After the read, you will learn all about the 5G Millimeter wave.
Compared with the previous 4G, 5G has many advantages. 5G will be the next generation of wireless communication technology. 5G will burst with unlimited energy in the future by virtue of the ultra-high wireless network speed, coverage, and responsiveness. Why can the speed of 5G be increased by 10 times or even 100 times? In fact, behind this involves a key technology, a 5G millimeter-wave.
Millimeter-wave is essentially a high-frequency electromagnetic wave, which is an electromagnetic wave with a wavelength of 1-10 millimeters. Generally speaking, it is an electromagnetic wave with a frequency between 30GHz and 300GHz. It is one of the main frequency bands used in 5G communications.
Two communication frequency bands are mainly used in 5G communication. Sub-6GHz is a low-frequency frequency band, and a frequency band below 6GHz is mainly used for communication. The millimeter-wave frequency band uses the high-frequency millimeter-wave of 24GHz-100GHz for communication, 5G’s use of millimeter-wave is mostly concentrated in several frequency bands of 24GHz/28GHz/39GHz/60GHz.
What mobile communication must solve is nothing more than coverage and capacity. In order to solve these two problems, 5G uses various frequency bands to complement each other.
700M: My frequency is low, I use a 4T4R RRU, and the transmit power is 4×40=160 watts!
2100M: My frequency is not high or low, I use 4T4R RRU, transmit power 4×60=240 watts!
3500M: My frequency is slightly higher. I use 64T64R AAU and transmit power of 320 watts!
Millimeter-wave: My frequency is high, using 4T4R AAU, with 768 antennas inside, and an EIRP of 65dBm! 65dBm = 3162 watts!
No wonder the 5G base station costs electricity, the original millimeter-wave AAU transmission power is so high!
Why use EIRP for 5G millimeter wave transmit power?
The full name of EIRP is Effective Isotropic Radiated Power, also called equivalent isotropic radiated power.
Antennas are inevitably used to transmit signals. General antennas do not emit evenly around but concentrate energy in the direction of the main lobe. EIRP means the signal strength in the direction of the antenna’s main lobe, which is equivalent to how much power a point source antenna is.
A point source antenna is an imaginary point antenna that will continuously spread the signal to the surroundings evenly. It is also called an isotropic antenna.
With less power, the directional antenna can transmit the signal as far as the point source antenna. Therefore, although the value of EIRP looks large, the actual transmitted power is not large.
The unit of antenna gain, dBi, refers to how many times the signal of the antenna’s main lobe is stronger than a point source antenna of the same power. But this is a relative value, and if the antenna is not connected to the RRU, the signal cannot be transmitted, and it is impossible to talk about how much power.
To see how much power is transmitted, the RRU must be taken into account. The RRU transmit power is x dBm, and the antenna concentration in the main lobe direction is y dBi, which is equivalent to a point source antenna of x + y dBm! In other words, EIRP = RRU transmits power + antenna gain.
The traditional RRU does not have an antenna connected to it, so it can only be measured by the transmit power, which is usually expressed in watts.
For example, the 700M RRU has 4 ports, and the maximum transmits the power of each port is 40 watts. Let’s say that the transmit power of this RRU is 4×40 watts.
For the AAU of the intermediate frequency (2600M or 3500M), although the device is an RRU and antenna combined, the antenna can be removed, and the transmission power of the rear RF interface can also be measured. Therefore, the transmission power is no problem when expressed in watts. The gain of the antenna can be said separately.
The millimeter wave is different. Its frequency band is high and the wavelength is small, so the antenna size is very small. An AAU can fit 768 or even 1024 antennas. Each antenna and the power amplifier unit on the back are integrated by a beamforming chip. It’s impossible to separate at all.
Therefore, millimeter-wave AAU can only test the signal strength emitted from the antenna through air propagation, it can only be expressed by EIRP. This testing method is also logically called OTA (Over The Air) testing.
3GPP's definition of base station types
Due to the difference between millimeter-wave and other frequency bands, 3GPP has long defined a series of codes to distinguish the expression and test methods of different types of base station power.
Therefore, the general meaning of this string of codes is the type of base station: 1-C, 1-H, 1-O, 2-O.
