From ORAN to Cell-Free RAN: Architecture, Performance Analysis, Testbeds and Trials

TL;DR

This paper explores the transition from ORAN to cell-free RAN architectures, analyzing their performance, implementation challenges, and experimental validation for 5G and 6G systems.

Contribution

It provides a comprehensive study of CF-RAN under ORAN, including theoretical analysis, implementation issues, and experimental results for uplink and downlink performance.

Findings

CF-RAN improves spectral efficiency and reliability.

Implementation challenges include synchronization and calibration.

Experimental results validate distributed reception and joint transmission.

Abstract

Open radio access network (ORAN) provides an open architecture to implement radio access network (RAN) of the fifth generation (5G) and beyond mobile communications. As a key technology for the evolution to the sixth generation (6G) systems, cell-free massive multiple-input multiple-output (CF-mMIMO) can effectively improve the spectrum efficiency, peak rate and reliability of wireless communication systems. Starting from scalable implementation of CF-mMIMO, we study a cell-free RAN (CF-RAN) under the ORAN architecture. Through theoretical analysis and numerical simulation, we investigate the uplink and downlink spectral efficiencies of CF-mMIMO with the new architecture. We then discuss the implementation issues of CF-RAN under ORAN architecture, including time-frequency synchronization and over-the-air reciprocity calibration, low layer splitting, deployment of ORAN radio units (O-RU), artificial intelligent based user associations. Finally, we present some representative experimental results for the uplink distributed reception and downlink coherent joint transmission of CF-RAN with commercial off-the-shelf O-RUs.