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17 January 2023

Small Cell Forum extends FAPI interface to further open RAN options

By Wireless Watch Staff

The Small Cell Forum has released a new addition to its FAPI (Functional API) family of interfaces, which is designed to provision Layer 1 system-on-chip (SoCs) with management plane capabilities for Open Fronthaul, the initial specification devised by the O-RAN Alliance.

The new spec provides some bridging between the two organizations’ preferred 3GPP functional splits (which define how MAC and PHY layer functions are split across the radio unit and the virtualized baseband in a vRAN). SCF has mainly focused on Split 6, in which Layer 1 functions are deployed on the RU, and O-RAN Alliance on Split 7.2, which divides Layer 1 between the RU and the baseband.

The spec is officially called SCF229 FAPI operations, administration and maintenance (OAM) protocol for inline high-PHY. This allows FAPI PHY, which sits between the radio and baseband, to support an O-RAN PHY split.

The new specification was the result of collaboration between Qualcomm and Mavenir, as well as reviewers from Picocom, Radisys and Reliance Jio.

Andrei Radulescu from Qualcomm, rapporteur for the FAPI document, said: “O-RAN Fronthaul M-Plane typically terminates in L2/L3, requiring the FAPI suite to convey O-RAN M-Plane content between L2/L3 and L1. This is taken care of in the new specification SCF229.”

SCF Forum also updated SCF222, creating version 6 of the 5G FAPI PHY API to add support for virtual functions and poolable carrier groups, to enable partitioning of L1 SoC resources and integration in virtualised interface in cloud RAN architectures.

Radulescu added: “This update brings the L1/L2 interface support to a fully cloudified environment; it also further advances MIMO signalling to support new architectures and macro deployments. The new SCF229 specification, together with the updates of the SCF222 are further indication of the FAPI suite evolving and meeting industry requirements, and it demonstrates SCF’s commitment to consistently updating and expanding the API.”