Synchronization in the O-RAN Alliance’s 5G Network Architecture

O-RAN Alliance: Redefining 5G Network Innovation

The O-RAN Alliance has emerged as the standard body that has the most important impact on the definition of 5G network architecture. The O-RAN Alliance has a vision of a disaggregated Radio Access Network (RAN) that can boost innovation while reducing deployment costs. This blog post focuses on the synchronization aspects of the O-RAN Alliance’s 5G network architecture.

Microchip Technology officially joined the O-RAN Alliance in August 2023. The O-RAN Alliance is an operator-led, standards-setting body that was established in 2018. O-RAN aims to disaggregate RAN with open and standardized interfaces following the trend started in data centers. Traditional single-vendor deployments with proprietary interfaces restrict innovation and hinder the evolution of the network architectures by limiting the ability to deploy future services.

One of the main objectives of mobile operators at O-RAN is to bring costs down and avoid being locked in with single-vendor solutions. With the goal of mixing and matching interoperable components from different vendors, O-RAN wants to create open and standardized software and hardware components to reduce costs.

Legacy cell sites consist of a Remote Radio Head (RRH), GNSS antenna and a Baseband Unit (BBU), which are deployed on cell sites. In contrast, the 5G network architecture has been disaggregated into Radio Units (RUs), Distributed Units (DUs) and Centralized Units (CUs). The centralization and sharing of BBUs as DUs and CUs result in significant operating expense savings in terms of power and cooling. Note that about 70% of the power energy of the RAN is consumed by the cell sites. The sharing of the BBU processors in a centralized location is also a significant capital expense saving since they were used only at a fraction of their full capacity on the cell sites. The RU, DU and CU software can be virtualized, containerized and deployed on cheaper general-purpose hardware.

In the previous generation of mobile networks, it was typical to deploy a Global Navigation Satellite System (GNSS)-based Primary Reference Time Clock (PRTC), as defined in ITU-T G.8272, locally at the cell site. Any change, upgrade or maintenance had to be made on each cell site. Note also that most of the GNSS antenna receivers are accurate within a range of 100 ns, which makes key features such as Carrier Aggregation (CA) very difficult to deploy.

For 5G, the O-RAN Alliance has clearly stated that network timing distribution is the preferred synchronization strategy using the open and standardized ITU-T G.8275.1 and ITU-T G.8275.2 protocols. The ITU-T G.8275.1 PTP Telecom profile is deployed in the fronthaul network from a Primary Reference Time Clock Telecom Grandmaster (PRTC/T-GM) that synchronizes Ethernet switches equipped with boundary clocks, DUs and RUs.

The deployment of a PRTC/T-GM in the fronthaul network is consistent with the 5G disaggregated RAN architecture and centralization of the timing functions in one location where they can be shared, pooled, maintained and upgraded in a flexible and economical manner. There is no longer a need to deploy a local PRTC/T-GM on each cell site location, nor to deploy more expensive oscillators on the cell sites.

TP4100

For example, a Microchip TP4100 PRTC/T-GM deployed in a fronthaul network centralized location can offer PTP ports, BITS ports (E1/T1), 1PPS/ToD ports, 1 PPS/10 MHz and a GNSS multi-constellation and multi-band port with optional expansion modules. It is possible to cascade the Microchip TP4100 to provide a higher-port density solution. It can also be locally upgraded to add future constellations. The Microchip TP4100 can also connect to a Cesium clock to realize an enhanced PRTC (ePRTC) solution, as defined in ITU-T G.8272.1, to mitigate GNSS disruptions for 40 days or longer.

For more information about our timing and synchronization products, please visit our TimeProvider^® 4100 series web page.

The benefits of O-RAN architecture are based on openness, interoperability and standardization, which allow mobile operators to choose open, off-the-shelf hardware and software components from multiple vendors. Microchip has conducted synchronization, interoperability and performance tests with the vast majority of the vendors in the mobile network ecosystem since 2008 during multi-vendor interoperability test showcases hosted by EANTC, an independent and internationally recognized test center. Microchip has also been participating in the IEEE^® 1588 PTP “plugfests” run by IEEE ISPCS for more than a decade to ensure interoperability with other components of the cellular network.