Pham Tien Dat

Coherent Radio-Over-Fiber and Millimeter-Wave Radio Seamless Transmission System for Resilient Access Networks

We propose a millimeter-wave (MMW) coherent radio-over-fiber (RoF) transmission system for application to an access network with a direct broadband last-mile wireless connection to an optical fiber network. The coherent RoF system comprises an optical two-tone RoF signal generator with an advanced modulation format for high-throughput transmission and employs a digital-signal-processing-aided coherent detection technique for MMW radio, which is a technique similar to that of optical digital coherent detection. As proof of concept, a 20-GBd quadrature phase-shift keying RoF transmission over 20 km of optical fiber before a radio transmission over 20 m of air is demonstrated. The results of the radio transmissions using Cassegrain-type antenna pairs with a gain of 50 dBi are consistent with theoretical estimations; this suggests the possibility of developing a midrange transmission system using a high-power MMW amplifier.

High-capacity wireless backhaul network using seamless convergence of radio-over-fiber and 90-GHz millimeter-wave

We propose and experimentally demonstrate a seamlessly converged radio-over-fiber (RoF) and millimeter-wave system at 90 GHz for high-speed wireless signal transmission. We successfully transmit and demodulate standard orthogonal frequency-division multiplexing-based wireless local access network (WLAN) signals, long term evolution eNB conformance test models, and long term evolution advanced signals over the system. Satisfactory transmission performance over the converged RoF and a 5-m 90-GHz wireless link is achieved. The measured root-mean-square error vector magnitude is well under the requirement defined by the standards. We also investigate the dependence of the transmission performance on the fiber length due to the effect of fiber dispersion and estimate the achievable wireless transmission distance. The estimated transmission range of both the fiber length and wireless link are sufficiently long for practical applications, such as mobile backhaul/fronthaul, wireless access network for WLAN signals. Possible solutions and the estimated transmission range are also discussed to use millimeter-wave and RoF system convergence for uplink transmission. The obtained results confirm the potential to use the system in future high-speed, small-cell mobile networks and in broadband wireless access networks.

WDM RoF-MMW and linearly located distributed antenna system for future high-speed railway communications

In this article, we propose dual-hop network architecture capable of providing high-speed communications to high-speed trains (HSTs). The system uses a seamless fiber-millimeterwave system for backhaul transmission from a central station to antennas on trains, and a highspeed in-train Wi-Fi network. The system can be combined with signal processing and network control technologies to compensate for interference and the Doppler effect, and to reduce the number of handovers. It can realize seamless connectivity between the inside and outside of trains to avoid penetration loss and help organize the in-train network optimally to increase coverage and data rate. We present and discuss the possible network architecture and technologies that can help realize the proposed network. We also present a proof-of-concept demonstration on a high-performance seamless fiber- MMW system that can be applied for applications in backhaul networks. The proposed network can be an attractive solution to provide broadband services such as video on demand and high-speed mobile signals to users on HSTs.

Radio-on-radio-over-fiber: efficient fronthauling for small cells and moving cells

A combination of fiber and radio links would be attractive for efficient fronthauling to small cells and moving cells. However, achieving connectivity by using wired-wireless media converters significantly increases system complexity, power consumption, and latency. A seamless combination of fiber and radio links in which photonics-based technologies are used to generate and transmit radiowave signals is more suitable. In this article, we present an overview of fiber-radio link combination for mobile signal transmission. We propose an efficient solution for future mobile fronthauling based on the analog transmission of mobile signals over a bidirectional seamless system. We discuss the potential as well as the challenges and perspectives of the systems applied for mobile fronthauling in small-cell- and moving-cell- based networks. We also present a proof-of-concept demonstration of the transmission of mobile signals over the system. Satisfactory performance is obtained for different high-speed advanced signals. The transmission range over fiber links and the estimated range of the radio links are sufficiently long to facilitate the practical implementation of the system. The system is scalable to include new deployments of small cells and wireless services using wavelength-division and subcarrier multiplexing techniques. It can provide a high-speed, low-latency, and flexible solution for fronthauling in new emerging wireless systems such as 5G networks.

