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Mark Schubin Corrects Dale's Technical Misreading
Dale
I just completed my review of that paper, and I'm afraid that much of what is said in the above paragraph is not correct. First, the paper was published in February 1995, not 1993. Second, although the paper DOES tout the use of frequency-domain equalizers (as opposed to the more common time-domain equalizers) for single-carrier signaling (e.g., 8-VSB), what it concludes that it is better than is OFDM, not COFDM. In fact, their conclusion is exactly the opposite when it comes to COFDM: "With coding, interleaving and weighted decoding, OFDM signaling eventually surpasses the performance of single-carrier transmission with frequency-domain equalization...." An earlier sentence (just before the conclusions) makes it perfectly clear: "Finally... COFDM leads to a slightly improved performance than single-carrier transmission."
Next there is the question of the modeling used. It was all based not on the 64-QAM used in terrestrial broadcast COFDM nor on 8-VSB but on QPSK, the modulation used in satellite systems. Furthermore, the channel degradations consisted of "a mild amplitude distortion" in one channel and a FIXED "25-dB notch in the signal spectrum" in the other. I found nothing about dynamic multipath. Can a frequency-domain equalizer deal with a fixed notch? Absolutely!
None of what I've written here is meant to disparage the PAPER ("Transmission Techniques for Digital Terrestrial TV Broadcasting" by Hikmet Sari, Georges Karam, and Isabelle Jeanclaude) in any way, but - the paper does NOT compare 8-VSB and COFDM, and - it does NOT conclude that 8-VSB is better than COFDM; if anything, it comes to the opposite conclusion.
All the paper does is tout frequency-domain equalization for single-carrier transmission, introducing a receiver complexity at least equal to that of COFDM. Fans of the paper might question why it isn't being implemented.
It does nothing to further matters to make false claims on either side.
I just completed my review of that paper, and I'm afraid that much of what is said in the above paragraph is not correct. First, the paper was published in February 1995, not 1993. Second, although the paper DOES tout the use of frequency-domain equalizers (as opposed to the more common time-domain equalizers) for single-carrier signaling (e.g., 8-VSB), what it concludes that it is better than is OFDM, not COFDM. In fact, their conclusion is exactly the opposite when it comes to COFDM: "With coding, interleaving and weighted decoding, OFDM signaling eventually surpasses the performance of single-carrier transmission with frequency-domain equalization...." An earlier sentence (just before the conclusions) makes it perfectly clear: "Finally... COFDM leads to a slightly improved performance than single-carrier transmission."
Next there is the question of the modeling used. It was all based not on the 64-QAM used in terrestrial broadcast COFDM nor on 8-VSB but on QPSK, the modulation used in satellite systems. Furthermore, the channel degradations consisted of "a mild amplitude distortion" in one channel and a FIXED "25-dB notch in the signal spectrum" in the other. I found nothing about dynamic multipath. Can a frequency-domain equalizer deal with a fixed notch? Absolutely!
None of what I've written here is meant to disparage the PAPER ("Transmission Techniques for Digital Terrestrial TV Broadcasting" by Hikmet Sari, Georges Karam, and Isabelle Jeanclaude) in any way, but - the paper does NOT compare 8-VSB and COFDM, and
- it does NOT conclude that 8-VSB is better than COFDM; if anything, it comes to the opposite conclusion.
All the paper does is tout frequency-domain equalization for single-carrier transmission, introducing a receiver complexity at least equal to that of COFDM. Fans of the paper might question why it isn't being implemented.
It does nothing to further matters to make false claims on either side.
TTFN,
Mark
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