KR20240069882A - Method and apparatus for transmitting/receiving a preamble for random access during handover in wireless communication system - Google Patents

Abstract

This disclosure relates to 5G or 6G communication systems to support higher data rates after 4G communication systems such as LTE. The present disclosure relates to a method and device for transmitting and receiving a preamble for random access that can reduce time delay during handover in a wireless communication system. Handover from a source cell to a target cell in a wireless communication system according to an embodiment of the present disclosure. A method of a terminal for random access includes the process of transmitting measurement information about the source cell and the target cell to the first base station of the source cell, and RRC including RACH configuration information of the target cell from the first base station. Receiving a message and sequentially transmitting at least one preamble for the random access to a second base station of the target cell based on the RACH configuration information, wherein the RACH configuration information is provided by the terminal. In a random access procedure, a plurality of SSB indexes and a plurality of preamble indexes mapped to a plurality of ROs for transmitting the at least one preamble are included as list information.

Description

Method and device for transmitting and receiving a preamble for random access during handover in a wireless communication system {METHOD AND APPARATUS FOR TRANSMITTING/RECEIVING A PREAMBLE FOR RANDOM ACCESS DURING HANDOVER IN WIRELESS COMMUNICATION SYSTEM}

This disclosure relates to a method and device for transmitting and receiving a preamble for random access in a wireless communication system.

Looking back at the development of wireless communication through each generation, technologies have been developed mainly for human services, such as voice, multimedia, and data. After the commercialization of 5G (5th-generation) communication systems, an explosive increase in connected devices is expected to be connected to communication networks. Examples of objects connected to the network may include vehicles, robots, drones, home appliances, displays, smart sensors installed in various infrastructures, construction machinery, and factory equipment. Mobile devices are expected to evolve into various form factors such as augmented reality glasses, virtual reality headsets, and hologram devices. In the 6G (6th-generation) era, efforts are being made to develop an improved 6G communication system to provide a variety of services by connecting hundreds of billions of devices and objects. For this reason, the 6G communication system is called a beyond 5G system.

In the 6G communication system, which is expected to be realized around 2030, the maximum transmission speed is tera (i.e. 1,000 gigabit) bps and the wireless delay time is 100 microseconds (μsec). In other words, compared to the 5G communication system, the transmission speed in the 6G communication system is 50 times faster and the wireless delay time is reduced by one-tenth.

To achieve these high data rates and ultra-low latency, 6G communication systems will operate in terahertz bands (e.g., 95 GHz to 3 THz). Implementation is being considered. In the terahertz band, the importance of technology that can guarantee signal reach, or coverage, is expected to increase due to more serious path loss and atmospheric absorption compared to the mmWave band introduced in 5G. The main technologies to ensure coverage are RF (radio frequency) devices, antennas, new waveforms that are better in terms of coverage than OFDM (orthogonal frequency division multiplexing), beamforming, and massive multiple input/output (Massive multiple input/output). Multi-antenna transmission technologies such as input and multiple-output (massive MIMO), full dimensional MIMO (FD-MIMO), array antenna, and large scale antenna must be developed. In addition, new technologies such as metamaterial-based lenses and antennas, high-dimensional spatial multiplexing technology using OAM (orbital angular momentum), and RIS (reconfigurable intelligent surface) are being discussed to improve coverage of terahertz band signals.

In addition, in order to improve frequency efficiency and system network, the 6G communication system uses full duplex technology where uplink and downlink simultaneously utilize the same frequency resources at the same time, satellite and Network technology that comprehensively utilizes HAPS (high-altitude platform stations), network structure innovation technology that supports mobile base stations and enables network operation optimization and automation, and dynamic frequency sharing through collision avoidance based on spectrum usage prediction. (dynamic spectrum sharing) technology, AI-based communication technology that utilizes AI (artificial intelligence) from the design stage and internalizes end-to-end AI support functions to realize system optimization, and overcomes the limits of terminal computing capabilities. Next-generation distributed computing technologies that realize complex services using ultra-high-performance communication and computing resources (mobile edge computing (MEC), cloud, etc.) are being developed. In addition, through the design of new protocols to be used in the 6G communication system, the implementation of a hardware-based security environment, the development of mechanisms for safe use of data, and the development of technologies for maintaining privacy, the connectivity between devices is further strengthened and the network is further improved. Attempts are continuing to optimize, promote softwareization of network entities, and increase the openness of wireless communications.

Due to the research and development of these 6G communication systems, a new level of hyper-connected experience (the next hyper-connected) is possible through the hyper-connectivity of the 6G communication system, which includes not only connections between objects but also connections between people and objects. experience) is expected to become possible. Specifically, it is expected that the 6G communication system will be able to provide services such as truly immersive extended reality (truly immersive XR), high-fidelity mobile hologram, and digital replica. In addition, services such as remote surgery, industrial automation, and emergency response through improved security and reliability are provided through the 6G communication system, enabling application in various fields such as industry, medicine, automobiles, and home appliances. It will be.

The present disclosure provides a method and device for transmitting and receiving a preamble for random access that can reduce time delay during handover in a wireless communication system.

Additionally, the present disclosure provides a method and device for transmitting and receiving preamble(s) for random access using a plurality of synchronization signal blocks (SSBs) in a wireless communication system.

According to an embodiment of the present disclosure, a method of a terminal for random access during handover from a source cell to a target cell in a wireless communication system includes providing measurement information about the source cell and the target cell to the first base station of the source cell. A process of transmitting, a process of receiving an RRC message including RACH configuration information of the target cell from the first base station, and based on the RACH configuration information, at least one signal for the random access to the second base station of the target cell A process of sequentially transmitting a preamble, wherein the RACH configuration information includes a plurality of SSB indexes and a plurality of preamble indexes mapped to a plurality of ROs for the UE to transmit the at least one preamble in a random access procedure. Include them as list information.

In addition, according to an embodiment of the present disclosure, in a wireless communication system, a terminal that performs random access during handover from a source cell to a target cell includes a transceiver, and, through the transceiver, the source cell and the first base station of the source cell. Transmit measurement information about the target cell, receive an RRC message including RACH configuration information of the target cell from the first base station through the transceiver, and, based on the RACH configuration information, through the transceiver, At least one processor configured to sequentially transmit at least one preamble for random access to a second base station of a target cell, wherein the RACH configuration information is configured to allow the terminal to transmit the at least one preamble in a random access procedure. List information includes multiple SSB indexes and multiple preamble indexes mapped to multiple ROs for

In addition, according to an embodiment of the present disclosure, a method performed at the base station of the target cell for random access during handover from a source cell to a target cell in a wireless communication system includes RACH of the target cell to the first base station of the source cell. Transmitting an RRC message including configuration information and sequentially receiving at least one preamble for the random access from a terminal based on the RACH configuration information, wherein the RACH configuration information allows the terminal to randomly access In an access procedure, a plurality of SSB indexes and a plurality of preamble indexes mapped to a plurality of ROs for transmitting the at least one preamble are included as list information.

