Fading Research Papers - Academia.edu (original) (raw)

We investigate microdiversity-augmented macrodiversity techniques in wireless communication networks. The setup consists of K widely separated access ports each carrying N antennas. The conventional selection macrodiversity (Scheme I) and... more

We investigate microdiversity-augmented macrodiversity techniques in wireless communication networks. The setup consists of K widely separated access ports each carrying N antennas. The conventional selection macrodiversity (Scheme I) and two proposed methods (Scheme II and Scheme III) for port selection are investigated and their performance are compared. Scheme II utilizes the advancement in distributed antennas and radio-on-fiber technologies whereas Scheme III utilizes these technologies in a way similar to the soft handover of CDMA systems. After the port selection, the microdiversity uses n strongest signals (n les N) of the selected port for diversity combining if practical constraints preclude the use of all N signals. Analytical performance expressions for the probability of error and outage probability for Scheme I are developed. Simulations are used to investigate Scheme II and Scheme III and it is observed that these latter schemes exhibit performance superiority over the conventional macrodiversity selection method. The power savings obtained using the proposed architecture and new selection schemes could be used either for coverage extension or to increase capacity in wireless networks

The power control of wireless networks is formulated using a stochastic optimal control framework, in which the evolution of the channel is described by stochastic differential equations. Under this scenario, average and probabilistic... more

The power control of wireless networks is formulated using a stochastic optimal control framework, in which the evolution of the channel is described by stochastic differential equations. Under this scenario, average and probabilistic Quality of Service (QoS) measures are introduced to evaluate the performance of any control strategy, while a solution of the stochastic optimal power control is obtained through

Cognitive Radios have been advanced as a technology for the opportunistic use of under-utilized spectrum since they are able to sense the spectrum and use frequency bands if no Primary user is detected. However, the required sensitivity... more

Cognitive Radios have been advanced as a technology for the opportunistic use of under-utilized spectrum since they are able to sense the spectrum and use frequency bands if no Primary user is detected. However, the required sensitivity is very demanding since any individual radio might face a deep fade. We propose light-weight cooperation in sensing based on hard decisions to mitigate the sensitivity requirements on individual radios. We show that the "link budget" that system designers have to reserve for fading is a significant function of the required probability of detection. Even a few cooperating users (~10-20) facing independent fades are enough to achieve practical threshold levels by drastically reducing individual detection requirements. Hard decisions perform almost as well as soft decisions in achieving these gains. Cooperative gains in a environment where shadowing is correlated, is limited by the cooperation footprint (area in which users cooperate). In essence, a few independent users are more robust than many correlated users. Unfortunately, cooperative gain is very sensitive to adversarial/failing Cognitive Radios. Radios that fail in a known way (always report the presence/absence of a Primary user) can be compensated for by censoring them. On the other hand, radios that fail in unmodeled ways or may be malicious, introduce a bound on achievable sensitivity reductions. As a rule of thumb, if we believe that 1/N users can fail in an unknown way, then the cooperation gains are limited to what is possible with N trusted users.

... and small scale fading in indoor wireless communication channels. Reinaldo A. Valenzuela, Dmitry Chizhik and Jonathan Ling ... References [I] R. A. Valenzuela, 0. Landron, DL Jacobs, "Estimating Local Mean Signal Strength of... more

... and small scale fading in indoor wireless communication channels. Reinaldo A. Valenzuela, Dmitry Chizhik and Jonathan Ling ... References [I] R. A. Valenzuela, 0. Landron, DL Jacobs, "Estimating Local Mean Signal Strength of Indoor Multipath Propagation", IEEE Trans. ...

When the mechanisms of fading channels were first modeled in the 1950s and 1960s, the ideas were primarily applied to over-the-horizon communications covering a wide range of frequency bands. The 3-30 MHz high-frequency (HF) band is used... more

When the mechanisms of fading channels were first modeled in the 1950s and 1960s, the ideas were primarily applied to over-the-horizon communications covering a wide range of frequency bands. The 3-30 MHz high-frequency (HF) band is used for ionospheric communications, and the 300 MHz-3 GHz ultra-high-frequency (UHF) and 3-30 GHz super-high-frequency (SHF) bands are used for tropospheric scatter. Although the fading effects in a mobile radio system are somewhat different than those in ionospheric and tropospheric channels, the early models are still quite useful to help characterize fading effects in mobile digital communication systems. This tutorial addresses Rayleigh fading primarily in the UHF band. That affects mobile systems such as cellular and personal communication systems (PCS). Part I of the tutorial itemizes the fundamental fading manifestations and types of degradation

In mobile radio systems the effects of fading can be counteracted by the use of diversity techniques either at the base station or the mobile. Since reducing fading, diversity schemes contribute to the reduction of the bit error rate that... more

In mobile radio systems the effects of fading can be counteracted by the use of diversity techniques either at the base station or the mobile. Since reducing fading, diversity schemes contribute to the reduction of the bit error rate that degrades the performance of any modulation scheme. This paper attempts to determine the performance of a typical TETRA system, without

Diversity methods provide the receiver with independently faded copies of the transmitted signal with the expectation that at least one of these replicas will be received correctly. There are ranges of techniques available through which... more

Diversity methods provide the receiver with independently faded copies of the transmitted signal with the expectation that at least one of these replicas will be received correctly. There are ranges of techniques available through which these faded copies can be recovered and used as part of arrangements for better reception. This paper proposes a method based on Space-Time Block Coding (STBC) with Multiple-Input Single-Output (MISO) and Multiple-Input Multiple-Output (MIMO) set-up for use in wireless channels. A special version of STBC called Alamouti code is used for exploiting the performance of MISO and MIMO in frequency-selective fading environment. Performance differences are observed with and without STBC in frequency selective faded channels. A comparison is made between the diversity gain of MISO and MIMO systems in terms of BER for two specific modulation schemes, namely BPSK and QPSK. The obtained results demonstrate that spatial diversity along with the power of STBC significantly improves the error performance in frequency selective wireless fading channels.

