The Autonomous Era in Construction: 5G Unleashing Smart Technologies
5G, artificial intelligence (AI), edge computing, and the expectations society and industry have of these enablers, have changed the way electronics work. 5G connects people, devices, and machines in new ways, while AI improves efficiency and automates processes. Edge computing facilitates faster data processing at the network’s edge, reducing latency and integrating advanced technologies. This requires us to rethink not only how things operate but also their potential changes in size and cost. To achieve this and bolster the semiconductor ecosystem and Europe’s technological leadership, the European Commission funds projects under the Chips Joint Undertaking (formerly Key Digital Technologies Joint Undertaking, KDT JU). The main objective is to link research, innovation and production, with a focus on facilitating the process of turning innovative ideas into commercial reality.
Turkcell and its subsidiary Turkcell Technology actively participate as industry partners in EU funded projects in addition to Celtic-Next, Eurogia and nationally funded projects. Their involvement aims to enhance expertise, integrate new technologies into the network, conduct extensive testing in various use cases, and contribute to the development process. This contribution is based on the expertise gained through project collaboration and their role in standardisation initiatives. Under the KDT roof, BEYOND5 (Building the fully European supplY chain on RFSOI, enabling New RF Domains for Sensing, Communication, 5G and beyond) and StorAIge (Embedded storage elements on next MCU generation ready for AI on the edge) are the two projects in which Turkcell is involved in. The primary objective of BEYOND5 is to establish a European supply chain for Radio-Frequency Electronics, thereby enabling new domains in sensing, communications, 5G radio infrastructure, and beyond. As a technology initiative, BEYOND5 brings together key European stakeholders across the value chain. This includes materials, semiconductor technologies, design, components, and system integration, facilitating a collaborative approach to innovation and development. In this context, the goal is to support various significant 5G applications, encouraging both short-term and long-term investments for commercial growth. On the other hand, the primary objective of the StorAIge project is to establish an advanced manufacturing platform for silicon embedded with Artificial Intelligence (AI) functionalities. This platform will focus on the prototyping high-performance, low-power Silicon on Insulator (SOI) components that prioritise both security and safety. The ultimate goal is to empower competitive AI applications at the edge. At the widest level, StorAIge is expected to increase the competence and competitiveness of European entities, including universities, research organisations and industry, in the field of edge AI hardware. This is essential to maintain Europe’s sovereignty and technological independence in this key enabling technology. Both projects aim to obtain key performance indicators for the developed technologies/hardware by testing them in diverse application areas/vertical sectors/use cases through demonstrations.
Construction 4.0 is one of the many application areas within BEYOND5 and StorAIge. The integration of new technologies into the industry has led to the emergence of a new industrial era known as Industry 4.0. However, these advances have had a relatively modest impact on the construction sector compared to other industries. The construction sector has made limited progress in digitalisation, due to the unique characteristics and challenges of the industry, as well as the limitations of the existing telecommunications infrastructure. The key performance indicators offered by 5G technology, such as high data rate and low latency, have given rise to the concept of “Construction 4.0.“. The possibilities offered by 5G technology are aimed at achieving the digitalisation goals in smart construction sites and meeting current objectives. Undoubtedly, the key technology of Construction 4.0 is 5G-enabled vehicular communication leading to autonomous/remotely controlled unmanned ground vehicles (UGVs) which will enable the refinement of construction sites away from humans, providing safer working environment for the workers and a more productive work process. Turkcell and its project partners are responsible for the autonomous operation / remote control of UGVs in an open-air smart construction site laboratory, located in Türkiye which will pave the way for future construction applications and digitalisation of this particular sector. Therefore, this article presents the state of the art of vehicular communication from the standardisation perspective, with the aim of providing a comprehensive literature and standardisation review.
The Society of Automotive Engineers (SAE) has defined six levels of design goals for autonomous driving, labelled from Level 0 (L0) to Level 5 (L5) (as shown in Figure 1) [1]. At L0, there is no automation, while L5 represents full automation with no need for a driver. The progression from L1 to L5 involves the incorporation of various new features into vehicles to enable higher levels of automation. The progress of the automotive industry through information and communication technologies is shown in a timeline in Figure 2, which represents some of these new features [2]. One of these features is effective communication which is critical to achieving the goals of autonomous driving.
