If the sub 6GHz 5g network is compared to the expansion of a single lane highway in an old city, millimeter wave 5g is equivalent to the construction of a new four to eight lane highway in a new city.    

Compared with sub 6GHz, millimeter wave not only has the advantages of large bandwidth, high capacity and low delay, but also because it is in the ultra-high frequency band, it is like an uncultivated virgin land and unpolluted pure land for the mobile industry, which can be used freely without worrying about wireless interference.    

Millimeter wave was once considered as the most valuable and potential spectrum resource in 5g era. However, at present, while the global sub 6GHz 5g is developing rapidly, the development of millimeter wave 5g is quite slow, and even falls into the embarrassing situation of "dilemma".
         
   

     

             
     

However, although the construction of 3.5GHz 5g network in South Korea is in full swing, the construction of 28ghz 5g is very slow. As of March 2021, the three major operators in South Korea have built only 91 28ghz 5g base stations, which is far from the original plan.      

   

South Korean regulators have repeatedly called on operators to speed up the construction of millimeter wave 5g, and even warned that if the set target can not be completed by the end of 2021, the 28ghz band will be recovered. However, the response of South Korean operators is only helpless. Operators said that the millimeter wave service mode is not clear, the maturity of technology and equipment is not high, and the coverage capacity is only 10% - 15% of 3.5GHz. A very dense base station needs to be deployed. The network investment cost increases exponentially compared with 3.5GHz. It is not suitable for building a national network and can only be used for hot spot areas and 5g private network deployment.

     

             
     

Korean operators also said that for the construction of 28ghz 5g, it is absolutely unnecessary for South Korea to compete with the United States because the penetration rate of optical fiber broadband in the United States is low. They hope to use 5g millimeter wave fixed wireless to replace optical fiber to enter the home. However, South Korea has high penetration rate of optical fiber broadband, and the millimeter wave band will be mainly used for mobile services and enterprise private networks, but for mobile services for consumers, A large number of base stations need to be deployed, and the network deployment cost is too high. For the 2B private network in the vertical industry, the current business model is not mature.      

   

Since the deployment cost of millimeter wave 5g network is too high and operators are unwilling to invest, let the three operators build and share. In view of the slow deployment progress of millimeter wave 5g, the Korean industry has put forward such suggestions.    

But the problem comes again. On the one hand, if the three operators jointly build and share the millimeter wave 5g public network, because the millimeter wave wireless coverage is too small, the communication interruption is easy to occur when the terminal moves from the network area of one operator to the area of another operator; On the other hand, 5g private network is the focus of competition among operators in 2B field in the future, and it is difficult for operators to reach co construction, sharing and cooperation.    

South Korea is not an example. The United States commercialized 5g millimeter wave as early as 2019. According to the latest test data of market research company opensignal, the availability of its 5g millimeter wave network is less than 1%. According to statistics, as of January 2021, only 8 operators in the world have provided 5g millimeter wave services. These data show the slow development of 5g millimeter wave in the world.    

2、What happened to 5g millimeter wave? Why is development so slow? Let's use a table to illustrate.      
         
   

Millimeter wave has the advantages of large bandwidth and high capacity. However, due to its high frequency, short wavelength, large free space propagation loss, penetration loss and diffraction loss, the coverage of a single cell is very small. The actual measurement shows that even if the terminal is in the Los environment, the coverage of the millimeter wave cell is only about 100 meters, almost the same as that of Wi Fi. Compared with sub 6GHz, the worse the millimeter wave diffraction ability, the worse the penetration ability, and it is difficult to penetrate obstacles such as walls, doors and room furniture. Therefore, in places with dense buildings in urban areas, operators need to build more base stations and ensure that the base stations and terminals are in line of sight state in order to achieve stable and high-speed communication.

     

     

Even if 5g private networks are deployed point by point for 2B scenarios, on the one hand, more base stations need to be built for larger parks and large factories; On the other hand, due to various obstacles such as walls, doors and equipment in indoor places such as factories, office buildings and hospitals, it is also necessary to deploy more base stations at multiple points to ensure that the line of sight environment between the terminal and the base station is maintained to maintain high-speed and stable communication, which will bring higher network deployment costs.

The solution is to improve the coverage through massive MIMO beamforming, but this will increase the number of antenna units, power amplifiers, low-noise amplifiers and other devices, and the cost of equipment will also increase. In addition, the coverage of millimeter wave can also be expanded by installing repeaters and reflective plates.    

Base station unit price    

Compared with sub 6GHz, millimeter wave not only needs to build more base stations, but also the bigger problem is that the unit price of millimeter wave base stations is about 30% to 40% higher than that of sub 6GHz.    

The main reasons are:
1) Most operators in the world deploy 5g network through sub 6GHz, which has scale advantages, while there are few millimeter wave base stations in the world, and the unit price is higher;
2) The Du and Ru of the sub 6GHz base station are separated, and the Du can be deployed centrally, while the Ru and Du of the millimeter wave base station are set together, so the price is more expensive;
3) There are internal architecture differences between the millimeter wave base station and the sub 6GHz base station (for example, there are more antenna units in the millimeter wave base station).    

Terminal ecology    

For sub 6GHz terminal ecology, there are more and more types of smart phones, 5g CPE and 5g modules, and the terminal ecology is growing, but the millimeter wave terminal ecology is still in a very early stage, especially in the 2B field. Meanwhile, global terminal chip manufacturers are more optimistic about the sub 6GHz ecology and will not develop a modem using millimeter wave alone, which means that there will be no 5g private network using millimeter wave independently.    

Construction and operating costs    

As mentioned earlier, if you use millimeter wave to build 5g public network, you need to deploy dense base stations, and the construction and operation costs increase exponentially compared with sub 6GHz. What if you use millimeter wave to deploy 5g private network? At present, one of the biggest obstacles to the development of 5g 2B private network is that its cost is higher than Wi Fi, and the cost of deploying 5g private network with millimeter wave is higher than that with sub 6GHz. Obviously, this further increases the threshold for enterprise 5g private network deployment.