SCF releases new FAPI specification

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SCF (Small Cell Forum), the global organization supporting the evolution and adoption of low-cost, agile mobile infrastructure, has released a new specification in the FAPI suite – SCF229 FAPI Operations, Administration and Maintenance (OAM) Protocol For Inline High-PHY, as well as an update to the SCF222 5G FAPI: PHY API specification.


FAPI PHY is an agnostic interface for baseband control in a variety of disaggregated and integrated architectures, it is used in millions of the world’s system-on-a-chip based small cells.

The newly introduced FAPI OAM (SCF229) interface, brings to Open RAN fuller virtualized support of inline High-PHY implementations in O-RAN Alliance architecture.

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

Andrei Radulescu, Staff Engineer at Qualcomm and rapporteur for the FAPI document, said: “O-RAN Fronthaul M-Plane typically terminate 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.”


The version 6 updates of 5G FAPI PHY API brings support for virtual functions and poolable carrier groups; these are key to partitioning L1 SoC resources and integration in virtualized interface in cloudified architectures. The release also includes several MIMO signalling updates:

· a new SU-MIMO Codebook report;

· compact SU/MI-MIMO CSI reports (compact UCI sub-band signalling, to decrease message size);

· compact signalling of semi-static beamforming groups;

· L2-based dynamic spatial stream weights;

· explicit association between spatial streams and port types, for better O-RAN 7.2x Fronthaul integration;

· the specification was further streamlined with multiple maintenance updates.

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. We have a strong working group team within SCF working on regular FAPI and nFAPI updates, which we will continue to release in 2023.”