Linear Response Modeling of High Luminous Flux Phosphor-Coated White LEDs for VLC

Abstract

The widespread deployment of LEDs for illumination purposes has open the door to the use of these devices for visible light communications (VLC). Most lighting fixtures are mounted with phosphor-based white LEDs, and a driver connected to the LED is also required for VLC. This paper shows that the parasitic effects introduced by this setup change the frequency response of the intrinsic LED. A linear model to characterize the whole setup is proposed, as well as a methodology to extract its parameters. This methodology allows the designer to characterize the frequency response of LEDs without the additional difficulty of knowing the specific parasitic components introduced by the setup. The proposed model offers an accurate estimation of the slope of the LED frequency response in order to broaden the frequency range in which the model is useful to characterize and simulate VLC links. This was corroborated with the characterization of three commercial white LEDs whose measured and modeled frequency responses matched perfectly.

Model and Methodology to Characterize Phosphor-Based White LED Visible Light Communication Links

“…In [ 3 ], a linear system model for the phosphor-coated white LED was proposed ( Figure 1 b), which separates the effect of the blue LED (electrical domain) and phosphor coating (optical domain). The model assumes that the optical power generated by the LED, , due to its modulating voltage, , is detected by a photodetector (PD) whose output voltage ( ) is proportional to this optical power, as shown in Figure 1 a. Additionally, all DC or bias terms at the LED or PD are not considered as the model only takes into account the data signals to be transmitted.…”

“…The parameters of LED1 and LED2 were obtained using the method described in [ 3 ] for a reference VLC channel with cm and perfect alignment between the LED and photodetector ( , ). The estimated parameters are indicated in Table 2 , and their frequency responses are shown in Figure 6 , where solid lines correspond to the measured frequency responses of LED1 and LED2, and dashed lines were obtained using Equation ( 9 ) with the extracted parameters.…”

“…The main limitation of phosphor-coated white LEDs for data transmission is their small modulation bandwidth: they usually have a dB frequency of a few MHz [ 2 , 3 ]. Therefore, to reach data rates of hundreds of Mb/s, as will be required in future data networks, it is necessary to develop advanced data transmission techniques, such as advanced modulations [ 4 , 5 , 6 ], multiple access techniques [ 7 , 8 , 9 ], LED non-linearity compensation [ 10 , 11 ] or the use of multiple LEDs for transmission [ 12 , 13 ].…”

“…The range of phosphor-based white LED models for VLC available in the literature is quite diverse, including first-order low-pass [ 19 ], which is combined with a second-order feature to model the yellow component [ 20 ], or a second-order one when parasitic components are included [ 21 ]. A linear model for white LEDs has recently been proposed [ 3 ]. This model separates, on the one hand, the frequency response of the LED and its fixture and, on the other hand, the response of the phosphor coating.…”

A Joint Illumination and Communication GaN MQW LED Model for Visible Light Communication System

“…The second representative LED model is proposed as the joint resistance and capacitance equivalent circuit named the "RC" equivalent circuit [22][23][24]. This kind of model takes into account the LED's parasitic components and models the carrier diffusion process in each layer of the LED as a differential resistance in parallel with a capacitance.…”