Small Cell Forum launches new 5G FAPI specs to align with 3GPP Rel-16 features and introduces MU/Massive-MIMO support

11th Nov 2021

London, UK, 11 November 2021 – Small Cell Forum (SCF) today announced the release of its updated 5G FAPI PHY specifications. The specifications are used in millions of the world’s system-on-a-chip (SoC) small cells – and can now be applied to macro cells as well. 

FAPI is a common standard agreed between chipset and component suppliers and mobile base station integrators. It is an API for hardware components implementing 3GPP physical layer functions, and for software stacks implementing MAC and higher layers. 

FAPI has already been widely adopted in the vast majority of 3G and 4G SoC-based small cells. Significant updates to the specifications in this release include: 

  • Support for two additional 3GPP Release 16 features: low-PAPR RS and 2-step RACH, for increased cell coverage and reduced access latency; 
  • Changes to support multi-user MIMO and massive MIMO, based on sounding reference signals (SRS), for increased cell capacity; 
  • High-performance operation (Control/User Plane separation, efficient padding, efficient DL Rate Matching, etc.), by reducing processing overhead; 
  • Alignment with split Option 7-2x, one of the split options adopted by O-RAN fronthaul specifications, for easier integration; 
  • Maintenance for continued support of Release 15. 

The FAPI specification has evolved over more than 10 years to keep ahead of market requirements. This update demonstrates the ongoing commitment of the ecosystem to continually improve the standard, adding new features and maintaining existing ones. 

“The current 5G PHY FAPI release represents a further maturation of the FAPI specifications, including a significant leap from an exclusive focus on the architectures generally associated with small cells, to now support architectures where the cloud boundary might lie between high PHY and low PHY with split option 7-2x,” said Andrei Radulescu, FAPI Rapporteur and Senior Staff Engineer, Qualcomm Technologies Inc. “The latest iterations of the specifications also reflect a focus on not just functionality but performance.” 

“All RANs have MAC-PHY interfaces. With small cells, the MAC and the PHY are usually provided by different vendors, and FAPI has enabled an open ecosystem”, added Vicky Messer, Director of Product Management and FAPI Lead at Picocom. “With Open RAN, a standardised MAC-PHY interface is essential for all classes of cell, and the Small Cell Forum has risen to the challenge of enhancing the FAPI specifications to embrace new requirements.”  

“We have a strong team of SCF members supporting the ongoing review and maintenance of these specifications going forward, and a clear roadmap for future developments,” concluded Radulescu. 

Subsequent iterations planned for 2022 include further tracking of 3GPP Release 16 features like NR positioning and UE power savings and a continued focus on High/Low PHY split features essential for cloudification. 

The complete SCF FAPI specifications suite comprises: