Empirical Analysis of Medium Wave Field Strength Prediction in Urban Environments

[EN] This paper presents results obtained from four extensive field trials of medium wave DRM (Digital Radio Mondiale) which were carried out in Madrid (Spain), Delhi (India) and Mexico D.F. (Mexico) using different transmission frequencies. The objective is to provide medium wave field strength spatial variability values for urban environments using empirical analysis methodology. The influence of the transmission frequency on medium wave propagation in urban environments is included. Both, long and short term components of the signal spatial variability are studied characterizing wide, medium and narrow streets, and the attenuation caused by different urban fast variation occurrences is statistically featured. All the results presented in this paper are essential for future network planning of new emerging digital broadcasting services and have been validated using the Generalized Lee Method

Performance analysis and coverage optimization methods for a digital radio system in the VHF bands

[no abstract

Estudio de la recepción del estándar de radio digital DRM (Digital Radio Mondiale) en onda media en interiores

Los sistemas de radio digital para la banda de Onda Media (DRM y HD Radio IBOC) son muy sensibles a la variación del campo eléctrico ya que el umbral entre la recepción correcta e incorrecta es muy abrupto y no gradual como en los sistemas analógicos. Se han llevado a cabo numerosas campañas de medidas en exteriores durante la última década y se han podido observar desvanecimientos importantes sobre todo en entornos urbanos. Dado que se presupone que muchos potenciales usuarios de los servicios de radio digital se situarán en interiores, es necesario caracterizar la recepción de señales en Onda Media en el interior de edificios, además de actualizar los niveles de ruido radioeléctrico, ya que se han podido detectar incrementos de nivel considerables en entornos urbanos exteriores. En esta tesis se han llevado a cabo extensas campañas de medidas en el interior de edificios con el objetivo de caracterizar estadísticamente la variabilidad espacial y temporal tanto de la señal como del ruido radioeléctrico en Onda Media en este tipo de entornos. El objetivo sería ofrecer las herramientas más precisas posibles para el cálculo o caracterización de la relación señal a ruido en interiores en Onda Media, de forma que los operadores de red puedan realizar una correcta planificación de red

Refraction interference elimination employing smart arrays at VHF

Radio interference from the Middle East is one of the most significant problems plaguing the local radio services in Cyprus today. The issue is particularly noticeable on the highway, where it affects in-car tuners in all coastal areas of the island when the weather is hot and humid. In this work, the problem of interference from the Middle East was explored in the context of field strength variations versus the type of propagation mechanism favouring the radio waves in Band II, allowing them to travel from the Middle East to beyond the horizon in Cyprus. This problem was significant, since no line of sight exists between the two regions. After in-depth analysis adhering to the ITU (International Telecommunications Union) Recommendations, it was demonstrated that interference is caused by “Tropospheric Ducting”, i.e., trapping of the overseas transmitted signals between two layers of the troposphere at different heights. The upper air data were obtained using the Weather Research Forecasting (WRF-ARW version 3.4) model. The results yielded by the present study confirm that this model provides accurate prediction of interference for up to five days in advance. The interference problem is widely recognized, and therefore many attempts have been made to explicate its causes and provide solutions. The aim of the present study was to present a robust solution based on an innovative receiving antenna design. The antenna is a receiver’s component that collects electromagnetic waves from various directions. The rationale behind focusing on a circular array topology is that its tuning ensures that the receiver processes the desired signal only, while rejecting the unwanted interference. This can presently only be achieved by a large directional external antenna that must be steered mechanically in the desired direction. As this arrangement is not practical, an innovative smart antenna was proposed as an alternative. A circular phased array is a very compact antenna that produces a predicted radiation pattern, whereby it receives maximum energy from the desired direction without the need for mechanical control. Circular arrays exhibit high gain as well as immunity to interference, making them ideal for use in high interference environments. This combination allows the antenna to be incorporated into a commercial deck receiver or installed on vehicles

