Internet of Things Communications: Large-Scale Antenna Array 5G Technology

As we all know, wireless communications rely on the spread of electromagnetic waves, the most precious resource than the band. In order to prevent the mutual interference of the mobile communication network, the radio television, the broadcasting, the military band and so on, each country makes a strict division of the use of the radio frequency band. According to the electromagnetic wave propagation characteristics in the air, 6G below the band because of its low attenuation in the air, penetration and other advantages, is considered a good band of resources, many rely on radio applications are concentrated in this band resources, so Very crowded.

In the face of strong demand, how to meet the needs of the lowest rate in the era of technological outbursts and set up a high-speed information pipeline for the society due to the shortage of resources? The "5G" is giving an answer. 5G (Fifth Generation), the fifth generation of wireless communication system, is another peak that communicators are climbing after they have gone through analog communications, second generation, third generation and the fourth generation LTE systems undergoing.

A system of innovation, which will contain innumerable innovations, 5G is also true. In 5G large-scale antenna array of key technologies, its application not only can greatly enhance the network capacity and user experience, but also will have a profound impact on the communications industry, 1 minute to download a high-definition movie era has been away from us It's

1, large-scale antenna array

Large-scale antenna array is based on the principle of multi-user beamforming, the arrangement of hundreds of antennas at the base station side, dozens of target receiver modulation their respective beams, through the spatial signal isolation, the same frequency resources at the same time the transmission of dozens of signal. This full exploitation of space resources can effectively utilize valuable and scarce band resources and increase network capacity several times.

2, why large-scale antenna array can shake the bottom of communication?

Large-scale antennas do not simply expand the number of antennas, as they can cause qualitative changes. According to the theorem of large numbers and the central limit theorem, the number of samples tended to be infinite, the mean tended to be expected, and the mean distribution of independent random variables tended to be normally distributed. Stochastic variables tend to be stable, which is the "big" beauty. In a single antenna to single antenna transmission system, due to the complexity of the environment, electromagnetic waves may propagate in the air through multiple paths and may weaken each other at reception points in opposite phases. In this case, the channel is likely to fall into a strong decline, affecting User received signal quality. When the number of base station antennas increases, hundreds of antennas with respect to the user's hundreds of antennas have their own channels, and their probability of falling into fading is greatly reduced, which is simple and easy for the communication system to handle .

3, What are the benefits of large-scale antenna?

First, of course, is to significantly increase network capacity.

Second, because there are a bunch of antennas at the same time, the signal superposition gain due to the wave shaping will allow each antenna to transmit at low power, avoiding the need for expensive, large dynamic range power amplifiers and reducing hardware costs.

Third, the flat fading channel created by the law of large numbers makes low-latency communication possible. In order to combat the deep channel fading, traditional communication systems need to use channel coding and interleaver to disperse continuous burst errors caused by deep fading into different time periods (the purpose of the interleaver is to mix different signals in different time periods, thus Scattered a short period of time continuous error), and this mixing process led to the receiver to fully accept all the data in order to obtain information, resulting in delay. Under a large-scale antenna, the fading due to the large number theorem disappears and the channel becomes good. The process of counteracting the deep weakening can be greatly simplified, so the delay can be drastically reduced. A perfect match for large-scale antennas is another key 5G technology - millimeter-wave. Millimeter-wave has a wealth of bandwidth, but strong attenuation, and large-scale antenna beamform just make up its short board.

4, the bottleneck problem to be solved

First of all, want to exert the potentiality of all aerials, the base station end needs accurate channel information, the visual understanding needs to know the position of different target customers in advance. How to accurately tell each antenna to this channel information with users is a tricky thing. Traditional mobile communication systems, which monitor the pilots (pilots, ie, a sequence of bits commonly known to base stations and handsets) sent by base stations via mobile phones, evaluate their channels and feed back to base stations are not feasible in large-scale antennas because of the large number of base station antennas , The uplink resources consumed by the handset when feeding back to the base station are too large. At present, the most feasible scheme is channel symmetry of uplink and downlink based on time division duplexing (TDD), that is, transmitting a pilot to a base station by a mobile phone, monitoring an uplink at a base station side, inferring from a base station to Handset downlink information. In order to obtain the uplink information, the mobile terminal needs to send pilots to the base station. However, the number of pilots is always limited, which inevitably needs to be reused in different cells, thereby causing pilot interference. Theoretical deduction shows that pilot interference is the ultimate barrier to limit large-scale aerials. In addition, many large-scale antenna beamforming algorithms are based on matrix inversion operations, whose complexity rapidly increases with the number of antennas and the number of users simultaneously serving them. As a result, the hardware can not complete the beamforming algorithm in real time. Fast matrix inversion algorithm is a way to overcome this problem.