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This work addresses the power penalty in a Visible Light Communication (VLC) emitter that re-uses illumination Light Emitting Diodes (LEDs) for high-speed communications. We quantify the effect of modulation depth for two widely explored modulation schemes in VLC, namely Orthogonal Frequency Division Multiplexing (OFDM) and Pulse Amplitude Modulation (PAM). Extra power is dissipated in the LED and in the modulator due to such modulation. Two popular highspeed VLC transmitter topologies, namely a Bias Tee (Bias-T) and a Serial FET (Serial-F), are compared in terms of efficiency, Extra Energy Per Symbol/Bit (EEPS/B) and complexity. This work presents a theoretical model and compares it to simulationresults. We show that PAM outperforms OFDM in terms of better Bit Error Rate (BER), larger dynamic range for modulation depth, less extra power loss, thus higher power efficiency for communication over an Additive White Gaussian Noise (AWGN) channel.

This article presents a modulator for optical wireless communication (OWC) via LEDs, controlled by a dual closed loop. While the potential communication speed and performance of OWC have received a lot of research attention, the design of appropriate modulator circuits has not been studied so widely. This article addresses the control aspects to minimize power losses and to ensure automatic adaptation to component spreads or aging, for “high-power” LED emitters. We initially address a “low-bandwidth– system, particularly suited for indoor camera-based detection, and then a “higher bandwidth” one for Li-Fi data communication. In contrast to maximizing data throughput as it applies to high-speed modulators, low-speed modulators aim at high power and high efficiency in general lighting applications. Specifically, for the high-power modulator, we propose a control strategy that allows a wide range of combinations of LED types and LED power supplies. The power consumption of the modulator is minimized by voltage margin setting that is automatically adapt to the modulation and the LED type using the nonlinear detector. The common industry practice is to use constant-current LED drivers for powering LEDs. After creating a theoretical framework of some generality to evaluate designs and control loops with rationals and verified models, we realize modulator designs that are supplied by constant current LED drivers and verify their performance by simulation and measurements.

This paper addresses the nonlinear memory effects in the response of typical illumination light emitting diodes (LEDs), in order to enhance the performance of visible light communication (VLC) systems. These LEDs have a limited bandwidth of only several MHz. To reflect the physical mechanisms in the quantum well, we describe the LED transient response by a nonlinear dynamic differential equation. Three different mechanisms of the nonlinearity are relevant in the double hetero-structure LEDs, which result in dynamic nonlinearities, that is, a mixture of nonlinearities and memory effects. Hitherto, generic pre-distorter and non-linear equalizers have been studied for the LEDs. Yet this paper shows that recombination rates of photon generation can be translated into an equivalent discrete-time circuit that can be inverted. This allows us to develop a new pre-distorter with a simpler and more efficient structure than previously studied and overly generic approaches. The novel pre-distorter along with a parameter estimation can effectively overcome LED nonlinearity for high-speed VLC with amplitude-based single carrier modulations, including ON-OFF keying and pulse amplitude modulation-4 systems, and with the multi-carrier orthogonal frequency-division multiplexing. We report experimentally obtained eye-diagrams, first to justify our choice for the LED model on which our nonlinear pre-distorter have been based, and second to verify the effectiveness in enhancing the VLC link performance to the extent predicted by our model.

This paper addresses dynamic nonlinear effects in the response of typical illumination Light Emitting Diodes (LEDs) to increase the reliability and data rate in Visible Light Communication (VLC) systems. These power LEDs have a limited bandwidth of only several MHz. To conceive a practical receiver, we describe the LED transient response by a nonlinear dynamic differential equation from the physical mechanisms in the Quantum Well (QW) of Double Hetero-structured (DH) LEDs. It includes the transient nonlinear relation between the input current and injection electron concentration, as governed by the dynamic rate equation. Also, we consider the static nonlinear (typically quadratic) relation between the injection electron concentration and output optical power is described by a square operator. Further we consider the static nonlinear relation between the injection current and output optical power, caused by the efficiency droop. We propose a novel post-distorter to overcome LED nonlinearities for high-speed Pulse Amplitude Modulation (PAM)-4 systems. Its performance is validated with measurements of a commercial blue LED.

Power loss is an important design factor for Visible Light Communication (VLC). Dissipating only a few percent of the illumination power can still result into a few watts of heat generation which requires additional provisions for cooling the modulator circuit. We show that a transistor in series with LED can be used in linear operation to apply amplitude modulation which only marginally sacrifices efficiency. Yet, this requires a novel active control loop. We report its performance and frequency response for VLC modulation. We show that the modulator also effectively cancels mains ripple. Based on our experimental experience, we also propose a model to quantify the power losses and verify these for pulse amplitude modulation.

This paper presents a number of novel methods to measure the junction temperature and to estimate the health of gallium nitride light-emitting diodes (LEDs). The methods are based on measurements of the dynamic impedance and optical output. Our experimental analysis reveals temperature sensitive parameters of the electrical and optical responses. Moreover, a correlation between the non-radiative current characterizing the active region defects and the small-signal impedance is shown. The demonstrated methods can be applied to enhance existing temperature-monitoring techniques. The derived dependencies also build a foundation for advanced in-field health monitoring of the LEDs using the infrastructure of visible light communication systems. Such methods and techniques are valuable for predictive maintenance of solid state lighting systems.

The visible light communication (VLC) can provide data transmission via the illumination light emitting diodes (LED). This paper introduces a new model to analyze the bit error rate (BER) of binary phase modulation in VLC for an arbitrary modulation depth and data duty cycle while taking into account both the Gaussian and signal-dependent shot noise. The impact of the driver design on the BER and its impact on ripple have not been considered in detail before. We compare two different LED driver schemes, namely directly adapting the driver control loop and binary shunting. We address data rate, BER, and power efficiency, for which we propose to use the extra energy per symbol above unmodulated light. We further introduce an analysis of the effect that (truncated) ripple interference has in the (matched or other) filter of the receiver. Ripple causes a harmful interference in VLC, and thus a BER expression is derived to include its effect. Two approximations are proposed to model the ripple interference, and their accuracies are compared by simulations. A low-pass filtering is proposed to alleviate the impact of ripple interference in VLC system.

This paper analyses the communication performance for visible light communication (VLC) with Manchester encoded amplitude modulation. In particular, it considers the ripple generated by the LED driver as an important noise contribution for VLC. The ripple depends on the oscillation frequency of the converter which typically is chosen to satisfy other performance criteria such as power conversion efficiency. This paper models the ripple as an additional noise if a buck converter LED driver is adapted for VLC. We argue that ripple can as a worst case be modeled as a random binary offset in the bit detection that randomly affects the distance between the data signal and the decision threshold. We derive expressions for the BER, propose approximations and we compare these with a simulation.

This paper presents a new analysis of the illumination and communication performance for visible light communication (VLC) with variable pulse position modulation (VPPM). In particular, it addresses the extra power losses due to the data modulation if a traditional buck converter LED driver is adapted for VLC. We compare VLC systems using two previously proposed driver schemes in the aspects of efficiency, illumination power, data rate and BER.