The research and development of OFDM/COFDM for digital television broadcasting has received considerable attention and has made a great deal of progress in Europe. OFDM/COFDM has already been implemented in digital audio broadcasting and is being considered for terrestrial digital television and HDTV broadcasting. The advantages of COFDM claimed by the advocates in Europe have also caught the attention of US broadcasters and generated enthusiasm although a digital modulation technique called 8-VSB has been selected by the FCC Advisory Committee on Advanced Television Service (ACATS) for the final testing. There is considerable debate in the industry over the use of COFDM vs. VSB or QAM for terrestrial HDTV broadcasting. In this paper, the history of research and development on OFDM and COFDM is reviewed. Then, the basic principles, performance and implementation of OFDM and COFDM are examined. Analysis is given to enable the selection of key elements for meeting the constraints of the required applications. Based on the ATV channel model, performance expectation of COFDM under imperfect channel conditions and implementation issues are examined in details. >

COFDM: an overview

OFDM for digital TV broadcasting

The behavior of orthogonal frequency division multiplexing (OFDM) signals in bandpass nonlinearity is presented. In particular, in-band bit-error-rate (BER) degradation and induced adjacent channel interference, as a result of amplitude limiting or clipping, are analyzed. In the presence of both nonlinear distortion and additive Gaussian noise, optimized output power back-off is provided to balance the requirements of the minimum BER and the tolerance of adjacent channel interference for a given OFDM system.

OFDM in bandpass nonlinearity

This article presents the results of the first digital terrestrial television field trials and coverage measurements in Spain. First of all the VIDITER project is presented. The main objective of this work is to study the behavior of a whole digital terrestrial television network, from source coding up to the final signal reception. At this point, the experimental network installed in Madrid is described. Next, the measurement campaign is explained, first, by describing the network configuration used for these first field trials, and then, paying attention to the criteria used to select the measurement points and the parameter set to be tested. Some of the results obtained are shown as a first approach to the figures needed to develop and plan a fully operational digital terrestrial television service.

Digital terrestrial television (COFDM 8K system) field trials and coverage measurements in Spain

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation technique which is very sensitive to impulsive noise (IN). In this paper, we research the behavior of the OFDM based broadcasting system Digital Radio Mondiale (DRM) against this kind of noise in function of its different transmission modes and interleaving options. This research involves an experiment in which a real DRM signal is modulated, transmitted, received, and demodulated. The results quantitatively show the improvement when deep cell interleaving is used, and also the little influence that transmission mode has on the behavior of DRM against IN. In this paper, it is also explained in a mathematical way why it is advisable to perform deep cell interleaving between several OFDM symbols and not within only one, in order to minimize the effect of IN.

Cell interleaving against impulsive noise in OFDM

Field trials have been carried out on the digital transmission of color TV signals in a standard European terrestrial channel of 8 MHz bandwidth. The goal was to obtain first practical results on the general properties of OFDM modulated digital TV signals under real transmission and reception conditions. A comparison of digitally modulated broadcast TV signals and VSB (vestigial sideband) modulated PAL signals was carried out in a UHF channel under normal and severe reception conditions. The field trials were carried out in September 1992 in a hilly region. The results of measurements for normal reception at a distance of 12 km from the transmitter are shown. For OFDM transmission the presentation of absolutely noise-free and interference-free pictures is possible down to a transmitter output power of 2 dBW (1.6 W) and a SNR in the received signal of 29 dB. To achieve the minimum requirements needed for analog PAL transmission (field strength 69 dBV/m and SNR of 38 dB) a peak power of 13 dBW (20 W) in the synch-pulse has to be used. >

http://ieeexplore.ieee.org/iel4/1037/7500/00697674.pdf

U. E. Kraus

Papers

Results of the first digital terrestrial television broadcasting field-tests in Germany