Iterative decoding convergence and termination of serially concatenated codes

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Description/Abstract

In this paper we demonstrate that previously proposed serially concatenated codes only facilitate iterative decoding convergence towards points that are near but not at the top-right hand corner of the EXIT chart, which typically results in an error floor. Furthermore, we propose a novel method for approaching the (1,1) point of the EXIT chart, where the Maximum Likelihood (ML) Bit Error Ratio (BER) performance is attained. Our method employs specifically designed termination sequences having a free distance of at least two to terminate an inner recursive code. Additionally, we provide optimal termination sequences for a range of inner code designs. Finally, we demonstrate that our novel approach facilitates useful BER reductions in the challenging application scenario when employing short frame lengths of the order of 100 bits, which are typical in wireless sensor networks, for example.