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  I. A CORESET is a Control Resource Set used in 5G (NR). It is a set of physical resources within a specific area of ​​the Downlink Resource Grid used to carry the PDCCH (DCI). In 5G (NR), the PDCCH is specifically designed to be transmitted within a configurable Control Resource Set (CORESET).   II. PDCCH Location The CORESET in 5G is similar to a Control Region in LTE because its Resource Set (RB) and OFDM symbol set are configurable, and it has a corresponding PDCCH search space. The flexibility of NR Control Region configuration, including time, frequency, parameter set, and operating point, allows it to meet a wide range of application scenarios. While PDCCHs in LTE Control Regions are allocated across the entire system bandwidth, NR PDCCHs are transmitted within a specially designed CORESET area, located in a specific region of the frequency domain, as shown in the diagram below.   III. 4G PDCCH and 5G PDCCH CORESET Frequency allocation in a CORESET configuration can be continuous or discontinuous. A CORESET configuration spans 1-3 consecutive OFDM symbols in time. REs in a CORESET are organized into REGs (RE groups). Each REG consists of 12 REs from one OFDM symbol in an RB. The PDCCH is confined to a CORESET and transmitted using its own demodulation reference signal (DMRS) to achieve control channel beamforming for the UE. To accommodate different DCI payload sizes or different coding rates, the PDCCH is carried by 1, 2, 4, 8, or 16 Control Channel Elements (CCEs). Each CCE contains 6 REGs. The CCE-to-REG mapping of a CORESET can be interleaved (for frequency diversity) or non-interleaved (for local beamforming). IV. CORESET Mapping Each 5G terminal (UE) is configured to blindly test multiple PDCCH candidate signals with different DCI formats and aggregation levels. Blind decoding increases the complexity of the UE, but is necessary for flexibly scheduling and processing different DCI formats with low overhead.   V. CORESET Characteristics The CORESET control resource set in 5G (NR) is similar to the LTE PDCCH control area; 5G (NR) CORESETs are divided into two types: general CORESETs and UE-specific CORESETs; Each active downlink BWP can configure up to 3 core sets, including general CORESETs and UE-specific CORESETs; A serving cell can have up to 4 BWPs, and each BWP can have up to 3 CORESETs, for a total of 12 CORESETs; Each CORESET can be identified by an index ranging from 0 to 11, named Control Resource Set Id; The Control Resource Set Id is unique within the same serving cell; When a specific CORESET is defined, its index is CORESET0; this CORESET is configured using a 4-bit information element in the MIB (Master Information Block), which is associated with the cell-defined synchronization signal and Physical Broadcast Channel (PBCH) block (SSB); CORESETs are only configured within their associated Bandwidth Weighted (BWP) Activation occurs only upon activation, except for CORESET0, which is associated with the initial bandwidth-weighted packet (the bandwidth-weighted packet with index 0); In the frequency domain, CORESETs are configured on 6 PRB frequency grids in units of 6 PRBs; In the time domain, CORESETs are configured as 1, 2, or 3 consecutive OFDM symbols.  

Compared to previous generations of technology, 5G (NR) has higher requirements for timing and synchronization accuracy. This is because the network needs synchronization to achieve functions such as carrier aggregation, Mass MIMO, and TDD (Time Division Duplex); key technologies such as enhanced boundary clocks, PTP (Precise Time Protocol), and TSN (Time Sensitive Networking) can meet its accuracy requirements; regarding timing and synchronization status reports, 3GPP defines them in TS38.413 as follows:     I. Timing Synchronization Status Report The purpose of the timing synchronization status report process in the 5G system is to enable NG-RAN nodes to provide RAN timing synchronization status information to the AMF in accordance with TS 23.501 and TS 23.502; the timing synchronization status report process uses signaling not associated with the UE. The successful report operation process is shown in Figure 8.19.2.2-1, where:   The NG-RAN node initiates the process by sending a TSCTSF timed synchronization status report message, indicated by the routing ID IE, to the AMF.   II. The purpose of the timed synchronization status report is to enable the AMF to request the NG-RAN node to start or stop reporting RAN timed synchronization status information as specified in TS 23.501 and TS 23.502. The successful synchronization status report operation process is shown in Figure 8.19.1.2-1 below. The reporting process uses non-UE associated signaling; where:     AMF initiates this process by sending a timing synchronization status request message to the NG-RAN node. If the RAN TSS request type IE contained in the timing synchronization status request message is set to "start", the NG-RAN node should start RAN TSS reporting for the TSCTSF indicated by the route ID IE. If the RAN TSS request type IE is set to "stop", the NG-RAN node should stop reporting the TSCTSF indicated by the route ID IE. III. The scheduled synchronization status report operation failed, as shown in Figure 8.19.1.3-1, where:     If an NG-RAN node is unable to report the timing synchronization status, the process should be considered a failure and a "Timing Synchronization Status Failed" message should be returned.  

