## 2 3 GPP Vehicular Communication Standards
### LTE and NR Use Cases  
In general, services for intelligent transport systems are known as Day 1, Day 2 and Day 3 services [11]. Day 1 services are basic services that refer to Awareness Driving. Thus, through the V2X service, it is possible to exchange warning information about position, speed, driving direction, etc. Day 2 services are referred to Sensing Driving, that is, through the use of sensors the vehicles obtain and share information from the environment to other vehicles. In this way, other vehicles can be warned of a potential danger related to vulnerable road users, driving at intersections, etc. Day 3 services refer to situations involving Cooperative Driving. Therefore, it refers to advanced services that involve the exchange of information related to maneuvering intent and trajectories. This form of communication allows road users to interact intelligently even in complex traffic situations. Day 3 services require high network performance in terms of latency and network reliability. TR 22.885 Rel-14 [4] defines a set of use cases, ranging from road safety services to complex services with stringent latency and network reliability requirements. For each of the use cases, specific latency parameters, packet sizes used to send V2X messages, and different UE data rates that the network must support are given. In this sense, not all services have the same potential requirements, for example, some services require low latencies to function properly, other services require high network reliability, i.e., low packet losses. Some services require the network to provide strict latency, reliability and bandwidth parameters. Thus, there is a direct relationship between the potential requirements for different services and the KPIs provided by the network. Table 1 shows some use cases defined for LTE V2X, where it can be noted that the requirements of latency, message packet size and speed support depend on the specific use case. Latency is a primary parameter for V2X services, since a delay in the transmission or reception of messages can affect the correct performance of the services offered and, in the worst case, can lead to counterproductive results. With respect to the size of the packets to be transmitted, it depends on the type of message being sent, whether it be by means of the V2V, V2I, V2P or V2N service. Additionally, it is essential that the network guarantees an adequate connection to vehicles circulating at high speeds. Other use cases defined for LTE V2X include: road safety services, speed warning messages in curves, collision warnings to pedestrians or cyclists. The 3 GPP in [5] has identified 25 new use cases for advanced V2X services. These use cases can be grouped into 4 areas:  
* Vehicle platooning: refers to dynamically formed vehicle platoons. Thus, a lead vehicle transmits information to the vehicles that are part of the platoon. In addition, the surrounding vehicles can receive information from the platoon via Road Site Units (RSUs). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Use Case** & **Latency** & **Packet Size** & **Packet Transmission** \\  & **(ms)** & **(Bytes)** & **Rate–Max. (pps)** \\ \hline Forward Collision Warning & 100 & 50–300 & 10 \\ Emergency vehicle warning & 100 & 50–1200 & 10 \\ Emergency Stop & 100 & 1200 & 10 \\ Queue Warning & 100 & 1200 & - \\ Automated Parking System & 100 & 50–400 & - \\ Pre-crash Sensing Warning & 20 & 50–300 & - \\ V2N Traffic Flow Optimization & 1000 & 50–300 & 1 \\ Road safety services & 100 & 300 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Potential requirements for LTE V2X [4]. The units for packet transmission are packets per second (pps). * Advanced driving: Both vehicles and RSUs can share data acquired by sensors to vehicles in their vicinity. Consequently, the vehicles can dynamically coordinate their trajectory. * Extended sensors: exchange of sensor data or video information between vehicles, pedestrians, RSUs, servers, etc.