Current “connected and automated vehicles” are expected to evolve into fully autonomous vehicles [3]. In order for autonomous vehicles to operate autonomously, they need to communicate with other vehicles and objects. As shown in Figure 3, this communication initially relied on WiFi-based technology IEEE 802.11p-based standard involving Wireless Access in Vehicular Environments (WAVE) at the Physical Layer (PHY) and the Medium Access Control (MAC) layers. The IEEE 802.11p-based standard featured two technologies: Dedicated Short-Range Communication (DSRC) used in the United States of America (USA) and Cooperative Intelligent Transport System (C-ITS) used in the EU [3–5]. A newer concept, Cellular-Vehicle-to-Everything (C-V2X) introduced by the Third Generation Partnership Project (3GPP), using cellular technology such as 4G (Long Term Evolution, LTE) for Vehicle-to-Everyting (V2X) communication utilizing the PC5 for short-range direct communication (an alternative to IEEE 802.11p-based technologies operating in the 5.9 GHz frequency band) and the UU interface for longer-range infrastructure communication within 4G/LTE (previously) and the 5G technology (now) [3–5].
C-V2X technology offers low-latency and high-reliability communications that enable vehicles to interact with each other (vehicle-to-vehicle, V2V), pedestrians (vehicle-to-pedestrian, V2P), roadside infrastructure (vehicle-to-infrastructure, V2I), and networks (vehicle-to-network, V2N), even without a cellular network, improving road safety and traffic efficiency. While autonomous vehicles are equipped with advanced sensors like cameras, LiDAR, radar, Global Navigation System Satellite (GNSS); C-V2X remains beneficial for Intelligent Transport System (ITS) with its ability of detecting potential hazards and road conditions from greater distances, overcoming challenges like non-line-of-sight (NLOS) obstacles. C-V2X handles NLOS problems through PC5 interface sidelink communication or cellular networks, adding extra safety features. Although vehicle sensors are fundamental for autonomous driving functionality and safety, the automotive industry recognizes that connectivity is essential to further enhance the safety and comfort of current autonomy level and beyond. As driving autonomy advances, integrating C-V2X connectivity becomes crucial beyond a certain level of autonomy [5]. With visualizing purpose, 5GAA’s visionary roadmap is given in Figure 4 which depicts expected timelines for the use cases according to the progress of the C-V2X technology [6].
There exist stringent requirements related to V2X applications to actualize the autonomous driving such as latency, reliability, data rate, and communication frequency. In light of these stringent requirements, a variety of international and regional standardisation bodies are actively engaged in the standardisation efforts associated with C-V2X. Noteworthy entities include [2]:
· The 3rd Generation Partnership Project (3GPP),
· The International Telecommunication Union (ITU),
· The European Telecommunications Standards Institute (ETSI),
· SAE,
· And International Organization for Standardisation (ISO).
Primarily, 3GPP assumes a pivotal role in directing the research and development of C-V2X wireless communications. This entails comprehensive efforts including requirements analysis, network architecture, security mechanisms, and related technical standards. ITU undertakes the responsibility of formulating and coordinating national and regional standards for spectrum allocation and security standards. Two ISO Technical Committees, namely the Road Vehicle Technical Committee (ISO/TC 22) and the Intelligent Transport Systems Technical Committee (ISO/TC 204), have actively enhanced coordination in the formulation of relevant technical standards for intelligent connected vehicle. ETSI is responsible for formulating standards regarding the overall V2X communications network architecture, management, security, and the formulation of standards with respect to service scenarios and network architectures of Mobile Edge Computing (MEC). Additionally, SAE has instituted a dedicated C-V2X working group tasked with the development of C-V2X related standards [2].
In the sequel, these efforts of the aforementioned standardisation bodies are briefly elaborated.
IEEE
IEEE 802.11p standard enables direct communication between vehicles (V2V) and vehicles to infrastructure (V2I) in the 5.9 GHz ITS frequency band. In 2010, the IEEE 802.11p technology standardisation was finalized [2,7,8]. Some application layer standards like SAE J2735 and J2945/1 have been completed by SAE [2,9,10]. Furthermore, in December 2018, the standardisation research for IEEE 802.11bd commenced, representing an enhanced iteration of IEEE 802.11p [2,11].
ITU
ITU, as the United Nations’ specialized agency responsible for information and communication technologies, operates as an intergovernmental international organization. Founded on May 17, 1865, it has 193 member states and over 700 departmental members. The ITU comprises a Plenary Conference, Council, General Secretariat, Radiocommunications Department (ITU-R), Telecommunications Standardisation Department (ITU-T), and Telecommunications Development Department (ITU-D). Both ITU-R and ITU-T conduct research regarding V2X technology [2].
