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Types Of Functional Splits In ORAN/5G NR

Types of Splits:

We have three categories of splits

  1. High Layer Splits
  2. Low Layer Splits
  3. Double Splits
  • High Layer Split: It consist of split 2,3,4 & 5.The benefits of opting this functional splits are drastically reduced bandwidth, latency tolerant i.e for long distances.
  • Low Layer Split: It consists of split 6,7 &8. The benefits of opting this functional split are cost effective RRH, Ideal for COMP. It has High Bandwidth requirements and very tight latency requirements.
  • Double Split: Double splits are the splits in which two splits have been considered between RAN i.e CU,DU & RU. Practically we have two double a) Option 2 & 6 , b) option 2 & 7.2.

Below figure represents the functional split:

B-Haul: Back Haul,F-Haul :Front Haul

Choosing a Functional Split:

When considering the functional split defining a fronthaul interface there are two competing interests:

a) There is a benefit in keeping an O-RU as simple as possible because size, weight, and power draw are primary deciding considerations and the more complex an O-RU, the larger, heavier and more power-hungry the O-RU tends to be.

b) There is a benefit in having the interface at a higher level which tends to reduce the interface throughput relative to a lower-level interface – but the higher-level the interface, the more complex the O-RU tends to be.

  • To resolve this, O-RAN has selected a single split point, known as “7-2x” but allows a variation, with the precoding function to be located either “above” the interface in the O-DU or “below” the interface in the O-RU.
  • O-RUs within which the precoding is not done are called “Category A” O-RUs while O-RUs within which the precoding is done are called 27 “Category B” O-RUs.
  • When O-RU Category A is supported by O-DU it is mandatory to support a total number of precoded streams of up to 8. Support for more than 8 precoded streams is optional.

Stay tuned for more updates on Split option 7.2x which is an ORAN Split.