Spectral and Energy Efficiency of Superimposed Pilots in Uplink Massive MIMO

Next generation wireless networks aim at providing substantial improvements in spectral efficiency (SE) and energy efficiency (EE). Massive MIMO has been proved to be a viable technology to achieve these goals by spatially multiplexing several users using many base station (BS) antennas. A potential limitation of Massive MIMO in multicell systems is pilot contamination, which arises in the channel estimation process from the interference caused by reusing pilots in neighboring cells. A standard method to reduce pilot contamination, known as regular pilot (RP), is to adjust the length of pilot sequences while transmitting data and pilot symbols disjointly. An alternative method, called superimposed pilot (SP), sends a superposition of pilot and data symbols. This allows to use longer pilots which, in turn, reduces pilot contamination. We consider the uplink of a multicell Massive MIMO network using maximum ratio combining detection and compare RP and SP in terms of SE and EE. To this end, we derive rigorous closed-form achievable rates with SP under a practical random BS deployment. We prove that the reduction of pilot contamination with SP is outweighed by the additional coherent and non-coherent interference. Numerical results show that when both methods are optimized, RP achieves comparable SE and EE to SP in practical scenarios.Comment: 32 pages, 12 figures, 3 tables. Submitted in March 2017 to IEEE Transactions on Wireless Communication

Network Deployment for Maximal Energy Efficiency in Uplink with Zero-Forcing

This work aims to design a cellular network for maximal energy efficiency (EE). In particular, we consider the uplink with multi-antenna base stations and assume that zero- forcing (ZF) combining is used for data detection with imperfect channel state information. Using stochastic geometry and a new lower bound on the average per-user spectral efficiency of the network, we optimize the pilot reuse factor, number of antennas and users per base station. Closed-form expressions are computed from which valuable insights into the interplay between the optimization variables, hardware characteristics, and propagation environment are obtained. Numerical results are used to validate the analysis and make comparisons with a network using maximum ratio (MR) combining. The results show that a Massive MIMO setup arises as the EE-optimal network configuration. In addition, ZF provides higher EE than MR while allowing a smaller pilot reuse factor and a more dense network deployment.Comment: 7 pages, 3 figures; presented at the Global Communications Conference (GLOBECOM'17), 4-8 December, 2017, Singapor

Network Deployment for Maximal Energy Efficiency in Uplink with Multislope Path Loss

This work aims to design the uplink (UL) of a cellular network for maximal energy efficiency (EE). Each base station (BS) is randomly deployed within a given area and is equipped with $M$ antennas to serve $K$ user equipments (UEs). A multislope (distance-dependent) path loss model is considered and linear processing is used, under the assumption that channel state information is acquired by using pilot sequences (reused across the network). Within this setting, a lower bound on the UL spectral efficiency and a realistic circuit power consumption model are used to evaluate the network EE. Numerical results are first used to compute the optimal BS density and pilot reuse factor for a Massive MIMO network with three different detection schemes, namely, maximum ratio combining, zero-forcing (ZF) and multicell minimum mean-squared error. The numerical analysis shows that the EE is a unimodal function of BS density and achieves its maximum for a relatively small density of BS, irrespective of the employed detection scheme. This is in contrast to the single-slope (distance-independent) path loss model, for which the EE is a monotonic non-decreasing function of BS density. Then, we concentrate on ZF and use stochastic geometry to compute a new lower bound on the spectral efficiency, which is then used to optimize, for a given BS density, the pilot reuse factor, number of BS antennas and UEs. Closed- form expressions are computed from which valuable insights into the interplay between optimization variables, hardware characteristics, and propagation environment are obtained.Comment: 30 pages, 5 figures, 2 tables, https://ieeexplore.ieee.org/document/8362685

Причины развития послеоперационного энтероколита при болезни Гиршпрунга у пациентов детского возраста

