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SUMMARY:Hard decisions do not cause a 2dB power loss - Dr Tobias Koch\, CU
 ED
DTSTART:20110629T131500Z
DTEND:20110629T140000Z
UID:TALK31703@talks.cam.ac.uk
CONTACT:Rachel Fogg
DESCRIPTION:This talk discusses the behavior of channel capacity when a on
 e-bit quantizer is employed at the output of the discrete-time average-pow
 er limited Gaussian channel. This problem is relevant for communication sy
 stems where the receiver uses digital signal processing techniques\, espec
 ially when high-resolution analog-to-digital converters are not feasible. 
 The focus is on the low signal-to-noise ratio regime\, where communication
  at very low spectral efficiencies takes place\, as in Spread Spectrum and
  Ultra-Wideband communications. It is well known that\, in this regime\, a
  symmetric one-bit quantizer reduces capacity by a factor of 2/pi\, which 
 translates to a power loss of approximately two decibels. Hence the rule o
 f thumb that "hard decisions cause a 2dB power loss."\n\nWe show that the 
 power loss of 2dB is not a consequence of the hard-decision decoder but of
  the suboptimal quantizer. In fact\, if an asymmetric quantizer is employe
 d\, and if asymmetric signal constellations are used\, then these two deci
 bels can be recovered in full.\n\n(Joint work with Amos Lapidoth)
LOCATION:LR3A Engineering\, Department of
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