Filterbanks implementing Reed-Solomon codes with applications to Soft-Decoding and CDMA/OFDM
Speaker: Geert Van Meerbergen, Katholieke Universiteit Leuven, Belgium
When: 2005-09-14 11:45:00
Venue: 78-420
Host: Raphael Cendrillon and John Homer
Abstract:The goal of this talk is to show how signal processing and coding
can be combined leading to some useful results. First, the link
between multirate signal processing and Reed-Solomon (RS) codes is
discussed. Basically, we show that the aliasing of a critically
subsampled filterbank matches remarkably well with the cyclic
character of an RS code. This filterbank representation of an RS
code essentially breaks the code in a number of component codes,
without breaking its overall optimality.
The usefulness of this result is now illustrated with 2
applications: The first application deals with soft decoding of RS
codes. It is discussed how the complexity problem of soft decoding
in general is tackled using Gallager's algorithm, which is the
main mechanism behind SISO decoding of sparse codes. Next, it is
shown how a sparse representation of an RS code can be obtained
using the filterbank decomposition developed in the first
part. This leads to a turbo-like SISO RS decoder.
The second application discusses more advanced modulation schemes,
dealing with frequency selective (OFDM) and/or multiuser channels
(CDMA). In this part, it is shown how the modulation scheme (which
is matched on the channel) does not very well match with the error
correcting code surrounding it. Since these modulation schemes as
well as RS codes show a filterbank like structure, they can be
merged together. This results in an OFDM (CDMA) scheme with an
error correcting code per band (user) which cooperate such that
the overall system is one large RS code. Essentially, the RS code
in its filterbank like form is seen to tolerate frequency
selective channels with multiple users. This leads to a number of
interesting results, e.g. in the context of bit-loading.
Biography:Geert Van Meerbergen received the Electrical Engineering degree
from the Katholieke Universiteit Leuven (KULeuven), Leuven,
Belgium, in 2001. Currently, he is working towards a Ph.D. degree
at the Electrical Engineering Department of the Katholieke
Universiteit Leuven funded by the Fund for Scientific Research -
Flanders (FWO - Vlaanderen). He received the best student paper
award at the 25th Symposium on Information Theory in the Benelux
in 2004. His research interests are in the area of code theory and
signal processing algorithms for communications.
Type: ITEE Seminar
Contact:Raphael Cendrillon and John Homer, seminar host (raphael@itee.uq.edu.au)
or Guido Governatori (ITEE seminar co-ordinator)
(guido@itee.uq.edu.au)