ГИРШСПРУНГА БОЛЕЗНЬ /ХИРАГАНГЛИОЗ ТОЛСТОЙ КИШКИ ВРОЖДЕННЫЙ /ХИРМЕГАКОЛОН ВРОЖДЕННЫЙ /ХИРТОЛСТАЯ КИШКА /ХИРКИШЕЧНИК ТОЛСТЫЙ /ХИРПОСЛЕОПЕРАЦИОННЫЕ ОСЛОЖНЕНИЯЭНТЕРОКОЛИТТРАНСАНАЛЬНОЕ ЭНДОРЕКТАЛЬНОЕ НИЗВЕДЕНИЕДЕТИТотальная мезоректумэктомия является фактором риска развития и формирования патологических пресакральных синусов. В результате резекции прямой кишки с тотальной мезоректумэктомией в тазу образуется объемная полость, ограниченная костными структурами. При накоплении в ней жидкости, крови увеличивается риск инфицирования и образования пресакральных абсцессов. Если патологическая полость не заживает на протяжении 12 месяцев, такой синус считают хроническим. Хронический пресакральный синус образуется у 5-9,5% пациентов, которым проводилась тотальная мезоректумэктомия. Основными факторами развития являются неоадъювантная химиолучевая терапия, высокая интраоперационная кровопотеря, опухоли больших размеров. Диагностика заключается в проведении следующих инструментальных методов: ректоскопия, проктография, магнитно-резонансная томография органов малого таза. Основным методом лечения при небольших синусах является использование фибринового клея и системы EndoVac. Фибриновый клей механически закрывает дефект, стимулирует пролиферацию фибробластов и служит матриксом для синтеза коллагена, процессов заживления раны. Чаще всего фибриновый клей применяется как завершающий этап терапии системой EndoVac, при котором губка, соответствующая размерам дефекта, устанавливается в полость абсцесса и меняется через каждые 48-72 часа. Степень эффективности 66-100%. В случаях больших размеров синусов, дренирующихся через небольшой дефект в анастомозе, или неэффективности системы EndoVac, для создания адекватного дренирования целесообразно применение методики эндоскопической марсупиализации. Данная методика позволяет сохранить колоректальный анастомоз. Пациентам с симптоматическим пресакральным синусом, у которых реверсия стомы невозможна, рекомендуется выполнять чрессфинктерную проктэктомию с тампонадой полости большим сальником.Total mesorectumectomy is a risk factor of development and formulation of pathological presacral sinuses. In the result of the rectum resection with total mesorectumectomy, the volumetric cavity is formed in the pelvisbounded by thebone structures. In case of accumulation of the liquid and blood in it, the risk of infection and the formation of presacral abscesses increases. If the pathological cavity does not heal during 12 months, such sinus is considered to be chronic. The chronic presacral sinus is formed in 5-9.5% of patients, those who underwent total mesorectumectomy. The main causes of development are neoadjuvantchemotherapy, high intraoperative bleeding, tumors of large size. The diagnostics includes the following instrumental methods: rectoscopy, proctography, magnetic resonance imaging of the pelvic organs. The basic methods of treatment in small sinuses are the application of fibrin glue and the EndoVac system. Fibringluecloses defects mechanically, stimulates proliferation of fibroblasts and provides matrix for the synthesis of collagen and for the processes of the wound healing. Fibrin glue is most often used as the final stage of the EndoVac system therapy, when a sponge, corresponding to the defect sizes, is placed in the abscess cavity, and is replaced every 48-72 hours. Treatment effectiveness is 66-100%. In the case of a large sinus, drained through a small defect in anastomosis or inefficiency of the EndoVac system, the method of endoscopic marsupialization is appropriate to be used. The given method allows saving the colorectal anastomosis. In patients with symptomatic presacral sinus in whom stoma reversionis impossible, transversal proctectomy with the cavity tamponade by greater omentum is advisable

