On the Suitability of Multicore Fiber for LTE–Advanced MIMO Optical Fronthaul Systems

This paper proposes and evaluates analytically and experimentally the suitability of spatial multiplexing in multicore fiber (MCF) for multiple-input multiple-output (MIMO) LTE-Advanced (LTE-A) optical fronthaul systems including carrier aggregation. The experimental test-bed comprises a 150-m optical fronthaul of four-core homogeneous MCF, which can be configured with different bending radius for analysis. Performance of linear crosstalk in MCF media is evaluated by simulation and validated by the experimental work in the laboratory with the radio-over-fiber transmission of full-standard LTE-A wireless signals considering both SISO and MIMO configurations. The optical fronthaul analysis evaluates both same-propagation and counter-propagation spatial multiplexing, i.e., all cores propagating in the same direction and two versus two cores propagating in opposite directions, corresponding to a dual LTE-A roof-mounted system. The performance of the MCF optical fronthaul system is evaluated using a single 20-MHz LTE-A carrier and also carrier-aggregated signals with 16QAM and 64QAM subcarrier modulation. The experimental results indicate that intercore crosstalk (IC-XT) increases up to 9.6 dB when raising the bending radius from 35 to 67 cm, being the bending radius a key parameter in MCF fronthaul systems. The demonstration performed at 1550.12 nm reported an increase of IC-XT of 4.6 dB with the bending radius, which deteriorates the quality of the SISO LTE-A signal up to 8.1 dB error vector magnitude (EVM). This IC-XT impairment can be mitigated using 2×2 MIMO processing, which reduces the EVM impact to less than 1 dB when increasing the MCF bending radius from 35 to 67 cm. The experimental results indicate that 3GPP MIMO LTE-A algorithms already in-place in the wireless LTE-A standard can be used to compensate the IC-XT in the 150-m multicore optical fronthaul system with spatial multiplexing.