Three typical scenarios of 5G
There are three typical scenarios for 5G. These three scenarios describe the needs of 5G and reflect the difference between 5G and 4G. As shown in the figure, the three scenarios are: enhanced mobile broadband communication (eMBB), large-scale machine-type communication ( eMTC) and ultra-high reliability and ultra-low latency communication (uRLLC).
- eMBB provides a higher transmission rate and user experience. The peak downlink transmission rate in 5G will reach 20Gb/s, while the peak downlink rate of 4G is only 1Gb/s. The ultra-high rate will make virtual reality and augmented reality possible;
- eMRT will realize the interconnection of everything, smart home, smart grid, etc.;
- uRLLC can reduce the communication delay to below milliseconds and realize tactile interconnection, while the delay in 4G is about 70 milliseconds. The ultra-low communication delay and high-reliability transmission of 5G can realize auto-driving of automobiles.
5G requirements
If only one formula is used to intuitively describe 5G requirements, I think it should be the following formula:
Therefore, improving network throughput can be achieved from three aspects, namely, increasing communication bandwidth, increasing cell density, and increasing spectrum efficiency. Correspondingly, it can be realized by the following technologies: millimeter wave communication, small cell, and massive MIMO technology.
1. Improve communication bandwidth-representative technology millimeter wave
Currently, most wireless communications use frequency bands below 6 GHz. However, with the increase in the number of users and smart devices, the limited spectrum bandwidth needs to serve more terminals, resulting in a serious decline in the service quality of each terminal. In order to solve the problem of limited spectrum resources, a feasible method is to develop new communication frequency bands and expand communication bandwidth. Because of this, many operators or equipment suppliers are currently carrying out millimeter wave frequency communication tests.
The millimeter wave frequency band refers to the 30-300 GHz frequency band (as shown in the figure above). Compared with the original frequency below 6 GHz, it is a very rich frequency band resource. The wavelength of radio waves in this frequency band is between 1-10 mm. Due to the short wavelength of millimeter wave, transmission loss is particularly serious in actual communication. Water vapor in the air will cause serious fading, and it is transmitted in the form of direct waves. It is a typical line-of-sight transmission method. The ability is extremely poor. Walls, leaves, etc. will cause the signal to be blocked, so at present, millimeter waves are mostly used for transmission between base stations and base stations, radars, satellites, etc. (base stations are set up high, and there is usually no building between them. Block).
Because the millimeter wave frequency band has high fading characteristics, it can be combined with massive MIMO technology to enhance signal strength, or combined with small cell technology to enhance the distance of signal propagation.
2. Improve cell density-representative technology Small cell heterogeneous network
Small Cell is a base station equipment with low transmit power and small coverage. Small Cell, as a supplement to 3G/4G macro cells, enables operators to provide users with better wireless broadband voice and data services at a lower cost. With the continuous improvement of LTE network capacity, mobile operators are worrying about increased data traffic. Many operators believe that offloading mobile data is a good way to efficiently use wireless spectrum resources. Small Cells are playing an increasingly important role in this regard. More Small Cells are used to cover blind areas and share flow pressure. Small Cell has the advantages of flexible and rapid deployment, which can solve the network coverage problems of hot spot absorption, blind spots, and weak coverage scenarios, and realize the ubiquity of the network.
Small Cell is a low-power wireless access node that works in an authorized frequency spectrum and covers a range of 10 to 200 m. In contrast, the coverage of a macro cell can reach several kilometers.
The product form of Small Cell is more flexible and can be divided into household Femtocel (2×50mW), outdoor Picocell (2×1W, outdoor blind/heat absorption), indoor Picocell (2×125mW, enterprise indoor coverage), Microcell (2 ×5W, outdoor blind compensation), all are managed by the operator.
Small Cell can be used indoors and outdoors to compensate for blind coverage, absorb hotspot services, and increase network capacity. The HetNet heterogeneous network is composed of multiple levels of Small Cell and Macro Cell. Through the combined use of macro-micro collaboration technology and anti-interference technology, the network capacity can be increased several times or even higher, greatly reducing the capacity pressure of the wireless network.
The realization of 5G will inevitably require some changes in the construction of infrastructure, which must be compatible with previous systems and provide stronger services. The deployment of small cells is one of the key technologies to improve spectrum utilization and enhance user service quality.
Small cell is different from the traditional macro base station. It only needs lower transmitting power and can be easily deployed on street lamps and other facilities to serve users in a small area, as shown in the figure above. Since the service range of small cells is small, the same spectrum resources can be reused between different small cells and between small cells and macro cells, forming a heterogeneous structure with traditional macro cells, greatly improving the system Spectrum utilization. In addition, the Small cell can play the role of relay, strengthen the signal strength and coverage, and increase the number of terminals served by the system.
3. Improve spectrum efficiency-representative technology massive MIMO, beamforming
Massive MIMO is one of the 5G key technologies with great potential. Compared with the 8 (or fewer) transmitting antennas used in 4G systems, massive MIMO will deploy hundreds of antennas on the same antenna array to increase the antenna array gain Raised to a new level! Massive MIMO has not yet been deployed and applied in practice. It is currently tested in laboratories or in some specific environments. However, it can be seen from the existing test results: Massive MIMO only requires simple linear precoding processing (such as MRT, ZF) can provide extremely high downlink transmission rates.
The beamforming/precoding technology is inseparable from the multi-antenna system. Beamforming technology can make the transmitted signal have a certain directivity, avoid interference to surrounding users, and at the same time increase the received signal power of designated users. With the increase in the number of antennas in the massive MIMO system, the system can serve more end users, and how to avoid user interference during signal transmission is an important issue. Beamforming technology is an indispensable part of massive MIMO system.
5G peak rate calculation formula
△ 5G carrier peak calculation formula
MIMO layer number: downlink 4 layers, uplink 2 layers.
Modulation order: downlink 8 order (256QAM), uplink 6 order (64QAM).
Encoding rate: 948/1024≈0.926.
Number of PRBs: 273, 12 in the formula means that each PRB contains 12 subcarriers.
The proportion of resource overhead means the proportion of radio resources used for control and not used for sending data. The protocol gives typical data: 14% for downlink and 8% for uplink.
The number of symbols means the number of symbols that can actually transmit data per second, which varies with different TDD frame structures. For details, please refer to the table in the second part above. Now take the value of the 2.5 millisecond dual-period frame structure: 18400 for downlink and 9200 for uplink.
△ Illustration of peak calculation factors for 5G carrier
Substituting the above data into the previous formula, we can get: the
downlink peak rate is: 1.54Gbps, the
uplink peak rate is: 308Mbps.
Now China Telecom and China Unicom are sharing the 100MHz bandwidth on the 3.5GHz frequency band, a single mobile phone The theoretical rate that can be achieved is the above two values.
If the two companies subsequently open 200MHz, because the bandwidth doubles, the rate will also double, and the downlink rate can be as high as 3.08Gbps!
This speed is enough to outsmart the crowd.
Broadband and narrowband services
Broadband services are relatively narrowband services. Generally speaking,
communication services with a rate lower than 2Mb/s are collectively referred to as narrowband services, such as services provided by telephone networks and N-ISDN.
For communication services higher than 2Mb/s, such as frame relay services, video on demand, ATM services, TV conferences, etc., are called broadband communication services.
There are two main broadband access technologies currently in use: ADSL and FTTX+LAN.
https://zhuanlan.zhihu.com/p/108553808
https://zhuanlan.zhihu.com/p/32935829
https://www.zte.com.cn/china/about/magazine/zte-technologies/2013/12/cn_940/414779.html