Pluggable Optics for CPRI Fronthaul Links

CPRI is a standardized protocol that outlines the digital interface between the RF Equipment and Radio Equipment Control of wireless base stations. The abbreviation of the CPRI is Common Public Radio Interface, and it ensures smooth integration and interoperability between the networking equipment from various vendors.

The entities cooperating to define and maintain the CPRI specification include; Nokia, NEC, Huawei, and Ericson. The currently available version of the CPRI is Version 7.0, whereas eCPRI is an enhanced CPRI version that is developed and standardized for 5G networks. The latest CPRI version offers a maximum line bit rate or operating speed of up to 24.3Gbps, and thus it can now accommodate 25Gbps SFP28 type optical transceivers.

In CPRI, a distributed architecture is used. The base stations comprising RECs are connected to remotely deployed radio-front equipment RRH or REs through an optical fiber cable carrying CPRI data. This architecture costs less to service providers because it allows the deployment of base stations in better environments, nearer to power and other utilities. At the same time, only the front-end radio equipment would be installed in remote locations and poor environments. Multiple remote radio front-end devices can be connected to one base station via network topology in typical networks.

Usually, CPRI links are built over optical fiber cables, which can be either:

Short distance links: These links stretch up or down the tower for connecting the Baseband Unit to Remote Radio Heads (RRHs). In most cases, the baseband units are enclosed inside a cabinet at the bottom of the tower. Whereas Remote Radio Heads are deployed at the top of the building or tower.

Long-distance links: In these CPRI links, the BBUs are deployed centrally in a Base Station located somewhere in a city. Whereas longer optical fiber cables connect scattered Remote Radio Heads to the baseband units.

BBUs are the based processing units, and RRUs are the remote radio units. These two types of units are interconnected through digital optical transceivers. RRUs, after processing radio filtering, frequency conversion, and radio amplification, emit digital baseband signals via antennas.

• One common protocol is made available for different base station manufacturers
• CPRI specifications are available for the general public and can be adapted by anyone
• It allows placement of radios far away (up to several miles) from the baseband unit
• CPRI supports various modulation schemes such as QAM
• These links can easily be deployed with the help of low-cost SFP and SFP+ modules

We have a complete range of cost-effective optical transceivers available for the deployment of CPRI based wireless fronthaul networks. These modules include industrial-grade SFP28, SFP+, and SFP. With the availability of these optical modules, one can decide to go with either single or dual fiber. The maximum transmission distance achievable through these modules for CPRI links is up to 80 kilometers.

The CPRI is a cost-effective method available for the deployment of 4G and 5G fronthaul links. It allows the network service providers to connect widely scattered remote radio units with centrally deployed base stations. Though we have a separate standard available for 5G, CPRI will continue to play a vital role because it connects 4G infrastructure to 5G networks.