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In this paper, we present and experimentally demonstrate a broadband intermediate frequency-over-fiber (IFoF) system with adaptive frequency transmit diversity for the next generation mobile fronthaul (MFH) applications. We propose to employ an integrated dual-parallel Mach-Zehnder Modulator (DPMZM) with adaptive dc-bias voltage setting for a simplified, efficient, and flexible IFoF communication system. The DPMZM is utilized to compensate the chromatic dispersion (CD) induced deep RF power fading impact, by taking advantage of the frequency transmit diversity of the two parallel modulators and optical paths. Using probe signals and the supervised machine learning (ML) technique, an accurate frequency response of the system is generated and utilized to design a dynamic allocation of IF channels to each DPMZM port. This ML-based link frequency response can capture the accumulated CD-induced power fading frequency region, as well as the random degradation caused by the used RF and optical devices characteristics and bandwidth limitation. Applying our proposed system, we successfully transmitted 15 IF channels with 1.2 GHz bandwidth and 64-QAM-OFDM modulated signals over 20-km fiber length, leading to about 1.18 Tbps CPRI-equivalent data rate. If we assume the maximum spectral efficiency of the LTE-A systems (i.e., 3.75 bit/s/Hz), the user throughput can be higher than 67 Gb/s. The obtained results show the potentials of DPMZM-based multi-IFoF system to satisfy the high capacity requirement of 5G mobile network and beyond.

This paper gives an overview of the recent trends of FSO systems for B5G/6G era, covering transceiver design, system architectures and integration with mmWave/THz links. The potential implementation of machine learning algorithms is also discussed.

We developed a novel full-duplex FSO transceiver with optical-image stabilizer (OIS) and free-space-optical circulator. The OIS technology, which is widely used by smartphones cameras, was successfully implemented to expand the transceiver field-of-view (FOV) and maintain laser beam alignment with efficient seamless coupling to fiber core.

A secure free-space optical (FSO) system using a Y-00 quantum stream cipher is proposed and error-free (BER-9) secure FSO transmission over 30 m is achieved with a real-time 1.5-Gb/s Y-00 cipher with 4096 intensity levels.

We report high-capacity intermediate-frequency-over-fiber (IFoF) transmission using parallel intensity/phase modulators (IM/PM). Thanks to the parallel IM/PM transmitter, we can avoid all the null frequencies caused by dispersion-induced RF power fading. Compared to other techniques to avoid RF power fading, the parallel IM/PM transmitter offers a simple solution because it does not rely on any sophisticated digital signal processing. We transmitted 14 $\times$ 1.2-GHz orthogonal-frequency-division-multiplexed signals over a 20-km single-mode fiber using the parallel IM/PM transmitter and achieved a Common Public Radio Interface equivalent data rate of 1.032 Tb/s. Thus, an IFoF system with the parallel IM/PM transmitter shows great potential to be applied to high-capacity mobile fronthaul links in the upcoming fifth-generation mobile system and beyond.

In this letter, we present a proof-of-concept of a real-time 10-Gigabit Ethernet (10GbE) standard data connectivity over a seamlessly converged intermediate frequency IF-over-fiber and millimeter wave links with remotely fed optical local oscillator (LO) signals. We demonstrate an error-free real-time transmission of $\pi /4$ -DQPSK-mapped 10GbE frames at 5-Gbit/s over $2\times 20$ -km single mode fiber and 20-m W-band (i.e., 96 GHz) wireless bridge. The 10GbE traffic is adjusted to the actual system capacity and transmitted using two parallel channels with a maximum rate of 1.25-GBaud per channel. We experimentally investigate and evaluate the impact of RoF and W-band links characteristics on the overall system performance. The obtained results demonstrate the potential use of the proposed system for the next generation agile and resilient access networks.

In this paper, an evolution scenario of optical access infrastructure that supports Beyond-5G mobile system is presented by referring two major technical trends of RAN slicing and RoF-based transmission scheme.

This paper discusses the potential of the Intermediate Frequency-over-Fiber (IFoF) technology for future mobile fronthaul links. The result of the recently achieved 1-Tb/s CPRI-equivalent-rate transmission with a parallel IM/PM transmitter is also presented.

This invited paper discusses the potential of the Intermediate Frequency-over-Fiber (IFoF) technology for future mobile fronthaul links. First, we explain the fundamental of IFoF and its advantages over the conventional digital-based schemes such as Common Public Radio Interface (CPRI) from the point view of centralized radio access network (C-RAN) architecture. Then, our recent results including the experimental demonstration of the 1-Tb/s CPRI-equivalent-rate transmission with a transmitter composed of parallel intensity/phase (IM/PM) modulators are presented.

Ultra high frequency radio frequency identification (UHF RFID) systems can use passive tags to reflect the signal from the reader’s transmitting antenna back to the reader’s receiving antenna for information delivery. This gives a cascaded channel that is a product of two fading components. In this work, the probability of detection, defined as the probability that the received power is above the receiver sensitivity, is derived when the two fading components suffer from correlated generalized Rician fading. This includes the Rayleigh, Rician, and Nakagami- $m$ channels in the literature as special cases. Numerical results are presented to show the effects of link distances, receiver sensitivities, and channel parameters on the detection probability.

This invited paper overviews the potential of the intermediate frequency-over-fiber (IFoF) technology for future mobile fronthaul links, and clarify its advantages and disadvantages by comparing digital-based transmission scheme. Our recent achievements including 1-Tb/s-class CPRI-equivalent rate transmission are also presented.

The future mobile access network exploiting Radio-over-Fiber transmission technology is overviewed in this paper. Relating recent achievements are introduced, and future issues to be further investigated are also explained.

In this paper, we introduce and demonstrate a high capacity intermediate frequency-over-fiber (IFoF) transmission system using integrated dual parallel Mach-Zehnder modulator (DP-MZM) for mobile fronthaul (MFH) applications. By using an optimized assignment of the multi-IF channels used to drive the DP-MZM and simple IF channels power weighting pre-emphasize in optical domain, the chromatic dispersion-induced RF power fading can be easily overcome. Each IF channel consists of 1.2-GHz orthogonal frequency-division-multiplexed (OFDM) signals, with 1000 subcarriers with 64 QAM-modulated symbols and 200 subcarriers with QPSK modulated pilots. Moreover, we evaluate the performance of our proposed system for different number of IF channels and data rates. Using our proposed system, we successfully transmitted (14 × 1.2-GHz) multi-IFoF signal with 1.032 Tbit/s CPRI-equivalent data rate over a 20-km single mode fiber. The obtained results demonstrate the potentials of DP-MZM based IFoF systems to provide massive data transfer for MFH.

We present and experimentally validate a simple and efficient technique to overcome the chromatic-dispersion-induced power-fading for broadband RoF systems. Using DP-MZM, the dispersion compensation is obtained by a complementary power-fading of the resulting electrical output from the two parallel MZMs.

We demonstrate the IF-over-Fiber transmission over 20-km SMF using a parallel IM/PM transmitter with 1.032-Tb/s CPRI-equivalent data rate, for the first time. Thanks to the transmitter, we can avoid dispersion-induced RF power fading without any sophisticated DSP.

The traffic in optical and mobile networks has been rapidly increasing. The peak rate of 5G mobile networks will be comparable to that of FTTH. In this paper, we will discuss integrated optical and wireless technologies for mobile front-haul networks towards 5G era and beyond.