# A Real-Time Data Delivery for Mobile Sinks Group on Mobile Cyber-Physical Systems
## 3 Performance Evaluation
### Simulation Environment and Results  
We have implemented the proposed mechanism in the network simulator NS-3. For application to industrial area, sensor nodes follow the reference of the Wireless HART [15], one of the well-known standards in IWSNs which employs an IEEE 802.15.4-based radio, frequency hopping, and retry mechanisms. We compare with M-Geocasting [10] and VLDD [11], which are group mobility support protocols. The simulation network space consists of 1000 sensor nodes uniformly deployed in a 500 m \(\times\) 500 m square area. Fifteen mobile sinks are in a group and the radio range of each sensor nodes is ~20 m. The source node generates 30 byte data packets with an interval of 400 ms and the time deadline for each packet is 400 ms. The simulation time is 50 s. We measure the in-time data delivery ratio, which means how many of data packets are received by the mobile sinks within the time deadline. The result in the figures is the average value of 100 times of simulation.  
Figure 6 shows the in-time data delivery ratio according to the end-to-end (E2E) distance. In this graph, the E2E distance indicates the Euclidean geographical distance between a source and the center of a movable area. In M-Geocasting, a number of packets are lost due to the fact that it exploits flooding and flooding makes broadcast storm. As VLDD is a passive forwarding for supporting group mobility based on the internal movement of each member sink, it causes temporal-useless data packets. In addition, we conduct a simulation with SPEED applying multiple destinations. With these simulation, as SPEED constructs multiple paths for each sink, the interference between multiple paths is frequently occurred. In our scheme, more than 80% of the packets could be received by the sinks of the mobile sink group via unicasting in movable area.  
In Figure 7, the in-time data delivery ratio is presented according to the movable area range of a mobile sink group. In M-Geocasting, as the movable area spans, a larger number of sensor nodes should participate in communication and the interference is more frequently occurred. When the range of the area is 70 m, in M-Geocasting, approximately 61 sensor nodes participate in its flooding area; however, there are only about 39 participating nodes in our scheme. In VLDD, as the area is wider, it might have a lower possibility to receive an in-time data packet due to its passive data forwarding. With the performance of the proposed scheme, we show that our proposed scheme could cover the wider movable area by multiple unicast forwarding.  
Figure 6: Comparison of in-time data delivery ratio according to end-to-end distance.  
Figure 8 shows that the in-time data delivery ratio is affected by the radio range of the sensor node. We vary the range from 15 m to 30 m. Our mechanism and VLDD show almost constant performance, although the range is varied. It is because that our mechanism and VLDD do not exploit the flooding. In M-Geocasting, as the range is wider, the number of one-hop neighbor nodes is increased. With the larger number of neighbor nodes, the number of branches in flooding is increased; however, the possibility of interference for each neighbors also increases dramatically. Therefore, the performance of data delivery ratio is rapidly degraded.  
Figure 8: Comparison of total in-time data delivery ratio according to radio range.  
Figure 7: Comparison of in-time data delivery ratio according to movable area range.