OpenAirInterface 5G Radio Access Network Project
The scope of the OAI 5G RAN project is to develop and deliver a 5G software stack under the OAI Public Licence V1.1.
The OAI 5G stack supports the following
- – Non Stand-Alone (NSA) gNB.
- – Stand-Alone (SA) gNB.
- – 5G NSA & SA UE
For the feature list, visit the OAI Wiki page
RAN Project Group Sub-Activities
L1-simulation framework: The RFsimulator replaces the radio board by software (TCP/IP) communication in order to make possible all functional tests without a RF board. The OAI gNB and the OAI UE communicate as if there were a RF interface between them, but without any real-time clock constraints. The I/Q samples can be transmitted over a radio channel simulator. The RFsimulator also supports MIMO.
L2-simulation framework: Using actual radios or even RFsimulator does not allow testing a large number of UEs. Therefore, the L2simulator offers the possibility of connecting the OAI UE with the OAI xNB (eNB in LTE and gNB in 5G) through the nFAPI interface defined by the Small Cells Forum (SCF). nFAPI splits the xNB into a MAC entity and a PHY entity. In OAI, the xNB MAC connects through the nFAPI interface to a channel proxy that simulates the channel and allows to connect many UEs to the MAC stub. Each UE is the simulated OAI UE that connects to the proxy.
The OAI L2-simulator is a flexible tool that can serve many purposes. As an example, some partners of OAI are interfacing it with the ETSI TTCN-3 testing language framework. This would allow for building a conformance testing tool for third-party UEs.
L1 improvements: OAI layer-1 is constantly benchmarked against the performance laid out for the 3GPP channel models. We are currently working on the PUSCH receiver and benchmarking it. The receiver performance is being evaluated and tested for MIMO channels for compliance with the 3GPP standard requirements for 2, 4, and 8 receive antennas. Corresponding work is also going on the CI test coverage for PUSCH to continuously test with the Fixed Reference Channels specified in the standard. Work is also ongoing to optimize the LDPC decoder performance. The OAI L1 architecture evaluations are also being investigated to introduce more multi-threaded processing e.g, in the inner-receiver parts including FFTs and encoders.
CU/DU: A CU/DU split version of the 5G gNB deployment is available in OAI. This has been validated in the 5G SA mode with the OAI RFsimulator. The split mode allows for:
– Control plane exchanges between the CU and DU entities over F1-C (control plane, Figure reference…) according to F1AP protocol (TS 38.473, Rel.16), supporting UE end-to-end registration and PDU Session establishment
– User plane traffic over F1-U (user plane, figure reference…) using gtp-u as per TS 29.281, Rel. 16
Recently, we have updated F1-C with UE context management procedures (extensions in F1AP and RRC layers). For F1-U (user plane) interface we have also put in place the functionality to send and receive the traffic over gtp-u at each block (CU and DU). These updates allow us to have successful traffic tests between the OAI UE and the core network in CU/DU split mode.
We are currently validating the performance of CU/DU split using real RF and COTS UEs, completing the interoperability testing that has started between OAI DU and a commercial CU from Accelleran. We have also started integrating the CU-C (control plane)/ CU-U (user plane) split over E1 interface (reference figure) and extend the support for multiple CUs/DUs
Multi antenna (MIMO): Multi-antenna operations are one of the key features of 5G for high throughputs. The primary focus is on the downlink, for which the ongoing work is on 2-layer MIMO. The gNB procedures (PHY and MAC) are ready and currently under test with COTS UE for standard compliance. The MAC procedures include analysis of CSI measurement reporting for CQI, RI, and PMI. 2-layers DL-MIMO can also be tested in simulations with OAI UE with up to 4 antennas. At the OAI UE side, only the PHY procedures are implemented, including channel estimation and equalization. Since CSI-RS receiver and CSI measurement procedures are still missing, full standard DL-MIMO procedures cannot be performed yet with OAI UE. Works are currently ongoing to extend the implementation to 4 layers on the physical layer of both gNB and UE. Physical layer implementation for UL-MIMO has just started.
T1-Offload: The goal of this project is to offload time-critical and processing intensive components of the OAI TX/RX processing to the Xilinx T1 telco card. The first integration of OpenAirInterface with the Xilinx T1 card has been done by offloading the LDPC channel decoding of the uplink receive chain. The entire segment process can be run on the T1 card with the offload solution. The T1 card supports the bbdev API from DPDK to offload the channel encoding and decoding. A shared library has been created to implement the interface for DPDK. The shared library translates the OAI descriptors for ULSCH decoding into the required parameters for LDPC decoding used by the DPDK API. The HARQ has been successfully validated with multiple code blocks. The HARQ data is stored in the internal memory of the T1 card and will be retrieved and combined for decoding when a retransmission is required. The integration of the T1 LDPC offload solution into the gNB softmodem is in progress. We just also managed to share the same T1 card with 2 DUs running independently on the same host. A demo of the OAI gNB running a high throughput scenario will be shown at the Mobile World Congress in Barcelona in February 2022.
OAI 5G RAN PG Roadmap – March 2022
The following chart gives the status of current 5G implementations in the OAI codebase and a developments roadmap roughly spanning three to four quarters. We shall keep revisiting the roadmap to give the OAI community constant visibility over a similar timeframe.
Continuous Integration and Data Center Deployment
The OAI DevOps team will support the 5G testing and Continuous Integration (CI) effort as well as data-center deployment of the RAN components.
A Continuous Deployment (CD) framework is also under design and will leverage the 5G site at EURECOM.
RAN Intelligent Control
Although not mentioned explicitly in the development plan, RAN Intelligent Control (RIC) is an important component of OpenAirInterface and its developments are part of the OAI MOSAIC5G Project Group.
PROJECT GROUP SPONSORSHIP MECHANISM
To accelerate the delivery of a feature-rich and stable 5G stack, the OSA launched a new sponsorship mechanism called PROJECT GROUP in Q1 2021 for its partners, especially the industry, who are invited to donate financial resources to developments through these PROJECT GROUPS.
The OAI 5G RAN PROJECT GROUP has the goal of developing a 3GPP compatible 5G gNB Radio Access Network (RAN) stack as open source software for the OAI community. The software is distributed under the OAI Public License V1.1. Parties seriously interested in leveraging the OAI 5G code for their use-cases and thus looking to influence the development roadmap can participate by joining the Alliance as Strategic Members and then participating in the OAI 5G RAN PROJECT GROUP in one of the donor categories. For more details on the working of the Project Group and sponsorship categories, please download the Project Group Charter.
For enquiries on how to participate in the OAI 5G RAN PROJECT GROUP, please write to: firstname.lastname@example.org
Please visit the home of the project on Gitlab: oai / openairinterface5G · GitLab (eurecom.fr)