Additionally, according to an embodiment of the present disclosure, in a wireless communication system, a base station of the target cell that supports random access during handover from a source cell to a target cell includes a transceiver, and, through the transceiver, a first base station of the source cell. At least one processor configured to transmit an RRC message including RACH configuration information of the target cell and sequentially receive at least one preamble for the random access from the terminal through the transceiver based on the RACH configuration information. The RACH configuration information includes list information of a plurality of SSB indexes and a plurality of preamble indexes mapped to a plurality of ROs for the terminal to transmit the at least one preamble in a random access procedure.

1A and 1B are diagrams showing an example of a handover procedure in a general wireless communication system;
Figure 2 is a diagram showing an example of RACH configuration information provided to the terminal through RRC information along with a handover command in a general handover procedure;
Figure 3 is a diagram to explain the increase in waiting time (delay time) that occurs when transmitting and receiving a preamble for random access in a general handover procedure;
FIG. 4 is a diagram illustrating a method of transmitting and receiving a preamble for random access during handover in a wireless communication system according to an embodiment of the present disclosure;
Figure 5 is a flowchart showing a method for transmitting and receiving a preamble for random access during handover in a wireless communication system according to an embodiment of the present disclosure;
6A, 6B, and 6C are diagrams showing various configuration examples of a terminal that performs a random access procedure during handover in a wireless communication system according to an embodiment of the present disclosure;
FIG. 7 is a diagram illustrating an example of an operation for transmitting and receiving a preamble for random access during handover according to an embodiment of the present disclosure, and
Figure 8 is a diagram showing the configuration of a network entity in a wireless communication system according to an embodiment of the present disclosure.

Hereinafter, the operating principle of the present disclosure will be described in detail with reference to the attached drawings. In the following description of the present disclosure, if a detailed description of a related known function or configuration is determined to unnecessarily obscure the gist of the present disclosure, the detailed description will be omitted. In addition, the terms described below are terms defined in consideration of the functions in the present disclosure, and may vary depending on the intention or custom of the user or operator. Therefore, the definition should be made based on the contents throughout this specification.

The advantages and features of the present disclosure and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms, and the present embodiments are merely intended to ensure that the disclosure is complete and are within the scope of common knowledge in the technical field to which the present disclosure pertains. It is provided to fully inform those who have the scope of the invention, and the present disclosure is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

At this time, it will be understood that each block of the processing flow diagrams and combinations of the flow diagram diagrams can be performed by computer program instructions.

Additionally, each block may represent a module, segment, or portion of code that includes one or more executable instructions for executing specified logical function(s). Additionally, it should be noted that in some alternative execution examples it is possible for the functions mentioned in the blocks to occur out of order. For example, it is possible for two blocks shown in succession to be performed substantially at the same time, or it is possible for the blocks to be performed in reverse order depending on the corresponding function.

At this time, the term '~unit' used in this embodiment refers to software or hardware components such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), and '~unit' performs certain roles. do. However, '~part' is not limited to software or hardware. The '~ part' may be configured to reside in an addressable storage medium and may be configured to reproduce on one or more processors. Therefore, as an example, '~ part' refers to components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, and procedures. , subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and 'parts' may be combined into a smaller number of components and 'parts' or may be further separated into additional components and 'parts'. Additionally, components and 'parts' may be implemented to regenerate one or more CPUs within a device or a secure multimedia card. Also, in an embodiment, '~ part' may include one or more processors.

In the present disclosure, “A/B”, “A or B”, “A and/or B”, “at least one of A and B”, “at least one of A or B”, “A, B or C”, Phrases such as “at least one of A, B, and C” and “at least one of A, B, or C” each refer to any one of the items listed together in that phrase, or all possible combinations thereof. It can be included. Terms such as "first", "second", or "first" or "second" may be used simply to distinguish one component from another, and may refer to that component in other respects, such as importance or order) is not limited.

Terms used in the following description to identify a connection node, a term referring to network entities, a term referring to messages, a term referring to an interface between network objects, and a term referring to various types of identification information. The following are examples for convenience of explanation. Accordingly, the present disclosure is not limited to the terms described below, and other terms referring to objects having equivalent technical meaning may be used.

In the present disclosure, a base station (BS) is a network entity that performs resource allocation for a terminal and can communicate with the terminal through a wireless network, including eNode B, Node B, gNB, RAN (Radio Access Network), and AN. It may be at least one of (Access Network), RAN node, Integrated Access/Backhaul (IAB) node, radio access unit, base station controller, node on the network, or TRP (transmission reception point). A terminal (user equipment: UE) may be at least one of a terminal, MS (Mobile Station), cellular phone, smartphone, computer, or multimedia system capable of performing communication functions.

The present disclosure relates to a number of SSBs when transmitting and receiving a preamble for random access in a handover (i.e., cell-to-cell mobility) process that occurs when a mobile terminal in a wireless communication system needs to change the base station to which it is connected. We proposed a method to reduce waiting time during handover and increase the probability of random access success by making it available.

First, to help understand the present disclosure, a general handover procedure in a wireless communication system will be described.

1A and 1B are diagrams illustrating an example of a handover procedure in a general wireless communication system. The example of FIGS. 1A and 1B shows a handover procedure in the LTE system, and the handover procedure in the 5G (NR) system is also performed in substantially the same manner as the procedure in FIG. 1. In LTE, LTE-A or 5G systems, L3 handover (i.e., cell-to-cell mobility) can be performed according to the procedures defined in 3GPP TS36.300 or TS38.300. The example of Figures 1a and 1b shows a procedure based on 3GPP TS36.300 release 16. In the case of a 5G system, the source eNB and target eNB roles are played by a mobility management entity (MME) that manages the source gNB, target gNB, and mobility of the terminal. ) Except that the role of the access and mobility management function (AMF) and the serving gateway (S-GW) that manage the delivery of user traffic are performed by the user plane function (UPF), the entire handover procedure is shown in Figures 1a and 1b. It is substantially the same as the example. In the description of FIGS. 1A and 1B, descriptions of content not directly related to the present disclosure may be omitted.

The handover procedure in FIGS. 1A and 1B can be broadly divided into four steps (hereinafter, steps 1 to 4).