The following 1 and 2 represent different frequency bands. 1 represents FR1, which is the Sub6G frequency band, and 2 represents FR2, which is the 5G millimeter wave, frequency band. The rest is the core code of the last digit, where C stands for Conduct, which means conduction, that is, traditional RRU tests can be used to test transmit power through cable connections.
H stands for Hybrid, which means hybrid, that is, the AAU of the intermediate frequency (2600M or 3500M) can remove the antenna and test the power like an ordinary RRU, but also install the antenna to test other indicators.
O stands for Over the air or OTA, which is the millimeter-wave AAU method. Radiofrequency and antenna are inseparable, and all indicators can only be tested through air propagation (the most important is EIRP).
How big is the transmit power of millimeter-wave AAU? In fact, the transmission power of the power amplifier inside the millimeter wave is very small. The AAU of the macro station is generally about 2 watts (33dBm), plus the antenna array gain, beamforming gain, etc., the external performance EIRP (equivalent isotropic radiated power) is reached 65dBm.
However, this 2 watt cannot be tested, it cannot be reflected externally, and it is of no significance. Therefore, the transmission power of 5G millimeter wave only reflects EIRP.
What exactly is a 5G millimeter wave and why is it so important?
A high transmission rate is a key technical indicator of 5G. So how to increase the transmission rate?
The transmission rate refers to the amount of data passing through the channel per unit of time. In the communications industry, there is a formula regarding the channel transmission rate:
n=Rb/B
In this formula, n is the frequency band utilization rate, Rb is the channel transmission rate, and B is the system bandwidth. Change this formula:
Rb=n×B
There is a positive relationship between transmission rate, frequency band utilization rate, and system bandwidth. The higher the frequency band utilization rate, the higher the transmission rate; the higher the system bandwidth, the higher the transmission rate. This shows that in order to increase the channel transmission rate, there are two ways to increase the frequency band utilization rate and the system bandwidth.
What we call wireless communication is the use of wireless electromagnetic waves for communication.
Frequency is an important attribute of electromagnetic waves.
The basic principle of wireless communication is to transform the audio-visual information into an electrical signal containing the audio-visual information, and then send the electrical signal to a high-frequency oscillating signal with a much higher frequency than the signal, and then use a transmitting antenna in the form of radio waves Spread around.
Frequency is an important characteristic of electromagnetic waves. Electromagnetic waves of different frequencies have different characteristics, which means that they have different uses. Therefore, we further divide electromagnetic waves and allocate them to different objects and uses.
For example, in the 4G LTE standard, our country mainly allocates a part of UHF spectrum resources. And there is a trend, from 1G to 2G, 3G and then to 4G, the frequency of the divided radio waves is getting higher and higher. This is actually to meet the need for higher transmission rates.
The signal is transmitted in the channel. The specific transmission method is in the form of symbol (symbol) transmission.
What is the frequency band? For the channel, it is the frequency range between the highest frequency and the lowest frequency of the signal allowed to be transmitted. To improve the utilization rate of the frequency band is simply to introduce more symbols per unit of time in the channel, thereby increasing the rate.
The modulation of the signal is to form different states of the carrier by manipulating the amplitude and phase of the radio wave. When the modulation method changes from simple to multi-system, the number of carrier states increases, which means that the amount of information represented by a symbol increases.
With the increase of symbols, the amount of information represented by one symbol increases, but the amplitude of the carrier remains unchanged, then the distance between the states of each symbol becomes smaller, so it is easy to be interfered with by noise and make the symbol deviate from its original position. Cause decoding errors, and power consumption will increase at the same time.
How to increase the bandwidth of the spectrum system?
5G millimeter waves are located in the overlapping wavelength range of microwaves and far-infrared waves. In fact, it also has two spectral characteristics.
The biggest feature of millimeter waves is that the frequency is very high. In the 3GPP protocol 38.101-2 Table 5.2-1, 3 frequencies are defined for the 5G NR FR2 band, which are:
n257 (26.5GHz~29.5GHz);
n258 (24.25GHz~27.5GHz);
n260 (37GHz~40GHz);
They all use the TDD format. The US FCC recommends that 5G NR use 24-25 GHz (24.25-24.45/24.75-25.25 GHz), 32 GHz (31.8-33.4 GHz), 42 GHz (42-42.5 GHz), 48 GHz (47.2-50.2 GHz), 51 GHz (50.4-52.6GHz), 70 GHz (71-76 GHz) and 80 GHz (81-86 GHz) these frequency bands.
