Spectral Efficiency Comparison Between Analog and Digital RoF for Mobile Fronthaul Transmission Link

Abstract

Mobile fronthaul requires an efficient transfer of radio signals between cell-site remote radio heads (RRHs) and a centralized baseband unit (BBU) to satisfy diverse requirements on system capacity, latency, and cost. Both analog radio-over-fiber (A-RoF) and digital radio-over-fiber (D-RoF) enable the realization of the mobile fronthaul transmission link. A-RoF can achieve high spectral efficiency while it is susceptible to the noise and inherent nonlinearities during the optical transmission. Nevertheless, D-RoF can achieve high signal fidelity by using high quantization bits while it is commonly considered as low spectral efficiency. Therefore, the spectral efficiency comparison between D-RoF and A-RoF is generally not a fair one under the same constraint of the optical transmission link. In this paper, we theoretically analyze the recovered signal fidelity for D-RoF and A-RoF under the constraint of spectral efficiency and channel condition. We reveal that under the same channel condition, D-RoF can achieve the same spectral efficiency as A-RoF with the same recovered signal-to-noise ratio (SNR). Provided that D-RoF consumes more bandwidth, it offers the key advantage of D-RoF that the achievable SNR exhibits exponential improvement as a trade-off of the link bandwidth. If keeping the same quantization bits for radio signals, the required SNR threshold for D-RoF decreases exponentially with respect to the link bandwidth. Extensive experiments are carried out to confirm the theoretical analysis over the same constraint of the optical transmission link.