What is 5G in the end? After reading the second!

The Internet has changed the world, and the mobile Internet has reshaped life. "You can't live without a network at home, and you can't forget to bring a mobile phone when you go out." It has become a common feeling for many people. People's requirements for the Internet are faster, more convenient, more powerful, and cheaper. The "more" demand is endless, which has led to the rapid advancement of mobile Internet technology and the rapid replacement of technical systems. Many users have just stepped into the threshold of 4G, and the 5G era is coming soon.

What kind of technology will 5G have? Many experts have had predictions, but there are none of the articles that can be read by laymen. After all, the threshold of communication is high, especially for the evolution of future technologies. This article is written in a very special way. The level of junior high school students can be understood. You only need to understand a formula [light speed = frequency & TImes; wavelength].

I. Introduction

1. Double hump law

After the emergence of a new technology concept, there will be a climax of research and discussion in the industry, this is the first hump. Relevant academic papers will be produced as hotspots. The piles of doctoral masters have completed their graduation thesis with this new technology. Although it is very lively, it is only limited to the level of academic research, and there are still many problems in the implementation of specific technologies. Or because of cost reasons, it is impossible to mass production.

The study discussed the climax of the climax, which is the first hump's whereabouts, followed by low-key and pragmatic technical research, which may be a decade or a few years. When the technical problems are solved, the rush of mass production and market entry will be ushered in. This is the second hump.

According to the International Telecommunication Union's plan for 2020, it will be fully entered into 5G in five years, and the core technology system has not yet been established.

Reviewing the history of 3G technology development, the International Telecommunication Union accepted the 3G technology proposal on June 30, 1998, and ushered in the first hump period. Until January 7, 2009, the Ministry of Industry and Information Technology officially issued three 3G license, this entered the second hump, the platform period lasted for 11 years, especially one of the three licenses of TD-SCDMA, until 2013 is really mature, the platform period is up to 15 years, can just mature 4G era It’s coming.

According to the "double hump law", the technology that will be promoted globally after 5 years should usher in the first hump around 2010, and will not be born two or three years before 2020, and then quickly be internationally telecommunication. The alliance is determined to be the global 5G standard, which violates the general rules of technological development and is unlikely to come true.

2, the limits of communication technology

Communication technology can be summarized in eight words, that is, modulation, demodulation, encoding, and decoding. These technologies have been developed to the present, and the efficiency of coding has approached the limit. Small, some industry bulls even think that communication has not been done, and switched to the medical equipment industry, using its solid communication skills in the development of sophisticated medical electronic equipment, in order to pursue a more promising future.

You may have questions: science and technology are getting stronger and stronger, why can't you break through the limits? In fact, the limit of communication technology is not a limitation of technical process, but an inference based on rigorous mathematics. It is basically impossible to break through in the future that can be met.

According to the "double hump law" of technology development and the development of communication technology, it is unlikely that an amazing new technology will emerge in the next few years. 5G technology should be a new combination of existing technologies, and it is 4G technology. Re-evolution.

Why do you have a "re" word? Because the last three letters of 4G LTE mean long-term evolution, 5G should be a re-evolution based on 4G.

Second, 5G key technology

1, increase bandwidth is the key

The most notable feature of 5G is its high speed, which is as high as 10 to 50 Gbps at a planned rate, and the per capita monthly flow is about 36 TB. What resources should be supported by such a high rate? Must rely on more bandwidth!

The bandwidth is represented by the letter B. It is like the width of the road. The maximum rate is expressed in C. It is like the maximum traffic volume of the road. Obviously, the maximum traffic volume of 4 lanes is 2 times that of 2 lanes, and the 8 lanes is 4 times that of 2 lanes. This is very understandable.

Increasing the number of lanes is the most direct and effective way to increase the maximum traffic volume. Similarly, the most direct and effective way to increase the rate is to increase the bandwidth. I still remember when I was a graduate student, the teacher said in a speech when talking about bandwidth: "You remember me: high speed is broadband, broadband is high speed!"

People are increasingly demanding communication speeds, forcing the bandwidth of the channel to be wider and wider. If the bandwidth of several telephone lines is not enough, then it will increase to several hundred. If hundreds of them are not enough, they will be replaced by coaxial cables. If it is not enough, it will be replaced by fiber. The bandwidth of wired communication is increasing from generation to generation.

While mobile communication uses a wireless channel, how does its bandwidth increase? The core method is to use a higher frequency band.

All of the junior high school know the formula of "light speed = frequency & TImes; wavelength". Knowing this formula can understand the above table. The frequency is inversely proportional to the wavelength. The product of the two is equal to the speed of light, that is, 300,000 km / sec.