We take 28GHz and 60GHz frequency bands as examples. There is a principle in the communication field. The maximum signal bandwidth of wireless communication is about 5% of the carrier frequency. Therefore, the corresponding spectrum bandwidths of the two are 1GHz and 2GHz, and the 4G-LTE frequency band has the highest frequency. The carrier is around 2GHz, the spectrum bandwidth is only 100MHz, and the 5G millimeter wave bandwidth is equivalent to 10 times that of 4G. This is the reason why the 5G signal transmission rate will be greatly improved in the future.
In addition to high speed, 5G millimeter waves have many other benefits. First of all, the beam of a millimeter wave is very narrow, and the same antenna size is narrower than a microwave, so it has good directivity and can distinguish small targets closer together or observe the details of targets more clearly.
What is a beam?
In the process of space propagation, the quality of the wireless signal will be attenuated, but its energy propagation is still directional, which forms a beam. In the communications field, the angle formed by the two sides at which the fixed power begins to drop is the width of the beam.
The beam width is related to the antenna gain. The so-called antenna gain is simply understood as the ability of the antenna to concentrate energy in a certain direction. Generally, the larger the antenna gain, the narrower the beam.
What does the antenna gain have to do with it? The answer is the wavelength.
The shorter the wavelength, the greater the antenna gain, and the narrower the beam. The 5G millimeter wave has a very short wavelength, which results in its narrow wave characteristics.
According to the communication principle, the length of the antenna is proportional to the wavelength, and the ratio is about 1/10~1/4. The wavelength of the 5G millimeter wave is at the millimeter level, and the corresponding antenna is shorter. Therefore, 5G millimeter wave technology is used in mobile phones. The size can also be smaller.
Another feature of 5G millimeter waves is their high transmission quality. This is mainly due to its very high frequency, so there are basically no interference sources in 5G millimeter wave communication, the electromagnetic spectrum is extremely clean, and the channel is very stable and reliable.
In addition, the security of 5G millimeter waves is relatively high, because millimeter waves propagate in the atmosphere and are greatly attenuated by the absorption of oxygen, moisture, and rainfall. The point-to-point through distance is very short. If the distance exceeds the distance, the signal will be very weak, which increases eavesdropping. And the difficulty of interference. As mentioned earlier, the millimeter wave has a narrow beam and low sidelobes, which also makes it difficult to intercept.
5G millimeter wave can greatly increase the transmission rate of wireless communication, and there are these incidental advantages. Why hasn’t it been commercialized in the field of mobile phone communication for so many years?
The main disadvantage of 5G millimeter wave is its poor transmission performance, which is reflected in three aspects.
The first is that these spectrums do not spread far away. For example, in omnidirectional transmission, the energy of these spectrums diverges relatively quickly, tends to weaken, and cannot spread far;
The second is the poor diffraction ability, which is easily blocked, reflected, and refracted by buildings and human bodies. The wavelength of visible light is shorter than millimeter waves and the frequency is higher, so it is difficult to pass through most objects;
The third is that millimeter waves are also limited by many spatial factors. One of the main factors is the high degree of absorption of these frequency spectra by water molecules. For example, when it rains, passes through leaves, and passes through the human body, these spectra weaken very quickly.
Another reason is that it has been difficult in the past to produce sub-micron-sized integrated circuit components that can work in the millimeter-wave frequency band, requiring a relatively large investment, which hinders its commercial use.
The millimeter-wave has these shortcomings, so it was difficult to be commercially available for a long time in the past. However, with the development of communication technology, the industry now has a relatively mature method of controlling millimeter waves. There are mainly beamforming technology, Massive MIMO antenna technology, and so on.
The short millimeter wave wavelength affects the antenna gain and indirectly affects the received power.
When the transmitting power of the transmitting end and the antenna gain are fixed, the receiving power of the receiving end is proportional to the effective aperture of the antenna and inversely proportional to the square of the distance between the transmitting antenna and the receiving antenna.
