Dispersion Limitation of Digital Signal and Carrier Distribution in Optical-Wireless Networks

Abstract

Modern communication systems, such as mobile 5G and future 6G require ultrawide bandwidths and low latencies in the anyhaul (i.e., front- and backhaul) networks interconnecting the data center and cloud-core with the subscribers through cell sites. Extremely high data rates and low latencies are expected in several applications. When integrating the building blocks into complete networks, a strict limitation is raised by the optical fiber. Dispersion effects significantly reduce the bitrate-distance product between the optical nodes. In the paper the effect of chromatic dispersion limitation is investigated both for baseband digital data and for microwave and millimeter-wave radio-frequency signals (RF), e.g. RF carriers. Experimental verification shows the limited bandwidth of the singlemode optical fiber as a function of fiber span and modulating frequency. In feasible systems the focus is on flexible and future-proof architectures. Future 6G and actual 4G/5G hybrid wireless-optical networks have simultaneous economic and technical goals to provide increased throughputs. Due to the high density of the cell sites it is crucial to reduce energy consumption, size and costs of radios and remote antenna heads. Some system design rules of thumb are listed in the paper, and finally the RF carrier generation methods are reviewed in the paper.