Near-ML detection for MDL-impaired few-mode fiber transmission

Few-mode fiber transmission systems are typically impaired by mode-dependent loss (MDL). In an MDL-impaired link, maximum-likelihood (ML) detection yields a significant advantage in system performance compared to linear equalizers, such as zero-forcing and minimum-mean square error equalizers. However, the computational effort of the ML detection increases exponentially with the number of modes and the cardinality of the constellation. We present two methods that allow for near-ML performance without being afflicted with the enormous computational complexity of ML detection: improved reduced-search ML detection and sphere decoding. Both algorithms are tested regarding their performance and computational complexity in simulations of three and six spatial modes with QPSK and 16QAM constellations.

Knowledge mediation and overlapping in interfirm networks

Purpose – The literature on interfirm networks devotes scant attention to the ways collaborating firms combine and integrate the knowledge they share and to the subsequent learning outcomes. This study aims to investigate how motorsport companies use network ties to share and recombine knowledge and the learning that occurs both at the organizational and dyadic network levels. Design/methodology/approach – The paper adopts a qualitative and inductive approach with the aim of developing theory from an in-depth examination of the dyadic ties between motorsport companies and the way they share and recombine knowledge. Findings – The research shows that motorsport companies having substantial competences at managing knowledge flows do so by getting advantage of bridging ties. While bridging ties allow motorsport companies to reach distant and diverse sources of knowledge, their strengthening and the formation of relational capital facilitate the mediation and overlapping of that knowledge. Research limitations/implications – The analysis rests on a qualitative account in a single industry and does not take into account different types of inter-firm networks (e.g. alliances; constellations; consortia etc.) and governance structures. Cross-industry analyses may provide a more fine-grained picture of the practices used to recombine knowledge and the ideal composition of inter-firm ties. Practical implications – This study provides some interesting implications for scholars and managers concerned with the management of innovation activities at the interfirm level. From a managerial point of view, the recognition of the different roles played by network spanning connections is particularly salient and raises issues concerning the effective design and management of interfirm ties. Originality/value – Although much of the literature emphasizes the role of bridging ties in connecting to diverse pools of knowledge, this paper goes one step further and investigates in more depth how firms gather and combine distant and heterogeneous sources of knowledge through the use of strengthened bridging ties and a micro-context conducive to high quality relationships.

Optimal packing for cascaded regenerative transmission based on phase sensitive amplifiers

We investigate the transmission performance of advanced modulation formats in nonlinear regenerative channels based on cascaded phase sensitive amplifiers. We identify the impact of amplitude and phase noise dynamics along the transmission line and show that after a cascade of regenerators, densely packed single ring PSK constellations outperform multi-ring constellations. The results of this study will greatly simplify the design of future nonlinear regenerative channels for ultra-high capacity transmission

Optimization of cascaded regenerative links based on phase sensitive amplifiers

We develop an analytical method for optimizing phase sensitive amplifiers for regeneration in multilevel phase encoded transmission systems. The model accurately predicts the optimum transfer function characteristics and identifies operating tolerances for different signal constellations and transmission scenarios. The results demonstrate the scalability of the scheme and show the significance of having simultaneous optimization of the transfer function and the signal alphabet. The model is general and can be applied to any regenerative system. © 2013 Optical Society of America.

Design of multilevel amplitude regenerative system

We propose a scheme for multilevel (nine or more) amplitude regeneration based on a nonlinear optical loop mirror (NOLM) and demonstrate through numerical modeling its efficiency and cascadability on circular 16-, 64-, and 256- symbol constellations. We show that the amplitude noise is efficiently suppressed. The design is flexible and enables variation of the number of levels and their positioning. The scheme is compatible with phase regenerators. Also, compared to the traditional single-NOLM configuration scheme, new features, such as reduced and sign-varied power-dependent phase shift, are available. The model is simple to implement, as it requires only two couplers in addition to the traditional NOLM, and offers a vast range of optimization parameters. © 2014 Optical Society of America.

Constructing spaces for strategic work:a multimodal perspective

In this paper we take seriously the call for strategy-as-practice research to address the material, spatial and bodily aspects of strategic work. Drawing on a video-ethnographic study of strategic episodes in a financial trading context, we develop a conceptual framework that elaborates on strategic work as socially accomplished within particular spaces that are constructed through different orchestrations of material, bodily and discursive resources. Building on the findings, our study identifies three types of strategic work - private work, collaborative work and negotiating work - that are accomplished within three distinct spaces that are constructed through multimodal constellations of semiotic resources. We show that these spaces, and the activities performed within them, are continuously shifting in ways that enable and constrain the particular outcomes of a strategic episode. Our framework contributes to the strategy-as-practice literature by identifying the importance of spaces in conducting strategic work and providing insight into the way that these spaces are constructed.

