# Energy Aware Cluster-Based Routing in Flying Ad-Hoc Networks
## 3 EALC Methodology
### Selecting Transmission Range  
Transmission range is the maximum acceptable distance between the transmitting node and the receiving node such that signal transmitted from the transmitting node can directly reach the receiving node with acceptable signal strength. Transmission power is the strength of the signal at the time of emission from the transmitting node. The transmission range R of a wireless node is tightly coupled with transmission power [8]. The First equation (Equation (1)) determines the relationship between \(R\) and \(P_{T}\)[25]:  
\[P_{T}=P_{R}+20\log\left(\frac{4\pi R}{\lambda}\right)-G_{T}-G_{R} \tag{1}\]  
\(G_{T}\) and \(G_{R}\) and represent the antenna gain of the transmitting and receiving side, respectively. \(\lambda\) represents the wavelength of the transmitted frequency and \(P_{R}\) is the receiver sensitivity. It can be depicted by Equation (1) that the more the transmission power, the higher the range will be. Furthermore, nodes with the higher transmission range have better connectivity. On the other hand, the higher transmission power consumes more energy that ultimately reduces the lifetime of the UAV node. Higher transmission power leads to higher transmission range, but increasing the power two times does not double the transmission range. Due to the logarithmic relationship between them, increasing the power 100 times increases the range only ten times. In other words, we can say that a slight reduction in the transmission range will lead to more power savings, while setting more transmission power than the application's requirement wastes a noteworthy amount of energy.  
Somehow, if we can analyze our operational requirements and application scenario, we can find the maximum distance the nodes can get apart. Adjusting the transmission power according to the requirements, we can save a notable amount of energy that ultimately enhances the lifetime of UAV nodes.  
Keeping the transmission power lower does not guarantee the optimization of the energy problem. Low power transmission provides a short communication range that results in a lower degree of the neighborhood. Even the nearby located nodes have poor connectivity and suffer from low link quality. With short transmission ranges, neighbor nodes change more rapidly. These rapid changes disturb the data route and often require the reestablishment of new routes. Establishing the new route is also an overhead in network communication. It consumes a huge amount of channel bandwidth and drains the extra energy as well. Poor link quality, changes of neighborhood and route reestablishment result in high a Packet Loss Ratio (PLR) and require re-transmission of data packets. Higher numbers of retransmissions consume even more energy because we have to send more packets to deliver the same information, so, it is desirable to keep a balance between transmission range and energy optimization. An optimal value or set of values must be calculated for each FANET application. At this optimal value, the energy consumption will be optimal. Higher or lower transmission ranges will shorten the node life.