5G base station is the core equipment of 5G network, which provides wireless coverage and realizes wireless signal transmission between wired communication network and wireless terminal. The architecture and shape of base stations directly affect how 5G networks are deployed. Since the higher the frequency, the greater the attenuation during signal propagation, the base station density of the 5G network will be higher.
As of May 2022, China has built nearly 1.6 million 5G base stations, becoming the first country in the world to build a large-scale 5G network based on the independent networking model. In 2022, China will add 887,000 new 5G base stations. The number of 5G base stations has reached 2.312 million, accounting for more than 60% of the world's total.
On July 23, 2022, the State Council Information Office held a regular policy briefing of the State Council. He Yaqiong, director of the Department of Consumer Products Industry of the Ministry of Industry and Information Technology, said that the "dual gigabit" network represented by gigabit optical network and 5G is a new type of network. The important support of infrastructure is also a key link in the development of smart home appliance applications. By the end of 2022, 2.312 million 5G base stations will be built and opened.
1. Architecture analysis of 5G base station
1.1 Logical shelf
5G base stations are mainly used to provide 5G air interface protocol functions and support communication with user equipment and core networks. According to logical function division, 5G base station can be divided into 5G baseband unit and 5G radio frequency unit, which can be connected through CPRI or eCPRI interface.
The 5G baseband unit is responsible for NR baseband protocol processing, including the entire user plane (UP) and control plane (CP) protocol processing functions, and provides the backhaul interface (NG interface) with the core network and the interconnection interface between base stations (Xn interface ).
The 5G radio frequency unit mainly completes the conversion of NR baseband signals and radio frequency signals and the sending and receiving and processing functions of NR radio frequency signals. In the downlink direction, the baseband signal from the 5G baseband unit is received, and after being processed by the transmission link (TX) such as up-conversion, digital-to-analog conversion, radio frequency modulation, filtering, and signal amplification, it is transmitted through the switch and antenna unit. In the uplink direction, the 5G radio frequency unit receives the uplink radio frequency signal through the antenna unit, and after receiving link (RX) processing such as low noise amplification, filtering, and demodulation, it performs analog-to-digital conversion and down-conversion, converts it into a baseband signal and sends it to 5G baseband unit.
1.2 Equipment system
In order to support a flexible networking architecture and adapt to different application scenarios, the 5G wireless access network will have a variety of base station equipment with different architectures and forms. From the perspective of equipment architecture, 5G base stations can be divided into different architectures such as BBU-AAU, CU-DU-AAU, BBU-RRU-Antenna, CU-DU-RRU-Antenna, and integrated gNB. From the perspective of equipment form, 5G base stations can be divided into baseband equipment, radio frequency equipment, integrated gNB equipment and other forms of equipment.
2. Key technologies of 5G base stations
The 5G base station construction network mostly adopts a hybrid layered network, which can ensure the easy management, scalability, and high reliability of the 5G network, and can meet the high-speed data transmission services of the 5G base station. At the same time, since 5G mainly realizes data service transmission, 5G base stations need to adapt to the complex application environment of high-rise buildings, rivers, lakes, mountains and canyons. In order to ensure the soundness and integrity of 5G base station construction, the following briefly introduces the key technologies of 5G base station construction.
2.1 MR technology
MR is a wireless communication environment assessment technology, which can send the collected information to the network administrator, and the network administrator can judge the value of the report, so as to optimize the wireless network communication performance. MR technology applications include coverage evaluation, network quality analysis, cross-area coverage analysis, network interference analysis, traffic hotspot area analysis, and carrier frequency hidden fault analysis. MR can render the uplink and downlink signal strength of mobile communication, and discover weak and blind areas of network coverage. It is not only objective and accurate, but also saves a lot of time and resources. It can detect network coverage problems in time and provide further basis for network coverage optimization. MR can realize 24 hours × 7 days real-time data collection, complete the quality analysis of uplink and downlink wireless networks, reflect the real situation of the call quality of the whole network, and improve the follow-up data support of the call of the whole network. When building a wireless network, if the crossover coverage is too large, it will interfere with the communication quality of other cells. MR can intuitively find the coverage boundary of the cell, judge whether there is crossover coverage, and adjust the wireless network structure. The analysis of traffic hotspot areas can realize the analysis of traffic density, distribution and resource utilization rate indicators, realize the comprehensive analysis of correlation, and formulate accurate planning for capacity sites and capacity expansion sites.
