Studies of Flatness of LiFi Channel for IEEE 802.11bb

A task group named IEEE 802.11 Light Communications Amendment-Task Group “bb” (TGbb) was established in July 2018. By bringing light-fidelity (LiFi) technology into the WiFi ecosystem, LiFi can take advantage of the globally recognized WiFi brand, while also improving its capability due to the fact that LiFi does not interfere with WiFi. Early discussions in the task group focused on the physical (PHY) layer. There are two major proposals for the PHY layer. The first one is to use the existing IEEE 802.11 chipsets with LiFi analog front-ends. This is done by means of the frequency up and down-conversions and adding a DC bias. The second proposal is to redefine a whole PHY layer and optimize it by means of adopting adaptive bit loading in order to combat the low-pass filter characteristics of the non-line-of-sight wireless optical channels. Each approach has advantages in terms of the low-entry barrier to the mass market and better performance, respectively. The root question in determining the common mode PHY between the two approaches is how frequent LiFi encounters flat channels. That is, if the channel is flat, then the gain of the adaptive bit loading is not significant. Therefore, this paper aims to investigate the flatness of many samples from the reference channel models defined in the TGbb. We find that the majority of the channels are flat if the signal bandwidth is 20 MHz.