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MIMO-Supporting Radio-Over-Fiber System and its Application in mmWave-Based Indoor 5G Mobile Network

We demonstrate 4 × 4 multiple-input and multiple-output (MIMO) supporting mmWave-based indoor 5G mobile network based on a distributed antenna system (DAS) that has over-the-air interface to receive the broadband wireless signal from, e.g., remote radio head (RRH) of mobile fronthaul. To realize the cost/bandwidth-efficient and low-latency-inducing indoor 5G DAS network, we exploit the radio-over-fiber (RoF) system that is based on the intermediate frequency-over-fiber (IFoF) technology. To be more specific, we make simultaneous use of wavelength- and frequency-division multiplexing in the IFoF link so as to transport 4 × 4 MIMO 5G signal of which the bandwidth is effectively 3.2 GHz (= 4 × 800 MHz, where each antenna deals with 800 MHz 5G signal). The 4 × 4 MIMO-supporting IFoF link has error vector magnitude (EVM) performance of <4.5% at all channels of downlink and uplink for up to 2 km. The whole RoF system, exploiting the IFoF link, mmWave frequency conversion module, and control /management plane, proves itself to meet the 3GPP-defined EVM requirement (i.e., 8%) at all channels. Based on the RoF system, we demonstrate the indoor 5G DAS network in conjunction with Korea Telecom 5G mobile network, i.e., 5G baseband unit and RRH, investigating the downlink and uplink throughputs. We achieve ∼4 Gb/s total throughput for end user, where the additional latency induced by the DAS network is only a few hundreds of nanoseconds other than the single mode fiber transmission delay.