Smart antennas help make 5G affordable (part 1)

In the future, the cellular industry will inevitably have to move to a new standard. Sooner or later, but the capacity of 4G networks will be insufficient. It's unavoidable. But one of the factors that can significantly accelerate the introduction of some abstract technology 5G, is the narrowness of the available radio frequency range. Available for commercial use, of course. The solution to the problem can be a transition to another part of the radio frequency spectrum - the millimeter range. We want to tell about the translation of one article about what prevents us from doing it now and what will help in the future.

Nearly urgent problem

The brutal shortage of frequencies available to cellular operators, forcing them to spend huge amounts of money on the acquisition of rights to use. Sometimes you even have to take steps such as absorbing competitors in order to get a piece of the radio frequency band that belongs to them. Such an unhealthy situation has developed because the industry throughout its 40-year existence relied solely on the UHF , 300 MHz-3 GHz. But it occupies only about 1% of the entire regulated frequency spectrum. Radio engineers have always considered it the most suitable for mobile networks. The wavelengths in this range are short enough so that small antennas can be dispensed with. But at the same time, the wavelength is still enough to bend and pass through obstacles such as buildings and vegetation. Even with a small radiation power, the decimeter range allows communication at a distance of several kilometers in almost any radio environment, at least in the megalopolis, even in the fields.

The problem is that the decimeter range is already not enough, regardless of how much the operators are willing to pay. The use of smartphones and tablets has increased many times, people are actively using the Internet on them, watching streaming video, sharing photos on the fly - today more information is transmitted “over the air” than ever before. Worldwide mobile traffic almost doubles every year, according to reports from Cisco and Ericsson , and this exponential growth will continue in the foreseeable future . By 2020, the average mobile user will download about 1 terabyte per year.

Various groups developing wireless standards have developed various recommendations for increasing the capacity of LTE networks . Here and the use of multiple antennas, and reducing the size of cells, and "smart" interaction between devices. But none of these solutions will allow to cope with the growth of traffic over the next 4-6 years. Industry representatives believe that 5G technology will be in demand by the end of this decade. And in order to deploy new networks, operators need to get new ranges. Just where to get them?
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Millimeters

The millimeter range lies in the range from 30 to 300 GHz. However, for our conditions, most of the adjacent centimeter range, 10-30 GHz, can also be attributed to it, because its waves go around obstacles in much the same way as millimeter ones. In most cases, government regulators can allocate a segment up to 100 GHz wide . This is more than 100 times the width of the range allocated today for the needs of cellular communication. That is, theoretically, operators will be able to increase the capacity by 100 times in comparison with LTE networks.

If it seems to you that all this sounds too good to be true, then you are not alone. Until very recently, most experts would say the same thing. Operators have always rejected the possibility of using the millimeter range, because the necessary equipment for this was too expensive. It is also widely believed that millimeter waves propagate worse under building conditions, are absorbed or dispersed by the atmosphere, raindrops and vegetation, and also cannot penetrate inside the premises.

However, all these ideas are now quickly refuted.

Story

The new millimeter technology for mobile communications has a long and interesting history. In 1895, a year before Guglielmo Marconi demonstrated his telegraph apparatus, the Hindu encyclopedist Jagdish Chandra Bose unveiled the world's first signal device on millimeter waves. Using a spark transmitter, he sent a signal at a frequency of 60 GHz to a funnel-shaped horn antenna with a detector located 23 meters through three walls and the body of the local governor. As a confirmation of the received signal, a simple device rang the bell, fired a gun and blew up a small mine.

However, the invention of Boche went beyond the walls of the laboratory only more than 50 years later. The first to use millimeter devices were the military and radio astronomers, who adapted them for radar and radio telescopes, respectively. A few decades later, automakers came up using millimeter frequencies to create cruise control and collision warning systems.

During the dotcom boom, millimeter-wave projects to create local area networks were pompously launched. For these purposes, many governments have allocated or put up huge frequency bands for auction. But the finished products came out with difficulty. Manufacturers quickly realized that millimeter RF circuits and antennas were very expensive. The semiconductor industry simply had no incentive to produce commercial devices fast enough to operate at such frequencies. So for about 20 years the millimeter range remained unclaimed.

Our days

But now the situation is changing. Thanks to Moore's law and the growing popularity of all options based on radar technology for expensive cars, today you can pack a ready-made millimeter radio in CMOS or silicon-germanium chip . So the price of millimeter devices is rapidly falling. Many high-end smartphones, televisions, and gaming laptops today contain wireless chipsets that work according to two competing standards: Wireless High Definition ( WirelessHD ) and Wireless Gigabit ( WiGig ).

These technologies are not intended to communicate, for example, a smartphone with a base station. They provide the transmission of large amounts of data, like uncompressed video, over short distances without uncomfortable Ethernet or HDMI cables. Both standards operate at frequencies around 60 GHz, in the 5-7 GHz wide band, depending on the requirements of a particular country. Such frequency bands are much wider than the fastest Wi-Fi networks and can provide bandwidth up to 7 Gbps.

Manufacturers of equipment for cellular networks also began to realize the advantages of ultra-wide bands in the millimeter range. Some have already begun to use millimeter components to provide high-speed communication at a direct line of sight between base stations and backbone networks, saving on the use of optical fiber.

However, experiments on the creation of cellular communications based on the new range are still underway. Below is a prototype network from Samsung. It includes an array of 64 antennas the size of a tablet, a phased antenna array, directing the signal to the desired point. Analog data is digitized, which allows fine-grained control of array segments and the use of spatial multiplexing (MIMO). The operator can choose whether to send data to several devices at the same time or concentrate the beam on a single device, increasing the download speed.



Despite the obvious progress in the introduction of millimeter devices, many experts are still skeptical about the idea that this range can provide a stable cellular connection. The main complaint is the impossibility of high-quality coverage, especially in conditions of dense development, because it is impossible to provide constant direct visibility between the base station and all end devices. If, for example, a user with a smartphone gets behind a tree or enters a staircase, then millimeter waves will probably not be able to break through these obstacles.

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Continuation of the material, read the next post. It will deal with a number of experiments to test the range and stability of communication in the millimeter range, the existing developments and future prospects of this technology.