Historically, in macro-cell-based networks, the radio access network (RAN) portion accounts for the largest share of energy consumption in mobile networks. With greater densification, the transition to small cells and increased virtualization of the radio processing functions, the relative energy use of the different network segments is changing. At the same time, open radio access networks (O-RAN) have emerged as a promising approach to support this evolution through open interfaces that enable a multi-vendor environment, support for hierarchical intelligent controls, and simplified, cost-effective radio units that facilitate large-scale deployments. This paper examines the impact of these changes on energy consumption in next-generation RAN architectures through transaction-based energy models. Transaction-based network energy models were developed in 2009 to understand the evolution of energy use in networks. Here we update these models with today's hardware and apply recently developed models for emerging architectures, considering current access point densification trends. Results indicate that efficiency improvements have followed predicted trends, which were largely based on semiconductor Moore's Law-related evolution. Emerging RAN architectures show improved energy per bit, although the processing energy becomes the largest contributor. Densification increases total energy consumption, but the relative contributions of processing and transport energy depend strongly on the location of the baseband processing.

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