Broad-band fading channels: Signal burstiness and capacity

Vijay G. Subramanian, Bruce Hajek

Research output: Contribution to journalArticlepeer-review


Médard and Gallager recently showed that very large bandwidths on certain fading channels cannot be effectively used by direct sequence or related spread-spectrum systems. This paper complements the work of Médard and Gallager. First, it is shown that a key information-theoretic inequality of Médard and Gallager can be directly derived using the theory of capacity per unit cost, for a certain fourth-order cost function, called fourthegy. This provides insight into the tightness of the bound. Secondly, the bound is explored for a wide-sense-stationary uncorrelated scattering (WSSUS) fading channel, which entails mathematically defining such a channel. In this context, the fourthegy can be expressed using the ambiguity function of the input signal. Finally, numerical data and conclusions are presented for direct-sequence type input signals.

Original languageEnglish (US)
Pages (from-to)809-827
Number of pages19
JournalIEEE Transactions on Information Theory
Issue number4
StatePublished - Apr 2002


  • Channel capacity
  • Fading channels
  • Spread spectrum
  • Wide-sense-stationary uncorrelated scattering (WSSUS) fading channels

ASJC Scopus subject areas

  • Information Systems
  • Computer Science Applications
  • Library and Information Sciences


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