5G entry lazy bag

To put it simply, 5G is the fifth-generation mobile communication technology. Its main features are millimeter-level wavelength, ultra-wideband, ultra-high speed, and ultra-low latency.


1G realizes analog voice communication, and mobile phones can only make calls without a screen;

2G has realized the digitalization of voice communication, and the function phone has a small screen and can send SMS;

3G realizes multimedia communication other than voice and pictures, and the screen becomes bigger and you can see pictures;

4G has realized local high-speed Internet access, and large-screen smartphones can watch short videos.

1G to 4G are all focused on more convenient and fast communication between people, and 5G realizes the interconnection of all things anytime, anywhere, so that human beings dare to look forward to participating with all things on the earth through live broadcast without time difference.


A Simple and Magical Formula


It's a formula that's as simple as it is magical. It is simple because it has only 3 letters in total. And it is said to be miraculous because this formula contains profound and profound mysteries of communication technology, and countless people on this planet are obsessed with it.


The above formula is the basic formula of physics, the speed of light = wavelength × frequency

Regarding this formula, it can be said that: whether it is 1G, 2G, 3G, or 4G, 5G, everything is the same, and everything is based on it, and it does not jump out of its "Five Fingers".



wired? wireless?


Communication technology, regardless of black technology or white technology, in the final analysis, can be divided into two types-wired communication and wireless communication. Information and data are transmitted in the air (invisible and intangible) and in physical objects (visible and tangible).



If it is transmitted on physical matter, it is wired communication, basically copper wires, optical fibers and other cables, collectively referred to as wired media. Spreading data on a wired medium, the rate can reach a very high value. Taking optical fiber as an example, in the laboratory, the maximum speed of a single optical fiber has reached 26Tbps. . . It is 26,000 times that of traditional network cables. . .



The part of air transmission is the bottleneck of mobile communication. The current mainstream 4G LTE has a theoretical rate of only 150Mbps, which is completely incomparable with wired networks.


The difference between wired and wireless


Therefore, if 5G is to achieve end-to-end high speed, the key point is to break through the bottleneck of the wireless part.


big wave


We all know that wireless communication is the use of electromagnetic waves for communication. Electric waves and light waves are both electromagnetic waves. The functional characteristics of electromagnetic waves are determined by their frequency. Electromagnetic waves of different frequencies have different properties and characteristics, and thus have different uses. For example, high-frequency gamma rays have great lethality and can be used to treat tumors.




We currently use mainly radio waves for communication. Of course, light wave communication is also on the rise, such as LiFi. Radio waves are a type of electromagnetic waves, and their frequency resources are limited. In order to avoid interference and conflicts, we further divide the lanes on the electric wave road and assign them to different objects and purposes.


For a long time, we have mainly used IF~UHF for mobile phone communication. For example, "GSM900" and "CDMA800" are often said, but they actually mean GSM with a working frequency band of 900MHz and CDMA with a working frequency band of 800MHz. Currently, the world's mainstream 4G LTE technical standards belong to UHF and UHF.


Hong Kong's mobile telecommunications network format currently adopts the second-generation European format GSM-900 , PCS ( GSM-1800 ), the third-generation UMTS , and the fourth-generation LTE format network. GSM is the network format adopted by most countries in the world except Japan , South Korea , and the Republic of China , while UMTS and LTE can pass almost all over the world.


You can see that with the development of 1G, 2G, 3G, and 4G, the frequency of radio waves used is getting higher and higher. This is mainly because the higher the frequency, the more abundant the frequency resources that can be used. The more abundant the frequency resources, the higher the transmission rate that can be achieved.

Higher frequency → more resources → faster speed


Frequency resources are like carriages. The higher the frequency, the more carriages, and the more information can be loaded in the same time. So, what is the specific frequency used by 5G?

The frequency range of 5G is divided into two types: one is below 6GHz, which is not too different from our current 2G/3G/4G. There is another kind, which is very high, above 24GHz.


Specifically, since the first half of 2018, the millimeter-wave spectrum auction was launched globally. At present, North America, Asia-Pacific, Europe and other regions have allocated spectrum in the millimeter-wave frequency band. 24.75GHz to 25.25GHz), 28GHz (27.5GHz to 28.35GHz), 37GHz (37GHz to 38.6GHz), 39GHz (38.6GHz to 40GHz) and 47GHz (47.2GHz to 48.2GHz) spectrum auctions for 5G commercial deployment Sufficient frequency resources are provided. South Korea completed the 28GHz (26.5GHz-29.5GHz) spectrum auction in 2019, and the millimeter-wave spectrum in Europe is concentrated at 26GHz (24.25GHz-27.5GHz), and some countries have completed spectrum auctions. Taiwan completed the 28GHz spectrum auction in January 2020. Mainland China covers the 26GHz frequency band and the 40GHz frequency band, with a total bandwidth of 9.75GHz. If it is calculated by 28GHz, according to the formula we mentioned above:


This is the first technical feature of 5G - millimeter wave.

Millimeter wave has many advantages compared with frequency bands below 6GHz. First, the millimeter wave spectrum resources are abundant, the carrier bandwidth can reach 400MHz/800MHz, and the wireless transmission rate can reach more than 10Gbit/s; second, the millimeter wave beam is narrow, has good directionality, and has high spatial resolution; third, The millimeter-wave wavelength is short, the antenna size is small, and the miniaturization and light weight of large-scale arrays are easier to realize; fourth, the millimeter-wave subcarrier spacing is large, and the single SLOT cycle (120kHz) is 1/4 of the low-frequency Sub-6G (30kHz). The air interface delay is reduced, which can meet the needs of the industry; fifth, the millimeter-wave indoor and outdoor isolation is good, which is more conducive to eliminating indoor and outdoor interference when different frame structures are used indoors and outdoors.



