New wireless broadband technologies in the 5G era

After the arrival of the 5G era, wireless broadband technology will present the outer circle as 5G performance and the inner circle as 4G performance. Compared with 4G, 5G has improved user experience 10 times, spectrum efficiency 3 times, mobility 3 times, and can support high-speed rail (note: high-speed rail speed is 500 kilometers per hour); wireless interface delay is reduced by 90% (no more than 1 millisecond), and can support cars on highways with a speed of 200 kilometers per hour to avoid collisions; connection density is increased by 10 times, and 1 million sensors can be connected to the Internet within 1 square kilometer, supporting large-scale Internet of Things; energy efficiency is increased by 100 times, traffic density is increased by 100 times, and peak rate is increased by 30 times.

Why is the performance of 5G much higher than that of 4G?

According to Shannon's theorem, to increase network capacity, it is nothing more than increasing the number of base stations (cell density), increasing the number of antennas (space division multiplexing), increasing bandwidth (more bandwidth resources), and increasing the signal-to-noise ratio. Large-scale antennas increase the number of antennas, ultra-dense networking increases the number of base stations, full spectrum access increases bandwidth, and new multi-sub access increases the signal-to-noise ratio. Of course, there are more technologies to support the development of 5G.

[[192684]]

Multiple-Output Multiple-Input (MIMO) Antennas

We use space division and beamforming to enable one antenna to target one terminal. We have already achieved beamforming for antenna arrays and smart antennas. 64 antennas are already commercially available, 128 antennas have been used in 4G, and some companies have even achieved 256 antennas. Therefore, large-scale antennas are the most important technology to support 5G and significantly increase 5G capacity.

Full Duplex

In the past, we had time-division duplex and frequency-division duplex, but now we need full duplex, that is, same frequency and same time. A big problem with same frequency and same time is self-interference (it will interfere with itself), and the solution is to offset the crosstalk by adjusting the delay and attenuation at the sending end. This is on the analog port, and it can also be offset on the digital port. If the interference of same frequency, same time, and full duplex can be offset, the capacity can be increased by 1 times.

Ultra-dense networking

We are currently increasing the density of cells, but the user experience is often better in the center of the cell. The experience at the edge of the cell is not good. So we hope to use distributed antennas, which can solve the problem of poor experience at the edge of the cell. But at this time, there is a lot of interference between the antennas. What should we do? Test all natural interferences and cancel them out through big data analysis. In this way, in theory, as long as all interferences are canceled out, the capacity of mobile communications will be maximized (Note: Of course, it is impossible to achieve this in practice), and the capacity can usually be increased by 2 orders of magnitude.

Therefore, through high-density networking, distributed multi-antennas, etc., we can perform joint data transmission, which can turn the interference of other base stations into useful signals, thereby improving the single-user throughput and the spectrum efficiency of the system.

TDD is the main mode of 5G

In addition, 5G requires a lot of bandwidth. With such a high peak value, the bandwidth spectrum needs to be very wide, and the operating frequency needs to be 6GHz and 70GHz. It is difficult to find paired frequencies at such high frequency bands, so TDD is the main mode of 5G. We can see that TDD has advantages in antennas, services, spectrum, and networks. The uplink and downlink channels on the antenna are of the same frequency.

In addition, in terms of services, TDD can achieve asymmetric allocation of uplink and downlink, which can adapt to needs more flexibly. It is easy to arrange duplex on the spectrum. Since it is TDD, it can adapt to fragmented frequencies and can be flexibly networked. Of course, to take advantage of these advantages, some technology is needed to support it.

Originally in 4G, TDD uplink and downlink were divided into two subframes. Now, in order to reduce latency, it must be arranged in one subframe, that is, a self-contained subframe, so that low latency can be achieved.

5G requires low-frequency spectrum access

MWC2015 (World Radio Conference) adopted a frequency of 1.4-1.5GHz, and the others have not been determined yet and will be determined in 2019. In July 2016, the FCC (Federal Communications Commission) approved the 5G frequency, which operates in the 28GHz, 37GHz, 39GHz, and 64GHz to 71GHz bands. In November 2016, the European Union released the 5G frequency, the low frequency band is 3.4-3.8GHz, and the licenses used for broadcasting and current television are also used for mobile communications. The high frequency bands are 24-28GHz, 31-33GHz, and 40-43GHz. In short, 5G has expanded to the millimeter wave band.

At present, China has only arranged 3.4~3.6GHz (still very narrow, only 200M). Therefore, China's 5G frequency faces great challenges.