Latency Analysis of SDR-based Experimental C-RAN / O-RAN Systems

A paradigm shift in radio access network (RAN) architectures was initiated by Cloud RAN (C-RAN) and now Open RAN (O-RAN) systems. Leveraging software defined radios (SDRs), it is possible to enhance scalability, flexibility, and cost efficiency; from prototyping to deployment. However, the feasibility of using SDRs in C-RAN / O-RAN deployments heavily depends on latency constraints, particularly for time-sensitive protocol operations. In this paper, we present results from an extensive experimental evaluation of latency in commonly used SDR platforms, including USRP B210, N210, N310, and X410. For this, we implemented a novel round trip time (RTT) measurement method at the SDR driver level for precise RTT analysis. Our findings highlight the impact of SDR hardware, the connection to the host computer, sampling rates, and protocol optimizations. While all tested SDRs meet the latency requirements for 4G/5G-based C-RAN implementations (less than 500 μs), some approach the 25 μs one-way O-RAN delay, and none currently satisfy the more stringent 9 μs requirements of WiFi. We identify key optimizations, such as reducing the maximum transmission unit used in the fronthaul link layer and leveraging data plane development kit (DPDK) for low-latency networking, that significantly improves the SDR performance. Our results show that, in an optimal setup using X410 USRP, 100Gbe Ethernet fronthaul, DPDK, and optimal maximum transmission unit (MTU) size, the worst-case RTT stays below 65 μs.