KR-20260067343-A - APPARATUS AND METHOD FOR PERFORMING INITIAL ACCESS PROCEDURE FOR MULTI-LINK OPERATION IN WIRELESS COMMUNICATION SYSTEM

Abstract

The present disclosure generally relates to a wireless communication system, and more specifically to an apparatus and method for performing an initial access procedure for multi-link operation in a wireless communication system. The terminal operation method of the present disclosure receives a synchronization signal block from a base station via a primary link and obtains a master information block by decoding a physical broadcast channel based on an SSB. The terminal receives a system information block based on an MIB and identifies the SSB information of a secondary link based on multi-link information included in the SIB. The multi-link information includes the center frequency, bandwidth, SSB period, number of SSBs in an SSB burst set, SSB time offset, etc. of the secondary link. The terminal selects at least one of the primary link or the secondary link and performs a random access procedure.

Inventors

• 장갑석
• 김용선
• 문성현
• 고영조

Assignees

• 한국전자통신연구원

Dates

Publication Date

20260512

Application Date

20251103

Priority Date

20241105

Claims (20)

1. In a terminal (User Equipment, UE) configured to perform a multi-link based initial connection in a wireless communication system, It includes a transceiver and a processor, and the processor, A Synchronization Signal Block (SSB) is received from a Transmission Reception Point (TRP), and the SSB is configured to identify a Physical Cell Identity (PCI), a Beam Index, and a TRP Index. Decode the Physical Broadcast Channel (PBCH) to obtain the Master Information Block (MIB), and Parsing the extended field of System Information Block 1 (SIB 1) to identify Random Access Occasions (RO) considering the TRP index, and A terminal configured to eliminate ambiguity in the preamble transmission timing and power calculation of a secondary link by controlling message 3 (Msg3) to include a Candidate Cell Indicator and at least one of an SSB Index, a TRP Index, and a PCI Index while performing 4-step Contention-Based Random Access (CBRA), and message 4 (Msg4) to include a Continuation Indicator, a PRACH Preamble Index, a PRACH Resource Index, or Tx Power.
2. A terminal according to claim 1, wherein the multi-link information of the SIB1 includes a center frequency, bandwidth, SSB periodicity, number of SSBs per burst, SSB time offset, PCI information, TRP index, or priority per secondary link.
3. A terminal according to claim 1, wherein the TRP-aware RO (TRP-aware RO) is mapped to a time-frequency resource as a combination of a beam index and a TRP index, and configured to distinguish multiple TRPs within the same PCI or TRPs of adjacent PCIs through wildcard mapping or group mapping.
4. A terminal according to claim 1, wherein PBCH scrambling or CRC masking is performed based on a seed or mask value set by at least one of a PCI index, a TRP index, or a beam index.
5. A terminal according to claim 1, wherein the reference signal (RS) or demodulation reference signal (DMRS) sequence is generated by a seed initialized to at least one of a PCI index, a TRP index, or a beam index, and mapped to a low-complexity sequence having only a real part or an imaginary part to reduce the complexity of the channel estimation operation of the terminal.
6. In a method for a terminal (User Equipment, UE) to perform a multi-link based initial connection in a wireless communication system, The process of receiving a Synchronization Signal Block (SSB) from a Transmission Reception Point (TRP), and A process of obtaining a Master Information Block (MIB) by decoding the Physical Broadcast Channel (PBCH) after identifying the Physical Cell Identity (PCI), Beam Index, and TRP Index, and A process of receiving System Information Block 1 (SIB1) and parsing multi-link information including the secondary link's SSB, Random Access Occasion (RO), and Priority, and A process of performing 4-step contention-based random access (CBRA) according to the above parsing result, wherein message 3 (Msg3) includes at least one of a candidate cell indicator, an SSB index, a TRP index, or a PCI index, and A method comprising a process for continuously proceeding with a secondary link connection, including a Continuation Indicator, a PRACH Preamble Index, a PRACH Resource Index, or Tx Power in Message 4 (Msg4).
7. A method according to claim 6, further comprising the process of measuring the Reference Signal Received Power (RSRP) or Reference Signal Received Quality (RSRQ) for a plurality of SSBs to identify the first best SSB as the primary link and the second best SSB as a secondary link candidate.
8. A method according to claim 6, further comprising the process of eliminating candidate cell ambiguity and maintaining the transmission speed during switching by identifying the SSB, Channel State Information-Reference Signal (CSI-RS), and Random Access Occasion (RO) of a secondary link based on a TRP Index while maintaining a primary link.
