lient(s). The preamble consists of two pieces: a CP and the preamble sequence itself. The sequence itself is a so-called Zadoff-Chu sequence which is a mathematical sequence designed to have a constant amplitude and to be orthogonal between sequences. Preamble formats can be split between long preambles and short preambles. Long preambles (length = 839 bits) are used in FR1/ < 6 GHz applications with a SCS of 1.25 or 5 KHz. They occupy 6 (1.25 KHz numerology) or 12 (5 KHz) numerology resource elements in the fre- quency domain. Definition of which long preamble format is to be used is done by the base station as part of the initial access (RACH) configuration. Short preambles (length = 139 bits) are used in both FR1/ < 6 GHz and FR2/mmWave applications with a SCS that is aligned to 86 Open Radio Access Network (O-RAN) Systems Architecture and Design "conventional" subcarriers, SO 15, 30, 60, or 120 KHz, allowing the same FFT to be used as for normal operation. They occupy 12 resource elements in the frequency domain. Like for shared channel operation, PRACH processing is also offloaded to the RU as opposed to sending time-domain IQ samples from RU to DU. This is done both to reduce compute resources in the DU and to limit bandwidth between the RU and the DU. Distributed unit/radio unit interface, Enhanced Common Public Radio Interface protocol overview In LTE macro cell deployments, CPRI is the dominant form of sample transport between BBU and RRH. The CPRI standard defines a GSM/Wideband Code Division Multiple Access (WCDMA)/LTE optimized synchronous framing mechanism that carries user data, manage- ment, and control. There is extensively flexibility for supporting multiple carriers and differ- ent sample widths over a single link. However, CPRI is defined for (mainly) 3GPP I/Q transport use cases and as such does not benefit from the flexibility and economy of scale provided by Ethernet. Given 5G trends, flexibility in partitioning and economy of scale, the interface between the DFE and the baseband processor i