Look at the data of the two yellow blocks in the table, the values ​​are all 3 to 30, but the units are different. The entire bandwidth of the very low frequency band is 27 kHz, and the entire bandwidth of the ultra-high frequency band is 27 GHz. The latter is 1 million times the former! It can be seen that the higher the frequency band and the larger the bandwidth, this is very easy to understand. It is like the low-income households and the rich and the rich have all the property, the latter will be much more than the former.

So the relationship comes: If you want to be faster in the 5G era, you have to use more bandwidth, and to get more bandwidth, you have to use a higher frequency band. Before 4G is used in the ultra-high frequency band, 5G has to develop to the ultra-high frequency or even higher frequency band. According to experts from the International Telecommunication Union, it is possible to use the frequency band of 30 GHz to 60 GHz in the future, and Russian experts have even proposed an 80 GHz solution.

The frequency band above 30 GHz is higher than the ultra-high frequency of the last item in the above table. The wavelength is naturally shorter than the centimeter segment, which is a shorter millimeter wave, so the millimeter wave becomes a 5G one. Key technology.

2, millimeter wave technology

The characteristics of radio wave propagation are interesting. The higher the frequency (ie, the shorter the wavelength), the more electromagnetic waves tend to travel in a straight line. When it is above the infrared and visible light, it does not bend at all. This is a gradual process.

Millimeter waves are generally not used in the field of mobile communications because their frequencies are close to infrared, the channels are too "straight" and they are not easily aligned when moved. Imagine a scene where you are holding a laser pointer to a pushpin on a distant wall. Is it a difficult thing?

For example, a satellite car is difficult to “move in”, and the body swings. The antenna (that is, the cauldron) is difficult to align with the satellite. Usually it can only work after parking, and the angle of the antenna must be finely adjusted to make it radio waves. The radiation direction is facing the satellite, otherwise it will not be able to communicate.

The mobile phone is mobile, and it is impossible to call the mobile phone to aim at the direction of the quasi-base station when it is called. This is really anti-humanity. Although there is a signal in the opposite direction, the intensity will be significantly weaker, and the experience will be much worse than before 4G.

There are five modes of propagation for electromagnetic waves. Compared to the 5G era in the future, we now have a much lower frequency of mobile phones, and their diffraction ability is good. The signal at the shadow of the building is not too big, because the signal can be reached around.

In the future, the frequency of 5G will be much higher, the diffracting power will drop, and the signal can only go straight and stupid. The corners of the past can reach the corner, what should I do? This leads to a new technology - micro base station technology.

3. Micro base station technology

Please fill in a scene with your brain. There is only one street lamp in the center of the community. The shadow area will of course be very large. If you set a lot of street lights evenly in the community, the shadow area will be much smaller. Therefore, turning a traditional macro base station into a micro-base station with more dense sites is an effective method for solving the millimeter wave "straight line problem".

This is just one reason for the micro base station, and there is a more powerful reason. The number of network access devices in the 5G era will increase exponentially, and the number of network access devices per unit area may increase to a thousand times. If the previous macro base station coverage mode is continued, even if the bandwidth of the base station is large, it will not be able to support it.

This reason is well understood. The previous macro base station covers 1000 Internet users. These users all divide the rate resource of this base station. After entering the 5G era, the user's rate requirement is much higher, and the resources of one base station are far from enough. Only more base stations can be deployed. For example, each base station can only be responsible for 20 users. There are fewer people sharing meals, and everyone can naturally eat more.

The miniaturization of the base station will increase the density of the layout. In order to avoid spectral interference between base stations, the radiation power spectrum of the base station will be reduced, and the radiation power of the mobile phone will also be reduced. There are two good things. One is that the power consumption is small, the standby time will increase, and the second is that the radiation to the human body will decrease. The traditional base station is like a fire stove in the middle of the house. The near-hot place is cold, and the 5G micro base station is like floor heating, and the heat is even and more comfortable.

After the number of micro base stations is greatly increased, the traditional iron tower and roof erection will be expanded. The street light poles, advertising light boxes, and the ceiling inside the building will be ideal locations for micro base stations.

What effect will the wavelength be shortened to millimeter waves? It will also affect the changes in the mobile phone antenna. This is another technology of 5G that is to be mentioned in the next section - high-order MIMO.

4. High-order MIMO

According to the antenna theory, the length of the antenna should be proportional to the wavelength, which is about 1/10~1/4. The current mobile phone uses the high frequency band (ie, decimeter wave). The long antenna line is about a few centimeters, usually installed in The upper part inside the phone case.

Why should the length of the antenna be between 1/10 and 1/4 of the wavelength? Why is it more effective because this ratio makes the radiation and reception of radio waves more efficient? I don't know this, I have to ask the physicist.

After the frequency of the mobile phone in the 5G era is increased by several tens of times, the length of the corresponding hand-wire antenna will also be reduced to one-tenth of the previous one, and it will become a micro-antenna of millimeter level. Many mobile phones can be deployed in the mobile phone, and even formed. Multiple antenna arrays.

