China Shenzhen Olax Technology CO.,Ltd Company News

  In the 5G (NR) system, AMF and SMF are two independent core network functional units. They are directly connected via the N11 interface; the 5G terminal (UE) connects to them directly or indirectly through N1, N2, N3, N4, and N11 interfaces, and the information exchanged is as follows:   I. Messages exchanged with SMF via the N1 interface include: A single N1 termination point is located in the AMF; the AMF forwards SM-related NAS information to the SMF based on the PDU session ID in the NAS message. Subsequent SM NAS exchanges (e.g., SM NAS message responses) received by the AMF via access (e.g., 3GPP or non-3GPP access) are transmitted through the same access. The serving PLMN ensures that subsequent SM NAS exchanges (e.g., SM NAS message responses) received by the AMF via access (e.g., 3GPP or non-3GPP access) are transmitted through the same access. The SMF handles the session management part of the NAS signaling exchanged with the UE. The UE can only initiate PDU session establishment in the RM-REGISTERED state. When an SMF is selected to serve a specific PDU session, the AMF must ensure that all NAS signaling related to that PDU session is handled by the same SMF instance. After successful PDU session establishment, the AMF and SMF store the access type associated with that PDU session.   II. Messages exchanged with SMF via the N11 interface include: The AMF reports the UE's reachability to the SMF based on the SMF's subscription, including: location information of the UE relative to the area of interest indicated by the SMF. The SMF indicates to the AMF when the PDU session is released. After successful PDU session establishment, the AMF stores the identifier of the SMF serving the UE, and the SMF stores the identifier of the AMF serving the UE, including the AMF set. When attempting to connect to the AMF serving the UE, the SMF may need to apply the behavior described in Section 5.21 for "other CP NFs".   III​. Messages exchanged with SMF via the N2 interface include: Certain N2 signaling (e.g., handover-related signaling) may require the joint action of the AMF and SMF. In this case, the AMF is responsible for ensuring coordination between the AMF and SMF. The AMF can forward SM N2 signaling to the corresponding SMF based on the PDU session ID in the N2 signaling. The SMF should provide the PDU session type and PDU session ID to the NG-RAN so that the NG-RAN can apply the appropriate header compression mechanism to packets of different PDU types. See TS 38.413 [34] for details.   IV. N3 interface interaction messages with the SMF include: Selective activation and deactivation of existing PDU session UP connections are defined in clause 5.6.8 of TS 23.501.   V. N4 interface interaction messages with the SMF include: When the UPF learns that a UE has received downlink data but there is no downlink N3 tunnel information, the SMF will interact with the AMF to initiate a network-triggered service request procedure. In this case, if the SMF learns that the UE is unreachable, or that the UE is only reachable for regulatory priority services, and the PDU session is not for regulatory priority services, the SMF should not send a downlink data notification to the AMF;

I. NTN Access: Random Access Channel (RACH) is a fundamental process for initial connection, uplink synchronization, and scheduling authorization between the terminal equipment (UE) and the network. While this is a mature and well-understood process in traditional terrestrial radio access networks (RANs), its implementation in Non-Terrestrial Networks (NTNs) presents a series of unique and more complex technical challenges. In terrestrial RANs, radio frequency signals typically propagate over short and predictable distances, and the propagation environment is relatively stable; however, in NTN networks involving Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geostationary Orbit (GEO) satellites, radio frequency signals are affected by extremely long propagation distances, rapid satellite movement, dynamic coverage areas, and time-varying channel conditions. All these factors significantly impact the timing, frequency, and channel reliability that traditional RACH processes rely on.   II. NTN Characteristics: Due to extremely long transmission distances, rapid satellite movement, and time-varying coverage and channel conditions, NTN presents unique critical drawbacks (e.g., large propagation delay, long round-trip time, Doppler shift, beam mobility, and large contention domain) that severely challenge and impact the terminal's random access channel (RACH) behavior and performance. Furthermore, satellites are subject to strict limitations in terms of spectrum availability and power budget, making efficient and robust random access mechanisms particularly crucial.   