These days, the news about satellite phones is on fire again.
According to media reports, Huawei’s Mate 50 series, which will be released on September 6, will have “satellite communication capabilities” that will allow it to send emergency text messages via a satellite system in places where there is no network.
It’s no coincidence that other gossips claim that Apple’s iPhone 13 has the hardware to connect to satellites. However, Apple and the carrier did not agree on a way to work together, so it was not made public. In the future, in iPhone 14, this feature is likely to be implemented.
The implication is that both Huawei and Apple are working on “satellite communications”. It seems that a new “track” has emerged.
So, is this really the case? Is the satellite era of cell phones really starting?
Today’s article, Xiaozao Jun will give you an in-depth interpretation.
Communication frequency problem:
In recent years, the news about satellite communication has always been a hot spot of concern for the media and the public.
Especially after Musk got it, there is news for three days, the hype about the threat of satellite communication to ground cellular mobile communication and the threat to 5G.
In fact, much of this hype lacks basic communications and common sense, and in addition to exposing some people’s eagerness for quick profits, is mainly to serve traffic and capital operations.
Satellite communications, now and in the future (at least 50 years), are unlikely to replace terrestrial mobile communications as the primary means of human communication.
Next, let me explain why –
First, it is important to understand and keep in mind that any wireless communication system is based on wireless electromagnetic waves for communication.
In wireless electromagnetic waves, there is an important property parameter, that is, the frequency.
Wireless electromagnetic waves with different frequencies have different characteristics, as shown in the following figure.
From a macroscopic point of view, there are mainly divided into light waves and electric waves.
Our human wireless communication, at present, mainly uses electric waves. The early use of low and medium frequency electromagnetic waves, but now gradually to high-frequency and even terahertz (is the middle of the above chart THz) development. There are also scientists, in the study of visible light communication (to the development of light waves).
In the wireless electromagnetic wave of this part, it seems that the frequency resources are quite a lot, but in fact, for each frequency, the relevant government departments have specified the corresponding purposes.
In terms of users, these bands are divided into military, private network use (public security, fire, railroad, power, etc.), operator use (public mobile communication), and so on.
In addition, there are ISM (Industrial, Scientific, Medical) license-free bands, which can be used without applying for authorization, such as our Wi-Fi band.
No one can just take up the frequency. For example, if I invent my own wireless communication device and then occupy the carrier’s 800 MHz band and transmit a wireless signal in that band, that would be illegal.
Cell phones for satellite communications, the first question to consider: what band it actually uses?
I don’t know if you have noticed, we buy a new phone, when it arrives, will see a blue label on the reverse side: the
This label is the phone’s network access license. Before any phone model is listed, the manufacturer has to get it to the Ministry of Industry and Information Technology to do the network access test. The test is passed before the license will be issued.
This means that the state for each electronic product, especially with wireless signal transceiver function of electronic products, are strict requirements: the requirements of the radio operating frequency must comply with the relevant national regulations, and must be consistent with the legitimate use of the product.
Our cell phones are designed to be used in three frequency bands.
One is the operating frequency of the operator’s cellular communication system (also known as the working band of the base station). In the case of the more common all-network phones now, they should support 2G / 3G / 4G / 5G bands. Each band is indicated on the official website.
Xiaomi a model supports the frequency band
The second type is Wi-Fi and Bluetooth. This is the unlicensed spectrum I mentioned earlier, the ISM band. As long as the transmit power meets the requirements (not too high), you can directly use it.
The third kind is the working band of the satellite positioning system. There are many kinds of GNSS systems, such as the U.S. GPS, China’s BeiDou (BDS), and Europe’s Galileo, and so on.
Numerous satellite navigation and positioning systems
So, here comes the question. Many people yell every day that cell phones communicate through satellites, really want to communicate, what frequency band to use?
Satellite communications are space radio communications, that have exceeded the radio management capabilities of a sovereign state. Therefore, the use of satellite communications operating frequency resources, to the International Telecommunication Union (ITU-R) for application.
ITU-R has clear documents with strict requirements on the declaration procedures and rules, often in parallel with the application for satellite orbit resources.
Satellite communication works in the microwave band, whose frequency range is from 1GHz to 40GHz. the frequency band, it can be divided into L, S, C, X, Ku, K, and Ka. among them, the K band is not suitable for satellite communication because it is in the frequency window where atmospheric absorption loss has the greatest impact. Therefore, the commonly used frequency bands for satellite communication are L, S, C, X, Ku, and Ka.
The Ka-band is worth mentioning.
The Ka-band is now becoming popular as the C and Ku bands are nearly saturated and can’t carry more services. the Ka-band is more susceptible to weather than the Ku-band but operates with more bandwidth and higher signal strength.
