Bearer network evolution strategy
The evolution strategy of the bearer network is as follows:
- The 5G bearer network should follow the principles and directions of fixed-mobile convergence and comprehensive bearer, and take into account the construction of the fiber-optic broadband network. The fiber-optic cable network should be used as a unified physical bearer network for fixed and mobile network services . To achieve resource sharing as much as possible, in order to achieve low-cost and rapid deployment, to form a differentiated competitive advantage of China Telecom.
- The bearer network should meet the performance requirements of 5G networks such as high speed, low latency, high reliability, and high-precision synchronization, with strong flexibility and support for network slicing.
- In scenarios where fiber resources are sufficient or CU/DU are deployed in a distributed manner, the 5G fronthaul solution is mainly based on direct fiber connection, and single-fiber bidirectional (BiDi) technology should be used; when fiber resources are insufficient and CU/DU are deployed in a centralized manner, WDM-based solutions can be used. Technical bearer solutions, including passive WDM, active WDM/M-OTN, WDM PON, etc.
- For 5G backhaul, the initial business volume is not too large, and a relatively mature IPRAN can be used. According to the development of the business, the OTN solution can be used in areas with large and concentrated traffic, and the PON technology can be used as a supplement in some scenarios. In the initial stage, new functions such as SR, EVPN, FlexE/FlexO interface, and M-OTN will be gradually introduced based on the commercial equipment to meet the 5G deployment requirements. The backhaul access layer will introduce higher-speed (such as 25G/50G) interfaces as needed; Adapt to the needs of 5G scale deployment, build a backhaul network with high speed, ultra-low latency, support for network slicing, and intelligent management and control based on SDN.
5G key technologies and networking solutions
NR New Radio Technology
The overall design of the NR air interface protocol layer is based on LTE with enhancements and optimizations. On the user plane, the SDAP layer is added on the PDCP layer, and the functions of the PDCP and RLC layers are optimized to reduce delay and enhance reliability. The RRC_INACTIVE state is newly added to the RRC layer of the control plane, which is beneficial to the terminal power saving and reduces the delay of the control plane. At the physical layer , NR optimizes the reference signal design, adopts more flexible waveform and frame structure parameters, reduces the overhead of the air interface, facilitates forward compatibility and adapts to the needs of various application scenarios.
Turbo codes are used for LTE traffic channels, and convolutional codes are used for control channels. NR adopts LDPC code that can be decoded in parallel in the traffic channel, and Polar code is mainly used in the control channel. The theoretical performance of the channel coding adopted by NR is better, and it has the characteristics of lower delay and higher throughput.
Unlike the LTE uplink that only uses the DFT-S-OFDM waveform, the NR uplink uses both the CP-OFDM waveform and the DFT-S-OFDM waveform, which can be adaptively converted according to the channel state. CP-OFDM waveform is a multi-carrier transmission technology, which is more flexible in scheduling and has better link performance in a high signal-to-noise ratio environment, which can be applied to cell center users.
Similar to LTE, the NR air interface supports time-frequency orthogonal multiple access. Non-orthogonal multiple access technology is also being studied to further enhance system capacity.
Compared with LTE, which uses relatively fixed air interface parameters, NR has designed a set of flexible air interface parameters, which can be adapted to the needs of different application scenarios through different parameter configurations. Different subcarrier spacing can realize slot/mini-slot with different lengths. The OFDM symbols in a slot/mini-slot include uplink, downlink and flexible symbols, which can be configured semi-statically or dynamically.
NR cancels the cell-level reference signal CRS in the LTE air interface, retains the UE-level reference signals DMRS, CSI-RS and SRS, and introduces the reference signal PTRS for phase noise in high frequency scenarios. The main reference signal of NR is only transmitted in the connected state or when there is scheduling, which reduces the energy consumption and networking interference of the base station.
More suitable for Massive MIMO system multi-antenna port transmission.
From the perspective of 3GPP protocol, the air interface design of NR is very flexible, but considering the complexity of device implementation and networking, in actual deployment, a concise and feasible technical solution should be tailored from the air interface protocol according to the application scenario and frequency resources.
Massive Antenna Technology
The number of antennas and ports of 5G base stations will increase significantly, which can support large-scale antenna arrays with hundreds of antennas and dozens of antenna ports. Improve the spectral efficiency of 5G systems to improve user experience in high-capacity scenarios with dense users. Large-scale multi-antenna systems can also control the phase and amplitude of the transmitted (or received) signal of each antenna channel, thereby generating a directional beam to enhance the signal in the beam direction, compensate for wireless propagation loss, and obtain shaping gain. Shape gain can be used to improve cell coverage, such as wide area coverage, deep coverage, high-rise coverage and other scenarios.
Massive Antenna Wave
bundle forming
modular large scale
antenna
Figure 2: Large-scale antenna technology and experiments
Large-scale antenna arrays can also be used in the millimeter-wave frequency band. The additional propagation loss caused by the millimeter-wave frequency band can be compensated for by techniques such as beamforming, beam scanning, and beam switching, so that the millimeter-wave frequency band base station can use for outdoor cellular mobile communications. Large-scale antennas also need to adopt a digital-analog hybrid architecture to reduce the number of millimeter-wave radio frequency components and reduce the cost of large-scale antenna components.
While improving the performance of large-scale antennas, the equipment cost, volume and weight also increase significantly compared with traditional passive antennas. From the perspective of operators, China Telecom regards large-scale antennas as large in size, heavy in weight, and difficult to test, deploy and maintain. and other issues, led the development and testing of the industry's first modular large-scale antenna prototype. After the large-scale antenna is modularized, it is easy to install, deploy, and maintain, which is expected to reduce operating costs, and it is easy to form different antenna forms for different application scenarios. At present, the 3GPP organization has completed the design of the large-scale antenna codebook for the modular form in the 5G NR standardization, and will continue to promote the industrialization of the technology in the future. Based on the actual deployment scenarios and needs, China Telecom will preferably use antenna equipment with a higher number of ports (64 ports) in hotspot high-capacity areas to improve system capacity; at the same time, because 192 oscillators can improve coverage by about 1.7dB compared to 128 oscillators, it is preferred A large-scale antenna device with 192 antenna elements is selected.