Using G.vlc in MIMO LiFi, the experience with Phoneline and PLC profiles

While radio-frequency (RF) communication dominates internet access today, it is not a good solution for environments where connection stability, low latency, and high security are strong requirements. For these scenarios, Light Fidelity (LiFi), a technology which uses electromagnetic waves in the visible or infra-red range of light, has been seen as a great alternative for free-space transmission. The growth of LiFi is also motivated by the need for a complementary solution to the crowded RF spectrum. Since light is confined by boundary walls, the entire spectrum used inside one room can be reused in neighbouring rooms. Consequently, LiFi is able to provide increased user density (bit/s/m2) with high security and a guaranteed level of quality-of-service (QoS), critical features required by, among others, internet of things (IoT) and in industry 4.0 applications.
Despite its advantages, the use of narrow light beams for communication has a weakness. In LiFi, since the non-line-of-sight (NLOS) channel is much weaker than the line-of- sight (LOS) channel, if the LOS link is blocked, a system which uses only one transmitter and one receiver has a high probability to fail. A solution for this problem, that is widely used by the lighting industry, is to provide uniform shadow-free illumination, which consists of the transmission of multiple signals through multiple light sources distributed over the ceiling of a room. The use of multiple transmitters and multiple receivers, widely employed in RF systems, is known as multiple-input multiple-output (MIMO) transmission schemes. MIMO is key in LiFi systems to improve robustness and increase data throughput.
The ITU G.9991, also known as G.vlc, specifies a system architecture, physical layer (PHY) and data link layer (DLL) for high-speed visible and infrared light communication. The G.vlc standard is a derivative of the G.hn (G.9960) standard, which provides a high-speed backbone for both LiFi and WiFi applications. G.vlc defines important features for dealing with the bandlimited and low-pass response of light sources commonly used in LiFi systems such as light-emitting diodes (LED). These features include orthogonal frequency-division multiplexing (OFDM), adaptative bit-loading, MIMO, M-ary quadrature amplitude modulation (QAM) and others. To accelerate LiFi adoption, a range of solutions entered the market using available G.hn chipsets. These chipsets are designed for home networking with data rates up to 1.7 Gbps operating over powerline, coax, twisted pair and plastic optical fibre. Nowadays, these chipsets are employed in LiFi systems, but the question regarding whether they are mature enough to solve LiFi challenges is still open.
In this context, the project “Enhance Lighting for the Internet of Things” (ELIoT) has been working on innovations to enhance the ITU G.9991 LiFi standard. In ELIoT, the use of LiFi systems in different link conditions is tested experimentally. The obtained results have allowed the project to gather valuable information that now needs to be reinjected into the chipset community. To build the experimental setups, project partners have focused on G.9991 compliant chipsets, since G.9991 is one of the first standards that have been approved in the light-based communication field and that provides the advantage to have several chipsets already available in the market.
This work provides an overview of the experimental results of using G.vlc in MIMO LiFi from both Eindhoven University of Technology (TU/e) and Signify Research labs. The technical findings highlight that, for a better LiFi experience, features such as faster channel estimation, profile selection, MIMO channel adaptation and MIMO change of mode, still have to be included in the next generation of components and standard recommendations. The discussion also opens the door for new research topics that have been identified as interesting paths for future projects beyond ELIOT timeframe.