# What is millimeter wave? What does it have to do with 5G?

Millimeter wave is one of the hot topics this year, because millimeter wave makes 5G technology possible. So, how did 5G networks develop themselves with the help of millimeter waves? With this question in mind, take a look at this article. In this article, I will introduce you to the basic knowledge of millimeter wave in an easy-to-understand manner, and explain the “flesh and blood” relationship between millimeter wave and 5G.

Millimeter wave is one of the hot topics this year, because millimeter wave makes 5G technology possible. So, how did 5G networks develop themselves with the help of millimeter waves? With this question in mind, take a look at this article. In this article, I will introduce you to the basic knowledge of millimeter wave in an easy-to-understand manner, and explain the “flesh and blood” relationship between millimeter wave and 5G.

What is millimeter wave

What exactly is millimeter wave? In fact, we can see through high school physics textbooks that it is essentially a high-frequency electromagnetic wave. It is an electromagnetic wave with a wavelength of 1-10 mm. Generally speaking, it is an electromagnetic wave with a frequency between 30GHz and 300GHz. It is one of the main frequency bands used in 5G communications.

Two communication frequency bands are mainly used in 5G communication. Sub-6GHz is a low-frequency frequency band, and it mainly uses frequency bands below 6GHz for communication. The millimeter wave frequency band uses 24GHz-100GHz high frequency millimeter waves for communication. At present, the use of millimeter waves by 5G is mostly concentrated in several frequency bands of 24GHz/28GHz/39GHz/60GHz.

The brief introduction of millimeter wave ends here. Back to the original question, what does the increase in network speed have to do with millimeter waves? Here we don’t need to mention those jerky and difficult technologies, just give an example to understand in minutes.

The basis of network communication speed is actually how much data can be received per unit time. A communication base station and a mobile phone are like the transmission of goods between two logistics sites. The goods are the data that needs to be transmitted. The electromagnetic waves that connect the two sites are the electromagnetic waves used in our communication. It is like a highway; Data transmission between the two is like cargo in a truck.

To transport all the goods to the other end, we can increase the capacity of the truck so that it can transport more goods at a time, so that when the truck speed is fixed (the electromagnetic wave transmission speed is fixed at the speed of light), the The goods will be delivered in a short time. Simply put, it is to increase the amount of data that can be carried in the communication electromagnetic wave to improve the communication efficiency and speed up the network speed.

For example, the 256-QAM currently used is based on this principle to increase the network speed, but this approach has certain limitations. It is not able to improve the efficiency indefinitely. This method will increase the power consumption of the radio frequency signal on the one hand, and on the other hand it will also make it more susceptible to noise interference and cause errors in decoding. The concept of switching to a truck is easier to understand. A truck is limited in size, and you can’t turn it into a train anyway.

Another way is to increase the lanes to increase the number of trucks that can travel together, which is to increase the bandwidth to achieve faster network speeds. This is actually not difficult to understand. The more lanes, the more trucks pass in a unit time, that is, the more data that can be received per unit time, the faster the network speed is reflected.

Well, the next step is about the millimeter wave. Through the above analysis, it is not difficult for us to conclude that the simplest and rude way to increase the network speed is to increase the bandwidth. According to the principle of communication, the frequency of a communication signal is proportional to its maximum bandwidth, which is about 5% of the frequency. Taking 28GHz millimeter wave as an example, its theoretical maximum bandwidth is 1.4GHz, which is compared with the current 4G LTE. Compared with the bandwidth of about 100Mhz for 800Mhz-2600MHz signals, there is inherently a bandwidth gap of more than ten times.

Millimeter wave single carrier can reach 100MHz bandwidth

Carrier aggregation technology can also increase bandwidth. It can integrate multiple carriers to achieve higher system bandwidth. However, the use of carrier aggregation is also restricted by spectrum resources. In the current 4G LTE spectrum resources, spectrum resources are very scarce. China Mobile, which has the most abundant spectrum resources in China, has only 130MHz spectrum resources. In comparison, the millimeter wave spectrum resources are very rich, and the frequency bands that can be allocated to operators are extremely wide, and even many continuous high-quality frequency bands can be allocated.