III. Impacts and Solutions: To overcome the difficulties that NTN presents for terminal access, 3GPP has addressed some issues in its specifications, but the following aspects require attention:   3.1 TA (Timing Advance) Challenges Impacts: In NTN networks, due to large cell areas, satellite movement, and varying distances between the UE and the satellite, timing advance estimation is far more complex than in terrestrial systems. Incorrect TA estimation can cause uplink transmissions to fall outside the satellite's reception window, resulting in collisions or complete reception failure. Solution: Advanced TA estimation techniques are needed, such as utilizing satellite ephemeris data, GNSS assistance, or predictive algorithms, to dynamically adjust UE timing alignment and maintain uplink synchronization.   3.2 Doppler Shift Effects Impacts: The relative motion between the satellite and the UE introduces significant Doppler shifts, especially in Low Earth Orbit (LEO) systems. These frequency shifts reduce preamble detection accuracy, impair frequency synchronization, and increase the likelihood of RACH attempt failures. Solution: Robust Doppler pre-compensation and frequency tracking mechanisms are required on both the UE and network sides to maintain reliable RACH performance under high mobility conditions.   3.3 Channel Condition Variations: Impact: NTN links are subject to atmospheric attenuation, shadowing, scintillation, and long-distance path loss. These factors increase the block error rate and may affect the UE's ability to correctly receive RAR messages after successfully transmitting the preamble. Solution: Adaptive modulation and coding, power control, and robust physical layer design are needed to maintain reliable RACH detection and processing under various channel conditions.   3.4 Wide Coverage and High Terminal Density: Impact: Satellite beams typically cover very large geographical areas, potentially serving thousands of UEs simultaneously. This significantly increases the level of RACH contention and the probability of collisions, especially in large-scale access scenarios. Solution: Efficient RACH resource partitioning, load-aware access control, and intelligent contention management mechanisms are needed to scale random access performance.   3.5 Increased RTT (Latency and Round-Trip Time): Impact:The large physical distance between the UE and the satellite introduces significant one-way propagation delay and longer RTT. For example, the round-trip time (RTT) for a geostationary orbit (GEO) satellite link can reach hundreds of milliseconds. These delays directly affect the timing of Random Access Response (RAR) message exchange, potentially leading to premature timer timeouts, increased access failure rates, and prolonged access delays. Solution: RACH-related timers, such as the Random Access Response (RAR) window and collision resolution timers, must be designed based on NTN-specific RTT values. NTN-aware timer configuration is crucial to prevent unnecessary retransmissions and access failures.   3.6 Increased Collisions: Impact: A large number of user equipment (UEs) contending for a limited number of RACH preambles increases the probability of preamble collisions, thereby reducing access efficiency and increasing latency. Solution: Advanced collision resolution schemes, dynamic preamble allocation, and NTN-optimized access barring techniques are key to reducing collision probability.   3.7 Synchronization Challenges: Impact: Initial synchronization in NTN is complicated by large timing uncertainties and frequency offsets. Failure to achieve accurate synchronization can prevent the user equipment (UE) from initiating the Random Access Channel (RACH) process altogether. Solutions: Enhanced synchronization techniques, combining precise timing acquisition, Doppler compensation, and satellite position awareness, are needed for successful random access.   3.8 Power Control Impact: UEs in NTN experience significant variations in path loss depending on their position relative to the satellite beam. Insufficient transmit power may lead to preamble detection failure, while excessive power can cause inter-UE interference. Solution: Adaptive and location-aware power control mechanisms are crucial for balancing detection reliability and interference management.   3.9 Beam Management Impact: NTN systems heavily rely on multi-beam architectures. UEs may need to perform beam acquisition or switching during the RACH process, which increases complexity and latency. Solution: Efficient beam discovery, beam tracking, and seamless beam switching mechanisms are essential for ensuring reliable RACH execution in beam-based NTN systems.

