Optical fiber multiplexing equipment essentially uses 8 to 16 wavelengths of coarse wavelength division to perform wavelength division multiplexing. It can synthesize optical signals of different wavelengths into a beam of light, and then decompose them at the receiving end, thereby realizing single-fiber multi-wavelength division. At present, the main manufacturers on the market include Ruisi Kangda, FiberHome, etc. The new optical fiber multiplexing equipment products mainly include 1:6 aggregation, 1:8 aggregation, 1:12 aggregation and 1:18 aggregation. The wavelength is between 1271nm and 1611nm, and the number of channels that can be synthesized or separated is 6, 8, 12 and 18 respectively. The maximum transmission capacity can reach 80Gbit/s, supporting multiple network frequency bands such as 2G, 3G, 4G and 5G. Compared with the old wavelength division multiplexing equipment, this new type of optical fiber multiplexing equipment is more advanced in technology, and the appearance, quality, and form of the equipment have become more refined. It can be used in various network construction environments, so that it can be deployed in multiple ways, which can timely alleviate the problem of insufficient fiber cores caused by large-scale site construction.

In the 4G network base station construction plan, major operators have classified base stations according to physical location and station size. This article classifies them according to macro base stations, micro base stations and indoor base stations. The macro base station is used as an example to illustrate the construction strategy of optical fiber multiplexing equipment. First, we define the baseband processing unit as BBU and the radio frequency processing unit as RRU. The optical signal is transmitted between BBU and RRU through the optical module. The RRU is connected to the antenna through the feeder, etc., and the signal is amplified to form 3 sectors, so as to achieve the signal coverage effect. Therefore, in this article, we regard the 3 RRUs that make up a base station as a group and define it as an optical direction.

As shown in Figure 1, a set of 1:6 aggregated optical multiplexing equipment consists of two optical fiber extenders. The network construction strategy is to use one set in each defined optical direction, and the core resources can be quickly expanded. The specific solution is to place the matching optical fiber extender on the near-end BBU side. To access the corresponding three RRUs, three optical ports are selected in the BBU, and 10Gbit/s color optical modules with wavelengths of 1271nm, 1311nm, and 1351nm are used for connection. At this time, the services of the three optical ports are converged on the single-core bidirectional optical fiber on the line side through wavelength division multiplexing technology, and transmitted to the optical cross-connect box at the remote RRU through optical fiber. In order to continue to transmit the optical signal to the remote RRU, another optical fiber extender is placed in the optical cross-connect box, and then connected to the RRU again through 10Gbit/s color optical modules with wavelengths of 1291nm, 1331nm, and 1371nm, respectively, to achieve optical path interconnection between the near-end BBU and the remote RRU, thereby completing the network construction.

Application scenarios of fiber multiplexing equipment in 5G construction

The application of fiber multiplexing equipment in 4G networks is becoming more and more mature. In the complex 5G network construction scenarios, fiber multiplexing equipment can also be used to achieve rapid optical cable reconstruction, using a pair or a single optical fiber to achieve the connection between multiple AAUs and BBU (CU+DU), so as to achieve the purpose of rapid construction of 5G networks.

5G network construction scenario in subway tunnels

As a densely populated area, the subway is indispensable for 5G network construction. However, in actual engineering construction, the construction of transmission optical cable resources is often built by the subway. The subway company owner often needs to consider the three operators' co-construction model to invest in the construction of optical cables, which makes it difficult to coordinate cable replacement when deploying 5G networks.

Therefore, in order to accelerate the completion of 5G network construction, 5G construction in key areas should be deployed in advance among operators. The original fiber core resources can be expanded by using fiber multiplexing equipment in the transmission line section from "Station A (near-end BBU)" to "Station B (far-end AAU)" in the subway to achieve rapid reconstruction. The specific construction plan is shown in Figure 2. The fiber resources between the original near-end BBU and the far-end AAU are excavated from the existing subway network by using 1:12 aggregate fiber multiplexing equipment, and then the optical signal is transmitted to one optical fiber for transmission through wavelength division multiplexing technology. The fiber core resources consume only one core to complete the network construction. It has strong scalability for high-density networking 5G networks, which is conducive to the rapid and large-scale deployment of 5G networks in special subway scenarios.

5G access network construction scenario based on C-RAN

Currently, C-RAN is a newly developed wireless access network architecture. Its baseband processing units are centrally deployed to form a baseband unit pool, which can reduce the number of physical computer rooms, thereby reducing the space occupied by computer rooms and reducing construction investment. By using high-speed optical transmission networks and distributed remote wireless modules, hierarchical collaboration between multiple cells can be achieved to achieve the purpose of resource sharing and dynamic scheduling, and build high-quality, high-speed, and low-consumption wireless networks.

In the 4G network era, due to the limitations of transmission resources and the influence of early site construction models, C-RAN has not been widely used in base station construction. However, in the post-4G era, facing the huge challenges brought by the rapid development of Internet companies, operators have proposed the concepts of cost reduction, efficiency improvement, and continuous profit growth in terms of energy consumption and operation and maintenance costs. Some provinces have begun to adopt CRAN to build sites. Therefore, in the 5G era, it will become a trend for network networking solutions to adopt C-RAN access network architecture. However, under this construction model, the demand for optical fiber resources in the transmission network is large. Faced with fierce market competition, it is urgent to quickly reconstruct optical fiber resources to achieve rapid site construction.

As shown in Figure 3, in the traditional network construction method, the transmission equipment forms a ring, and the BBU equipment at each construction site is scattered and not placed in a centralized manner. Therefore, only two optical fibers on the ring are needed. The C-RAN network construction method is to centrally handle the BBUs corresponding to multiple sites, that is, to centrally place the BBUs in a computer room with a good geographical location and suitable for access to form a BBU pool. We call this pooled computer room a C-RAN computer room. As shown in Figure 3, the BBU pool has a total of 3 BBUs and 9 AAUs (or RRUs). According to calculations, the required fiber core resources reach 18 cores. If direct optical cables are used, the network construction cannot be completed quickly.