Downlink Fronthaul Compression in Frequency Domain using OpenAirInterface

This paper presents a compression scheme developed for the transport of downlink radio signals in packet fronthaul of centralized-radio access networks (C-RAN). The technique is tailored to frequency-domain functional splits, in which inactive LTE (or 5G NR) resource elements may not be transmitted in the packets. This allows decreasing the link data rate, especially when the cell load is low. The compression scheme is based on two parts: transmission of side information to indicate active and inactive resource elements of the LTE; and nonuniform scalar quantization to compress the QAM symbols of the active resource elements. The method was implemented in the OpenAirInterface (OAI) software for a real-time evaluation. The testbed results show a significant reduction in the link usage with a relative low computational cost.