# Communication Manager for Hyper-Connected RPAS Environments
## 2 Related Work  
The availability of robust communication links is one of the most crucial factors in enabling the possibility of reliable RPA operations (pursuing the 3R approach). In many works, the communication between devices (RPA-RPA or RPA-RPS) is just taken for granted, and it is assumed that it will always support the whole system. However, depending on the operation scenario, this supposition may only sometimes be true. It can be hard to obtain a good (i.e., robust, redundant) communication channel between RPAs to the RPS or between the RPAs themselves. This challenge is amplified in environments where RPAs may encounter unplanned/unexpected conditions (i.e., urban environments full of obstacles or interference, or the military domain). This point is quite a common problem in traditional communication networks that is even more intensified by the volatile/dynamic nature of these flying network nodes. The different solutions are commonly found in one of the following two domains: One alternative is strengthening the communication channel using a more robust technology or redundant communication channels. The other not necessarily exclusive alternative is strengthening the network, providing redundant paths to the destination (multi-path) or more reliable intermediate nodes. Using alternative or multiple communication channels has only sometimes been an option for RPAs because it implies onboarding more transmission/reception devices, and the payload, in some cases, may be pretty limited. However, nowadays, RPAs can carry payloads of much more than simple communication gadgets thanks to the rapid evolution in the miniaturization of devices. This fact allows RPAs to become powerful IoT components, offering not only sensing but also communication services and onboard data analysis. For example, authors in [11] employ LoRa, Wi-Fi, and LTE networks to provide the RPA systems with broadband and cellular wireless network support. This multi-interface concept is increasingly present in the multi-RPA environment and will be treated in this paper. Authors in [12] propose a solution for RPAs in which 4G and 5G cellular technologies are combined to maximize the operating range in areas where commercial 5G is not yet deployed. Therefore, their system uses the best available alternative based on radio parameters such as the Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ). The utilization of cellular technologies in RPAs is becoming increasingly relevant, turning the RPAs into flying base stations or mobile end users. Regarding the second possibility and the usage of redundant paths to a particular destination, there are plenty of initiatives using RPAs as communication relays. For instance, the authors in [13] present a tactical data link that guarantees control reliability in emergencies and introduces tactical data to link RPAs as communication relays. The authors in [14] propose using other RPAs that are part of the system as communication relays to enable two-hop connectivity and enhance extensive reliability. However, nowadays, there is a notorious trend towards the idea of being able to configure flying communication networks based on RPAs acting as network nodes and bringing to aerial communications the same advantages that we may have with a meshed ground network [15; 16]. Figure 1 shows multiple paths and technologies. This figure also serves as a reference scenario for the Labyrinth project where various network nodes (either RPAs in the air, ground RPS, or a UTM provider) enable the multi-path network configuration possibility through multiple channel alternatives. One of the most relevant challenges in these flexible and, at the same time, complex scenarios is the management of the communication networks from their initial configuration and establishment through the maintenance of the communications service up to the response to network failures.