The bit error rate performance of non-line-of-sight ultraviolet communication through atmospheric turbulence is studied. The communication performance degradation under different strengths of turbulence is evaluated. Particularly, under strong turbulence conditions, the communication distance can be shortened by 30%, or at a given distance the communication rate can be reduced by half than the counterpart of no turbulence.
In visible light communication, orthogonal frequency division multiplexing （OFDM） is an effective approach to improve the system speed. However, the nonlinearity of the light-emitting diode （LED） suppresses the trans- mission performance. The low-frequency part of the transmitted signal from LED suffers more from nonlinearity. Therefore, a pre-equalization scheme which suppresses the low frequency part of the OFDM signal and enhances the high frequency part can decrease the impact of LED nonlinearity. The experimental results show that the bit-error rate performance is largely enhanced by the pre-compensation.
For nonline-of-sight ultraviolet communication links, a simple and concise parametric expression （PE） of channel path loss is valuable for link performance analysis in typical scenarios. It is observed that the light energy in the scattering volume can be approximated using a line integral. Combining curve fitting for the scattering phase function and the mean value theorem of integrals, we propose a simple but highly accurate PE. It matches well with the Monte Carlo simulations for typical LED-based communication with small beam divergence （〈45°）; when the beam divergence is smaller than 10°, their differences are less than 1 dB in most geometrical conditions. The proposed PE also shows good consistency with our outdoor experimental measurements, and the reported experimental results in the literature.
In this letter, we present a scheme generating OFDM signals in optical domain instead of electrical domain by transmitting subcarrier signals with multiple LEDs. According to the simulation, this scheme can effectively eliminate signal degradation caused by the high peak-to-average power ratio of OFDM signals in traditional transmitter. Computational complexity in digital part of the transmitter can be reduced by using look-uo table. Receiver will stay unchanged.
An endless polarization stabilization control system is proposed in this letter. The system is independent of transmission data rate and modulation format, and it does not need high-speed circuit to track fast polarization change. Adaptive inertia weight particle swarm optimization algorithm is used and the effectiveness of polarization stabilization control is experimentally verified.
We demonstrate a visible light communication system based on DC-biased optical orthogonal frequency-division multiplexing（DCO-OFDM） and achieve a bit rate of 481 Mb/s at a communication distance of 65 cm by employing single 1 W commercial phosphorescent light-emitting diode（LED）. The average bit error rate of the received data is 2.3×10-3, which is below the forward error correction limit, 3.8×10-3. The effect of signal clipping in DCO-OFDM system is studied and resource allocation algorithms are utilized. At least 13% capacity improvement can be obtained by suitable signal clipping and resource allocation.
