O-RAN
ETSI has adopted PAS (Publicly Available Specification) ETSI TS 103 982, that specifies the overall architecture of O-RAN and describes architecture elements and relevant interfaces that connect them.
The O-RAN architecture is builds upon 3GPP RAN standards towards openness and intelligence by adopting RAN splits, new interfaces, RICs, and Service Management and Orchestration (SMO). It adopts split 2 (also referred to as higher-layer split, HLS) between PDCP and RLC protocols within the New Radio (NR) air interface stack; and split 7.2x (also referred to as lower-layer split, LLS) within the PHY layer. The corresponding elements of O-RAN are called O-RAN Central Unit (O-CU), O-RAN Distributed Unit (O-DU), and O-RAN Radio Unit (O-RU). O-CU is further split into the control plane (O-CU-CP), which covers Radio Resource Control (RRC) with Packet Data Convergence Protocol-Control Plane (PDCP-C) protocols, and the user plane (O-CU-UP) covering and Service Data Adaptation Protocol (SDAP) with PDCP-User Plane (PDCPU). O-DU, in turn, encompasses Radio Link Control (RLC), Medium Access Control (MAC), and a high-physical layer, including the MAC scheduler. Finally, O-RU includes lowphysical layer functionality like Orthogonal Frequency Division Multiple Access (OFDMA) processing, beamforming, and Radio Frequency (RF) front end.An essential element introduced in O-RAN is the RAN Intelligent Controller (RIC), a separated-out entity from the processing units that allow access to RRM functions. RIC is split onto Non-Real-Time RIC (Non-RT RIC) and Near-Real-Time RIC (Near-RT RIC). The former works in the timescale of above 1 s, is used for non-real-time radio resource management, higher layer procedure optimization, and policy optimization in RAN, and enables the artificial intelligence (AI) and machine learning (ML) workflow for RAN components. In addition, it provides policy-based guidance for the applications in Near-RT RIC and delivers Enrichment Information (EI) for the Near-RT RIC’s applications. Near-RT RIC, on the contrary, is part of the RAN to enable control and optimization of algorithms for radio resource management, and it works with the control loop in a timescale of longer than 10ms and shorter than 1s utilizing the use-case specific applications called xApps.O-RAN is the main standardization body specifying the O-RAN reference architecture, interfaces, deployment scenarios, use cases, etc. Alliance specifies new interfaces, including Open Fronthaul (OFH), which connects O-DU to O-RU, E2, and A1 serving as control loop connections, and O1, O2, OFH M-plane - i.e. management interfaces. O-CU-CP, O-CU-UP, and O-DU are called E2 Nodes in the O-RAN architecture. This is because they are connected via the E2 interface to the Near-RT RIC, by which their functionality can be controlled through external applications xApps.Near-RT RIC is one of the critical elements in the O-RAN architecture, which allows feeding intelligence into the operations of the RAN. It creates a platform on which the software providers could build xApps to control the RAN per-use case to allow the optimization of radio resources for specific scenarios. To date, several open-source projects are used to implement Open RAN systems. Such platforms may provide the entire stack, including RAN software, RICs, SMO, or a subset of those components.
Open radio access network (O-RAN) is a type of radio access network (RAN) that allows interoperability between cellular network equipment developed by different vendors. O-RAN aims to transform the traditional monolithic hardware-centric RAN design into one that uses separate building blocks with open and standardized interfaces. As a result, wireless network equipment providers can focus on providing specific software components rather than building an entire RAN. This componentization enables wireless service providers to mix and match components sourced from multiple vendors. You can use MATLAB® and 5G Toolbox™ to generate fronthaul control and user (CU) plane messages for O-RAN conformance tests.
How MATLAB and 5G Toolbox can help you generate CU plane messages for testing O-RAN designs:
How MATLAB and 5G Toolbox can help you generate CU plane messages for testing O-RAN designs:
O-RAN ArchitectureThe left side of figure depicts how a traditional RAN uses blocks, such as baseband unit (BBU) and radio unit (RU), provided by a single vendor. To accommodate more flexibility in the design of radio access networks, the O-RAN Alliance has developed O-RAN protocols, allowing the baseband and radio units to be split into three different modules and their protocol layers, each of which can be provided by different vendors:O-RU (O-RAN radio unit), which processes the RF and lower part of the physical layer (Low-PHY)O-DU (O-RAN distributed unit), which takes on tasks of the upper part of the physical layer (High-PHY), medium access control (MAC), and radio link control (RLC)O-CU (O-RAN central unit), which manages the packet data convergence protocol (PDCP), service data adaptation protocol (SDAP), and radio resource control (RRC) protocol entitiesIn the O-RAN context, the interface between O-CU and the core network is known as backhaul, the interface between O-DU and O-CU is known as midhaul, and the interface between O-DU and O-RU is called fronthaul. You can use MATLAB and 5G Toolbox to develop algorithms that generate data for Fronthaul and other O-RAN interfaces, as depicted in Figure 2. You can also use MATLAB, Simulink®, and Wireless HDL Toolbox™ to reduce the complexity of your implementation and then integrate, test, and validate your O-DU and O-RU systems on FPGA through Model-Based Design.
