The biggest feature of mmWave is that it is rich in frequency band resources. Compared with the Sub-6 frequency band, it can only allocate resources at 5MHz, 10MHz and 20MHz, mmWave can easily allocate bandwidth resources of more than 100MHz, and even reach 400MHz or 800MHz. Based on such abundant frequency bandwidth resources, the wireless transmission speed of mmWave 5G can easily exceed Sub-6 by several times.
In addition to high speed, the large bandwidth of mmWave can also bring lower air interface delay, which is conducive to the deployment of highly reliable and low-latency services. mmWaves have high frequencies and short wavelengths, so the size of the antenna is smaller (antenna size is proportional to wavelength). Under the same volume, more antennas can be integrated, narrower beams can be formed, and very high spatial resolution. mmWaves also support centimeter-level positioning, especially in indoor environments, which is very useful. mmWave has very obvious advantages and also has obvious disadvantages, that is, the coverage capability. mmWave coverage is truly poor. The working frequency is high and the diffraction ability is poor. Under the same conditions, the penetration loss is also high, and the signal is easily blocked by occlusion.
According to test data, the loss of concrete walls to mmWaves may be as high as 60 to 109 dB. This means that mmWaves hardly have the ability to penetrate walls. It is almost impossible to cover indoors through outdoor macro stations. Glass is also the enemy of mmWaves, which will bring significant losses. Even people or trees can have a significant impact on mmWaves. Therefore, how to reasonably deploy mmWaves and how to improve the coverage of mmWaves are the prerequisites for the successful commercialization of mmWaves.
At present, the main methods and ideas for improving mmWave coverage include:
1. Directly increase the transmit power, such as EIRS (equivalent isotropic radiated power), thereby improving the coverage.
2. Use array antennas (an inevitable choice for mmWaves), and make reasonable use of beamforming and beam management. Wide beams are suitable for increasing the coverage area, and narrow beams are suitable for increasing the coverage distance. The two are balanced.
3. Introduce constant dielectric constant lens antenna (such as Lunbo lens antenna) to obtain higher antenna gain.
4. Use reflector and other devices to reduce coverage blind spots by increasing the reflection path.
5. Introduce new material technologies such as silicon carbide and gallium nitride to increase power and performance.
6. High-frequency and low-frequency mixed networking is used to make up for the weakness of high-frequency coverage, and at the same time, take advantage of high-frequency and large traffic.
7. Adopt MTRP, IAB and other technologies to optimize link routing, improve signal coverage and enhance signal.