Connecting the RRU AAU Optical Cable

The field optical cable is a kind of metal-free optical cable specially designed for rapid wiring or repeated retractable system use in field operations and complex social environments. Most of the cores of field optical cables are 1, 2, and 4 cores. The section data structure of a field optical cable is introduced below.

Field cable structure

The single-core optical cable in the above optical cable part is a light yellow cable between the two active connector plugs in the commonly used single-core jumper network. Many people call it soft optical fiber, but its standard name is "single-core indoor optical cable".

Indoor fiber optic cable

Field fiber optic cables are often used with removable connector plugs, since single-fiber cables are ideal for patch cords (with removable connector plugs at both ends) or pigtails (with removable connector plugs at one end).

To facilitate quick deployment, field fiber optic cables are usually used as fiber optic cable assemblies, including: field fiber optic cables, fiber optic cable connectors, and retractable racks. For portability, the field optical cable has a smaller diameter and lighter weight.

field cable

In order to meet the requirements of fast wiring and repeated unplugging in the field and in complex environments, field optical cables also have the characteristics of tension resistance, pressure resistance, high strength-to-weight ratio, good flexibility, easy bending, oil resistance, wear resistance, flame retardancy, and wide temperature range, etc. features.

1. Development status of optical cable for RRU/AAU connection

The BBU/DU and RRU/AAU of the base station need to be connected through optical cables. However, the RRU/AAU is mostly installed outdoors, such as iron towers, etc., and the optical cable connecting to the BBU/DU is required to have the characteristics of convenient mobile connection, outdoor use, safety and reliability.

Current status of field optical cable

Field optical cables meet these requirements well, so field optical cables are widely used for connection between base station BBU/DU and RRU/AAU.

The connection between the antenna end of the field optical cable and the AAU of the 5G base station is shown below.

Base station cable

Open the outdoor quick-lock fiber optic connector, and you can see the fiber optic cable on the active connector. The active connector plugs into the optical module on the AAU. The field optical cable is far away from the active connector at the antenna end, and is usually directly inserted into the e)CPRI interface optical module of the BBU/DU equipment baseband board (E) in DRAN mode. In CRAN mode, it may be plugged into the ODF unit of a base station/outdoor network cabinet, or the port of the passive wavelength division multiplexer/demultiplexer, and then connected to the BBU/DU device through the access cable for ordinary users.

2. The use of RRU/AAU connecting optical cables is confusing

Although the mechanical and protective properties of the field optical cable far exceed the actual requirements, the operators still feel that it is not enough. A layer of metal armor (the flexible steel pipe below) is added to the field optical cable to make its pressure resistance up to 3000N/100mm;

How to Protect Field Fiber Optic Cables

The tensile strength of the single-core optical cable in the field optical cable is low (40N), and it is not resistant to ultraviolet rays. Therefore, when the field optical cable is connected to the AAU, an outdoor quick-lock connector should be used to fix the sheath of the field optical cable to avoid direct stress on the single-core optical cable. However, the height of the outdoor quick lock connector is less than 10 cm. When the length of the single-core optical cable at both ends of the field optical cable exceeds the height of the outdoor quick-lock connector, the outdoor quick-lock connector cannot be fixed on the sheath of the field optical cable, which will force the single-core optical cable at the AAU end to be exposed outdoors.

Since the length of a single purchase of an outdoor optical cable is determined, the commonly used ones are: 40 meters, 50 meters, 60 meters, 70 meters, and 80 meters. During construction, the remaining length of each cable shall not exceed 10 meters. Usually a base station (physical station) includes several logical stations, and each logical station needs to lay at least 3 on-site optical cables, so that the total length of the remaining on-site optical cables of the base station can exceed 100 meters. The common steel pipe towers on the roadside are basically stuffed with wild optical cables.

3. What kind of optical cable is needed for RRU/AAU connection

The RRU/AAU connection optical cable customized by the operator is not suitable for outdoor use due to its metal components, so it is actually an armored optical fiber jumper for outdoor use, but we are still used to calling it an outdoor optical cable.

The RRU/AAU optical cable specified by YDT 2289 does not have the characteristics of wear resistance, impact resistance, bending resistance, oil resistance, and temperature adaptability of field optical cables, and has lower requirements than ordinary communication optical cables, but requires flame retardancy. The remaining length of the RRU/AAU optical cable can be controlled by field termination of the optical cable at the equipment end (that is, making active connector plugs).

The optical cable at the RRU/AAU end is still prefabricated in the factory. After the optical cable at the equipment end is cut according to the actual length, as with the FTTH household optical cable, a section of pigtail is welded on site for termination, and the welding point is protected by a protective box.