# DDS: A Delay-Constrained Duty-Cycle Scheduling Algorithm in Wireless Sensor Networks
## 5 Performance Evaluation
### Evaluation Results
#### 5.3.2 Effects of the Deadline Success Ratio  
In order to evaluate the effects of the required DSR on network performance, we varied the DSR from 80% to 97% while the other parameters were kept to default values. With a higher required DSR \(\gamma\), z in Equation (25) increases, since it is extracted from the standard normal table with the given \(\gamma\). As a result, the duty cycle interval decreases.  
With regard to the achieved DSR, as is shown in Figure 5a, DDS obtains the best performance when the required DSR is greater than 90%. DDS, SROD-MM, and OGP satisfy the required DSR. On the other hand, SROD-WA does not satisfy a required DSR that is higher than 85%. Even at the lowest DSR (i.e., 80%), OAPF does not meet the requirement. For example, with a required DSR of 95%, the achieved DSRs under DDS, SROD-WA, OAPF, and OGP are 99.1%, 91.6%, 81.2%, and 98.6%, respectively.  
It should be highlighted that the achieved DSR of the five schemes improves as the required DSR increases. However, OAPF obtains a low DSR due to the many collisions and the lack of a packet recovery mechanism. Although SROD-WA implements a packet recovery mechanism that is the same as that used by DDS, the achieved DSR under SROD-WA is still low because there are more collisions with a longer duty cycle interval. Meanwhile, since a retransmission mechanism is implemented in the OGP algorithm, the achieved DSR of OGP is relatively high.  
As seen in Figure 5b, the energy consumption by DDS is approximated to two extended DASE algorithms and smaller than OAPF and OGP. For instance, when the required DSR is 95%, the total energy consumption under DDS, SROD-MM, and SROD-WA is around 760 J, while OAPF and OGP spend 101.2% and 109.7% more energy than DDS, respectively. Additionally, the total energy consumption by the schemes has a similar trend that is relatively flat as the required DSR increases (i.e., as the duty cycle interval decreases). This is because the decrement of the duty cycle interval has two opposing effects on energy consumption. First, with a shorter duty cycle interval, the energy consumed by the schemes increases because of the increase in the number of total awake periodsfor the nodes. Second, when the duty cycle interval decreases (i.e., the wake-up frequency for the nodes increases), the transmitters' waiting time for forwarding candidates is shorter. This leads to the decrease in energy consumption. As a result, the total energy consumption is relatively flat rather than notably increasing.  
In terms of average E2E delay, DDS outperforms SROD-MM and SROD-WA, as shown in Figure 5c. The average E2E delay of the five schemes linearly decreases as the required DSR increases from 80% to 97%. The duty cycle interval is reduced as the required DSR increases. With a lower duty cycle interval, nodes wake up more frequently, which leads to the decrease in E2E delay. For instance, as the required DSR varies from 80% to 97%, the average E2E delay under DDS decreases from 10.7 s to 7.2 s. With a required DSR of 90%, the average E2E delay from DDS is 8.8 s. This value is greater than 2.8 times the average E2E delay from OAPF and smaller than 18.1% of the average E2E delay from SROD-MM. The reason comes from the fact that OAPF and OGP aim to reduce the E2E delay by using a short period for transmitting data packets. On the other hand, the objective of DDS is to minimize energy consumption while satisfying the required DSR.