Impact of Spatial Filtering on Distortion from Low-Noise Amplifiers in Massive MIMO Base Stations

In massive MIMO base stations, power consumption and cost of the low-noise amplifiers (LNAs) can be substantial because of the many antennas. We investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. A polynomial model is used to characterize the nonlinear LNAs and to derive the second-order statistics and spatial correlation of the distortion. We show that, with spatial matched filtering (maximum-ratio combining) at the receiver, some distortion terms combine coherently, and that the SINR of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, it is studied how the power from a blocker in the adjacent frequency band leaks into the main band and creates distortion. The distortion term that scales cubically with the power received from the blocker has a spatial correlation that can be filtered out by spatial processing and only the coherent term that scales quadratically with the power remains. When the blocker is in free-space line-of-sight and the LNAs are identical, this quadratic term has the same spatial direction as the desired signal, and hence cannot be removed by linear receiver processing

Out-of-Band Radiation Measure for MIMO Arrays with Beamformed Transmission

The spatial characteristics of the out-of-band radiation that a multiuser MIMO system emits in the environment, due to its power amplifiers (modeled by a polynomial model) are nonlinear, is studied by deriving an analytical expression for the continuous-time cross-correlation of the transmit signals. At a random spatial point, the same power is received at any frequency on average with a MIMO base station as with a SISO base station when the two radiate the same amount of power. For a specific channel realization however, the received power depends on the channel. We show that the power received out-of-band only deviates little from the average in a MIMO system with multiple users and that the deviation can be significant with only one user. Using an ergodicity argument, we conclude that out-of-band radiation is less of a problem in massive MIMO, where total radiated power is lower compared to SISO systems and that requirements on spectral regrowth can be relaxed in MIMO systems without causing more total out-of-band radiation

Spatial Characteristics of Distortion Radiated from Antenna Arrays with Transceiver Nonlinearities

The distortion from massive MIMO (multiple-input--multiple-output) base stations with nonlinear amplifiers is studied and its radiation pattern is derived. The distortion is analyzed both in-band and out-of-band. By using an orthogonal Hermite representation of the amplified signal, the spatial cross-correlation matrix of the nonlinear distortion is obtained. It shows that, if the input signal to the amplifiers has a dominant beam, the distortion is beamformed in the same way as that beam. When there are multiple beams without any one being dominant, it is shown that the distortion is practically isotropic. The derived theory is useful to predict how the nonlinear distortion will behave, to analyze the out-of-band radiation, to do reciprocity calibration, and to schedule users in the frequency plane to minimize the effect of in-band distortion

Thomson scattering of chiral tensors and scalars against a self-dual string

We give a non-technical outline of a program to study the (2,0) theories in six space-time dimensions. Away from the origin of their moduli space, these theories describe the interactions of tensor multiplets and self-dual spinning strings. We argue that if the ratio between the square of the energy of a process and the string tension is taken to be small, it should be possible to study the dynamics of such a system perturbatively in this parameter. As a first step in this direction, we perform a classical computation of the amplitude for scattering chiral tensor and scalar fields (i.e. the bosonic part of a tensor multiplet) against a self-dual spinnless string.Comment: 24 pages, LaTeX, 2 figures. v2: added discussion on supersymmetry in Ch.

Economic interests cloud hazard reductions in the European regulation of substances of very high concern

Here we investigate how the conflicts between hazard reduction and economic interests have shaped the regulation of substances of very high concern (SVHCs) under the Authorization program of the European chemical regulation Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH). Since regulation starts with listing SVHCs on the Candidate List, we analyze the relative importance of toxicological properties, economic motivations, and available scientific knowledge on the probability of inclusion on the Candidate List. We find that the most important factor in whether a substance is listed is whether it is being produced in, or imported into, the European Economic Area (EEA), with the regulators less likely to place a substance on the list if it is currently being produced or imported in the EEA. This evidence suggests that regulators have listed chemicals of secondary importance leading to lesser than anticipated hazard reductions, either because production and imports had already ceased before the listing, or because the compound has never been produced or imported in the EEA at all