I. Reachability In mobile communication networks, UE reachability refers to the network's ability to locate a terminal device (UE) to transmit data, which is particularly important for UEs in an idle state. It involves states such as CM-IDLE, modes such as MICO (Mobile Initiated Connection Only), and the process by which the UE or network (AMF, UDM, HSS) notifies other parties when the UE is active or has access to specific services (e.g., SMS or data). During this process, data is buffered, and the terminal (UE) is paged when necessary to achieve terminal power saving (PSM/eDRX). 3GPP defines it in TS23.501 as follows;   II. CM-IDLE State For non-3GPP access networks (untrusted, trusted non-3GPP access networks) and W-5GAN, where the UE corresponds to 5G-RG in the W-5GAN case and W-AGF in the case of supporting FN-RG. For N5CW devices accessing 5GC via a trusted WLAN access network, their UEs correspond to TWIF. Specifically, the UE cannot page via a non-3GPP access network. If the UE state in the AMF is CM-IDLE or RM-REGISTERED for the non-3GPP access network, there may be PDU calls where the last route was through the non-3GPP access network and user plane resources are lacking. If the AMF receives a message from the SMF containing a non-3GPP access type indication, corresponding to a PDU session of a UE in the CMIDLE state of non-3GPP access, and this UE has registered for 3GPP access in the same PLMN as the non-3GPP access, then regardless of whether the UE is in the CM-IDLE or CM-CONNECTED state on the 3GPP access, it can execute network-triggered service requests via the 3GPP access. In this case, the AMF will provide indication that the process is related to non-3GPP access (as described in Section 5.6.8) – the UE's behavior upon receiving such a network-triggered service request is specified in Section 5.6.8.   III. CM-CONNECTED State for non-3GPP access networks (untrusted, trusted non-3GPP access networks) and W-5GAN, where the UE corresponds to 5G-RG in the case of W-5GAN and W-AGF in the case of FN-RG support. For N5CW devices accessing 5GC through a trusted WLAN access network, the UE corresponds to TWIF. A UE in the CM-CONNECTED state is defined where:   the AMF knows the UE's position at the N3IWF, TNGF, TWIF, and W-AGF node granularities. When the UE is unreachable from the perspective of N3IWF, TNGF, TWIF, and W-AGF, i.e. when the non-3GPP access connection is released, N3IWF, TNGF, TWIF, and W-AGF will release the N2 connection.

5G (NR) allows terminals (UEs) to access the system via trusted non-3GPP, untrusted non-3GPP, and W-5GAN systems; for this purpose, 3GPP defines the following in TS23.501:   I. Registration Management For terminals (UEs) accessing the 5G system via W-5GAN, the corresponding term is 5G-RG, while for FN-RG it corresponds to W-AGF. For N5CW terminals (UEs) accessing the 5GC via a trusted WLAN access network, the corresponding term is TWIF. When accessing via non-3GPP, the terminal (UE) and AMF should enter the RM-DEREGISTERED state as follows:   - After an explicit deregistration procedure is performed at both the UE and AMF; - After the network's non-3GPP implicit deregistration timer expires at the AMF; - After the UE's non-3GPP deregistration timer expires at the UE. ---Assuming sufficient time is allowed for the UE to reactivate the UP connection of an established PDU session, regardless of whether the session was established via 3GPP or non-3GPP access.   II. Terminal (UE) Access When a UE registers via non-3GPP access, it starts a UE non-3GPP deregistration timer based on the value received from the AMF during the registration process when entering the non-3GPP access CM-IDLE state. In non-3GPP access mode, the AMF runs a network non-3GPP implicit deregistration timer. When the CM state of the registered UE changes to CM-IDLE via non-3GPP access mode, the network non-3GPP implicit deregistration timer will start at a value greater than the UE non-3GPP deregistration timer value. For UEs registered via non-3GPP access mode, access point changes (e.g., WLAN AP changes) should not cause the UE to perform the registration process. The UE should not provide 3GPP-specific parameters (e.g., indications of MICO mode preferences) during registration via non-3GPP access mode.   III. Upon successful connection management, a UE accessing the 5GC via non-3GPP will transition to CM-CONNECTED (non-3GPP access). Specifically: For untrusted non-3GPP access to the 5GC, the non-3GPP access connection corresponds to an NWu connection. For trusted access to the 5GC, the non-3GPP access connection corresponds to an NWt connection. For N5CW devices accessing the 5GC via a trusted LAN, the non-3GPP access connection corresponds to a Yt' connection. For wired access to the 5GC, the non-3GPP access connection corresponds to Y4 and Y5 connections.   ***A UE will not establish multiple non-3GPP access connections to the 5GC simultaneously; non-3GPP access connections can be released through an explicit deregistration procedure or an AN release procedure.

