This manuscript is accepted for publication at Computer Communications. The final version of this manuscript can be accessed at: https://doi.org/10.1016/j.comcom.2024.06.017. Light fidelity (LiFi) is an emerging wireless networking technology of visible light communication (VLC) paradigm for multiuser communication. This technology enables high data rates due to the availability of large visible light spectrum. While current studies have shown the potential for LiFi technology, they borrow the MAC layer protocols from traditional WiFi. However, a number of prior studies have shown the challenges faced by the MAC layer of WiFi in the presence of large number and types of devices. In this work, we show that hybrid coordination function controlled access (HCCA) MAC protocol in LiFi provides higher throughput than the traditional  carrier sense multiple access with collision avoidance (CSMA/CA) mechanism to user devices. We also show that HCCA has the limitation of higher message overhead in the presence of large number of devices. We utilize both theoretical analysis and extensive simulations to study these performance tradeoffs and identify a threshold when a LiFi access point should switch to HCCA from CSMA/CA and vice-versa. Finally, based on our findings, we design a hybrid MAC mechanism that switches between HCCA and CSMA/CA based on the number and type of devices present. Our evaluation shows that this hybrid mechanism can outperform both HCCA and CSMA/CA individually in the presence of different number of devices.

In the realm of forthcoming wireless communication systems, various technologies have emerged, with intelligent reflective surfaces (IRSs) standing out as a promising contender for enhancing spectral and energy efficiency. The effectiveness of such systems is significantly impaired by the nonlinear characteristics inherent in their components. This work examines the collective impact of nonlinearity stemming from memory effects in high power amplifiers (HPAs) and phase noise from theIRS on an orthogonal frequency division multiplexing (OFDM)system. Specifically, the performance is evaluated by deriving mathematical expressions for determining the outage probability(OP), spectral efficiency (SE), and energy efficiency (EE) in an OFDM communication system augmented by an IRS, while considering the effects of non-ideal HPA and phase noise in the IRS. We validate our analytical results through comparison with simulations, confirming the accuracy of our approach. Our findings highlight the significant impact of HPA nonlinearity and IRS phase noise on the performance of the above communication system.

The recent advancements in visible light communication (VLC) will pave the path for high precision, cost-effective, power-efficient, and secure indoor communication networks. The characteristics of VLC make them a potential candidate for the 6th generation of cellular standards, specifically for applications related to short distance and high throughput communication scenarios. However, indoor VLC faces some challenges such as line-of-sight (LoS) link blockages due to obstacles, and uneven power distribution due to unguided non-Line of Sight (NLoS) reflections from the wall which limits its large scale deployment in dense scenarios. In this paper, we have proposed an intelligent reflecting surface (IRS)-aided indoor VLC system with an optimal irradiance angle guided toward the user subject, which can facilitate optimal orientation of the IRS element in order to maximize the received power at the user. Further, we also derive the closed-form expression for the obtained optimal irradiance angle, essentially a cosine of the angle of irradiance for an element of IRS based on the location of IRS and the receiver’s (users) position. In the designing of the irradiance angle, we considered all 4 vertical walls of the room for placing the IRS. In addition, for a given receiver, we have proposed an algorithm to find the optimal orientation of an element of IRS that will produce the maximum power at the receiver. The proposed algorithm returns the rotation angles which will result in the optimal orientation of the element with the time complexity of O(1).

Vehicle-to-Everything (V2X) using Visible Light Communication (VLC) channels can be seen as an economically viable option to replace the existing modes of vehicular communications in the near future. In this paper, we have analyzed the performance of VLC based V2X communication under various environmental deterrents viz. Light Fog, Dense Fog, Light Smoke and Dense Smoke using a proof-of-concept testbed. A series of experiments were conducted to investigate the effects of environmental deterrents over VLC based Line-of-Sight as well as non-Line of Sight V2X transmission with respect to distance and angular variations. On-Off-keying (OOK) modulation has been selected as the modulation scheme, as defined in VLC standard (IEEE 802.15.7) for the transmission of information bits between a transmitter LED and a photo-diode receiver. The experimental results show the feasibility of VLC-based V2X systems with reliable data transmission under different environmental deterrents with a fairly good signal-to-noise ratio (SNR), even under dense-fog and smoke conditions where the attenuation in average optical power at the receiver, is quite high.