Resumen El presente artículo argumenta tres formas en que el olvido se presenta en la esfera de lo social: i) un olvido moderno, que se vehiculiza por la velocidad con que en la actualidad se viven los acontecimientos y su abultamiento;... more

Resumen El presente artículo argumenta tres formas en que el olvido se presenta en la esfera de lo social: i) un olvido moderno, que se vehiculiza por la velocidad con que en la actualidad se viven los acontecimientos y su abultamiento; ii) un olvido que se delinea cuando los marcos sociales de la memoria, como el tiempo, el espacio y el lenguaje se van desvaneciendo, derruyendo, y entonces los significados que antes guardaban se diluyen, y iii) un olvido más institucional, ligado a las prácticas del poder, uno que tiene largo aliento y desde milenios atrás se practica. Son esas las tres formas de olvido que aquí se desarrollan. Previo a ello, se introduce la idea de forma que se suscribe para argumentar el olvido social. Abstract In this written it is argued three ways in which the oblivion is presents in the social sphere: i) a modern oblivion which is mobilises thanks to thespeed in which the events and its saturation occur currently; ii) an oblivion that is traced when the memory´s social frames like language, space and time are fading, destroying and so the meanings that those kept before are diluted and, iii) an oblivion much more institutional linked to the authority´s practices, an oblivion which has long-winded and which is practiced since millennium ago. Those are the threeways of oblivion that are developed here. Previously it is introduced the idea of form which is subscribed here in order to argue the social oblivion.

Fade depth prediction on airborne line-of-sight communication links is considered. There is no specific model for this scenario at the moment. The two ray multipath model, adapted to a realistic scenario of hilly or mountainous terrain,... more

Fade depth prediction on airborne line-of-sight communication links is considered. There is no specific model for this scenario at the moment. The two ray multipath model, adapted to a realistic scenario of hilly or mountainous terrain, was used to account for flight and terrain geometry and for antenna parameters. Surprisingly, it was found that (i) in many practically important cases the fade depth depends on the path clearance angle only and (ii) the two-ray model predicts roughly the same fade depth dependence on the path clearance angle as the well-known Olsen-Segal model. This may be considered as a theoretical justification, to the best of our knowledge for the first time, of the path elevation angle factor in that model

Fading is caused by reflection, diffraction and scattering of transmitted signal so that multiple copies of the signal with varying delays can be received at the receiver with different phases. We have evaluated the performance of... more

Fading is caused by reflection, diffraction and scattering of transmitted signal so that multiple copies of the signal with varying delays can be received at the receiver with different phases.
We have evaluated the performance of transmission modes by calculating the probability of Bit Error Rate (BER) versus the Signal Noise Ratio (SNR) under the various wireless channel models i.e. Gaussian, Rayleigh, Rician and Nakagami. We consider the data modulation and data rate to analyze the performance that is BER vs. SNR. We also consider multipath received signals. The simulation results had shown the performance of transmission modes under different fading channel models. Based on simulation results, we observed that some transmission modes are not efficient for digital communication.

Feathers are found in cultural heritage collections of tribal arts from the Americas, Africa, and the Pacific as well as in contemporary art, European and American fashion, and in taxidermy and ornithology specimens. Although museum... more

The International Journal of Computer Networks & Communications (IJCNC) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Computer Networks & Communications. The journal... more

The International Journal of Computer Networks & Communications (IJCNC) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Computer Networks & Communications. The journal focuses on all technical and practical aspects of Computer Networks & data Communications. The goal of this journal is to bring together researchers and practitioners from academia and industry to focus on advanced networking concepts and establishing new collaborations in these areas.

The Acrobat Family is one of Pablo Picasso's highly rated works from his Rose Period. The painting was one of the first two works by the artist acquired by the Stein's, and in 1922 it came to Gothenburg Art Museum. In catalogues, the... more

The Acrobat Family is one of Pablo Picasso's highly rated works from his Rose Period. The painting was one of the first two works by the artist acquired by the Stein's, and in 1922 it came to Gothenburg Art Museum. In catalogues, the materials used for the work are described as a mix of gouache, pastel, watercolour and Indian ink on cardboard; however, the information is often contradictory and inaccurate. An extensive scientific investigation of the painting was carried out to unravel Picasso's technique, materials and the object's condition. The results indicate that the cardboard is of an acidic nature and the techniques used by the artist are based on different binding media, possibly oil, wax and polysaccharides. Interesting results have been achieved on the discoloured blue areas, where ultramarine blue and Prussian blue are the main components.