Tham khảo tài liệu 'mobile robots book 2011 part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Effective Heuristics for Route Construction of Mobile Data Collectors 241 The performance on experiments A1-A3 is better than B1-B3. This is obvious because most of the events come from a specific part of the network which helps the mobile collector to optimize its collection route more than when the events are scattered as in experiments B1-B3. This also appears on the distance ratio of the mobile collector shown in Figure 7 c . As the events are scattered randomly over the sensing field the mobile collector is required to travel more for the collection which appears on the distance ratio for experiments B1-B3. It is hard to conclude about the dependence of a value on the results however a around leads to minimum results for the performance metrics described. Impact of the Speed of the Mobile Collector To get an insight into the relative performance of the two algorithms two constrained topologies are used to show the impact of the mobile collector speed on the data collection time and the request collection time. The topologies considered employ 100 sensor nodes uniformly distributed in a square area of 100 x 100 m2 . A concentric and random sensing rate topology is used with the sensing base rate equals 2 secs. These are labeled as Topology A and Topology B. Figure 8 a and 8 b plot the performance of the two algorithms for different speed values for the mobile collector. The DI-R construction algorithm outperforms the MST-R construction algorithm however when the speed of the mobile collector increase this difference vanishes. Also previously the algorithms performed better on the concentric sensing rate topology than on the random topology this does not hold when the speed of the mobile collector is increased. 6. Conclusion and Future Directions Sensor networks operate under limited energy constraints. Eliminating the relaying overheads can extend the sensor lifetime and prolong the network operational time. In this context mobile elements robots are .