Single-collision-induced path loss model of reflection-assisted non-line-of-sight ultraviolet communications

Theoretical and experimental studies on channel impulse response of short-range non-line-of-sight ultraviolet communications

A theoretical channel impulse response (CIR) model of short-range non-line-of-sight (NLOS) ultraviolet communications (UVC) in noncoplanar geometry under the single-scatter condition is proposed. Simulation results obtained from the widely accepted Monte-Carlo (MC)-based channel model of NLOS UVC are provided to verify corresponding theoretical results obtained from the proposed theoretical single-scatter CIR model. Additionally, an outdoor experiment with a light-emitting diode (LED) as the light source is first designed to measure the channel step response of NLOS UVC and to further validate the proposed theoretical single-scatter CIR model. By varying the different parameters of the transmitter and the receiver, such as the baseline range, the inclination angle, the azimuth angle, the beam divergence angle, and the field-of-view angle, the results of the proposed theoretical single-scatter CIR model and the MC-based channel model are exhibited and further analyzed in detail. Results indicate that the computational time cost by the proposed theoretical single-scatter CIR model is decreased to less than 0.6% of the MC-based one with comparable accuracy in assessing the temporal characteristics of NLOS UVC channels. Additionally, theoretical results obtained from the proposed theoretical single-scatter CIR model manifest satisfactory agreement with corresponding experimental measurements.

Ultraviolet communication with a large scattering angle via artificial agglomerate fog

Considering strong signal attenuation of the large-angle non-line-of-sight (NLOS) link achieved due to the ultraviolet (UV) scattering properties, we propose to increase the UV communication link gain under a large scattering angle via generating agglomerate fog within a certain range as a secondary light source. In this study, a channel model with locally strong scatterers from agglomerate fog is proposed based on Monte Carlo ray-tracing approaches. Mie theory is adopted to calculate the atmospheric channel parameters, to further evaluate the link gain of a channel under non-uniform atmosphere. The performance of scattering system in the presence of fog conditions depends on the relative positions of the light source to the fog and to the receiver. The link gain results reveal the transmission capabilities for different scattering channel geometries, and give the optimal spray point location within a 10 m communication range. We further establish a foggy NLOS system using an agglomerate fog generator to verify our research in the real environment. The results show that the received signal strength of the NLOS link can be effectively enhanced by constructing scatterers in the atmospheric channel, which significantly decreases the bit-error rate (BER).

266 nm ultraviolet communication under unknown interference using UVC micro-LED

Ultraviolet C (UVC) micro light-emitting diode (LED) can achieve symbol communication rate up to 100Msps at distance 40 meters without transmitter-side lens to guarantee certain communication mobility. We consider what we believe to be a new scenario where high speed UV communciation is realized under unknown low-rate interference. The signal amplitude properties are characterized, and the interference intensity is categorized into three cases, namely weak, medium and high interference intensity. The achievable transmission rates for the three cases are derived, where the achievable transmission rate for medium interference intensity can approach those in weak interference intensity and strong interference intensity cases. We provide Gaussian approximation and related log-likelihood ratio (LLR) calculation, which are fed into the subsequent message-passing decoder. In the experiment, the data is transmitted with symbol rate 20 Msps under unknown interference with symbol rate 1 Msps, received by one photomultiplier tube (PMT). Experimental results show that the proposed interference symbol estimation approach shows negligibly higher bit error rate (BER) compared with those with perfect knowledge on the interference symbols.