Massive MIMO with I/Q imbalance: Performance analysis and compensation

In this paper, we consider the uplink of a single-cell massive multiple-input multiple-output (MIMO) system with inphase and quadrature-phase imbalance (IQI). This scenario is of particular importance in massive MIMO systems, where the deployment of lower-cost, lower-quality components is desirable to make massive MIMO a viable technology. Particularly, we investigate the effect of IQI on the performance of massive MIMO employing maximum-ratio combining (MRC) receivers. In order to study how IQI affects channel estimation, we derive a new channel estimator for the IQI-impaired model and show that IQI can substantially downgrade the performance of MRC receivers. Moreover, a low-complexity IQI compensation scheme, suitable for massive MIMO, is proposed which is based on the IQI coefficients' estimation and it is independent of the channel gain. The performance of the proposed compensation scheme is analytically evaluated by deriving a tractable approximation of the ergodic achievable rate and providing the asymptotic power scaling laws assuming transmission over Rayleigh fading channels with log-normal large-scale fading. Finally, we show that massive MIMO effectively suppresses the residual IQI effects, as long as, the compensation scheme is applied.

Energy efficiency optimization in hardware-constrained large-scale MIMO systems

Large-scale multiple-input multiple-output (MIMO) communication systems can bring substantial improvement in spectral efficiency and/or energy efficiency, due to the excessive degrees-of-freedom and huge array gain. However, large-scale MIMO is expected to deploy lower-cost radio frequency (RF) components, which are particularly prone to hardware impairments. Unfortunately, compensation schemes are not able to remove the impact of hardware impairments completely, such that a certain amount of residual impairments always exists. In this paper, we investigate the impact of residual transmit RF impairments (RTRI) on the spectral and energy efficiency of training-based point-to-point large-scale MIMO systems, and seek to determine the optimal training length and number of antennas which maximize the energy efficiency. We derive deterministic equivalents of the signal-to-noise-and-interference ratio (SINR) with zero-forcing (ZF) receivers, as well as the corresponding spectral and energy efficiency, which are shown to be accurate even for small number of antennas. Through an iterative sequential optimization, we find that the optimal training length of systems with RTRI can be smaller compared to ideal hardware systems in the moderate SNR regime, while larger in the high SNR regime. Moreover, it is observed that RTRI can significantly decrease the optimal number of transmit and receive antennas.

Massive MIMO in sparse channels

Massive multi-user multiple-input multiple-output (MU-MIMO) systems are cellular networks where the base stations (BSs) are equipped with hundreds of antennas, N, and communicate with tens of mobile stations (MSs), K, such that, N ≫ K ≫ 1. Contrary to most prior works, in this paper, we consider the uplink of a single-cell massive MIMO system operating in sparse channels with limited scattering. This case is of particular importance in most propagation scenarios, where the prevalent Rayleigh fading assumption becomes idealistic. We derive analytical approximations for the achievable rates of maximum-ratio combining (MRC) and zero-forcing (ZF) receivers. Furthermore, we study the asymptotic behavior of the achievable rates for both MRC and ZF receivers, when N and K go to infinity under the condition that N/K → c ≥ 1. Our results indicate that the achievable rate of MRC receivers reaches an asymptotic saturation limit, whereas the achievable rate of ZF receivers grows logarithmically with the number of MSs.

'That Puissant City': John Milton's Roman Sojourns 1638-1639

John Milton’s sojourns in Rome (1638-9) are attested by his comments in Defensio Secunda, by the minutes of the English College, by Latin encomia which he received from Roman academicians, and, not least, by his Latin letter to Lucas Holstenius (19/29 March 1639), and several Latin poems which he composed in the course of his residency in the capital city: Ad Salsillum, and three Latin epigrams extolling the praises of the virtuosa soprano, Leonora Baroni. Read together, these texts serve to reveal much about Milton’s participation in, and reaction to, the ‘Puissant City’, (History of Britain, Bk 2).

The present monograph presents fresh evidence of Milton's integration into the academic and cultural life of seventeenth-century Rome. It argues that his links with two Roman academies: the Accademia dei Fantastici and Accademia degli Umoristi constitute a sustained participation in an academic community paralleling that of his independently attested performance in Florentine academies (on which I have published extensively). It also investigates his links with Alessandro Cherubini, David Codner, Giovanni Batista Doni, and the Baroni circle hymned in three published anthologies.

Chapter 1: Milton and the Accademia dei Fantastici investigates the cultural climate surrounding Milton's Ad Salsillum by examining two of that academy's publications: the Poesie dei Signori Accademici Fantastici di Roma (Rome, 1637) and the Academia Tenuta da Fantastici a. 12 di Maggio 1655 (Rome, 1655), the latter celebrating the creation of Fabio Chigi as Pope Alexander VII on 5 April 1655. Read in a new light, Milton’s self-fashioning, it is argued, takes its place not only alongside Salzilli’s encomium in Milton's honour, and his Italian sonnets in the 1637 Poesie, but also in relation to other poems in that collection, and the academy's essentially Catholic eulogistic trend. The chapter also provides fresh evidence of Salzilli’s survival of the illness described in Milton’s poem by his epistolary correspondence with Tomaso Stigliani.

