Simplified MAP algorithms for iterative receivers

Abstract

Wireless communication systems user error correcting code (ECC) techniques for high receiver performance, so receiver requires detector to compensate wireless channel effect and decoder to extract original information from coded information. Hence, the receiver of coded system has concatenated structure with detector and decoder naturally. Since both detector and decoder are required to estimate same original message, it is expected that detector and decoder can show their capabilities with improved quality when they take a signal processing iteratively like turbo engine. This idea causes iterative signal processing (ISP) techniques based on turbo principle. ISP was first developed as a decoding algorithm of turbo codes. After amazing appearance of turbo codes, ISP became general receiver technique and has applied to various wireless communication systems for improving receiver performance. If soft-decision is possible in receiver, ISP is also possible with iterative receiver structure. In recent, iterative techniques are not optional but essential because it is a applicable to wide area of communication system. In this thesis, we focus on iterative receiver techniques with maxi-mum a $\It{a posteriori}$ (MAP) algorithm. MAP algorithm is frequently used for soft-decision method in iterative receiver because of high performance. However, Map algorithm requires so high complexity that implementation is very hard. Thus, we propose a new MAP algorithm with reduced trellis search, so complexity decreases. Receiver can achieve exact MAP performance with proposed MAP algorithm. Since maximum likelihood (ML) detection is not practical in multiple input multiple output(MIMO) channel because of high implementation complexity, trellis-based detection is frequently used for achieving high performance with maximum likelihood sequence detection(MLSD) based on Viterbi algorithm instead of conventional ML. If receiver knows trellis structure of MIMO channel, trellis-base...