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A simple and magical formula

Today's story starts with a formula.

This is a simple and magical formula. It's simple because it has only three letters. It is magical because this formula contains a broad and profound mystery of communication technology, which is haunted by countless people on this planet.

This formula is it——

 

I believe many students recognize this formula. If you don't recognize it and you are a science student, please remember to call your middle school physics teacher when you are free!

Explain the above formula, which is the basic formula of physics,Speed of light = wavelength & times; Frequency.

For this formula, it can be said as follows:Whether it's 1g, 2G, 3G, 4G, 5g, everything changes. They all make an article on it and don't jump out of its "Five Finger Mountain".

And listen to me slowly.

two

wired? Wireless?

Communication technology, no matter what black technology or white technology, can be divided into two types in the final analysis——Wired communication and wireless communication.

When I call you, the information and data are either transmitted in the air (invisible and untouchable) or in kind (visible and tangible).

If it propagates in physical matter, it is wired communication, which basically uses copper wire and optical fiber. These cables are collectively referred to as wired media.

When data is transmitted on wired media, the rate can reach a very high value.

Take optical fiber as an example. In the laboratory,The maximum speed of a single fiber has reached 26tbps... It's 26000 times the traditional network cable...

Optical fiber

The air communication is the bottleneck of mobile communication.

At present, the mainstream mobile communication standard is 4G LTE, and the theoretical rate is only 150Mbps (excluding carrier aggregation). There is no way to compare this with wired.

Therefore, if 5g wants to achieve end-to-end high rate, the key is to break through the bottleneck of wireless.

three

What a magical wave

As we all know, wireless communication is the use of electromagnetic waves for communication. Both radio waves and light waves belong to electromagnetic waves.

The functional characteristics of electromagnetic wave are determined by its frequency.Electromagnetic waves of different frequencies have different properties and characteristics, so they have different uses.

For example, high frequency γ Radiation, with great lethality, can be used to treat tumors.

Constant frequency of electromagnetic wave

At present, we mainly use radio waves for communication. Of course, light wave communication is also rising, such as lifi.

Lifi (light fidelity), visible light communication

No bias, back to the radio first.

Radio wave is a kind of electromagnetic wave, and its frequency resources are limited.

In order to avoid interference and conflict, we further divide lanes on the road and allocate them to different objects and purposes.

Use of radio waves of different frequencies

Please pay attention to the red font in the figure above. All along, we mainly useIf ~ UHF for mobile phone communication.

For example, the frequently mentioned "GSM900" and "cdma800" actually mean GSM with an operating frequency band of 900MHz and CDMA with an operating frequency band of 800MHz.

At present, the world's mainstream 4G LTE technical standard belongs toUHF and UHF.

Our country mainly uses UHF:

As you can see, with the development of 1g, 2G, 3G and 4G, the radio frequency used is higher and higher.

Why?

This is mainly because,The higher the frequency, the richer the frequency resources that can be used.The more abundant the frequency resources, the higher the transmission rate can be achieved.

Higher frequency → more resources → faster speed

Shouldn't it be difficult to understand? Frequency resources are like cars. The higher the frequency, the more cars, and the more information can be loaded at the same time.

So, what is the frequency of 5g?

As shown in the figure below:

5g frequency range is divided into two types: one is below 6GHz, which is not much different from our current 2 / 3 / 4G. Another one is very high,Above 24GHz.

At present, it is mainly used internationally28GHzTest (this frequency band may also become the first commercial frequency band of 5g).

If calculated at 28ghz, according to the formula mentioned above:

Well, this is the first technical feature of 5g——

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Millimeter wave

Please allow me to send the frequency comparison table again:

Please pay attention to the bottom line. Is it "millimeter wave"?

Go on, go on!

Well, since the frequency is so high, you must ask:"Why didn't we use high frequency before?"

The reason is simple - not that I don't want to use it, but that I can't afford it.

Remarkable characteristics of electromagnetic wave: the higher the frequency, the shorter the wavelength, and the closer to linear propagation (the worse the diffraction ability).The higher the frequency, the greater the attenuation in the propagation medium.

Look at the laser pen (wavelength about 635nm). The light emitted is straight. If you block it, you can't get through it.

Look at satellite communication and GPS navigation (wavelength about 1cm). If there is an obstruction, there will be no signal.

The big pot of satellite must be calibrated and aimed at the direction of the satellite, otherwise even a little skew will affect the signal quality.

If high frequency band is used in mobile communication, its biggest problem isThe transmission distance is greatly shortened and the coverage capacity is greatly weakened.

Covering the same area,The number of 5g base stations required will greatly exceed 4G.

What does the number of base stations mean? Money! Investment! Cost!

The lower the frequency, the cheaper the network construction and the more favorable the competition. This is why, in recent years, China Telecom, China Mobile and China Unicom have fought for the low frequency band.

Some bands are even called——Golden band.