Step 1: The serving eNB/gNB transmits configuration information (measurement object, report configuration, measurement ID, etc.) for measuring channel status to the terminal (101), and the terminal determines the channel status (i.e., reception) based on the configuration information. signal strength/quality) is measured and reported to the serving eNB/gNB (102). At this time, the terminal measures the received signal strength/quality of the source cell (serving/source eNB/gNB/cell) (hereinafter referred to as “source cell”) and neighboring cells (neighbor eNB/gNB/cells) and periodically or at set events. When occurs, the measurement information can be transmitted to the source cell.

Step 2: This is the handover preparation step. The source cell that has received measurement information from the terminal decides whether to trigger handover based on the measurement information (103), and when it decides to trigger handover, the received signal among neighboring cells (neighbor eNB/gNB/cells) A handover request message to perform a handover procedure with one target cell (target eNB/gNB/cell) (hereinafter referred to as “target cell”) with good strength/quality is transmitted (104). The target cell that receives the handover request message performs acceptance control for handover (105), and when accepting the handover, sends a response message containing cell setting information for the handover procedure to the target cell to the source cell. Send (106). The response message may include the identifier of the target cell, frequency information, preamble information required in the random access procedure to the target cell, resource information, and identification information (cell radio network temporary identity: C-RNTI) of the terminal used in the target cell. there is.

Step 3: This is the handover execution step. The source cell transmits a handover command including the cell configuration information for a handover procedure to the target cell to the terminal (107). The terminal that receives the cell configuration information of the target cell through a handover command from the source cell (ie, old cell) switches RF (radio frequency) to perform a handover procedure to the target cell (ie, new cell). The terminal decodes the master information block (MIB) of the target cell to obtain the system frame number (SFN) of the target cell (i.e., acquires downlink (DL) synchronization) and performs a random access procedure to the target cell. Uplink allocation (UL grant) and timing advance (TA) can be obtained. The terminal transmits a preamble to the target cell in the random access procedure (109), and receives a random access response (RAR) message including the uplink allocation (UL grant) from the target cell that received the preamble (110a) , 110b). The terminal receiving the RAR message transmits an RRC message (msg3) including the C-RNTI of the terminal through a physical uplink shared channel (PUSCH) (111). The RRC message (msg3) can use the RRCConnectionReconfigurationComplete message in the case of an LTE system, and the RRCReconfigurationComplete message in the case of a 5G system. On the other hand, when supporting handover without a random access procedure (Rach-less handover), in operation 107 of step 3, the timing advance (TA) value is set to the terminal in advance to synchronize the uplink between the terminal and the target cell. It can be delivered to in advance. Additionally, when supporting DAPS (Dual application protocol stack), the terminal can maintain the connection with the source cell even after receiving the handover command from the target cell in operation 107. At this time, the source cell transmits an early status transfer to the target cell (108a). Afterwards, the DL packet transmitted from the source cell to the terminal is duplicated and delivered to the target cell, and the transfer operation is completed by transmitting a handover success message from the target cell to the source cell through operation 111a.

Step 4: This is the handover completion step. If the handover is successful as in steps 1 to 3, an operation to change the data path from the source cell to the target cell is performed in operations 112 to 118.

Hereinafter, we will describe the delay time (i.e. handover interruption time) due to an increase in waiting time that occurs when transmitting and receiving a preamble between a terminal and a target cell in a random access procedure performed during handover in a wireless communication system.

This delay time may occur during the “Detach from old cell and synchronize to new cell” operation to operation 111 in the example of FIG. 1A.

Generally, in a handover procedure, a terminal that disconnects from a source cell decodes the MIB of the target cell to connect to the target cell. After the MIB decoding is completed, in the case of Rach-based handover, the UE receives the target cell's PRACH resource period information (see "prach-config-index" in TS36/38.331), SSB and SSB for transmitting the preamble in the random access procedure. Transmit a preamble for random access to the target cell to the RO corresponding to the "SSB index" specified through the mapping information of the RACH opportunity (RO) in the PRACH resource and the combination of available preamble indexes. do. In the case of the Rach-based handover, if the terminal succeeds in receiving RAR from the target cell, the terminal can know the timing advance (TA) information in the RAR and the grant location of the PUSCH, and the terminal transmits an RRC message to the target cell with the corresponding information. By doing this, the random access procedure can be completed. Meanwhile, in the case of Rach-less handover, the UE already knows the UL grant period of the target cell received through SFN information and handover command without transmitting a preamble to the target cell, so it sends an RRC message through operation 110a in FIG. 1a. It can be transmitted directly to the target cell through PUSCH (physical uplink shared channel). This disclosure is proposed to reduce time delay due to an increase in waiting time occurring in the Rach-based handover.

Figure 2 is a diagram showing an example of RACH configuration information provided to the terminal through RRC information along with a handover command in a general handover procedure. The example in Figure 2 illustrates the case where 2.5 ms is used as PRACH available resource per 10 ms (10 slots per 10 ms).

The RACH configuration information in FIG. 2 may refer to, for example, RACH-ConfigDedicated information in TS 38.331. The RACH-ConfigDedicated information is included in cell configuration information, and the RRCReconfiguration message that the UE receives from the source cell in operation 107 of FIG. 1A may include the cell configuration information for the target cell. The RACH-ConfigDedicated information may include information indicating the mapping relationship between the SSB index 21 and RO 22, as in the example of FIG. 2. The preamble index 23 represents the index of the preamble used by the terminal when performing a random access procedure by selecting a candidate beam of the target cell identified by the SSB index 21. In the example of FIG. 2, ssb-per RACH-Occasion is the number (m) of available SSBs per RACH-Occasion (RO), and the terminal uses one SSB indicated by the RO (e.g. RO#0) through RRC information. A random access procedure can be performed using the preamble corresponding to . In the example of Figure 2, PRACH-config-index (23) is a parameter that indicates when (or period) the terminal can transmit a preamble and what type of preamble format should be transmitted. If the SSB index mapped to RO#3 in slot#3 (201) of SFN1 is indicated as SSB#3 through RRC information received along with the handover command from the source cell, the UE moves from RO#3 to SSB#3. If the corresponding preamble is transmitted to the target cell and an RAR for the transmission of the preamble is not received from the target cell, the preamble cannot be retransmitted in another slot (for example, slot #7 (202), etc.) within the same SFN1. The preamble can be retransmitted in the same slot #3 of SFN.