I. Service Support Similar to 2G, 3G, and 4G mobile communication systems, 5G (NR) systems support services categorized into three main types: voice, data, and video. A cellular mobile system consists of two basic parts: the mobile terminal (UE) and the network (composed of base stations and backend data connection components such as the core network and fiber optics).   II. System Characteristics 5G is developed according to 3GPP standards Release 15 and higher, and is backward compatible with LTE and LTE-Advanced Pro. Currently, 5G systems are being developed in multiple frequency bands to support spectrum regulation worldwide. A 5G system can be composed of three parts: UE (i.e., the terminal - mobile phone) gNB (i.e., the base station) CN (i.e., the core network)   III. 5G Network Deployment 5G deployment is divided into Non-Standalone (NSA) and Standalone (SA) architectures. Specifically:   In NSA, the UE operates simultaneously on both the LTE eNB and the 5G gNB. In this mode, the UE uses the C-plane (control plane) of the LTE eNB for initial synchronization, and then camps on the U-plane (user plane) of the 5G gNB for traffic exchange. In SA, the UE operates only in the presence of a 5G base station (gNB). In this mode, the UE uses the control plane of the 5G base station for initial synchronization, and then also camps on the user plane of the 5G base station for traffic exchange.   IV. Service Call Flow 4.1 Voice Call Flow 5G voice calls establish a circuit between the caller and the called party to enable voice transmission and reception over the 5G network. Voice calls are of two types: Mobile-initiated call Mobile-terminated call Regular voice calls can be made using 4G/5G phones without any applications. 4.2 Data Call Flow 5G data calls establish a virtual circuit between the caller and the called party to enable data transmission and reception over the 5G network. Data calls are of two types: Mobile-initiated packet-switched call Mobile-terminated packet-switched call Specific services include normal internet browsing and uploading/downloading after establishing an internet connection with the 5G network and the 5G phone (i.e., the terminal).   4.3 Video Call Flow 5G video calls establish a connection between two phones (or terminals) and use a packet-switched connection for video transmission and reception; it uses applications such as WhatsApp, Facebook Messenger, and GTalk over the internet connection.

