5G networks are gradually maturing, what solutions are there for 5G transmission?
1 Introduction
At present, the development of 5G technology is very rapid. The three major domestic operators have already embarked on 5G deployment. On June 25, 2017, China Mobile's first 5G base station was officially opened in Guangzhou University City, which also marked the gradual opening of 5G network applications. Before the formal deployment of 5G, how to achieve the high-standard bearer requirements of the 5G network and combine the existing network architecture to save construction investment to the greatest extent has become the focus and research hotspot of the entire optical communications industry. Therefore, this article will propose next Various transmission bearing schemes, and discuss the advantages and disadvantages of various transmission schemes and their scope of application.
2 5G's requirements and challenges for bearer networks
"5G" is the fifth-generation mobile communication technology. The ITU has officially named the 5G standard as IMT-2020, which is an extension of the "4G" currently being promoted, but the industry generally believes that 5G and 4G It is completely different. 5G is not only a technological update, but also a brand new technology. It is a powerful communication network that truly realizes ubiquitous, intelligent, integrated, high-speed, and green. It is an evolution and revolution in wireless access technology.
5G makes it possible to interconnect all things, providing high-speed, safe and free connections between people, people and things, and things and things. It will also drive more new business scenarios. Typical application scenarios include wide coverage and high access. Density, high access rate, burst traffic and low latency, these applications will lead us into the era of artificial intelligence.
(1) Continuous wide area coverage: With the goal of ensuring user mobility and business continuity, providing users with seamless high-speed business experience, such as unmanned driving;
(2) Hotspot high capacity: mainly for local hotspot areas, it can provide users with 1 Gbps user experience rate, tens of Gbps peak rate, and meet the extremely high traffic density requirements of the network; the throughput per unit area has been significantly improved, and the hotspot area has tens of Tbps /km2 traffic density requirements, such as virtual office;
(3) Low power consumption and large connection: application scenarios that target sensing and data collection, have the characteristics of small data packets, low power consumption, and massive connections. The network is required to support more than 100 billion connections to meet 1 million/ km2 connection density index requirements, but also to ensure the ultra-low power consumption and ultra-low cost of the terminal, such as the Internet of Things and smart cities;
(4) Low latency and high reliability: It has extremely high index requirements for latency and reliability, and it is necessary to provide users with millisecond end-to-end latency and close to 100% service reliability assurance, such as the Internet of Vehicles.
In view of the main application scenarios of 5G, the following requirements and challenges that bearer networks face are summarized as shown in Table 1:
Table 1 The main 5G scenarios and key performance challenges released by IMT-2020.
Wide coverage and high capacity will require 5G base stations to be more compact, easy to install in various scenarios, and have more powerful functions; low power consumption requires 5G networks to be green and low Carbon energy saving, for example, the battery life is 100 times that of the 4G network, and the terminal can be used for 5 to 10 years; and the network requirements such as low latency, high reliability, and large bandwidth require the 5G network architecture to be further flattened. It will be a powerful base station Overlay a large server cluster.
5G business requirements and changes in network architecture will put forward new requirements for network functions, which will directly affect the technical indicators of the bearer network, such as bandwidth, delay, clock accuracy and reliability, etc., so research how to meet the premise of 5G technical indicators In the 5G era, the technological evolution of the optical transport network is particularly important, which will be a key prerequisite for the promotion and application of 5G.
3 Discussion on 5G Transmission Scheme
This section will focus on the selection of transmission network technology and networking schemes in the initial stage of 5G construction.
3.1 Scheme 1: End-to-end packet-enhanced OTN networking scheme
As shown in Figure 1, the 5G transmission access layer uses a 100G wave packet network, and the convergence layer uses a T-level WDM networking mode.
Figure 1 Wave packet network 5G bearer solution
(1) Networking plan
1) Fronthaul solution: The base station is connected to the DU (Distribute Unit) through bare fiber to meet the needs of future mobile users for large bandwidth, low latency, and high reliability information transmission.
