## 5 Experimental Section
### Environment Setup
For fair and extensive comparison of the proposed algorithm, we implemented other four data gathering schemes that adopt opportunistic forwarding or proxy based strategies:* (1) Epidemic [31]: \(MC\) moves according to the way-point mobility model, yet nodes take advantage of all chances of communications, data are exchanged among any nodes if possible and finally gathered by the \(MC\);
* (2) PROPHET [32]: \(MC\) moves as the same pattern in Epidemic, yet data are exchanged according to the data forwarding probability based on the movement history;
* (3) PDA [13]: a node contact graph is created to compute the data gathering location where \(MC\) could contact with more nodes during some time period; \(MC\) is then programmed to move to the gathering point to gather the data;
* (4) PROXY: nodes with more contacts are promoted as proxy nodes. Proxy nodes broadcast their location information to notify neighboring nodes for opportunistic data collection, and \(MC\) would visit the proxy nodes according to a scheduled trajectory. The trajectory planning is similar to reference [25] based on the solution of the Traveling Salesman Problem. \begin{table}
\begin{tabular}{c c l} \hline \hline
**Parameter** & **Value** & **Description** \\ \hline \(N\) & \(36\) & number of nodes \\ \hline \(field\) & 800*800 m\({}^{2}\) & area of the sensing field \\ \hline \(grid\) & 10*10 & grid partition of the field \\ \hline \(i\_n,t\_n\) & \(5,30\) & initial and total number of epochs \\ \hline \(|epoch|\) & \(1.44*10^{4}\) s & length of an epoch \\ \hline \(|W|\) & \(8\) & number of epochs in observing window \\ \hline \(\Upsilon\) & 1800 s & data gathering round for \(MC\) \\ \hline \(slot\_n\) & \(9\) & number of slots (200 s/slot) \\ \hline \(sp1\),\(sp2\) & [2, 4], [10, 20] m/s & node and \(MC\)’ range of speed \\ \hline \(ps\) & \(\sim N(0.2,0.1)\) & nodes’ basic probability that stops at a grid \\ \hline \(sd\) & \(\sim N(360,60)\) & nodes’ stop duration at a grid \\ \hline \(C\) & 24,31,36,45, & set of hot communities \\  & 50,54,67,76,83 & set of hot communities \\ \hline \(hot\_r\) & \([1,3]\) & rang of number of hot communities for a path \\ \hline \(path\_m\) & \(2\) & maximal number of paths a node has \\ \hline \(gird\_r\) & \([4,10]\) & range of number of grids in a path \\ \hline \(\alpha\) & \(0.5\) & balance factor at Equation (8) \\ \hline \(th\) & \(0.4\) & threshold for proxy node selection \\ \hline \(cache\_s\) & 128 M & size of cache for a node \\ \hline \(packet\_s\) & 1 K & size of a packet \\ \hline \(R\) & 30 m & nodes’ communication range \\ \hline \(B\) & 64 KBps & bandwidth for communication \\ \hline \(event\_s\) & 64 K & size of date generated by an event \\ \hline \(\lambda\) & 600 s & Poisson parameter for events \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Default parameters of the simulations. Epidemic and PROPHET are two classic routing protocols for opportunistic data forwarding; PDA is based on the opportunistic forwarding and contact graph; PROXY is close to ADG in that ordinary nodes route their data to the proxy nodes using opportunistic forwarding schemes, e.g., the Spray and Wait scheme [33]. The differences lies in that in PROXY the selection of proxy nodes does not consider the mode of node movements (e.g., stationary stay, contact duration), and proxy nodes have to proactively broadcast their locations to notify \(MC\) when \(MC\) schedules its path to gather data from the proxy nodes.