 
Summary: On the Excess Distortion Exponent for Memoryless
Gaussian SourceChannel Pairs
Yangfan Zhong, Fady Alajaji and L. Lorne Campbell
Department of Mathematics and Statistics
Queen's University, Kingston, ON K7L 3N6, Canada
Email: {yangfan,fady,campblll}@mast.queensu.ca
Abstract For a memoryless Gaussian source under the
squarederror distortion fidelity criterion and a memoryless ad
ditive Gaussian noise channel with a quadratic power constraint
at the channel input, upper and lower bounds for the joint
sourcechannel coding excess distortion exponent (which is the
exponent of the probability of excess distortion) are established.
A necessary and sufficient condition for which the two bounds
coincide is provided, thus exactly determining the exponent. This
condition is observed to hold for a wide range of sourcechannel
parameters.
I. INTRODUCTION
In [5], Csisz´ar studies the joint sourcechannel coding
(JSCC) excess distortion exponent under a fidelity criterion
for discrete memoryless systems i.e., the largest rate of
