## 3 Dual-Stack Single-Radio Communication Architecture (DSSRCA)
### Experimental Evaluation
#### 3.4.1 Best-Effort Protocol Experimentation  
These experiment were performed using one wireless sensor (MICAz) deployed 70 cm above the ground level and a MDC. The MICAz sensor was configured to transmit 20 bytes of payload per message, with an unlimited number of messages in the buffer, whenever it was in the communication range of the MDC. Both, a remotely piloted UAV and a bicycle were used as MDC. Let us start by addressing the experiments using the UAV. The UAV was supposed to perform a rectilinear flight, approaching the sensor and departing from it at constant speed and altitude (see [36]). Figure 4 shows the flight data collected in one of the experiments, with distance at the top, altitude in the middle, and speed at the bottom. While the distance (to the sensor) is calculated by the UAV, altitude and speed are obtained from the GPS. As one can see, the altitude and the speed presented significant variations (while the original intention was to keep it constant). This implied changing the distance of \begin{table}
\begin{tabular}{c c c} \hline
**Parameters** & **Sink Node/UAV** & **Sensor** \\ \hline Radio Mode & Microchip MRF24J40 MC & MICAz MPR2400 CA \\ Antenna & Full-wave dipole & Half-wave dipole \\ Tx Power & +19 dBm (UAV-BS) –2 dBm (UAV-WSN) & –1 dBm \\ Automatic HW Re-transmission & 3 & 3 \\ Channel & 11 & 11 \\ \hline \end{tabular}
\end{table} 
Table 1: Physical layer settings and other aspects of the experiments. the UAV to the sensor in a non-linear manner, making it impossible to obtain a proper estimate of the message reception rate with respect to the distance. An interesting phenomenon to be observed is the action of the re-transmissions protocol at the sensor side. As stated before, it makes three re-transmissions attempts before stopping sending messages to the UAV. At this point, the sensor waits for a new _request message_, so that it can start transmitting again. Figure 5, presents the total number of messages received by the UAV during the 110 s of the experiment. The pie graph is used to divide the messages according to the number of re-transmissions necessary to deliver these messages. The results show that 91% are delivered in the first transmission attempt, which represents a very good transmission quality for the experimented distance. It is important to notice that 453 re-synchronization messages (_request message_) were transmitted by the UAV along the experiment. We consider this number to be higher than desired, so improving it will be the focus of further investigation. These experiments allowed us to conclude that it is very difficult for an amateur pilot to perform a smooth flight trajectory. Only very experienced pilots or autonomous aircrafts would be able to achieve this goal, which would allow testing of the proposed communication prototype in a more suitable manner. Therefore, it was decided that further experiments use the bicycle. In respect to the experiments with the bicycle, as previously mentioned, they make it easier for one to control both the bicycle path and its speed. The bicycle traveled on a rectilinear path so that it first approached the MICAz and then distanced itself away. The bicycle started at 125 m away from the sensor and stopped 125 m past it. The target speed was 7 m/s (see [37]). Figure 4: UAV experiment flight log with respect to (**a**) distance; (**b**) altitude; and (**c**) speed. Figure 6 shows the number of messages collected by the bicycle with respect to the sensor distance. This analysis is interesting in this experiment because the bicycle moves at a constant speed, without stopping. As expected, the distance directly affects the link quality. When the distance between bicycle and sensor increases, the number of messages collected by the bicycle decreases. Therefore, this experiment helps evaluate the distance that is most suitable to start collecting data. The graph in Figure 7 shows the latency of the messages transmitted by the sensor.