# A Comprehensive Worst Case Bounds Analysis of IEEE 802.15.7
## 6 Discussion and Future Work  
In this paper we have derived the expressions to calculate the worst case bounds of the time-critical mechanisms of IEEE 802.15.7. We also provide an in depth numerical analysis of throughput and delay bounds of the VLC network. Such analyses are paramount to accurately design such VLC networks to meet the desired delay requirements imposed by the application. In fact, as observed, high superframe orders are not guaranteed to ensure an efficient usage of the GTS mechanism, as despite the increase in available bandwidth, there is also a significant increase in delay. Such trade-off must be accounted by the network designer. Furthermore, we also explored the variance in the performance for the different PHY layers of this protocol. Despite the high data rate PHYs, supporting large throughput, if the MAC network settings are not adequate, such benefits can actually harm the efficiency of the network due to the same above-mentioned reasons. We also proposed and analyzed the impact of a CAP reduction technique to improve the scalability of these network infrastructures, without a steep increase in delay. We also observed that in cases of sporadic traffic, there must be an efficient switching of this technique to ensure proper utilization of the available bandwidth. Overall, VLC time-critical supporting features are quite interesting for many applications, but these can be further improved with additional mechanisms. Many of those techniques have already been explored for protocols such as the IEEE 802.15.4, and an evaluation study of such adaptation would be in order. First there is a need for additional flexible mechanisms that can improve the stock performance of these networks and enable a more efficient usage of guaranteed bandwidth. For instance, as shown in the analysis, unused GTS slots result in wasted bandwidth, and those have an impact on the overall delay performance of the network. Mechanisms such as ref. [33; 34] could be deployed, with minimum adaptations into these networks to enable flexible superframe order tuning. Also, possibilities of sharing GTS slots have also been explored in ref. [35] could enable a more efficient usage of this resource without imposing change in superframe size. Such proposals if coupled with the possibility of efficient routing can further decrease the latency and improve the overall reliability of the network. In its radio frequency based counterpart standards that support low-rate communication, there have been works [36; 37] that rely on efficient scheduling algorithms and routing layers (RPL) to achieve such goals. The same principles could be applied. Furthermore, although the best-effort mechanisms were not explored in the analysis carried out in this work, it is clear that traffic differentiation techniques such as ref. [38] should be explored for improved performance and support of different traffic performance levels. Figure 13: Adverse delay impact of CAP reduction. Finally, the IEEE 802.15.7 standard does not provide any specific security mechanism. In safety oriented applications like vehicular communication and body sensor networks, a strong security infrastructure is mandatory to assure the veracity of the data. However, from some research works based on security [39] on low-rate wireless sensor networks it is evident that the network suffers in terms of latency when there is an overhead due to stronger security. Hence, there is a need for low weight security mechanisms that will not greatly diminish the Quality-of-Service of the overall network. Many of these techniques have been successfully evaluated in low-rate communications standards such as the IEEE 802.15.4, which as observed, closely resembles the structure of 802.15.7 [40]. Such advantage should be further explored by migrating, with the necessary adaptations, such mechanisms into this VLC counterpart to maximize the already powerful potential of visible light communications, particularly in critical applications.