106 research outputs found
Simplified Log-MAP Algorithm for Very Low-Complexity Turbo Decoder Hardware Architectures
No full textMotivated by the importance of hardware implementation in practical turbo decoders, a simplified, yet effective, n-input max∗ approximation algorithm is proposed with the aim being its efficient implementation for very low-complexity turbo decoder hardware architectures. The simplification is obtained using an appropriate digital circuit for finding the first two maximum values in a set of n data that embeds the computation of a correction term. Various implementation results show that the proposed architecture is simpler by 30%, on average, than the constant logarithmic-maximum
a posteriori (Log-MAP) one, in terms of chip area with the same delay. This comes at the expense of very small performance degradation, in the order of
0.1 dB for up to moderate bit error rates, e.g., 10e−5, assuming binary turbo codes. However, when applying scaling to the extrinsic information, the proposed algorithm achieves almost identical Log-MAP turbo code performance for both binary and double-binary turbo codes, without increasing noticeably the implementation complexity
Log-MAP Decoding of Turbo Codes and Turbo Trellis-Coded ModulationUsing Piecewise-Linear Approximations of the max* Operator
No full text
Frame Synchronization in Frequency Uncertainty
No full textThis paper addresses the problem of robust frame
synchronization for TDM/TDMA systems in the presence of
frequency errors, accomplished through data-aided recognition
of the Unique Word (UW) preamble in the transmission flow.
Robust detection design is performed applying, through approximations,
the Maximum Likelihood (ML) criterion coupled to Post
Detection Integration (PDI), to obtain a novel detector identified
as Balanced-GPDI (B-GPDI). This new approach considerably
outperforms other schemes available in the literature, at the cost
of a moderate complexity increase. This is possible thanks to an
optimized use of coherent accumulation, which enhances the correlation
term in the decision variable, along with highly accurate
modeling of the energy correction factor. To limit complexity
increase and memory requirements, several approximations of
the exact B-GPDI are proposed and discussed in the paper, to
provide the designer with practical solutions that are still able
to outperform other approaches in specific application scenarios.
In particular, approximations for low and high Signal-to-Noise
Ratio (SNR) are presented. Different application scenarios are
considered in the paper for numerical analysis. In particular,
the cases of forward link Continuous Transmission (CTX) and
return link Burst Transmission (BTX) are addressed
On Practical Implementation and Generalizations of max* Operator for Turbo and LDPC Decoders
No full textdoi:10.1155/2007/25361 Research Article Performance Analysis of SSC Diversity Receivers over Correlated Ricean Fading Satellite Channels
No full textThis paper studies the performance of switch and stay combining (SSC) diversity receivers operating over correlated Ricean fading satellite channels. Using an infinite series representation for the bivariate Ricean probability density function (PDF), the PDF of the SSC output signal-to-noise ratio (SNR) is derived. Capitalizing on this PDF, analytical expressions for the corresponding cu-mulative distribution function (CDF), the moments of the output SNR, the moments generating function (MGF), and the average channel capacity (CC) are derived. Furthermore, by considering several families of modulated signals, analytical expressions for the average symbol error probability (ASEP) for the diversity receivers under consideration are obtained. The theoretical analy-sis is accompanied by representative performance evaluation results, including average output SNR (ASNR), amount of fading (AoF), outage probability (Pout), average bit error probability (ABEP), and average CC, which have been obtained by numerical techniques. The validity of some of these performance evaluation results has been verified by comparing them with previously known results obtained for uncorrelated Ricean fading channels. Copyright © 2007 P. S. Bithas and P. T. Mathiopoulos. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1
BICMC and TD Comparative Performance Study of 16-APSK Signal Variants for DVB-S2 Systems
No full textA comparative performance study, in terms of Bit Interleaved Coded Modulation Capacity (BICMC) and Total Degradation (TD), between Amplitude Phase Shift Keying (APSK) signal variants for the 2nd generation Digital Video Broadcasting via Satellite (DVB-S2) system is presented. Motivated by the observation that the presence of more signal points in the outer ring of 16-APSK signals appears to improve the performance in a non-linear (NL) channel, we investigate the performance of 2-14 and 3-13 APSK signals with two novel bit-to-symbol mappings as alternatives to the 4-12 APSK, which is currently proposed as the modulation scheme for the DVB-S2 standard. Performance evaluation results are obtained for an air-interface based on this standard, which includes a Non-Linear (NL) High Power Amplifier (HPA), predistortion, raised cosine Nyquist filters and Low-Density Parity-Check (LDPC) codes. Performance results have shown that the proposed 3-13 APSK signal not only achieves the best BICMC performance with higher gains occurring at high signal-to-noise ratios, but also outperforms, in terms of TD performance, all the other considered 16-ary APSK signal variants
Differential detection of correlative encoded continuous phase modulation schemes using decision feedback
No full textPerformance evaluation of selection diversity receivers over arbitrarily correlated generalised Gamma fading channels
No full textA new software radio based distributed base station architecture and its application to 3G UMTS employing signal combining techniques
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