    C-V2X (Cellular Vehicle-to-Everything) technology was first proposed by 3GPP in the 4G (LTE) era with Release 14, and has evolved with each subsequent version, now capable of supporting modern transportation needs.Intelligent Transportation Systems (ITS), in addition to communication, involve numerous manufacturers, vehicles, and municipal aspects, and while its development has been slower, significant progress has been made, and there are high expectations for C-V2X. All of this is based on the following aspects:   I. C-V2X technology can improve road safety, traffic efficiency, and road information distribution efficiency. Compared to traditional in-vehicle sensors, it is relatively low-cost and highly effective. 3GPP actively promotes the standardization of LTE-V2X and NR-V2X, which has encouraged many organizations to develop C-V2X technology. However, the deployment of PC5-based C-V2X still faces some challenges.   II. C-V2X is an ecosystem that requires the active participation of industry stakeholders, including road traffic management departments, autonomous driving developers, network operators, and governments. To improve the level of C-V2X, governments need to promote the construction of road traffic facilities and unify relevant standards. For example, traffic light control systems need to be upgraded from traditional equipment to equipment with stronger processing capabilities. To transmit traffic information in a timely manner, the traffic light control system needs to send signal change information at a preset frequency of at least 10Hz. However, existing equipment in Taiwan cannot meet this requirement, necessitating an intermediate conversion process. However, the disadvantage of this process is that it increases message transmission delay. Therefore, there is a delay between the traffic light control console and the traffic lights, which violates Intelligent Transportation System (ITS) standards. This problem makes it difficult for C-V2X devices to obtain correct timing information for synchronization in SPAT applications. To address these issues, the government must establish unified standards to promote the upgrading of traffic light control systems.   III. Standardization of C-V2X technology application layer specifications. Some organizations follow European standards, some adopt American standards, and others combine both to develop national standards. It is currently unclear which standard will be adopted globally. Unifying standards and weighing the advantages and disadvantages of various standards should be part of the government's smart city agenda.   IV. 5G Sidelink Technology Applications: While C-V2X services have been tested and trialed in many regions, full 5G coverage still requires time. Initial applications will primarily focus on those with less demanding KPI (Key Performance Indicator) requirements. Once 5G achieves full coverage and Sidelink technology is fully implemented, C-V2X will reach a new level, where bandwidth, low latency, and high throughput will become key elements in its application scenarios; 5G NR-V2X deployment will lead to a comprehensive integration of the entire ecosystem.   V. Synchronized Development of Vehicles and Roadside Infrastructure: According to the international standard SAE J3016, autonomous driving is defined in levels 0-5; C-V2X services, in addition to the vehicles themselves, also place high demands on roads and related infrastructure; furthermore, a large amount of private and confidential information from IP cameras will be transmitted in public spaces, making information security protection a critical issue in PC5-based C-V2X deployment; countries need to develop relevant standards to define security policies; regulations and insurance claim mechanisms for road traffic accidents in intelligent transportation systems (ITS) are also under development.

