The growth of Internet of Things (IoT) devices has brought about a new era of connectivity, but it also presents the difficulty of effectively monitoring power use. Introducing PassiveLiFi, a cutting-edge technology that merges Light Fidelity (LiFi) with Radio Frequency (RF) backscatter to provide a communication system that operates without batteries and consumes little power. PassiveLiFi aims to transform the Internet of Things (IoT) by using the current light infrastructure and radio frequency (RF) technologies.

“LiFi for Low-Power and Long-Range RF Backscatter” is a publication by Muhammad Sarmad Mir, Borja Genoves Guzman, Ambuj Varshney, and Domenico Giustiniano.

The Birth of PassiveLiFi

PassiveLiFi is specifically designed to harness the unutilized capabilities of merging LiFi for transmitting data from a source to a receiver, and RF backscatter for transmitting data from the receiver back to the source. The technology use optical communication to deliver data to a passive tag, which then relays data via radio frequency signals. The use of light for both data transmission and clock generation in the IoT tag prevents the need for a power-intensive oscillator, resulting in a substantial reduction in energy usage.


Innovative Design and Key Components

  1. LiFi Transmitter:

The LiFi transmitter has several functions inside the PassiveLiFi system. It supplies the required lighting, energises the IoT tag for operation without batteries, and produces baseband signals for transmission in the downlink. The transmitter may produce visible light chirps for uplink RF backscatter by adjusting the light intensity. (See Figure 1: LiFi Transmitter and Passive Tag Setup)

Fig. 1: PassiveLiFi: hardware prototypes of LiFi transmitter and passive tag. The tag comprises a solar cell array for energy harvesting and downlink communication (top side), a LiFi module for downlink, a harvester circuit and an RF backscatter module for uplink communication (bottom side).

  1. IoT Tag:

The passive IoT tag is outfitted with a solar cell array to gather energy and a LiFi receiver for receiving downlink communication. The energy that is collected is used to power the tag, which utilises the received light signals to produce an RF backscatter signal for communication in the opposite direction. This architecture guarantees optimal performance of the tag even under low-light situations. (See Figure 2: Downlink and Uplink Communication)

Fig. 2: Downlink (left): Light intensity is changed to send data to the passive tag at a fixed clock rate. Uplink (right): Carrier and baseband delegated to the infrastructure. Chirps are complex to generate at the tag, and hence we delegate them to the light infrastructure. The light intensity is changed to generate visible light chirps at a varying clock rate. This chirp is then mixed in the tag with the input RF carrier for RF backscatter.

Overcoming Challenges 

Delegating Oscillators:PassiveLiFi solves the issue of energy consumption in conventional RF backscatter systems by using the LiFi transmitter to provide essential clock signals, significantly reducing the energy needs of the tag. This approach also extends the communication range.

Optimising Solar Cells: The device employs a single solar cell for both energy harvesting and communication, an improvement over previous systems that required separate cells. The use of solar cells for both functions is optimised to achieve maximum efficiency. (See Figure 3: Effect of Solar Cell Area on Communication and Harvesting)

Fig. 3: Effect of solar cell area on communication and harvesting using up to five solar cells in parallel or series. The energy harvesting ability improves when the solar cells are connected in parallel, whereas connecting them in series improves their ability to receive downlink communication.


Impressive Performance 

  • PassiveLiFi demonstrated a communication range of up to 350 meters while using just 3.8µW of power in its basic mode, almost doubling the efficiency compared to earlier systems like EDISON. It can function at very low power levels while maintaining long-distance communication.
  • Using chirp spread spectrum (CSS) modulation, PassiveLiFi ensures that uplink communication is energy-efficient and resistant to noise and interference. This feature enables the system to decode messages weaker than the background noise, ensuring reliable communication in real-life settings.


Real-World Applications 

  • PassiveLiFi can be easily incorporated into the current lighting infrastructure of smart houses. Envision temperature sensors installed in every room that use backscatter technology to transmit data to a central control unit, enabling effective climate management without the need on batteries.
  • PassiveLiFi may use the existing artificial lighting in agricultural environments like as greenhouses to both provide electricity and establish communication with sensors that monitor environmental variables. This not only decreases the expenses associated with installation but also guarantees uninterrupted surveillance without the inconvenience of replacing batteries.


Passive LiFi is a cutting-edge technology in the field of IoT that provides a sustainable and effective solution to the power consumption issues faced by conventional IoT systems. By integrating the most advantageous aspects of LiFi and RF backscatter technologies, it establishes the foundation for a future in which IoT devices may function independently, fuelled by the same light that lights our surroundings. This innovative solution not only improves the functionality and dependability of IoT devices but also supports global environmental objectives by decreasing dependence on batteries and minimising electrical waste.