ITU-R holds a significant position in radio spectrum and satellite orbit management. To guarantee smooth radio communication operations without interference, radio rules and regional regulations are devised. These legal documents are consistently updated via international and regional radio communication conferences. Moreover, ITU-R prepares proposals to enhance radio communication system operational performance and its quality by radio related standardisation efforts [2].
ITU-R has conducted comprehensive studies on ITS deployment scenarios, technical standards, and frequency utilization across diverse countries. As a result of these analysis, proposals and corresponding reports have been prepared, outlining frequency utilization, deployment scenarios, technical standards, and application guidelines. Within ITU-R’s M.2121–0 proposal in 2019 [2,12], it is defined that the 5.9 GHz frequency spectrum, or a portion thereof, is the internationally recognized and unified frequency for ITS purposes. During the World Radiocommunication Conference 2019 (WRC-19), following extensive discussions, the matter concerning ITS frequency allocation was addressed within the framework of the WRC proposal. National regulatory bodies across different countries took into account the latest iteration of this proposal. The coexistence of ITS stations alongside existing fixed satellite services was an additional consideration. WRC-19 introduced Item 1.12, which encourages the relevant authorities of various nations to adopt the 5.9 GHz band or a portion thereof as the preferred global or regionally unified ITS frequency band [2].
ITU-T’s primary role involves investigating technical and operational concerns and generating recommendations for standardisation in these areas. This covers the study and formulate of unified telecommunication network standards involving interface standards with radio systems. The overall objective is to advance and actualize telecommunication standardisation worldwide [2].
The SG17 working group has undertaken extensive research with respect to ITS and connected vehicle safety. This effort has led to the initiation of several standard projects, covering areas such as software upgrades, security threats, misbehaviour detection, data classification, V2X communications security, MEC, and on-board Ethernet security [2].
Currently, the ITU-T has released X.1373 [2, 13], titled “Secure Software Update Capability for ITS Communication Devices.” This standard establishes a secure software update scheme between remote update servers and vehicles. It defines security control measures and outlines the process and content of security updates [2].
ITU-T is actively involved in the development of several important standards related to V2X communication security: X.1372 [2,14]: “Security Guidelines for Vehicle-to-Everything (V2X) Communication Systems”, X.srcd (Security Requirements of Categorized Data in V2X Communication [2, 15]., X.1371: “Security Threats to Connected Vehicles” [2,16].
Through the development of these standards, ITU-T aims to establish a solid foundation of security guidelines and requirements to safeguard V2X communication systems from potential threats and vulnerabilities [2].
SAE
To advance C-V2X related standards and foster industrialisation in the United States, SAE established the C-V2X Technical Committee in 2017. Its primary aim was to develop technical requirement standards for on-board V2V communications (SAE J3161/1) [2,17] for C-V2X, akin to J2945/1 for DSRC (IEEE 802.11p). Essential parameters, functional requirements, and performance criteria were delineated in the SAE J3161/1 [2,17] standard for V2V profiles, along with J3161/0 [2,18] for V2I/I2V profiles.
Consequently, standards for C-V2X deployment profiles (J3161/1 and J3161/0) and Validation Test Procedures for LTE-V2X V2V Safety Communications (J3161/1A) [2,19] were introduced to stimulate relevant research and development efforts.
The SAE’s Technical Committee for Automotive Electronic System Safety holds the responsibility for standardising security within automotive electronic system networks. It has developed the pioneering guidance document, J3061(cyber security guide book for cyber physical vehicle systems) [2,20], which serves as a cybersecurity manual for cyber-physical vehicle systems. J3061 establishes a comprehensive lifecycle framework wherein network security is upheld throughout all stages, spanning from concept and production to operation, service, and retirement. This document furnishes an essential foundation for the development of automotive electronic systems featuring network security requirements. It defines fundamental principles for network security in vehicle systems and sets the groundwork for subsequent standardisation endeavours in V2X security [2].
ETSI
The ETSI ITS Technical Committee (ETSI TC ITS) holds the responsibility for formulating standards concerning the comprehensive V2X communications network architecture, its management, and security. Notably, this committee has created the communication standards for ITS-G5, including the physical and access layer protocols for short-range communications.
With the goal of establishing C-V2X communication capabilities, ETSI expedited the standardisation process, successfully finalizing the core C-V2X standardisation efforts. ETSI defined the protocols for the access layer, network and transport layer, as well as the application layer of C-V2X, thereby ensuring the comprehensive availability of the C-V2X protocol stack [2,21]. In January 2020, ETSI formally issued the EN 303 613 standard [2, 22], officially recognizing C-V2X as the designated access layer technology for ITS.
