Title :
LMMSE turbo equalization based on factor graphs
Author :
Guo, Qinghua ; Ping, Li
Author_Institution :
City Univ. of Hong Kong, Hong Kong
fDate :
2/1/2008 12:00:00 AM
Abstract :
In this paper, a vector-form factor graph representation is derived for intersymbol interference (ISI) channels. The resultant graphs have a tree-structure that avoids the short cycle problem in existing graph approaches. Based on a joint Gaussian approximation, we establish a connection between the LLR (log-likelihood ratio) estimator for a linear system driven by binary inputs and the LMMSE (linear minimum mean-square error) estimator for a linear system driven by Gaussian inputs. This connection facilitates the application of the recently proposed Gaussian message passing technique to the cycle-free graphs for ISI channels. We also show the equivalence between the proposed approach and the Wang-Poor approach based on the LMMSE principle. An attractive advantage of the proposed approach is its intrinsic parallel structure. Simulation results are provided to demonstrate this property.
Keywords :
equalisers; graph theory; intersymbol interference; mean square error methods; turbo codes; Wang-Poor approach; intersymbol interference channel; joint Gaussian approximation; linear minimum mean-square error; log-likelihood ratio estimator; tree-structure; turbo equalization; vector-form factor graph representation; Equalizers; Gaussian approximation; Intersymbol interference; Iterative algorithms; Iterative decoding; Linear systems; Message passing; Parity check codes; Performance loss; Tree graphs;
Journal_Title :
Selected Areas in Communications, IEEE Journal on
DOI :
10.1109/JSAC.2008.080208