667 research outputs found
Balanced Objective-Quantifiers Method (BOQM) For Software Intensive Organizations Strategies
Spanish university facilitates a method to link the strategic management with Software and Process improvement based on measurement. The method uses the process philosophy to build measurable information in Indicators templates (Based on ISO/IEC 15939) and a Balanced Scorecard (BSC) template, the process is followed by the participation of SIO’s roles such as the CEO, TI director, CPO, and others measurement roles such as measurement analyst, measurement librarian, and the measurement user
Multipath and interference errors reduction in gps using antenna arrays
The Global Positioning System (GPS) is a worldwide satellite based positioning system that provides any user with
tridimensional position, speed and time information. The measured pseudorange is affected by the multipath propagation,
which probably is the major source of errors for high precision systems. After a presentation of the GPS and the basic
techniques employed to perform pseudorange measurements, the influence of the multipath components on the pseudorange
measurement is explained. Like every system the GPS is also exposed to the errors that can be caused by the interferences,
and a lot of civil applications need robust receivers to interferences for reasons of safety. In this paper some signal array
processing techniques for reducing the code measurement errors due to the multipath propagation and the interferences are
presented. Firstly, a non-adaptive beamforming is used. Secondly, a variant of the MUSIC and the maximum likelihood
estimator can be used to estimate the DOA of the reflections and the interferences, and then a weight vector that removes
these signals is calculated. In the third place, a beamforming with temporal reference is presented; the reference is not the
GPS signal itself, but the output of a matched filter to the code. An interesting feature of the proposed techniques is that they
can be applied to an array of arbitrary geometry.Peer ReviewedPostprint (published version
Code-timing synchronization in DS-CDMA systems using space-time diversity
The synchronization of a desired user transmitting a known training sequence in a direct-sequence (DS) asynchronous code-division multiple-access (CDMA) sys-tem is addressed. It is assumed that the receiver consists of an arbitrary antenna array and works in a near-far, frequency-nonselective, slowly fading channel. The estimator that we propose is derived by applying the maximum likelihood (ML) principle to a signal model in which the contribution of all the interfering compo-nents (e.g., multiple-access interference, external interference and noise) is modeled as a Gaussian term with an unknown and arbitrary space-time correlation matrix. The main contribution of this paper is the fact that the estimator makes eÆcient use of the structure of the signals in both the space and time domains. Its perfor-mance is compared with the Cramer-Rao Bound, and with the performance of other methods proposed recently that also employ an antenna array but only exploit the structure of the signals in one of the two domains, while using the other simply as a means of path diversity. It is shown that the use of the temporal and spatial structures is necessary to achieve synchronization in heavily loaded systems or in the presence of directional external interference.Peer ReviewedPostprint (published version
Maximum likelihood time-of-arrival estimation using antenna arrays: Application to global navigation satellite systems
The problem of estimating the time-of-arrival (TOA) of a known signal in the presence of interferences and multipath propagation is addressed. This problem, is essential in high precision receivers of the Global Navigation Satellite Systems. This paper presents the maximum likelihood TOA estimator when an antenna array is used in the receiver. The desired signal impinges the array with a known direction-of-arrival (DOA) vector, which allows to model all the undesired signal as unknown and arbitrary spatially correlated noise. This simplified model makes only the desired parameters remain in the formulation explicitly, then avoiding complex maximization schemes needed by other models. The fact that estimator is formulated in the frequency domain permits the introduction of the temporal correlation of the noise. Simulation results illustrate the satisfactory performance of the estimator.Peer ReviewedPostprint (published version
Método Objetivo-Cuantificadores Balanceado (MOCB) para estrategias en organizaciones intensivas de software
Universidad española facilita un método para unir la gestión estratégica con la mejora del proceso software basado en la medición. El método usa la filosofÃa de procesos para construir información medible en plantillas indicadores (ISO 15939) y una plantilla del CMI, el proceso es seguido por la participación de roles de la SIO tales como el CEO, Director TI, Dirección de proyectos, y otros roles de medición como el analista de medición, el bibliotecario de medición, y el usuario de medición
A polynomial rooting approach for synchronization in multipath channels using antenna arrays
The estimation of the delay of a known training signal received
by an antenna array in a multipath channel is addressed.
The effect of the co-channel interference is taken
into account by including a term with unknown spatial correlation.
The channel is modeled as an unstructured FIR
filter. The exact maximum likelihood (ML) solution for
this problem is derived, but it does not have a simple dependence
on the delay. An approximate estimator that is
asymptotically equivalent to the exact one is presented. Using
an appropriate reparameterization, it is shown that the
delay estimate is obtained by rooting a low-order polynomial,
which may be of interest in applications where fast
feedforward synchronization is needed.Peer ReviewedPostprint (published version
A reduced-complexity and asymptotically efficient time-delay estimator
This paper considers the problem of estimating the time delays of multiple replicas of a known signal received by an array of antennas. Under the assumptions that the noise and co-channel interference (CCI) are spatially colored Gaussian processes and that the spatial signatures are arbitrary, the maximum likelihood (ML) solution to the general time delay estimation problem is derived. The resulting criterion for the delays yields consistent and asymptotically efficient estimates. However, the criterion is highly non-linear, and not conducive to simple minimization procedures. We propose a new cost function that is shown to provide asymptotically efficient delay estimates. We also outline a heuristic way of deriving this cost function. The form of this new estimator lends itself to minimization by the computationally attractive iterative quadratic maximum likelihood (IQML) algorithm. The existence of simple yet accurate initialization schemes based on ESPRIT and identity weightings makes the approach viable for practical implementation.Peer ReviewedPostprint (published version
Developments in Aerospace Software Engineering practices for VSEs: An overview of the process requirements and practicesof integrated Maturity models and Standards
As part of the evolution of the Space market in the last years – globally referred to as Space 2.0 - small companies are playing an
increasingly relevant role in different aerospace projects. Business incubators established by European Space Agency (ESA) and similar
entities are evidence of the need of moving initiatives to small companies characterized by greater flexibility to develop specific activities.
