Resource Allocation in LiFi OFDMA Systems

Light Fidelity (LiFi) is a recently proposed technology that combines illumination and high speed wireless communication using light emitting diodes (LEDs). Unlike radio frequency (RF) channels, LiFi channels do not exhibit fading characteristics as the detector size is much larger than the wavelength. Another distinguishing feature is that LiFi channels are mainly affected by the low-pass filtering effect caused by LEDs, while the multipath effect is inconspicuous. Therefore, unlike in RF systems, LiFi systems can hardly achieve the conventional multi-user diversity gain when using orthogonal frequency division multiplexing access (OFDMA). Due to the LED characteristics, users with high direct current (DC) signal-to-noise ratio (SNR) may be able to use a large modulation bandwidth in LiFi systems. This means that users with good channel conditions can be more likely to utilise high-frequency resources. In this paper, resource allocation (RA) in OFDMAbased LiFi systems is investigated and an optimal RA scheme and a low- complexity RA scheme are proposed. Simulation results show that by efficiently using high- frequency bandwidth resources, the RA schemes in OFDMA systems outperform those in TDMA systems in terms of both data rate and user fairness. Also, the low-complexity RA scheme is able to achieve nearoptimal performance at a reduction of 90% in computational complexity.