To meet the demands for V2X computing and processing capabilities, along with seamless cross-platform interoperability, ETSI has undertaken a comprehensive array of standardisation initiatives related to the service scenarios and network architecture of MEC technology. Notably, in 2017, ETSI greenlit projects encompassing “API (Application Programming Interface) specification for App mobility” and “MEC support for V2X.” Building on this, the “V2X API specification” project was introduced in 2018, aimed at establishing MEC APIs that cater specifically to V2X functionalities [2,23].
With the objective of enhancing security measures, ETSI TC ITS has developed corresponding technical specifications. These encompass a range of aspects, notably security architecture, security services, security management, and privacy protection.
3GPP
C-V2X is primarily driven by 3GPP and built upon the advancement of 4G/5G cellular communication technologies. This communication involves linking with networks and infrastructure, including fixed or dynamic objects. The 3GPP C-V2X technology operates within a dedicated frequency band for ITS applications and fulfills V2X communication needs. Across multiple releases, 3GPP demonstrated C-V2X’s support through 4G (LTE), 5G, and beyond. 3GPP’s efforts toward introducing the C-V2X standard marked significant progress toward achieving autonomous driving design goals and enhancing vehicular communication.
3GPP consists of technical specification groups (TSGs) focusing on core network & terminals (CT), service & system aspects (SA), and radio access network (RAN) as given in Figure 5 [3]. These TSGs produce specifications and technologies through technical reports released periodically. Starting from 3GPP Rel-14, 3GPP releases signify the successful shift from 802.11p-based technology to cellular based V2X communication, initially 4G and now 5G, that have played a vital role in the success of C-V2X applications.
The roadmap of 3GPP’s V2X standardisation is provided in Figure 6. The standardisation of C-V2X by 3GPP occurred in two phases: LTE-V2X and NR-V2X [2, 24–29]. The standardisation of LTE-V2X was covered by 3GPP Rel-14 and Rel-15 technical specifications. The LTE-V2X standardisation within 3GPP Rel-14 was concluded in March 2017. This phase focused on fulfilling the communication needs of fundamental road safety services. It introduced the sidelink (PC5 interface) communication mode, functioning in the 5.9 GHz frequency band, as well as optimizations for the public mobile cellular network communications interface (Uu Interface). Moreover, the enhanced LTE-V2X standardisation through 3GPP Rel-15 was completed in June 2018. Building upon LTE technology, this phase introduced enhancements like carrier aggregation (CA), high-order modulation, and other advancements to enhance system performance [2].
While 5G discussions were initiated in Rel- 14 [3, 30], 5G Phase-1 (5G system — 5GS) commenced in Rel-15 [3, 31, 32]. Notably, the 5G standard’s new air interface (NR) within 3GPP Rel-15 was geared towards improving the enhanced mobile broadband experience (eMBB). However, it did not have specific design and optimization for V2X services. [2] The support for V2X communication continued in subsequent releases with enhancements known as enhanced V2X (eV2X), considering the integration of 5G NR for future V2X scenarios. Rel-14 and Rel-15 also introduced support for advanced driving, remote driving, extended sensors, and vehicle platooning [3].
The development of NR-V2X is guided by 3GPP Rel-16 [3,33], Rel-17 [3, 34], Rel-18 [3, 35], and related evolution technical specifications. With a focus on addressing the needs of advanced V2X (aV2X) applications such as automated driving and platooning, 3GPP Rel-16 initiated the NR-V2X Study Item (SI) in June 2018. This effort delved into V2X communications technologies for the PC5 interface using 5G NR and explored enhancements for the Uu Interface (RP-181429 2018) [2, 26]. The completion of the SI occurred in March 2019 [2]. And 5GS (5G Phase 2) was introduced in Rel-16 (TR 21.916) which expanded on the 5G specifications by enhancing architectural aspects and service-oriented functionalities for V2X communication. This version of 5G, presented in Rel-16, supports aV2X services [3]. In parallel, the NR-V2X Work Item (WI) [2,26,27] started.
NR-V2X incorporates both PC5 and Uu interfaces to cater to aV2X applications. The PC5 interface accommodates unicast, multicast, and broadcast scenarios, making it adaptable for diverse V2X applications. NR-V2X is designed to function within cellular coverage, partial coverage, and even in areas with no coverage. With a general architecture, NR-V2X supports over sidelink in the low, medium frequency, and mmWave bands. It also facilitates the coexistence of LTE-V2X and NR-V2X. Additionally, it introduces network slicing, MEC, QoS (Quality of Service), and others related to Uu Interface, ensuring the fulfillment of V2X requirements such as low latency, high reliability, and large bandwidth. Rel-16 NR-V2X standardisation concluded in June 2020 [2].