2.2 64QAM technology
64QAM can reasonably improve SINR, conduct scientific planning and design for 5G networks, reduce the complexity of 5G network deployment, reduce co-channel interference and weak coverage problems caused by overlapping coverage, and increase coverage while meeting the requirements of wide coverage of 5G networks The depth of the 5G network improves the comprehensive coverage of the 5G network, thereby achieving continuous and seamless coverage of hotspot areas, not only enabling more users to access the 5G network, but also enjoying high-quality communication services. The application of 64QAM in 5G network communication is divided into two steps, namely modulation and demodulation. The 64QAM modulation process is as follows: 64QAM can form a mapping of input 6-bit data; multi-level quadrature amplitude modulation generates a 64QAM intermediate frequency signal; parallel-to-serial conversion changes two parallel code streams into one serial code stream, which can increase Double the rate, the code stream is changed from binary to octal, and then the modulated RF signal can be output. The 64QAM demodulation process is as follows: When the 5G network transmits signals, due to the limitations of the natural environment or the carrier itself, the signal transmission is inevitably subject to noise interference and the signal is distorted. If the distortion is small, it can be directly judged as 0 or 1. If the distortion is serious, If the signal cannot be judged directly, hard judgment and soft judgment methods can be used to identify the signal accurately and quickly.
2.3 Anti-interference technology
A large number of wireless devices need to be deployed during the construction of 5G network base stations. The number of these wireless devices is very large, and the installation and deployment locations are also very complicated. There will be mutual interference between them. The main reasons for the interference include the failure of the devices themselves. The channel often transmits wrong signals during operation, which affects its own signal quality; the installation and configuration of 5G network equipment is seriously irregular, which affects the sensitivity of 5G signal transmission. 5G network interference mainly refers to radio interference, including intermodulation interference and out-of-band interference. Therefore, during the construction of 5G base stations, designers and construction personnel need to solve the problem of signal interference from the source, which can not only ensure the stability of the signal, but also greatly improve the efficiency of control and management. Specifically, first of all, conduct full electromagnetic detection on the radio transmission equipment of the base station to minimize the interference caused by the equipment itself; secondly, strengthen the inspection of the power generation equipment on a regular basis, and deal with it in time if any problem is found, thereby reducing the risk of signal existence. interference.
2.4 Massive MIMO technology
Multiple-Input Multiple-Output (MIMO) technology, also known as multi-antenna technology, makes full use of space resources by setting multiple antennas at both ends of the communication link, and can provide diversity gain to improve system performance. Reliability, providing multiplexing gain to increase the spectral efficiency of the system, providing array gain to improve the power efficiency of the system, has been one of the mainstream technologies in the field of wireless communication for nearly 20 years. MIMO technology has been adopted by 4G standards such as LTE/LTE-Advanced of the 3rd Generation Partnership Project (3GPP) and WiMAX of the Institute of Electrical and Electronics Engineers (IEEE). However, the number of antennas configured in the base station of the existing 4G system is small (generally no more than 8), and the performance gain of MIMO is greatly limited. In response to the shortcomings of traditional MIMO technology, Marzetta of Bell Laboratories in the United States proposed the concept of Massive MIMO (Massive MIMO or Very Large MIMO) in 2010. In a massive MIMO system, the base station is equipped with dozens to hundreds of antennas, which is 1 to 2 orders of magnitude more than the number of antennas in the traditional MIMO system; the base station makes full use of the spatial freedom of the system to serve several users in the same time-frequency resource.
The evolution from traditional MIMO to massive MIMO is a process from quantitative change to qualitative change. Since the number of base station antennas and the number of space division users of massive MIMO are orders of magnitude higher than those of traditional MIMO, the two have similarities and differences in the basic principles and specific methods of wireless communication. In the basic theory of massive MIMO, Fruitful results have been achieved in channel measurement and modeling, channel information acquisition, wireless transmission, experiments and tests. Massive MIMO has passed ideal laboratory verification and closer to the actual field test, and obtained a huge performance gain in line with expectations. In the future, various R&D institutions will further conduct networking verification to lay a good foundation for the future commercial use of massive MIMO in 5G systems.
3. 5G base station test plan
5G mobile communication technology can meet people's needs for fast-growing mobile communication services such as high speed, large capacity, high reliability, and low latency. As one of the key technologies of 5G mobile communication, massive MIMO active antenna technology can greatly improve spectrum utilization efficiency through spatial multiplexing, and combined with new coding technology can greatly improve communication system capacity and communication rate. Therefore, massive MIMO active antenna technology is commonly used in 5G mobile communication base stations, but what follows is how to test 5G base station antennas.
For traditional base stations, the antenna and RRU (Radio Remote Unite, radio frequency remote unit) are separated from each other, and they are connected by radio frequency cables. They are relatively independent and their performance does not affect each other. Their respective performances can be tested independently. test. The radiation performance test of the antenna can be done in the microwave anechoic chamber through the far-field or near-field method. The far-field or near-field test of the passive antenna is a mature test method widely used to test the performance of the antenna. The radio frequency index of RRU can be measured through conduction in the laboratory.
