Comments on “transmission techniques for digital terrestrialTV broadcasting” [and reply]

We are responding to the paper by Sari et al. (see ibid., vol.33, no.2, p.100, 1995), referred to as SKJ, in which it is claimed that single-carrier (SC) transmission with frequency-domain equalization (FDE) is generally superior to coded orthogonal frequency-division multiplexing (COFDM) for terrestrial broadcasting. After pointing out a few additional considerations and briefly discussing the questions of carrier frequency offset and the effect of transmitter nonlinear distortion, we deal with the main issue: the performance of the two systems in the presence of strong echoes as would be encountered in single-frequency networks (SFNs). Any high performance communication system should incorporate sophisticated error-correction methods to achieve the desired performance. Therefore, a comparison based on uncoded or even trellis-coded transmission performance, as presented in SKJ, does not properly represent the tradeoffs involved in SC vs. COFDM terrestrial broadcast. A comparison should be based upon the most powerful practical coding system. For example, based on existing knowledge, a concatenated block and trellis coding system that incorporates adequate interleaving and maximum-likelihood decoding (using channel state information) offers a good solution. Using these techniques, we give an example of the performance of both kinds of systems with echoes ranging up to 0 dB. We find that it is possible to make the bit error rate of both systems improve with large echoes. SKJ reply that the basic message they want to convey through their article is that a well designed single-carrier system (with frequency-domain equalization) achieves similar performance to COFDM while avoiding its two well known problems of sensitivity to nonlinear distortion and carrier synchronization difficulties