Abstract
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This paper concerns the soft-in soft-out detection in a coded communication system, where the
transmitted symbols are discrete valued, and the exact a posteriori probability (APP) detection often involves
prohibitive complexity. By using the properties of Gaussian functions, an approximate approach to the APP
detection is devised with the idea that, in the computation of the APP of each symbol, the remaining symbols
are distinguished based on their contributions to the APP of the concerned symbol, and the symbols with
less contributions are approximated as (continuous) Gaussian variables [hence the name partial Gaussian
approximation (PGA)] to reduce the computational complexity. The connection between the PGA detector
and the reduced dimension maximum a posteriori detector (RDMAP) is investigated. It is shown that, PGA is
equivalent to RDMAP, but it has a complexity much lower than that of RDMAP, i.e., PGA can be regarded as
an efcient implementation of RDMAP. In addition, the application of PGA in intersymbol interference (ISI)
channel equalization is also investigated.We show that PGA allows further signicant complexity reduction
by exploiting the circulant structure of the system transfer matrix, which makes PGA very attractive in
handling severe ISI channels with large memory length.