Chapter 2: Milton and the Vatican argues for links between Milton’s Latin letter to Holstenius and a range of Holstenius’ published works: his edition of the axioms of the later Pythagoreans gifted by him to Milton, and his published neo-Platonic works. This is achieved by mutual appropriation of Similitudes in a series of Miltonic similes, the anabasis/katabasis motifs in a reworking of the Platonic theory of the transmigration of souls, and allusion to etymological details highlighted in Holstenius’ published editions. The chapter also reveals Milton’s alertness to typographical procedures and, by association, to Holstenius’ recent role (1638) as Director of the press of the Biblioteca Vaticana.

Chapter 3: Milton and the Accademia degli Umoristi argues for Milton’s likely participation in this Roman academy, as suggested by his links with its members. His three Latin epigrams in praise of Leonora Baroni, the only female member of the Umoristi, have hitherto been studied in relation to the 1639 Applausi in her honour. In a new reading, Milton, it is suggested, invokes and interrogates Catholic doctrine before a Catholic audience only to view the whole through the lens of a neo-Platonic Hermeticism (by echoing the phraseology of the sixteenth-century Franciscan Hannibal Rosselli) that refreshingly transcends religious difference. Crucially, the hitherto neglected L’Idea della Veglia (Rome, 1640) includes further encomiastic verse, sonnets to, and by Leonora, and details of the conversazioni hosted by her family at the precise time of Milton’s Roman sojourns. Milton may well have been a participant. The chapter concludes in an assessment of his links with the youthful prodigy Alessandro Cherubini, and of his audience with Francesco Barberini.

Chapter 4: Milton at a Roman Opera analyses the potential impact of ‘Chi Soffre, Speri’, which he attended on 18/28 February 1639, mounted by Francesco Barberini to inaugurate the recently completed theatre of the Palazzo Barberini. A detailed analysis of the opera's libretto, music, and theatricality casts a backward glance to Milton's Comus, and a forward glance to Paradise Lost. It also assesses Milton’s musical interests at this time, as attested by his links with Doni, and his purchase of works by Monteverdi and others.

Chapter 5: Milton’s English Connections in Rome develops the work of Miller and Chaney by investigating Milton’s co-diners at the English College in Rome on 30 October 1638, and by analysing his links between David Codner (alias Matteo Selvaggio), and the family of Jane Savage, Marchioness of Winchester, lamented by Milton in 1631. It also assesses his potential relations with the Englishman Thomas Gawen, who ‘accidentally sometimes fell into the company of John Milton’ (Antony Wood).

Ex Vivo Smooth Muscle Pharmacological Effects of a Novel Bradykinin-Related Peptide, and Its Analogue, from Chinese Large Odorous Frog, Odorrana livida Skin Secretions

Bradykinin-related peptides (BRPs) are one of the most extensively studied frog secretions-derived peptide families identified from many amphibian species. The diverse primary structures of BRPs have been proven essential for providing valuable information in understanding basic mechanisms associated with drug modification. Here, we isolated, identified and characterized a dodeca-BRP (RAP-L1, T6-BK), with primary structure RAPLPPGFTPFR, from the skin secretions of Chinese large odorous frogs, Odorrana livida. This novel peptide exhibited a dose-dependent contractile property on rat bladder and rat ileum, and increased the contraction frequency on rat uterus ex vivo smooth muscle preparations; it also showed vasorelaxant activity on rat tail artery smooth muscle. In addition, the analogue RAP-L1, T6, L8-BK completely abolished these effects on selected rat smooth muscle tissues, whilst it showed inhibition effect on bradykinin-induced rat tail artery relaxation. By using canonical antagonist for bradykinin B1 or B2 type receptors, we found that RAP-L1, T6-BK -induced relaxation of the arterial smooth muscle was very likely to be modulated by B2 receptors. The analogue RAP-L1, T6, L8-BK further enhanced the bradykinin inhibitory activity only under the condition of co-administration with HOE140 on rat tail artery, suggesting a synergistic inhibition mechanism by which targeting B2 type receptors.

The Outer Solar Systems Origins Survey. I. Design and First-quarter Discoveries

We report the discovery, tracking, and detection circumstances for 85 trans-Neptunian objects (TNOs) from the first 42 deg2 of the Outer Solar System Origins Survey. This ongoing r-band solar system survey uses the 0.9 deg2 field of view MegaPrime camera on the 3.6 m Canada–France–Hawaii Telescope. Our orbital elements for these TNOs are precise to a fractional semimajor axis uncertainty <0.1%. We achieve this precision in just two oppositions, as compared to the normal three to five oppositions, via a dense observing cadence and innovative astrometric technique. These discoveries are free of ephemeris bias, a first for large trans-Neptunian surveys. We also provide the necessary information to enable models of TNO orbital distributions to be tested against our TNO sample. We confirm the existence of a cold "kernel" of objects within the main cold classical Kuiper Belt and infer the existence of an extension of the "stirred" cold classical Kuiper Belt to at least several au beyond the 2:1 mean motion resonance with Neptune. We find that the population model of Petit et al. remains a plausible representation of the Kuiper Belt. The full survey, to be completed in 2017, will provide an exquisitely characterized sample of important resonant TNO populations, ideal for testing models of giant planet migration during the early history of the solar system.