    Compared to 4G systems, 5G (NR) has achieved breakthrough improvements in key performance indicators of mobile communication; it also supports various emerging application scenarios. Based on the success of 5G (NR) systems, 6G is expected to emerge around the end of 2030. 3GPP SA1's multiple studies on Rel-19 not only demonstrate the additional capabilities that 5G systems will bring, but also provide guidance for the future capabilities required for 6G systems.   I. 3GPP Standards The entire development of mobile communication from GSM (2G), WCDMA (3G), LTE (4G) to NR (5G) has adopted 3GPP, the only and globally leading communication standard. During this period, almost all mobile phones and devices connected to cellular networks supported at least one of these standards. Besides contributing to the enormous success of 4G systems (commonly known as LTE), 3GPP has also significantly improved the performance of cellular communication systems in 5G.   II. 5G Standards and Functions Since the first commercial deployment of 5G systems in 2018, as shown in Figure 1, 3GPP has continuously added new functions in subsequent versions, including:     Rel-15, Rel-16, and Rel-17 are the first three versions supporting 5G systems, providing the basic functionalities that distinguish 5G from 4G systems. Rel-18, Rel-19, and Rel-20 add advanced features to 5G systems and are also known as 5G-Advanced. The second and third phase working groups in 3GPP developed the Rel-18 system architecture and protocols, while the first phase working group of 3GPP discussed 6G system architectures beyond the Rel-19 5G system.   III. Overall Progress of Rel-19 At the SA1#97 (February 2022) and SA1#98 (May 2022) meetings, the 3GPP SA1 working group reached an agreement on the Rel-19 Research Item Descriptions (SIDs), as shown in Table 1. Many projects are gradually moving towards application.     As the research title suggests, 3GPP standards are addressing the more specific needs of industries considering using 3GPP-based communication systems. Previous versions of 3GPP standards have added support for various industries, such as machine-to-machine communication. 3GPP has also introduced features such as support for low-power IoT communication, wide-coverage IoT communication, and vehicle-to-vehicle communication.   However, previous versions' support is insufficient for some other industries, and new research is striving to meet their needs. For example, the research on Metaverse services (FS_Metaverse) will address the requirements of 3GPP-based systems in carrying traffic for applications in metaverse scenarios.   On the other hand, as industries adopt 3GPP-based communication technologies, new scenarios are constantly emerging, requiring 3GPP to conduct further research. For instance, the research on satellite access (FS_5GSAT_ph3) is attempting to meet the additional needs of the satellite industry, building upon previous research.

In a 5G broadcast system, session modification will update the PDU (Packet Data Unit) session; the update can be triggered by events such as the terminal device (UE), the network, or a radio link failure. The MBS session update process is specifically handled by the SMF, involving the UPF updating the user plane connection; then the UPF notifies the access network and AMF to modify session rules, QoS (Quality of Service), or other parameters.   I. Session Modification Initiation in 5G Systems can be triggered by multiple network elements, namely: UE-Initiated:The UE requests changes to its PDU session, such as modifying packet filters or QoS for a specific service. Network-Initiated:The network (typically a Policy Control Function (PCF)) initiates modifications, such as applying new policy rules or QoS changes. Access Network-Initiated: Events such as radio link failures, user inactivity, or mobility restrictions may trigger modifications, causing the AN to release the session or modify its configuration. AMF-Initiated:The AMF may also trigger modifications, such as due to unspecified network failures.   II. The MBS successful modification broadcast session modification procedure aims to request the NG-RAN node to update MBS session resources or areas related to previously established broadcast MBS sessions; this procedure uses non-UE associated signaling. A successful modification is shown in Figure 8.17.2.2-1, where:   MF initiates this process by sending a "BROADCAST SESSION MODIFICATION REQUEST" message to the NG-RAN node, in which:   If the "Broadcast Session Modification Request" message contains an "MBS Service Area" IE, the NG-RAN node should update the MBS service area and send a "Broadcast Session Modification Response" message. If the "Broadcast Session Modification Request" message contains an "MBS Session Modification Request Transmission" IE, the NG-RAN node should replace the previously provided information with the newly received information and update the MBS session resources and area according to the request, and then send a "Broadcast Session Modification Response" message. If the "Broadcast Session Modification Request" message includes a "List of Supported User Equipment Types" IE (if supported), the NG-RAN node should consider this in the MBS session resource configuration. If the MBS NG-U fault indication IE is included in the broadcast session modification request message within the MBS session setup or modification request transmission IE and is set to "N3mb path failure," the NG-RAN node can provide new NG-U transport layer information to replace the failed transport layer information, or switch data transmission to another 5GC according to the N3mb path failure broadcast MBS session recovery procedure specified in TS 23.527.   III. MBS Modification Failure In the live network, NG-RAN nodes may experience broadcast session modification failures for various reasons; the modification failure is shown in Figure 8.17.2.3-1, where:   If an NG-RAN node fails to update any requested modifications, the NG-RAN node should send a "Broadcast Session Modification Failure" message.  

