Coded Orthogonal Frequency Division Multiplex Research Articles

Very High-Performance Echo Canceller for Digital Terrestrial Television in Single Frequency Network

The principal aim of this paper is to cancel out the natural and man-made echoes in single-frequency networks (SFN). The challenge is to detect and remove feedback echoes and enhance the intelligibility of the essential parameters in SFN of digital terrestrial television broadcasting (DTTB) transmitter systems, especially the Modulation Error Ratio (MER), with optimizing coverage areas. We suggest a Digital Video Broadcasting (DVB) gap filler (GF) with two types of echo cancelling: Digital Adaptive Equalizer (DAE) and Doppler Enhanced Echo Canceller (DEEC). The proposed GF outperforms standard GF (SGF), finite impulse response filter (FIR GF), and adaptive GF (AGF) techniques by 33%, 17%, and 13%, respectively. Furthermore, the obtained MER makes the proposed GF (PGF) ideal for operating in SFN using Coded Orthogonal Frequency Division Multiplex (COFDM) technique.

Efficient Power Allocation in Turbo Decoded OFDM Systems Using Logarithmic Maximum A-Posteriori Algorithm and Soft Output Viterbi Algorithm Under Various Fading Environments

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation technique which is gaining wide popularity in Wireless cellular networks as it is used to mitigate the multipath effects and to achieve high data rate. The Coded Orthogonal Frequency Division Multiplex (COFDM) technique is an extension of the conventional OFDM systems as they provide reliable reception of signals affected by strong distortions. The increase spectral efficiency in turn increases power. Therefore power optimization has to be considered, when coding is incorporated into the existing system. In this paper, the conventional Viterbi decoder is used along with soft coding technique which provides better convergence property. These results are compared to the Soft Output Viterbi Algorithm (SOVA) and Logarithmic Maximum A-posteriori Decoder (Log-Map) which give better performance than conventional Viterbi algorithm. The power optimization is done in all the cases and the advantages of multicarrier modulation are thus reassured without much channel information feedback from receiver to transmitter.

Vorhersage und Messung der Bitfehlerrate in COFDM-Gleichwellennetzen

For the digital terrestrial transmission scheme Digital Audio Broadcasting (DAB) and Digital Video Broadcasting (DVB-T), the prediction of the Bit Error Rate (BER) for a specific reception area is a characteristic variable. State-of-the-art methods to determine the BER for Coded Orthogonal Frequency Division Multiplex (COFDM) are either restricted to some typical propagation scenarios with simple echo profiles or they use general statistic channel models, which allow an analytical derivation of the BER. These methods and scenarios are suitable to investigate the general system behavior or to simulate different competing transmission schemes. For radio network planning they are not appropriate. This is mainly due to the very general results, which have no direct link to the actual propagation situation. Based on detailed qualitative and quantitative investigations of all relevant disturbance factors for DAB and DVB-T, this paper presents a new and very fast BER calculation method, which uses the results of wave propagation prediction models. The approach is verified by measurements in the L-band in an operational DAB network.

A Multicarrier Scheme for HIPERLAN

After a short description of the principles of a multicarrier COFDM (Coded Orthogonal Frequency Division Multiplex) scheme some simulation results concerning bit- and packet error rates gained with three different characteristic multipath channels are presented and discussed. Aspects of COFDM design principles and complexity of the modulation and demodulation part of the system, as well as effects of the non-linearity of amplifiers will be addressed.

Coded orthogonal frequency division multiplex [TV broadcasting

Technological evolution and the ever-increasing demand for higher-quality services give broadcasters a strong incentive to completely digitize their broadcasting networks. This digitization, which is already well advanced in many program production areas and transmission links, now has to be extended to complete the last link in the broadcast chain; i.e., from broadcast transmitter to consumer receivers. It is therefore necessary to develop wholly new techniques for the broadcasting of digitally coded TV programmes. Thus an efficient baseband digital coding must be combined with a robust digital modulation and channel coding scheme that can meet the requirements of every mode of broadcast reception. This article presents the research work related to the coded orthogonal frequency division multiplex (COFDM) technology, which has now been completed in the field of digital radio (DAB), and which is under progress in the field of digital terrestrial TV.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Advanced television systems for terrestrial broadcasting: Some problems and some proposed solutions

The first part of this paper discusses the requirements that must be met by a new television broadcasting system to maximize its acceptability to the various stakeholders, including broadcasters, equipment manufacturers, program producers, regulatory authorities, and viewers. The most important performance factors are efficient use of over-the-air spectrum, coverage versus quality, cost, interoperability, and the existence of a practical transition scenario. It is concluded that all receivers need not have the same peformance, and that low-cost receivers must be available for noncritical locations in the home. If this variation in price and performance is made possible by appropriate system design, then interoperability is facilitated and nondisruptive improvement over time is made possible, as desired by the Federal Communications Commission. In the second part of the paper, techniques that may permit meeting these requirements are discussed. These include joint multiresolution source and channel coding, multicarrier modulation, and hybrid analog/digital coding and transmission. The analog transform coefficients are subjected to spread-spectrum processing, and coded orthogonal frequency-division multiplex (COFDM) is applied to the complex hybrid symbols to be transmitted through the channel. Various methods of equalization and of improving noise, interference, and multipath rejection are compared. Finally, an example is given of a system that meets the various requirements by making use of a number of the techniques discussed. The system provides extended coverage, albeit at lower quality than currently proposed all-digital systems, and equal or higher quality than such systems in much of their service area. It also features self-optimization at each receiver depending on signal quality and receiver characteristics, and facilitates the design of receivers of lower cost and performance for less-critical applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>