Rel-17 NR-V2X addresses scenarios involving vulnerable road users (VRU) besides aV2X applications. Key mechanisms were developed to enhance sidelink reliability and reduce transmission latency in Rel-17 NR-V2X, including power-saving and inter-UE coordination mechanisms among terminals for sidelink communication [2]. Both Rel-16, and Rel-17, address NR sidelink communication and its enhancements [3, 36]. These enhancements focus on critical aspects such as resource allocation, power efficiency, and high Quality of Service (QoS) to ensure successful V2X communication.
Rel-17 and Rel-18 [3,35] are exploring new use-case scenarios, such as AI-based sidelink communication for devices and communication between robots and machines. In its ongoing development, 3GPP is progressively enhancing sidelink communication to cater to vehicular devices utilized in V2X services within Rel-18. An evolutionary goal encompasses augmenting sidelink data rates by introducing CA functionality to sidelink communication, expanding sidelink operation into unlicensed spectrum areas, and strengthening sidelink support in frequency range 2 (FR2) [37]. Additionally, sidelink positioning and relay capabilities will be included [2]. 3GPP is set to explore mechanisms facilitating the coexistence of LTE V2X and NR V2X devices within a shared frequency channel and by Rel-18 [37], it seeks to introduce new features like advanced 5G, AI-driven evolved 5G, and extended reality services[3]. Rel-18 NR-V2X began in December 2021 and is scheduled for completion by the end of December 2023 (RP-213678 2021) [2, 29].
Research and standardisation efforts for the security mechanisms of LTE-V2X initiated by 3GPP SA3 in Rel-14. This led to the development of the 3GPP TS 33.185 standard specification (v14.1.0, 2018), outlining the security architecture and mechanisms for LTE-V2X. In the current Rel-17, 3GPP SA3 is extending its focus to enhance the security of NR-V2X. The emphasis is on addressing security requirements and key issues specific to NR-V2X [2].
The standard documents of 3GPP provide comprehensive guidelines for various V2X scenarios, but they are spread across different documents. Table 1 categorizes these documents based on their technological evolution, such as 4G, 4G and 5G, and 5G for V2X services. The organization also highlights the release numbers, illustrating the focus of different topics across releases.
Use-cases and services from TR 22.885 support V2X communication types, addressing safety and non-safety issues through 4G technology. TR 22.885 serves as the foundational source for identifying 4G V2X use-cases and their potential requirements. It offers detailed descriptions, service flows, requirements, and more for each use-case such as emergency vehicle warning, road safety services, wrong-way driving warning, curve speed warning etc. TR 22.885 also covers coverage, spectrum, security, mobility, future-proofing, and deployment considerations. It presents essential V2X deployment examples. These identified use-cases and details complement the 3GPP standardisation documents for both 4G and 5G V2X communication services [3].
The table also provides insights on the yearly progression of technical specifications (TS) and reports (TR). The annual breakdown of these documents emphasizes the production of updated documents, with a notable concentration in the year 2020. These documents are complemented by contributions from 2018 and 2019. Particularly, Rel-16 played a significant role in supporting V2X services by generating a substantial portion of TS documents, followed by contributions from Rel-14 and Rel-15. Interestingly, the TS documents produced in Rel-16 extended beyond just supporting 5G V2X services. Consequently, Rel-17 continued the trend established by Rel-16, addressing the support for V2X services through 5G technology. This visual representation highlights the chronological progression of TS document production and the growing emphasis on V2X services’ development and integration with advanced communication technologies [3].
The automotive industry must prioritize key aspects in V2X development to enhance the ecosystem. These encompass standardised protocols for interoperability, robust security measures, reliable infrastructure, testing, regulatory support, and stakeholder collaboration. These efforts contribute to improved product quality, economic growth, and safer transportation solutions.
C-V2X applications evolve through stages, enhancing safety and enabling automated driving. It shifts from confined to open areas and medium/low to high-speed scenarios. In the industry, C-V2X progresses in two stages: Short-term use involves V2V cooperation and V2I cooperation for driving assistance and automation in confined spaces, supported by real-time cooperative data through LTE-V2X and 4G cellular. Automated driving for commercial vehicles with moderate or low speeds is applied in specific settings like unmanned logistics, supported by LTE-V2X and 5G eMBB, enhancing production and cost savings [2, 3].