Multi-antenna arrays require that the distance between the antennas be kept above half a wavelength and the area of ​​the handset is small. Today's cell phone antennas are a few centimeters long and multi-antenna arrays are difficult to set up. With the reduction of the length of the antenna, especially the millimeter-sized antenna of the 5G era, it is possible to deploy a multi-antenna array, which brings about the realization of high-order MIMO technology.

What is MIMO? The English abbreviation means “multiple in and out”. High-order MIMO means that there are many pairs of channels in parallel communication between the base station and the mobile phone. Each pair of antennas transmits one channel of information independently, which can be multiplied after being aggregated. Rate, of course this is a great thing.

I wonder if you have thought about this problem: because the base station does not know where you are, the electromagnetic wave it uses to communicate with you is omnidirectional, just like the light from the light bulb, only the radiation reaching your mobile phone is useful. Radiation in other directions is wasted, and this huge useless radiation has become a disturbance to other mobile phones.

As shown in the above figure, because the energy of the flashlight is more concentrated, it is farther than the bulb, and the relationship between the base station and a certain mobile phone is equivalent to the relationship between the light source and the object to be irradiated.

Now the relationship between the base station and the mobile phone is the light bulb mode. Regardless of the orientation of the mobile phone, the signal for the mobile phone will be omnidirectional radiation. Of course, most of the energy in the opposite direction is wasted, and it has become a Interference from other mobile phones.

Can you change the lamp mode to a directional flashlight mode? That is, the omnidirectional radiation pattern on the left side of the above figure is changed to the narrow lobe pattern on the right side, thereby improving the energy use efficiency. This is the beamforming technique to be mentioned in the next section.

5, beam shaping technology

China's leading 3G international standard TD-SCDMA has six technical characteristics, one of which is a smart antenna. Antenna arrays are arranged on the base station. By controlling the phase of the RF signal, the lobes of the electromagnetic waves after interaction become very narrow. And point to the phone it serves, and it can change direction depending on the mobile phone's movement.

From omnidirectional signal coverage to precision directional service, this new form of radio beam does not interfere with beams in other directions, allowing more communication links to be provided in the same space. This space-utilized radio beam technology is a spatial multiplexing technique that can greatly improve the service capacity of a base station.

Unfortunately, this technology has not been applied in the 3G era, but when the number of 5G networked devices has increased by hundreds of times, the capacity increase brought by this beamforming technology is very valuable. Shape technology is likely to become one of the key technologies of 5G.

Beamforming technology can not only greatly increase the capacity, but also greatly improve the positioning accuracy of the base station. The accuracy of current mobile phone base station positioning is very poor, which is the mode derived from the omnidirectional radiation of the base station. When the beamforming technology is successfully applied, the radiation lobes of the mobile phone to the mobile phone are very narrow, which knows the direction angle of the mobile phone relative to the base station, and by deriving the distance between the mobile phone and the base station by the received power level, Realize the precise positioning of mobile phones, and thus expand a lot of positioning value-added services.

6, comprehensive analysis

Any key technology that needs to be updated must be a mature technology that has undergone many years of research. It is still 5 years to enter the 5G era according to the plan. It is unlikely that a new technology will suddenly appear and be absorbed into the 5G international standard. Investigate the 5G technology development context and find the answer from mature technology.

It is very difficult to speed up in the case of large coverage of traditional macro base stations. The improvement of 20% spectrum utilization rate is an amazing achievement. In the face of the thousand times speed increase requirement in the 5G era, this method of internal tapping is not feasible. Only by greatly increasing the bandwidth is possible.

Increasing the bandwidth is the starting point, and the resulting millimeter wave, micro base station, high-order MIMO, beamforming, etc. are all logical trends. As long as the base station is made small enough and its service range is narrowed, the resources obtained by a single user can be large enough and the speed can be increased fast enough.

Therefore, there is no revolutionary breakthrough in any of the key technologies of 5G. The improvement of its comprehensive capabilities over a thousand times is more due to the re-layout of mobile networks.

Third, postscript

You can understand this 5G science, and you can understand the reasons for the five major technologies of a ring, and even think that this is justified. In fact, this kind of legibility is not easy to achieve, especially for communication majors with high technical thresholds. The more easy it is for an outsider to understand the author's skill, this is really not the mother to sell melons. It is a consensus in the education sector.

The real truth is not cumbersome, it is often a matter of words. It is difficult to extract this sentence for more people to understand. I have written a lot of science, and now I am most satisfied with this, because this is not about "what", but "why", what is good to say, why is it difficult to say, especially to give "why" The layman makes it clear that they should be understood in a proper way. The content order and writing of this article have been repeatedly considered and rewritten repeatedly.

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