# Faudistic Platooning: Subdivide Platoons, Unite Networks, and Conquer Efficiency and Reliability
## 4 Feudalistic Platooning
### Concept  
_Feudalistic Platooning_ does not substitute a general platooning concept for the platoon level and control level--extends it instead. Furthermore, it is able to combine two or more networks. In the following, we describe _Feudalistic Platooning_ on the back of ad hoc (IEEE 802.11p) and cellular networks (LTE and C-V2X). However, networks are interchangeable. Moreover, cellular coverage is not a prerequisite for an operational _Feudalistic Platooning_ system: occasional and partial availability is sufficient. LTE is used to access a central server (VI). This means that the central server may be accessed from every cell (V) (see Figure 1). It collects and stores platoon information. Furthermore, it is the source of its distribution. A more detailed description of the central server can be found in Section 4.5. An already existing platoon may activate and also deactivate _Feudalistic Platooning_ at any time. To perform _Feudalistic Platooning_, the platoon is divided into smaller convoys of vehicles, so-called vassalages. Each of those vassalages consists of at least three, and up to many platooned vehicles. Within a vassalage, each vehicle acts according to specified roles that depend on their position within the vassalage. Independently of their role, all vehicles emit vehicle status information in terms of CAMs and notify events using DENMs. They send both types of information redundantly using the ad hoc and C-V2X networks. Once performing _Feudalistic Platooning_, the ad hoc network is used exclusively for vehicle status and event information. Received packets of this type are not forwarded. We distinguish between four different roles, where roles IV, III, and II need to be occupied:  
* Lord (IV): the mid vehicle of the vassalage responsible for shipping data, i.e., it collects vehicle status and event information from all vehicles within its vassalage which it regularly reports to a central server. Furthermore, it performs ordering, i.e., it periodically requests information from other vassalages at the central server. Cellular coverage is required to do this. Received data may be shared among all vehicles of the vassalage using C-V2X that is available both in and outside of cellular coverage. The selection of the mid vehicle ensures the shortest communication paths. One of  
Figure 1: _Feudalistic Platooning_: Vehicle group as vassalages of variable size that act according to specific roles: knight (green); lord (red); merchant (purple); and peasant (no color). the two mid vehicles may be selected in the event of an even number of vehicles in the vassalage. * Knight (III): the first vehicle of the vassalage receives data over C-V2X from the merchant of the preceding vassalage when there is one in this position. It may distribute the received data among all vehicles within the vassalage, again using C-V2X. The selection of the first vehicle ensures the closest communication distance to preceding vassalage. * Merchant (II): the last vehicle of the vassalage which collects status and event information from all vehicles within its vassalage which it sends to its follower, i.e., the knight of following vassalage--if there is one. C-V2X is used to transmit the data. Selecting the last vehicle ensures the closest communication distance to the following vassalage. * Peasant (I): any remaining vehicle within the vassalage which does not have to handle additional communication tasks. A further two additional roles are introduced during the setup phase:
* Claimant: the vehicle part of a platoon and ready to perform _Feudalistic Platooning_. * Outlaw: the vehicle part of a platoon not ready/capable of performing _Feudalistic Platooning_. Vehicles within a vassalage perform dynamic platooning [20]: due to data redundancy, they may be able to drive at smaller inter-vehicle distances compared to a normal platoon within the same environment. Exclusive usage of the ad hoc network for vehicle status and event information ensures the best reliability possible.