6G

- Dec 20, 2019-

6G

 6G, the sixth generation mobile communication standard, is also called the sixth generation mobile communication technology. The main promotion is the development of the Internet of Things. As of November 2019, 6G is still under development. 6G transmission capacity may be increased by 100 times compared to 5G, and network latency may be reduced from milliseconds to microseconds.
On November 3, 2019, the Ministry of Science and Technology, together with the Development and Reform Commission, the Ministry of Education, the Ministry of Industry and Information Technology, the Chinese Academy of Sciences, and the Natural Science Foundation of China organized a 6G technology research and development work in Beijing.

6G

basic concepts
6G, the sixth generation mobile communication standard, is a conceptual wireless network mobile communication technology, also known as the sixth generation mobile communication technology. The main promotion is the development of the Internet.
The 6G network will be a fully connected world with terrestrial wireless and satellite communications integrated. By integrating satellite communications into 6G mobile communications and achieving seamless global coverage, network signals can reach any remote village, allowing patients in deep mountain areas to receive telemedicine and children to receive distance education. In addition, with the global satellite positioning system, telecommunication satellite system, earth image satellite system and 6G ground network, the full coverage of ground and air can also help humans predict the weather and quickly respond to natural disasters. This is the future of 6G. 6G communication technology is no longer a breakthrough in simple network capacity and transmission rate. It is also to narrow the digital divide and achieve the "ultimate goal" of interconnecting everything. This is the significance of 6G.

Related technologies
Terahertz
6G will use the terahertz (THz) frequency band, and the "densification" of 6G networks will reach an unprecedented level. By then, our surroundings will be full of small base stations. The terahertz band refers to 100GHz-10THz, which is a frequency band much higher than 5G. From communication 1G (0.9GHz) to 4G (above 1.8GHZ), the frequency of the wireless electromagnetic waves we use is increasing. Because the higher the frequency, the larger the allowed bandwidth range, and the larger the amount of data that can be transferred per unit time, which is what we usually call "the network speed has become faster." However, another main reason for the development of frequency bands is that low-band resources are limited. Just like a highway, even if it is wide, there is a limit to the number of cars that can be accommodated. When the road is not enough, the vehicle will be blocked and unable to move freely. At this time, it is necessary to consider developing another road. The same is true for spectrum resources. With the increase in the number of users and the number of smart devices, the limited spectrum bandwidth needs to serve more terminals, which will cause the service quality of each terminal to deteriorate severely. The feasible method to solve this problem is to develop new communication frequency bands and expand the communication bandwidth. The 4G main frequency bands of the three major operators in China are located in a part of the frequency band between 1.8GHz-2.7GHz, and the mainstream frequency band of 5G defined by the International Telecommunications Standards Organization is 3GHz-6GHz, which belongs to the millimeter wave frequency band. At 6G, it will enter the higher frequency terahertz band, and at this time will also enter the sub-millimeter wave band. "The terahertz is called sub-millimeter in astronomy," said Gou Lijun, a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences. "The stations of such observatories are generally very high and very dry, such as Antarctica and Chile's acatama desert." Then, When it comes to the "densification" of the network in the 6G era, we will be surrounded by small base stations? This involves the coverage of the base station, that is, the transmission distance of the base station signal. Generally speaking, there are many factors that affect the coverage of the base station, such as the frequency of the signal, the transmit power of the base station, the height of the base station, and the height of the mobile terminal. In terms of the frequency of the signal, the higher the frequency, the shorter the wavelength, so the signal's diffraction ability (also called diffraction, when an obstacle is encountered during the propagation of electromagnetic waves, when the size of this obstacle is close to the wavelength of the electromagnetic wave, the electromagnetic wave can Diffraction from the edge of the object. Diffraction can help shade diffraction can help cover the shadow area), the worse the loss, the greater the loss. And this loss will increase with the increase of the transmission distance, and the range covered by the base station will decrease accordingly. The frequency of the 6G signal is already in the terahertz level, and this frequency is close to the spectrum of the molecular rotation energy level, and it is easily absorbed by water molecules in the air, so the distance traveled in space is not as far as the 5G signal, so 6G needs more base stations to "relay." The frequency band used by 5G is higher than 4G. Without considering other factors, the coverage of 5G base stations is naturally smaller than that of 4G. With the higher frequency band of 6G, the coverage of base stations will be smaller. Therefore, the density of 5G base stations is much higher than that of 4G. In the 6G era, the density of base stations will not increase.

Spatial multiplexing
6G will use "spatial multiplexing technology", 6G base stations will be able to access hundreds or even thousands of wireless connections at the same time, and its capacity will reach 1000 times that of 5G base stations. I mentioned earlier that 6G will use the terahertz band, although this high-band frequency resource is abundant and the system capacity is large. However, mobile communication systems using high-frequency carriers face the severe challenges of improving coverage and reducing interference.
When the frequency of a signal exceeds 10 GHz, its main propagation mode is no longer diffraction. For non-line-of-sight propagation links, reflection and scattering are the main signal propagation methods. At the same time, the higher the frequency, the greater the propagation loss, the shorter the coverage distance, and the weaker the diffraction ability. These factors will greatly increase the difficulty of signal coverage. Not only 6G, but also 5G in the millimeter wave band. 5G uses Massive MIMO and beamforming to solve these problems. Our mobile phone signal is connected to the operator's base station, more accurately, the antenna on the base station. Massive MIMO technology is very simple to say, it is actually to increase the number of transmitting antennas and receiving antennas, that is, to design a multi-antenna array to compensate the losses on the high-frequency path. With the configuration of multiple MIMO antennas, the amount of data to be transmitted can be increased, and the spatial multiplexing technology is used. At the transmitting end, the high-rate data stream is divided into multiple lower-rate sub-data streams, and different sub-data streams are transmitted on the same frequency band on different transmit antennas. Since the spatial subchannels between the antenna arrays at the transmitting end and the receiving end are sufficiently different, the receiver can distinguish these parallel sub-data streams without paying extra frequency or time resources. The advantage of this technology is that it can increase channel capacity and increase spectrum utilization without consuming additional bandwidth and consuming additional transmit power. However, MIMO's multi-antenna array concentrates most of the transmitted energy in a very narrow area. That is, the larger the number of antennas, the narrower the beam width. The advantage of this is that there will be less interference between different beams and between different users, because different beams have their own focus areas, these areas are very small, and there is not much intersection between each other. But it also brings another problem: the narrow beam emitted by the base station is not 360-degree omnidirectional, how to ensure that the beam can cover users in any direction around the base station? At this time, it's time for beamforming technology to show its magic. To put it simply, beamforming technology uses complex algorithms to manage and control the beam to make it look like a "spotlight." These "spotlights" can find out where the phones are all gathered, and then cover the signal with more focus. 5G uses MIMO technology to improve spectrum utilization. 6G is in a higher frequency band, and further development of MIMO in the future is likely to provide key technical support for 6G

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