In any case, satellite communication bands are different from carrier cellular communication bands. Ordinary cell phones currently sold in the market simply do not support the radio operating frequency of communication satellites, so naturally, they cannot communicate with satellites.
Only special satellite phones provided by satellite communication service providers can establish connections with these communication satellites. These satellite phones are also charged to the corresponding satellite phone service provider.
As mentioned earlier, cell phones can communicate with GPS and Beidou, which are positioning and navigation satellites. Strictly speaking, it is not a communication satellite. However, our country’s Beidou is very powerful. In addition to positioning, navigation and timing services, it has one more function than GPS, and that is short message communication capability.
That is, in addition to location information, it can communicate with short messages (RDSS protocol). How short is it? Up to 78 decimal digits / English / numbers, or 39 Chinese characters.
This is what the Huawei MATE 50 “satellite communication” feature refers to. With the short message communication channel of the BeiDou positioning satellite, it can send and receive SMS messages for emergency communication in case of emergency.
This is just a short text message, no data service, no pictures, no phone calls or videos.
This and everyone in the normal sense of understanding of satellite communications, or a big difference. The special satellite phone mentioned earlier is able to make phone calls and use data services (Internet access).
Currently, on the market, none of the cell phones support the frequency band of communication satellites. So, is it possible to add it?
Not so simple.
Cell phone support for communication band, not just add an antenna. It involves SoC chip, baseband, RF, and software part of the transformation, is a very large and complex work.
It’s not that it can’t be done, but it doesn’t make sense.
Because the vast majority of cases, the phone has a base station signal or Wi-Fi signal, there is no need to add unnecessary costs for rare cases. (Engage in an external satellite communication kit, but more feasible.)
This and amphibious car reasoning is the same.
The car plus the function of the ship is not impossible. However, the price will be multiplied several times, the utilization rate is extremely low, not conducive to the popularity of the car.
So, the cell phone is not modified to support the existing satellite communications operating frequency, is there no way to satellite communications?
Neither.
We can think in another way. If the phone does not support the satellite communication frequency, then, simply let the satellite directly use the ground cellular base station frequency.
In fact, that’s what U.S. carrier T-Mobile is doing with Musk’s new project. They let satellites use part of the 5G band, improve the antenna, and then send wireless communication signals to the ground.
This works with the important premise that low-orbit satellites must be used.
Over the years, there has been a very important trend in satellite communications, and that is the rise of low-orbit satellites.
Previously, the cost of launching a satellite was very high, so it was hoped that a satellite would cover a large area. To cover a large area, you have to put the satellite higher. As shown in the figure below.
High orbiting satellites, although covering a large area, are far away, making communication more difficult. At that time, communication technology was also not very mature, so the bandwidth of the wireless channel was relatively low, and the communication rate was relatively slow. This low-rate communication can only barely meet the needs of positioning navigation and so on.
Now, with the maturity of the technology, coupled with the widespread use of one-arrow N-satellite technology, the cost of launching satellites has decreased. Private companies represented by Musk Space-X, using rocket recovery technology, have reduced the cost of satellite launches, making it possible to lay a large number of low-orbit communication satellites.
Intensive phobia caution
Low orbit satellites, closer to the ground, are line-of-sight coverage if the weather factor is put aside, so it is possible to provide signal service to ground users.
The orbital altitude of the SpaceX satellite was originally 1110 km to 1325 km but was later lowered to 540 to 570 km.
In short, it is the same as hanging the base station in the sky, which is a little farther away.
So, what is the bandwidth rate that T-Mobile can provide with this satellite communication technology?
2-4 Mbps.
Yes, you read that right, and when the ADSL dial-up Internet a level. Barely make calls, send pictures, video, then, enough.
Musk’s SpaceX communication satellites mainly use satellite communications dedicated frequency band, based on the number of existing satellites advantage, currently can reach about 300Mbps service rate.
SpaceX communication satellite is a conventional satellite communication system, not the phone to achieve this rate, but it is equipped with satellite communication equipment. This equipment has a “pot” (butterfly antenna), routers and so on.
SpaceX communications satellite equipment out of the box
SpaceX communication satellite equipment antenna deployment state
So, why can’t cell phones achieve higher satellite communication rates?
This has a lot to do with cell phone hardware. In particular, the type of antenna causes a great impact.
Antenna type problem
Our current cell phones have built-in antennas, and the antennas are inside the phone. A dedicated satellite phone will have a larger and more eye-catching antenna, as shown in the following figure.
Satellite phone
According to the antenna principle, when the length of the antenna is 1/4 of the radio signal wavelength, the transmitting and receiving conversion efficiency of the antenna is higher. The fact that the antenna of a satellite phone is so large means that this communication system operates at a longer wavelength. It also means that it operates at a shorter frequency (frequency = speed of light ÷ wavelength).