Figure 1. Comparison between traditional radio access network (RAN) and open radio access network (O-RAN) architectures.
Figure 1. Comparison between traditional radio access network (RAN) and open radio access network (O-RAN) architectures.
The O-RAN Alliance has selected split 7.2x, which lies between the lower part of the physical layer (Low-PHY) and the upper part of the physical layer (High-PHY). The open fronthaul interface between O-DU and O-RU is defined at the 7.2x split.
Figure 2. O-RAN protocol components (O-RU, O-DU, and O-CU) and their protocol entities.
Figure 2. O-RAN protocol components (O-RU, O-DU, and O-CU) and their protocol entities.
O-RAN Fronthaul signal processingIn downlink (DL) processing, for example, the sequence of operations can be subdivided between the ones preceding the 7.2x split and the ones following it. On one side of the 7.2x split, the functionality goes up to resource element mapping in the O-DU as follows:
Figure 3. O-RAN protocol hierarchy and 5G NR functional split options.
- The user bits are received from the medium access control (MAC) layer.
- These bits, organized as transport channels, undergo 5G NR higher layer signal processing operations including data encoding, scrambling, modulation, layer mapping, and precoding and resource element mapping.
- The resulting IQ samples generate the 5G NR resource grid.
- Precoding and digital beamforming
- Cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) signal generation, which is composed of inverse fast Fourier transform (IFFT) followed by cyclic prefix insertion
- Digital-to-analog conversion and analog beamforming
- Over-the-air analog signal transmission on the designated antenna port at designated RF frequency
Figure 3. O-RAN protocol hierarchy and 5G NR functional split options.
To enable sending information between the two 7.2x splits in the open fronthaul, you must follow these instructions: On the O-DU side, the High-PHY information is first compressed, then encapsulated within enhanced common public radio interface (eCPRI) packets and finally embedded within Ethernet frames and transmitted. On the O-RU side, the received Ethernet frames are acquired, eCPRI packets are extracted, the data within packets are decompressed, and then Low-PHY operations are performed. These steps are depicted in Figure 5. The need for compression stems from the limited capacity of the open fronthaul. The O-RAN Alliance suggests different compression and decompression methods to reduce the bandwidth of the transmission.
Figure 4. Signal flow and signal processing steps in downlink open fronthaul.
Figure 4. Signal flow and signal processing steps in downlink open fronthaul.
O-RAN modeling and simulation with MATLABUsing MATLAB and 5G Toolbox, you can generate fronthaul control and user (CU) plane messages for O-RAN compression conformance tests. You can use 5G Toolbox to generate and decode those packets. All the physical layer functions that belong to the High-PHY and the Low-PHY are available in the toolbox.
Open fronthaul modeling and simulation in 5G Toolbox enables you to:
Open fronthaul modeling and simulation in 5G Toolbox enables you to:
- Apply High-PHY operations and then extract IQ data in 7.2x split, which is the data coming from the resource grid.
- Compress the data using one of the compression methods available. Supported compression methods are block floating point (BFP), block scaling, and mu-law, as defined in TS O-RAN.WG4.CUS Annex A.1.1, A.2.1, and A.3.1, respectively.
- Build the O-RAN fronthaul CU-plane messages, as defined in TS O-RAN.WG4.CUS, and write the messages to a PCAP file. These fronthaul messages would be sent from the O-RAN distributed unit (O-DU) to the O-RAN radio unit (O-RU).
- Decode the CU-plane messages in the O-RAN radio unit (O-RU).
- Recover the resource grid, uncompress the data, and continue with the Low-PHY operations.
Open RAN conceptWith its software-centric approach, O-RAN is revolutionizing the way we deploy, manage, and evolve our networking infrastructure.The Open Radio Access Network aims to enable disaggregated, virtualized, programmable, and data-driven intelligent network with open interfaces to support various real-time and non-real-time applications for different classes of users and multiple industry verticals in beyond 5G and 6G networks while providing interoperability among multi-vendor network functions and components.Advantages:
- avoid vendor-lock
- enable faster innovation
- reduce CAPEX
- quick time-to-market
- enable design flexibility
- enable new services and application
- technology maturity
- interoperability and integration
- complex automation
- price OPEX?
- performance
- inertia
Open RAN language RDSLThe open architecture of Open RAN means hardware and software can be sourced from different suppliers. These component parts need to seamlessly communicate with each other to maximise Open RAN’s energy efficiency, low latency, and capacity. The RDSL new language is key to achieving this goal, creating a fully open, virtualised, and interoperable mobile base station.Vodafone, Cirrus360, and Intel have demonstrated a computer language framework for Open Radio Access Networks (RAN) that automates the process of introducing and running software across hardware from multiple vendors.The RAN Domain Specific Language (RDSL), which is described in a white paper shared with the wider RAN community (see link below), provides operators with a faster and more cost-effective way to fine tune software to sync perfectly with silicon chips and other hardware that make up an Open RAN mobile site.