C-V2X Integration Solutions: The 5G network-based PC5 C-V2X system integration solutions currently include the following categories:   Converting traffic light control signals into C-V2X internal messages recognizable by RSU/OBU to implement SPAT applications. Autonomous vehicles are usually equipped with cameras and artificial intelligence to recognize traffic light information. However, recognition accuracy is easily affected by adverse weather or obstructions. This solution enhances robustness against any conditions that may hinder visual recognition.   Utilizing artificial intelligence technology, which has demonstrated excellent performance in multiple fields, for VRUCW applications. Deep learning-based vulnerable road user detection and collision warning functions can be implemented through a PC5-based C-V2X system architecture.   Integrating C-V2X into the autonomous driving system (ADS) to enhance safety. The ADS can monitor road conditions, detect potential problems, and take measures to avoid traffic accidents. The success of these projects will lay a solid foundation for the upcoming 5G NR-V2X.   I. Traffic Light Control System Integration: To implement SPAT applications locally, the system architecture shown in Figure 1 has been designed. The PC5-based C-V2X SPAT application has been successfully launched, where: Figure 1. Traffic Light Control System Integration Architecture Diagram   The system can directly collect traffic light information from the traffic light controller. The traffic light acquisition program is responsible for receiving roadside traffic light information; this includes traffic light phase, color, and remaining time, which are all sent to the roadside unit (RSU). The RSU reads this information and packages it into C-V2X protocol messages. The RSU broadcasts the C-V2X messages to the on-board unit (OBU) via the PC5 interface. The on-board unit (OBU) installed in the autonomous vehicle analyzes and filters this information, and then sends it to the autonomous driving system industrial PC (IPC) for deceleration or stop control. The user interface (UI) displays C-V2X technical information in an intuitive way.   II. VRUCW Application System Integration: The C-V2X VRUCW application based on PC5 is shown in Figure (2), where: Figure 2. Schematic Diagram of VRUCW Integration System The VRUCW application can be considered a P2I2V service (Pedestrian-Infrastructure-Vehicle). IP cameras must be installed in the road area for line-of-sight (LOS) and non-line-of-sight (NLOS) monitoring. It uses an AI server equipped with a series of deep learning technologies (such as CNN (Convolutional Neural Network) and SSD (Single Shot Detector)). If any pedestrian passes through the camera's coverage area, the system will detect the object. The AI ​​server transmits the analysis results, including target recognition and motion prediction, to the Roadside Unit (RSU), which then broadcasts this information to all On-Board Units (OBUs) within its coverage area. The OBU is responsible for integrating vehicle information (such as speed, heading, and position) to determine if there is a collision risk. We use a target classification algorithm to determine the pedestrian's direction for subsequent calculation of the likelihood of a collision warning. Assuming there is a collision risk between the pedestrian and the vehicle, for example, if the distance between them is within 50 meters and the vehicle's speed exceeds 10 km/h, we trigger a collision warning through the algorithm.   III. Autonomous Driving System Integration: The integration of PC5-based C-V2X with the autonomous driving system is currently designed and implemented as shown in Figure (3), where: Figure 3. Schematic Diagram of Autonomous Driving Integration System The Roadside Unit (RSU) receives information from the traffic light controller or the AI server. It then broadcasts this information within its coverage area using a predefined message format. The On-Board Unit (OBU) receives the broadcast messages through PC5-based C-V2X communication. The OBU connects to the industrial PC (IPC) of the autonomous driving system via the TCP/IP protocol. The OBU receives Global Navigation Satellite System (GNSS) and Controller Area Network (CAN) messages from the vehicle. The OBU uses advanced internal algorithms to determine if the situation is dangerous. It then sends corresponding warning messages to the autonomous driving system's IPC based on the situation.   At this point, the C-V2X technology is integrated into the autonomous driving system as expected.

