As a user in the new era, you can't lack network without anything. What you care about most when you go out is whether there is a 4G network here? Can I use it? Is it fast? I believe everyone will have a similar question: I plan to travel to the United States once and shop in Hong Kong when I come back. I wonder if the machine support on hand does not support the local 4G network? Now let's teach you to understand the mysterious 4G network parameters.

The dilemma of 4G LTE

At present, the 4G network we use, that is, the fourth generation mobile communication network LTE (Long Term Evolution, Chinese for long-term evolution technology). Although the technology is upgraded greatly, the main workflow is similar to the previous 2G and 3G. As shown in the figure above, the mobile device processes all kinds of information we input into digital signals, and then loads them onto electromagnetic waves through FM and AM to exchange information with the base station, so the invisible electromagnetic waves are very important carriers in the whole process.

Electromagnetic wave is a very precious resource. In wireless communication, electromagnetic wave with the frequency between 30MHz and 40GHz is usually used. It is delicate and vulnerable to interference and impact. To solve the problem of "too few monks and too many monks", all countries and regions will carry out standardized management of this resource: in China, the Radio Administration Bureau of the Ministry of Industry and Information Technology is responsible for unified planning; In the United States, the FCC is responsible for management and auction.

However, the core technology of LTE network, OFDM (Orthogonal Frequency Division Multiplexing), essentially divides the entire frequency band into numerous small channels for transmission, so 3GPP had to formulate a very complex LTE frequency band due to the dual reasons of technology and history (2G and 3G construction occupied some resources). More experts have drawn a painstaking picture of the commonly used 0-4000MHz frequency band, which shows how complex and irregular the frequency band distribution of the 4G network we are using is. It is really not easy to support all of it.

This is also the fundamental reason why Qualcomm and other communication manufacturers put forward the concept of "All Netcom and All 4G", and why the machines sold overseas cannot support domestic 4G networks. For example, the frequency band supported by overseas machines is Band 1, and the domestic operators have set up Band 3. Therefore, the communication between the machine and the base station is like chicken talking with duck.

To go a little further, due to the problems of LTE frequency band and the abundant resources of high frequency, the interference is not serious compared with low frequency, and 5G networks are basically developed to higher 3.4GHz or higher. As the first 5G modem in the market, the Snapdragon X50 supports 28GHz millimeter wave, which basically indicates that the future 5G network will avoid the congested low-frequency zone.

Of course, it does not mean that low frequency is useless. According to the communication theory, for the same transmission power and the same receiving power, the higher the frequency, the faster the electromagnetic wave attenuation, which will lead to a smaller coverage radius, that is, low frequency can obtain greater coverage. This is why all operators like the spectrum resources near 700MHz. The FCC recently opened a 600MHz spectrum auction, and operators will use it for LTE deployment. Qualcomm took the lead in saying that the latest Snapdragon X20 LTE modem directly supports 600MHz, and the X16 LTE integrated with Snapdragon 835 has also confirmed its support.

Without much to say, since we know that there are many LTE bands, the networks set up by operators in various countries and regions are mixed. The simplest way to deal with this situation is naturally to cultivate internal skills. Finding a machine that supports more LTE bands can quickly cut through the mess and solve it in an instant. Similar to the All Netcom machines advertised by some domestic manufacturers, most of them only support the LTE frequency bands installed by the three major domestic operators. Only FDD's Band 1/2/3/5/8 and TDD's Band 38/39/40/41 add up to nine frequency bands. It is "dangerous" to go abroad.

Let's change to the platform version HTC U11 using Snapdragon 835. All LTE bands are indicated in the network support. There are 15 bands in total for the FDD supported Band 1/3/4/5/7/8/12/17/20/28/32 and TDD supported Band 38/39/40/41, covering all LTE bands in China. In other words, the platform version U11 can use the 4G networks of three major operators in China, However, due to the manufacturer's restrictions on CDMA that has not been added to Telecom, it is impossible to use Telecom's 2 and 3G.

Similarly, the Hong Kong version of Samsung Galaxy S8 using Qualcomm Snapdragon 835 is more abundant in network support. It directly supports all 2 and 3G systems in China. The LTE band is also quite powerful, supporting 20 bands of FDD Band 1/2/3/4/5/7/8/12/13/17/18/19/20/25/26/28 and TDD Band 38/39/40/41. Such network support not only perfectly supports domestic 2, 3 and 4G networks, but also has no pressure to go abroad.