Severity as a Priority Setting Criterion: Setting a Challenging Research Agenda

Priority setting in health care is ubiquitous and health authorities are increasingly recognising the need for priority setting guidelines to ensure efficient, fair, and equitable resource allocation. While cost-effectiveness concerns seem to dominate many policies, the tension between utilitarian and deontological concerns is salient to many, and various severity criteria appear to fill this gap. Severity, then, must be subjected to rigorous ethical and philosophical analysis. Here we first give a brief history of the path to today’s severity criteria in Norway and Sweden. The Scandinavian perspective on severity might be conducive to the international discussion, given its long-standing use as a priority setting criterion, despite having reached rather different conclusions so far. We then argue that severity can be viewed as a multidimensional concept, drawing on accounts of need, urgency, fairness, duty to save lives, and human dignity. Such concerns will often be relative to local mores, and the weighting placed on the various dimensions cannot be expected to be fixed. Thirdly, we present what we think are the most pertinent questions to answer about severity in order to facilitate decision making in the coming years of increased scarcity, and to further the understanding of underlying assumptions and values that go into these decisions. We conclude that severity is poorly understood, and that the topic needs substantial further inquiry; thus we hope this article may set a challenging and important research agenda

En utvärdering av hur olika metoder i Skogshögskolans boniteringssystem påverkar skattningen av ståndortsindex

Det för skogsbruket viktiga boniteringssystemet grundas på skattningar av ståndortsindex (SI). SI beskriver markens naturgivna produktionsförmåga genom att ge en skattning av hur höga de grövsta träden kommer att vara vid en referensålder. I detta arbete jämfördes metoder för att skatta ståndortsindex med ståndortsegenskaper (SIS) med äldre respektive nyare formler för skattning av ståndortsindex med övre höjd och höjdutvecklingskurvor (SIH). Detta utfördes genom analyser av data från svenska långtidsförsök med gallring och gödsling (GG-försöken) rörande tall (Pinus sylvestris) och gran (Picea abies). Resultaten visade statistiskt signifikanta skillnader mellan äldre och nyare formler för SIH på tall men inte på gran. Det fanns statistiskt signifikanta skillnader mellan skattningar med SIS och SIH för bägge trädslagen. Det fanns ingen skillnad mellan skattad höjdtillväxt med nya formler för SIH och den uppmätta faktiska höjden. Resultaten stöddes till viss del av andra undersökningar gjorda i området. Datasetet som användes i arbetet var av för liten omfattning för att bredare slutsatser skulle kunna dras och författarna ansåg att ytterligare studier inom området behövs.The use of site index (SI) is of great importance for forestry. SI describes the natural productivity of the soil by giving an estimation of how tall the thickest trees will be at a certain reference age. This thesis compares methods of estimation for SI by site factors (SIS) with older and newer formulas for estimation of SI by top height and height development curves (SIH). These analyses were done using data from Swedish long term experiments with thinning and fertilization done for Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). The results showed statistically significant differences between older and newer formulas for SIH for pine but not for spruce. There were statistically significant differences between estimations for SIH and SIS for both pine and spruce. There was no difference between estimated height development with the newer formulas and the actual measured heights. The results were partly supported by other studies. The data set used in this thesis was too small to allow wider conclusions and the authors came to the conclusion that further studies in the area were necessary

Does the scientific knowledge reflect the chemical diversity of environmental pollution? – A twenty-year perspective

Environmental policymaking relies heavily on the knowledge of the toxicological properties of chemical pollutants. The ecotoxicological research community is an important contributor to this knowledge, which together with data from standardized tests supports policy-makers in taking the decisions required to reach an appropriate level of protection of the environment. The chemosphere is, however, massive and contains thousands of chemicals that can constitute a risk if present in the environment at sufficiently high concentrations. The scientific ecotoxicological knowledge is growing but it is not clear to what extent the research community manages to cover the large chemical diversity of environmental pollution. In this study, we aimed to provide an overview of the scientific knowledge generated within the field of ecotoxicology during the last twenty years. By using text mining of over 130,000 scientific papers we established time-trends describing the yearly publication frequency of over 3500 chemicals. Our results show that ecotoxicological research is highly focused and that as few as 65 chemicals corresponded to half of all occurrences in the scientific literature. We, furthermore, demonstrate that the last decades have seen substantial changes in research direction, where the interest in pharmaceuticals has grown while the interest in biocides has declined. Several individual chemicals showed an especially rapid increase (e.g. ciprofloxacin, diclofenac) or decrease (e.g. lindane and atrazine) in occurrence in the literature. We also show that university- and corporate-based research exhibit distinct publication patterns and that for some chemicals the scientific knowledge is dominated by publications associated with the industry. This study paints a unique picture and provides quantitative estimates of the scientific knowledge of environmental chemical pollution generated during the last two decades. We conclude that there is a large number of chemicals with little, or no, scientific knowledge and that a continued expansion of the field of ecotoxicology will be necessary to catch up with the constantly increasing diversity of chemicals used within the society