Since the RRU/AAU of 4G/5G is usually installed outdoors, the operating temperature range of the optical module is relatively strict.
However, the BBU/DU is usually installed in the equipment room, and it is obviously unnecessary if pre-transmitted optical modules are required to meet the above operating temperature requirements. In YD/T1351-2019, the operating temperature of optical modules is divided into commercial grade: 0 degrees to 70 degrees and industrial grade: -40 degrees to 85 degrees. For optical modules used in the engine compartment, the operating temperature meets commercial grade requirements.
The transmission performance of low-speed optical modules is not affected by the operating temperature. For example, the current color optical modules used for 4G forward transmission mostly have an operating temperature range of 0 to 70°C. There is no report of network failures caused by changes in operating temperature. However, the dispersion cost of the 5g forward color optical module (see "Influence of dispersion in the 5g forward passive wavelength division scheme") is higher than normal temperature (15℃～35℃). The dispersion cost of optical modules with wavelengths of 1351nm and 1371nm increases even as high as 2-3dB.
When passive wavelength division is used for 4g pre-transmission, each optical module usually uses an adjacent wavelength. For example, the 6-in-1 system uses 1271 nm and 1291 nm, 1311 nm and 1331 nm, 1351 and 1371 nm, as shown below.
Optical module temperature
However, if the wavelength of 5G forward transmission is allocated according to the above method, an optical module with a wavelength of 1371 nm will be installed on the AAU side, which may cause a large dispersion cost due to the influence of temperature.
The optical modules used in the fronthaul are designed to be integrated transceiver management modules, and each optical module includes two different ports for information transmission and reception. The reception of the optical module is not very sensitive to the wavelength range, so we only need to pay attention to the transmission of one wavelength of the optical module when using it. For example, an optical module with a transmission wavelength of 1271nm can be used by a paired enterprise with an optical module with a transmission wavelength of 1291nm, or can be used by a pair of students with an optical module with a transmission wavelength of 1331nm.
Optical module
Therefore, it is recommended to install optical modules with three wavelengths (1331 nm, 1351 nm, 1371 nm) in the equipment room forward, and use commercial optical modules; install the first three wavelengths (1271 nm, 1291 nm, 1331 nm) on the AAU side. Optical modules, you need to use industrial-grade optical modules.