Over the medium and long term, the integration of C-V2X with cutting-edge technologies including AI, big data, radar, and video perception will pave the way for the evolution from “individually intelligent vehicles” to a realm of “connected vehicles with cooperative intelligence.” This transition will culminate in automated driving across open roads and diverse weather conditions, relying on NR-V2X and 5G eMBB technologies. Challenges encompass the coexistence of automated and human-driven vehicles, interactions with pedestrians, and dealing with complex traffic scenarios. Addressing these challenges calls for technical advancements and policy revisions in traffic management and industrial oversight. The pursuit of advanced automated driving will entail considerable time devoted to cross-border testing, collaborative trials, and consensus-building grounded in practical experience [2, 3].
In summary, C-V2X communication holds transformative potential for the automotive industry. Addressing challenges and gaps is crucial for successful implementation. Some of the identified gaps and challenges in the standardisation process are given in the sequel.
a. Challenges in Radio Access Network (RAN)
· Frequency utilization [38]: Given the cooperative nature of the V2X network, it becomes crucial to employ a uniform access layer technology across all vehicles. Both C-V2X and ITS-G5 technologies operate within the same 5.9 GHz frequency range, which is partitioned into channels exclusively reserved for ITS communication. In Rel-16, 5G V2X featuring an NR sidelink is closely related to LTE-based V2X sidelink communication, but it lacks backward compatibility with the legacy system. In cellular networks, this issue is not significant because base stations support both technologies, and services are ultimately managed over IP networks. This allows legacy devices to access the same services as newer ones.
However, in the case of direct communication, such as CA service, an ITS station serves as both a service provider and a client simultaneously. Consequently, services cannot seamlessly transition across different radio link technologies without a noticeable degradation in service quality. For example, when using the CA service with legacy ITS stations, the new ITS stations must use the same radio technology as the older nodes or be compatible with both the new and old radios. Otherwise, they cannot effectively support each other’s services.
The absence of backward compatibility in Rel-16 poses challenge, as concurrent utilization of Rels-14/15 and Rel-16 would demand additional bandwidth. Concerns also arise regarding the simultaneous use of these technologies across subsequent channels.
· Subcarriers or Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) [38]: As depicted in Table 5.2.2.2, the key distinction between C-V2X and DSRC technologies lies in their channel access methods. DSRC relies on WiFi technology, utilizing CSMA for channel access. Consequently, transmitted frames are not precisely aligned. The radio first checks for ongoing transmissions and then attempts to transmit data if the channel is available. This approach is simple and robust, albeit potentially suboptimal.
In contrast, C-V2X employs radio resource blocks which are obtained by partitioning the accessible frequency band into segments, allocated in a distributed manner (in Mode 2 or Mode 4). These resource blocks necessitate precise time scheduling, addressed through GNSS signals (in Mode 2 or Mode 4). This approach comes with its own set of advantages and disadvantages. One notable benefit is the extended coverage range. The 5.9 GHz spectrum is dedicated to ITS safety applications, and communication over this channel operates in a distributed manner. Consequently, regulations stipulate the maximum permissible transmission power for devices to prevent channel congestion. The distinguishing factor between DSRC and C-V2X lies in the latter’s employment of a narrower frequency band while maintaining the same transmission power for message transmission. This narrower band contributes to reduced noise levels, resulting in an increased coverage range.
Another advantage of employing radio resource blocks is the potential for channel allocation to be executed by an external entity (i.e., Mode 3), leading to improved channel utilization. However, this approach could introduce a vulnerability in the form of a single point of failure, which is undesirable within such systems.
The stringent alignment of resource blocks introducing a dependence on GNSS signals (in Modes 2/4), potentially constraining communication unnecessarily in urban canyons or tunnels is the disadvantage. The concurrent transmission of packets can elevate the likelihood of simultaneous transmissions, leading to packet loss. Additionally, the system experiences a minor increase in latency due to the scheduling process. The use of fixed radio resource blocks can also lead to suboptimal utilization in scenarios involving variable packet lengths, a common characteristic in standardised direct V2X communication.
