On the Convergence Speed of Spatially Coupled LDPC Ensembles

Spatially coupled low-density parity-check codes show an outstanding performance under the low-complexity belief propagation (BP) decoding algorithm. They exhibit a peculiar convergence phenomenon above the BP threshold of the underlying non-coupled ensemble, with a wave-like convergence propagating through the spatial dimension of the graph, allowing to approach the MAP threshold. We focus on this particularly interesting regime in between the BP and MAP thresholds. On the binary erasure channel, it has been proved that the information propagates with a constant speed toward the successful decoding solution. We derive an upper bound on the propagation speed, only depending on the basic parameters of the spatially coupled code ensemble such as degree distribution and the coupling factor $w$. We illustrate the convergence speed of different code ensembles by simulation results, and show how optimizing degree profiles helps to speed up the convergence.Comment: 11 pages, 6 figure

Massive MIMO: How many antennas do we need?

We consider a multicell MIMO uplink channel where each base station (BS) is equipped with a large number of antennas N. The BSs are assumed to estimate their channels based on pilot sequences sent by the user terminals (UTs). Recent work has shown that, as N grows infinitely large, (i) the simplest form of user detection, i.e., the matched filter (MF), becomes optimal, (ii) the transmit power per UT can be made arbitrarily small, (iii) the system performance is limited by pilot contamination. The aim of this paper is to assess to which extent the above conclusions hold true for large, but finite N. In particular, we derive how many antennas per UT are needed to achieve \eta % of the ultimate performance. We then study how much can be gained through more sophisticated minimum-mean-square-error (MMSE) detection and how many more antennas are needed with the MF to achieve the same performance. Our analysis relies on novel results from random matrix theory which allow us to derive tight approximations of achievable rates with a class of linear receivers.Comment: 6 pages, 3 figures, to be presented at the Allerton Conference on Communication, Control and Computing, Urbana-Champaign, Illinois, US, Sep. 201

Kooperation oder Konfrontation? Der Aufstieg Chinas in der globalen politischen Ökonomie

Welche Folgen zeitigt der rasante Aufstieg Chinas? Im Anschluss an Erkenntnisse der Chinaforschung und politökonomischer Ansätze wird die Volksrepublik China als eine Variante der nachholenden (staats-)kapitalistischen Entwicklung analysiert, die an einer wirtschaftlichen und geopolitischen Aufwertung interessiert ist. Dabei verkörpert die inter- und transnationale Einbettung des neuen chinesischen Kapitalismus in ein instabiles Weltsystem trotz des Bemühens der Staatsführung um eine verantwortungsvolle Großmachtpolitik einen spannungsreichen Prozess. Zwar bleibt die chinesische Volkswirtschaft abhängig von den alten Zentren des globalen Kapitalismus. Daraus folgt jedoch nicht umstandslos eine reibungslose Zusammenarbeit. Im Gegenteil weisen aktuelle Währungsdispute mit den USA im Zuge des globalen Wirtschaftseinbruchs auf politisch vermittelte Standortkonflikte hin. Perspektiven einer konfliktarmen Integration Chinas müssen daher relativiert werden - wie zusätzlich die Führungsrolle des Landes im ostasiatischen Regionalisierungsprozess illustriert -, ohne voreilige Schlussfolgerungen hinsichtlich militärischer Zusammenstöße und eines Übergangs zu einer neuen globalen chinesischen Hegemonie zu übernehmen. Abgezielt wird darauf, die Vorteile einer politökonomischen Betrachtungsweise bei der Beantwortung einer Frage herauszustellen, die üblicherweise in einer Perspektive der Internationalen Beziehungen, das heißt fokussiert auf zwischenstaatliche Beziehungen, behandelt wird.What has been the impact of China's rapid rise? Referring to findings of current research on China as well as theories of political economy, this paper analyzes the People's Republic of China as a variety of a (state-led) capitalist catch-up development process that is focused on economic and geopolitical upgrading. Despite efforts by China's political leadership to act as a responsible superpower, the international and transnational embedding of the new Chinese capitalism is fraught with tension. The Chinese economy remains dependent on the old centers of global capitalism, but this has not paved the way for smooth cooperation. On the contrary, the latest currency disputes between China and the US during the global economic slump are indicative of politically charged conflicts between the world's relevant economic regions. Thus, the prospect of China being integrated harmoniously seems to be overly optimistic - as is also demonstrated by China's efforts to play a leading role in the East Asian regionalization process. At the same time, one has to be careful not to draw (the wrong) conclusions about the inevitability of military conflict and a transition towards a new global Chinese hegemony. The paper aims to highlight the advantages of a political economy approach in answering a question that has primarily been addressed from International Relations perspectives, i.e. focused on relations between states

China’s rise in a liberal world order in transition – introduction to the FORUM

In a time of great uncertainty about the future and resilience of the liberal world order this Forum focuses on China’s rise and interplay with the foundations of that liberal order. The key question is the extent to and variegated ways in which China - with its (re)ascendance to power and potential global leadership – is adapting to and perhaps even strengthening liberal institutions and rules of the game, confronting them, or developing alternative paths. In this introduction to the Forum we advance three key points based on the contributions. First, contrasting the orthodox binary scenarios of either inevitable conflict or co-optation offered in the mainstream IR debate, the Forum highlights the possibility of a third scenario of China’s interplay with the liberal world and its key actors, institutions, and rules. A hybrid and variegated scenario that entails both conflict and adaptation, differently entangled in different issue areas. Second, it stresses the need to conceptualize and empirically comprise the essentially interlinked nature of domestic state-society models and the global political economy. Third, we argue for a perspective that incorporates underlying economic and social structures and the power relations embedded therein

Projections of Economic Impacts of Climate Change on Marine Protected Areas: Palau, the Great Barrier Reef, and the Bering Sea

Climate change substantially impacts ecological systems. Marine species are shifting their distribution because of climate change towards colder waters, potentially compromising the benefits of currently established Marine Protected Areas (MPAs). Therefore, we demonstrate how three case study regions will be impacted by warming ocean waters to prepare stakeholders to understand how the fisheries around the MPAs is predicted to change. We chose the case studies to focus on large scale MPAs in i) a cold, polar region, ii) a tropical region near the equator, and iii) a tropical region farther from the equator. We quantify the biological impacts of shifts in species distribution due to climate change for fishing communities that depend on the Palau National Marine Sanctuary, the Great Barrier Reef Marine National Park Zone, and the North Bering Sea Research Area MPAs. We find that fisheries sectors will be impacted differently in different regions and show that all three regions can be supported by this methodology for decision making that joins sector income and species diversity