Priyatamkumar, R. M. Banakar, B. Shankaranand · IGI Global eBooks · 2006
Turbo codes exhibit excellent performance gains. Turbo equalization is an iterative equalization and decoding technique. It can achieve equally impressive performance gains for communication systems. Turbo codes are send digital data over channels that require equalization, i.e. those which suffer from inter-symbol interference (ISI). Turbo equalizers have been shown to be successful in mitigating the effects of inter-symbol interference introduced by partial response modems and by dispersive channels for code rates of R>1/2. The performance of iterative equalization and decoding (IED) using an M-BCJR equalizer is analyzed. Bit error rate (BER), frame error rate simulations and extrinsic information transfer (EXIT) charts are used to study and compare the performances BCJR equalizers on precoded and non-precoded channels. We predict the BER performance of Turbo equalizer using the M-BCJR equalizer from EXIT charts and explain the discrepancy between the observed and predicted performances.
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Seok-Jun Lee, Naresh R. Shanbhag, Andrew C. Singer · 2003
In this paper, we propose a low complexity architecture for turbo equalizers. Turbo equalizers jointly equalize and decode the received signal by exchanging soft information iteratively. The proposed architecture employs early termination of the iterative process when it does not impact the bit-error rate (BER). Early termination enables the powering down parts of the soft-input soft-output (SISO) equalizer and decoder thereby saving power. Simulation results show that the complexity is reduced by 20% /spl sim/ 59% and 8% /spl sim/ 58% in equalization and decoding, respectively. In addition, the number of iterations is reduced by 30% /spl sim/ 47% with negligible degradation in BER.
Cited by 7
Dayan Guimarães, André Fonseca dos Santos · Anais do XXII Simpósio Brasileiro de Telecomunicações · 2005
Combining a maximum a posteriori (MAP) equalizer and a D-dimensional Single-Parity Check Turbo Product Code (SPC-TPC) in a novel way, a Block Turbo Equalizer structure is proposed here. The proposed scheme has a potential for reduction in complexity, when compared to other block turbo equalizers. Simulations reveal attractive performance results.
Cited by 1Open access
Dimitris Ampeliotis, Kostas Berberidis · Lecture notes in computer science · 2005
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CHENG Xiang1, YUAN Dong-feng1 · SHILAP Revista de lepidopterología · 2006
In order to reduce the equalization delay induced by iteration, two parallel methods were proposed respectively based on maximum a-posteriori probability （MAP） and linear minimum mean-squared error （LMMSE） equalization algo-rithm in Turbo equalization. Through theoretical analysis, simulation and hardware complexity discussion, it is concluded that the proposed two parallel equalization schemes can fully reduced the equalization delay with small hardware com-plexity and excellent performance.
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Rih‐Lung Chung, Jeng‐Kuang Hwang · 2004
Turbo equalizer (TEQ) is well known for its tremendous performance gain over a severe intersymbol interference (ISI) channel. However, the original MAPSE-based (maximum a posteriori symbol estimation) equalization algorithm is still not practical for implementation under long channel memory and high modulation level scenarios. In this paper, we consider using the much simpler decision-feedback equalizer (DFE) structure designed by a Bayesian MMSE (BMMSE) criterion to tackle the above computational problem. In so doing, the DFE makes use of the feedback extrinsic likelihoods from the decoder as the estimate of the a priori probabilities of transmission symbols, and BMMSE design formulae are derived for symbol-updating of the feedforward and feedback filter coefficients. To further reduce the computational load, a turbo block Bayesian decision-feedback equalizer (TBB-DFE) is then proposed which updates the DFE coefficient only once a block. The simulation results show that for a severe 5-tape ISI and 8-PSK case, while the conventional nonturbo DFE receiver completely fails, and the MAPSE has too many trellis states, our TBB-DFE receiver can attain a BER of 10/sup -3/ at an E/sub b//N/sub 0/ of 19 dB after 6 iterations. Thus the TBB-DFE can serve as a low-complexity TEQ approach under high-level modulation and long channel memory situation.