From its inception during the 4G (LTE) era to the present day, C-V2X has been developing for 10 years. During this time, manufacturers from many countries have participated in research and testing, and the technology has been successfully implemented.   I. C-V2X technology progress demonstrates a path towards 5G evolution. While 802.11p-based V2X technology is widely adopted by manufacturers, the 5GAA has proposed standards for C-V2X development;   In China, the first C-V2X trial was launched in 2016, using chipsets from CATT (Datang), Huawei HiSilicon, and Qualcomm. Multi-vendor interoperability testing of PC5-based LTE-V2X applications was completed in Shanghai in November 2018, and a C-V2X "four-layer" interoperability application demonstration focusing on security mechanisms was organized in Shanghai in October 2019. In Japan, C-V2X trials began in 2018, with application scenarios including V2V, V2P, V2I, and V2N operations in wide-area communication based on cellular networks, and supporting cloud access; South Korea successfully demonstrated 5G C-V2X communication between autonomous driving test vehicles (AVs) in 2019.   C-V2X Development Blueprint: The U.S. Federal Communications Commission (FCC) officially announced the allocation of 5.9GHz intelligent transportation system (ITS) spectrum for C-V2X in December 2019; finally, in November 2020, it decided to reserve 30 megahertz of spectrum in the 5.895–5.925GHz band for ITS radio services using C-V2X technology. Meanwhile, Europe is developing a new EN (European Standard) to define the application of C-V2X as an access layer technology for C-ITS (Cooperative Intelligent Transportation Systems), which has been approved by the European Telecommunications Standards Institute (ETSI). Australia initially launched road testing of C-V2X technology in Victoria at the end of 2018. Based on 3GPP versions and supply chain readiness, the long-term blueprint for global traffic efficiency and basic safety C-V2X application use cases, developed by 5GAA in September 2020, has been fully realized.   III. C-V2X Technology Applications: Currently, C-V2X is gaining momentum in markets such as the United States, Europe, Australia, China, Japan, and South Korea. C-V2X is becoming dominant globally, with many countries and governments prioritizing it in their intelligent transportation system plans; countries and regions such as the United States and China have already begun issuing licenses for vehicles using C-V2X technology.

I. The PC5 interface is a direct communication interface used between terminals in 5G (NR) C-V2X (Cellular Vehicle-to-Everything) technology, allowing direct communication between vehicles, pedestrians, and infrastructure without going through the cellular network. This is crucial for low-latency safety functions in connected cars and autonomous driving (such as collision warning, sensor sharing, and platooning). In the evolution from LTE-V2X to 5G NR-V2X, as shown in the table below, the PC5 interface (based on the network) can provide ultra-reliable, low-latency communication (URLLC) for advanced mobile applications of V2X;   PC5-based C-V2X Mode 4 does not require a cellular network, only two devices are needed: RSU (Roadside Unit) and OBU (On-Board Unit) to deploy C-V2X V2I/V2V/V2P application scenarios, where:   RSU: The wireless transmission device can provide direct link communication through the PC5 interface without a cellular network. Road signs, traffic lights, and IP camera information within a preset area can be broadcast to vehicles in real time via the RSU. Another practical scenario is that the RSU can be equipped with a SIM card to transmit road information through the cellular network, thus developing more public safety applications. OBU: The wireless communication device is installed in the vehicle and enhances the sensor capabilities of autonomous vehicles by communicating directly with RSUs and other OBUs. The OBU is responsible for broadcasting the vehicle's location, direction, and speed information to other preset devices while receiving data from other vehicles as input for its internal algorithms to avoid potential accidents.   II. PC5 supports C-V2X application scenarios. When using C-V2X applications, RSU and OBU devices must be equipped with chipsets compliant with the 3GPP C-V2X standard (such as those from Qualcomm, Intel, Huawei, Datang, and Autotalks).   PC5-based C-V2X has been field-tested, and many applications have been implemented in commercial deployment scenarios; these application scenarios specifically include: SPAT (Signal Phase and Timing Message): A V2I service that integrates traffic signal controllers (light color and remaining time) with remote wireless transmission equipment (RSU), which broadcasts this information to the OBU. The driver or autonomous driving control unit can use this information to decide whether to change routes or accelerate. TSP (Traffic Signal Priority): A connected vehicle (V2I) service that allows high-priority vehicles such as ambulances, fire trucks, and police cars to send priority signals when approaching signal-controlled intersections so that they can pass through. VRUCW (Vulnerable Road User Collision Warning): A connected vehicle (V2P) service that alerts the driver or autonomous