In this general handover procedure, the UE can check the SSB index for random access to the target cell through the reserved resources in the RACH configuration information received along with the handover command, and the target cell can provide content free random access (CFRA) to the UE. preamble), and the UE transmits a preamble for random access from the RO mapped to one SSB index and one preamble index specified in the RACH configuration information (i.e. RACH-ConfigDedicated) to the target cell. I do it.

Figure 3 is a diagram to explain the increase in waiting time (delay time) that occurs when transmitting and receiving a preamble for random access in a general handover procedure.

In the example of FIG. 3, during the handover process from the source cell 310 to the target cell 320, the terminal 330 transfers one SSB index (for example, SSB#3) specified in the RACH configuration information to the target cell 320 and This shows an example of transmitting a preamble for random access from one RO (eg, RO#3) mapped to a preamble index to a target cell.

Referring to FIG. 3, when the source cell 310, which has received measurement information from the terminal 330, decides to trigger a handover based on the measurement information, the source cell 310 determines the target cell 320 in operation 301. ) to send a handover request message. In operation 302, when the target cell 320 accepts the handover request, it transmits a response message containing cell configuration information of the target cell 320 to the source cell 310. In operation 303, the source cell 310 transmits an RRC message (i.e., RRCReconfiguration message) including a handover command and the cell configuration information to the terminal 330. The cell configuration information includes RACH configuration information, and the RACH configuration information includes one SSB index and one preamble mapped to an RO for the UE to transmit a preamble in a random access procedure, as shown in the example in [Table 1] below. Includes index. [Table 1] below shows an example where the SSB index is indicated as SSB#3 and the preamble index is indicated as “59”. In the example of FIG. 3, SSB#3 has the best received signal strength/quality based on the measurement information of the terminal 330 among the beams of candidate SSBs (SSB#1, ..., SSB#8) in the target cell 320. Corresponds to the beam.

[Table 1]

In operation 304, the terminal 330 performs a random access procedure for uplink synchronization with the target cell 320. In the random access procedure, the terminal 330 generates one SSB index (SSB) based on the RACH configuration information. #3) and one RO (RO#3) mapped to the preamble index transmits a preamble for random access to the target cell.

However, in the operation of FIG. 3, an increase in waiting time (delay time) may occur when transmitting and receiving a preamble for random access. Specifically, as illustrated at the bottom of FIG. 3, the terminal 330 randomly accesses the target cell 320 using one SSB index (SSB#3) and a preamble index mapped to the RO (RO#3) of SFN#n. Although the preamble for is transmitted (31), the terminal 330 may fail to receive a random access response (RAR) message from the target cell 320 depending on the network situation (32). In this case, after RAR reception failure at the RO (RO#3) of SFN#n, a waiting time (33) is required until the preamble is retransmitted from the next RO of SFN#n+1. The terminal 330 may retransmit the preamble in RO#3 of SFN#n+1 after the waiting time (33) (34). Therefore, as the waiting time (T _wait ) 33 increases, the handover interruption time (T _interrupt ), when user traffic is interrupted, may increase. The handover interruption time (T _interrupt ) can be expressed as [Equation 1] below. T _RACH is the time taken in the random access procedure.

[Equation 1]

T _interrupt (interruption time) = T _wait + T _RACH (random access duration)

Additionally, if the terminal 330 fails to transmit a preamble to this RO due to a problem with the network environment or terminal capabilities, the terminal 330 can transmit the preamble after waiting until the next RO capable of transmitting the preamble arrives. In addition, due to the speed of the terminal 330, problems in terminal processing when decoding the MIB received from the target cell 320, and rapid changes in the RF environment such as fast fading, the preamble transmitted from the intended first RO location may be affected. If the terminal does not receive RAR, it must wait for at least the next cycle of RO, which may result in the logical preamble retransmission cycle being significantly longer. Due to this increase in waiting time 33, the terminal 330 may be placed in a traffic disconnection state, and if the number of beams carrying SSB increases in a communication environment such as massive MIMO in the 5G system as well as the later 6G system, the terminal 330 may be in a traffic disconnection state. The impact of waiting time (33) is expected to increase further. Therefore, a method is required to reduce the waiting time (delay time) that occurs when transmitting and receiving a preamble for random access in a handover procedure.

To this end, the present disclosure provides a method to reduce the waiting time (delay time) that occurs when transmitting and receiving the preamble by allowing multiple ROs mapped to multiple SSB indexes of the target cell to transmit a preamble for random access. I suggest.

FIG. 4 is a diagram illustrating a method of transmitting and receiving a preamble for random access during handover in a wireless communication system according to an embodiment of the present disclosure. In this disclosure, the source cell and target cell can be understood as the source base station and target base station, respectively, in a handover procedure.

The present disclosure relates to wireless communication in which, in a random access procedure during handover, the target cell instructs the UE a preamble index and an SSB index for random access (i.e., corresponding to the beam index of the target cell from which the UE receives the SSB in the target cell). It can be applied to the system.

In the present disclosure, the target cell provides RACH configuration information (included in cell configuration information) including indexes of a plurality of preambles that can be received in the random access procedure of the terminal and list information of SSB indexes corresponding to the preamble indexes. It is set and delivered to the source cell, and the source cell can transmit an RRC message (i.e. RRCReconfiguration message) including a handover command and cell configuration information of the target cell to the terminal. Then, the terminal performs a random access procedure by sequentially transmitting a preamble starting from the preamble index corresponding to the nearest RO, based on the list information of a plurality of preamble indexes and SSB indexes mapped to a plurality of ROs in the RACH configuration information. can do. The list information can be understood as SSB beam list information for preamble transmission in a random access procedure.

According to this disclosure, compared to the existing method of transmitting a preamble for random access from one RO mapped to one SSB index and one preamble index to the target cell, the waiting time that occurs when transmitting and receiving the preamble for random access in the handover procedure (Delay time) can be greatly reduced.

Specifically, referring to FIG. 4, when the source cell 410, which has received measurement information from the terminal 430, decides to trigger a handover based on the measurement information, in operation 401, the source cell 410 is the target cell. Send a handover request message to (420). In operation 402, when the target cell 420 accepts the handover request, it transmits a response message including cell configuration information of the target cell 420 to the source cell 410. In operation 403, the source cell 410 transmits an RRC message (i.e., RRCReconfiguration message) including a handover command and the cell configuration information to the terminal 430. The cell configuration information includes RACH configuration information proposed in this disclosure, and the RACH configuration information is mapped to a plurality of ROs for the UE to transmit a preamble in a random access procedure, as shown in the example in [Table 2] below. It includes multiple SSB indexes and multiple preamble indexes.

