Comparative study of turbo decoding techniques: an overview

Abstract

Abstract-In this contribution, we provide an overview of the novel class of channel codes referred to as turbo codes, which have been shown to be capable of performing close to the Shannon Limit. We commence with a brief discussion on turbo encoding, and then move on to describing the form of the iterative decoder most commonly used to decode turbo codes. We then elaborate on various decoding algorithms that can be used in an iterative decoder, and give an example of the operation of such a decoder using the so-called Soft Output Viterbi Algorithm (SOVA). Lastly, the effect of a range of system parameters is investigated in a systematic fashion, in order to gauge their performance ramifications.

Hybrid Turbo FEC/ARQ Systems and Distributed Space-Time Coding for Cooperative Transmission

“…Figure 5 shows the general structure of the parallel Punctured Turbo Codes [27]. These are parallel concatenated convolutional codes in which the information bits are first encoded by a RSC (Recursive Systematic Convolutional) encoder, and (after passing through an interleaver) encoded again by a second RSC.…”

Towards closing the capacity gap on multiple antenna channels

“…Such techniques have been reported to achieve impressive results for codes with long codeword length. Following the seminal paper by Berrou et al [8], there have been many results on turbo decoding, with performances approaching the Shannon limit on single-input single-output systems (see [9] and references therein). More recently, low-density parity check (LDPC) codes, long neglected since their introduction by Gallager [10] have also been resurrected (see, e.g., [11], [12]).…”

Chip interleaved turbo codes for DS-CDMA in a Rayleigh fading channel with diversity reception

“…The channel is assumed to be a frequency non-selective slow Rayleigh fading channel with f D T=0.001, which corresponds to a maximum Doppler frequency f D of 128Hz for an information data rate of 64k bits/s and a chip rate of 4.096M chips/s. The turbo decoder used in this paper is based on the log-MAP algorithm [2]. The simulation conditions are summarized in Table 1.…”

“…The received signal soft values for the turbo decoder input is given by (2). Signal-to-noise ratio (SNR) per symbol for the 0 th data symbol is given by γ ξ ξ ξ2Re …”

“…Interleaver spreads the coded bits out in time so that even if there is a deep fade, the neighboring bits are not corrupted by noise at the same time. However, it is observed [2] that the bit error rate (BER) performance even with channel interleaving degrades compared to that in an additive white Gaussian noise (AWGN) channel. This is because, although the fading channel can be memoryless with a conventional channel bit-interleaving, the probability density function (pdf) of the received coded bit energy cannot be altered (it still has an exponential distribution in a Rayleigh fading channel).…”