What’s The Importance of Modulation Techniques in Infrared LiFi Systems?

Credit to Signifi

Firstly, let’s define the meaning of modulation. Modulation can be defined as the process of changing a simple, steady wave (called a carrier wave) so that it can carry a message, data, or sound. Modulation techniques play a big part in LiFi systems.

To put it simply, without modulation, a lightbulb is just a lightbulb. Modulation is the crucial translation step that turns a basic light fixture into a high-speed data transmitter.

Because infrared light is invisible to the human eye, engineers no longer have to worry about providing room illumination, preventing visual flicker, or supporting dimming switches. However, modulation techniques remain absolutely critical, just for a different set of reasons.

Here is why modulation is vital specifically for infrared LiFi systems:

1. Conquering the "Noisy" Infrared World

While IR is invisible to us, it is everywhere. Sunlight, incandescent lightbulbs, and thermal heat sources emit massive amounts of ambient infrared radiation. Without modulation, a LiFi receiver would be blinded by this background "noise." Modulation acts as a strict filter, by encoding the data into specific, ultra-fast, high-frequency pulse patterns, the receiver can easily ignore the steady background "heat" of the room and lock onto the data stream.

2. Optimising the "Uplink" and Battery Life

In most LiFi setups, visible light is used for the downlink (ceiling to your laptop), but infrared is used for the uplink (your laptop back to the ceiling). This is because users don't want a bright white flashlight beaming out of their phone or computer while they work.

Because the uplink relies on battery-powered mobile devices, the modulation technique must be incredibly power-efficient. Schemes like Pulse Position Modulation (PPM) are heavily favoured in IR systems because they can transmit a lot of data using very short, infrequent flashes of light, saving your device's battery life.

3. Strict Eye-Safety Compliance

Just because you can't see infrared light doesn't mean it can't hurt you. High-intensity IR light can cause thermal damage to the human retina. Infrared LiFi systems are bound by strict international eye-safety regulations (like Class 1 laser/LED safety standards). Modulation techniques are essential here—they allow the system to transmit very fast, high-power bursts of data while keeping the average continuous optical power low enough to remain perfectly safe for human eyes.

4. The "Positive Light" Constraint Remains

Just like visible LEDs, an infrared LED still cannot produce "negative" light. Engineers are still restricted to Intensity Modulation/Direct Detection (IM/DD). Therefore, to achieve those massive gigabit speeds, they still have to use complex modulation like Optical OFDM to convert standard digital signals into strictly positive (real) intensity variations that an IR diode can physically transmit.

In summary, while visible LiFi modulation is about balancing data with human comfort, infrared LiFi modulation is all about maximizing power efficiency, cutting through environmental noise, and ensuring eye safety.