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

Cooperation and competition in the cargo liner shipping industry

It is widespread international practice that cargo liners meet at regular conferences to fix prices and quotas for individual routes. Presently, however, the respective European regulation granting liners an exemption from competition laws is under review. Liners claim that conferences are a necessary pre-condition for the provision of reliable services. In contrast, we demonstrate that there is little evidence for a destabilizing effect of competition, while conferences can themselves give rise to instability. The liners association (ELAA) has, in response to the EU review process, proposed an information exchange system as an alternative. In our view this has some merits. Transfer of data might even be mandatory, information output should be aggregated and anonymized and made available to the general public. We are skeptical, however, about any discussions between liners that go further than anonymized information exchange. -- In der Containerseeschifffahrt ist es weltweit üblich, dass sich die Reeder in Konferenzen über Frachtraten und -quoten für spezifische Handelsrouten abstimmen. In Europa wird jedoch die Regulierung, die diese Ausnahme vom Wettbewerbsrecht erlaubt, von der EU-Kommission zur Zeit überprüft. Die Reeder argumentieren, dass Konferenzen nötig sind, um ein stabiles Angebot sicherzustellen. Wir kommen jedoch zu dem Schluss, dass es keine Anhaltspunkte für außerodentlich destabilisierende Effekte von Konkurrenz gibt. Im Gegenteil zeigt sich, dass eher die Konferenzen destabilisierende Effekte erzeugen können. Die Assoziation der Reedereien (ELAA) hat, unter dem Druck der Überprüfung durch die EU, als Alternative die Einrichtung eines Informationsaustauschsystems vorgeschlagen. Dies hat aus unserer Sicht einige Vorteile. Man könnte die Übermittlung von Daten sogar zur Pflicht machen; der daraus gewonnene Informations-Output sollte aggregiert und anonymisiert sein und der allgemeinen Öffentlichkeit zur Verfügung gestellt werden. Wir sind jedoch skeptisch gegenüber Diskussionen zwischen den Reedern, die über den anonymisierten Informationsaustausch hinausgehen.

Sensitivity and Selectivity on Aptamer-Based Assay: The Determination of Tetracycline Residue in Bovine Milk

A competitive enzyme-linked aptamer assay (ELAA) to detect tetracycline in milk was performed by using two different aptamers individually; one is 76 mer-DNA aptamer and the other is 57 mer-RNA aptamer. The best optimum condition was obtained without monovalent ion, Na+ and also by adding no Mg2+ ion in the assay buffer, along with RT incubation. The optimized ELAA showed a good sensitivity (LOD of 2.10 × 10−8 M) with a wide dynamic range (3.16 × 10−8 M ~ 3.16 × 10−4 M). In addition, the average R.S.D. across all data points of the curve was less than 2.5% with good recoveries (~101.8%) from the milk media. Thus, this method provides a good tool to monitor tetracycline in milk from MRLs' point of view. However, this ELAA method was not superior to the ELISA method in terms of specificity. This paper describes that it does not always give better sensitivity and specificity in assays even though aptamers have several advantages over antibodies and have been known to be good binders for binding assays

Microscopic theory of the Casimir force at thermal equilibrium: large-separation asymptotics

We present an entirely microscopic calculation of the Casimir force $f(d)$ between two metallic plates in the limit of large separation $d$. The models of metals consist of mobile quantum charges in thermal equilibrium with the photon field at positive temperature $T$. Fluctuations of all degrees of freedom, matter and field, are treated according to the principles of quantum electrodynamics and statistical physics without recourse to approximations or intermediate assumptions. Our main result is the correctness of the asymptotic universal formula f(d) \sim -\frac{\zeta(3) \kB T}{8\pi d^3}, $d\to\infty$. This supports the fact that, in the framework of Lifshitz' theory of electromagnetic fluctuations, transverse electric modes do not contribute in this regime. Moreover the microscopic origin of universality is seen to rely on perfect screening sum rules that hold in great generality for conducting media.Comment: 34 pages, 0 figures. New version includes restructured intro and minor typos correcte

