Reduced Switching Connectivity for Large Scale Antenna Selection

In this paper, we explore reduced-connectivity radio frequency (RF) switching networks for reducing the analog hardware complexity and switching power losses in antenna selection (AS) systems. In particular, we analyze different hardware architectures for implementing the RF switching matrices required in AS designs with a reduced number of RF chains. We explicitly show that fully-flexible switching matrices, which facilitate the selection of any possible subset of antennas and attain the maximum theoretical sum rates of AS, present numerous drawbacks such as the introduction of significant insertion losses, particularly pronounced in massive multiple-input multiple-output (MIMO) systems. Since these disadvantages make fully-flexible switching suboptimal in the energy efficiency sense, we further consider partially-connected switching networks as an alternative switching architecture with reduced hardware complexity, which we characterize in this work. In this context, we also analyze the impact of reduced switching connectivity on the analog hardware and digital signal processing of AS schemes that rely on channel power information. Overall, the analytical and simulation results shown in this paper demonstrate that partially-connected switching maximizes the energy efficiency of massive MIMO systems for a reduced number of RF chains, while fully-flexible switching offers sub-optimal energy efficiency benefits due to its significant switching power losses.Comment: 14 pages, 11 figure

Hybrid Analog-Digital Precoding Revisited under Realistic RF Modeling

In this paper we revisit hybrid analog-digital precoding systems with emphasis on their modelling and radio-frequency (RF) losses, to realistically evaluate their benefits in 5G system implementations. For this, we decompose the analog beamforming networks (ABFN) as a bank of commonly used RF components and formulate realistic model constraints based on their S-parameters. Specifically, we concentrate on fully-connected ABFN (FC-ABFN) and Butler networks for implementing the discrete Fourier transform (DFT) in the RF domain. The results presented in this paper reveal that the performance and energy efficiency of hybrid precoding systems are severely affected, once practical factors are considered in the overall design. In this context, we also show that Butler RF networks are capable of providing better performances than FC-ABFN for systems with a large number of RF chains.Comment: 12 pages, 5 figure

Enhancing Coexistence in the Unlicensed Band with Massive MIMO

We consider cellular base stations (BSs) equipped with a large number of antennas and operating in the unlicensed band. We denote such system as massive MIMO unlicensed (mMIMO-U). We design the key procedures required to guarantee coexistence between a cellular BS and nearby Wi-Fi devices. These include: neighboring Wi-Fi channel covariance estimation, allocation of spatial degrees of freedom for interference suppression, and enhanced channel sensing and data transmission phases. We evaluate the performance of the so-designed mMIMO-U, showing that it allows simultaneous cellular and Wi-Fi transmissions by keeping their mutual interference below the regulatory threshold. The same is not true for conventional listen-before-talk (LBT) operations. As a result, mMIMO-U boosts the aggregate cellular-plus-Wi-Fi data rate in the unlicensed band with respect to conventional LBT, exhibiting increasing gains as the number of BS antennas grows.Comment: To appear in Proc. IEEE ICC 201

Indoor Massive MIMO Deployments for Uniformly High Wireless Capacity

Providing consistently high wireless capacity is becoming increasingly important to support the applications required by future digital enterprises. In this paper, we propose Eigen-direction-aware ZF (EDA-ZF) with partial coordination among base stations (BSs) and distributed interference suppression as a practical approach to achieve this objective. We compare our solution with Zero Forcing (ZF), entailing neither BS coordination or inter-cell interference mitigation, and Network MIMO (NeMIMO), where full BS coordination enables centralized inter-cell interference management. We also evaluate the performance of said schemes for three sub-6 GHz deployments with varying BS densities -- sparse, intermediate, and dense -- all with fixed total number of antennas and radiated power. Extensive simulations show that: (i) indoor massive MIMO implementing the proposed EDA-ZF provides uniformly good rates for all users; (ii) indoor network densification is detrimental unless full coordination is implemented; (iii) deploying NeMIMO pays off under strong outdoor interference, especially for cell-edge users

Etude de la congélation comme technique de traitement des eaux : applications spécifiques