This is also why, in the 5g era, operators desperately fight against equipment manufacturers and hope that base stations will reduce prices.

Therefore, based on the above reasons, under the premise of high frequency, in order to reduce the cost pressure of network construction,5g must find a new way out.

What are the ways out?

First, the micro base station.

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Micro base station

There are two kinds of base stations, micro base station and macro base station. Just look at the name. The micro base station is very small and the macro base station is very large!

Acer station:

It is common outdoors. Build one to cover a large area

Micro base station:

Does it look cool?

There are smaller ones, the size of a palm

In fact, there are many micro base stations now, especially in urban areas and indoors.

In the 5g era, there will be more micro base stations installed everywhere, almost everywhere.

You will certainly ask, will so many base stations have an impact on the human body?

My answer is - No.

In fact, contrary to traditional cognition, in fact,The more base stations, the less radiation!

Think about it. In winter, in a group of people's houses, is it better to have a high-power heater or several low-power heaters?

High power scheme ▼

Low power scheme ▼

The picture above is clear at a glance.The base station is small and the power is low. It's good for everyone.If only one large base station is used, it is not good if it is close, radiates greatly, is far away, and has no signal.

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Where's the antenna?

Have you found that in the past, mobile phones had long antennas, and early mobile phones also had protruding small antennas. Why do our mobile phones now have no antennas?

In fact, we don't need antennas, but oursThe antenna is getting smaller.

According to the antenna characteristics, the antenna length should be directly proportional to the wavelength, about 1 / 10 ~ 1 / 4.

As time changes, the communication frequency of our mobile phones becomes higher and higher, the wavelength becomes shorter and shorter, and the antenna becomes shorter!

In millimeter wave communication, the antenna has also become millimeter...

This means that the antenna can be plugged into the mobile phone, or even many...

This is the third killer mace of 5g——

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Ｍassive MIMO

(multi antenna technology)

MIMO is "multiple input multiple output", which is transmitted by multiple antennas and received by multiple antennas.

In the LTE era, we already have MIMO, but the number of antennas is not large. It can only be said to be the primary version of MIMO.

In the 5g era, MIMO technology continues to be carried forward, and now it has become an enhanced version of massive MIMO (massive: large-scale, large-scale).

Multiple antennas can be plugged into the mobile phone, not to mention the base station.

In previous base stations, there were only a few Antennas:

In the 5g era, the number of antennas is not calculated by root, but by "array"... "Antenna array"... At first glance, we need to get the rhythm of dense phobia...

However, the distance between antennas should not be too close.

Because of the requirements of antenna characteristics, multi antenna arrays require the distance between antennas to be kept at more than half a wavelength. If the distance is close, it will interfere with each other and affect the transmission and reception of signals.

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Beamforming

Has everyone seen a light bulb glow?

In fact, when the base station transmits signals, it is a bit like a light bulb.

The signal is emitted around. For light, of course, it illuminates the whole room. If you just want to illuminate an area or object, most of the light is wasted...

So is the base station. A lot of energy and resources are wasted.

Can we find an invisible hand to bind the scattered light beam?

This not only saves energy, but also ensures that there is enough light in the area to be illuminated.

The answer is: Yes.

This is called beamforming

The antenna array is arranged on the base station. By controlling the phase of the RF signal, the lobe of the interacting electromagnetic wave becomes very narrow, points to the mobile phone it provides, and can change the direction according to the mobile phone.

This spatial multiplexing technology changes from omnidirectional signal coverage to accurate directional service, and there is no interference between beams,Providing more communication links in the same space greatly improves the service capacity of the base station.

Straight can be broken into curved... What else can't the communication brick family do?

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Don't charge me, will you?

In the current mobile communication network, even if two people dial each other's mobile phone face-to-face (or the mobile phone transmits photos), the signals are transferred through the base station, including control signaling and data packets...

In the 5g era, this is not necessarily the case.

The fifth feature of 5g - D2D, that is, device to device.

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Ｄ２Ｄ

In the 5g era, if two users under the same base station communicate with each other, their data will no longer be forwarded through the base station, but directly from mobile phone to mobile phone...

In this way, a lot of air resources are saved and the pressure of the base station is reduced.

But if you think you don't have to pay, you'll break Tucson.

The control message still needs to go from the base station. You use spectrum resources. How can the operator's father let you go...

Postscript

I believe you have a deep understanding of 5g and the communication knowledge behind it through this article. And all this comes from a mathematical formula that primary school students can understand. Isn't it?

Communication technology is not mysterious. As the most dazzling gem in the crown of communication technology, 5g is not an unreachable innovative revolutionary technology. It is more the evolution of existing communication technology.

As an expert said——

The limit of communication technology is not the limitation of technology, but an inference based on rigorous mathematics. It is basically impossible to break through in the foreseeable future.

How to further explore the potential of communication within the scope of scientific principles is the tireless pursuit of many strivers in the communication industry.

Well, that's all for today.

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