Browse by author
Lookup NU author(s): Dr Pei Xiao
The system under study is a coded asynchronous DS-CDMA system with orthogonal modulation in time-varying Rayleigh fading multipath channels. Information bits are convolutionally encoded, block interleaved, and mapped to M-ary orthogonal Walsh codes, where the last step is essentially a process of block coding. This paper aims at tackling the problem of joint iterative decoding of this serially concatenated inner block code and outer convolutional code and estimating frequency-selective fading channels in multiuser environments. The (logarithm) maximum a posteriori probability, (Log)-MAP criterion is used to derive the iterative decoding schemes. In our system, the soft output from inner block decoder is used as a priori information for the outer decoder. The soft output from outer convolutional decoder is used for two purposes. First, it may be fed back to the inner decoder as extrinsic information for the systematic bits of the Walsh codeword. Secondly, it is utilized for channel estimation and multiuser detection (MUD). We also show that the inner decoding can be accomplished without extrinsic information, and in some cases, e.g., when the system is heavily loaded, yields better performance than the decoding with unprocessed extrinsic information. This implies the need for correcting the extrinsic information obtained from outer decoder. Different schemes are examined and compared numerically, and it is shown that iterative decoding with properly corrected extrinsic information or with non-extrinsic/extrinsic adaptation enables the system to operate reliably in the presence of severe multiuser interference, especially when the inner decoding is assisted by decision directed channel estimation and interference cancelation techniques. © 2006 IEEE.
Author(s): Xiao P, Strom EG
Publication type: Article
Publication status: Published
Journal: IEEE Transactions on Wireless Communications
Year: 2006
Volume: 5
Issue: 3
Pages: 591-602
Date deposited: 09/12/2010
ISSN (print): 1536-1276
ISSN (electronic): 1558-2248
Publisher: IEEE
URL: http://dx.doi.org/10.1109/TWC.2006.1611089
DOI: 10.1109/TWC.2006.1611089
Altmetrics provided by Altmetric
