# Mobile Autonomous Sensing Unit (MASU): A Framework That Supports Distributed Pervasive Data Sensing
## 5 MASU Empirical Evaluation
### Evaluation Results
#### 5.4.1 Benefits of Collaborative Sensing  
Next, we present various tests done using the Prototype I to assess the usefulness of sharing data among MASU units, instead of working autonomously. Although this assessment only considers the advantages of collaborative sensing in terms of the battery consumption, other aspects must also to be taken into account, such as better information quality and social welfare (the benefit of the entire community of users). First, we evaluated the battery consumption produced by a sensing activity in different devices. Figure 14 shows the results obtained when the devices are not performing any sensing or sharing activities, and also when they are sensing GPS data. This graph indicates that there is a significant cost in battery lifetime, due to the sensing operations. Moreover, this cost differs across devices, having the device A the highest cost. This difference in battery consumption can be caused by differences in the versions of the operating system or the GPS sensing chips. Then, we evaluated the costs involved in a collaborative sensing activity considering heterogeneous devices. Therefore, we compared the total battery consumption when sensing data and transmitting it \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **A1, A2, A3** & **B** & **C** & **D** & **E** \\ \hline Device Type & Smartphone & Smartphone & Smartphone & Tablet & Tablet \\ \hline Model & HTC Desire & HTC One & Samsung Note II & Google Nexus 7 & Google Nexus 7 \\ \hline Android & 2.3.3 & 4.4.3 & 4.4.2 & 4.4.4 & 5.0.2 \\ Version & & & & & \\ \hline \multirow{2}{*}{Chipset} & Qualcomm QSD 8250 & Qualcomm APQ 8064T & Samsung Exynos & \multirow{2}{*}{Nvidia Tegra 3} \\  & Snapdragon S1 & Snapdragon 600 & 4412 Quad & & \\ \hline \multirow{2}{*}{CPU} & \multirow{2}{*}{1 GHz Scorpion} & Quad-core 1.7 GHz & Quad-core 1.6 GHz & Quad-core 1.2 GHz & Quad-core 1.2 GHz \\  & & Krait 300 & Cortex-A9 & Cortex-A9 & Cortex-A9 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Devices used in the evaluation of the prototype. Figure 14: Sensing costs for different devices. using the two local data retrieval mechanisms: AllJoyn and CoAP. We conducted two different sets of experiments, where four different devices share GPS data, using AllJoyn and CoAP, respectively. Figure 15 depicts the results when the device A1 is sensing and transmitting GPS data (Producer role) and devices A2, B and C are receiving it (Consumers). As expected, the energy consumption is higher in the transmitting device than in the receiving ones for both, AllJoyn and CoAP protocols. In addition, the energy consumption is higher when using AllJoyn than when using CoAP for both, transmitting and receiving devices. Nevertheless, for some receiving devices, the energy drain is very similar for both protocols. Notice that the battery consumption differs according to the device type, even when they have same role (Consumers) and protocol active. This shows the effect of the devices heterogeneity on the collaborative sensing activity. These results can be anticipated since the CoAP protocol is very simple and it is therefore, expected to consume less energy than a more complex protocol (like AllJoyn) that includes network and service discovery functionalities. We then conducted a number of tests in order to verify the benefits of collaborative sensing. Unlike the previous tests, here we aim not only to evaluate the overall costs of collaborative sensing, but also to isolate the costs related to the data retrieval mechanisms used by the MSU framework. Thus, we intend to differentiate between the sensing costs (which are required even when the units work in a stand-alone fashion) and the costs caused by the collaborative activity itself. For these tests, we considered the worst case scenario, that is, when sharing data using the most energy-intensive protocol. Consequently, the application executing the MSU framework had only the AllJoyn protocol activated.