Shulou(Shulou.com)11/24 Report--

With a shrill roar, a behemoth in the shape of a giant bird galloped along the runway and soared into the air for 90,000 miles.

Every day, there are countless such behemoths, carrying the "essence of the universe, the primate of all things", soaring ten thousand meters above the sky.

But these passengers are in anxiety all the time. That is because the mobile phone, the window through which they communicate with the world, can only be in flight mode, from tightly connected networks to silent islands.

Please look at their inner monologues:

"I was supposed to have a meeting with the client, but it had to be postponed."

"how much I want to show my girlfriend the beautiful scenery overlooking the window …... let's take some pictures!"

"I wish I could play games in these boring hours, but without the Internet, I couldn't connect to the server!"

These strong needs are calling for a good friend we have long been accustomed to: 5G, you hurry up to heaven!

In fact, the global coverage of communications satellites has already turned the 10,000-meter high-altitude Internet surfing into a reality, but due to the small bandwidth and high cost, it naturally leads to a high price. Therefore, except for a few business people who have experienced it, most people choose to be patient.

This gives room for another way of thinking to expand. That is: aren't there many 5G base stations on the ground? If the signal can be sent to the sky and the mobile phone can receive the signal on the plane, won't it be able to surf the Internet normally?

Sounds like a good idea! But when you think about it, there seems to be a lot of problems.

1. How far can the base station send the signal? Generally speaking, in dense urban areas, the coverage of base stations is only a few hundred meters, and a few kilometers in remote areas will come to an end. at first glance, it does not seem to have the ability to cover ten thousand meters in the air.

In fact, when building a 5G network, how many base stations are needed first need to carry out network planning. Network regulations are mainly considered from two aspects: capacity and coverage.

The so-called capacity is to serve an area to meet everyone's Internet needs, how many base stations are needed. Since the capacity of each base station is certain, it is necessary to calculate the number of base stations from the dimension of capacity. To cover a big city normally, tens of thousands of ground base stations may be needed.

The so-called coverage is the maximum distance that the signal emitted by the base station can be received by your mobile phone after experiencing space propagation loss, various trees blocking, obstacle reflection and refraction, and the signal transmitted by the mobile phone can also be successfully received by the base station.

Generally speaking, the base station is a behemoth relative to the mobile phone, and the transmission power of the signal is much stronger than that of the mobile phone, so it can be transmitted very far in theory.

For example, the TV tower used in many cities is actually equivalent to a super-large base station. Because of its high power and high height, one tower can cover the whole city.

If the antenna of the base station is aimed at the sky to transmit the signal, because there is no occlusion, the propagation loss is relatively small, and the propagation range of the signal will be wider. This is pure line-of-sight straight line propagation.

Moreover, because the airplanes in the sky are relatively sparse, the number of passengers is small, and fewer people surf the Internet at the same time, when covering the sky, the first consideration is coverage rather than capacity.

As shown in the following figure, the sky coverage radius of the base station is obtained by making a tangent to the earth from the height of the base station and extending the line until it is the same as the cruising altitude of the aircraft in the sky: d=d1+d2.

If the cruising altitude of the aircraft is 12000 meters, the coverage radius of a ground-to-air base station can theoretically reach 400km. Taking into account some margin, more than a dozen base stations can cover a route, covering only a few hundred stations across the country.

However, there are still problems to consider, the base station can transmit the signal so far, but the mobile phone is only more than 100 grams, weak chicken, can it receive the signal from the base station hundreds of kilometers away?

Moreover, the communication is two-way, downlink is important, uplink is also very critical. The transmission power of the 5G mobile phone is only 0.4 watts at most. Can the signal travel hundreds of kilometers to the base station?

This leads to the following question.

2. Can the mobile phone receive a signal from the base station on the ground at an altitude of 10,000 meters? Actually, it doesn't work. Not only can the mobile phone not receive the signal from the base station on the plane, but also the signal sent by the base station is impossible to receive.

What are we going to do? Let the plane collect and distribute it.

By retrofitting the aircraft and installing a high-gain professional antenna on its belly, it can communicate with base stations hundreds of kilometers away.

After receiving the signal from the base station, the plane converts the 5G signal into wifi signal through a device called CPE (Customer Premises Equipment), so that all passengers can connect to wifi to surf the Internet.

Finally, the uplink data of all users are converged on the CPE, and then converted into 5G signals, which are sent through the airborne antenna and received and processed by the base station on the ground, thus achieving a closed loop of bit life.

3. Will there be the influence of Doppler shift when the plane is flying so fast? I will. But it can be corrected by frequency offset compensation.

The so-called Doppler effect means that when the aircraft flies towards the base station at high speed, the frequency of the signal will be positive offset and higher and higher, while when the aircraft leaves the base station, the frequency of the signal will become lower and lower because of the negative offset.

According to research, if the 4.9GHz spectrum is used, the frequency offset will reach 5MHz at the aircraft speed of 1200km / h, and the system can work normally only after the special correction algorithm of the base station and CPE is used.

To sum up, through a series of ground-to-air coverage technologies, we can make the ground base stations cover the sky and make it possible to enjoy 5G at an altitude of 10,000 meters.

The aforementioned 5G requirements such as teleconferencing, HD video, and even cloud games can be carried out smoothly, making the otherwise monotonous and anxious journey more convenient and enjoyable.

This article comes from the official account of Wechat: wireless Deep Sea (ID:wuxian_shenhai), author: mayfly acquisition

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.