# A Comprehensive Worst Case Bounds Analysis of IEEE 802.15.7
## 1 Introduction  
Recent developments in information and communications technology originated an urgent requirement to develop a fifth and sixth generation of networks with an unprecedented system-level spectral efficiency, which can offer higher data rates, massive device connectivity, at ultra-low latency, everything with improved energy efficiency and robust security. With the increasing amount of connected devices, enabled by the IoT paradigm, generating unprecedented amounts of traffic, wireless devices are fighting for a portion of an already crowded radio-frequency (RF) or wireless-fidelity (WiFi) spectrum. This demand has been motivating researchers to explore alternatives in the electromagnetic spectrum, new techniques, and new network architectures to address them, while still being able to meet stringent Quality-of-Service requirements. In this line, Visible Light Communication (VLC) has been introduced as a promising solution for 5G and beyond. Its reliance upon the Light Emitting Diode (LED) technology outperforms other lighting sources with increased performance and efficiency, at a fraction of the cost and weight, while its usage of an untapped and free portion of the electromagnetic spectrum (visible light range) holds the promise of achieving much higher bandwidth utilization for wireless data transmission, in some cases up to 3 Gbps [1], while co-existing with RF communications. However, VLC has several advantages over the traditional wireless technologies that go beyond spectral efficiency or resilience to RF interference. VLC can operate within a confined space making it more secure than the radio waves that easily penetrate through walls, making them prone to security risks. Notably, the IEEE 802.15.7 standard opens up the possibility of adoption of standardized VLC communication into a plethora of application domains such as indoor localization, gesture recognition and vehicular networking. It supports high data rate visible light communication (up to 96 Mbps) with almost 300 THz of available bandwidth [2]. However, not all applications present the same kind of requirements, particularly in what concerns timeliness. For supporting such time critical applications, the MAC layer of IEEE 802.15.7 adopts a periodically synchronized superframe structure, which can provide guaranteed bandwidth via its Guaranteed Time Slot (GTS) mechanism. However, to effectively harness the potential of such time-critical communication mechanisms, it is vital to carry out an accurate planning of these network infrastructures, particularly in terms of timeliness and throughput. To accomplish this, it is fundamental to model the performance limits of such networks, in order to understand their behavior under worst-case conditions. The contributions in this paper are threefold:  
* First, we provide a comprehensive overview on the technical aspects of the IEEE 802.15.7 and a functional overview of its MAC sub-layer. * Second, we provide a detailed formal modeling of the protocol using network calculus, enabling the computation of the worst case bounds for GTS utilization in a star topology. * Third, we complement our network modeling with a detailed numerical analysis in which we investigate the performance limits under different network configurations. * Fourth, we briefly analyze the impact of a technique to improve the scalability of the network. In the following section, we provide a set of related works that will serve as a baseline for our work. We then provide a brief technical overview the operational layers of IEEE 802.15.7, which is followed by an in-depth functional overview of the MAC sub-layer. Then in Section 4, we derive a formal model to determine the worst case bounds of an IEEE 802.15.7 VLC star topology, using network calculus. In Section 5, we provide a numerical analysis to complement our network model, we analyze the impact of several network parameters upon the performance limits of such network. We finally conclude the paper by summarizing some lessons learned and proposing future research pathways.