Performance Of Turbo Equalization Research Articles

Turbo equalization based on joint Gaussian, SIC-MMSE and LMMSE for nonlinear satellite channels

The nonlinear distortion of wideband signal due to the filtering and efficiently operated high power amplifiers limits the performance of satellite communications. Volterra series can be used to describe the nonlinear satellite channels effectively. Most existing equalizers simply ignore the nonlinear terms or treat all the nonlinear combinations of symbols as interference. In this study, by properly exploiting information from nonlinear terms, we propose three turbo equalizers for nonlinear satellite channels, namely, joint Gaussian (JG), soft interference cancellation-minimum mean square error (SIC-MMSE) and linear minimum mean square error (LMMSE) equalizers. In JG and SIC-MMSE-based equalizers, both the linear and nonlinear terms that contain the symbol of interest are considered as desired signals. Accordingly, the required statistics are calculated based on the a priori probabilities of coded bits from output of channel decoder. For LMMSE-based equalizer, we propose to calculate the extrinsic information from output of equalizer by excluding the prior information in both the linear and nonlinear terms. Simulation results demonstrate that the proposed equalizers significantly outperform the method which ignores the presence of nonlinear interferences. Moreover, the nonlinear terms that contain the symbol of interest can be exploited to further improve the performance of turbo equalization.

터보 부호 기반의 터보 등화기 실험 성능 분석

In this paper, We analyzed the performance of turbo equalizer using turbo codes thorough the under water experiment. To compensate the distorted signal induced by multipath effect, we apply the iterative turbo codes that iteratively exchange probabilistic information between LMS-DFE and turbo decoder, thereby reducing the error rates significantly. We showed the successful of turbo decoding of iterative turbo equalizer is 93%.

Analysis and Realization on Turbo Equalization based on 64-QAM in OFDM System

With the development of the mobile communication, the related technologies have gone through a rapid growing phase from 1G to 3G, until 4G. The technology evolution targets to improve the performance of overall system, and promote the related services and applications. In this paper, author makes analysis on Turbo equalization based on M-QAM modulation in OFDM system. Since Turbo equalization is an iterative receiver algorithm repeating equalization and channel decoding to improve the performance of the receiver, there researches on Turbo codes and turbo equalization have been emphasis, especially on the error-correction during these years. Due to the operations of equalization and decoding are repeated several times in one process, the computational complexity is increased in the receiver. Author aims at the cost function of CMA (Constant Modulus Algorithm) to change or recreate a new algorithm, and then as a contrast with the error functions, we can see the advantages about this change. Finally, author makes simulations on the Turbo equalization based on 64-QAM in OFDM system. Compared with the Turbo equalization based on 16-QAM, the performance of Turbo equalization based on 64- QAM is more efficient.

Turbo Equalization Effect for Nonbinary LDPC Code in BPM R/W Channel

It is expected for the nonbinary low-density parity-check (LDPC) coding and iterative decoding system to introduce the turbo equalization in order to enhance the error correction ability in the bit-patterned medium (BPM) R/W channel. In this paper, we investigate the effect of the turbo equalization on the bit-error rate (BER) performance of nonbinary LDPC coding and iterative decoding system over Galois filed GF(2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> ) in BPM R/W channel with write-error at an areal recording density of 2 Tbit/inch <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> considering the coding rate loss. The performance of turbo equalization using the nonbinary LDPC coding and iterative decoding system is evaluated by computer simulation, and it is compared to that without turbo equalization. The results show that the nonbinary LDPC and iterative decoding system with the turbo equalization has the larger write-margin compared to that without turbo equalization.

An Analytical Approach for Finite Block Length Performance Analysis of Turbo Frequency-Domain Equalization

Turbo frequency-domain equalization has been shown to be an efficient technique in overcoming intersymbol interference (ISI). To analyze this system, the extrinsic information transfer (EXIT) chart can be employed to avoid extensive simulations. The histogram-based approach in the EXIT chart makes this method considerably complex in analyzing the performance of turbo equalizers over nonstatic channels. Likewise, the EXIT chart accurately predicts the performance only for systems with extremely large block lengths due to the asymptotic analysis that is utilized in this tool. In this paper, we propose a new method to solve these issues. The analytical approach in our method in deriving the equalizer curve eliminates the need for histogram generation. This makes the implementation of this method remarkably simpler than that of the EXIT chart. Utilizing the empirically generated decoder bit-error-rate curve in this method enables us to accurately predict the performance of systems with reasonably small block lengths. Through comparative simulations, we demonstrate the efficiency of this method in predicting the bit-error-rate performance of a turbo frequency-domain equalizer for different constellations and different equalizer schemes.

Turbo Equalization With Single-Parity Check Codes and Unequal Error Protection Codes

The performance of turbo equalization with interleaved single-parity check codes on partial-response channels is evaluated. Single-parity check codes are weak codes, but are shown to have modest performance gain. The proposed system achieves gains of 3.5, 3.4, 2.7, and 2.4 dB with code rates of 19/20,24/25,49/50, and 63/64, respectively, at a BER of 10-5. The complexity of the proposed decoder is significantly lower than that of turbo equalization using standard low-density parity-check codes. These single-parity check codes are modified to be unequal error protection codes, designed to decrease the probability that Viterbi error events span Reed-Solomon symbol boundaries, resulting in a decrease of the sector error rate. Once such code gains an additional 0.1 dB over a single-parity check code of the same code rate of 24/25

Performance of turbo equalizers for optical PMD channels

This paper investigates the performance of iterative (turbo) equalization to mitigate the effects of a polarization-mode dispersion (PMD) in nonreturn-to-zero (NRZ) intensity-modulated optical-fiber transmission systems. A PMD can lead to severe distortions in the received electrical signal and is a key limiter for the development of high-bit-rate transmission over currently used fibers. In order to reduce the distortions due to a PMD, the performance of symbol-by-symbol maximum a posteriori (sbs-MAP) soft-in/soft-out (SISO) decoders is studied. The SISO algorithms are adapted to the noise statistics of the optical channel where the photo detector leads to a non-Gaussian signal-dependent noise at the receiver side. The modified SISO algorithms are successfully employed for turbo equalization and results show that iterative (turbo) equalization and decoding for the compensation of a PMD can lead to a tremendous reduction in the bit error ratio (BER). Moreover, it is shown that, due to the robustness of mutual information, the extrinsic information transfer (EXIT) chart can be applied for the design of iterative receivers in optical transmission systems even with a non-Gaussian noise

On the performance of turbo equalization for precoded ISI channels

AbstractIn this paper, we present a semi‐analytical approach for analyzing the serial concatenation (SCC) of a high rate convolutional code and a precoded intersymbol interference (ISI) channel. The significance of the proposed approach is that it can be used to identify, for a given outer high rate code and fixed ISI channel, the precoder that results in the lowest error rate floor. In estimating the bit error performance in the floor region, we use analytical techniques developed for trellis codes to compute the overall system minimum squared Euclidean distance, and then use a semi‐analytical approach to find the corresponding multiplicity. We also demonstrate via simulations that the proposed technique may be extended to fading ISI channels with favorable results. We give examples that support our analysis. Copyright © 2006 John Wiley &amp; Sons, Ltd.