Page 77 - Kaleidoscope Academic Conference Proceedings 2024

ENABLING FIBER–WIRELESS TECHNOLOGIES FOR RADIO COMMUNICATIONS IN
MILLIMETER-WAVE AND TERAHERTZ-WAVE BANDS IN IMT-2030 AND BEYOND

Pham Tien Dat, Yuya Yamaguchi, Kouichi Akahane

National Institute of Information and Communications Technology, Tokyo, Japan

ABSTRACT addition, line-of-sight communication is required because of
the large shielding loss, which makes antenna installation
Radio communications in high-frequency bands are crucial difficult and expensive. The penetration of mmW signals is
for providing high-speed and low-latency services. Research also limited, making it challenging to extend the
efforts are being made worldwide; however, several communication coverage to wide areas and indoor
bottlenecks still exist, such as high free-space loss, weak environments. The coexistence of multiple RANs in
penetration, and limited coverage, making the deployment of different frequency bands and the use of integrated access
high-frequency radio communications challenging. To attain and backhaul (IAB) have been proposed to expand coverage
sustainable development goals, cost-effective, high-speed, and increase the throughput of radio communications in the
and energy-efficient communication infrastructure should be mmW and terahertz (THz) bands [3]. These methods are
developed. Photonic technology and its convergence with promising for improving the network efficiency. However,
radio counterparts are promising for high-frequency radio their implementation remains difficult, particularly for
communications. In this paper, we present key fiber–wireless communication with indoor users. Electronics-based
technologies, including a high-speed fiber–wireless bridge solutions, such as reflecting radio signals on reconfigurable
system for fixed wireless access and emergency intelligent surfaces [4] and using smart repeaters [5], have
communications, transparent relay and routing of radio been recently proposed; however, the system is relatively
signals for coverage extension, and simultaneous generation, complicated, and the coverage extension is still limited. New
transmission, and reception of multiple radio signals in solutions are in high demand to facilitate communications in
different frequency bands, to overcome the bottlenecks. For the mmW and THz bands, which are crucial in 6G networks.
each technology, we present the system concept and proof- Photonic technology is promising for the generation,
of-concept demonstration. The achieved results reveal the transmission, and reception of radio signals; thus, it can be
potential of the proposed solutions and can pave the way for used as an efficient solution. A fiber–wireless bridge system
the deployment of radio access networks in the millimeter- can provide a high-speed and easy-to-install solution for
wave and terahertz-wave bands in IMT-2030 and beyond. fixed access and emergency communication. However, the
cost, complexity, and power consumption increase
Keywords – 5G-Advance and 6G, convergence of wired significantly when an electronic method [6] or optical
and wireless, millimeter-wave, emergency communications coherent detection [7] is used. The direct detection and
downconversion of radio signals using photonic technology
1. INTRODUCTION is promising for simplifying the systems [8, 9]. However, a
system that can provide a transmission capacity of up to 100
Telecommunications plays a vital role in attaining Gb/s is yet to be demonstrated. For radio coverage extension
sustainable development goals, and millimeter-wave (mmW) application, radio-over-fiber (RoF) systems are useful [10,
frequency resources are essential for high-speed and low- 11]. Radio signals can be converted into optical signals for
latency communications, especially for indoor offices, transmission and regenerated to communicate with users at
hotspots, and fixed wireless access (FWA). mmW is the ends of the links. However, a system that can relay
allocated worldwide; and by 2022, they were available in 31 signals at a data rate exceeding 40 Gb/s has not yet been
countries [1]. Currently, research efforts are being made for reported. Photonic technology is also promising in
ultra-high-speed, large-capacity, and ultra-low-latency facilitating multi-RAN and IAB technologies. However, to
communications in 6G networks. Radio access networks date, there have been no reports on these applications.
(RANs) are expected to continue up to 100 GHz and beyond
in international mobile telecommunications (IMT) 2030 [2]. In this paper, we present key fiber–wireless technologies to
However, the use of mmW bands remains limited because of facilitate radio communications in the mmW and THz bands.
several bottlenecking challenges. The propagation loss First, a high-speed fiber–wireless bridge system was
increases significantly in the mmW band, making the cell demonstrated using photonic technology for radio signal
size much smaller than that in the microwave band. In generation, transmission, reception, and downconversion.

978-92-61-39091-4/CFP2268P @ITU 2024 – 33 – Kaleidoscope