# Virtual Sensing Directional Hub MAC (VSDH-MAC) Protocol with Power Control
## 2 Medium Access Control Protocol
#### VSDH-MAC Channel Access Algorithm
At higher offered load values, the value of the Jain's fairness index decreases, as more nodes try to gain access at a given time and some nodes are forced into back-off. Since the CSMA/CA protocol is a random access scheme with back-off, it suffers from low fairness performance due to the back-off mechanism. When a sensor node fails to acquire the channel, it will double its back-off window. Under heavy loads, the fairness performance is poor as once a sensor node is able to transmit a packet it will have much better probability of getting access to the channel again than other sensor nodes who might have back-off waiting periods. On the other hand, since the VSDH-MAC performs selective back-off using the CTS SINR threshold, it reduces the number of nodes entering back-off. Figure 12 shows the relationship between throughput and number of nodes within the network. As the number of nodes in the network increases, the collisions of RTS at the hub increase, sending more nodes into NAV (back-off) hence reducing the throughput. However, as the number of nodes approach a certain threshold, the network throughput levels off to a near constant value. Figure 3:0 [PERSON]’s fairness index improvements with the power control mechanism applied compared to VSDH-MAC with no power control and the modified directional CSMA/CA in a network with 50 nodes. ## 5 Conclusions

In this paper, it is shown that the proposed VSDH-MAC and DIFS-VSDH-MAC protocols offer excellent performance in dealing with the trade-off between throughput and node energy consumption. The use of virtual carrier sensing provides the lowest energy consumption, but with a small increase in energy consumption the inclusion of actual carrier sensing provides almost twice the throughput. The major advantage of the VSDH-MAC and DIFS-VSDH-MAC protocols is that they exploit the potential of directional antennas and spatial reuse in achieving high overall network throughput, energy efficiency and improved fairness. It is also worth noting that contention-based protocol tends to have low latency compared to contention-free protocol under low traffic load. Simulation results have shown that the VSDH-MAC protocol is able to provide better throughput and energy efficiency performance than other directional IEEE 802.11 DCF protocols. It should also be noted that we have found the use of real, rather than ideal antenna patterns can make a substantial difference in the network performance, with ideal antennas, the throughput appears to be larger than possible with real antennas, due to the capacity reduction brought about by beam overlap. Further work is required to consider the performance of the VSDH-MAC and DIFS-VSDH-MAC protocol for mobile WSN scenarios. In addition, three-dimensional (3D) scenarios and the effects of non-line of sight transmission should be considered. Conceptualization, A.C., J.D., P.M. and T.H.L. ; data curation, A.C.; formal analysis, A.C., J.D. and P.M.; methodology, A.C., J.D., P.M. and T.H.L. ; software, A.C. and P.M.; validation, A.C.; writing--original draft, A.C., J.D. and P.M.; writing--review and editing, A.C., J.D., P.M. and T.H.L. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The work of [PERSON] was supported by The 2017-2020 National Measurement System Programme of the UK government's Department for Business, Energy and Industrial Strategy (BEIS), under Science Theme Reference EMT20 of that Programme. The authors declare no conflict of interest. ## References

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Figure 3:1 Impact of number of nodes on maximum throughput. * _[PERSON] et al. (2014)_ [PERSON]; [PERSON]; [PERSON] Survey on the Characterization and Classification of Wireless Sensor Network Applications. _IEEE Commun. Surv. Tutor._**2014**, _16_, 1860-1890. [CrossRef]
* _[PERSON] et al.