driving control unit when a potential pedestrian collision risk is detected by roadside IP cameras and roadside units (RSUs). ICW (Intersection Collision Warning): A connected vehicle (V2V) service that warns the host vehicle of a collision risk when approaching an intersection. EBW (Emergency Brake Warning): Another connected vehicle (V2V) service that warns the host vehicle when a remote vehicle ahead performs emergency braking. The host vehicle receives the alert from the vehicle ahead and determines whether a collision will occur. DNPW (Do Not Pass Warning): A connected vehicle (V2V) service used when the host vehicle plans to overtake a vehicle ahead from the opposite lane. The host vehicle sends an alert to nearby vehicles traveling in the opposite direction. The host vehicle's on-board unit (OBU) will receive the DNPW message to determine if it is safe to overtake. HLW (Hazardous Location Warning): A connected vehicle (V2I) service that warns the host vehicle of potential hazardous situations, such as deep water after heavy rain, potholes on the road, or slippery road surfaces.   All of the above application scenarios are deployed using PC5-based C-V2X direct communication technology; due to performance limitations, 4G (LTE) cellular networks cannot support them. 5G (NR) provides development opportunities for time-sensitive applications.

  The C-V2X system applied to ITS (Intelligent Transportation Systems and Automated Driving) is based on 3GPP standards, and its development spans from the 4G (LTE) era to the current 5G (NR). The relevant details are as follows:   I. LTE-V2X: The first phase of 3GPP Rel-14 was completed in March 2017, establishing initial standards supporting V2V services and V2X services utilizing cellular infrastructure. The main security features of C-V2X under 3GPP Rel-14 are implemented through cellular networks or PC5 interface Sidelink communication. To support C-V2X communication based on the unlicensed 5.9GHz spectrum, a new LTE-V2X frequency band 47 (with bandwidths of 10MHz and 20MHz) was introduced. 3GPP Rel-14 also introduced two new physical channels for PC5-based C-V2X communication: PSSCH (Physical Sidelink Shared Channel) and PSCCH (Physical Sidelink Control Channel). PSSCH is used to carry data, while PSCCH contains control information for decoding the data channel at the physical access layer.   To accelerate LTE-V2X development, LTE-D2D (Device-to-Device) modes 3 (centralized scheduling mode) and 4 (decentralized scheduling mode) were adopted to support Sidelink communication via PC5, where:   Mode 3: Cellular network allocates resources. Mode 4: Cellular network coverage is not required.   Vehicles can utilize a sensing-based semi-persistent scheduling (SPS) scheme to autonomously select radio resources with the support of congestion control mechanisms.   2.LTE-V2X Second Phase: In June 2018, 3GPP Rel-15 completed the second phase of 3GPP V2X standards, introducing enhanced V2X services (including platooning, extended sensors, advanced driving, and remote driving), building a stable and robust ecosystem around LTE-V2X, including:   Platooning: Vehicles dynamically form platoons and travel together. All vehicles in the platoon exchange information to safely maintain small distances. Extended Sensing: Raw or processed sensor data is exchanged between vehicles, roadside units, pedestrian devices, and V2X application servers to enhance environmental awareness beyond the detection range of individual sensors (e.g., by exchanging real-time video). Advanced Driving: Enables semi-autonomous or fully autonomous driving. Perception data and driving intentions obtained from local sensors are exchanged with nearby vehicles for synchronization and coordination. Remote Driving: A remote driver or V2X application controls a remote vehicle (e.g., providing assistance to disabled passengers, driving vehicles in hazardous environments, performing predictable route driving, etc.).   3.5G-V2X: As the third phase of V2X, 5G (NR)-V2X is backward compatible with the upper layers of LTE-V2X. To meet the low latency and high reliability requirements of advanced V2X services, NR-V2X is designed to support these applications. As a type of V2N application, 5G URLLC (Ultra-Reliable Low-Latency Communication) network slicing can provide advanced autonomous driving functions with higher QoS (Quality of Service) for L3 (conditional automation) and L4 (highly automated) driving.   4.5G-V2X Features: To meet the needs of some advanced application scenarios that require the transmission of periodic traffic, in addition to broadcasting, 5G NR-V2X introduces two new communication types: unicast and multicast. Similar to LTE-V2X, 5G NR-V2X defines two Sidelink communication modes: Mode 1 and Mode 2, where:   NR-V2X Mode 1 defines a mechanism that allows vehicles to communicate directly when wireless resources are allocated to vehicles by the cellular network base station through the Uu interface. NR-V2X Mode 2 supports direct vehicle communication via the PC5 interface outside the cellular network coverage area.   3GPP Rel-16 was officially frozen in July 2020; during the development of 3GPP NR Release 17, a new Sidelink communication relay architecture was proposed to support some advanced V2X services.

