Modulation Compression in Next Generation RAN: Air Interface and Fronthaul Trade-offs

Modulation compression is a technique considered in the recent Open-RAN (O-RAN) framework, which has continued the 3GPP effort toward the definition of new virtualized and multi-vendor RAN architectures. Basically, fronthaul compression is achieved by means of reducing the modulation order, thus enabling a dramatic reduction of the required fronthaul capacity with a simple technique. In this work, we provide a survey of the architectures, functional splits, and fronthaul compression techniques envisioned in 3GPP and O-RAN. Then we focus on assessing the trade-offs that modulation compression exhibits in terms of reduced fronthaul capacity vs. the impact on the air interface performance, through a dynamic multi-cell system-level simulation. For that, we use an ns-3-based system-level simulator compliant with 5G New Radio (NR) specifications and evaluate different traffic load conditions and NR numerolo-gies. In a multi-cell scenario, our results show that an 82 percent reduction of the required fronthaul capacity can be achieved with negligible air interface performance degradation by reducing the modulation order down to 64-QAM for different numerologies and load conditions. A higher modulation order reduction without degradation is permitted in low/medium traffic loads (reaching up to 94 percent fronthaul capacity reduction).