Referring to the traditional base station test method, it is easy to propose a solution to split the active antenna system into two parts, the passive antenna array and the RRU, for antenna radiation performance test and RF conduction test respectively. In fact, according to laboratory test experience, the beamforming pattern measured by "passive antenna array + power division network + signal source" is consistent with the OTA (Over the Air, air interface radiation) test of 5G base station active antenna integration. The results were inconsistent. There are also differences between the RF performance conduction test results of the "RRU+coupling board" and the RF radiation indicators measured by the integrated OTA. The reason is that for 5G base station antennas, the antenna and RRU are integrated together. On the one hand, interference factors such as electromagnetic coupling and active standing waves cannot be completely eliminated; It is completed by a series of active devices on the antenna, which is very different from the way that the passive antenna array performs amplitude-phase weighting through a passive power division network. Therefore, for 5G base stations using massive MIMO active antenna technology, the integrated OTA test method can effectively reflect its performance indicators. Especially in the millimeter wave frequency band, the frequency band is higher, the device size is smaller, and the electromagnetic interference problem is more prominent. Split testing will be very difficult, and only an integrated OTA test solution can be used.
The 3GPP 5G new air interface protocol that was frozen in December 2017 has written OTA test specifications for all radio frequency performance indicators of 5G base stations, which means that 5G base station antenna integrated OTA testing will become the main solution for 5G base station hardware performance testing . However, OTA testing of radio frequency indicators still faces many difficulties.
The 1-H, 1-O and 2-O station types defined in the 5G standard all specify the corresponding OTA radio frequency test items. Especially for 1-O and 2-O station types, there is no antenna interface for traditional conduction tests. All radio frequency test items need to be tested in an OTA environment. The test items include transmit power, modulation quality, occupied bandwidth, Adjacent channel leakage power ratio, spurious, intermodulation, sensitivity, blocking, etc. Therefore, full anechoic chambers for OTA testing, such as: far field, compact field, middle field, small field with plane wave generator, etc., have become necessary environmental choices. In the 3GPP standard, four options are proposed: far field, compact field, one-dimensional compact field, and near field, and recommendations for calibration and test methods of MU (Measurement Uncertainty) and related test items for different fields are given. For the one-dimensional compact field, existing institutions have developed plane wave generators based on similar principles, and have also carried out a lot of system testing and verification work.
4. Base station power supply for 5G base stations
The 5G base station AAU adopts Massive MIMO (large-scale multiple-input multiple-output) technology, which increases the power of the equipment. The power of the 5G base station is about 3 to 4 times that of the 4G base station; Supporting electricity has brought greater difficulties. If the original switching power supply is directly shared, the problems of insufficient switching power supply capacity and insufficient battery backup time will be brought about; if it is necessary to build or replace the switching power supply, a large amount of investment will be wasted. Operators have different requirements for the power backup time of 5G base stations and original base stations. How to configure switching power supplies and batteries;
4.2 Traditional switching power supply
Using traditional switching power supplies to power 5G is the most commonly used 5G power supply construction solution. Traditional switching power supply: When the total capacity of the switching power supply is sufficient, the original switching power supply can be directly used to expand the rectifier module and battery. When the total capacity of the switching power supply is insufficient, a new switching power supply can be replaced or newly built.
Advantages: Using the original base station switching power supply, only need to expand the rectifier module, which can save a lot of investment, shorten the construction period, and quickly deliver the project. When the traditional switching power supply is used for power supply, the AC power can be used to supply power to the equipment after one conversion through the switching power supply. The number of power conversions is small and the conversion efficiency is high.
Disadvantages: AAU (Active Antenna Unit) uses 48V power supply, the power supply distance is short, and the loss is large. When the same set of switching power supply is used to power the original equipment and the 5G equipment, the backup time of the 5G equipment is the same as that of other original equipment. If the capacity of the original battery is insufficient, the new battery needs to be connected in parallel with a battery switching system (also called a battery sharing manager), which will increase the construction cost.
4.3 DC/DC Converter
The DC/DC (direct current/direct current) converter powers 5G, adding DC/DC equipment on the basis of the traditional power supply scheme.
Advantages: less equipment is added, and the power supply distance is longer.
Disadvantages: There are many times of electric energy conversion, and the energy loss is large during the conversion process.
4.4 HVDC remote power supply
High-voltage DC remote power supply, this solution is based on the traditional switching power supply, adding DC remote power supply equipment to power 5G equipment.
Advantages: The power supply distance is long, and 5G application scenarios are basically unlimited. It is suitable for long-distance and high-power power supply scenarios. If a new optical cable is required between two stations, a photoelectric composite cable can be used to reduce the construction cost of optical cables and reduce costs.
Disadvantages: more equipment needs to be added, and the power loss in a short distance is large due to the large number of conversions. Compared with the traditional switching power supply, the investment is large.
4.5 Distributed power supply
Distributed power supply is often used for 5G power supply in stock base stations and new base stations.