Based on secondary school physics knowledge, wireless signals at lower frequencies (larger wavelengths) have a greater ability to bypass and travel farther. This matches the scenario of satellite communication.
The signal receiving and transmitting ability of the whip antenna is ultimately weaker. Stronger than it is the dish antenna, which is commonly known as the “pot”.
The dish antenna, as long as the orientation is right, can achieve better communication.
So, I would like to ask, if a cell phone is for satellite communication, do you want to carry another pot on the phone? Then this pot, you still make efforts to find the right orientation.
Even if you are willing to carry this pot, you still face a problem — the problem of transmitting signals.
The dish antenna, as long as the orientation is right, can achieve better communication.
So, I would like to ask, if a cell phone is for satellite communication, do you want to carry another pot on the phone? Then this pot, you still make efforts to find the right orientation.
Even if you are willing to carry this pot, you still face a problem — the problem of transmitting signals.
The satellite transmits a signal to the cell phone, you can adjust the transmitting power. Cell phones to the satellite to transmit signals, which is difficult.
Handheld communication terminal, transmitting power is strictly limited. You do not want to hold a microwave oven in your hand, for communication, right?
With the cell phone milliwatt wireless transmitting power, trying to get the satellite to receive such a signal, how difficult is it? You can imagine for yourself.
What’s more, it is thousands or even 100,000,000 cell phones, sending signals to satellites in space, do you think, the satellite can capture all the signals?
Musk’s SpaceX communication satellite, there is also the problem of insufficient uplink rate. This is a dead end.
Capacity issues
Okay, let’s move on to the next analysis.
Next, let’s talk about capacity.
Musk’s SpaceX communication satellites claimed to be 12,000 satellites, are used to cover the world. A simple average, is China’s 9.6 million square kilometers, the Earth’s area of 510 million square kilometers, about 1.88%. If the satellite, there are only 226.
What about the number of terrestrial base stations?
The total number of base stations in China is about 10.35 million. For China Mobile alone, it’s about 5.5 million.
226 vs 5500000, even a fool can see that there is no substitution here. If there were no terrestrial cellular base stations, how many satellites would we need to get everyone online at high speed?
To take a step back, even if the satellite can be a point to multi-point, to undertake a huge amount of mobile broadband connectivity needs, then, the signal back (that is, the satellite will send the signal to the ground station), and how to do that? Data centers are on the ground, cloud services are also on the ground, not back to the transmission can not ah.
The current 5G base stations, which cover an area of a few square kilometers to a few dozen square kilometers, with a few hundred users, have to reach a 25Gbps level of forwarding transmission bandwidth. Satellite communication, is it possible to achieve a 25Gbps communication rate with ground stations?
Previously, China did a test mission on the satellite, using a high-speed high-order coherent laser communication terminal, to achieve a rate of 10Gbps transmission.
It seems to be not much different from 25Gbps, but this is wireless communication, stability, and anti-interference are far less than fiber. Moreover, the number of satellites is far less than that of base stations, and if it is to be compared with land base stations, its quantity demand is great.
Indoor coverage problem
In short, if satellite communications replace terrestrial cellular base station communications, then, indoor signal coverage, what to do? Basement, tunnel, what to do? What should we do if we encounter bad weather?
Conclusion
So much has been said, you should see. Satellite communication is completely unable to replace the ground cellular communication system. If someone tells you that communication satellites will replace base stations, either silly or bad.
As a special communication technology, the role of satellite communication is positioned to remain a supplement to the terrestrial cellular communication system.
There are three categories of applications for satellite communications.
1, in sparsely populated areas, in areas where fiber optics and base stations are not easily deployed, satellites will be of great use. In foreign countries, in the central and western parts of China, there are still many such areas. For some outdoor enthusiasts, mineral exploration, nature conservation, and other special work crowd, satellite phones are very useful.
2, the sea and the sky scenes, such as sailing ships, and civil aviation aircraft, there is a strong demand for satellite communications. Especially in civil aviation, these years, business people and other high-value people, the demand for air communication is very large, and the development of such applications is fast.
3, emergency disaster relief scenarios. When earthquakes, floods and other natural disasters, and ground communication systems fail, it is necessary to use the satellite, for emergency communications.
When we look at satellite communications, we must be rational and objective. Its market volume and cellular mobile communication are not at all a level. However, it faces a niche market, there is really a lot of room for development.
Over the years, the 3GPP’s NTN (Non-terrestrial networks), SaT5G, and TC12, are all studying air-ground integrated communications.
I think the market potential is there, but it is not as big as we think. NTN, in particular, focuses on the convergence of satellite communications and 5G, and is a satellite complement to 5G. It is not a departure from cellular communication, and we should have a basic understanding.
For satellite communications, in addition to technical bottlenecks, there are also a series of legal, environmental, political and other factors involved. Due to the limitation of space, we will not introduce them one by one.