1. Broadcast Session Release: In mobile communications systems, this refers to the process by which a user equipment (UE) terminates reception of broadcast signals from a 5G network, similar to ending a streaming media session. This occurs when the user explicitly terminates the session, the broadcast ends, or the device moves out of broadcast coverage. The network element (Broadcast/Multicast Service Center) will tear down the session to ensure efficient data transmission to multiple users simultaneously. Releases include:     User-Initiated Release: The user manually stops the broadcast, similar to closing a streaming app. Network-Initiated Release: The broadcast session ends due to the completion of content playback or termination by the network operator. This may be due to the end of a live event or scheduled broadcast. Device-Initiated Release: The device moves out of broadcast coverage, resulting in signal loss and session termination. The Broadcast/Multicast Service Center (BM-SC) manages broadcast sessions and can initiate releases based on network policies or user actions.   2. Broadcast Session Release Process: The purpose is to release resources associated with a previously established MBS broadcast session. The release uses non-UE-associated signaling. A successful release operation is shown in Figure 8.17.3.2-1, where:       The AMF initiates this procedure by sending a Broadcast Session Release Request message to the NG-RAN node. Upon receipt of the Broadcast Session Release Request message, the NG-RAN node shall respond with a Broadcast Session Release Response message. The NG-RAN node shall cease broadcasting and release all MBS session resources associated with the broadcast session. Upon receipt of the Broadcast Session Release Response message, the AMF shall transparently transmit the Broadcast Session Release Response Transport IE (if any) to the MB-SMF.

  Efficient spectrum utilization is crucial in mobile communications. As operators strive to provide faster data rates and better connectivity, carrier aggregation (CA) has become one of the most important features introduced in 3GPP R10 (LTE-Advanced) and further developed in 5G (NR).   1. Carrier Aggregation (CA) increases bandwidth and throughput by combining multiple component carriers (CCs). The bandwidth of each component carrier ranges from 20 MHz in LTE to 100 MHz in 5G (NR). Therefore, the total bandwidth of LTE-Advanced (5CCs) can reach 100 MHz, while the total bandwidth of 5G (NR) (16CCs) can reach 640 MHz. The principle is that by combining carriers, the network can send and receive more data simultaneously, thereby improving efficiency and user experience.   2. Aggregation Types: In 4G and 5G, carrier aggregation can be categorized based on how carriers are organized across or within different frequency bands:   Intra-band contiguous | Adjacent carriers within the same band | Band 3: 1800 MHz (10+10 MHz contiguous) Intra-band non-contiguous | Carriers within the same band but with frequency separation | Band 40: 2300 MHz (20+20 MHz with a gap) Inter-band aggregation | Carriers from different bands | Band 3 (1800 MHz) + Band 7 (2600 MHz)   The figure above visually illustrates the intra-band non-contiguous type, where both carriers belong to Band A but there is a gap in the spectrum between them.   3. Intra-band contiguous carrier aggregation (ICCA) works by combining adjacent carriers within the same band. Non-contiguous intra-band carrier aggregation (NCCA) goes a step further and allows aggregation of non-adjacent carriers within the same band. This is particularly important for operators dealing with fragmented spectrum allocations.   4. Intra-Band Non-Contiguous Carrier Aggregation (ICA) is a feature enabled in 4G and 5G to fully utilize fragmented spectrum. Carrier aggregation (CA) allows operators to combine multiple carriers (called component carriers (CCs)) to create wider bandwidth channels, thereby improving throughput and enhancing the user experience.