Le travail présenté dans ce mémoire est relatif au traitement des eaux résiduaires par congélation. L’objectif de cette étude est de proposer un nouveau procédé de traitement d’eaux résiduaires simple et adapté à tous les types d’effluents. \ud La première partie de ce travail concerne le développement du nouveau procédé de traitement. Une méthodologie de traitement basée sur le principe de la congélation a été étudiée et optimisée. Elle repose sur le fait que lorsque l’on congèle une solution aqueuse, les cristaux de glace formés sont constitués d’eau pure et le soluté ou polluant se concentre dans la phase liquide résiduelle. Les produits de la séparation par congélation sont donc, une phase solide de glace pure, recyclable suivant sa pureté et une phase liquide concentrée qui peut être soit incinérée soit réutilisée suivant sa composition. Les résultats obtenus ont montré que la méthode proposée est parfaitement adaptée à l’élimination des polluants solubles et insolubles et qu’elle permet d’obtenir des efficacités d’épuration très élevées, supérieures dans la plupart des cas à 80%. \ud La deuxième partie du travail a permis de montrer l’intérêt de ce nouveau procédé de traitement dans le dessalement de l’eau de mer, ainsi que dans le traitement d’eaux résiduaires industrielles complexes, notamment de l’industrie pétrolière et de l’industrie textile. La méthode proposée présente les avantages de s’affranchir des diverses compositions des eaux résiduaires et de s’inscrire dans la logique de traitement des effluents de ces industries. De même, des essais terrain dans une Station de Sport d’Hiver ont montré l’intérêt du froid naturel pour épurer par congélation des eaux résiduaires urbaines avec de rendements très élevés supérieures à 80%.\ud La dernière partie de cette étude a permis de simuler l’emploi du procédé de cristallisation continu Bremband en vue d’une application industrielle du procédé de traitement d’eaux résiduaires par congélation en utilisant le froid naturel comme source d’énergie.\ud This manuscript is about the wastewater treatment by freezing. This study aims to propose a new process of wastewater treatment, which is simple and adapted to all effluent types. \ud The first part of this research concerns the development of the new process of treatment. A treatment method based on the principle of freezing has been studied and optimized. This method is based on the fact that when an aqueous solution is frozen, the formed ice crystals consist of pure water and the pollutant concentrates in the residual liquid phase. The products of separation by freezing are thus, a solid phase of pure ice, which can be recycled according to its purity and a concentrated liquid phase which can either be incinerated or re-used according to its composition. Results show that the proposed method is perfectly adapted to the elimination of the soluble and insoluble pollutants. It also allows obtaining very high efficiencies of purification, most of the cases higher than 80%. \ud The second part of the study shows the interest of this new treatment process in seawater desalination, as well as in the treatment of complex industrial wastewater, particularly of oil industry and textile industry. The proposed treatment method presents advantages of being an applicable process in a general way to the diverse wastewater types. In addition, it can be easily adapted in the logic of treatment of these industries. In the same way, some ground tests in a winter sports resort showed the interest of the natural cold to purify urban wastewater by freezing with very high efficiencies, higher than 80%.\ud The last part of this research made it possible to simulate the use of the continuous crystallization Bremband process for an industrial application of the freezing process in wastewater treatment by using the natural cold like a source of energy. \ud \u

Uplink Sounding Reference Signal Coordination to Combat Pilot Contamination in 5G Massive MIMO

To guarantee the success of massive multiple-input multiple-output (MIMO), one of the main challenges to solve is the efficient management of pilot contamination. Allocation of fully orthogonal pilot sequences across the network would provide a solution to the problem, but the associated overhead would make this approach infeasible in practical systems. Ongoing fifth-generation (5G) standardisation activities are debating the amount of resources to be dedicated to the transmission of pilot sequences, focussing on uplink sounding reference signals (UL SRSs) design. In this paper, we extensively evaluate the performance of various UL SRS allocation strategies in practical deployments, shedding light on their strengths and weaknesses. Furthermore, we introduce a novel UL SRS fractional reuse (FR) scheme, denoted neighbour-aware FR (FR-NA). The proposed FR-NA generalizes the fixed reuse paradigm, and entails a tradeoff between i) aggressively sharing some UL SRS resources, and ii) protecting other UL SRS resources with the aim of relieving neighbouring BSs from pilot contamination. Said features result in a cell throughput improvement over both fixed reuse and state-of-the-art FR based on a cell-centric perspective