Capacity Crunch

A. Ellis, N. M. Suibhne, D. Saad, D. Payne

This issue of Philosophical Transactions of the Royal Society, Part A represents a summary of the recent discussion meeting ‘Communication networks beyond the capacity crunch’. The purpose of the meeting was to establish the nature of the capacity crunch, estimate the time scales associated with it and to begin to find solutions to enable continued growth in a post-crunch era. The meeting confirmed that, in addition to a capacity shortage within a single optical fibre, many other ‘crunches’ are foreseen in the field of communications, both societal and technical. Technical crunches identified included the nonlinear Shannon limit, wireless spectrum, distribution of 5G signals (front haul and back haul), while societal influences included net neutrality, creative content generation and distribution and latency, and finally energy and cost. The meeting concluded with the observation that these many crunches are genuine and may influence our future use of technology, but encouragingly noted that research and business practice are already moving to alleviate many of the negative consequences.

H. Waldman

Since the turn of the century, when the Internet traffic became dominant in the communication networks, the average growth rate of the traffic has been about 40%/year, which doubles the traffic every two years, thus multiplying it by a factor of one thousand in twenty years. The main strategy to absorb this unusual growth rate has been bandwidth mining through successive generations of WDM equipment with increasing number of wavelengths, but this approach is nearing exhaustion now. It is estimated that the current traffic growth rate, which remains unabated, will lead to a capacity crunch in the optical fiber networks in the next decade. The paper will discuss the implications of this impending crunch, the strategies that are foreseen to face it, and the research efforts to address the issues and propose solutions.

P. Winzer

Optical networks are facing fundamental capacity scalability problems owing to Shannon limits in silica fiber, frequently summarized as the “optical networks capacity crunch.” We explore the possibility of scaling communication capacities through the use of significantly higher carrier frequencies, such as the extreme ultraviolet or the soft x-ray spectral region, in analogy to the 3–7 orders of magnitude increase in carrier frequencies when optical fiber replaced microwave transmission technologies in the late 1970s. We find that only very limited capacity gains on the order of 10 may be achieved relative to the 1550-nm telecommunications band without fundamentally increasing a system's received energy per bit, its relative bandwidth, or its degree of spatial parallelism. Conversely, we predict the required reduction of waveguide losses that would be needed to make higher carrier frequencies a viable proposition from an energy efficiency point of view. Our analyses include the use of as of yet unexplored quantum communication techniques, whose required energy per bit we find to be lower-bounded by $\boldsymbol{kT}/\log _2\boldsymbol{e}$ at any carrier frequency, which may have implications beyond the communications applications discussed in this paper.

L. A. J. Mesquita, K. Assis, R. Almeida

Qi Zhou, Rui Zhang, You-Wei Chen, Shuyi Shen, Shang-Jen Su, Jeff Finkelstein, G. Chang

We experimentally demonstrate a capacity-approaching transmission in 5G fronthaul utilizing PS-PAM8 and DNN. An 80-Gb/s over 20-km SSMF transmission performance is realized with a beyond 7.3-dB gross gain over uniform PAM modulations with linear post-equalization.