As observed, the modulation employed by these communication technologies shows a certain degree of similarity. Nevertheless, the design of channel access (the MAC) holds significant implications for the performance of these technologies. Hence one can outperform the other according to the scenario-specific conditions.
b. Challenges Related to Use Cases
· Communication Range [38]: One of the most notable advantages of PC5 (and Uu)-based communication compared to 802.11p-based communication is the extended communication range. However, this increased range also entails a higher volume of received packets to manage. Processing a greater number of received packets necessitates more computational effort and, in practical terms, a more powerful — and consequently more expensive — processor unit.
· Vulnerable road user (VRU) scenarios [38], involving pedestrians, cyclists, and the like, represent active areas of research within the V2X domain. Given the specific channel access technology outlined in Table 2, V2X radios typically exhibit high power consumption. However, VRUs often carry user equipment with limited battery capacity, posing constraints on the practicality of V2X radio chips for them. Addressing this challenge encompasses multiple approaches. One approach involves connecting to Roadside Units (RSUs) through alternative channel access technologies like Bluetooth, WiFi, or standard cellular communication. This allows VRUs to convey information to RSUs for subsequent communication. Another promising strategy involves utilizing V2X radios in a transmission-only mode, conserving battery life while sacrificing reception capability. Additionally, the requirement for a GNSS signal in C-V2X communication could introduce additional battery consumption concerns.
· Non-GNSS applications [38]: The channel access technology of C-V2X PC5 mandates synchronization among user equipment. In the case of Mode 4/Mode 2 communication, this synchronization is achieved through GNSS signals. Relying on GNSS signals is generally unproblematic, given that one of the crucial pieces of information exchanged through V2X is the sender device’s own position, sourced from GNSS chips themselves. However, future positioning methods, such as ultra-wideband-based positioning, could potentially offer operational viability for V2X even in such challenging environments. Nevertheless, V2X applications necessitate relative position data, which can hold value even in the absence of an absolute position reference. It is evident that dependence on GNSS signals might impose constraints on the applicability of C-V2X technology in specific locales, like urban canyons or tunnels.
· Positioning [38]: Within safety-critical vehicular applications, the relative positions of traffic participants assume paramount importance. One evident approach involves harnessing diverse sensory data, such as LiDARs or radars. The gathered data can also be disseminated through standardised messages. Additionally, emerging technologies like UWB offer a means to acquire relative position information through radio-based communication. Multiple efforts are being undertaken within the context of 5G to acquire positioning data. The techniques in the below contribute to these efforts
o Cell-identity-based
o Angle-based
o Range-based
o Fingerprinting-based
o 5G-network-based positioning
o Assisted positioning in 5G networks
o Employment of machine learning techniques.
The potential accuracy of these approaches holds promise. Nonetheless, each of these techniques relies on 5G cells to compute position values. Yet, for safety-critical direct communication scenarios, depending solely on cell towers is impractical. While an ITS station equipped with both 5G Uu and PC5 could improve the accuracy of ego position information, further advancements are required.
c. Architecture based Challenges
· UU interface of cellular communication [38]: In the realm of 5G development, significant efforts have been dedicated to improving cellular communication performance. Notably, there has been a substantial reduction in communication latency. This latency reduction opens up possibilities for leveraging this technology in V2X communication. One key advantage of this approach is the existing infrastructure, particularly RSUs, which are already deployed. Additionally, the advent of MEC enables the use of virtualized RSUs as cost-effective alternatives to physical installations.
However, in cases involving device-to-device communication, the challenge of routing among the devices arises. When these devices are subscribed to different mobile network operators, the multiple mobile network operators (MNOs) problem arises where certain advantages, such as low latency, may no longer be guaranteed.
· Backward Compatibility issue [38]: As evident, achieving backward compatibility between Rels-14/15 and Rel-16 for C-V2X is unfeasible. In cellular networks, this isn’t a major concern since base stations support both technologies, and service is managed over IP networks, enabling legacy and new devices to access the same services. In contrast, in scenarios involving direct communication like CA service, an ITS station acts as both a service provider and a client simultaneously. This implies that services cannot seamlessly transition across different radio link technologies without a decline in service quality.
For instance, when employing the CA service with legacy ITS stations, new ITS stations must utilize the same radio technology as the legacy nodes (or support both the old and new radios). Failure to do so would result in an inability to facilitate each other’s services effectively.
d. Other challenges
· Interference management [39]: Managing interference is crucial for successful C-V2X implementation. Sources like other wireless systems, environment, and user behavior can degrade communication performance and safety. Researchers are investigating adaptive power control, interference cancellation, frequency hopping, AI-based interference prediction, and beamforming to mitigate these challenges. These solutions have trade-offs, such as impacting reliability or increasing latency. Effective interference management requires coordination among stakeholders, including vehicle manufacturers, infrastructure providers, and wireless carriers.