Therefore, the influence of wavelength on the antenna aperture size will also indirectly affect the power. Compared with the centimeter wave or even longer wavelength bands used in the past, the millimeter wave has a shorter wavelength and serious signal attenuation, which leads to a reduction in the signal power received by the receiving antenna. The power at the receiving end is also reduced.
In this case, we need to increase the number of transmitting antennas and receiving antennas.
Massive MIMO technology is based on this idea. It also has a name called Multiple-Input Multiple-Output. It is transmitted by multiple antennas and received by multiple antennas.
In fact, the multiple-input multiple-output MIMO technology is not a new technology. The traditional TDD network can achieve multiple inputs and multiple outputs with 2 antennas, 4 antennas, or even 8 antennas. Under the 5G massive MIMO concept, the number of antennas can theoretically be hundreds of thousands. Considering various factors such as cost, it is mainly 64/128/256 at this stage.
Under the massive MIMO technology, the main advantage is naturally that good signal quality can be obtained even when the power of a single antenna is very low because there are many antennas at the same time, and the signal is superimposed with the support of beamforming technology. To meet the power requirements of the system, it also avoids the hardware cost of using a large dynamic range power amplifier.
Another important advantage is the increased communication capacity. Massive MIMO has the characteristics of beam spatial multiplexing, making full use of multipath components in spatial propagation, using multiple data channels (MIMO sub-channels) to transmit signals on the same frequency band, so that the capacity increases linearly with the increase in the number of antennas.
In a massive MIMO system, the number of base station antennas increases to form an array. In addition to the horizontal direction, beamforming, and beam steering can also be performed in the vertical direction, thereby improving the coverage of the entire space, and beamforming technology can be used to transmit the signal Focusing on one point in space allows the base station to accurately distinguish each user, thereby improving the spatial resolution capability.
In massive MIMO technology, beamforming, this technology can be said to be the basic technology of massive MIMO.
The beam of the millimeter-wave is very narrow, and when omnidirectionally transmitted, there will be signal attenuation losses of up to tens of dB, resulting in limited propagation distance.
The main idea of beamforming technology is to concentrate the scattered beams without spreading or wasting and forming a directional emission. Specifically, by adjusting the phase of each antenna, the signal can be effectively superimposed, and a stronger signal gain can be generated to overcome the loss. So that the emitted energy can be collected at the user’s location.
5G millimeter wave applications
The future application scenarios of the 5G millimeter wave may exceed imagination. The characteristics of millimeter-wave determine that it can be mainly used in large-bandwidth and high-capacity scenarios. The eMBB scenario for high-frequency bands can be used in hotspot areas with high population density and large network capacity requirements.
5G millimeter wave is very suitable for deployment in densely populated areas such as large venues such as concerts and stadiums. It can bring multi-gigabit speeds, low latency, and unlimited capacity experience, and can bring unique personalization to audiences’ experience.
The wavelength of a millimeter wave is very small, so the antenna can also be made small so that when a 5G millimeter wave is deployed in the future, there will be many micro base stations deployed on the basis of ordinary macro base stations. You may see them on the streets and indoor corners of urban areas.
In this way, a 5G millimeter-wave can better deploy applications in indoor scenes. This is its strength. It adopts 1:1 or partial co-location to achieve uplink and downlink coverage comparable to WiFi, and it can also use larger bandwidth to meet the requirements. Gigabit refers to the demand for burst rate, in short, it is to make your Internet experience better.
In addition, millimeter waves can also be used for fixed wireless broadband access services to meet the transmission needs of typical 4K and 8K TVs, and to meet the video needs of suburban residential areas. A typical scenario is to buy a CPE device at home to deploy a wireless network. You can watch ultra-high-definition video up to 8K through the TV network.
Millimeter waves can also have very important applications in the field of car networking. It can provide the higher data transmission rate and accuracy required for networked car communication while improving the resolution of radar operations to achieve more accurate driving safety assistance.
Another important application field of 5G millimeter waves is the military. In fact, the millimeter wave has already been applied in the military field. Its abundant frequency resources are not only an important means of broadband communication but also provide another effective way of anti-interference and anti-interception.
With the continuous advancement of the 5G commercial deployment process and the launch of 5G terminals in the future, millimeter waves will truly serve our daily network needs. Even the super performance of millimeter waves will give us fresh terminal equipment. The past life, entertainment, and work methods have brought about earth-shaking changes.
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