1. The purpose of the Location Reporting Control procedure is to allow the AMF to request the NG-RAN node to report the terminal (UE)'s current location, or the last known location (with timestamp), or the UE's location in the target area in the CM-CONNECTED state (as described in TS 23.501 and TS 23.502). This procedure uses UE-related signaling.   2. The successful reporting operation flow is shown in Figure 8.12.1.2-1 below, where: The AMF initiates this procedure by sending a Location Reporting Control message to the NG-RAN node. Upon receiving the Location Reporting Control message, the NG-RAN node shall perform the requested location reporting control operation for the (UE).   3. The Location Reporting Request Type IE indicates whether the NG-RAN node: Reports directly; Reports on serving cell change; Reports the terminal's (UE's) presence in the target area; Stops reporting on serving cell change; Stops reporting the terminal's (UE's) presence in the target area; Cancels the terminal's (UE's) location reporting; Reports on serving cell change and reports the terminal's (UE's) presence in the target area. If the Location Reporting Request Type IE in the LOCATION REPORTING CONTROL message includes an Area of ​​Interest List IE, the NG-RAN node shall store this information and use it to track the UE's presence in the Areas of Interest defined in TS 23.502. NOTE: The NG-RAN reports the UE's presence for all Location Reporting Reference ID sets for inter-NG-RAN node handovers. If the Additional Location Information IE is included in the LOCATION REPORTING CONTROL message and is set to "Include PSCell," the NG-RAN node shall include the current PSCell in the report if dual connectivity is activated. If Report on Serving Cell Change is requested, the NG-RAN node shall also provide this report when the UE changes PSCell and when dual connectivity is activated. If Report on Serving Cell Change is requested, the NG-RAN node shall send the report immediately and whenever the UE's location changes. If the Event Type IE is set to "Cess UE presence in area of ​​interest" and if the Additional Cancel Location Reporting Reference ID List IE is included in the Location Reporting Request Type IE in the Location Reporting Control message, the NG-RAN node shall (if supported) stop reporting UE presence for all received location reporting reference IDs.  

1. User equipment (UE) radio capabilities refer to the set of radio interface features supported by the UE. The UE reports these capabilities to the network so that the network can optimize service and resource allocation. These capabilities include supported radio access technologies (2G, 3G, 4G, 5G), supported frequency bands (low, mid, and high), and advanced features such as carrier aggregation, MIMO, and beamforming. The network uses this information during registration to customize the configuration for improved performance and compatibility.   2. 5G UE radio capabilities include: RAT and frequency band support: Information about the radio access technologies (such as 5G) and frequency bands (low, mid, and high bands) on which the UE can operate. Carrier aggregation: The ability to combine multiple frequency bands to increase data rates and capacity. Modulation and coding schemes: Supported methods for encoding and transmitting data. Advanced features: Support for features such as MIMO (multiple-input, multiple-output) and beamforming, which enhance signal quality and efficiency. Protocol stack parameters: Functionality related to the PDCP, RLC, and MAC layers. Radio Frequency Parameters: Specific characteristics of radio frequency components. FGI (Function Group Indicator) and Function ID: Identifiers used to indicate a function set and optimize signaling between the UE and the network. 3. The UE Radio Capability Information Indication procedure is intended to enable the NG-RAN node to provide information related to the UE's radio capabilities to the AMF. The UE Radio Capability Information Indication procedure uses UE-related signaling; successful operation is indicated as shown in Figure 8.14.1.2-1 below, where: The NG-RAN node controlling the UE-associated logical NG connection initiates the procedure by sending a UE Radio Capability Information Indication message containing UE radio capability information to the AMF.   The UE Radio Capability Information Indication message may also include paging-specific UE radio capability information in the UE Radio Paging Capability IE. If the UE Radio Paging Capability IE includes the UE NR Radio Paging Capability IE and the UE Radio Paging Capability E-UTRA IE, the AMF shall (if supported) use it as specified in TS 23.501. The UE radio capability information received by the AMF shall replace the UE radio capability information previously stored in the AMF, as specified in TS 23.501. If the UE Radio Capability Information Indication message contains the UE Radio Capability - E-UTRA Format IE, the AMF shall (if supported) use it as specified in TS 23.501. If the UE Radio Capability Information Indication message contains the XR Device (with 2Rx) IE, the AMF shall (if supported) store this information and use it accordingly.

