## 6 Performance Evaluations
### Performance with Varying Traffic Loads  
In the performance evaluation, we first simulate diverse traffic rates from all the deployed sensor nodes. In Figure 4, the energy efficiency of ATLAS is compared with the other protocols as a function of traffic load. As delineated in Figure 4(a), the duty-cycle of the protocols increases with increased data generation rate. At a low load, the duty-cycle in ATLAS rises marginally; however, as the load increases, the sensor nodes operate more in active mode in order to handle the data due to the traffic load adaptability. In contrast, the IEEE 802.15.4 protocol maintains a fixed duty-cycle of \(50\%\), irrespective of the traffic load. In LDTA-MAC, although the duty-cycle at high traffic is almost equal to the ATLAS, under low traffic it is relatively high. In terms of energy consumption, a low duty cycle is anticipated at very low traffic for energy conservation, and at a moderate traffic of 12 Pkts/s, ATLAS has only an 11% duty-cycle. Conversely, LDTA-MAC has a 20% duty-cycle under the same traffic load. Figure 4: Energy efficiency over diverse traffic loads: **(a)** Average duty cycle; and **(b)** Average energy consumption. The average energy consumption of the protocols is shown in Figure 4(b). According to the results, the energy expenditure for ATLAS is significantly lower than that for the other two protocols. The main reason for this is the maintenance of an adaptively long inactive period during low traffic periods as well as better energy utilization under high traffic loads. Note that as the traffic load increases the energy consumption also increases for ATLAS. The LDTA-MAC and IEEE 802.15.4 have almost identical high energy cost under low traffic conditions since they employ a fixed CAP concept, thereby increasing the energy consumption. Furthermore, the long range transmissions of the sensor nodes (in single-hop) increase the energy costs for both LDTA-MAC and IEEE 802.15.4. However, at high rates of data generation, the LDTA-MAC wastes less energy for collision drops than that of IEEE 802.15.4 due to its traffic adaptive CFP use. Still it consumes more energy than ATLAS due to the use of a fixed CAP and single-hop oriented direct communications. On the other hand, only CFP property of the superframe is exploited in ATLAS under high traffic conditions, thereby maximizing energy conservation. In Figure 5, the data fidelity in terms of aggregate throughput and delivery ratio of the protocols are observed. As shown in Figure 5(a), even though the aggregate throughput of all the protocols increases with the traffic load, the variation is noticeable especially under high traffic loads. The proposed ATLAS protocol achieves a maximum throughput of 78 kbps at a high rate of 15 Pkts/s, and the average per node throughput is 12.18 Pkts/s. In contrast, for the same data generation rate, adaptive CFP allocation seems advantageous to LDTA-MAC as it achieves a throughput of 55 kbps with a per node throughput of 8.7 Pkts/s, which is higher than the static CAP, CFP and IP based IEEE 802.15.4 protocol, but not better than our protocol. The load specific and more appropriate use of CAP, CFP and IP operations help ATLAS to achieve a superior throughput performance compared to the other protocols. The delivery ratio shown in Figure 5(b) also reflects the throughput performance and proves the data fidelity effectiveness of ATLAS over the other protocols. At different traffic loads, the maximum and minimum delivery ratio of ATLAS are \(99.6\%\) and \(60.2\%\), respectively; for LDTA-MAC which are \(99\%\) and \(42.18\%\), respectively. The delivery ratio of IEEE 802.15.4 is the worst amongst the simulated protocols since it can hardly handle the heavy traffic of the network. Figure 5: Data fidelity over diverse traffic loads: **(a)** Aggregate throughput; and **(b)** Packet delivery ratio. The proposed ATLAS protocol outperforms both the LDTA-MAC and IEEE 802.15.4 protocols in achieving lower delay.