Fronthaul, also known as mobile fronthaul, is a term that refers to the fiber-based connection of the centralized radio access network (C-RAN), a new type of cellular network architecture of centralized baseband units (BBUs) and remote radio units (RRUs) at the access layer of the network.

Fronthaul originated with LTE networks when operators first moved their radios closer to the antennas, which gained International Telecommunication Union (ITU) approval in 2012. Fronthaul complements the backhaul connections between the central office and BBU, enabling the rapid transfer of data and denser network coverage.

Fronthaul is used to support all generations of wireless communications. With the increasing demand for fifth-generation (5G) technology, C-RAN deployments fronthaul has accelerated in recent years.

What is 5G fronthaul?

5G fronthaul facilitates enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (uRLLC) and massive machine-type communication (mMTC) for internet of things (IoT) networks. 5G provides gigabit (Gb) speeds and low latency, and it helps establish fronthaul transport capacity.

Fronthaul enhances network performance, making it more flexible and efficient. However, many factors must be considered before adopting it, including the type of spectrum, amount of fiber on the ground, available expertise and network topology.

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

CWDM 25G SFP28 solution adopts 6 or 12 wavelengths from 18 wavelengths (from 1271nm to 1611nm) defined by ITU-T G.694.2 standard. The 6-wavelength 25G CWDM solution adopts 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 Figure - 1. Besides, the optical module at AAU side needs to use cooled directly modulated lasers (DMLs) to meet industrial-grade applications.

The 12-wavelength 25G CWDM solution comes at a mixed transmission situation of 4G and 5G. To improve reliability and reduce component costs, the wavelength of 1271nm~1371nm operate at 25Gbit/s data rate for 5G fronthaul network while the 1471nm~1571nm wavelengths operate at 10Gbit/s data rate for 4G fronthaul network, as shown in Figure - 2.

The advantages of 25G SFP28 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.