## 3 System Model
### Intra-Cluster Communication Session
Figure 16: Throughput _vs._ arrival rate, SNR threshold 9 dB. Figure 18 illustrates the system energy performance against the varying node densities in the network. The proposed system model performance is compared with a DDRS cooperative MAC [30]. DDRS is a reactive cooperative MAC protocol employing cooperative transmission in the event that Direct Transmission Mode has failed. EEMACCSN and DDRS are both cooperative MACs, with EEMACCSN having a better energy performance. The results in Figure 18 further demonstrate that a good MAC protocol design has great influences on the total energy consumption of the networks. Figure 10:0 EEMACCSN node state behaviour _vs._ arrival rate. Figure 10:1 Energy performance _vs._ number of nodes (N). ## 6 Conclusions

This work proposes a dynamic MAC framework for cluster-based wireless sensor networks. The proposed model features an adaptive cross-layer scheduling for the node activity. The sensor nodes transceiver module in the proposed model transitions between three states--sleep, active and back off--depending on the schedule. It also features a cooperative communication between clusters and the base station. The cooperation of nodes is decided based on the received SNR--if it is below the threshold, the nodes cooperate to enhance the reliability of the network. An analytical model for the proposed framework was developed and its performance evaluated based on the results. The results indeed show the improved performance on the energy consumption, channel capacity, throughput and delay on wireless sensor by using the proposed framework. The energy performance has a direct positive impact on the lifetime of the wireless sensor network as indicated by the results and this improvement of the network lifetime overcomes the main design challenge of this network type. The accuracy of our model is concluded from the consistency observed from the analytical and simulation results. ## Acknowledgments

This work was sponsored by the Centre of Excellence (CRART) research unit of the Discipline of Electrical, Electronic and Computer Engineering, University of KwaZulu-Natal, Durban, South Africa. ## Author Contributions

For the preparation of this manuscript, [PERSON] designed and conducted the simulations of the protocol. [PERSON] and [PERSON] analyzed the data, results and verified the theory. The manuscript write up was a combined effort from the three Authors. ## Conflicts of Interest

The authors declare no conflict of interest. ## References

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