  As an advanced wireless communication technology currently applied in ITS (Intelligent Transportation Systems), C-V2X can not only address the problem of over one million deaths annually from road traffic accidents, but also extend the blind spot detection capabilities in autonomous driving coverage. Its technical standards and application modes are as follows:   I. Technical Advantages: C-V2X can aggregate information collected in collaborative sensing, update maps using precise road structure information, and distribute localized high-definition (HD) maps based on vehicle location. These enhanced advanced services, such as blind spot detection, remote sensing, remote driving, and platooning, all benefit from C-V2X technology. It can improve road capacity, driver safety, and comfort; as shown in Figure 1, these are the advantages that C-V2X technology brings to autonomous driving. Figure 1. Schematic Diagram of C-V2X Technology Integration and Application   II. Standard Mode: Using 3GPP (3rd Generation Partnership Project) 4G (LTE) or 5G (NR) connections for signal transmission and reception, it operates in two complementary transmission modes; The first is direct communication with vehicles, infrastructure, and pedestrians; in this mode, C-V2X operates independently of the cellular network and uses the PC5 interface for communication. The second is cellular network communication. C-V2X utilizes traditional mobile networks, enabling vehicles to receive road and traffic condition information in their area – this mode uses the Uu interface for communication.   III. Application Prospects: With technological evolution and deployment, fatal accidents caused by human error or road conditions, and serious traffic congestion caused by special circumstances or accidents will no longer be a problem. Through vehicle-to-vehicle (V2V) and vehicle-to-pedestrian (V2P) technologies in C-V2X, risks can be detected before they become threats, and through C-V2X vehicle-to-infrastructure (V2I) and vehicle-to-network (V2N) technologies, warnings can be issued before traffic congestion occurs. These technologies are being put into use successively. The collaborative application of C-V2X, intelligent transportation systems, and 5G will help achieve safer roads and more efficient travel.   IV. Technology The integrated low-latency, high-reliability C-V2X technology enables vehicles to communicate with other vehicles (V2V), pedestrians (V2P), roadside infrastructure (V2I), and the network (V2N), regardless of whether a cellular network is used, thereby improving road safety and traffic efficiency. Autonomous vehicles are typically equipped with advanced sensors: cameras, LiDAR, radar, Global Navigation Satellite System (GNSS), and Controller Area Network (CAN). So why is C-V2X technology still needed for intelligent transportation systems? This is because C-V2X can detect potential hazards and road conditions over long distances. Even fully equipped autonomous vehicles cannot detect non-line-of-sight (NLOS) objects. C-V2X can overcome the NLOS problem by using PC5 interface sidelink communication or cellular networks to provide additional safety features. Vehicle sensors provide the basic functions of autonomous driving; this will not change in the future and is crucial for safety. However, the automotive industry has realized that connectivity is essential for further improving the safety and comfort of L3 (Level 1: Conditional Automation) or L4 (Level 2: High Automation) driving; to achieve higher levels of autonomous driving, vehicles must be interconnected through C-V2X technology.