4.6 Distributed power supply + blade battery
Distributed power supply + blade battery power supply for 5G is often used in stock base stations and new base stations.
5. Base station energy consumption of 5G base stations
5.1 Energy consumption problem
The power consumption of base stations is dominated by electricity. Compared with 4G networks, 5G not only increases power consumption by more than three times, but also doubles the demand for 5G base stations due to the attenuation of coverage. Therefore, for operators, 5G base stations The high power consumption has even become the primary reason for restricting 5G network construction.
The main energy consumption of 5G base stations is concentrated in the four parts of base station, transmission, power supply and computer room air conditioner, and the electricity bill of base station accounts for more than 80% of the overall network energy consumption. In the energy consumption of the base station, the power consumption of the baseband unit (BBU) responsible for processing signal codec is relatively small, while the radio frequency unit (RRU/AAU) is the main source of power consumption.
According to calculations, based on the current average transfer price of 1.3 yuan/kWh, the annual electricity bill for a 4G base station is 20,280 yuan, and the annual electricity bill for a 5G base station will be as high as 54,600 yuan.
At present, the computer rooms of mobile communication base stations are fully enclosed computer rooms, and the power supply equipment, transmitting equipment, and transmission equipment in the computer room are all relatively large heating elements. It is necessary to maintain a certain working environment temperature in the computer room (base station environmental standard GB50174-93 stipulates that the base station temperature is 18°C-28°C for many years), which is mainly achieved by air conditioning. The refrigeration system must continuously cool down the base station, which is also one of the important reasons for the high operating costs.
5.2.1 Change from power transfer mode to direct power supply mode. On March 24, the Ministry of Industry and Information Technology issued the "Notice on Promoting the Accelerated Development of 5G", pointing out that for supporting facilities such as base stations and computer rooms that meet the conditions, the transfer of power supply to direct power supply will be accelerated. In the absence of subsidies, the price of direct power supply is about 20% lower than that of transfer power supply.
5.2.2 Policy support. Many local governments have proposed directional support such as lowering electricity charges in their 5G strategic planning. Local governments have introduced policies to open up various municipal public resources to speed up the construction of 5G networks. Financial support has also become the focus of local policy support.
6. Difficulty analysis of 5G base stations
The full cloudification of 5G networks brings functional flexibility, but also brings many technical and engineering challenges:
6.1 Network cloudification makes it difficult to delineate and locate cross-layer faults, and the later upgrade process is also more complicated and inefficient.
6.2 The introduction of edge computing doubles the number of network elements and increases the difficulty of problem location.
6.3 Micro-services, more customized services for users, also put forward extremely high requirements for business orchestration capabilities.
6.4 In terms of transmission, a large number of tunnels change dynamically, and manual planning, analysis and adjustment cannot meet business needs; the construction and maintenance of high-precision clocks are demanding and difficult, and new support methods are needed. For large-width transmission, once a failure occurs, technical means for faster recovery are required, otherwise it will cause greater impact and loss.
7. Construction achievements of 5G base stations
As of the end of 2022, the province has built 27,831 new 5G base stations throughout the year, and a total of 85,149 5G base stations have been built, and the total number of base stations has risen to the 10th place in the country.
As of the end of 2022, Chongqing has 19.04 5G base stations per 10,000 people, higher than the national average of 16.39, ranking first in the west.
On January 18, 2023, the State Council Information Office held a press conference: Tian Yulong, chief engineer and spokesperson of the Ministry of Industry and Information Technology, introduced that 887,000 new 5G base stations will be added in 2022 (currently 2.312 million, total Accounting for more than 60% of the world), 110 cities in China have reached the gigabit city construction standard; the number of mobile Internet of Things connections has reached 1.84 billion, and China has become the first country in the world's major economies to achieve "superman"; 5G users have reached 561 million households, accounting for 1/3 of mobile phone users, 2.75 times the global average.
On February 28, 2023, the National Bureau of Statistics issued the "Statistical Bulletin of the People's Republic of China on National Economic and Social Development in 2022". According to preliminary calculations, by the end of 2022, there will be 10.83 million mobile phone base stations, including 2.31 million 5G base stations.
On April 20, 2023, the reporter learned from the press conference of the State Council Information Office that by the end of the first quarter, my country had built a total of more than 2.64 million 5G base stations, and 110 Gigabit cities had been built across the country. Network IPv6 traffic exceeded 50% for the first time, and the comprehensive capabilities of computing power infrastructure have been significantly improved. 5G has been applied in many fields such as industry, medical care, education, transportation, and tourism, and has been fully integrated into 52 major categories of national economy.
As of the end of April 2023, Beijing has built 313,000 communication base stations, including 90,000 5G base stations, accounting for 28.7% of the total number of base stations. The number of 5G base stations per 10,000 people ranks first in the country.