5G technology competition, millimeter wave and Sub-6

　　The competition of 5G technology routes is essentially a competition of frequency bands. At present, the world uses two different frequency bands to deploy 5G networks. The frequency band between 30-300GHz is called millimeter wave; the other is concentrated in the 3GHz-4GHz frequency band, called Sub-6.

　　Due to the physical characteristics of radio waves, the short wavelength and narrow beam characteristics of millimeter waves enhance signal resolution, transmission security and transmission speed, but the transmission distance is greatly reduced.

　　According to Google's 5G coverage test for the same range and the same number of base stations, the 5G network deployed with millimeter waves can cover 11.6% of the population at a rate of 100Mbps and 3.9% of the population at a rate of 1Gbps; while the 5G network using the Sub-6 frequency band can cover 57.4% of the population at a rate of 100Mbps and 21.2% of the population at a rate of 1Gbps.

　　It can be seen that the coverage of 5G networks operated under Sub-6 is more than 5 times that of millimeter waves. In addition, to build millimeter wave base stations, about 13 million base stations need to be installed on utility poles, which will cost $400 billion, so as to ensure a coverage rate of 72% at a speed of 100 Mbps per second in the 28GHz band and a coverage rate of about 55% at a speed of 1Gbps per second. Sub-6 only needs to install 5G base stations on the original 4G base stations, which greatly saves deployment costs.

　　In the commercial scope, from coverage to cost, Sub-6 is superior to millimeter waves in the short term.

　　However, the reasons are as follows: 1. The spectrum resources are rich, the carrier bandwidth can reach 400MHz/800MHz, and the wireless transmission rate can reach more than 10Gbps; 2. The millimeter wave beam is narrow, has good directivity, and has extremely high spatial resolution; 3. The size of millimeter wave components is small, which is easier to miniaturize than Sub-6GHz devices; 4. The subcarrier interval is large, and the single SLOT cycle (120KHz) is 1/4 of the low-frequency Sub-6GHz (30KHz), and the air interface delay is reduced. In the application of private networks, the advantage of millimeter waves is almost crushing Sub-6.

　　At present, the vehicle-to-ground communication private network realized by millimeter wave communication in the rail transit industry can achieve a transmission rate of 2.5Gbps under high-speed dynamic conditions, and the transmission delay is 0.2ms, which has a very high value for private network promotion.

　　For private networks, such as rail transit, public security monitoring and other scenarios, the technical advantages of millimeter waves can be fully utilized to achieve true 5G speed.