This paper presents a study on the influence of the extrinsic information scaling coefficient value (eic) on the bit and frame error rate (BER/FER), for single and double binary turbo codes (S/DBTC) decoded with maximum a posteriori (MAP) and maximum logarithmic MAP (MaxLogMAP) component algorithms. Firstly, we estimate the distance spectrum of the code with the so-called error impulse method (EIM), and we analyze its dependence as well as the dependence of the asymptotic FER on eic. Secondly, we estimate the actual FER using Monte Carlo simulations with eicas a parameter. The comparison of the FER(eic) curves obtained by the two methods allows us, on the one hand, to assess the quality of the decoding algorithms, and on the other hand, to estimate the very low BER/FER performance of TCs, where the Monte Carlo method is practically unusable. The results presented also provide a practical guide for the appreciation of the optimal value of the scaling factor, eic. We may notice that also the MAP algorithm performance could be improved using eic <1.

This paper presents a survey of two techniques intended for improving the performance of conventional turbo codes (TCs). The first part of this work is dedicated to explore a hybrid concatenation structure combining both parallel and serial concatenation based on a three-dimensional (3D) code. The 3D structure, recently introduced by Berrou et al., is able to ensure large asymptotic gains at very low error rates at the expense of an increase in complexity and a loss in the convergence threshold. In order to reduce the loss in the convergence threshold, the authors consider first a time-varying construction of the post-encoded parity. Then, they investigate the association of the 3D TC with high-order modulations according to the bit-interleaved coded modulation approach. The second part of this study deals with irregular TCs. In contrast to 3D TCs, although irregular TCs can achieve performance closer to capacity, their asymptotic performance is very poor. Therefore, the authors propose irregular turbo coding schemes with suitable interleavers in order to improve their distance properties. Finally, a modified encoding procedure, inspired from the 3D TC, makes it possible to obtain irregular TCs which perform better than the corresponding regular codes in both the waterfall and the error floor regions.

In this paper, exact diversity-multiplexing trade-off (DMT) at finite signal to noise ratio (SNR) for multiple-input multiple-output (MIMO) systems with dual antennas at the transmitter (2xNr) and/or at the receiver (Ntx2) is derived over Rayleigh fading channels. We derive the outage probability of the mutual information between transmitted and received signals versus SNR. It is shown that at realistic SNRs, achievable diversity gains are significantly lower than asymptotic values. While space-time codes (STCs) for MIMO systems are conventionally designed to achieve the asymptotic DMT frontier, this finite-SNR DMT could provide a new insight to design STCs for practical MIMO systems optimized at operational SNRs.

The digital video broadcasting, return channel via satellite second generation (DVB-RCS2) linear modulation scheme offers significantly better performance than that of the first generation (DVB-RCS) both at the physical layer and at the link layer. The DVB-RCS2 design allows for optimizing the link margin by implementing adaptive coding and modulation (ACM) in the return link, controlled by the central system controller, resembling the ACM as supported for the DVB-S2-based forward link. The gain of the return link ACM complements performance improvements at layers 1 and 2. The performance enhancement of the DVB-RCS2 comes with a higher computational complexity compared with that of the DVB-RCS but mainly at the gateway, whereas the computational load increase of the terminal is minimal.