Carrier aggregation that has to be mentioned

As mentioned earlier, LTE is divided into many small frequency bands, and each band is basically limited by the actual bandwidth, so the download speed will be greatly limited. But this is a 4G network. The speed of up and down transmission must be greatly improved than that of 3G. In order to solve this problem, Carrier Aggregation (CA) technology came into being.

Carrier aggregation technology is the development of traditional multi carrier technology. The core idea is to divide multiple continuous or discrete spectrum into multiple component carriers, allowing terminals to transmit and receive data on multiple subbands at the same time. A simple analogy is to combine several small water pipes to form a large water pipe, so that the speed of water injection and pumping can be accelerated.

Here we have to mention the Snapdragon X5 LTE modem launched by Qualcomm in 2013. In addition to the title of the world's first All Netcom, it is also the first commercial modem supporting LTE carrier aggregation technology, with a downlink speed of 150Mbps of Cat. 4; Later, Qualcomm brought carrier aggregation to the uplink. The uplink of the Snapdragon X12 LTE modem integrated in the Snapdragon 820/821 reached 150 Mbps of LTE Cat. 13.

Taking the HTC U11 of the platform version equipped with Snapdragon 835 as an example, the network details show that it supports up to 4CA carrier aggregation, the downlink speed can reach up to 800Mbps, and the uplink speed can reach up to 75Mbps. Sony XZ Premium, also equipped with Snapdragon 835, has become the world's first mobile device with a downlink speed of 1Gbps gigabit speed by virtue of 4CA carrier aggregation. The latest Snapdragon X20 LTE modem released by Qualcomm has achieved a downlink speed of LTE Cat. 18 1.2Gbps through 5CA carrier aggregation.

Generally speaking, modems that support more frequency bands and more carrier aggregation will have more advantages in speed. For example, some models of domestic manufacturers only support 3CA carrier aggregation, and the maximum speed "only" can reach 600Mbps, which is much slower than the HTC U11 and Soni XZ Premium using Snapdragon 835 just mentioned, Consumers who want to speed up will have to see clearly from multiple perspectives in the future.

VoLTE & ViLTE

Thanks to the efforts of a number of communication manufacturers, the speed of LTE network has been greatly improved compared with that before. With the support of high-speed wireless network, a variety of novel services can be provided. Among them, VoLTE (Voice over LTE), which is the voice scheme based on LTE network, is the most familiar.

Different from the previous 2 and 3G calls, they need to rely on the traditional circuit switched voice network, VoLTE is based on the IP Multimedia Subsystem (IMS) network. On the LTE, the voice service is transmitted as a data stream in the LTE data bearer network using a specially made configuration file for the control plane and the media plane of the voice service. This is no essential difference from networking through the LTE. At the same time, due to the larger bandwidth of VoLTE, the voice quality and quality of voice services have been greatly improved compared with those of 2 and 3G, and the connection speed can also be improved. At present, both China Mobile and China Unicom have launched VoLTE services in some regions. After ensuring that the machine supports VoLTE and opens services, you can experience voice calls in the new era.

Because of the existence of VoLTE, the circuit switching network that traditional 2 and 3G must rely on has become replaceable. Some overseas operators have gradually canceled 2G networks and changed to VoLTE. Domestic operators are also clearing some 2G bands for LTE network construction. This trend means that VoLTE will become the standard configuration of mobile phones in the future, and functional phones are no exception. Today, only the primary card of dual card mobile phones supports LTE, and the secondary card only supports 2 and 3G. Qualcomm foresaw this trend. Its latest Snapdragon X20 LTE is the world's first modem that supports dual cards and dual VoLTE. At the same time, it announced that it will update support for machines that use Snapdragon modems in large numbers through OTA, hoping that other manufacturers can keep up with this trend.

The upgrade of VoLTE, Video over LTE, that is, the video solution based on the LTE network is ready. It can provide better video calls and various video based services. I believe this will become another development direction after VoLTE.

tail

To sum up, if you want to select a 4G machine with excellent experience, excellent network support is essential. There are three key points: first, look at the number of LTE bands supported, and the more the better, so as to ensure that there are signals no matter where you are; Secondly, we will see how many carriers are supported for aggregation. Generally speaking, the more the carrier is, the faster the speed will be to ensure that the machine will not get stuck; Finally, let's see whether it supports 4G exclusive features such as VoLTE. If you don't even have basic features, can you expect it to provide a better experience?

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P. S. The pictures in the text are from the Internet

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