The rapid expansion of the Internet of Things (IoT) has intensified the need for sustainable, battery‑free communication solutions. This paper presents a comprehensive Simulink model of a modified Passive LiFi system that combines Visible Light Communication (VLC) for optical downlink with RF backscatter for ultra‑low‑power uplink transmission. To overcome limitations in standard Simulink libraries, custom behavioral models are developed for key components, including a solar cell equivalent circuit, a boost converter replacing the switching regulator for stable high‑frequency modulation, and an optocoupler‑based gate driver. The model encompasses the complete communication chain: LiFi transmitter with chirp‑modulated OOK, tag‑side signal conditioning (HPF, comparator), and CSS demodulation at the receiver. System performance was evaluated in terms of BER, SNR, CDF analysis confirms close statistical agreement with experimental Passive LiFi results. The framework provides a flexible, reproducible platform for early‑stage design exploration of hybrid LiFi–RF backscatter systems without costly hardware prototyping.