Hierarchical TV Transmission by Spread–Spectrum Multiplexing

A potential drawback of digital transmission is that slight corruption of the digital signal due to poor reception can result in serious subjective degradation of the decoded signal. This problem is avoided in hierarchical digital TV transmission which uses broadened power spectra to achieve a dispersive threshold and reduce the effects of digital corruption. We have constructed a prototype adaptive weighted code division multiplexing (AW–CDM) model to investigate some features of the technique. — In the prototype AW–CDM model, the hierarchical information is divided into 128 orthogonal spread–spectrum binary subchannels, each of which has a different priority and therefore a different threshold. The model's transmission rate is 9.7 Mbps in the 6MHz band. The hierarchical information used is the video and audio signal, which is hierarchically coded into 3 layers: layer III (5.91 Mbps: detail), layer II (1.38 Mbps: medium) and layer I (0.38 Mbps: core). Indoor transmission tests prove layers III, II and I to be retrievable under conditions of carrier–to–noise ratio (CNR)=13.2 dB, 8.3 dB and 0 dB, respectively. The prototype AW–CDM model can, of course, be applied to HDTV transmission by simply changing the binary subchannels into multiple, e.g., quaternary or octonary, subchannels.

Published

1994-02

Content type

Original Research

DOI

10.5594/M00862

ISBN

978-1-61482-921-8