# MAC/PHY Comprehensive Visible Light Communication Networks Simulation
## 2 Related Work  
In this section, the current state-of-the-art solutions on VLC network simulation are analyzed. This work is primarily focused on the IEEE 802.15.7 standard, since it is the most studied reference in the literature. Nonetheless, as mentioned in Section 1, ITU G.9991 standard on high-speed VLC transceivers is already published and there are other undergoing standards such as IEEE 802.15.13 [13]and IEEE 802.11 bb [14]. However, these last two standards are not VLC-specific, but broader in terms of working wavelength. It has been observed that papers addressing VLC MAC-layer simulation or system-level simulation are scarce in the literature. These simulations enable a deep comprehension of the network performance, allowing the detection of issues prior to the system's physical implementation. Furthermore, network performance simulation can also be used to optimize MAC-layer configuration or even rapid prototyping novel protocols. In this analysis, the contributions to the aforementioned topic have been categorized depending on their consideration of the impact of physical phenomena. Some works address network simulation only from a MAC-layer viewpoint, whilst others include some physical layer parameters such as the Signal-to-Noise Ratio (SNR) on their schemes. However, no scheme combining physical and MAC simulation was found. [PERSON] et al. analyzed the performance of the IEEE 802.15.7 CSMA/CA mechanism under saturated traffic conditions using Markov chains [15]. The authors focused primarily on obtaining a modeling tool rather than simulating actual VLC networks, since no real-world metrics taking into account the standard presented. Moreover, the model's accuracy is limited to small network sizes and a significant convergence between the model and simulation is obtained above 12 users, which may be unlikely to occur in reality due to the reduced coverage area of VLC access points [16]. Some months later, [PERSON], [PERSON], and [PERSON] carried out a similar work but for unsaturated traffic in Ref. [17]. The work was based on the same model, but some approximations made for saturated traffic were accommodated for the new conditions. IEEE 802.15.7 standard considers only half-duplex transmission since communications are controlled by the central node using a superframe structure, as it will be described in Section 3. [PERSON] et al. simulated a contention-based full-duplex communication mode, in which the access point (or central node) can also initiate data transmissions in the downlink [18]. The authors showed that the standard may benefit from this type of access in star topologies, significantly increasing the downlink throughput. Nonetheless, as it happened with [PERSON] et al., the physical layer was not considered, and their results must be carefully considered. In addition, a relevant number of authors have proposed the use of different working wavelengths for downlink and uplink [19; 20]. Therefore, downlink could be carried out using the broadcast mode of the standard, whilst the uplink could still use the mechanisms used for star topology. In Ref. [21], the impact of the hidden node problem during channel contention was studied. Due to the directivity of VLC endpoints, the emitter was not able to detect surrounding nodes outside of its Field Of View (FOV). This situation leads to a misuse of the channel, producing collisions. This work presented a comparative study of the metrics between a network in which there are no hidden nodes and a network in which nodes are unable to properly sense the channel. Nevertheless, the work did not consider the NLOS contribution caused by multipath propagation in the scenario, which may allow channel occupation detection in real scenarios. Unlike the previous works, [PERSON] and [PERSON] included some physical parameters into an extended version of [PERSON]'s Markov chain model, resulting in a 3D graph structure [11].