[Table 2]

In operation 404, the terminal 330 starts a random access procedure for uplink synchronization with the target cell 320. In the random access procedure, the terminal 430 generates a plurality of SSB indexes mapped to a plurality of ROs (e.g. RO#2, RO#3, RO#4, RO#5) based on the RACH configuration information. The preamble can be transmitted sequentially/selectively using (SSB#2, SSB#3, SSB #4, SSB#5) and multiple preamble indices. According to the method of FIG. 4, waiting time (delay time) when transmitting and receiving a preamble for random access can be reduced. Specifically, as illustrated at the bottom of FIG. 4, the terminal 430 performs random access to the target cell 320 using the SSB index (SSB#3) and preamble index mapped to the RO (RO#3) of SFN#n. However, the terminal 430 may fail to receive a random access response (RAR) message from the target cell 420 depending on network conditions (41). In this case, in the case of the conventional method described above, after RAR reception failure in the corresponding RO of SFN #n, a waiting time (33) is required until the preamble is retransmitted in the next RO of SFN #n + 1, but according to the method of FIG. 4, Even if RAR reception for the preamble transmitted from RO#3 of SFN#n fails, the terminal 430 uses the SSB index (SSB#4, SSB#5) and preamble index mapped to RO#4 and RO#5, respectively. The RAR can be received from the target cell 420 by sequentially or selectively transmitting a preamble for random access to the target cell 420 (42). Accordingly, according to the present disclosure, as shown by reference number 43 in FIG. 4, the waiting time is not required until the next RO#3 of SFN#n+1 for retransmission of the preamble, so the waiting time can be reduced, and user traffic The handover interruption time (T _interrupt ) can be reduced.

Figure 5 is a flowchart showing a method for transmitting and receiving a preamble for random access during handover in a wireless communication system according to an embodiment of the present disclosure.

Referring to FIG. 5, in operation 501, the source cell transmits configuration information for measuring the channel state to the terminal, and in operation 502, the terminal measures the channel state (i.e., received signal strength/quality) based on the configuration information. and reports to the source cell. At this time, the terminal can measure the received signal strength/quality of the source cell and transmit the measurement information to the source cell periodically or when a set event occurs.

In operation 503, the source cell that has received measurement information from the terminal determines whether to trigger handover based on the measurement information. If it decides to trigger handover, in operation 504, the source cell determines the received signal strength/strength among neighboring cells. A handover request message is transmitted to perform a handover procedure with one target cell with good quality. The target cell that has received the handover request message in operation 505 performs acceptance control for the handover, and if it accepts the handover, in operation 506, the target cell sets up a cell for the handover procedure to the target cell to the source cell. Send a response message containing information. In the present disclosure, the above-described RACH configuration information including a plurality of SSB indexes and a plurality of preamble indexes mapped to a plurality of ROs for the UE to transmit a preamble in a random access procedure as list information may be included in the cell configuration information. there is. The response message may also include the identifier of the target cell, frequency information, and identification information (C-RNTI) of the terminal used in the target cell.

In the present disclosure, the target cell can generate/set the list information using the method 1-1) or 1-2) below. The list information may be referred to as beam list information.

1-1) A method in which the UE includes information about a plurality of beams (i.e., beams corresponding to SSB indices) of the target cell reported through the measurement report in operation 501 in the list information.

1-2) A method in which the target cell generates the list information according to the source cell or beam(s) of the terminal (e.g., Network sniffing, UE based ANR (automatic neighbor relation), etc. can be used.) The network sniffing is This is a method in which cells receive signals from neighboring cells for a certain period of time and share beam information between cells. The UE based ANR is a system information block of the neighboring cell(s) when the UE performs an operation such as handover. : SIB) is decoded first and delivered to the source cell, and the source cell uses that information to create a Naver list of neighboring cell(s).

The source cell that has received the cell configuration information of the target cell including the RACH configuration information allocates downlink resources to the terminal in operation 507 and sends an RRC message (i.e. An RRCReconfiguration message) can be sent to the terminal. In the present disclosure, the list information included in the RACH configuration information may be selectively given priority using the method 2-1) or 2-2) below. The priority may be assigned to the target cell or source cell.

2-1) Priority list information: The preamble index mapped to the SSB index corresponding to the target cell's Best beam (i.e. the beam with the strongest received signal strength of the SSB at the terminal) is CFRA (contention-free random access). Designate (1 ^st priority), and specify the preamble index (s) mapped to the SSB indexes for the remaining beam (s) transmitting SSB (s) in the target cell by contention-based random access (CBRA) (2 ^nd priority), a method of generating list information of preamble indexes mapped to SSB indexes

2-2) List information without priority: A method of generating list information by specifying preamble indexes for all beams transmitting SSBs in the target cell as CFRA, regardless of the Best beam of the target cell. This method is used to generate list information by specifying CFRA. It can be used when a cell knows all load information of neighboring cell(s).

In operation 509, the terminal that has received cell configuration information including the RACH configuration information of the target cell through a handover command from the source cell (i.e. old cell) uses RF to perform a handover procedure to the target cell (new cell). Switching, decoding the MIB of the target cell to obtain the SFN of the target cell (i.e., acquiring downlink (DL) synchronization). Afterwards, the terminal starts a random access procedure to obtain uplink synchronization.

The terminal that starts the random access procedure in operation 510 sequentially or selectively transmits a preamble using multiple SSB indexes and multiple preamble indexes mapped to multiple ROs based on RACH configuration information including the list information. can do.

In the present disclosure, the terminal can sequentially or selectively transmit the preamble using one of the methods 3-1) to 3-3) below.

3-1) The UE can sequentially transmit the preamble for all ROs in the list information, starting from the SSB index mapped to the RO that can be tried first. In this case, the terminal can sequentially transmit the preamble starting from the RO that has reached the time when the preamble can be transmitted, regardless of whether RAR for the previously transmitted preamble is received.

3-2) If the RAR window in which the terminal can receive the RAR for the previously transmitted preamble has not expired (i.e., if the success/failure of the previous preamble transmission has not yet been determined), the preamble at that time is transmitted. You may not.

3-3) The terminal can perform one RA procedure at a time. That is, the UE can sequentially perform the RA procedure for multiple SSB indexes in the following manner: when the RAR window expires for one preamble transmission -> wait after performing power ramping -> perform the next RA procedure.

In operation 511, the terminal may receive a RAR message including an uplink allocation (UL grant) from the target cell that received the preamble. In operation 512, the terminal receiving the RAR message transmits an RRC message (msg3) including the C-RNTI of the terminal through PUSCH. For the 5G system, the RRC message (msg3) can use the RRC Reconfiguration Complete (RRRCeconfigurationComplete) message.

