Sub-Band Full-Duplex for 5G New Radio: Challenges, Solutions and Performance

Recently, multiple works in the literature have presented encouraging results on the feasibility of in-band full-duplex (IBFD) communications in point-to-point and single cell arrangements, where the IBFD capability is provided by the base station. However, in multi-cell networks, in addition to high self-interference, full-duplex operations also face the severe problems of base station-to-base station cross-link interference (CLI), inter-sector CLI, user equipment-to-user equipment CLI, and inter-operator interference. Due to these difficulties, the research and engineering communities have recently proposed to adopt sub-band full-duplex (SBFD), as an intermediary step towards IBFD in the evolution of 5G New Radio systems. With SBFD, cellular base stations may operate the downlink and uplink on different non-overlapping frequency sub-bands within a time division duplexing carrier, which helps reduce self-interference and CLI due to the frequency isolation between the uplink and downlink sub-bands. In this paper, we focus on Frequency Range 1 operation, investigate the novel SBFD concept, and compare it to traditional time division duplexing, using realistic assumptions on multi-cell deployments, adjacent channel leakage, CLI and self-interference cancellation techniques. Our results indicate that SBFD operation may primarily be a candidate for low power deployments, with complexity and feasibility challenges in scenarios using high base station transmission power, sectorization, and in the presence of multiple operators.

I. Introduction

The evolution of cellular networks and their enabling technologies is driven by the rapidly increasing number of subscriptions worldwide, the insatiable demand for broadband mobile data and Internet-of-Things connectivity services, and the growing interest in entirely new bandwidth-hungry applications. Such applications arise, for example, in augmented and extended reality, smart factory, digital airspace and integrated localization, sensing and communications use cases [1]–[3]. The global mobile data traffic is projected to grow with a compound annual growth rate of around 25% through 2028, while the number of 5G subscriptions are forecasted to reach 4.6 billion globally by 2028 [4]. To meet the steadily increasing demand for mobile services, the research and standardization communities have been continuously improving and exploring existing and new technology enablers, such as the further evolution of advanced and distributed antenna systems, ultra densification, utilizing sub-Terahertz bands, novel positioning and sensing schemes, innovative solutions for coverage extension by reconfigurable intelligent surfaces and novel duplexing schemes in cellular networks [5]–[8].