3GPP continued to evolve 5G-Advanced in Release 19, enhancing a range of business-driven features and introducing a series of innovations, further strengthening 5G capabilities. Through forward-looking research on channel modeling, it serves as a bridge to 6G.     1. MIMO, a cornerstone of 5G technology, was introduced in Release 19 with the fifth stage of its evolution, designed to improve beam management accuracy and efficiency. Release 19 supports user equipment-initiated beam reporting, allowing user equipment to trigger reports without relying on base station (gNB) requests. Another key enhancement in Release 19 is the expansion of the number of CSI reporting ports from 32 to 128, enabling better support for larger antenna arrays. This is crucial for scaling MIMO systems in high-capacity scenarios. Coherent joint transmission capabilities have been enhanced to address challenges in non-ideal synchronization and backhaul scenarios (such as inter-site coherent joint transmission). Release 19 also introduced new measurement and reporting mechanisms to address time misalignment and frequency/phase offset between Transmitter Relays (TRPs). To further improve uplink throughput, Release 19 enhances the non-coherent uplink codebook for UEs equipped with three transmit antennas. Furthermore, asymmetric configurations are supported, where a UE receives downlink transmissions from a macro base station while simultaneously sending data to multiple micro TRPs in the uplink. These configurations include enhanced power control mechanisms and path loss adjustments to optimize performance in heterogeneous network environments.   2. Mobility management is another key focus in Release 19. Specifically, extended LTM, originally introduced in Release 18 for intra-CU (Central Unit) mobility, expands support for inter-CU mobility, enabling smoother transitions between cells associated with different CUs. To further optimize mobility, Release 19 introduces conditional LTM, combining the advantages of LTM's reduced outage time with the reliability of CHO. Furthermore, event-triggered Layer 1 measurement reporting reduces signaling overhead compared to periodic reporting. Combining CSI reference signal (CSI-RS) measurements with SSB measurements enhances mobility performance.   3. The evolution of NR NTN continues in Release 19, with 3GPP defining new reference satellite payload parameters to account for the reduced equivalent isotropically radiated power (EIRP) density per satellite beam compared to previous releases. To accommodate the reduced EIRP, this release explores downlink coverage improvements. Given the expected large number of user equipment (UE) within satellite coverage, Release 19 also aims to increase uplink capacity by incorporating orthogonal cover codes into the DFT-s-OFDM-based PUSCH. To support MBS within NTNs, 3GPP enhances MBS by defining a signaling mechanism for specifying target service areas. Another major advancement in Release 19 is the introduction of a regenerative payload feature, enabling 5G system functions to be implemented directly on the satellite platform. Unlike the transparent payload supported in previous releases, regenerative payloads allow for more flexible and efficient NTN deployments. Furthermore, NR NTN is evolving to support RedCap user equipment (UE).   4. 5G-Advanced is optimized to better accommodate XR applications, including enabling transmission and reception during gaps or restrictions caused by RRM measurements and RLC acknowledgment modes. Furthermore, Release 19 explores improvements to PDCP and uplink scheduling mechanisms, with a particular focus on integrating latency information. 3GPP is also researching technologies to more efficiently support XR applications, ensuring they meet the diverse and stringent QoS requirements associated with multimodal XR use cases.   5. AI/ML: At the NG-RAN architecture level, 3GPP is leveraging AI/ML to address more use cases in Release 19. One new use case is AI/ML-based network slicing, where AI/ML is used to dynamically optimize resource allocation across different network slices. Another area of ​​focus is coverage and capacity optimization, leveraging AI/ML to dynamically adjust cell and beam coverage, a technique commonly known as cell shaping.   6. Functional Enhancements include: Sidelink: This work focuses on multi-hop UE-to-network sidelink relay for mission-critical communications, particularly in public safety and out-of-coverage scenarios; Network Energy Saving: This includes on-demand SSBs in the SCell for connected mode UEs configured with Carrier Access Control (CA); on-demand SIB1 (System Information Block Type 1) for idle and inactive mode UEs, as well as adjustments to common signal and channel transmissions; Multi-Carrier Enhancement: An enhancement allows for the use of a single DCI to schedule multiple cells with different subcarrier spacing values ​​or carrier types.