In operations 511 and 512, if there is only one RAR message transmitted from the target cell, the terminal may transmit an RRC message (msg3) through the corresponding UL grant. As an optional embodiment, if the target cell receives a second preamble from the terminal before transmitting a RAR message for the first preamble received from the terminal, the target cell transmits RAR messages for both preambles to the terminal. can do. In this case, the target cell receives two different preambles from the same C-RNTI and allocates a different UL grant to each, so it can check the UL resource to receive the RRC message (msg3), and the terminal can receive two RAR messages. For this, one RRC message (msg3) can be transmitted. Meanwhile, if the target cell receives another preamble with the same C-RNTI after receiving the RRC message (msg3) from the terminal, reception of that preamble can be ignored. Additionally, in the present disclosure, the target cell may transmit a RAR message (each may include a different TC-RNTI) for all preambles received from the terminal, and may allocate a UL grant to the terminal in each RAR message. Additionally, the terminal may transmit the RRC message (msg3) in response to the RAR message first received from the target cell. In operation 512, the terminal transmits a ReconfigurationComplete message for the first received RAR message, and the random access procedure using the remaining preamble index(s) ends.

In the present disclosure, the base stations of the source cell and/or target cell include a Radio Resource Control (RRC) layer to generate the above-mentioned measurement information and list information, a lower layer that receives measurement information from the terminal, and a peripheral It can support functions such as the aforementioned network sniffing and ANR that determine the situation. In addition, the base stations of the present disclosure transmit measurement information on multiple beams reported by the terminal to the handover target base station using SCTP (stream control transmission protocol), etc. (e.g., handover request) or transmit the list information to the source base station. It is a functional block that includes an interface including a function to transmit and may include a Data Unit (DU) and/or a Central Unit (CU).

In addition, in the present disclosure, when creating/setting the list information, the base station of the target cell may set the list information differently depending on the presence or absence of information on neighboring base stations, and the reported beam information in the handover request received from the base station of the source cell You can create the list information using . In addition, the base station of the target cell knows all information about its surrounding base stations, and if it is determined that mobility information for the next few seconds can be inferred through load information of surrounding base stations or AI (Artificial Intelligence) learning, the base station of the target cell It is also possible to create/set the list information using only the information you have. Additionally, the base station of the target cell may set priorities to the list information as described above depending on the presence of surrounding base stations or internal operation of the base station.

In addition, in the present disclosure, the terminal includes at least one MAC entity (Medium Access Control) (or at least one random access controller) that supports transmission of a preamble and monitoring reception of a RAR message according to the operation of the present disclosure in a random access procedure, An RRC layer capable of receiving and decoding an RRC message (i.e. RRCReconfiguration message) containing cell configuration information including the measurement report and RACH configuration information of the target cell, receiving and decoding the MIB of the target cell to obtain an SFN, and It may include at least one lower layer (PHY layer) that supports reception monitoring. The base stations and terminals of the source cell and/or target cell may be implemented to include a transceiver for transmitting and receiving signals through a wireless network, and at least one processor (or controller), and the at least one processor (or controller) and/or transceiver can be understood as a component combining software and/or hardware corresponding to functional blocks such as MAC entity, lower layer, and RRC layer that control operations according to embodiments of the present disclosure. there is.

Additionally, in the present disclosure, the terminal may receive the list information from the target cell via the source cell in a handover procedure, and based on the list information according to the number of MAC entity(s) and/or RAC(s) within the terminal. You can decide how to transmit the preamble. Even when the terminal uses one MAC entity and one RAC like an existing terminal, the preamble can be transmitted according to an embodiment of the present disclosure by performing one RA procedure at a time.

FIGS. 6A, 6B, and 6C are diagrams showing various configuration examples of a terminal that performs a random access procedure during handover in a wireless communication system according to an embodiment of the present disclosure.

Figure 6a is an example of a terminal using multiple MAC entities. In this case, the terminal may include multiple MAC entities 610a, ..., 610d, and lower layers 620a, ..., 620d connected to the multiple MAC entities 610a, ..., 610d. A terminal with the configuration of FIG. 6A can sequentially/selectively transmit preambles in multiple ROs under the control of MAC entities 610a, ..., 610d, and receive RAR for a previously transmitted preamble. Regardless of whether or not, the preamble can be transmitted when the RO reaches the transmission-capable point. For example, LL #1 (620a) -> RO#3, LL#2 (620b) -> RO#4, LL#3 (620c) -> RO#5, … It is possible to perform the RA procedure for each RO sequentially as many as the number of LL / MAC entities, as in the method of . The number of MAC entities and lower layers is an example, and at least two or more MAC entities and lower layers may be included in the terminal.

Figure 6b is an example of a terminal using multiple random access controllers (RACs) included in one MAC entity. In this case, the terminal may include one MAC entity 630 and lower layers 640a, ..., 640d connected to the MAC entity 630. The terminal with the configuration of FIG. 6B can sequentially/selectively transmit preambles from multiple ROs under the control of multiple RACs 630a within the MAC entity 630, and may transmit preambles sequentially/selectively for the previously transmitted preamble. Regardless of whether RAR is received, the preamble can be transmitted when the RO reaches the transmission-capable point. For example, LL #1 (640a) -> RO#3, LL#2 (640b) -> RO#4, LL#3 (640c) -> RO#5, … It is possible to sequentially perform the RA procedure for each RO as many as the number of RACs in the LL/MAC entity, as in the method of .

Figure 6c is an example of a terminal using one RAC included in one MAC entity. In this case, the terminal may include one MAC entity 650 and one lower layer 660 connected to the MAC entity 650. The terminal with the configuration of FIG. 6C has one RAC and can therefore perform one RA procedure at a time. When the RAR window expires for one preamble transmission, the UE can perform the RA procedure for each RO by performing power ramping and then waiting -> performing the RA procedure for the next RO.

In order to support terminal operations with the configurations of FIGS. 6A, 6B, and 6C, information indicating the number of MAC entities/RACs and/or the maximum number of MAC entities/RACs that the terminal can support (support_multiple_mac_entity, maximum_number_of_mac_entity) is provided to the terminal. It may be included in the terminal capability information transmitted to this base station.

For example, information indicating whether the terminal supports multiple MAC entities, multiple RACs, or one MAC entity/RAC, such as support_multiple_mac_entity = choice {MAC, RAC, NONE}, may be included in the terminal capability information. You can. Also maximum_number_of_mac_entity = choice {1… } Information that can indicate the maximum number of MAC entities or RACs in the terminal may be included in the terminal capability information in the form of }.

