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Proceedings Paper

QAM and VSB for digital transmission on hybrid fiber-coax
Author(s): Kenneth J. Kerpez
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Paper Abstract

This paper presents a comparison of the two most common modulation systems for downstream digital transmission on hybrid fiber/coax: quadrature amplitude modulation (QAM), and vestigial sideband modulation (VSB). Both modulations use multiple signal levels to send multiple bits per Hertz with similar bandwidth efficiency. Detailed calculations of QAM and VSB performance on hybrid fiber/coax are reported here. It is shown that, since VSB has a higher symbol rate, it has at most one-half dB less received SNR than QAM because of dispersion and jitter. This difference is negligible. Proposals for VSB recover the carrier with a pilot tone and a PLL, and proposals for QAM use all-digital data-directed carrier recovery. Simulations reported here show that QAM and VSB have very similar carrier recovery performance. It is concluded that, for hybrid fiber/coax, the performance and inherent cost of QAM and VSB are very similar, although the two systems have many implementation differences and are incompatible.

Paper Details

Date Published: 24 November 1995
PDF: 12 pages
Proc. SPIE 2609, Hybrid Fiber-Coax Systems, (24 November 1995); doi: 10.1117/12.227271
Show Author Affiliations
Kenneth J. Kerpez, Bell Communications Research (United States)


Published in SPIE Proceedings Vol. 2609:
Hybrid Fiber-Coax Systems
Wai Sum Lai; Sam T. Jewell, Editor(s)

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