3GPP defined the functional splits in 38.801 to formalize potential protocol split options. Functional splits are intended to allow functions to run in a central location ( ex. Data Center ) Vs. distributed in the radio heads ( ex Site Location).
There are 4 factors to be taken into consideration when choosing the right functional split as below:
- Fronthaul interface throughput and latency requirements.
As more functionality is pushed toward a central location (lower level split), fronthaul throughput increases, and latency requirements get tighter. - Implementation complexity.
There is a benefit to a low-complexity radio head (size, weight, power, and design efforts are low) which tends to be supported with a lower level (Option 7.2x split in ORAN). - Feature support.
Centralization of processing can allow for more advanced features to be implemented such as Coordinated Multi-Point transmission and reception (CoMP). - Resource sharing.
One of the main objectives of Open RAN/Cloud RAN/C-RAN initiatives was resource pooling/sharing given the peak versus average use of RF resources.