Replacing the Soft FEC Limit Paradigm in the Design of Optical Communication Systems

The FEC limit paradigm is the prevalent practice for designing optical communication systems to attain a certain bit-error rate (BER) without forward error correction (FEC). This practice assumes that there is an FEC code that will reduce the BER after decoding to the desired level. In this paper, we challenge this practice and show that the concept of a channel-independent FEC limit is invalid for soft-decision bit-wise decoding. It is shown that for low code rates and high order modulation formats, the use of the soft FEC limit paradigm can underestimate the spectral efficiencies by up to 20%. A better predictor for the BER after decoding is the generalized mutual information, which is shown to give consistent post-FEC BER predictions across different channel conditions and modulation formats. Extensive optical full-field simulations and experiments are carried out in both the linear and nonlinear transmission regimes to confirm the theoretical analysis

Nonlinear Frequency-Division Multiplexing in the Focusing Regime

Achievable rates of the nonlinear frequency-division multiplexing (NFDM) and wavelength-division multiplexing (WDM) subject to the same power and bandwidth constraints are computed as a function of transmit power in the standard single-mode fiber. NFDM achieves higher rates than WDM.Comment: Invited paper to be presented at The Optical Fiber Communications Conference and Exposition (OFC), March 201

Why compensating fibre nonlinearity will never meet capacity demands

Current research efforts are focussed on overcoming the apparent limits of communication in single mode optical fibre resulting from distortion due to fibre nonlinearity. It has been experimentally demonstrated that this Kerr nonlinearity limit is not a fundamental limit; thus it is pertinent to review where the fundamental limits of optical communications lie, and direct future research on this basis. This paper details recently presented results. The work herein briefly reviews the intrinsic limits of optical communication over standard single mode optical fibre (SMF), and shows that the empirical limits of silica fibre power handling and transceiver design both introduce a practical upper bound to the capacity of communication using SMF, on the order of 1 Pbit/s. Transmission rates exceeding 1 Pbit/s are shown to be possible, however, with currently available optical fibres, attempts to transmit beyond this rate by simply increasing optical power will lead to an asymptotically zero fractional increase in capacity.Comment: 4 pages, 2 figure

Bipartite Matching with Linear Edge Weights

Consider a complete weighted bipartite graph G in which each left vertex u has two real numbers intercept and slope, each right vertex v has a real number quality, and the weight of any edge (u, v) is defined as the intercept of u plus the slope of u times the quality of v. Let m (resp., n) denote the number of left (resp., right) vertices, and assume that m geq n. We develop a fast algorithm for computing a maximum weight matching (MWM) of such a graph. Our algorithm begins by computing an MWM of the subgraph induced by the n right vertices and an arbitrary subset of n left vertices; this step is straightforward to perform in O(n log n) time. The remaining m - n left vertices are then inserted into the graph one at a time, in arbitrary order. As each left vertex is inserted, the MWM is updated. It is relatively straightforward to process each such insertion in O(n) time; our main technical contribution is to improve this time bound to O(sqrt{n} log^2 n). This result has an application related to unit-demand auctions. It is well known that the VCG mechanism yields a suitable solution (allocation and prices) for any unit-demand auction. The graph G may be viewed as encoding a special kind of unit-demand auction in which each left vertex u represents a unit-demand bid, each right vertex v represents an item, and the weight of an edge (u, v) represents the offer of bid u on item v. In this context, our fast insertion algorithm immediately provides an O(sqrt{n} log^2 n)-time algorithm for updating a VCG allocation when a new bid is received. We show how to generalize the insertion algorithm to update (an efficient representation of) the VCG prices within the same time bound

Supporting Academic Integrity in a Fully-Online Degree Completion Program Through the Use of Synchronous Video Conferences

Since 2012, we have used synchronous, web-based video conferences in our fully-online degree completion program. Students are required to participate in four live video conferences with their professor and a small group of peers in all upper division online courses as a minimum requirement for passing the class. While these synchronous video conferences create some challenges in implementation, they address concerns about academic integrity in three important ways. First, they provide a structured space for faculty to be present with students in a face-to-face manner. Second, they provide important checks to avoid impersonation schemes which are a common concern with online coursework. Third, they assist students in keeping up on the course material, which may mitigate the temptation to cheat. As distance learning courses and online programs have exploded in number, the issue of academic integrity has taken center stage for program design. In this paper, we share a case of a program built to address academic integrity issues through the regular and highly structured use of small group video conferencing as a requirement for all courses. We describe the video conferencing protocol of our online program and suggest best practices for using video conferencing to address concerns about online coursework/programs. We examine this protocol from a theoretical perspective of the Social Shaping of Technology in order to highlight the importance of viewing video conferencing as a social and technical practice

Experimental Investigation of Deep Learning for Digital Signal Processing in Short Reach Optical Fiber Communications

We investigate methods for experimental performance enhancement of auto-encoders based on a recurrent neural network (RNN) for communication over dispersive nonlinear channels. In particular, our focus is on the recently proposed sliding window bidirectional RNN (SBRNN) optical fiber autoencoder. We show that adjusting the processing window in the sequence estimation algorithm at the receiver improves the reach of simple systems trained on a channel model and applied "as is" to the transmission link. Moreover, the collected experimental data was used to optimize the receiver neural network parameters, allowing to transmit 42 Gb/s with bit-error rate (BER) below the 6.7% hard-decision forward error correction threshold at distances up to 70km as well as 84 Gb/s at 20 km. The investigation of digital signal processing (DSP) optimized on experimental data is extended to pulse amplitude modulation with receivers performing sliding window sequence estimation using a feed-forward or a recurrent neural network as well as classical nonlinear Volterra equalization. Our results show that, for fixed algorithm memory, the DSP based on deep learning achieves an improved BER performance, allowing to increase the reach of the system.Comment: Invited paper at the IEEE International Workshop on Signal Processing Systems (SiPS) 202

Transformation of sovereignty discourse in Turkish politics

This dissertation offers an analysis of the transformation of sovereignty discourse in Turkey and illustrates the various discursive utilizations of the concept in connection with purposes of competing ideologies in turning points of Turkish politics. Rather than discussing whether or not sovereignty is obsolete in the face of growing globalization and fragmentation, this study underlines the need to reappraise the implications of the role that sovereignty plays in conditioning the coherence of opposing political ideologies. To this end, four critical ‘moments’ are studied by employing a discourse-theoretic approach: dislocation brought by the Ottoman disintegration; creation of the Turkish nationstate; disruption engendered by globalization during the post-1980 Turkey; transformation unleashed by Turkey’s ‘Europeanization’ during the 2000s. By illustrating the historico-political production/reproduction of sovereignty in relation to ideologies of Ottomanism, Turkish Nationalism, Populism, Statism, Second Republicanism and Europeanism, the findings refute the conventional view that presents sovereignty as a fixed, neutral and timeless organizing principle of modern politics. Instead, it is shown that sovereignty acts as an empty-signifier embodying a broad plurality of meanings to allow power blocs to produce political frontiers and uphold associated antagonisms. It is argued that only by deconstructing this highly politicized and contentious nature of the concept that we can start to question the unconditional, absolute and state-centric doctrine of sovereignty prevailing in Turkey