Base station traffic forecast: The average bandwidth of 5G base stations will exceed 1 G, and the peak value may exceed 10 G; for S111 stations, CIR/PIR will reach 4 G/16 G.
2) Mid-transmission scheme: DU converges the base station and then connects to the physical network optical fiber distribution terminal; after the physical network fiber converges the DU uplink optical cable, the DU passes through the physical network optical crossover to form a ring, and the physical network optical fiber passes through the backbone optical cable or wavelength division equipment Upload to the central office CU (Centralized Unit, centralized unit).
Access layer traffic forecast: According to 6 stations in each access ring, one station reaches the peak bandwidth, the access ring bandwidth will reach 40G. Considering the density of 5G base stations, 100G networking is more likely;
3) Backhaul scheme: CU backhauls to 5G core network via 100 G~T WDM or trunk fiber optic cable.
Convergence layer traffic prediction: Considering that multiple access rings will be converged in the WDM ring at the convergence layer, it is possible to achieve T-level networking.
(2) Advantages of Option One
1) Large bandwidth: Convergence of packet technology and over 100 G optical transmission technology, which can effectively support a thousand times the access rate of 5G networks;
2) Low latency: Converged form, flexibly realizes service pass-through node optical layer pass-through, coping with the huge challenge of 5G end-to-end ultra-low latency
3) High physical link security: DU to optical fiber physical network optical communication adopts dual uplink, and physical network optical communication to MS-OTN also adopts dual uplink connection, which greatly improves the security of DU equipment;
4) Large capacity and few nodes: After connecting DU through MS-OTN and then connecting to CU (wireless access control equipment), it can effectively converge the upstream optical cable, save CU ports, and enable CU to cover a larger area and reduce CU Deploy points to effectively reduce equipment networking, transmission lines, maintenance and other requirements;
5) The line bandwidth is easy to upgrade: MS-OTN equipment only needs to be plugged in, and the line bandwidth can be easily expanded from 100 G to 400 G. The equipment does not change, the machine room does not change, and the expansion is smooth to achieve "super 100 G" bandwidth.
(3) Disadvantages of Option One
1) Large investment: Two high-speed and high-performance OTN ring networks need to be built. Based on the use of existing network OTN equipment, more nodes still need to be added, which is a huge investment;
2) The network is more complex: More new MS-OTN equipment is used for 5G base station information transmission, which increases the complexity of the network.
3.2 Scheme 2: Fixed-Mobile Converged Carrier Solution The
fixed-mobile converged 5G bearer solution is shown in Figure 2:
Figure 2 Fixed-mobile converged 5G bearer solution
(1) Networking plan
1) Fronthaul solution: The base station is connected to the DU through a bare fiber to meet the large bandwidth and low delay information transmission needs of future mobile users; the indoor small base station (RRU+DC part) can be integrated with the ONU and is easy to deploy.
2) Mid-transmission plan:
◆ DU is connected to the PON port of the OLT equipment after converging the base station optical cable;
◆After the OLT sinks to the cell, it simultaneously accesses wired PON services and wireless 5G base stations;
◆After the optical fiber of the physical network intersects and converges the upstream optical cable of the OLT, it upstreams to the central office CU through the backbone optical cable equipment.
3) Backhaul scheme: CU is backhauled to the 5G core network through the relay optical cable.
(2) Advantages of Option Two
1) Simple networking: use the existing network structure, upgrade OLT equipment, and increase the number of optical switches in the physical network to complete the networking;
2) Convergence of fixed and mobile: wired and wireless integrated bearer, improve equipment utilization efficiency, effectively save computer room space and energy consumption, and achieve simultaneous upgrade of wired and wireless business bandwidth and performance;
3) Large-bandwidth transmission: In addition to the use of super 10 G or even 100 G PON OLT equipment for DU equipment carrying, the entire optical link is directly accessible, supporting 5G ultra-large bandwidth applications;
4) High physical link security: DU (5G wireless access unit) adopts dual uplinks to OLT, and OLT to physical network optical switching also uses dual uplinks as much as possible, and physical network optical switching is in a ring structure, which greatly improves DU The safety of the equipment;
5) The line bandwidth is easy to upgrade: OLT equipment can be upgraded smoothly, without changing the equipment, without changing the machine room, and smoothly expanding, realizing "super 100 G" bandwidth;
6) Save physical network optical fiber resources: Using OLT equipment as the convergence point between CU and DU can greatly converge the base station's uplink optical cables and reduce the consumption of optical fiber physical network resources.