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Dimitris Ampeliotis, Kostas Berberidis · INFM-OAR (INFN Catania) · 2005
Publication in the conference proceedings of EUSIPCO, Antalya, Turkey, 2005
Cited by 3Open access
Li, Qiang, Mow, Wai Ho, Li, S.Q. · Rare & Special e-Zone (The Hong Kong University of Science and Technology) · 2006
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P. S. Sanoopkumar, Stephen McWade, Arman Farhang · 2023
Orthogonal time frequency space (OTFS) is a promising candidate waveform for the next generation wireless communication systems. OTFS places data in the delay-Doppler (DD) domain, which simplifies channel estimation in high-mobility scenarios. However, due to the 2-D convolution effect of the time-varying channel in the DD domain, equalization is still a challenge for OTFS. Existing equalizers for OTFS are either highly complex or they do not consider intercarrier interference present in high-mobility scenarios. Hence, in this paper, we propose a novel two-stage detection technique for coded OTFS systems. Our proposed detector brings orders of magnitude computational complexity reduction compared to existing methods. At the first stage, it truncates the channel by considering only the significant coefficients along the Doppler dimension and performs turbo equalization. To reduce the computational load of the turbo equalizer, our proposed method deploys the modified LSQR (mLSQR) algorithm. At the second stage, with only two successive interference cancellation (SIC) iterations, our propose detector removes the residual interference caused by channel truncation. To evaluate the performance of our proposed truncated turbo equalizer with SIC (TTE-SIC), we set the minimum mean squared error (MMSE) equalizer without channel truncation as a benchmark. Our simulation results show that the proposed TTE-SIC technique achieves about the same bit error rate (BER) performance as the benchmark.
Cited by 1
P. S. Sanoopkumar, Stephen McWade, Arman Farhang · arXiv (Cornell University) · 2023
Orthogonal time frequency space (OTFS) is a promising candidate waveform for the next generation wireless communication systems. OTFS places data in the delay-Doppler (DD) domain, which simplifies channel estimation in highmobility scenarios. However, due to the 2-D convolution effect of the time-varying channel in the DD domain, equalization is still a challenge for OTFS. Existing equalizers for OTFS are either highly complex or they do not consider intercarrier interference present in high-mobility scenarios. Hence, in this paper, we propose a novel two-stage detection technique for coded OTFS systems. Our proposed detector brings orders of magnitude computational complexity reduction compared to existing methods. At the first stage, it truncates the channel by considering only the significant coefficients along the Doppler dimension and performs turbo equalization. To reduce the computational load of the turbo equalizer, our proposed method deploys the modified LSQR (mLSQR) algorithm. At the second stage, with only two successive interference cancellation (SIC) iterations, our proposed detector removes the residual interference caused by channel truncation. To evaluate the performance of our proposed truncated turbo equalizer with SIC (TTE-SIC), we set the minimum mean squared error (MMSE) equalizer without channel truncation as a benchmark. Our simulation results show that the proposed TTE-SIC technique achieves about the same bit error rate (BER) performance as the benchmark.
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Qiang Li, Wai Ho Mow, Shaoqian Li · 2006
We present a robust algorithm to SNR mismatch for turbo equalizer, which is called the scaled Max-Log-MAP (SMLM) algorithm. For low and moderate loss channel, its performance is very close to that of Log-Map (LM) with exact SNR, while a gap still exists for high loss channel. So we further present a switching scheme between SMLM and LM for high loss channels using the SNR of soft output extrinsic information, which not only obtains good performance close to that of LM with ideal knowledge of SNR, but insensitive to SNR mismatch.
Cited by 1
Aruna Tripathy · 2014
The turbo equalizer (TEQ) is a baseband signal processor that combines the tasks of channel equalization and channel decoding in a closed loop by using turbo principles. The basic objective of a TEQ is to take care of interference in a communication system arising due to a host of reasons and correct the random errors caused by additive white Gaussian noise (AWGN) simultaneously. All the TEQs reported in literature can be broadly categorized into three types; the trellis based equalizers, the apriori aided minimum mean square error (MMSE) filters and the soft interference canceller (SIC) type of filters. Pivotal to the operation of all the TEQs is the flow of the extrinsic information between the equalizer and the channel decoder. The extrinsic information is the information about a given bit available by the use of knowledge about other bits in a transmitted data stream. Most often, the extrinsic information is modeled as a Gaussian random variable. However, a generic mathematical model capturing the operations of a TEQ seems to be missing in literature. It is with this motivation that we propose a suitable mathematical model for a TEQ under converging conditions. This is the log likelihood ratio (LLR) enhancement model that describes the evolution of the extrinsic information as observed at the equalizer output. The LLR becomes a monotonically increasing function of the signal to noise ratio (SNR) from the no apriori condition to the perfect apriori condition about the transmitted bits.
