The connected car concept is gaining momentum from the point of view, not only of research, but also of standardization and industrial development. Today there are many options for connecting a vehicle, in terms of to whom and how. In addition to making use of any conventional cellular technology, and connecting the vehicle to a base station or infrastructure element, vehicles can connect wirelessly and directly to each other using different technologies, both from the Institute of Electrical and Electronics Engineers (IEEE) and from the 3rd Generation Partnership Project (3GPP). This article offers a rigorous and detailed review of the system architecture aspects involved in the support of vehicular communications by the 3GPP fifth-generation (5G) standard, with special emphasis on its most recent iteration: Release 16.

Long-Term Evolution (LTE) is the new standard recently specified by the 3GPP on the way towards fourth-generation mobile. This paper presents the main technical features of this standard as well as its performance in terms of peak bit rate and average cell throughput, among others. LTE entails a big technological improvement as compared with the previous 3G standard. However, this paper also demonstrates that LTE performance does not fulfil the technical requirements established by ITU-R to classify one radio access technology as a member of the IMT-Advanced family of standards. Thus, this paper describes the procedure followed by the 3GPP to address these challenging requirements. Through the design and optimization of new radio access techniques and a further evolution of the system, the 3GPP is laying down the foundations of the future LTE-Advanced standard, the 3GPP candidate for 4G. This paper offers a brief insight into these technological trends.

One of the objectives of METIS-II project is to facilitate discussion on scenarios, use cases, KPIs and requirements for 5G, building upon the comprehensive work conducted in the METIS-I project and taking the work of other European projects as well as other bodies such as ITU-R, NGMN, etc. into account. This paper analyses the landscape of 5G use cases and presents METIS-II 5G use cases that cover the main 5G services, have stringent requirements and whose technical solutions are expected to serve other similar use cases as well. It also links these use cases to the business cases defined by 5G PPP so that requirements of vertical industries can be taken into account when designing the 5G Radio Access Network (RAN).

The concept of sustainability has been recently extended to cover economic and social factors besides the traditional environmental ones. This paper reflects on the potential of mobile communication standards towards achieving sustainable mobility, with focus on vehicular communications and use cases in smart cities scenarios. In this context, intelligent transportation systems, including connected and autonomous vehicles, will be key for developing affordable and sustainable infrastructures and services. We start by identifying three current technology trends, namely, towards climate neutral; cloudification and edge computing; and big data and artificial intelligence, and then we examine their capability to enable sustainable Vehicle-to-Everything (V2X) communication systems in beyond 5G and 6G networks. In the second part of the paper, a set of selected use case categories involving connected and autonomous vehicles is presented, showcasing the potential impact of the selected technology trends. Finally, a review of the estimates of the quantitative savings that could be achieved in environmental-related parameters such as energy/fuel consumption and greenhouse gas emissions is provided.

The long-term evolution multimedia broadcast multicast service (MBMS) infrastructure has been shown to efficiently fulfill the requirements of classical vehicle-to-vehicle services, such as cooperative awareness message and decentralized environmental notification message delivery, which involve the transmission of the same message to a set of destination receivers in close proximity. When targeting autonomous driving applications, related 5G V2X services, such as cooperative collision avoidance (CCA), impose challenging latency and reliability requirements that cannot be generally guaranteed using the current MBMS architecture. In this paper, we propose a low-latency multicast scheme aimed at decreasing the end-to-end (E2E) communication latency. The proposed approach concentrates the multicast network functionalities into the layer-2 of the base stations (BSs) protocol stack, including a message passing between neighboring BSs, to achieve a fast management of multicast groups and a reduction of the communication path through the network infrastructure. The results show that the proposed technique can substantially decrease the E2E latency of conventional MBMS and ensure the correct operation of demanding services, such as CCA moving toward 5G communication systems.

Mobile network operators are interested in providing Vehicle-to-Vehicle (V2V) communication services using their cellular infrastructure. Regional split of operators is one possible approach to support multi-operator infrastructure-based cellular V2V communication. In this approach, a geographical area is divided into non-overlapping regions, each one served by a unique operator. Its main drawback is the communication interruption motivated by the inter-operator handover in border areas, which prevents the fulfillment of the maximum end-to-end (E2E) latency requirements of fifth generation (5G) V2V services related to autonomous driving. In this work, we enable a fast inter-operator handover based on the pre-registration of the users on multiple operators, which substantially reduces the handover time to guarantee maximum E2E latency values of 100 ms in non-congested scenarios. To further reduce the latency of time-critical services to always less than 70 ms, even with the handover interruption time, while providing a latency around 20 ms in the majority of locations, we propose to complement the former technique with a mobile edge computing approach. Our proposal consists in the localization of application servers and broadcasting entities in all the base stations, to avoid the communication through the core network, together with the use of a new set of nodes in the base stations of cross-border areas called inter-operator relays, to minimize the communication latency between operators. Based on analytic and simulation results, it is demonstrated that the proposed techniques are effective to support low-latency infrastructure-based cellular V2V communications in multi-operator environments with regional split.