SISTEMAS DE GESTIÓN AMBIENTAL BASADOS EN ISO 14001: BENEFICIOS E IMPLICACIONES DEL MARCO REGULATORIO VENEZOLANO

Los propósitos del desarrollo sostenible combaten la explotación de recursos naturales y la contaminación ambiental ocasionada por procesos industriales. Durante el siglo XXI, el entorno empresarial se ha comprometido con la preservación del medioambiente tanto por razones legales como por la necesidad de implementar buenas prácticas comprometidas con el ambiente. La serie de normas ISO 14000 proveen un modelo de Sistema de Gestión Ambiental basado en políticas y objetivos para un desempeño ecoeficiente. Las empresas venezolanas deben dar cumplimiento a las disposiciones legales en materia ambiental con el fin de fomentar una cultura ecológica traducida en productos y servicios derivados de procesos que no amenazan las condiciones ambientales, capaces de dinamizar el rendimiento empresarial. El propósito de este artículo es analizar los Sistemas de Gestión Ambiental basados en la norma ISO 14000 considerando los beneficios de la gestión ambiental y las implicaciones del marco regulatorio para empresas venezolanas

Hermeneusis de la gerencia universitaria venezolana desde el enfoque del paradigma emergente

La gerencia universitaria debe poseer las competencias para transformar su estructura en medio de una realidad cambiante, siendo capaz de enfrentar los desafíos a través de estrategias que redefinan su pertinencia social. Esta investigación tuvo como propósitos develar las significaciones atribuidas a la gerencia de la Universidad de Carabobo así como comprender e interpretar los constructos emergidos con fundamento en el estado del arte y el referencial teórico. El estudio se enmarcó en el paradigma interpretativo con enfoque cualitativo; la episteme se construyó a partir del vivencialismo experiencial. Metodológicamente, se utilizó la fenomenología hermenéutica; se seleccionaron intencionalmente cinco gerentes universitarios, como técnica de recogida de información se empleó la entrevista en profundidad administrada bajo modalidad virtual sincrónica entre abril y mayo del 2020. Se siguió el protocolo de delimitación de unidades categoriales y subcategoriales para fundamentar el análisis de los testimonios, sistematizados a través de matrices axiales de codificación abierta, selectiva y cromática. Se develó que, ante la intermitencia prolongada de la autonomía deliberante, la gerencia universitaria ha instaurado un modelo de gestión similar al de gobernanza nacional, introduciendo flagelos que mancillan la cultura y trastornan los fines institucionales; haciéndose de las fuentes del poder jerárquico para sopesar su escaso liderazgo. La diáspora, el déficit presupuestario, la insuficiencia salarial, la profunda crisis nacional y el esquema de gestión autoritario, se convierten en aspectos que impiden trascender a un modelo de universidad competitivo e idóneo que contribuya al desarrollo de la región

Cultura Corporativa como Predictora del Compromiso Organizacional: Caso de un Retail Chileno

La cultura corporativa es un sistema interconectado de creencias, expectativas y presunciones subyacentes que definen las formas de ser y hacer en la empresa; su inclusión como variable de gestión empresarial incide y predice el comportamiento de otras variables como el compromiso organizacional. El objetivo fue conocer el grado de influencia de la cultura corporativa sobre el compromiso organizacional de los colaboradores de París del Grupo Cencosud, a partir de una metodología cuantitativa correlacional-causal aplicando la Denison Organizational Culture Survey y la Affective Continunance and Normative Commiment Scales a 87 colaboradores, confirmándose 5 de las 6 hipótesis planteadas que demuestran que las dimensiones participación, consistencia, adaptabilidad y misión de la cultura corporativa se relacionan e influyen en el compromiso normativo y de continuidad, pero no en el compromiso afectivo. Los colaboradores sienten identidad por deuda moral hacia la empresa y por la necesidad personal de conservar su membresía; sin embargo, no existe un genuino deseo de permanecer. El análisis de variables demográficas revela que la edad se incluye en el modelo predictivo debido a que los colaboradores más jóvenes experimentan mayor compromiso porque buscan un buen desempeño laboral para obtener beneficios contractuales. Se recomienda ampliar el universo muestral en futuros estudios, y analizar otras variables de la dinámica organizacional para auscultar la dimensión emocional que experimentan los colaboradores

