Nonlinear equalization of Hammerstein OFDM systems

A practical orthogonal frequency-division multiplexing (OFDM) system can generally be modelled by the Hammerstein system that includes the nonlinear distortion effects of the high power amplifier (HPA) at transmitter. In this contribution, we advocate a novel nonlinear equalization scheme for OFDM Hammerstein systems. We model the nonlinear HPA, which represents the static nonlinearity of the OFDM Hammerstein channel, by a B-spline neural network, and we develop a highly effective alternating least squares algorithm for estimating the parameters of the OFDM Hammerstein channel, including channel impulse response coefficients and the parameters of the B-spline model. Moreover, we also use another B-spline neural network to model the inversion of the HPA’s nonlinearity, and the parameters of this inverting B-spline model can easily be estimated using the standard least squares algorithm based on the pseudo training data obtained as a byproduct of the Hammerstein channel identification. Equalization of the OFDM Hammerstein channel can then be accomplished by the usual one-tap linear equalization as well as the inverse B-spline neural network model obtained. The effectiveness of our nonlinear equalization scheme for OFDM Hammerstein channels is demonstrated by simulation results.

Computing the Cassels–Tate pairing on the 3-Selmer group of an elliptic curve

We extend the method of Cassels for computing the Cassels-Tate pairing on the 2-Selmer group of an elliptic curve, to the case of 3-Selmer groups. This requires significant modifications to both the local and global parts of the calculation. Our method is practical in sufficiently small examples, and can be used to improve the upper bound for the rank of an elliptic curve obtained by 3-descent.

Student and library services in cooperation

Abstract At Ångström Laboratory, one of the largest campuses at Uppsala University, the Library and the Student Services Office merged in November 2012. This merger is a pilot project to improve service for students and faculty. Ångström Laboratory has around 900 staff and almost 10,000 students, of whom most also spend time at other campuses. In this paper we describe the background and the implementation of the pilot project. One of the main reasons for moving together was the wish to gather together all kinds of student services, including the distribution of written examinations in one place. The central location and open environment of the Library made it a good choice. The heart of the Library and Student Services is an open office consisting of two service desks located in the library area. There are silent study areas; computers for searching and printing, an area for relaxing with newspapers and journals, meeting rooms and offices for the staff. The result is a lively place with a cosy atmosphere. As the Library and the Student Services still belong to different parts of the University we are now starting to find out how best to collaborate. To understand more we log all the questions we get and the services we deliver. We also have meetings together and use the same lunch room to get to know each other and our different functions. We will define which matters can be solved in common, and how we can back each other up when necessary.

Informal sanctions and conditional cooperation: : A natural experiment on voluntary contributions to a public good.

In a natural experiment, this paper studies the impact of an informal sanctioning mechanism on individuals’ voluntary contribution to a public good. Cross-country skiers’ actual cash contributions in two ski resorts, one with and one without an informal sanctioning system, are used. I find the contributing share to be higher in the informal sanctioning system (79 percent) than in the non-sanctioning system (36 percent). Previous studies in one-shot public good situations have found an increasing conditional contribution (CC) function, i.e. the relationship between expected average contributions of other group members and the individual’s own contribution. In contrast, the present results suggest that the CC-function in the non-sanctioning system is non-increasing at high perceived levels of others’ contribution. This relationship deserves further testing in lab.

International cooperation and competition policy

The objective of this paper is to argue that the dissemination of competition laws is positive for the world economy. However, the benefits derived depend crucially on adequate enforcement and institutional building in the various jurisdictions for which international cooperation within WTO and in other fora is crucial. The paper addresses two issues. Section 1 underlines a few aspects of the increasing importance of competition policy in the developing world. The second section provides a few suggestions for the international cooperation agenda.

Global governance, currency and trade: implications of one on the other, common problems and how to address cooperation through law at the international level

How to deal with the impacts of the exchange rate on the trade balance of Brazil? There is not a single answer to such question. In order to find out some legal approaches for this matter, this paper aims to describe and analyze the role of the IMF, WTO and the governments of Brazil and the United States on the currency misalignments, especially the extraterritorial effects of such misalignment on the Brazil’s bilateral trade with the United States. The article concludes that the Currency Swap Agreements and other bilateral solutions may minimize the distortions that the Brazilian balance of payment against the USA is carrying, due to the lack of legal solutions for the problem of the exchange rate misalignments that Brazil is facing.

Competition and cooperation between international courts: a critical approach to the new paradigms of cross-border dispute resolution model

This article examines the arising cross-border dispute resolution models (Cooperation and Competition among national Courts) from a critical perspective. Although they have been conceived to surpass the ordinary solution of a Modern paradigm (exclusive jurisdiction, choice of court, lis pendens, forum non conveniens, among others), they are insufficient to deal with problems raised with present globalization, as they do not abandon aspects of that paradigm, namely, (i) statebased Law; and (ii) standardization of cultural issues.