In addition, in this disclosure, the terminal capability information supports a preamble transmission function using multiple SSB indexes and multiple preamble indexes mapped to multiple ROs according to embodiments of the present disclosure, such as support_multiple_preamble = choice {boolen}. It may include information indicating terminal recognition.

FIG. 7 is a diagram illustrating an example of an operation for transmitting and receiving a preamble for random access during handover according to an embodiment of the present disclosure.

The operation example in FIG. 7 assumes that list information as shown in [Table 3] and [Table 4] below is provided to the terminal from the target cell through the source cell.

[Table 3]

[Table 4]

Referring to FIG. 7, the UE transmitted a preamble for random access to the target cell using the SSB index (SSB#3) and preamble index (59) mapped to the RO (RO#3) of SFN1 (71), but the network Depending on the situation, the terminal may fail to receive a random access response (RAR) message in the RAR window 701 for the SSB index (SSB#3) from the target cell. In this case, even if the terminal fails to receive RAR for the preamble transmitted from RO#3 of SFN1, the SSB index (SSB#4, SSB#5) and preamble index (17, 22) mapped to RO#4 and RO#5, respectively ) can be used to sequentially transmit a preamble for random access to the target cell (72, 73) and receive RAR from the target cell (74). The example of FIG. 7 shows the RAR window (702) for the SSB index (SSB#4) among the RAR windows (702, 703) for the SSB index (SSB#4, SSB#5) mapped to the preamble index (17, 22). This is an example of a case where RAR is successfully received. If the RAR is successfully received, the terminal terminates all related timers, does not perform preamble transmission of the preamble index 35 in SFN1 (76), and may not perform preamble retransmission of the preamble index 59 in SFN2. There is (75). In the existing method, when RAR reception for the first SSB#3 fails, a waiting time (712) of T _wait 10 ms or more is required, whereas according to the operation of the present disclosure, such as the example in FIG. 7, RAR reception for the first SSB#3 Even if this fails, the waiting time 711 can be significantly reduced to, for example, T _wait 1 to 4 ms. Therefore, according to the present disclosure, the handover interruption time (T _interrupt ) in which user traffic is interrupted can be significantly reduced.

Meanwhile, as an optional embodiment, in the example of FIG. 7, if the preamble transmission attempted in slot #7 for SSB #3 is determined to have failed, when slot #11 for SSB #4, where a new preamble transmission is possible, is reached, The random access procedure for SSB#3 can be terminated and the counter for SSB#3 transmission inside the terminal is increased by "1". The terminal can newly start a random access procedure for SSB#4 in slot#11, and when success/failure has not yet been determined for SSB#4, the preamble may not be transmitted even if the next slot timing available for transmission comes. Additionally, if all preamble transmissions in the middle fail and slot #7 of the next SFN2 arrives, the terminal sets the retransmission counter inside the terminal according to the counter for SSB#3 inside the terminal and increases the preamble ramping step (i.e., transmits The preamble can be retransmitted (by increasing the power).

In addition, as an optional embodiment, in a terminal using multiple MAC entities or multiple RACs, the terminal ID such as the TC-RNTI for the first received RAR among the multiple preambles transmitted by the terminal is the same as its C-RNTI. You can find uplink resources capable of msg3 transmission by mapping them to the terminal ID. Additionally, if a RAR other than the first received RAR is received, the terminal may ignore the other RAR, and upon receiving the RAR, the terminal may terminate all random access procedures other than the corresponding random access procedure.

FIG. 8 is a diagram showing the configuration of a network entity in a wireless communication system supporting RIS according to an embodiment of the present disclosure. The configuration of FIG. 8 may correspond to one of the base station, terminal, and RIS device described in the embodiments of FIGS. 4 to 8.

The network entity in FIG. 8 may include a processor 801, a transceiver 803, and a memory 805. In the embodiments of FIGS. 1 to 13 , the processor 801, transceiver 803, and memory 805 of the network entity may operate according to the communication method of the network entity described above. However, the components of the network entity are not limited to the examples described above. For example, a network entity may include more or fewer components than those described above. In addition, the processor 801, transceiver 803, and memory 805 may be implemented in the form of a single chip. The transceiver 803 is a general term for a receiver of a network entity and a transmitter of a network entity, and can transmit and receive signals to and from a terminal or another network entity. At this time, the transmitted and received signal may include at least one of control information and data. To this end, the transceiver 803 may include a wired or wireless transceiver and may include various components for transmitting and receiving signals. The transceiver 803 may receive a signal, output it to the processor 801, and transmit the signal output from the processor 801. Additionally, the transceiver 803 may receive a communication signal, output it to the processor 801, and transmit the signal output from the processor 801 to another network entity through a network. The memory 805 may store programs and data necessary for operation of a network entity according to at least one of the embodiments of FIGS. 4 to 8. Additionally, the memory 805 may store control information or data included in signals obtained from a network entity. The memory 805 may be composed of a storage medium such as ROM, RAM, hard disk, CD-ROM, and DVD, or a combination of storage media. Additionally, the processor 801 may control a series of processes so that the network entity can operate according to at least one of the embodiments of FIGS. 1 to 8. For example, the processor 801 may include at least one processor.

Methods according to embodiments described in the claims or specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

When implemented as software, a computer-readable storage medium that stores one or more programs (software modules) may be provided. One or more programs stored in a computer-readable storage medium are configured to be executable by one or more processors in an electronic device (configured for execution). One or more programs include instructions that cause the electronic device to execute methods according to embodiments described in the claims or specification of the present disclosure.

These programs (software modules, software) include random access memory, non-volatile memory including flash memory, read only memory (ROM), and electrically erasable programmable ROM. (EEPROM: Electrically Erasable Programmable Read Only Memory), magnetic disc storage device, Compact Disc-ROM (CD-ROM: Compact Disc-ROM), Digital Versatile Discs (DVDs), or other types of It can be stored in an optical storage device or magnetic cassette. Alternatively, it may be stored in a memory consisting of a combination of some or all of these. Additionally, multiple configuration memories may be included.

In addition, the program may be operated through a communication network such as the Internet, an intranet, a local area network (LAN), a wide LAN (WLAN), or a storage area network (SAN), or a combination thereof. It may be stored on an attachable storage device that is accessible. This storage device can be connected to a device performing an embodiment of the present disclosure through an external port. Additionally, a separate storage device on a communication network may be connected to the device performing an embodiment of the present disclosure.

