Why 7.2x split is the Best Split Option?
March 13, 2022

O-RAN’s proposed concepts and architectures use a split-RAN concept. There are eight known ways to functionally split the RAN, and each one proposes splitting the processing so that different parts of the protocol stack process on different hardware. The below figure summarizes the eight options:

O-RAN proposes using option 7-2 which splits the physical layer (PHY) into a high-PHY and a low-PHY.
For option 7-2, the uplink (UL), CP removal, fast Fourier transform
(FFT), digital beamforming (if applicable), and prefiltering (for PRACH (Physical Random Access Channel) only) functions all occur in the RU. The rest of the PHY is processed in the DU.
For the
downlink (DL), the inverse FFT (iFFT), CP addition, precoding functions, and digital beamforming
(if applicable) occur in the RU, and the rest of the PHY processing happens in the DU.

RAN Split Options (Source NGNM 2018)

2G, 3G, and 4G use Common Public Radio Interface (CPRI), which is passed on an option 8 split. Moving to the 7-2 split reduces traffic between the DU and RU. O-RAN has specified a version of the 7-2 split. The 7.2x split is the best balance between bringing this technology to market quickly and deployment cost. It reduces confusion about split specifics while making traffic reduction gains and improvements.

Operators must make trade-offs between latency requirements and fronthaul bandwidth availability, especially for the splits 2,8, and 7-2.

Latency requirements Vs. fronthaul bandwidth availability

Split option 7.2x

In this option (as per Dell technologies), the PHY layer’s functional modules are distributed between Low-PHY and High-PHY based on Open RAN specifications.

The Split 7.2x objectives are:

  • Minimize impact on transport bandwidth while maximizing virtualization in gNB CU and gNB DU.
  • Enable simple, low-cost RRU designs for wide adoption.
  • Eliminate performance loss compared to integrated solutions with ideal fronthaul.
  • Eliminate limitation on receiver architecture for performance.
  • Eliminate redesign for NR as opposed to LTE.
  • Provide increased scalability with fixed-rate streaming interface – transport data rate scales with traffic and bandwidth
  • Centralize scheduling.
  • Support advanced signal processing such as UL compression.

Support & Share