# How far can 5G base station signals be transmitted?

With the accelerated construction of 5G, there are more and more 5G base stations on the ground. If the 5G signal on the ground can be transmitted to the sky, will the mobile phone be able to receive the signal on the plane and then be able to call the Internet normally?

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 end. It doesn't look like it has the ability to cover 10,000 meters. When building a 5G network, how many base stations are needed in the end requires network planning first. Network planning is mainly considered from two aspects: capacity and coverage.

### 1. What is 5G capacity?

The so-called capacity is how many base stations are needed to serve an area and satisfy everyone's Internet needs. Since the capacity of each base station is fixed, the number of base stations must be calculated from the dimension of capacity. To cover a large city normally, the required ground base stations may have to be tens of thousands.

### 2. What is 5G coverage?

The so-called coverage is the maximum distance that the signal transmitted by the base station has experienced spatial propagation loss, blocked by various trees, and reflected and refracted by obstacles, and finally can be received by your mobile phone, and the signal transmitted by the mobile phone can also be successfully received by the base station.

Generally, the base station is a giant compared to the mobile phone, and the signal transmission power is much stronger than that of the mobile phone, so theoretically, it can transmit very far. For example, the TV towers in use in many cities are actually equivalent to an oversized base station. Due to the large power and high height, one tower can cover the entire city.

If the antenna of the base station is aimed at the sky to transmit the signal without any obstruction, the propagation loss is relatively small, and the signal propagation range will be wider. This is pure line-of-sight propagation. And the planes in the sky are relatively sparse, the number of passengers is not many, and there are fewer people going online at the same time, so when the sky is covered, what needs to be considered is the coverage rather than the capacity.

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

If the cruising altitude of the aircraft is 12,000 meters, the coverage radius of a ground-to-air base station can theoretically reach 400 kilometers. Considering some margins, more than a dozen base stations can cover one route, and only a few hundred sites are needed to cover the whole country.

There is still a problem to consider. The base station can transmit the signal so far, but the mobile phone only has more than 100 grams, and the receiving ability is very weak. Can it receive signals from the base station hundreds of kilometers away? Communication is two-way, the downlink is important, and the uplink is also very critical. The transmit power of a 5G mobile phone is 0.4 watts at most. Can the signal sent from it travel hundreds of kilometers to reach the base station?

Actually it won't work. Not only can the mobile phone not receive the signal from the base station on the plane, it is also impossible to receive the signal sent by the base station.

If you want to send and receive information smoothly on the plane, you need to modify the plane and install a high-gain antenna on the abdomen, so that you can communicate with each other from base stations hundreds of kilometers away.

After the aircraft receives the signal from the base station, it uses the CPE equipment to convert the 5G signal to a WiFi signal, so that all passengers can connect to the WiFi Internet. The user's uplink data is aggregated on the CPE, and then converted into a 5G signal, sent out through the airborne antenna, and received and processed by the base station on the ground, achieving a closed loop of bit life.

If you want to enjoy 5G at an altitude of 10,000 meters, a series of air coverage technologies are needed to allow ground base stations to cover the sky. The development of 5G itself is a process of long-term evolution. I believe that in the future 5G will truly serve our daily network needs, and even spawn more fresh terminal equipment. Our lifestyle, entertainment and work methods will undergo earth-shaking changes.