Resumo em Inglês:

Receivers for wireless Orthogonal Frequency Division Multiplexing (OFDM) systems usually perform the channel estimation based on pilot carriers in known positions of the channel spectrum. Interpolation between pilot carriers is applied to determine the channel transfer function in all carrier frequencies. Channel variations along time are compensated by means of interpolation between successive channel estimates on the same carrier frequency. However, not rarely, the fast channel variations exceed the time interpolator capability, as is the case for mobile operation. In this article we present a new channel compensation technique based on the concurrent operation of two stochastic gradient time-domain algorithms, one which minimizes a cost function that measures the received signal energy dispersion and other which minimizes the Euclidean distance between the received digital modulation symbols and the ones in the reference constellation assigned to each OFDM sub-channel. Results show that the new technique advantageously improves the system robustness to fast channel variations since, with a low computational cost, it dramatically reduces the demodulator symbol error rate even when the receiver is operating in an intense dynamic multipath scenario.

Resumo em Inglês:

This paper presents a new complex valued radial basis function (RBF) neural network (NN) with phase transmittance between the input nodes and output, which makes it suitable for channel equalization on quadrature digital modulation systems. The new Phase Transmittance RBFNN (PTRBFNN) differs from the classical complex valued RBFNN in that it does not strictly rely on the Euclidean distance between the input vector and the center vectors, thus enabling the transference of phase information from input to output. In the context of blind channel equalization, results have shown that the PTRBFNN not only solves the phase uncertainty of the classical complex valued RBFNN but also presents a faster convergence rate.comes the abstract of the paper.

Resumo em Inglês:

This paper presents the architecture, design, validation, and hardware prototyping of the main architectural blocks of main profile H.264/AVC decoder, namely the blocks: inverse transforms and quantization, intra prediction, motion compensation and deblocking filter, for a main profile H.264/AVC decoder. These architectures were designed to reach high throughputs and to be easily integrated with the other H.264/AVC modules. The architectures, all fully H.264/AVC compliant, were completely described in VHDL and further validated through simulations and FPGA prototyping. They were prototyped using a Digilent XUP V2P board, containing a Virtex-II Pro XC2VP30 Xilinx FPGA. The post place-and-route synthesis results indicate that the designed architectures are able to process 114 million samples per second and, in the worst case, they are able to process 64 HDTV frames (1080x1920) per second, allowing their use in H.264/AVC decoders targeting real time HDTV applications.

Resumo em Inglês:

As in all main terrestrial DTV Systems, the Brazilian middleware, named Ginga, supports both declarative applications (through its presentation, or declarative, environment Ginga-NCL) and procedural applications (through its execution, or procedural, environment Ginga-J). Since hybrid applications are common, either type of Ginga application may make use of facilities of both presentation and execution application environments. This paper focuses on the presentation environment Ginga-NCL. The main Brazilian inovations are then presented, regarding the Ginga architecture, the declarative NCL language specification, the editing commands for live application production, and the transport data structure.

Resumo em Inglês:

The recent development of the research on digital terrestrial television in Brazil has led the country's government to state a series of premises in which the government shows to care not only for technology improvement, but also to use this development as a tool for ameliorating the Brazilian social context, in what concerns digital inclusion. These premises and necessities have generated some peculiarities in the development process, which directly influenced in the functionalities granted by the Brazilian's middleware choice. This paper, thus, seeks to explain all the architecture of the Java part - called Ginga-J - of the Ginga middleware, highlighting the new features, especially when confronting the Brazilian middleware with the other middlewares worldwide defined.

Resumo em Inglês:

The objective of this paper is to present a general overview of the Innovative Modulation System Project -MI-SBTVD - developed for the Brazilian Digital TV System. The MI-SBTVD Project includes an LDPC high performance error correcting code, an advanced transmit spatial diversity and an efficient multi-carrier modulation scheme. The building blocks of the system, its characteristics and most relevant innovations are presented. The performance of the whole system under different channels is compared with the performance of the present-day Digital Television standards. The complete system was implemented in FPGA using VHDL language and rapid prototyping tools for DSP algorithms.

Resumo em Inglês:

Recently, it has been proposed the use of WiMAX for the return channel in digital television systems using a new frequency profile bellow 1 GHz, which has been calledWiMAX-700. The profile operates from 400 MHz to 960 MHz as primary band, which includes the UHF band, and optionally from 54 MHz to 400 MHz as secondary band. This work presents some aspects of the WiMAX- 700 technology and some simulation results of models designed to determine the system capacity concerning the number of actives subscriber stations, according to specific proposed scenarios, traffic sources profiles, specifics propagation, and coverage conditions. The results presented in this work provide elements to determine the suitability of WiMAX-700 technology as the return channel for the interactive digital television applications.

Resumo em Inglês:

In early 2003, the Brazilian government accelerated the decision process on analog to digital transition of terrestrial TV broadcast infrastructure, naming this initiative The Brazilian Digital Television System (SBTVD). This paper describes the access device architecture we have proposed for the SBTVD, as well as related issues. We focused on several requirements among which: flexibility to support the social economical diversity enabling market implementations that can vary on cost, complexity and applications; digital inclusion targeting a minimal cost architecture providing a simple access device to information and services by convergent broadcast and point-to-point telecommunication means; and scalability targets incorporating state-of-the-art technology, considering emerging services and the current legacy analog TV infrastructure available in Brazil. We cover the following specific topics: an architecture overview considering scalability, interoperability and regional and international requirements, operating system and middleware interfaces, audio and video coding formats and associate standards, technical and economical analysis, usability and user interface consistency. Finally two prototypes for the outlined access device architecture are reported.