Massive MIMO is a Reality -- What is Next? Five Promising Research Directions for Antenna Arrays

Massive MIMO (multiple-input multiple-output) is no longer a "wild" or "promising" concept for future cellular networks - in 2018 it became a reality. Base stations (BSs) with 64 fully digital transceiver chains were commercially deployed in several countries, the key ingredients of Massive MIMO have made it into the 5G standard, the signal processing methods required to achieve unprecedented spectral efficiency have been developed, and the limitation due to pilot contamination has been resolved. Even the development of fully digital Massive MIMO arrays for mmWave frequencies - once viewed prohibitively complicated and costly - is well underway. In a few years, Massive MIMO with fully digital transceivers will be a mainstream feature at both sub-6 GHz and mmWave frequencies. In this paper, we explain how the first chapter of the Massive MIMO research saga has come to an end, while the story has just begun. The coming wide-scale deployment of BSs with massive antenna arrays opens the door to a brand new world where spatial processing capabilities are omnipresent. In addition to mobile broadband services, the antennas can be used for other communication applications, such as low-power machine-type or ultra-reliable communications, as well as non-communication applications such as radar, sensing and positioning. We outline five new Massive MIMO related research directions: Extremely large aperture arrays, Holographic Massive MIMO, Six-dimensional positioning, Large-scale MIMO radar, and Intelligent Massive MIMO.Comment: 20 pages, 9 figures, submitted to Digital Signal Processin

Optimized Iterative (Turbo) Reception for QAM OFDM with CFO over Unknown Double-Selective Channels

A novel iterative (turbo) receiver is introduced, suitable for orthogonal frequency division multiplexing (OFDM) employing quadrature amplitude modulation (QAM) and receiver diversity. The system operates over a double-selective channel and includes a carrier frequency offset (CFO). We propose a maximum a posteriori probability expectation-maximization (MAP-EM) receiver with a different EM parameter division than standard methods. In such standard MAP-EM receivers, the E-step parameters correspond to the channel, while the M-step parameters correspond to the CFO and data symbols. This standard receiver parameter division results into a highly complex receiver for QAM, due to the large modulated symbol alphabet size, and the non-constant constellation symbol amplitude. In this paper, a new receiver framework introduces a different parameter division that leads to reduced complexity turbo receivers for QAM signaling, while still achieving close to optimal system performance. The new approach adapts the sum-product algorithm (SPA) parameter framework to the MAP-EM receiver. Thus, in the new receiver framework, the E-step parameters are data symbols, while the M-step parameters are the channel and the CFO. We evaluate the performance of the proposed receiver with and without automatic repeat request (ARQ), where in the former case packet combining applies to further improve performance

The goal dependent automaticity of drinking habits

In recent treatments of habitual social behaviour, habits are conceptualised as a form of goal-directed automatic behaviour that are mentally represented as goal-action links. Three experiments tested this conceptualisation in the context of students’ drinking (alcohol consumption) habits. Participants were randomly assigned to conditions where either a goal related to drinking behaviour (socialising) was activated, or an unrelated goal was activated. In addition, participants’ drinking habits were measured. The dependent variable in Experiments 1 and 2 was readiness to drink, operationalised by speed of responding to the action concept “drinking” in a verb verification task. Experiment 3 used uptake of a voucher to measure drinking behaviour. Findings supported the view that when habits are established, simply activating a goal related to the focal behaviour automatically elicits that behaviour. These findings are consistent with a goal-dependent conception of habit. Possibilities for interventions designed to attenuate undesirable habitual behaviours are considered

5-Amino­pentan-1-ol

The title compound, C5H13NO, is an aliphatic amino­alcohol with both functional groups residing on terminal C atoms. Apart from the hy­droxy group, all non-H atoms are nearly co-planar, the maximum deviation of an atom taking part in the least-squares plane defined by the mentioned non-H atoms being 0.029 (1) Å. In the crystal, O—H⋯N and N—H⋯O hydrogen bonds connect the mol­ecules, forming a three-dimensional network