High bandwidth, good resources, and fast speed are the advantages of millimeter wave and the fundamental reason why 5G uses millimeter wave as a carrier. At present, millimeter wave technology has been relatively mature. Qualcomm has demonstrated this aspect for us. It uses 8 100MHz channels to form a high bandwidth of 800MHz, and the network speed is close to 5Gbps, compared with Sub-6GHz. The maximum speed has increased exponentially.

The use of millimeter waves is also difficult

Millimeter wave is actually not a new technology. It appeared long ago, but it has not been widely used. Because it is greatly restricted by environmental factors in communication. Because of its short wavelength, the diffraction ability is not strong, and the penetration into the building is almost no. A slight obstacle will cause the signal propagation to be blocked. Water molecules in the air can also absorb millimeter waves, causing its energy to attenuate, and its propagation range is extremely limited. Even the human body can cause fatal interference to millimeter waves, and human hands can completely block millimeter wave signals. For technical solutions for millimeter wave applications, the communications industry now has mature solutions. The transmission of 4G signals belongs to regional coverage, similar to water ripples, without very precise directionality. The transmission of millimeter wave signals can be regarded as point-to-point dynamic transmission. It can accurately identify the position and distance between the base station and the mobile phone, gather the millimeter wave signals together to form a high-energy beam, and then use beam tracking The technology directly carries out directional transmission. This transmission method is concentrated in energy, has good anti-interference, and perfectly compensates for the inherent shortcomings of millimeter waves, so that it can support commercial environments.

Receiving and transmitting millimeter waves in mobile terminals are also problems that need to be solved. The millimeter wave has a short wavelength, and the corresponding antenna length is also short, which can reduce the space occupied by the antenna inside the mobile phone, which is the advantage of the millimeter wave. However, the use of millimeter waves in mobile phone terminals also faces design problems in all aspects of radio frequency transmission, antenna, amplification, and reception.

Fortunately, there are also complete solutions for the use of millimeter waves in mobile terminals. Among them, Qualcomm’s solution is the most representative. The new generation millimeter wave antenna module QTM525 built by it integrates a series of functions such as antenna, signal transmission and reception, and amplification in millimeter wave transmission. Among the “pocket” modules. As long as the mobile terminal uses this module, it can directly solve the problem of millimeter wave communication. The QTM525 millimeter wave antenna module can deploy four in one mobile phone, covering the four sides of the mobile phone in all directions, so that users can always ensure the smoothness of a set of antennas and ensure the smoothness of the millimeter wave communication regardless of whether they are held horizontally or with one hand. reliable.

The QTM525 millimeter wave antenna module has excellent volume control. The mobile phone equipped with this module can control the thickness of the mobile phone to 8mm, which is equivalent to the current 4G mobile phone. It can continue the slim design characteristics of the mobile phone. It can make 5G mobile phones It has an exquisite and slim design like the 4G mobile phone version.

QTM, 525 is actually Qualcomm’s second-generation 5G millimeter wave antenna module. As early as last July, Qualcomm released the first generation of millimeter wave module QTM052, which cooperates with the Snapdragon X50 modem to provide millimeter wave support for the world’s first batch of 5G mobile phones. In view of the fact that most of the 5G mobile phones listed this year will use the combination of Snapdragon 855 mobile platform + Snapdragon X50, millimeter wave is no longer a problem for the 5G mobile phone terminals that support millimeter waves launched by several manufacturers. After the operator’s network is built, users can experience the rapid experience brought by millimeter waves.

Millimeter wave is an indispensable part of 5G

We have already made it clear from the beginning that millimeter wave is a part of 5G communication and one of the two main frequency bands in 5G communication. What it brings to 5G is not only extremely fast network speed, but also important for 5G differentiated experience. component.

5G network is a complex network environment. Millimeter wave is the core experience around the center of the circle in the most closed loop. It presents extreme speed, but the coverage of network signals is limited; Sub-6GHz frequency band takes into account both speed and The signal coverage has a balanced performance; in addition, the gigabit LTE network is also indispensable in the 5G environment. It has the best signal coverage and can ensure that users are not covered by 5G signals. A terrible cliff experience.

Both millimeter wave and Sub-6GHz are an indispensable part of 5G. As the most technically difficult one, millimeter wave may not be taken seriously in the early stage of 5G, but 5G lacking millimeter wave, to borrow a popular phrase now, that is 5G without soul.