Software is a key component in most aerospace projects, and the success of the initiatives and projects usually depends on the capability
of developing reliable software following well-defined standards. But small entities face some difficulties when adopting software development
standards that have been conceived thinking on larger organizations and big programs. The need of defining software development
standards tailored to small companies and groups is a permanent subject of discussion not only in the aerospace field, and has led in
recent years to the publication of the ISO/IEC 29110 series of systems and software engineering standards and guides, aimed to solve the
issues that Very Small Entities (VSEs) () – settings having up to twenty-five people -, found with other standards like CMMI or SPICE.
This paper discusses the tailoring defined by different aerospace organizations for VSEs in the aerospace industry, and presents a conceptual
arrangement of the standard based on meta-modeling languages that allow the extension and full customization with the incorporation
of specific software engineering requirements and practices from ECSS (European Cooperation for Space Standardization)
Diseño de una metodologÃa CASE de desarrollo de software
En la actualidad existe una gran expectación ante la
introducción de nuevas herramientas y métodos para el
desarrollo de productos software, que permitirán en un
futuro próximo un planteamiento de ingenierÃa del proceso
de producción software. Las nuevas metodologÃas que
empiezan a esbozarse suponen un enfoque integral del
problema abarcando todas las fases del esquema productivo.
Sin embargo el grado de automatización conseguido en el
proceso de construcción de sistemas es muy bajo y éste está
centrado en las últimas fases del ciclo de vida del
software, consiguiéndose asà una reducción poco
significativa de sus costes y, lo que es aún más
importante, sin garantizar la calidad de los productos
software obtenidos.
Esta tesis define una metodologÃa de desarrollo
software estructurada que se puede automatizar, es decir
una metodologÃa CASE. La metodologÃa que se presenta se
ajusta al modelo de ciclo de desarrollo CASE, que consta
de las fases de análisis, diseño y pruebas; siendo su
ámbito de aplicación los sistemas de información.
Se establecen inicialmente los principios básicos
sobre los que la metodologÃa CASE se asienta.
Posteriormente, y puesto que la metodologÃa se inicia con
la fijación de los objetivos de la empresa que demanda un
sistema informático, se emplean técnicas que sirvan de
recogida y validación de la información, que proporcionan
a la vez un lenguaje de comunicación fácil entre usuarios
finales e informáticos. Además, estas mismas técnicas
detallarán de una manera completa, consistente y sin
ambigüedad todos los requisitos del sistema.
Asimismo, se presentan un conjunto de técnicas y
algoritmos para conseguir que desde la especificación de
requisitos del sistema se logre una automatización tanto
del diseño lógico del Modelo de Procesos como del Modelo
de Datos, validados ambos conforme a la especificación de
requisitos previa.
Por último se definen unos procedimientos formales que
indican el conjunto de actividades a realizar en el proceso
de construcción y cómo llevarlas a cabo, consiguiendo de
esta manera una integridad en las distintas etapas del
proceso de desarrollo.---ABSTRACT---Nowdays there is a great expectation with regard to
the introduction of new tools and methods for the software
products development that, in the very near future will
allow, an engineering approach in the software development
process. New methodologies, just emerging, imply an
integral approach to the problem, including all the
productive scheme stages. However, the automatization
degree obtained in the systems construction process is very
low and focused on the last phases of the software lifecycle,
which means that the costs reduction obtained is
irrelevant and, which is more important, the quality of the
software products is not guaranteed.
This thesis defines an structured software development
methodology that can be automated, that is a CASE
methodology. Such a methodology is adapted to the CASE
development cycle-model, which consists in analysis, design
and testing phases, being the information systems its field
of application.
Firstly, we present the basic principies on which CASE
methodology is based. Secondly, since the methodology
starts from fixing the objectives of the company demanding
the automatization system, we use some techniques that are
useful for gathering and validating the information, being
at the same time an easy communication language between
end-users and developers. Indeed, these same techniques
will detail completely, consistently and non ambiguously
all the system requirements.
Likewise, a set of techniques and algorithms are shown
in order to obtain, from the system requirements
specification, an automatization of the Process Model
logical design, and of the Data Model logical design. Those
two models are validated according to the previous
requirement specification.
Finally, we define several formal procedures that
suggest which set of activities to be accomplished in the
construction process, and how to carry them out, getting
in this way integrity and completness for the different
stages of the development process
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