Phase noise influence in coherent optical DnPSK systems with DSP based dispersion compensation

We present a comparative study of the influence of dispersion induced phase noise for n-level PSK systems. From the analysis, we conclude that the phase noise influence for classical homodyne/heterodyne PSK systems is entirely determined by the modulation complexity (expressed in terms of constellation diagram) and the analogue demodulation format. On the other hand, the use of digital signal processing (DSP) in homodyne/intradyne systems renders a fiber length dependence originating from the generation of equalization enhanced phase noise. For future high capacity systems, high constellations must be used in order to lower the symbol rate to practically manageable speeds, and this fact puts severe requirements to the signal and local oscillator (LO) linewidths. Our results for the bit-error-rate (BER) floor caused by the phase noise influence in the case of QPSK, 16PSK and 64PSK systems outline tolerance limitations for the LO performance: 5 MHz linewidth (at 3-dB level) for 100 Gbit/s QPSK; 1 MHz for 400 Gbit/s QPSK; 0.1 MHz for 400 Gbit/s 16PSK and 1 Tbit/s 64PSK systems. This defines design constrains for the phase noise impact in distributed-feed-back (DFB) or distributed-Bragg-reflector (DBR) semiconductor lasers, that would allow moving the system capacity from 100 Gbit/s system capacity to 400 Gbit/s in 3 years (1 Tbit/s in 5 years). It is imperative at the same time to increase the analogue to digital conversion (ADC) speed such that the single quadrature symbol rate goes from today's 25 GS/s to 100 GS/s (using two samples per symbol). © 2014 by Walter de Gruyter Berlin/Boston.

Optimal packing for cascaded regenerative transmission based on phase sensitive amplifiers

We investigate the transmission performance of advanced modulation formats in nonlinear regenerative channels based on cascaded phase sensitive amplifiers. We identify the impact of amplitude and phase noise dynamics along the transmission line and show that after a cascade of regenerators, densely packed single ring PSK constellations outperform multi-ring constellations. The results of this study will greatly simplify the design of future nonlinear regenerative channels for ultra-high capacity transmission. © 2013 Optical Society of America.

Efficiency of regenerative schemes

We explore the efficiency of various regeneration schemes in communication systems. We discuss new efficient schemes for multilevel phase and amplitude regeneration and illustrate it on example of 16-symbol constellations. © 2014 IEEE.

Between global ambitions and local change:how multi-level cooperation advances norm implementation in weak states

The purpose of this article is to investigate in which ways multi-level actor cooperation advances national and local implementation processes of human rights norms in weak-state contexts. Examining the cases of women’s rights in Bosnia and Herzegovina and children’s rights in Bangladesh, we comparatively point to some advantages and disadvantages cooperative relations between international organisations, national governments and local NGOs can entail. Whereas these multi-level actor constellations (MACs) usually initiate norm implementation processes reliably and compensate governmental deficits, they are not always sustainable in the long run. If international organisations withdraw support from temporary missions or policy projects, local NGOs are not able to perpetuate implementation activities if state capacities have not been strengthened by MACs. Our aim is to highlight functions of local agency within multi-level cooperation and to critically raise sustainability issues in human rights implementation to supplement norm research in International Relations.

Reconstructing institutional complexity in practice:a relational model of institutional work and complexity

This article develops a relational model of institutional work and complexity. This model advances current institutional debates on institutional complexity and institutional work in three ways. First, it provides a relational and dynamic perspective on institutional complexity by explaining how constellations of logics - and their degree of internal contradiction - are constructed rather than given. Second, it refines our current understanding of agency, intentionality and effort in institutional work by demonstrating how different dimensions of agency interact dynamically in the institutional work of reconstructing institutional complexity. Third, it situates institutional work in the everyday practice of individuals coping with the institutional complexities of their work. In doing so, it reconnects the construction of institutionally complex settings to the actions and interactions of the individuals who inhabit them. © The Author(s) 2013.

State control and corporate governance in transition economies:25 years on from 1989

Research Question/Issue - Which forms of state control over corporations have emerged in countries that made a transition from centrally-planned to marked-based economies and what are their implications for corporate governance? We assess the literature on variation and evolution of state control in transition economies, focusing on corporate governance of state-controlled firms. We highlight emerging trends and identify future research avenues. Research Findings/Insights - Based on our analysis of more than 100 articles in leading management, finance, and economics journals since 1989, we demonstrate how research on state control evolved from a polarized approach of public–private equity ownership comparison to studying a variety of constellations of state capitalism. Theoretical/Academic Implications - We identify theoretical perspectives that help us better understand benefits and costs associated with various forms of state control over firms. We encourage future studies to examine how context-specific factors determine the effect of state control on corporate governance. Practitioner/Policy Implications - Investors and policymakers should consider under which conditions investing in state-affiliated firms generates superior returns.