# Communication Interface Manager for Improving Performance of Heterogeneous UAV Networks
## 2 Related Works
### Heterogenous Systems  
Among the works applying heterogeneous interfaces, [27] presented a communication architecture in which UAV nodes communicate over a cellular network and an IEEE 802.11p network. The purpose of the study was to provide a secure positioning algorithm for UAVs swarms, using RSSI beacon frames sent by UAVs as a distance estimate. The authors considered a communication scenario where UAVs use the cellular network (3G or 4G) to send messages to this base and IEEE 802.11p interfaces for U2U communication, operating at 5.8 GHz. Network management is centralized, as only beacon messages are exchangedbetween UAVs. The results showed that the uncertainty rates in relation to the calculation of the distances between UAVs, generated by RSSI values received by the triangulation of neighboring nodes, is reduced to a distance up to 50 m between them. However, it gradually increases above this distance.  
A still-open challenge is the access of multi-UAV networks to remote areas, using the limited range of wireless transmissions that operate in unlicensed bands. In [28], the authors used retransmission and routing algorithms to provide a wider range in wireless transmissions in multi-UAV networks. The system uses a wireless interface that operates at 2.4 GHz for communications between the cluster-leading UAV and its base, and a 5 GHz interface in U2U transmission. Management is centralized, as UAVs advance their positions in accordance with the improvement in the RSSI signal received between the swarm leader and the base. The results demonstrated that it is a scalable solution, extending the reach of communication inserting new UAVs, and improving the UAVs' network connectivity.  
In [29], the authors developed a communication system that divides UAVs into cluster heads and members of the cluster. The cluster head UAVs are equipped with interfaces of LTE and WiFi technologies in access point (AP) mode, and the members of the cluster are equipped only with WiFi interfaces in this mode. Cluster heads can connect to a virtual private network (VPN) server to receive control commands through the LTE interface and receive data from the sensors through the WiFi interfaces present in the cluster members. The authors evaluated the system using bandwidth consumption, latency, and received strength signal (RSS). The results demonstrated that the latency is stable up to a distance of 18 m between the cluster heads and the member clusters with support for real-time video transmissions, presenting rates between 4 and 6 Mbps and RSS above \(-60\) dBm considering pre-existing integrated communication interfaces in UAVs (without hardware extensions).  
The experimental performance of commercially quadrocopters communicating via IEEE 802.11a was evaluated [10], comparing the infrastructure of one-hop and two-hop wireless communications. The main purpose of this research was analyzing the network layer versus MAC layer relaying in terms of throughput and link quality. The results showed that with the two-hop networks infrastructure, the standard 802.11a using the routing protocol based on number of hops is insufficient for multi-UAV systems if high throughput is necessary to deliver large amounts of sensor data or if stable links are required to support users.