Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

Gaussian Mixture Model-based Quantization of Line Spectral Frequencies for Adaptive Multirate Speech Codec

In this paper, we investigate the use of a Gaussian MixtureModel (GMM)-based quantizer for quantization of the Line Spectral Frequencies (LSFs) in the Adaptive Multi-Rate (AMR) speech codec. We estimate the parametric GMM model of the probability density function (pdf) for the prediction error (residual) of mean-removed LSF parameters that are used in the AMR codec for speech spectral envelope representation. The studied GMM-based quantizer is based on transform coding using Karhunen-Loeve transform (KLT) and transform domain scalar quantizers (SQ) individually designed for each Gaussian mixture. We have investigated the applicability of such a quantization scheme in the existing AMR codec by solely replacing the AMR LSF quantization algorithm segment. The main novelty in this paper lies in applying and adapting the entropy constrained (EC) coding for fixed-rate scalar quantization of transformed residuals thereby allowing for better adaptation to the local statistics of the source. We study and evaluate the compression efficiency, computational complexity and memory requirements of the proposed algorithm. Experimental results show that the GMM-based EC quantizer provides better rate/distortion performance than the quantization schemes used in the referent AMR codec by saving up to 7.32 bits/frame at much lower rate-independent computational complexity and memory requirements

Digital communications over fading channels

In this report, the probabilities of bit error for the most commonly used digital modulation techniques are analyzed. Analytic solutions are developed for the probability of bit error when the signal is affected by the most commonly encountered impairment to system performance for a wireless channel, the transmission of the signal over a fading channel. In this report, the effect of a slow, flat Ricean fading channel on communications systems performance is examined. Since channel fading significantly degrades the performance of a communication system, the performance of digital communication systems that also use forward error correction channel coding is analyzed for hard decision decoding and, where appropriate, for soft decision decoding. Diversity, another technique to mitigate the effect of fading channels on digital communication systems performance, is also discussed. Also included is a discussion of the effect of narrowband noise interference, both continuous and pulsed, on digital communication systems. We then discuss the analysis of the probability of bit error for the combination of error correction coding and diversity. Following this, we briefly discuss spread spectrum systems. Next, we examine the link budget analysis and various models for channel loss. Finally, we examine in detail the second generation digital wireless standard Global System for Mobile (GSM).Approved for public release; distribution is unlimited

Journal of Telecommunications and Information Technology, 2001, nr 3

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DRM analysis using a simulator of multiprocessor embedded system

Mestrado em Engenharia Electrónica e TelecomunicaçõesOs sistemas multiprocessador são uma tecnologia emergente. O projecto Hijdra, que está a ser desenvolvido na “NXP semiconductors Research” é um sistema multiprocessador de tempo real que corre aplicações com constrangimentos do tipo “hard” e “soft”. Nestes sistemas, os processadores comunicam através de uma rede de silício. As aplicações que correm no sistema multiprocessador consistem em múltiplas tarefas que correm em processadores embutidos. Achar soluções para o mapeamento das tarefas é o maior problema destes sistemas. Uma aplicação para este sistema que tem vindo a ser estudada é o “Car Radio”. Esta dissertação diz respeito a uma aplicação de rádio digital (DRM) na arquitectura Hijdra. Neste contexto, uma aplicação de um receptor de DRM foi estudada. Um modelo de análise de “Data Flow” foi extraído a partir da aplicação, foi estudada a latência introduzida na rede de silício pela introdução de um novo processador (acelerador de Viterbi) e foi estudada a possibilidade do mapeamento das várias tarefas da aplicação em diferentes processadores a correr em paralelo. Muitas estratégias ainda ficaram por definir a fim de optimizar o desempenho da aplicação do receptor de DRM de modo a esta poder trabalhar de uma forma mais eficaz. ABSTRACT: Multiprocessor systems are an emerging technology. The Hijdra project being developed at NXP semiconductors Research is a multiprocessor system running with both hard and soft real time streaming media jobs. These jobs consist of multiple tasks running on embedded multiprocessors. Finding good solutions for job mapping is the main problem of these systems. One application which has being studied for Hijdra is the “Car Radio”. This thesis concerns the study of a digital radio receptor application (DRM) in Hijdra architecture. In this context, a data flow model of analysis was extracted from the application, the latency introduced by the addition of a new tile (Viterbi accelerator) and eventual speed gains were studied and the possibility of mapping the different tasks of the application in different processors was foreseen. Many strategies were yet to be defined in order to optimize the application performance so it can work more effectively in the multiprocessor system

Signal Processing Research Program

Contains table of contents for Part III, table of contents for Section 1, an introduction and reports on fourteen research projects.Charles S. Draper Laboratory Contract DL-H-404158U.S. Navy - Office of Naval Research Grant N00014-89-J-1489National Science Foundation Grant MIP 87-14969Battelle LaboratoriesTel-Aviv University, Department of Electronic SystemsU.S. Army Research Office Contract DAAL03-86-D-0001The Federative Republic of Brazil ScholarshipSanders Associates, Inc.Bell Northern Research, Ltd.Amoco Foundation FellowshipGeneral Electric FellowshipNational Science Foundation FellowshipU.S. Air Force - Office of Scientific Research FellowshipU.S. Navy - Office of Naval Research Grant N00014-85-K-0272Natural Science and Engineering Research Council of Canada - Science and Technology Scholarshi

Proceedings of the Mobile Satellite Conference

A satellite-based mobile communications system provides voice and data communications to mobile users over a vast geographic area. The technical and service characteristics of mobile satellite systems (MSSs) are presented and form an in-depth view of the current MSS status at the system and subsystem levels. Major emphasis is placed on developments, current and future, in the following critical MSS technology areas: vehicle antennas, networking, modulation and coding, speech compression, channel characterization, space segment technology and MSS experiments. Also, the mobile satellite communications needs of government agencies are addressed, as is the MSS potential to fulfill them