**2.3. Aggregation factor**

Here a robot aggregates its own generated data and received data from adjacent upper nodes before transmission. The sink does not participate in data aggregation. When data aggregation occurs at a robot node, the aggregation factor denotes the proportion of aggregated data size and local generated data size. It means that the aggregated data size is AF times of the generated data size. AF=1 means that aggregated data have the same data size with generated data, and we assume there is one generated data at one time.

$$AF = \frac{\text{Aggregated data size}}{\text{Generated data size}} \tag{1}$$
