The O-RAN Radio Interface allows the development of a complete solution to support all the features required by an advanced fronthaul interface. In the LTE and 5G radio mobile architectures, fronthaul is the transport network interconnecting the Remote Radio Units (RRUs) to the Baseband Units (BBUs) and relies on different topologies, such as point-to-point, point-to-multipoint, and ring. To match modern network requirements in efficiency and flexibility, the fronthaul network is packet-based, relying either directly on the Ethernet network protocol or on a UDP/IP stack.
The O-RAN Radio IF system, shown in the following figure, built from the O-RAN Radio Interface and other Xilinx® IP, is a computing platform designed to support the management of the user, control, and synchronization planes, working as an intelligent and adaptable network interface submodule within an implementation of a 5G RRU.
The O-RAN Radio IF supplies IP, drivers, and software APIs to implement supported protocols. The O-RAN Radio IF IP is implemented in the programmable logic (PL), and the drivers and software APIs run on Linux on the Arm® processor. In the following figure, the O-RAN Radio IF C library, the libmetal driver, and the O-RAN Radio IF IP core comprise the solution and are required for full protocol support; the O-RAN Radio IF C example application provides code to demonstrate the solution.
The C-Plane and U-Plane are handled in hardware. The subsystem configuration and other user services can be handled by a software API library running on the embedded processor with dedicated hardware features, such as packet timestamping at the PCS/PMA level. Because no more circuit-based interconnections are available, it is also necessary to synchronize each node through the packet network; the synchronization plane therefore relies on a PTP protocol such as IEEE 1588 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems (IEEE 1588), and on Synchronous Ethernet.
The O-RAN Radio IF system provides a platform to run the Linux PTP Precision Time Protocol (ptp4l) software application for IEEE 1588 hardware timestamping and control of the hardware-based timer. The O-RAN Radio IF core can realign its internal timers to the Start of Radio Frame information transported by the synchronization plane. Control plane management relies on protocols such as SNMP and ICMP, running on an IP stack and implemented in software on the embedded processor.
The O-RAN Radio IF system deals with two different packet flows:
- O-RAN C-Plane and U-Plane traffic: Time-sensitive and high-priority flow handled by dedicated and adaptable O-RAN Radio IF hardware
- Lower priority traffic flows: Including O-RAN S-Plane and M-Plane and other non-O-RAN protocols, all of which can be managed by the Zynq® UltraScale+™ MPSoC processor, or CIPS in Versal® .
The O-RAN Radio IF can filter each incoming downlink packet in real time, recognize messages carrying antenna-carrier data, and forward them to the managing hardware, while redirecting all remaining traffic to the embedded processor through a DMA interface. In the uplink direction, the subsystem must arbitrate access to the supported Ethernet ports between the higher priority stream generated by the O-RAN Radio IF core and that coming from the embedded processor.