90-GHz radio-on-radio-over-fiber system for linearly located distributed antenna systems

To realize a high-speed and high-capacity transmission link for fast mobile vehicles such as a bullet train, we propose a wavelength-division-multiplexing radio-on-radio-over-fiber (WDM-RoRoF) system with a linearly located distributed antenna system (DAS) on the 90-GHz band. All the conventional microwave (MW) radio signals such as mobile telecommunication and broadcast signals are encapsulated in a single millimeter-wave (MMW) carrier radio. Centralized control at a central office using the information of the position of a car can optimize and distribute the suitable RoRoF signal to each remote cell over optical fibers. An optical two-tone generator with an optical modulator can easily generate a 90-GHz RoRoF signal, and then, a high-speed photomixer directly converts from an RoRoF signal to an MMW RoR signal, which is composed of an MW signal with a 90-GHz carrier component, for irradiation over air. Heterodyne frequency down-conversion performs the direct frequency conversion from the MMW signal to an MW signal available to consumers.

5G transport networks: the need for new technologies and standards

Mobile transport networks will play a vital role in future 5G and beyond networks. In particular, access transport networks connecting radio access with core networks are of critical importance. They will be required to support massive connectivity, super high data rates, and real-time services in a ubiquitous environment. To attain these targets, transport networks should be constructed on the basis of a variety of technologies and methods, depending on application scenarios, geographic areas, and deployment models. In this article, we present several technologies, including analog radio-over-fiber transmission, intermediate-frequency- over-fiber technology, radio-on-radio transmission, and the convergence of fiber and millimeter-wave systems, that can facilitate building such effective transport networks in many use cases. For each technology, we present the system concept, possible application cases, and demonstration results. We also discuss potential standardization and development directions so the proposed technologies can be widely used.

Performance of a 90-GHz radio-on-radio-over-fiber system suitable for communications in high-speed railways

We propose a radio access network suitable for communications in high-speed railways employing a radio-on-radio-over-fiber and distributed antenna system. We present a proof-of-concept demonstration of wireless signal transmission over the system at 90 GHz. Standard LTE-A signals using QPSK, 16-QAM and 64-QAM modulation are successfully transmitted and demodulated. Satisfactory transmission performance with measured root-mean-square EVM well under the standard requirement is achieved. The obtained results indicate the potential to make use of the system in high-speed rail communications.

Full-Duplex Transmission of LTE-A Carrier Aggregation Signal Over a Bidirectional Seamless Fiber-Millimeter-Wave System

We propose a flexible and high-performance fronthaul system for future mobile networks using a seamless combination of fiber-optic and millimeter-wave (MMW) systems. The proposed system employs a high-quality optical MMW signal generation at the transmitter and a stable and high-performance MMW self-homodyne detection at the receiver. In the downlink direction, successful transmission of intraband and interband carrier aggregation (CA) long-term evolution-advanced (LTE-A) signals over the system is experimentally confirmed. We also confirm satisfactory performance for the transmission over a fiber-wireless bridge using a cascade of the seamless system and a conventional radio-over-fiber (RoF) link. In the uplink direction, we successfully demonstrate the transmission of an intraband CA LTE-A signal over a cascade of a radio-on-radio and a RoF system. In addition, we confirm that the full-duplex transmission of LTE-A signals over the proposed bidirectional system does not experience performance degradation compared to the case with half-duplex transmission. The proposed system is a potential solution for mobile-signal transmission in future networks.

Bidirectional transmission of LTE-A carrier aggregation signal over a seamless fiber-wireless system in W-band

We present a high-speed and low-latency seamless fiber-millimeter-wave system for future mobile front-haul networks. The bidirectional transmission of a downlink interband and an uplink intraband carrier aggregation LTE-A signal over the system is successfully demonstrated.

Evaluation of frequency fluctuation in fiber-wireless link with direct IQ down-converter

We demonstrate 12-Gbaud QPSK signal transmission in a fiber-wireless link and compare a modulator-based optical two-tone generator and an optical heterodyning with free-running lasers. The obtained frequency fluctuation of the two-tone system meets the requirements of the radio regulations.