According to the  5G SA Cell Search & Network Entry Matrix , a UE completes frame synchronization after reading the MIB, not the SS. The SS (Synchronization Signal) is used for initial detection and coarse timing synchronization, but it does not provide enough information for frame synchronization. The MIB (Master Information Block) is part of the SSB (Synchronization Signal Block) and contains essential system information, such as system frame number and subcarrier spacing, which are needed for frame synchronization.

According to the  Radio Resource Control , the maximum number of RRC_CONNECTED UEs depends on the number of available C-RNTIs (Cell Radio Network Temporary Identifiers) in a cell. The number of C-RNTIs is limited by the size of the RNTI field in the DCI (Downlink Control Information) format. For NR TDD cells, the RNTI field size is 16 bits, which allows up to 65,536 C-RNTIs. For NR FDD cells, the RNTI field size is 14 bits, which allows up to 16,384 C-RNTIs. Therefore, an NR TDD cell can support more RRC_CONNECTED UEs than an NR FDD cell under the same gNodeB.

According to the  5G NR Protocol Structure Changes - An Overview , the PCFICH and PHICH channels have been deleted from the physical layer in 5G compared with LTE, because they are no longer needed due to the flexible frame structure and numerology of 5G NR.

According to the  HCIA-5G V2.0 Exam Outline , user capacity usage is an NR system indicator that is at the base station level, which corresponds to option C. It reflects the number of users that can be served by a base station. PRB usage, PDCCH resource usage, and paging resource usage are NR system indicators that are at the cell level, which correspond to options A, B, and D. They reflect the utilization of physical resources in a cell.

According to the  Beamforming techniques for massive MIMO systems in 5G , these statements are correct about downlink beamforming. Beamforming is a technique that uses multiple antennas to steer the transmitted signal toward the intended user or direction. Static beams are used for broadcast channels, such as MIB and SIB, which are transmitted to all UEs in a cell. Dynamic beams are used for traffic channels, such as PDSCH and PDCCH, which are transmitted to specific UEs based on their channel conditions and locations. Both broadcast channels and traffic channels support beamforming, but with different beamforming methods and performance requirements.

According to the  HCIA-5G V2.0 Exam Outline , the 3.5 GHz+2.1 GHz uplink and downlink decoupling/super uplink architecture uses spectrum sharing technologies such as Dynamic Spectrum Sharing (DSS) and Spectrum Sharing (SS) to enable 3.5 GHz NR and 2.1 GHz LTE to share only the uplink spectrums, while the downlink spectrums are used exclusively by each technology.

 According to the  5G NR Uplink Power Control Procedure , SIB2 is the message that contains the PRACH power control parameters, such as msg3-Alpha, p0-NominalWithoutGrant, and p0-AlphaSets. These parameters are used by the UE to determine the transmit power of the PRACH preamble.

The link budget parameters that may differ depending on use in either densely populated urban areas or rural areas are area coverage rate, shadow fading margin, and penetration loss. The area coverage rate is the percentage of area within a cell that can receive a signal above a certain threshold.  In densely populated urban areas, the area coverage rate may be lower than in rural areas due to more interference and obstacles  13 . The shadow fading margin is an additional margin added to the link budget to account for the variation of signal strength due to obstacles in the propagation path.  In densely populated urban areas, there may be more buildings and structures that cause shadow fading than in rural areas, so a larger shadow fading margin may be needed  14 . The penetration loss is the loss of signal strength when it passes through walls or windows into buildings.  In densely populated urban areas, there may be more indoor users than in rural areas, so a larger penetration loss may be considered  15 . The antenna gain is not a parameter that depends on use in either densely populated urban areas or rural areas.  It is a parameter that depends on the antenna design and configuration, which are usually fixed for a given system  16 .

According to the  5G-NR (EN-DC) Bearer Concept , in MR-DC (Multi-Radio Dual Connectivity) architecture, data split on a base station can be affected by the following factors:

PDCP layer buffer: The PDCP layer buffer stores user plane data before sending it to lower layers. The buffer size and occupancy can affect how data is split between LTE and NR bearers.

X2 latency: The X2 latency is the delay between LTE and NR base stations over the X2 interface. The X2 latency can affect how data is split between LTE and NR bearers by causing reordering or duplication of packets.

Air interface latency: The air interface latency is the delay between base stations and user equipment over the air interface. The air interface latency can affect how data is split between LTE and NR bearers by causing reordering or duplication of packets.

The RLC layer buffer does not affect data split on a base station because it is located below the PDCP layer where data split occurs.

According to the  5G EN-DC Architecture and Interfaces , there are two methods that can be used to support X2 interconnection between an eNodeB and a gNodeB in NSA networking:

Interconnection through CI interfaces on the UMPT boards in different subracks: The UMPT is a universal main processing and transmission unit that provides main processing and transmission functions for a subrack. The UMPT has two CI interfaces that can be used for X2 interconnection with other base stations. The CI interfaces support CPRI, OBSAI, and eCPRI protocols and can use optical fibers or electrical cables for transmission. The CI interfaces can be configured as master or slave interfaces depending on the network topology.

IPRAN interconnection between subracks: IPRAN is an IP-based radio access network that uses IP transport technologies to carry base station traffic over Ethernet or MPLS networks. IPRAN can support X2 interconnection between different base stations by using IP routers or switches. IPRAN can provide flexible networking, high bandwidth, low latency, and high reliability for X2 interconnection.

The other two methods are not valid for X2 interconnection between an eNodeB and a gNodeB:

Interconnection via backplane in a subrack: This method is only applicable for X2 interconnection between two eNodeBs or two gNodeBs that are installed in the same subrack. The backplane is the internal bus that connects different boards within a subrack. The backplane supports CPRI, OBSAI, and eCPRI protocols and can provide high-speed data transmission between boards.

Interconnection through HEI interfaces on the UBBP boards in different subracks: This method is not supported by Huawei base stations. The HEI interface is a high-speed Ethernet interface that is used for data transmission between base stations and core networks or transport networks. The HEI interface supports S1, Xn, F1, E1, and N2 protocols and can use optical fibers or electrical cables for transmission. The HEI interface cannot be used for X2 interconnection between base stations.

Therefore, the correct answer is A and D.