Analysis of Alternative Massive MIMO Designs : Superimposed Pilots and Mixed-ADCs

The development of information and communication technologies (ICT) provides the means for reaching global connectivity that can help humanity progress and prosper. This comes with high demands on data traffic and number of connected devices which are rapidly growing and need to be met by technological development. Massive MIMO, where MIMO stands for multiple-input multiple-output, is envisioned as a fundamental component of next generation wireless communications for its ability to provide high spectral and energy efficiency, SE and EE, respectively. The key feature of this technology is the use of a large number of antennas at the base stations (BS) to spatially multiplex several user equipments (UEs). In the development of new technologies like Massive MIMO, many design alternatives need to be evaluated and compared in order to find the best operating point with a preferable tradeoff between high performance and low cost. In this thesis, two alternative designs for signal processing and hardware in Massive MIMO are studied and compared with the baseline operation in terms of SE, EE, and power consumption. The first design is called superimposed pilot (SP) transmission and is based on superimposing pilot and data symbols to remove the overhead from pilot transmission and reduce pilot contamination. The second design is mixed analog-to-digital converters (ADCs) and it aims at balancing high performance and low complexity by allowing different ADC bit resolutions across the BS antennas. The results show that the baseline operation of Massive MIMO, properly optimized, is the preferred choice. However, SP and mixed ADCs still have room for improvement and further study is needed to ascertain the full capabilities of these alternative designs.Mindre typografiska fel är korrigerade i den elektroniska versionen. / Minor typographic errors are corrected in the electronic version.</p

Scalability of Device-to-Device Communications in Cellular Networks

In current cellular networks the demand of traffic is rapidly increasing and new techniques need to be developed to accommodate future service requirements. Device-to-Device (D2D) communications is one technique that has been proposed to improve the performance of the system by allowing devices to communicate directly without routing traffic through the base station. This technique has the means to improved performance and support new proximity based services.   Nowadays new applications based on geographical proximity are becoming more and more popular suggesting that D2D communications will have a high de- mand in the near future. Thus the study of the scalability of D2D communications is of paramount importance.   We define the scalability of D2D communications underlay cellular networks as the maximum number of D2D links that can share the cellular resources while assuring QoS to both D2D links and cellular users. In this thesis we study the scalability of D2D communication underlay cellu- lar networks in a multi-cell environment. We propose interference coordination schemes to maximize the number of D2D links while assuring QoS to D2D links and cellular users.   Three interference coordination schemes have been proposed considering dif- ferent levels of available channel state information (CSI). The first scheme is called no CSI centralized (N-CSIC) scheme and it is based on a centralized solution where no CSI is needed. The second is partial CSI distributed (P-CSID) scheme and it is based on a distributed solution where partial CSI is available. The last scheme is named full CSI optimal (F-CSIOp) scheme and it is achieved by formulating an optimization problem considering full CSI to be available.   Extensive mathematical and numerical analysis is conducted to develop and evaluate the proposed schemes. The results show that F-CSIOp scheme offers the best performance followed by the P-CSID and finally N-CSIC, thus a clear relationship is found between complexity and performance.   The P-CSID offers a practical solution for a low complexity interference co- ordination scheme that achieves good scalability and capacity for a wide range of strict QoS requirements. Moreover the results show that further improvement can be achieved if proper selection of the involved parameters is done along with the implementations of closed loop power control (CLPC) schemes.   The N-CSIC scheme provides a good solution for low SINR values of D2D links when the QoS of cellular users is low. Thus it is a good candidate for applications like sensor networks or M2M communications where the SINR requirements are rather low and there are no primary users to impose more interference constraints.   Finally we conclude that good scalability and capacity can be achieved with the proposed low complexity interference coordination schemes for D2D communications and provide interesting topics for future research