Hybrid CSMA/CA and HCCA uplink medium access control protocol for VLC based heterogeneous users

Abstract

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 the hybrid-coordination-function-controlled-access (HCCA) MAC protocol in LiFi provides higher throughput than the traditional CSMA/CA mechanism to user devices. We also show that HCCA has the limitation of higher message overhead in the presence of a large number of devices. We also evaluate the collision probability, busy channel probability, and delay for HCCA and CSMA/CA MAC protocol. 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.