9. A method according to claim 6, further comprising a process that triggers to continuously perform additional 4-step Contention-Based Random Access (CBRA) or Contention-Free Random Access (CFRA) on a secondary link when the Continuation Indicator is set to '1'.
10. In claim 6, the mapping of the SSB, the Reference Signal (RS), and the Physical Broadcast Channel (PBCH) is, The Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) are mapped to the PCI Index, RS is mapped to the TRP Index, and PBCH is mapped to the Beam Index, or A method comprising a process that follows at least one of a configuration in which RS is mapped to a Beam Index, PBCH is mapped to a TRP Index, and PSS and SSS are mapped to a PCI Index.
11. In a base station (BS) of a wireless communication system, It includes a transceiver and a processor, and the processor, Transmit the Master Information Block (MIB) through the TRP-aware Synchronization Signal Block (SSB) and the Physical Broadcast Channel (PBCH), and Broadcasts multi-link information including the secondary link's SSB, Random Access Occasion (RO), and Priority as an Extended Field of System Information Block 1 (SIB1), and Upon receiving a random access preamble at the terminal, a random access response (Random Access Response, RAR, Msg2) and message 4 (Msg4) are constructed and transmitted based on at least one of the included SSB indicator (Synchronization Signal Block Indicator), TRP indicator (TRP Indicator), or PCI indicator (Physical Cell Identity Indicator), and A device controlled to indicate continuous access to the secondary link side via a Continuation Indicator.
12. An apparatus according to claim 11, wherein PBCH scrambling or CRC masking is performed based on at least one of a PCI index, a TRP index, and a beam index, and the reference signal (RS) is configured to be inserted into the PBCH without overlapping.
13. A device according to claim 11 that is controlled to minimize the TRP identification delay of a terminal by selecting and applying a shared mapping of PCI, beam, and TRP among SSB configuration options according to an operation scenario.
14. A device according to claim 11 that, upon receiving that the candidate cell indicator of a terminal is '1', includes SSB information, PRACH Preamble Index, PRACH Resource Index, or Tx Power information in message 2 (Msg2) or message 4 (Msg4) for a secondary link to indicate continuous random access.
15. A device according to claim 11 that monitors the channel status of a primary link or a secondary link and, when a critical condition is satisfied, switches the primary link through a Radio Resource Control (RRC) reconfiguration or Medium Access Control (MAC) control element (CE) and controls the reconfiguration of the previous primary link into a secondary link.
16. A method performed by a base station (BS) to support a multi-link based initial access in a wireless communication system, The process of transmitting a Master Information Block (MIB) through a TRP-aware Synchronization Signal Block (SSB) and a Physical Broadcast Channel (PBCH), and The process of broadcasting the secondary link's SSB, Random Access Occasion (RO), and Priority through System Information Block 1 (SIB1), and A process of constructing Message 2 (Msg2) or Message 4 (Msg4) in response to at least one of a Candidate Cell Indicator, SSB Index, TRP Index, or PCI Index included in Message 1 (Msg1) or Message 3 (Msg3) of the terminal, and A method comprising a process for indicating sequential random access of a secondary link through a Continuation Indicator.
17. A method according to claim 16 comprising the process of transmitting a message 4 (Msg4) with a Continuation Indicator set to '1' in a Non-Line-of-Sight (NLoS) environment during multi-link operation to indicate additional random access to the secondary link side.
18. A method according to claim 16, wherein the Random Access Response (RAR, Msg2) includes link-specific SSB information, and if necessary, includes a process of verifying secondary link settings through a Hybrid Automatic Repeat Request Acknowledgment (HARQ ACK).
19. In claim 16, the mapping of the SSB, the Reference Signal (RS), and the Physical Broadcast Channel (PBCH) is, The Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) are mapped to the PCI Index, RS is mapped to the TRP Index, and PBCH is mapped to the Beam Index, or A method comprising the process of selecting and applying at least one of the configurations in which RS is mapped to the Beam Index, PBCH is mapped to the TRP Index, and PSS and SSS are mapped to the PCI Index.
20. A method according to claim 16 comprising the process of controlling to maintain link-specific synchronization in a multi-TRP environment by instructing a terminal to have a different Timing Advance (TA) for each TRP.

