a Mobile, Deutsche Telekom AG, NTT DOCOMO Inc. and Orange but by now membership has increased after including the "Who's Who" in the wireless industry. The O-RAN public website can be found at Ref1. O-RAN is defined from the onset to be operator-driven rather than system vendor-driven, to ensure that the O-RAN goals (see next) are not interfered with. The stated target of O-RAN is to break the closed nature of current radio access network (RAN) implementations. O-RAN explicitly aims specifically at 3GPP networks, as opposed to 802.11 (Wi-Fi) and other wireless standards. By opening the 3GPP implementation, O-RAN means to decouple hardware and software implementations allowing vendors (hardware, soft- ware, and systems) to focus on providing components rather than complete solution. Aim is to follow what happened in wireline software-defined networking (SDN) (think of switches, routers, and firewalls), which have moved from proprietary, hardware-centric implementations to a software-centric implementation that executes on general-purpose, Arm, RISC-V, or x86 hardware. O-RAN is organized into working groups that own specific hardware, software, and sys- tem components. These working groups are shown in Fig. 1-1. Note that the contributions of these working groups are "live" and continuously updated. Descriptions and ownership as we are describing below are therefore per definition in flux. Check out the O-RAN member website (where parts of these descriptions are taken from) for the latest updates. Working Group 1: Use Cases and Overall Architecture Workgroup WG1 focuses on use cases and system-level requirements as well as organizing proof of concepts to showcase O-RAN products to the wider market. This working group is operator- led (AT&T, CMCC). Working Group 2: Non-Real-Time RIC and A1 Interface Workgroup Open Radio Access Network (O-RAN) Systems Architecture and Design. DOI: https://doi.org/10.1016/B978-0-323-91923-4.00013-6 © 2022 Elsevier Inc. All rights reserved. 2 Open Radio Access Network (O-RAN) Systems A