25G CWDM SFP28 Application In 5G Fronthaul Network

Author Yana

Date 10/29/2021

25G SFP28 CWDM transceiver, as a core component of transmission equipment and base stations, is an effective solution used in 5G fronthaul networks. This paper gives a brief introduction to 25G CWDM SFP28 transceivers and introduces the working principle and advantages of when it was applied in 5G fronthaul network.

What is 25G SFP28 CWDM?

The 25G SFP28 CWDM (Coarse wavelength division multiplexing ) transceiver designs for 5G fronthaul, and supports 25G Ethernet and CPRI (Common Public Radio Interface) /eCPRI (Enhanced Common Public Radio Interface), links reach up to 10km over single-mode fiber (SMF), which is fully compliant with the SFP28 MSA, CPRI and eCPRI standard. The wavelengths of 1270nm~1370nm and 1470nm~1570nm are normally used.

Fig. 1 - QSFPTEK 25G SFP28 CWDM Transceiver

What is 5G Fronthaul, Middlehaul and Backhaul?

5G end-to-end network including transport network, the core network (CN), and radio access network (RAN). 5G is the era of the interconnection of all things. Mobile phones, autonomous vehicles, internet of things terminals, etc. are connected to the 5G wireless access network through the 5G new radio interface, and then the signals are transmitted to the 5G CN through the transport network, it can be seen in Fig. 2.

In order to meet the requirements of large bandwidth and low latency for 5G, RAN has evolved from a two-level structure of baseband unit (BBU) and remote radio unit (RRU) in 4G network to a three-level structure of centralized unit (CU), distributed unit (DU), and active antenna unit (AAU). Fig 3 is the structure evolution from 4G to 5G network.

According to the different deployment methods, the 5G transport network can be divided into fronthaul (AAU to DU), middlehaul (DU to CU), and backhaul (CU to the core network), as shown in Fig. 2. 25G CWDM SFP28 transceivers are demonstrated capable of supporting 10km transmission, covering almost all scenarios of 5G fronthaul.

Fig. 2 - 5G Front-haul, Middle-haul and Back-haul

Fig. 3 - Structure Evolution From 4G to 5G Network

How is 25G SFP28 CWDM applied in the 5G Fronthaul Network?

25G SFP28 CWDM solution adopts 6/12 wavelengths from 18 wavelengths (from 1271nm to 1611nm) defined by ITU-T G.694.2 standard. The 6-wavelength 25G CWDM solution adopts the first 6 short wavelengths (1271nm~1371nm), as industry chain maturity and the smaller influence of the transmitter dispersion penalty (TDP). It has become a consensus that the AAU side adopts the 1271nm, 1291nm, and 1311nm wavelengths while the DU side adopts 1331nm, 1351nm and 1371 nm, as shown in Fig.4. Besides, the optical module at AAU side needs to use cooled directly modulated lasers (DMLs) to meet industrial-grade applications.

Fig. 4 - 25G CWDM SFP28 6-Wavelength Solution for 5G Fronthaul

The 12-wavelength 25G CWDM solution comes at a mixed transmission situation of 4G and 5G. To improve reliability and reduce component costs, the first wavelength of 1271nm~1371nm operate at 25Gbit/s data rate for 5G fronthaul network while the latter 1471nm~1571nm wavelengths operate at 10Gbit/s data rate for 4G fronthaul network, as shown in Fig.5 Taking the smooth upgrading of the 4G base station to 5G into account, the 25G SFP28 connector is the priority, therefore, the 12-wavelength solution is seldom used in the actual scenario.

Fig. 5 - 25G CWDM SFP28 12-Wavelength Solution for 5G Fronthaul

The advantages of 25G SFP28 CWDM in 5G Fronthaul Network

The optical module solution of 5G fronthaul includes optic fiber direct interconnect, CWDM, MWDM, LWDM and DWDM, etc. Compared to optic fiber direct interconnect solution, CWDM SFP28 transceivers solution can effectively reduce the consumption of optical fiber resources and reduce the cost of network construction. MWDM and LWDM solutions give maintenance, management, and reliability advantages over the CWDM SFP28 solution, but their industry chain is not mature currently and technical costs are more than double that of CWDM. Consequently, 25G CWDM has great significance for the coverage of the 5G fronthaul network in an efficient and economic way.

Conclusion

25G SFP28 CWDM solution offers distinct advantages in 5G fronthaul network construction especially in fiber resource shortage situations, which efficiently reduces the construction cost, and shortens the construction cycle.

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