# Faudistic Platooning: Subdivide Platoons, Unite Networks, and Conquer Efficiency and Reliability
## 5 Results
### Framing within Recent Selected Publications  
Recent publications in the field of platooning focus on all layers: the vehicle layer, platoon layer, and transport layer. Table 3 lists their used communication technologies, mentions their key contributions, and highlights open questions. We emphasize that _Feudalistic Platooning_ does not replace a single one of them, but its appropriate embedding addresses most of the open questions. These are explained as follows:  
* The connection of all vehicles at any point in time: independent of the used communication technology, listed publications assume the connection of all vehicles at any point in time. This cannot be guaranteed under all circumstances and thus, the operability of the platoon is questionable. Especially when only cellular networks are used, handover scenarios lead to temporary connection losses. We explain in Section 5.3 how _Feudalistic Platooning_ stays operable and circumvents handover problems.
* Strong data dependency: listed publications introduce strong data dependency, either assuming each vehicle is aware of every other vehicle or leader information is available throughout the platoon. This causes a large uplink and consequently also large downlink data traffic in cellular networks and drastically increases the ad hoc network load once single broadcasts are no longer sufficient. _Feudalistic Platooning_ is able to steer message flow according to the needs of the vehicle controller. Critical data can be exchanged on a time-variable basis. Non-critical data are exchanged whenever possible (see Section 5.3).
* Network election: publications that consider the availability of both ad hoc and cellular networks assume that the data needed for the vehicle layer are exchanged using the ad hoc network. In contrast to that, data for upper layers are exchanged using the cellular network. However, the selection of the communication technology, e.g., on per-packet basis [12], would be possible at least for the vehicle layer and partly for the platoon layer. _Feudalistic Platooning_ exploits the availability of multiple networks and adds redundancy on critical data. Data from higher layers can still be transmitted. Their timescale is increased anyways and thus, their criticality decreases [42].
* Heterogeneous platoons: vehicles within a platoon are heterogeneous by nature. Vehicles differ in type and in load. Thus, they offer different acceleration and deceleration capabilities. This needs to be considered by the vehicle layer [20]. In _Feudalistic Platooning_, vassalages can be used to group vehicles according to different indicators, e.g., according to their braking capability.
* Surrounding traffic and its variability: considering surrounding traffic is challenging. Increased inter-vehicle distance between two vassalages in a feudalistic platoon considers surrounding traffic already up-front. Variable vassalage size can counteract time-variable traffic density and its impact on the network quality (see Section 5.3).  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Publication** & **Communication** & **Key Contribution** & **Open Questions** \\ \hline COMPANION—Towards & Hybrid network: & Comprehensive system that includes: & (i) Connection loss and \\ Co-Operative Platoon & (i) Cellular—3G for & (i) Strategic layer (i.e., transport layer); & system operability; \\ Management of & communication with & (ii) Tactical layer (i.e., platoon layer); & (ii) No communication \\ Heavy-Duty Vehicles [43]. & central server; & (iii) Operational layer (i.e., vehicle). & flow: broadcast/multicast \\ Year: 2015. & (ii) IEEE 802.11p for & & or retransmission required; \\  & intra-platoon & & (iii) Surrounding traffic. \\  & communication with & & \\  & extended ITS-G5 & & \\  & messages. & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Recent selected publications on different layers: used communication technologies, key contributions and open questions. The latter could be addressed by _Feudalistic Platooning_.