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 towards 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 versus 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 numerologies. In a multi-cell scenario, our results show that an 82% reduction of the required fronthaul capacity can be achieved with negligible air interface performance degradation by reducing the modulation order down to 64QAM, for different numerologies and load conditions. A higher modulation order reduction without degradation is permitted in low/medium traffic loads (reaching up to 94% fronthaul capacity reduction).