Hierarchical TV Transmission by Spread-Spectrum Multiplexing
In digital broadcasting, adverse receiving conditions can lead to serious reductions in the quality of the received picture or a complete loss of picture. Graceful degradation is a technique that mitigates such threshold effect by making some level of picture quality available in adverse receiving conditions. Therefore, methods to ensure graceful degradation, which improves the breakdown characteristics of digital signals at their threshold, are of particular interest now. This article proposes an adaptive weighted code division multiplexing (AW-CDM) as a hierarchical transmission system to achieve graceful degradation simply by power-controlled spread-spectrum multiplexing. In the prototype AW-CDM model, the hierarchical TV signals (highs, middles, and lows) are divided into 128 orthogonal spread-spectrum binary subchannels, each of which has a different priority and threshold. The model's transmission rate is 9.7 Mbits/sec in the 6-MHz band. Indoor transmission tests prove highs, middles, and lows 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 ADTV transmission by simply changing the binary subchannels into octonary subchannels.
- Print ISSN
- 0036-1682
- Published
- 1994-12
- Content type
- Original Research
- DOI
- 10.5594/J15873