(3) Disadvantages of Option Two
1) Need to overcome the problem of OLT's large delay: Because the OLT's upstream adopts TDMA (Time Division Multiplexing), the upstream information flow delay temporarily cannot meet the ultra-low delay requirements of 5G. Therefore, if the OLT is used to converge to carry wireless and wired services, the OLT delay needs to be optimized, or the end-to-end QoS guarantees the needs of low delay, high reliability and large bandwidth for 5G base station service transmission;
2) The coverage of CU is limited: because DU is directly connected to CU through optical fiber physical network, and the single ring of optical fiber physical network can only carry 4-6 optical circuits, the coverage radius of each optical circuit in dense urban areas is about 1 km. This means that the number of base stations that can be accessed within the coverage area of the CU is limited by the coverage area and the capacity is limited, and the effectiveness of the CU cannot be maximized.
3.3 Other transmission schemes
In addition to the above two schemes, the following schemes can also be used:
(1) Scheme 3: Taking scheme one as the basic network architecture, combining scheme two, specifically using MS-OTN equipment at the access layer as integrated access equipment. MS-OTN is simultaneously connected to the base station and OLT equipment, and the base station completes the wireless connection. In, the OLT equipment completes wired access.
(2) Scheme 4: Taking scheme 2 as the basic network architecture, replacing the OLT equipment with ultra-low latency switches, and adopting Layer 3 switches or routers for backhaul.
(3) Scheme 5: Taking scheme 2 as the basic network architecture, replace OLT equipment with high-speed IPRAN equipment.
(4) Scheme 6: With scheme 3 as the basic network architecture, the MS-OTN ring of the access layer is not constructed temporarily, and the DU is directly connected to the CU through the optical fiber physical network. This scheme occupies more fiber core resources, and is suitable for a small number of supplementary points, but not for large-scale construction.
In the actual construction process, the specific transmission networking scheme to be adopted mainly depends on the following conditions:
(1) CU positioning: CU positioning in the network hierarchy, that is, CU location selection, coverage area, and access user scale. If the CU is at the convergence level with wide coverage and large capacity, it is more reasonable to adopt option one; on the contrary, if the CU is at the access convergence level and the location is similar to the location of the 4G BBU computer room, option five can be adopted.
(2) Capital investment: The size of the investment also plays an important role in the choice of network architecture. Option 1 and Option 3 have huge investments, but the network architecture is clear and reasonable, and can meet various indicators of 5G transmission. Plans 2, 3, and 5 have lower investment and are suitable for the pilot phase or the construction of a small number of supplementary points.
(3) Technological advancement: Technological advancement can also change network construction methods. For example, OLT equipment can solve delay and synchronization, IPRAN equipment can solve technical problems such as bandwidth, and 5G network access methods will be more abundant.
In actual construction, the networking method should be selected flexibly according to the specific situation, in order to achieve the optimal network and the least investment effect.
4 Concluding remarks
5G is gradually maturing. Not only is the increase in traffic brought to the transmission network, the requirements of low latency, high reliability, flexibility and intelligence are all challenges to the existing network architecture. Therefore, this article combines specific construction requirements and provides Multiple transmission solutions. With the further clarification of the 5G standard, the author believes that the transport network still needs to focus on the positioning of the CU, the network level, and the coverage density, which will determine which transmission networking scheme is more reasonable, and prepare in advance according to the optimal bearing scheme Optical fiber and equipment room resources are fully prepared for the deployment of 5G.