## 5 Performance Evaluations
### Simulation Results
#### 5.2.2 Comparison in an Expanding Obstacles Scenario  
In this section, we compare SPEED, GPSR and our algorithm under different obstacle area conditions on the following aspects: average delivery delay, energy consumption and packet delivery ratio. There are 100 nodes in the sensor field and the transmission rate is 50 packets per second. The initial area of the obstacle for the whole sensor field is 5% and it finally increases to 50% and the shape of the obstacle does not change. For the instance where the obstacle is expanding, the transmission rate and the number of nodes are constant. Moreover, the area of the sensor field is constant. It means that, the density of nodes is becoming higher per unit time. Therefore, we only need expand the area of the obstacle in the sensing field, we can compare two aspects of performance: expanding obstacle and higher density. Concerning SPEED, GPSR and our algorithm, when the area of the obstacle is changed, the performance of delivery delay, energy consumption on the boundary and the packet delivery ratio would have a significant influence. In the following, we will introduce the performance comparison with changing obstacle area.  
In Figure 8, the X axis is the changing range of obstacle area and the Y axis is the average delivery delay. In the initial phase, the obstacle area is only 5% of the whole sensor field. We can see that because of the transmission rate, the average delivery delay of SPEED is obviously becoming higher. Concerning GPSR and our algorithm, the average delivery delay is relatively low. The reason why SPEED has a higher delay is that once the congestion occurs in some path, SPEED would adopt the backpressure mechanism to balance the congestion to other paths. Therefore, it leads to the result of higher delivery delay for packets. With the expansion of the obstacle area, the influence becomes more obvious, and the density is also becoming higher. From Figure 8, we can see that the performance of average delivery delay of our algorithm is better than SPEED and GPSR. Because the obstacle is expanding, the probability of passing the zero out-degree nodes is becoming higher for the packets. Based on this condition, SPEED and GPSR need more intermediate forwarding of their packets to depart from the concave region. However, concerning our algorithm, this problem had been solved in the network initialization phase.  
Figure 8: Average delivery delay with expanding obstacle area.  
In Figure 9, we compare the energy consumption of boundary nodes in SPEED, GPSR and our algorithm under the expanding obstacle condition. From Figure 9, we can see that when the obstacle is expanding, the nodes expend more and more energy. The main reason is that more and more nodes are located at the boundary of the obstacle. In our algorithm, we try to avoid packet forwarding by the boundary nodes and achieve the goal of load balance. Therefore, the performance of energy consumption is better than that of SPEED and GPSR.  
We next compare algorithms under the condition of expanding obstacle with packet delivery ratio in Figure 10. Concerning our algorithm, the probability of congestion occurring is lower because the game process and the packet delivery ratio is relatively higher. Concerning GPSR, with the expanded obstacle, the concave region is also expanding. Then, the probability of packets entering the concave region is higher and these packets need to be forwarded by the boundary nodes. This would lead to the result that the packet delivery ratio would become lower. Concerning SPEED, although it also adopts a greedy algorithm like GPSR, once the congestion occurs, SPEED would inform the upstream nodes to  
Figure 10: Packet delivery ratio with expanding obstacle area.  
Figure 9: Energy consumption with expanding obstacle area.  
set up a new path for forwarding packets. This could relatively improve the performance to some extent. From Figure 10, we can see that our algorithm has better performance on packet delivery ratio than SPEED or GPSR.