Selection of DNA aptamers that bind to influenza A viruses with high affinity and broad subtype specificity

AbstractMany cases of influenza are reported worldwide every year. The influenza virus often acquires new antigenicity, which is known as antigenic shift; this results in the emergence of new virus strains, for which preexisting immunity is not found in the population resulting in influenza pandemics. In the event a new strain emerges, diagnostic tools must be developed rapidly to detect the novel influenza strain. The generation of high affinity antibodies is costly and takes time; therefore, an alternative detection system, aptamer detection, provides a viable alternative to antibodies as a diagnostic tool. In this study, we developed DNA aptamers that bind to HA1 proteins of multiple influenza A virus subtypes by the SELEX procedure. To evaluate the binding properties of these aptamers using colorimetric methods, we developed a novel aptamer-based sandwich detection method employing our newly identified aptamers. This novel sandwich enzyme-linked aptamer assay successfully detected the H5N1, H1N1, and H3N2 subtypes of influenza A virus with almost equal sensitivities. These findings suggest that our aptamers are attractive candidates for use as simple and sensitive diagnostic tools that need sandwich system for detecting the influenza A virus with broad subtype specificities

Agroecologia e educação no campo: um sonho se tornando realidade na Escola Latino-Americana de Agroecologia.

Este trabalho relata a experiência de gênese da Escola Latina Americana de Agroecologia e sua importância para as comunidades camponesas em geral.Disponível também em: Cadernos de Agroecologia, V. 5, n.1, 2010

Iterative Inversion of (ELAA-)MIMO Channels Using Symmetric Rank-11 Regularization

While iterative matrix inversion methods excel in computational efficiency, memory optimization, and support for parallel and distributed computing when managing large matrices, their limitations are also evident in multiple-input multiple-output (MIMO) fading channels. These methods encounter challenges related to slow convergence and diminished accuracy, especially in ill-conditioned scenarios, hindering their application in future MIMO networks such as extra-large aperture array (ELAA). To address these challenges, this paper proposes a novel matrix regularization method termed symmetric rank-$1$ regularization (SR-$1$R). The proposed method functions by augmenting the channel matrix with a symmetric rank-$1$ matrix, with the primary goal of minimizing the condition number of the resultant regularized matrix. This significantly improves the matrix condition, enabling fast and accurate iterative inversion of the regularized matrix. Then, the inverse of the original channel matrix is obtained by applying the Sherman-Morrison transform on the outcome of iterative inversions. Our eigenvalue analysis unveils the best channel condition that can be achieved by an optimized SR-$1$R matrix. Moreover, a power iteration-assisted (PIA) approach is proposed to find the optimum SR-$1$R matrix without need of eigenvalue decomposition. The proposed approach exhibits logarithmic algorithm-depth in parallel computing for MIMO precoding. Finally, computer simulations demonstrate that SR-$1$R has the potential to reduce iterative iterations by up to $33\%$, while also significantly improve symbol error probability by approximately an order of magnitude.Comment: 13 pages, 12 figure

Nonlinear Distortion Radiated from Large Arrays and Active Reconfigurable Intelligent Surfaces

Extremely large aperture arrays (ELAAs) and reconfigurable intelligent surfaces (RISs) are candidate enablers to realize connectivity goals for the sixth-generation (6G) wireless networks. For instance, ELAAs can provide orders-of-magnitude higher area throughput compared to what massive multiple-input multiple-output (MIMO) can deliver through spatial multiplexing, while RISs can improve the propagation conditions over wireless channels but a passively reflecting RIS must be large to be effective. Active RIS with amplifiers can deal with this issue. In this paper, we study the distortion created by nonlinear amplifiers in both ELAAs and active RIS. We analytically obtain the angular directions and depth of the nonlinear distortion in both near- and far-field channels. The results are demonstrated numerically and we conclude that non-linearities can both create in-band and out-of-band distortion that is beamformed in entirely new directions and distances from the transmitter