Bis(piperidin-1-yl)methanone

The title compound, C11H20N2O, is a urea derivative bearing two piperidine moieties in place of the amino groups. The mol­ecule shows approximate non-crystallographic C 2 symmetry. The six-membered rings adopt 1 C 4 and 4 C 1 conformations and their mean planes make a dihedral angle of 35.87 (5)°. In the crystal, inter­molecular C—H⋯O contacts connect the mol­ecules into infinite strands along the a axis

Split ticket voting in mixed member proportional systems: the hypothetical case of the Netherlands

"In Mixed Member Proportional systems, voters are able to split their vote. To what extent do voters use this opportunity, which voters seem to use this opportunity most and what are the potential consequences of split ticket voting? These questions are answered by comparatively analyzing motives for split ticket voting and factors that facilitate such behavior and apply them to the Dutch situation. Moreover, we employ various simulations based on the last three parliamentary elections in order to assess the potential consequences of split ticket voting under different electoral system proposals. In general, these results indicate that split ticket voting will not have substantial effects on the distribution of seats in parliament." (author's abstract

Bis(2-hy­droxy­phen­yl)methanone

In the title compound, C13H10O3, a benzophenone derivative, the least-squares planes defined by the C atoms of the 2-hy­droxy­phenyl rings inter­sect at an angle of 45.49 (3)°. The substituents on the aromatic systems are both orientated towards the central O atom. Intra- as well as inter­molecular O—H⋯O hydrogen bonds are observed, the latter giving rise to the formation of centrosymmetric dimers. The closest centroid–centroid distance between two π-systems is 3.7934 (7) Å

2-[(4-Methyl­phen­yl)sulfan­yl]aniline

The least-squares planes defined by the aromatic moieties in the title aniline derivative, C13H13NS, are nearly perpendicular to each other, forming a dihedral angle of 87.80 (7)°. Apart from a weak intramolecular N—H⋯S hydrogen bond, a co-operative set of N—H⋯N hydrogen bonds present in the crystal structure leads to the formation of tetra­meric units

Underpricing in the cryptocurrency world:evidence from initial coin offerings

Purpose The purpose of this paper is to analyze underpricing in initial coin offerings (ICO). It bridges the gap between findings in initial public offering (IPO) literature and empirical results from ICOs. Design/methodology/approach The sample set consists of 279 ICOs between April 2013 and January 2018. A regression analysis is performed with data from the ICOs. Findings The results show an average level of underpricing of ICOs of 123 percent in the USA and 97 percent in the other countries. The results for the US ICOs are significantly higher than for US IPOs on average and also higher than US IPOs at the beginning of the dot.com bubble. The authors also study the determinants of ICO underpricing. The authors use proxies based on asymmetric information from the IPO literature as well as ICO-related variables. First-day trading volume and a good sentiment on the ICO market go together with more ICO underpricing. Moreover, hot markets make first-day investors to benefit less. Finally, companies that use a large issue size or a pre-ICO (a sale of cryptocurrencies before the ICO) leave less money on the table. Practical implications The research may help in reducing underpricing, as the authors find that issuers can reduce it by holding a pre-ICO and by considering larger issue sizes. If they do so, investors will get fewer opportunities to benefit from underpricing. Investors can, nevertheless, also profit from the knowledge generated in this paper. When market sentiment is positive and first-day trading volume is expected to be high, investing in ICOs is likely to give them higher first-day returns. Finally, the authors hope that this paper will serve as a basis for further research into the exciting and dynamic world of cryptocurrencies. Originality/value There is hardly any research on underpricing of ICOs. The paper is interesting for its table with a brief comparison of ICOs and IPOs. It also searches for variables from the asymmetric information theory behind IPOs to be applied in explaining ICOs. It shows high levels of ICO underpricing in comparison to IPOs. It also gives suggestions for issuers of (and investors in) ICOs