In the specific embodiments of the present disclosure described above, components included in the invention are expressed in singular or plural numbers depending on the specific embodiment presented. However, singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present disclosure is not limited to singular or plural components, and even components expressed in plural may be composed of singular or singular. Even expressed components may be composed of plural elements.

Meanwhile, in the detailed description of the present disclosure, specific embodiments have been described, but of course, various modifications are possible without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure should not be limited to the described embodiments, but should be determined not only by the scope of the patent claims described later, but also by the scope of this patent claim and equivalents.

Claims (20)

In a terminal method for random access during handover from a source cell to a target cell in a wireless communication system,
Transmitting measurement information about the source cell and the target cell to the first base station of the source cell;
Receiving a radio resource control (RRC) message including random access channel (RACH) configuration information of the target cell from the first base station;
Based on the RACH configuration information, sequentially transmitting at least one preamble for the random access to the second base station of the target cell,
The RACH configuration information includes a list of a plurality of synchronization signal block (SSB) indexes and a plurality of preamble indexes mapped to a plurality of ROs (RACH Occasions) for the terminal to transmit the at least one preamble in a random access procedure. How to include it.
According to claim 1,
The at least one preamble is transmitted sequentially starting from the SSB index mapped to the RO that can be tried first for ROs in the list information.
According to claim 2,
In response to transmission of the preamble, receiving a random access response (RAR) message from the second base station,
The transmitting process further includes sequentially transmitting the preamble, starting from the RO that has reached a time point at which the preamble can be transmitted, regardless of whether the RAR message is received for the previously transmitted preamble.
According to claim 1,
In the list information, the preamble index mapped to the first SSB index corresponding to the SSB beam with the strongest received signal strength among the plurality of SSB indexes is designated as contention-free random access (CFRA), and the SSBs in the target cell are A method in which preamble indices mapped to SSB indices corresponding to the remaining SSB beams being transmitted are designated as content-based random access (CBRA).
According to claim 1,
A method in which preamble indexes mapped to the plurality of SSB indexes in the list information are designated as CFRA.
According to claim 1,
A method in which the terminal sequentially transmits the at least one preamble within the same system frame number (SFN) using at least one medium access control (MAC) entity or at least one random access controller (RAC).
According to claim 1,
When the terminal transmits the at least one preamble using one MAC entity or one RAC, power ramping is performed after expiration of the RAR window for one preamble transmission, and then sequentially performs the next random access procedure. How to transmit a preamble.
In a terminal that performs random access during handover from a source cell to a target cell in a wireless communication system,
transceiver; and
Transmitting measurement information about the source cell and the target cell to the first base station of the source cell through the transceiver,
Receives a radio resource control (RRC) message including random access channel (RACH) configuration information of the target cell from the first base station through the transceiver,
At least one processor configured to sequentially transmit, through the transceiver, at least one preamble for the random access to a second base station of the target cell based on the RACH configuration information,
The RACH configuration information includes a list of a plurality of synchronization signal block (SSB) indexes and a plurality of preamble indexes mapped to a plurality of ROs (RACH Occasions) for the terminal to transmit the at least one preamble in a random access procedure. A terminal containing .
According to claim 8,
The at least one preamble is transmitted sequentially starting from the SSB index mapped to the RO that can first attempt the ROs in the list information.
According to clause 9,
The at least one processor receives, through the transceiver, a random access response (RAR) message from the second base station in response to transmission of the preamble, and determines whether the RAR message is received for a previously transmitted preamble. Regardless, the terminal is further configured to sequentially transmit the preamble starting from the RO that has reached the time point at which the preamble can be transmitted.
According to claim 8,
In the list information, the preamble index mapped to the first SSB index corresponding to the SSB beam with the strongest received signal strength among the plurality of SSB indexes is designated as contention-free random access (CFRA), and the SSBs in the target cell are The preamble indexes mapped to the SSB indexes corresponding to the remaining SSB beams being transmitted are designated as content-based random access (CBRA).
According to claim 8,
The preamble indexes mapped to the plurality of SSB indexes in the list information are designated as CFRA.
According to claim 8,
The at least one processor is configured to sequentially transmit the at least one preamble within the same system frame number (SFN) using at least one medium access control (MAC) entity or at least one random access controller (RAC). Terminal.
According to claim 8,
When the terminal transmits the at least one preamble using one MAC entity or one RAC, the at least one processor performs power ramping after expiration of the RAR window for one preamble transmission through the transceiver. A terminal configured to transmit the next preamble in sequence in the next random access procedure after performing ramping.
In a method performed at a base station of a target cell for random access during handover from a source cell to a target cell in a wireless communication system,
Transmitting a radio resource control (RRC) message including random access channel (RACH) configuration information of the target cell to the first base station of the source cell;
Based on the RACH configuration information, sequentially receiving at least one preamble for the random access from the terminal,
The RACH configuration information includes a list of a plurality of synchronization signal block (SSB) indexes and a plurality of preamble indexes mapped to a plurality of ROs (RACH Occasions) for the terminal to transmit the at least one preamble in a random access procedure. How to include it.
According to claim 15,
In the list information, the preamble index mapped to the first SSB index corresponding to the SSB beam with the strongest received signal strength among the plurality of SSB indexes is designated as contention-free random access (CFRA), and the SSBs in the target cell are A method in which preamble indices mapped to SSB indices corresponding to the remaining SSB beams being transmitted are designated as content-based random access (CBRA).
According to claim 15,
A method in which preamble indexes mapped to the plurality of SSB indexes in the list information are designated as CFRA.
In the base station of the target cell that supports random access during handover from a source cell to a target cell in a wireless communication system,
transceiver; and
Transmitting, through the transceiver, a radio resource control (RRC) message including random access channel (RACH) configuration information of the target cell to the first base station of the source cell,
Based on the RACH configuration information, at least one processor configured to sequentially receive at least one preamble for the random access from the terminal through the transceiver,
The RACH configuration information includes list information of a plurality of synchronization signal block (SSB) indexes and a plurality of preamble indexes mapped to a plurality of ROs (RACH Occasions) for the terminal to transmit the at least one preamble in a random access procedure. Base station including.
According to claim 18,
In the list information, the preamble index mapped to the first SSB index corresponding to the SSB beam with the strongest received signal strength among the plurality of SSB indexes is designated as contention-free random access (CFRA), and the SSBs in the target cell are The preamble indexes mapped to the SSB indexes corresponding to the remaining SSB beams being transmitted are designated by the base station as content-based random access (CBRA).
According to claim 18,
A base station in which preamble indexes mapped to the plurality of SSB indexes in the list information are designated as CFRA.

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