Description

Apparatus and method for performing initial access procedure for multi-link operation in a wireless communication system The present disclosure generally relates to a wireless communication system, and more specifically to an apparatus and method for performing an initial connection procedure for multi-link operation in a wireless communication system. 6th Generation (6G) mobile communication, a next-generation wireless communication system, aims to utilize ultra-high frequency bands including the terahertz (THX) band, operate ultra-wideband frequencies, and provide ultra-low latency communication services. To achieve these goals, multi-link operation technology is emerging as a core technology. In existing 5th Generation (5G) New Radio (NR) systems, communication via a single link was predominant. Terminals establish a connection with a base station in a single frequency band and transmit and receive data through that link. While this single-link based system has the advantage of being simple to implement, it suffers from a problem where communication reliability drops significantly if link quality deteriorates or a failure occurs. In particular, when using ultra-high frequency bands, high path loss and signal blocking due to shielding occur frequently. Furthermore, it is difficult to meet the increasing data transmission rate requirements with a single link alone. Accordingly, the need for multi-link operation technology that simultaneously utilizes multiple frequency bands or multiple base stations has emerged. However, in multi-link systems, the initial connection procedure becomes complex. The terminal must perform synchronization for each of the multiple links, acquire system information for each link, and select the optimal link to attempt a connection. If the existing single-link-based initial connection procedure is applied as is, there are issues such as significantly increased connection delays and higher power consumption by the terminal. Furthermore, from the perspective of the base station, there is a need for a method to efficiently provide Synchronization Signal Block (SSB) information for multiple links. Transmitting independent system information for each link significantly increases overhead, while providing integrated information presents a problem where terminals find it difficult to distinguish between each link. FIG. 1a illustrates intra-cell mTRP and inter-cell mTRP scenarios according to various embodiments of the present disclosure. FIG. 1b is an illustrative diagram explaining the problem of a single TA in an intra-cell mTRP scenario according to various embodiments of the present disclosure. FIG. 1c is an illustrative diagram explaining the problem of a single TA in an Inter-cell mTRP scenario according to various embodiments of the present disclosure. Figure 1d is an example of a scenario illustrating a problem during random access to a secondary link. FIG. 1e is an illustrative diagram explaining the ambiguity of the transmission of a Channel State Information Reference Signal (CSI-RS) belonging to a non-serving Central Unit (CU) according to various embodiments of the present disclosure. FIG. 2 illustrates an mTRP scenario in which terminal 0 is connected to TRP 0 and TRP 1, respectively, according to one embodiment of the present disclosure. FIG. 3 illustrates an example of a multi-link system connection setup and link connection according to one embodiment of the present disclosure. FIG. 4 shows a first example of an SSB configuration according to one embodiment of the present disclosure. FIG. 5 shows a second example of an SSB configuration according to one embodiment of the present disclosure. FIG. 6 shows a third example of an SSB configuration according to one embodiment of the present disclosure. FIG. 7 shows a fourth example of an SSB configuration according to one embodiment of the present disclosure. FIG. 8 shows the frequency domain structure of a synchronization signal in an IFFT input section according to one embodiment of the present disclosure. FIG. 9 illustrates a PBCH transport process according to one embodiment of the present disclosure. FIG. 10 illustrates examples of proposed Random Access Occasion (RO) cases according to one embodiment of the present disclosure. FIG. 11 illustrates the first-1 procedure of a multi-link initial random access setup according to one embodiment of the present disclosure. FIG. 12 illustrates the first-second procedure of multi-link initial random access setup according to one embodiment of the present disclosure. FIG. 13 illustrates the first-third procedure of multi-link initial random access setup according to one embodiment of the present disclosure. FIG. 14 illustrates the first-fourth steps of a multi-link initial random access setup according to one embodiment of the present disclosure. FIG. 15 illustrates the first-fifth steps of a multi-link initial random access setup according to one embodiment of the present disclos