Title :
Iteratively decodable codes for bridging the shaping gap in communication channels
Author :
N. Varnica; Xiao Ma;A. Kavcic
Author_Institution :
Div. of Eng. & Appl. Sci., Harvard Univ., Cambridge, MA, USA
fDate :
6/24/1905 12:00:00 AM
Abstract :
We consider the power-constrained complex memoryless additive white Gaussian noise channel whose channel inputs are drawn from a finite alphabet. It is well known that if the probability mass function over the finite alphabet is uniform, a shaping gap is created that asymptotically approaches 1.53 dB as the constellation cardinality approaches infinity. In a recent paper, we proposed a method to compute the shaping gap for a finite alphabet size and finite SNR. Here, we take advantage of the constellations that can be represented as cross products of the in-phase (real) and quadrature (imaginary) unidimensional constellations. For a 256-QAM constellation, we construct separate simple in-phase and quadrature inner trellis codes whose combined information rate bridges (and nearly closes) the shaping gap. We then demonstrate that a judiciously constructed outer iteratively decodable low-density parity-check code performs inside the shaping gap, which is very near the channel capacity.
Keywords :
"Iterative decoding","Communication channels","Convolutional codes","Channel capacity","AWGN channels","Additive white noise","H infinity control","Bridges","Gaussian noise","Quadrature amplitude modulation"
Conference_Titel :
Signals, Systems and Computers, 2002. Conference Record of the Thirty-Sixth Asilomar Conference on
Print_ISBN :
0-7803-7576-9
DOI :
10.1109/ACSSC.2002.1197140