# Communication Interface Manager for Improving Performance of Heterogeneous UAV Networks
## 2 Related Works
### Homogeneous Systems  
Among the researchers that applied homogeneous solutions, [PERSON] et al. [20] used a double-stack communication architecture applying bidirectional communication to a UAV node, which establishes communication with the wireless sensor network (RSSF) and its sink node using the same radio. In addition to establishing the link, this architecture provides different QoS characteristics, such as best-effort and reliability responsible for maintaining UAV-RSSF and UAV-Sink links, respectively. The results demonstrated that it can maintain two-way communication using a single radio, based on a flexible communication infrastructure, which defines the protocol stack to be applied according to the detected communication, mobile data collector (MDC), or communications with the sink. [PERSON] et al. [21] proposed a system with more than one UAV to provide real-time communication. The main objective was to demonstrate that with low-cost hardware and devices easily found in the market, it is possible to create FANETs that meet the requirements of real-time applications. The authors employed an Ar.Drone 2.0, a closed architecture commercial flight unit, along with a Raspberry Pi Model B card with two IEEE 802.11n interfaces, one to allow communication with the other UAV and the other to receive streaming video of the Ar.Drone 2.0 flight. However, the authors only performed latency tests using two UAVs, one static and one that performed a fixed trajectory along the signal range of the static UAV, without evaluating the effects of the use of the second interface in this communication, which could have caused variations due to network coexistence. [PERSON] et al. [10] proposed a validation of a multi-antenna extension to IEEE 802.11a to be used on multi-UAVs networks and showed the impact of UAV's height and orientation variations on the link quality for single-hop and two-hops networks. The authors conduct outdoor experiments, measuring the communication performance in terms of throughput and link quality. IEEE 802.11a in access point mode (ground station) and IEEE 802.11s extension in mesh point mode were used to provide one-hop communication (from a single UAV to a ground station) and two-hops communication (mesh networking between two UAVs and one ground station), respectively. Experimental results show that stable throughput can be achieved using two-hop networks where all traffic goes through an access point UAV as relay. The authors conclude that the standard mesh protocol will be insufficient for multi-UAV systems if high throughput is necessary to deliver large amounts of sensor data (e.g., in SAR missions) or if stable links are required to support users. The use of one UAV in AP mode in two-hop architecture implies in lower jitter. This highlights the difficulty one can find for defining a communication system that can support different network requirements. [PERSON] et al. [22] developed a solution employing changes in the MAC layer of the communication standard to IEEE 802.11p, using optimization mechanisms to avoid inefficiency in the prioritization of traffic (idle time) resulting from the use of the enhanced distributed channel access (EDCA) mechanism. EDCA is applied by the IEEE 802.11p standard to prioritize messages in access classes (AC) (voice, video, best effort, and background). The objective is to propose a solution to the problem of reliability in traffic safety messages in vehicular networks. This solution can also be considered by networks composed of UAVs, as it considers the mobility characteristics that also exist in these networks. The proposed mechanism allowed a reduction of 20% in the packet loss rate, improving the network throughput with each addition of new vehicles, presenting performance similar to IEEE 802.11p EDCA without changes for cases with small numbers of vehicles. In [23], the problem of user-demand-based UAV assignment over geographical areas subject to high traffic demands was investigated.