements. Fig.12 The elements shown include blocks that may be at least one of a hardware device, or a combination of a hardware device and a software module.

[0108] The description of the foregoing specific embodiments will fully reveal the general nature of the embodiments herein, and others can easily modify such specific embodiments and / or adapt them to various applications without departing from the general concept by applying current knowledge, and therefore, such adaptations and modifications should and are intended to be understood within the meaning and scope of equivalents of the disclosed embodiments. It will be understood that the words or terms used herein are used for descriptive purposes and not for limitation. Therefore, although the embodiments herein have been described with respect to preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications within the spirit and scope of the embodiments as described herein.

Claims

1. A method performed by a terminal in a wireless communication system, the method comprising: Sending a measurement report of at least one candidate target cell to the source base station; receiving a radio resource control RRC message from a source base station, the RRC message including configuration information of at least one conditional handover CHO candidate target cell associated with a channel state information reference signal CSI-RS and information on conditions for performing CHO, the configuration information of at least one CHO candidate target cell associated with the CSI-RS being sent from the target base station to the source base station; determining, based on the configuration information included in the RRC message, whether a result of measurement of at least one of the CSI-RSs of at least one CHO candidate target cell satisfies a condition for performing CHO; as well as Based on the condition for performing CHO being satisfied, synchronization with the target cell is performed.

2. The method of claim 1, wherein: Determination further includes: Based on the measurement result, a target cell is determined from at least one candidate target cell.

3. The method of claim 2, wherein: The determined reference signal received power RSRP of the target cell is higher than a threshold.

4. The method of claim 1, further comprising: Perform CHO with the target cell based on the configuration information.

5. The method of claim 1, wherein: The configuration information of at least one CHO candidate target cell associated with the CSI-RS further includes: at least one of period information for the CSI-RS, an identifier of the CSI-RS, and a physical cell identifier for the CSI-RS.

6. A method performed by a source base station in a wireless communication system, the method comprising: receiving a measurement report of at least one candidate target cell from a terminal; receiving a handover command message from a target base station, the handover command message including configuration information of at least one conditional handover CHO candidate target cell associated with a channel state information reference signal CSI-RS; as well as sending a radio resource control RRC message including configuration information of at least one CHO candidate target cell associated with the CSI-RS and information on conditions for performing CHO to the terminal, In which, whether the measurement result of at least one of the CSI-RSs of at least one CHO candidate target cell meets the conditions for performing CHO is determined by the terminal based on the configuration information included in the RRC message, and synchronization with the target cell is performed by the terminal based on that the conditions for performing CHO are met.

7. The method of claim 6, wherein: The target cell is determined by the terminal from at least one candidate target cell based on the measurement result.

8. The method of claim 7, wherein: The determined reference signal received power RSRP of the target cell is higher than a threshold.

9. The method of claim 6, wherein: The CHO with the target cell is performed by the terminal based on the configuration information.

10. The method of claim 6, wherein: The configuration information of at least one CHO candidate target cell associated with the CSI-RS further includes: at least one of period information for the CSI-RS, an identifier of the CSI-RS, and a physical cell identifier for the CSI-RS.

11. A terminal in a wireless communication system, the terminal comprising: Transceiver; as well as At least one processor configured to: sending a measurement report of at least one candidate target cell to the source base station via the transceiver, receiving a radio resource control RRC message from a source base station via a transceiver, the RRC message including configuration information of at least one conditional handover CHO candidate target cell associated with a channel state information reference signal CSI-RS and information on a condition for performing the conditional handover CHO, the configuration information of at least one CHO candidate target cell associated with the CSI-RS being sent from the target base station to the source base station, determining whether a result of measuring at least one of the CSI-RSs of at least one CHO candidate target cell satisfies a condition for performing CHO based on the configuration information included in the RRC message, and Based on the condition for performing CHO being satisfied, synchronization with the target cell is performed.

12. The terminal according to claim 11, wherein: The at least one processor is further configured to: Based on the measurement result, a target cell is determined from at least one candidate target cell.

13. The terminal according to claim 12, wherein: The determined reference signal received power RSRP of the target cell is higher than a threshold.

14. The terminal according to claim 11, wherein: The at least one processor is further configured to: Perform CHO with the target cell based on the configuration information.

15. The terminal according to claim 11, wherein: The configuration information of at least one CHO candidate target cell associated with the CSI-RS further includes: at least one of period information for the CSI-RS, an identifier of the CSI-RS, and a physical cell identifier for the CSI-RS.

16. A source base station in a wireless communication system, the source base station comprising: Transceiver; as well as At least one processor configured to: receiving, via the transceiver, a measurement report of at least one candidate target cell from the terminal, receiving configuration information of at least one conditional handover CHO candidate target cell associated with a channel state information reference signal CSI-RS from a target base station via a transceiver, and sending, via the transceiver, to the terminal a radio resource control RRC message including configuration information of at least one CHO candidate target cell associated with the CSI-RS and information on conditions for performing CHO, In which, whether the measurement result of at least one of the CSI-RSs of at least one CHO candidate target cell meets the conditions for performing CHO is determined by the terminal based on the configuration information included in the RRC message, and synchronization with the target cell is performed by the terminal based on that the conditions for performing CHO are met.

17. The source base station according to claim 16, wherein: The target cell is determined by the terminal from at least one candidate target cell based on the measurement result.

18. The source base station according to claim 17, wherein: The determined reference signal received power RSRP of the target cell is higher than a threshold.

19. The source base station according to claim 16, wherein: The CHO with the target cell is performed by the terminal based on the configuration information.

20. The source base station according to claim 16, wherein: The configuration information of at least one CHO candidate target cell associated with the CSI-RS further includes: at least one of period information for the CSI-RS, an identifier of the CSI-RS, and a physical cell identifier for the CSI-RS.

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