No abstract

A novel orthogonal frequency division multiplexing (OFDM) technique called DC-biased optical OFDM (DCO-OFDM) as-applied to indoor visible light communication (VLC) systems was analysed in this study. Line-of-sight (LOS) and non-LOS (NLOS) models were assumed and the luminance intensity and multipath dispersion of a single reflection were measured for indoor LOS and NLOS models; 1-dB and 3-dB DC biases were applied to DCO-OFDM with 4-, 64-, or 128-QAMs for BER analysis, respectively. The quantity of lighting equipment appropriates for communication based on the model room was determined, as well as the optimal number of sources dependent on illuminance, mean density of pedestrians, room model. The results showed that as M and DC bias values increase, SNR grows excessively (about 2.5 dB) in the LOS model. Reflection, additionally, has a severe impact on BER in NLOS conditions (nearly 10−3) regardless of M or DCdB value. Compared to the LOS model, the NLOS model requires a loss of about 12 dB of DCO-OFDM SNR.

In this paper, a novel OFDMA architecture based on the characteristics of the indoor visible light communication network is introduced. It is characterized by a microcell structure and frequent terminal switching. The OFDM proposed in this paper adopts DCO-OFDM modulation technology, which is determined by the consideration of the nonlinear and non-negative signal transmission characteristics of LEDs, and the SLM algorithm is also introduced to reduce PAPR. The simulation results demonstrate that the SLM algorithm can effectively reduce the PAPR of DCO-OFDM, which increases the probability that the signal in the entire system is lower than the PAPR threshold. Compared with the SLM algorithm, its CDF probability is increased by about 40%, and the SNR is also improved by 2.5 dB. The proposed OFDMA is a semi-distributed structure that is controlled by the DME to allocate subcarriers to each AP, and each has the ability to allocate subcarriers independently. Based on this architecture, an idea of dynamic subcarrier allocation is proposed, and uses the optical power received by the terminal as the SIR index to allocate different subcarriers to different SIR terminals and optimize the utilization of resources. The results of the modeling and simulation indicate that when the subcarrier allocation algorithm and method of reducing PAPR via SLM are combined, the BER of the system is significantly improved; when the SNR is 13 dB, the BER can be reduced to less than 10-6. This method can help the system reach the perfect communication target with a lower SNR, allowing the system to achieve better BER performance with less power consumption.