## 4 Performance Evaluation, Analysis and Discussion
Only one acknowledgement is sent for an A-MPDU which consists of maximum six MPDUs. In the case of high BER, there is probability of packet loss and then retransmission of the whole A-MPDU. However, the use of block acknowledgement make a receiving node capable to only sends a collective acknowledgement against those MPDUs which are received correctly. The sending node only retransmits the lost MPDUs which plays it role to reduce the average delay values. It is noted that performance optimization is achieved in terms of received packets and average delay by using different levels of frame aggregation for slotted CSMA/CA in CAP mode. In the  
Figure 12: Energy consumption analysis of aggregation with received packets. Figure 13: Energy consumption analysis of aggregation with delay. proposed patient monitoring system, we have two type traffic patterns: the first one is the high-periodic traffic where a huge number of small packets generate and other is low-periodic traffic which generates data with medium or low rate. To fulfil the requirements, we check the performance of the hybrid mode which means the nodes with high-periodic traffic characteristic are assigned the GTS slots, whereas the low-periodic traffic nodes use CAP. For the proposed patient monitoring system, ECG and EEG nodes are requested for three GTS slot for each. A coordinator can assign maximum seven GTS slots out of total 16 superframe slots. Figure 14 provides a comparative analysis of received packets between GTSon (where a few nodes request GTS slots) and GTSoff (all nodes use CAP). The different DC options are used to evaluate the performance of these modes. From Figure 14, a significant improvement in GTSon mode is observed for the number of received packets from 6000 to 10,500 for the DC option 2, 4. The reason is that the high-periodic traffic nodes get a guaranteed time slots in every superframe duration, so there are less chances of data loss due to contention and collision. Figure 14 shows that the hybrid scheme involving CFP and CAP is more suitable for the patient monitoring system with high-periodic and low-periodic traffic patterns. Figure 14 proves that a hybrid (combination of CFP and CAP mode) sort of MAC mechanism fulfils the requirement of the proposed patient monitoring system. Therefore, to further improve the performance in terms of received packets we apply the proposed aggregation mechanism to check the full capacity of aggregation mechanism with GTSon mode. Figure 15 presents a comparative analysis of the received packets with non-aggregated GTSon mode and for aggregate-mode with different levels. A significant improvement can be seen with the frame aggregation levels. The frame aggregation mechanism significantly increases the number of received packets by reducing the delay. For example, with DC option 2, 4 if we use the 3 rd level aggregation, then the maximum capacity goes from 10,000 to 24,000. It is concluded from the results of Figure 15 that for patient monitoring systems which use multiple sensors having different requirement works well with the hybrid channel access mode (GTSon). Moreover, with the help of frame aggregation mechanism, their performance can be further optimized to fulfil the requirements of patient monitoring systems which require time bounded services, reliable communication and efficient energy consumption. Figure 14: GTSon vs. GTSoff comparison. Figure 16 presents the energy consumption analysis for the scenario mentioned in Figure 15. Overall, the GTSon mode provides slightly better energy consumption with the bounded delay. The reason is that the nodes contend for fewer slots in the GTSon mode as compared to the GTSoff mode. Figures 17-19 provide an analysis of received packets for an individual node, that the number of packets received by the coordinator from an individual node. Figure 17 provides a comparative analysis of received packets with GTSon and GTSoff mode. In GTSon mode we assigned 3 GTS slots to ECG sensor and 3 GTS slot to EEG, the remaining seven nodes use slotted CSMA/CA in CAP mode.