Why the future of wireless may not be RF
As technology evolves, the next big question is what we’ll be using for wireless communication. Geoff Meads explains why the future might not be as we assume.
If the press is to be believed, 5G is the future of wireless communications. Everything from cell phones to autonomous cars is moving towards the low latency, high bandwidth promise that the various forms of 5G offer. However, 5G also perpetuates (and even worsens in some cases) some of the inherent problems that older wireless standards suffer from.
One of the largest issues with cellular communications is power consumption. In his 2011 Ted Talk, Harald Hass suggested that most cellular transmitters (the masts you see by the roadside) are only 5% efficient. That means 95% of the power supplied to them is dissipated as heat and produces no useful signal output. With 5G, especially the variants that use the 60GHz band, we’ll need far more transmitters per square kilometre than 4G so power consumption will worsen. Not good.
To further develop the availability of the Internet, especially in the developing world, we need data delivery methods that are more efficient. Or, preferably, methods that use pre-existing infrastructure. The answer just might be super simple…
What is Li-Fi?
In short, ‘Li-Fi’ is the idea of transmitting data using light pulses. The idea is an old one. Alexander Graham Bell is reported to have shown the idea for basic message transmission using light as early as the 1880s. Today, we use light to move data over fibre optics. So why hasn’t this technology been developed further? Why aren’t we using light more widely for data?
The answer lies in the inherent problems with traditional light emitters or lamps. Until recently, lamps were typically constructed using a coil of hot wire in a gas. When a current passes through the wire it glows and, voila, we have light!
The problem with data transmission is that this type of light can’t be switched on and off fast enough. If you turn off a conventional lamp, its light output takes a short time to fully diminish. For data transmission, we need the lamp to turn on and off very fast. A conventional lamp just won’t do that.
LED lamps have been around since the 1960s, but they have only been able to produce light strong enough to illuminate a room for the past fifteen years or so. An LED lamp can be switched on and off much faster than a conventional lamp so modulating data onto an LED’s light output is certainly possible. Not only are LEDs good for transmitting data but they are now just about everywhere. There’s a huge install base of LED lighting in locations as diverse as your house, your car, the planes we fly in and even your smartphone’s torch. Maybe we could deliver data with those…
How about a receiver?
If LEDs hold the secret to data transmission using light, what technology do we need to receive it? Well, there are various devices that vary their output for a given light input and many, if not all of these, are potential candidates.
Anyone who has studied even basic electronics will know of a device called an LDR or Light Dependant Resistor. These devices, as the name suggests, vary their resistance depending on the amount of light they are receiving. Sadly, LDRs have a similar flaw to conventional light bulbs in that their response time to change is rather slow (typically around 10ms for a conventional LDR). So, LDRs aren’t the answer.
One possible answer lies with a device called a photodiode or phototransistor. These are semi-conductor devices that produce a small amount of electrical current when exposed to light. Their reaction time is much faster than an LDR and, just like LEDs, they are everywhere. The most common occurrences are within solar panels and the sensors in digital cameras, yes including your smartphone camera.
The bandwidth question
So just how much data might we be able to pass over a Li-Fi connection? In his later Ted Talk in 2016, Harald Hass showed a working, short rage demonstration of Li-Fi achieving 50Mbs. That’s easily enough to carry a compressed stream of HD video. Today Li-Fi devices are getting faster all the time with some suggestions are that 100Gbs and beyond is possible.
These speeds might seem implausible at first, after all, it’s just a simple LED lamp and solar panel. However, when we look deeper, we realise that the visible light spectrum, the part of the electromagnetic spectrum that Li-Fi uses, is 10,000 times as large as the radio spectrum. In short, the possibilities of using light for data transmission look pretty good.
You might also be wondering how bright the light needs to be for transmission to work. After all, it would be frustrating if you had to have your room lights on at full power just to read Facebook on your phone. Again, from Harald Hass’s talk, light levels so low that they are barely perceptible to the human eye can still be used for transmission. That’s a relief.
The other big question – security
As with any discussion of network technology, it’s not long before the question of data security raises its head. Well, there’s some good news here. Although light (and any data modulated onto it) can be seen by any device in reasonable proximity, a light source can be made to be highly directional, reducing the risk of being readable by the wrong device. For example, a car headlight uses a simple parabolic reflector to direct light in a narrow beam so that it only shines forward. Light transmissions of even narrow beams can be made using lasers.
There is more good news for those concerned about security too. Firstly, modern data encryption methods are extremely strong and already deployed in WiFi networks. Adding those to Li-Fi is pretty much plug-and-play. Secondly, light operates as a line-of-sight transmission. If something gets in the way, the transmission can’t be received. If you need to keep a Li-Fi transmission secure from outsiders, just shut the door and you’re done.
And finally, deployment
We’ve already mentioned that there is a huge install base of LEDs out there right now waiting to send you data. All those room lights, streetlights and even car headlights can be used to send data from one place to another and at very high speeds. It’s energy-efficient, relatively easy to deploy and at least as secure as the alternatives.
So, who do we think might be ideal candidates to deploy Li-Fi in the home? Perhaps installers that are already proficient at both data and lighting?