# On the Needs and Requirements Arising from Connected and Automated Driving
## 6 Related Challenges and Existing Research Works
When considering the great potential of the high data rate, the utilization of mmWave bands holds great potential. However, beamforming associated to the operation on mmWave frequencies imposes a challenge in highly dynamic V2X environments. * **Local data scheduling and delivery**: in some use cases (e.g., HD map dissemination), the data might be generated and available before the vehicle approaches a target area. This means that the network should consider the geographical area of the data when scheduling data delivery. Multimedia Broadcast/Multicast Service (MBMS) [29] can play a key role to send the common data of interest to a group of vehicles with one transmission instead of unicast. Although being suitable to this purpose, as, for instance, analyzed in [29] to improve the resource utilization and in [30] for co-existence with direct vehicle-to-vehicle communications, MBMS has a main drawback in terms of high signaling for MBMS group creation, joining, notification, session start, etc. This might impact the capability of the network in delivering the desired data before the vehicles approach a reference area. In addition, MBMS is efficient when the number of UEs receiving the same content is reasonably high, and this condition might not be valid in some scenarios where the geographical areas for data delivery might be small (e.g., in the order of a few tens of meters), with few involved vehicles. Small geographical areas also bring additional issues in terms of higher number of groups to be managed and additional joining/leaving signaling. * **Accurate localization of vehicles and vulnerable road users**: accurate location is a one of the key enablers for several use cases that are related to connected vehicle systems. However, having a solution that can provide very accurate (centimeter level) location estimate in a very short time (low latency) is yet a challenge. Regardless of the localization technology (satellite-based or cellular-based), the problems arise from two fronts: (1) the errors affecting the position-related measurements due to propagation of radio signals in a multipath environment and (2) the delay to process and/or feed location-information to the location server. Research is on-going on finding 5G radio-assisted positioning techniques for both vulnerable road users and vehicles with the aim to increase the availability of very accurate localization. This could potentially be achieved thanks to new triangulation algorithms running in multiple base stations with Multi-Input Multi-Output (MIMO) beamforming at mmW frequencies, for example. * **Accurate channel modeling**: it is fundamental to the design of the reliable V2X communication systems. Recent surveys of existing state of the art vehicular channel measurements and models can be found in [31; 32]. However, each of the existing models were designed for a specific scenario and therefore cannot be applied for the variety of scenarios (e.g., urban, rural, and highways) encountered in the vehicular environments. It is worth mentioning that there is a lack of a clear guidance that helps radio designers how to select the appropriate V2X channel model and the right combinations of parameters to be used for each of the high reliability use cases discussed in this paper. * **Support of vehicular use cases with Multi-access edge computing (MEC):** edge computation capabilities can be particularly useful for computation-sensitive V2X use cases. Therefore, the joint optimization of MEC capabilities and mobile network resources may be beneficial, allowing for the offloading of computation tasks close to the access node. How MEC can be used in the network architecture supporting C-V2X is described in [33], while service migration in compliance with ETSI MEC is further addressed in [34]. * **Multi-connectivity**: it could improve the service availability by jointly using several communication modes or technologies instead of only relying on one mode/technology (i.e., only Uu or only SL) that might not be able to support some use cases.