Using light bulbs to surf the Internet? Speed ​​of 100Gbps? Is the much-anticipated Li-Fi really that great?

I have told you before that our current wireless communications are all based on electromagnetic waves.

Using electromagnetic waves for communication requires occupying electromagnetic wave spectrum resources.

Although spectrum resources cannot be seen or touched, they are very valuable.

According to the frequency (wavelength) of spectrum resources, electromagnetic waves are mainly divided into radio waves and light waves. All along, we mainly use "radio waves" for wireless communication and use the spectrum resources of radio waves.

The radio spectrum resources have been divided a little bit to the east and a little bit to the west, and there are not many left.

Radio waves are not enough, so people naturally wonder if light waves can be used.

Optical wave frequency resources are abundant, the frequency band is wide, and the available resources are relatively abundant.

The technology that uses light waves for wireless communication is usually called "optical communication".

Please note that the optical communication we usually refer to is more about fiber optic communication. In fact, fiber optic communication belongs to wired communication.

But there is no way, the name has been used by everyone, it is difficult to get it back...

Therefore, in order to distinguish it from fiber optic communication, our "true optical communication" is also called "visible light communication" (VLC).

Visible light communication has its own standard - IEEE 802.15.7 VLC.

Its precise definition is: a communication method that uses light in the visible light band as an information carrier to directly transmit optical signals in the air.

"Li-Fi", which has been very popular in recent years, is a type of "visible light communication" technology.

In 2011, German physicist Harald Haas and his team at the University of Edinburgh in the UK invented a patented technology that uses flashing lights to transmit digital information, which is Li-Fi.

Li-Fi, Light Fidelity. Do you think this name is similar to Wi-Fi? It was named this way because its application scenarios are similar to Wi-Fi, and people thought it was likely to replace Wi-Fi.

The working principle of Li-Fi is not complicated: install a microchip on an ordinary LED bulb, and control it to flash millions of times per second, with light representing 1 and off representing 0. Because the frequency is too fast, the human eye cannot perceive it at all, but the photosensitive sensor can receive these changes. In this way, binary data is quickly encoded into light signals and effectively transmitted. The computer or mobile phone under the light can read the "Morse code" in the light through a special receiving device, and can communicate.

Everyone should note that Haas can only be regarded as the inventor of Li-Fi, but he is not the inventor of visible light communication.

Visible light communication was proposed as early as around 2000 and originated in Japan.

Let's take a look at the development history of visible light communication:

• In 2000, Japanese researchers proposed and simulated an indoor communication system that used LED lighting as a communication base station for wireless information transmission. At that time, the optical communication transmission rate was only tens of KB per second.
• In 2003, Japan established the VLCC Visible Light Communication Alliance, which quickly became an international organization.
• In 2008, the maximum transmission distance of visible light communication was 2000 meters and the transmission rate was 1022bit/s.
• In 2010, visible light communication technology using LED traffic lights as transmitters had a transmission rate of 4800kb/s and a distance of 300 meters.
• In 2010, a team from the Fraunhofer Institute in Germany increased the communication rate to 513Mbps, setting a world record.
• In 2013, Fudan University developed an offline data transmission rate of 3.75Gbps, setting a world record.
• In 2013, British researchers refreshed the offline rate to 10Gbps.
• In 2015, China increased the real-time communication rate to 50Gbps.

According to foreign media reports, researchers at Oxford University have completed a 100Gbps visible light communication experiment and named it "ultra-parallel visible light communication", and even predicted that the maximum rate of the communication system can reach 3Tbps!

In fact, the birth and rapid development of visible light communication is due to the explosion of LED technology.

Since its birth, LED has been developing at a rate of 20 times brighter and 100 times cheaper every decade, with the technology becoming more mature and its functions being continuously improved.

Because of this, visible light communication took advantage of this opportunity and became popular.

In addition to speed, visible light communication has many other advantages.

According to statistics, the number of devices supporting Wi-Fi wireless connections will reach 1.7 billion in 2020. However, as the number of devices continues to increase, Wi-Fi networks based on traditional RF (radio frequency) technology may not be able to meet device connection needs in 2025.

In terms of cellular communications, in China alone, there are nearly 6 million mobile communication base stations, most of the energy is used for cooling, and the efficiency is only 5%.

LED light sources are different. There are about 40 billion LED bulbs in the world. Just add a microchip to these LED bulbs to transform them into signal transmitters, and the scale of the communication network formed is amazing. The cost of doing so is much lower than deploying Wi-Fi hotspots, and there is no need to build new infrastructure.

Moreover, as mentioned earlier, the spectrum resources of radio waves are becoming increasingly scarce, and the network has become overcrowded. The width of the visible light spectrum is 10,000 times that of the radio frequency spectrum, which means that it can bring higher bandwidth and abundant resources. With optical communication, there is no need to worry about insufficient spectrum, and it can also alleviate the current shortage of wireless spectrum resources around the world.

In addition, visible light is green and has no radiation harm to humans.

Therefore, using light as a medium for wireless communication is a healthier and more desirable direction for human development. At the same time, using light for communication can reduce energy consumption because it does not need to provide additional energy like base stations, which is more environmentally friendly.

If we consider safety, it is also an advantage. Visible light communication can block the light and prevent it from leaking out. . .

However, visible light communication actually has many disadvantages.

• First of all, everyone should have thought of it. For something like Li-Fi, the downlink rate is fine, but what about the uplink? Can you install a light bulb on your phone?
• Then, there is the interference of ambient light. It is fine to use it in a closed room, but when it is outdoors, the light source is messy and this is greatly affected.
• Another factor is distance. The rate of visible light communication seems very high, but the test in the laboratory is done under ideal conditions at short distances. You can't hold your phone next to a light bulb to surf the Internet. If you are a little further away, the rate will drop sharply. Moreover, if you turn your back to the light source and block the light, there will be no signal...

In short, visible light communication does beat traditional radio frequency communication in terms of theoretical transmission rate, deployment, cost, zero electromagnetic radiation, etc. However, due to its inherent defects, it is definitely impossible to expect it to replace Wi-Fi or mobile communication base stations in a short period of time.

Therefore, we should be more patient with visible light communication and Li-Fi!