# Cellular-V2X Communications for Platooning: Design and Evaluation
## 7 Discussions  
The conducted analysis helps us to derive some key insights into the potential of the C-V2X technology in supporting platooning applications.  
Results clearly shows that enabling the simultaneous PM-to-PM transmission mode, after the PL transmits its CAM, significantly reduces the CAM cycle completion time. Such a feature uniquely characterizes the conceived proposal, which oversteps the sequential transmission mode reminiscent of TDMA solutions built on top of IEEE 802.11p.  
In addition, when moving to the specific C-V2X settings, the main findings are as follows. CQI reporting is shown to highly improve the resource utilization. Adapting the MCS to the actually experienced channel quality of the receiver, makes more efficient the short-distance PM-to-PM transmissions, overall reducing the interference.  
In addition, enabling frequency reuse, which is the among the key features of V2V-enabled cellular networks compared to the infrastructureless 802.11 technology, ensures high-reliability, low latency and high capacity. Thus, it is particularly promising in the view of enabling platoon vehicles to exchange CAMs very frequently thus, able to keep very small inter-vehicle distances.  
In particular, with values of the completion of a CAM cycle in the order of 30 ms, the transmission of 30 CAMs/second could be accommodated as recommended in [22].  
The achieved encouraging results coupled with the recent and planned advancements of the cellular technology in the roadmap towards 5G new radio make us confident that there is room for improvements.  
The latency incurred by the dynamic scheduling approach could be further reduced if a different numerology is considered, i.e., TTI values shorter than 1 ms. Such an option is under investigation in 3 GPP Release 15 and its benefits have been preliminarily studied in [36; 37]. Thus, in the near future the usage of the dynamic scheduling could be incentivized. Additionally, lighter signaling procedures could be devised aimed to reduce the latency incurred in getting the resource grants from the eNodeB prior to CAM transmissions. The comparison of such techniques against the semi-persistent scheduling scheme would be a subject matter of future works.  
With such advancements, up to 50 and 100 CAMs per second could be further supported in the view of high-density platooning scenarios with high level of vehicle automation [22].  
Figure 9: Metrics evaluated with and without frequency reuse, simultaneous transmissions and CQI reporting enabled (\(L=10\)). (**a**) Average allocated RBs per TTI; (**b**) Ratio of successfully completed CAM cycles; (**c**) Average completion time of one CAM cycle.  
Another issue that needs to be addressed for platooning exploiting C-V2X communications is the management of mobility. In fact, a platoon moving on a highway will traverse multiple cell areas and it is likely that vehicles are under control of different eNodeBs. In this case, continuity of inter-cell V2V communications should be guaranteed, for instance providing coordination mechanisms among neighboring eNodeBs. On the other hand, _bulk handover_ solutions could be envisaged to allow all vehicles in a platoon to perform handover at the same time, reducing both latency and the amount of signaling.