Since the high frequency is so good, you will definitely ask: "Why didn't we use high frequency before?"


It's not that I don't want to use it, but the cost is too high. The salient features of electromagnetic waves: the higher the frequency, the shorter the wavelength, and the closer it is to propagating in a straight line (the poorer the diffraction and wall-penetrating ability). The higher the frequency, the greater the attenuation in the propagation medium. For example, a laser pointer has a wavelength of about 635nm, and the emitted light is straight, and it cannot pass through if it is blocked. Looking at satellite communication and GPS navigation, the wavelength is about 1cm. If there is an obstruction, there will be no signal.



The circular satellite antenna must be calibrated to the direction of the satellite, otherwise, even a little crookedness will affect the signal quality.


If mobile communication uses high-frequency bands, its biggest problem is that the transmission distance is greatly shortened and the coverage ability is greatly weakened. To cover the same area, the number of 5G base stations required will greatly exceed that of 4G.



A large number of base stations means an increase in cost. The lower the frequency, the lower the cost of network construction and the more favorable the competition. That's why, in recent years, major telecom operators have fought for the auction of low-frequency bands. Some frequency bands are even called - golden frequency band.



This is why operators in the 5G era strongly demand that equipment manufacturers lower the price of base stations. This is also the absolute competitive advantage of ZTE and Huawei in all countries in the world. The price is too cheap.


However, based on the above reasons, under the premise of high frequency, in order to reduce the cost pressure of network construction, 5G has found a new way out - micro base station. There are two types of base stations, micro base stations and macro base stations. As you can tell from the name, the micro base station is very small, and the macro base station is very large!


Macro base station: Common outdoors, build one to cover a large area


Micro base station: there are smaller ones, as big as the palm of your hand.

In fact, there are many micro base stations, especially in urban areas and indoors, which can often be seen. After the popularization of 5G in the future, there will be more micro base stations, and they will be installed everywhere, almost everywhere.


Do base stations have a big impact on the human body?


With so many new base stations around, will it have a greater impact on the human body? Actually no, contrary to the traditional perception, in fact, the more base stations there are, the smaller the radiation will be! Just imagine, in winter, in a house with a group of people, is it better to have one high-power heater or several low-power heaters?


The base station is thin and low power, which is good for everyone. If only one large base station is used, the radiation will be large if it is close, and there will be no signal if it is far away, which is not good.



Antenna to the left


In the past, mobile phones had very long antennas, and early mobile phones also had small protruding antennas. Why do our mobile phones have no antennas now? In fact, it's not that we don't need antennas, but our antennas are getting smaller. According to the characteristics of the antenna, the length of the antenna should be proportional to the wavelength, about 1/10~1/4.


As time changes, the communication frequency of our mobile phones is getting higher and higher, the wavelength is getting shorter and shorter, and the antenna is getting shorter. For millimeter wave communication, the antenna also becomes millimeter-level. This means that the antenna can be inserted into the inside of the mobile phone, and even many roots can be inserted. This is the third killer feature of 5G - Massive MIMO (multi-antenna technology)



MIMO is "Multiple-Input Multiple-Output" (Multiple-Input Multiple-Output), multiple antennas transmit, and multiple antennas receive. In the LTE era, we already have MIMO, but the number of antennas is not too many, it can only be said to be the primary version of MIMO. In the 5G era, MIMO technology continues to be developed, and now it has become an enhanced version of Massive MIMO (Massive: large-scale, a large number). Many antennas can be plugged into a mobile phone, let alone a base station. In previous base stations, there were only a few antennas. In the 5G era, the number of antennas is not counted by root, but by "array" and "antenna array".


However, the distance between the antennas should not be too close. Due to the requirements of the antenna characteristics, the multi-antenna array requires the distance between the antennas to be kept above half a wavelength. If the distance is close, they will interfere with each other and affect the sending and receiving of signals.



are you straight or crooked


You've all seen a light bulb glow, right? In fact, when the base station transmits a signal, it is a bit like a light bulb shining. The signal is emitted to the surroundings. For light, of course, it illuminates the entire room. If you just want to illuminate a certain area or object, then most of the light is wasted. . .



The same is true for the base station, a lot of energy and resources are wasted. Can we find an invisible hand to bind the scattered beams? This not only saves energy, but also ensures that the area to be illuminated has enough light. The answer is: yes. Here it is - Beamforming



The antenna array is arranged on the base station, and by controlling the phase of the radio frequency signal, the lobe of the interacted electromagnetic wave becomes very narrow and points to the mobile phone it provides services, and can change direction according to the movement of the mobile phone.



This spatial multiplexing technology has changed from omnidirectional signal coverage to precise directional services, without interference between beams, providing more communication links in the same space, and greatly improving the service capacity of the base station.



It's not easy to collect money, it's not worth it


In the current mobile communication network, even if two people dial each other's mobile phones face to face (or transfer photos between mobile phones), the signals are relayed through the base station, including control signaling and data packets. In the 5G era, this situation is not necessarily the case. The fifth major feature of 5G - D2D, which is Device to Device (device to device).


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 will be directly transferred from the mobile phone to the mobile phone. . .

In this way, a lot of air resources are saved, and the pressure on the base station is also reduced. However, if you think that you don't have to pay for it, then you are too young too simple! Control messages still have to go from the base station. If you use spectrum resources, the operator may let you go. . .


postscript


Communication technology is not mysterious. As the most dazzling jewel in the crown of communication technology, 5G is not an innovative and revolutionary technology that is out of reach. It is more of an evolution of existing communication technology. As an expert said - the limit of communication technology is not the limitation of technology, but the deduction based on rigorous mathematics, which 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 strugglers in the communication industry.