# CoDA: Collaborative Data Aggregation in Emerging Sensor Networks Using Bio-Level Voronoi Diagrams
## 5 Simulation Results  
This study uses a simulation for performance evaluation of the proposed protocol, which uses the network simulation software NS2 [46] to set up the model and environment needed by the experiment. In the experiment, we assume that the sensor nodes are distributed in a square area, and the location of each sensor node is randomly generated. In order to reduce the error, we repeat the experiment 100 times. Figure 5 shows the placement of relay nodes and their coverage area in CoDA, HCDD [47], and DDB [48], where there are 200 sensor nodes distributed in the field of four square sides with a length of 400 m.  
By comparison, we can find that the number of relay nodes in CoDA is 14, which is a minimum feasible topology for relay nodes. Also, HCDD and DDB can achieve the coverage of the whole network by deploying more relay nodes, but the number of relay nodes is 16 and 17, respectively. Next, the number of relay nodes required by each algorithm is analyzed under different experimental scenarios. Two sets of experiments are carried out, where the communication radius of the sensor nodes is set to 50 m, and the communication radius of the relay node is 100 m. The number of sensor nodes deployed in the network increased from 200 to 800. The tests were repeated 10 times, respectively, and the average number of required relay nodes was obtained. Figure 6a,b show the number of relay nodes required for each algorithm with different node density, where the horizontal axis represents the number of sensor nodes and the vertical axis represents the number of relay nodes. In the first scenario of experiments, the density of the sensor is set to 0.25, and the density of the sensor is 0.5  
Figure 5: The placement of relay nodes in different protocols. in the second scenario. It can be seen that the number of relay nodes for each algorithm has a linear increasing trend under the condition that the distribution density of sensor nodes is constant. As it can be seen from the Figure 6, the number of relay nodes demonstrates a linear increasing trend under the condition that the distribution density of sensor nodes being kept constantly. When the number of sensor nodes is equal, the number of relay nodes in HCDD is of the most, and the least number of relay nodes in CoDA can cover most of the area. According to the slope of the graph, with the increase of the number of sensor nodes, the gap between the numbers of relay nodes being arranged in the three algorithms is more and more large. By contrast between Figure 6a and 6b, we can observer that the greater the distribution density is, the fewer the number of relay nodes need to be arranged, which demonstrates the characteristic of geometric coverage for the relay node arrangement. Next, the number of relay nodes generated by different protocols is analyzed under the condition that the region size is fixed and the radius of the relay node is different. In two scenarios, the sensor nodes are evenly distributed in the 800 m \(\times\) 800 m fixed area. The sensor node communication radius r = 50 m, the communication radius of relay node is 100 m and 200 m. As shown in Figure 7a,b, with the increase of the density of sensor nodes, the number of nodes generated is gradually increased, and the rate of growth slows down gradually in the fixed area. It can be observed that the distribution density is sensitive to the variation of \(R\). Figure 6: Comparison of number of relay nodes in different distribution density. Figure 7: Comparison of number of relay nodes in different coverage radius. Coverage rate is usually regarded as an index for measuring the quality of service [49; 50]. Here, We define it as a proportion of active nodes in the network at a certain time \(t\), i.e., \(Cov(t)=1-\frac{n_{b}(t)}{N}\), where \(n_{b}(t)\) is the number of nodes out of range of arbitrary relay nodes. In this test, the transmission radius of all relay nodes is fixed so as to analyze the relationship between the coverage rate and the number of relay nodes in different protocols.