EAGER: Terabit DSL

Brown University, Providence RI

Investigators

Abstract

EAGER: Transmitting data at a terabit per second on twisted copper wires The transmission of data using twisted copper-wire pairs was pioneered by Alexander Graham Bell in 1881. Today, there are well over a billion such twisted pairs installed globally, an infrastructure which has been the basis for nearly all telephone connections for over 100 years. In the late 1980s Digital Subscriber Line (DSL) services were developed, in which an RF signal carrying digital data was essentially piggy-backed on top of the same copper wires used for analog voice signals. Through advances in data encoding and frequency multiplexing, these systems can now typically deliver data at gigabit per second rates. The astounding (and ongoing) commercial success of DSL arises largely from the fact that these services do not require new wire or fiber connections (which cost thousands of dollars per customer to install), but instead can deliver high bit rates to customers using the existing infrastructure. However, advances in encoding and multiplexing have nearly reached their limit, so the only way to further increase the data rate is to increase the frequency of the RF carrier wave, since there is more bandwidth available at higher frequencies. The proposed research will explore the use of these existing copper twisted-cables for transmission of signals at much higher frequencies than those that have previously been employed in DSL systems. Similar multiplexing and encoding schemes will be necessary, due to the unavoidable mixing of these high-frequency signals as they propagate along these non-uniform cables. If these signal processing approaches are still useful at high frequencies, and if the overall signal loss is not too high, then this initial demonstration will validate the feasibility of operating a DSL-like system with a data rate of a terabit per second, vastly higher than anything that has been envisioned previously. This would open up an entirely new realm for fixed (not wireless) data services. This EAGER proposal suggests a radically new way to think about DSL transmission systems. In all discussions to date, the fundamental physics of the electromagnetic signal propagation is described using the language of transmission lines. Conventionally, a transmission line guides an electrical signal by propagation of a time-varying voltage between a pair of electrically isolated conductors. However, when the free-space wavelength of the guided wave approaches the relevant dimensions (e.g., the distance between the two conductors), it is more appropriate to describe this transmission process using the language of waveguides. Inspired by the fact that the typical free-space distance between wires in a twisted-wire pair can be on the order of a millimeter, this project seeks to study the use of millimeter waves or terahertz waves as the carriers for modulated digital data on twisted-pair cables, acting as waveguides. This proposal seeks to initiate a research collaboration between the PI at Brown University and engineers at ASSIA, Inc. This company specializes in the software and signal processing that enables efficient use of spectrum in DSL systems. Their expertise, in particular in the area of vectoring (conceptually equivalent to MIMO in wireless systems), combined with the PI's expertise in millimeter-wave and terahertz waveguides, represents a unique team which is ideally positioned to carry out the proposed exploratory research program. The approach involves the experimental characterization of the waveguide modes (all output modes for each possible input excitation) for a set of model cable systems, starting from a simple single-twisted-pair and working up to more complicated (and longer) waveguides. The effects of modal dispersion, dielectric loss, and bends will be studied, and the results will be used as inputs in channel models developed by ASSIA to predict the rate and range performance characteristics. This work represents the first realistic exploration of the idea of using millimeter waves for long-distance guided-wave data transmission. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.