· Channel estimation [39]: Channel estimation in C-V2X involves assessing wireless channel attributes between transmitters and receivers, like signal strength, delay and doppler shift. Challenges arise from vehicle mobility and a complex environment with interferences. Researchers explore techniques such as pilot-based estimation, real-time tracking, and prediction using artificial intelligence (AI) and machine learning (ML) algorithms. Future solutions may incorporate advanced antenna technologies like massive multiple input multiple output (MIMO) and beamforming. Standardised channel models also aid in enhancing wireless channel estimation accuracy in C-V2X.
· Edge and Cloud AI adoption [39]: Edge and cloud AI tecniques processing diverse data efficiently and ensuring data privacy for C-V2X presents another challenge. Lightweight models are needed for real-time performance without impacting communication. Integrating AI seamlessly with the communication system while preserving performance is another hurdle. Future solutions may involve lightweight AI models, federated learning, hybrid architectures like fog computing, and integration with blockchain for enhanced security and privacy.
· Network slicing for V2X [39]: Network slicing is a significant challenge in C-V2X. It involves dividing a single network into virtual networks to meet different service requirements. This needs accurate data collection, smart resource sharing, and advanced AI tools. Everything must work together to match changing network conditions and service needs, pushing technology limits.
· Security [39]: Security in C-V2X faces significant challenges. It must protect data between vehicles and infrastructure, like location and speed, from being stolen or altered by attackers. Also, attacks like network jamming could disrupt communication. Researchers are exploring solutions like encryption, digital signatures, and secure protocols to safeguard data. Ensuring the security of infrastructure, including RSUs and networks, is another challenge. Researchers are looking at secure designs, intrusion detection, and management systems. Standardising security methods is vital for compatibility and safety across different vendors. Possible solutions include advanced encryption, secure hardware, and AI-based intrusion prevention. Secure protocols and standards are also essential for a safe C-V2X environment.
· AI and ML applications [3]: The recent introduction of AI and ML in 3GPP’s releases and technical documents has sparked interest in creating a joint solution that brings intelligence to vehicles. This means aligning the intelligence in the network with that inside the vehicles, as automotive OEMs continue to enhance the intelligence within vehicles themselves. In the realms of autonomous driving, eHealth, and industry 4.0, Communication Service Providers (CSPs) are compelled to elevate the automation level of their networks. This elevation is necessary to accommodate the demanding needs of these applications, which include ultra-low latency and on-the-fly resource allocation to meet predefined Service Level Agreements (SLAs).
The roadmap for 5G-Advanced and subsequent generations involves the development of Rel-19 and Rel-20 by 3GPP, alongside contributions and recommendations from organizations like ETSI, ITU, and the 6G Infrastructure Association (5GIA before) [38].
Official discussions concerning the specific content of 3GPP Rel-19 began in April 2023, with the goal of finalizing Rel-19 specifications by December 2025. Several Work Items are currently under discussion within the standardisation working groups, covering various aspects, including network sharing, integrated sensing and communication, mobile virtual services, studies related to satellite access (phase 3), UAV (phase 3), energy efficiency, service robot networks with ambient intelligence, interworking with non-3GPP networks, multi-path relay, and more [38].
For Rel-20, which is currently in the research phase, detailed standardisation information is pending. Similarly, Rel-21, considered the first tangible 3GPP 6G release, is undergoing vision and requirements phases throughout 2023. Nevertheless, the domain beyond 5G and 6G remains an active research area, expected to address preconceived challenges and anticipated requirements [38].
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[1] https://ec.europa.eu/commission/presscorner/detail/en/ip_23_6167
[2] Building the fully European supplY chain on RFSOI, enabling New RF Domains for Sensing, Communication, 5G and beyond. https://www.chips-ju.europa.eu/projects/beyond5, ID: 876124
[3] Embedded storage elements on next MCU generation ready for AI on the edge. https://www.chips-ju.europa.eu/projects/storaige, ID: 101007321
Acknowledgement: This article is a result of the BEYOND5 (www.beyond5.eu) project which has received funding from the ECSEL Joint Undertaking (JU) under grant agreement No 876124. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and France, Germany, Turkey, Sweden, Belgium, Poland, Netherland, Israel, Switzerland, Romania. This project has received funding from the ECSEL Joint Undertaking (JU) under grant agreement No 101007321. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and France, Belgium, Czech Republic, Germany, Italy, Sweden, Switzerland, Turkey.