A Simulation Study of Cooperative Communications over HF Channels

The High Frequency (HF) band lies within 2-30 MHz of the electromagnetic spectrum. In this part of the spectrum, propagation via direct wave, surface wave, and ionospheric refraction mechanisms provides means of communications from line-of-sight to beyond-line-of-sight ranges. The characteristics of ionospheric channel impose fundamental limitations on the performance of HF communication systems. The major impairment is fading which results in random fluctuations in the received signal level and affects the instantaneous signal-to-noise ratio. This requires the deployment of powerful diversity techniques to mitigate the degrading effects of fading on the performance. The range of wavelengths in HF band unfortunately restricts the use of spatial diversity (i.e., deployment of multiple antennas) for most practical purposes. This thesis focuses on an alternative method to exploit the spatial dimension of the HF channel. Specifically, we aim to extract distributed spatial diversity through relay-assisted transmission. Towards this main goal, we consider multi-carrier HF communication and investigate the performance of cooperative OFDM over HF channels

Journal of Telecommunications and Information Technology, 2011, nr 3

kwartalni

Statistical characterization of correlation-based time/frequency synchronizers for OFDM

Orthogonal Frequency Division Multiplexing (OFDM) has been widely adopted as a modulation format for reliable digital communication over multipath fading channels, e.g. IEEE 802.11g WiFi networks, as well as broadband wireline channels, e.g. DSL modems. However, its robustness to channel impairments comes at the cost of increased sensitivity to symbol timing and carrier frequency offset errors, and thus requires more complex synchronization methods than conventional single-carrier modulation formats. In this thesis, a class of synchronization methods based upon the intrinsic autocorrelation structure of the OFDM signal is studied from a statistical perspective. In particular, the reasons for the existence of irreducible time and frequency offset estimation errors in the limit of increasing signal-to-noise ratio (SNR) are investigated for correlator-based synchronizers for the non-fading channel case and several fading channel models. It is demonstrated that the primary source of irreducible synchronization errors at high SNR is the natural random distribution of signal energy in the cyclic prefix of the OFDM symbol. Comparisons of the distribution of correlator output magnitude between the non-fading and fading channel cases demonstrates that fading skews the distribution with respect to the non-fading case. A potential mechanism for reducing the effect of innate signal energy variability, correlator output windowed averaging, is studied from the perspective of its influence on the distribution of interpeak intervals in the temporal correlator output signal. While improved performance is realized through averaging for the non-fading channel case, this technique is not as effective for fading channels. In either instance, the windowed averaging method increases the latency of the synchronization process and thus introduces delay in the overall demodulation process

New advances in vehicular technology and automotive engineering

An automobile was seen as a simple accessory of luxury in the early years of the past century. Therefore, it was an expensive asset which none of the common citizen could afford. It was necessary to pass a long period and waiting for Henry Ford to establish the first plants with the series fabrication. This new industrial paradigm makes easy to the common American to acquire an automobile, either for running away or for working purposes. Since that date, the automotive research grown exponentially to the levels observed in the actuality. Now, the automobiles are indispensable goods; saying with other words, the automobile is a first necessity article in a wide number of aspects of living: for workers to allow them to move from their homes into their workplaces, for transportation of students, for allowing the domestic women in their home tasks, for ambulances to carry people with decease to the hospitals, for transportation of materials, and so on, the list don’t ends. The new goal pursued by the automotive industry is to provide electric vehicles at low cost and with high reliability. This commitment is justified by the oil’s peak extraction on 50s of this century and also by the necessity to reduce the emissions of CO2 to the atmosphere, as well as to reduce the needs of this even more valuable natural resource. In order to achieve this task and to improve the regular cars based on oil, the automotive industry is even more concerned on doing applied research on technology and on fundamental research of new materials. The most important idea to retain from the previous introduction is to clarify the minds of the potential readers for the direct and indirect penetration of the vehicles and the vehicular industry in the today’s life. In this sequence of ideas, this book tries not only to fill a gap by presenting fresh subjects related to the vehicular technology and to the automotive engineering but to provide guidelines for future research. This book account with valuable contributions from worldwide experts of automotive’s field. The amount and type of contributions were judiciously selected to cover a broad range of research. The reader can found the most recent and cutting-edge sources of information divided in four major groups: electronics (power, communications, optics, batteries, alternators and sensors), mechanics (suspension control, torque converters, deformation analysis, structural monitoring), materials (nanotechnology, nanocomposites, lubrificants, biodegradable, composites, structural monitoring) and manufacturing (supply chains). We are sure that you will enjoy this book and will profit with the technical and scientific contents. To finish, we are thankful to all of those who contributed to this book and who made it possible.info:eu-repo/semantics/publishedVersio