The equivalent circuit model for two commercial high power LEDs for illuminance is proposed and extensive measurements have been carried out to verify the accuracy of the model. In addition, the frequency response of two LEDs in the optical domain can be estimated using the transfer function of electrical equivalent circuit. It is shown that, the electrical parasitics in the chip and packaging introduce significant attenuation beyond a resonance frequcency. Care should be taken when designing high-speed driver and/or equalization circuits for VLC systems.
Introduction: Emerging evidence has demonstrated that circRNAs are implicated in the progression of cervical cancer (CC). However, the roles and underlying mechanisms of circRNAs remain unclear in CC. Methods: QRT-PCR was performed to detect hsa_circ_0008285 expression in CC tissues and cell lines. The roles of hsa_circ_0008285 on CC progression were explored by function assays. Next, the underlying mechanisms of hsa_circ_0008285 in CC progression were determined by bioinformatics analysis, dual-luciferase reporter and RIP assays. Results: In the present study, we identified a new circRNA hsa_circ_0008285, which was significantly up-regulated in CC tissues and cell lines. Loss-of-function assays showed that hsa_circ_0008285 suppression reduced the proliferation and invasion of CC cells in vitro and reduced tumor growth in vivo. In mechanism, bioinformatics analysis, dual-luciferase reporter and RIP assays showed that hsa_circ_0008285 served as a sponge for miR-211-5p in CC. Next, we confirmed that SOX4 served as a target gene for miR-211-5p in CC. Additionally, we revealed that miR-211-5p inhibitors abolished the effects of hsa_circ_0008285 on SOX4 expression in CC cells. Conclusion: Therefore, our research highlighted that hsa_circ_0008285 promoted CC progression via serving as a ceRNA of miR-211-5p to release SOX4, which might provide a potential therapeutic target for tumor treatment.
In this Letter, we propose a new configuration for visible light communication systems, which results in doubling of the data rate due to the use of polarization division multiplexing. As light-emitting diodes are unpolarized incoherent light sources, we isolate both the perpendicular s and parallel p modes for independent modulation. For the first time, to the best of our knowledge, we show that it is possible to transmit and successfully recover two separate orthogonal frequency division multiplexing (OFDM) signals on each polarization (pol-OFDM). Furthermore, we compare the performance of the pol-OFDM system with the transmission of a single conventional OFDM signal without a polarizer over the same physical link. We show that similar bit error rates can be achieved while obtaining ∼ 45 % improvement in both the data rate and spectral efficiency due to polarization multiplexing.
An equivalent circuit model for a typical commercial light-emitting diode (LED) used in visible light communication (VLC) applications is proposed. The parameters of the elements in the model are extracted from the measured impedance using a vector network analyser. The model shows high accuracy in fitting the measured results and shows the effect of bonding/packaging parasitics and the electrostatic discharge (ESD) component on the LED's impedance and bandwidth. This study aims to raise the designer's awareness when designing and fabricating high-speed LED/µLED devices to achieve the optimal modulation bandwidth in the emerging VLC applications.
With advances in solid-state lighting, visible light communication (VLC) has emerged as a promising technology to enhance existing light-emitting diode (LED)-based lighting infrastructure by adding data communication capabilities to the illumination functionality. The last decade has witnessed the evolution of the VLC concept through global standardisation and product launches. Deploying VLC systems typically requires replacing existing light sources with new luminaires that are equipped with data communication functionality. To save the investment, it is clearly desirable to make the most of the existing illumination systems. This paper investigates the feasibility of adding data communication functionality to the existing lighting infrastructure. We do this by designing an experimental system in an indoor environment based on an off-the-shelf LED panel typically used in office environments, with the dimensions of 60 × 60 cm2. With minor modifications, the VLC function is implemented, and all of the modules of the LED panel are fully reused. A data rate of 40 Mb/s is supported at a distance of up to 2 m while using the multi-band carrierless amplitude and phase (CAP) modulation. Two main limiting factors for achieving higher data rates are observed. The first factor is the limited bandwidth of the LED string inside the panel. The second is the flicker due to the residual ripple of the bias current that is generated by the panel’s driver. Flicker is introduced by the low-cost driver, which provides bias currents that fluctuate in the low frequency range (less than several kilohertz). This significantly reduces the transmitter’s modulation depth. Concurrently, the driver can also introduce an effect that is similar to baseline wander at the receiver if the flicker is not completely filtered out. We also proposed a solution based on digital signal processing (DSP) to mitigate the flicker issue at the receiver side and its effectiveness has been confirmed.
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