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Xiao, P, Carrasco, R, Wassell, I · Surrey Research Insight Open Access (The University of Surrey) · 2007
In this paper, we study the performance of the turbo equalization schemes for systems with space-time block code (STBC) using the extrinsic information transfer (EXIT) chart, which is shown to be very useful for analyzing the convergence behavior of turbo equalizers, predicting the expected BER performance of the STBC coded systems, determining the SNR threshold for a target BER, as well as facilitating the proper choice of equalizers and channel codes for specific channel conditions
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Yu. B. Nechaev, A A Malyutin, I. O. Dvorakova · 2013
Fast and numerically stable algorithm for calculation of turbo-equalizer coefficients of serial modem, based on the Levinson-Durbin method and considering standard specificity of inverted parameter matrix: band type, hermiticity, toeplitz and positive definiteness, and its special correlation with a vector of absolute terms, is proposed. Results of accuracy and numerical stability of algorithm were obtained by modeling.
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Mohamed Lassaad Ammari · Journal of Communications Software and Systems · 2011
In this paper, we consider the transmission of turbo coded symbols in the indoor radio environment. The system isaffected by the intersymbol interference (ISI) caused by the multipath time-delay spread of the transmission medium. To reduce the channel effect, we propose to use a blind turbo equalizer combining channel estimation, equalization and turbo decoding. The equalizer consists of an interference canceller (IC) and a MAP-BCJR decoder. To improve system performances, we redefine the channel reliability factor used by the MAP-BCJR decoding algorithm. We propose a new metric that takes into account the statistics of the signal at the equalizer output. The channel coefficient estimation is performed using a recursive least squares (RLS) algorithm. A blind receiver initializationtechnique is proposed. This technique is based on a soft decisiondirected least mean square algorithm (soft DD-LMS). For the proposed turbo detector, the ISI cancellation, channel estimation and decoding are jointly performed through an iterative process where modules exchange a soft information.
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Pei Xiao, Rolando Carrasco, Ian Wassell · 2006
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Blackmon, Fletcher A · Defense Technical Information Center (DTIC) · 2003
The present invention provides a receiver for underwater acoustic telemetry that combines a decision feedback adaptive-equalizer structure with a turbo-equalizer structure. The turbo-equalizer structure is of significantly reduced complexity because the decision feedback adaptive-equalizer structure is operable to pre-process a plurality of data channels to provide a single symbol data output stream for application to the input of the turbo equalizer. The turbo-equalizer structure is also of reduced complexity due to use of a correlator to provide channel response data to the turbo equalizer. The channel response data is produced by comparing received data comprising a training sequence with a locally produced training sequence. (2 figures)
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Alexander N. Lozhkin · IEICE Transactions on Communications · 2006
With the growing demand for mobile communications, multicarrier (MC) schemes are receiving an increasing amount of attention, primarily because they handle frequency selective channels better than ordinary single-carrier schemes. However, despite offering several advantages, MC systems have certain weak points. One is their high sensitivity to interchannel interference (ICI). The influence of Doppler shift and ICI are the focus of this paper. Newly proposed B3G/4G systems are developed for data transmission rates higher than those of the IEEE 801.11 It is then necessary that the bandwidth of the subcarrier be small. Moreover, for a higher carrier frequency and mobile speed, the influence of the Doppler shift will be large; therefore, the influence of ICI becomes severer. Using a Markov chain approach, we synthesized a turbo equalizer (TE) that minimizes ICI when interference affects the arbitrary number M of adjacent subchannels. This approach shows the complexity of the proposed algorithm exhibits linear growth with respect to M and independence with respect to the total number of subchannels in the multicarrier system. The proposed ICI cancellation scheme can also be effective in the case of multiple Doppler frequency offsets. This makes the proposed approach attractive for practical implementations.
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Bong-Jun Kim, Heung‐Gyoon Ryu · Journal of the Institute of Electronics and Information Engineers · 2014
디지털 역지향성 안테나 시스템은 사전정보 없이 입사된 신호를 신호의 위상을 추정하여 추정한 각도만큼 다시 돌려서 신호가 수신된 방향으로 재전송하는 시스템이다. 디지털 역지향성 안테나는 모든 방향에 대해 전력을 송출해야 하는 무지향성 안테나에 비해 신호가 수신된 방향으로 신호를 재전송하기 때문에 입사된 방향으로 신호가 집중되어 지향성이 높아지므로 전력의 소모를 줄일 수 있다. 일반적으로 디지털 역지향성 안테나는 다중경로 환경에서 단일 안테나 시스템에 비해 좋은 성능을 보이는 것으로 알려져 있지만, 심각한 ISI의 영향에서는 성능의 저하가 일어난다. 본 논문에서는 이러한 문제점을 극복하기 위해 심각한 ISI의 보상이 가능한 터보등화기를 결합하여 역지향성 안테나를 제안하였다. 제안하는 터보등화기를 이용한 디지털 역지향성 안테나를 통해 심각한 ISI 환경에서의 BER 성능을 개선하였다.BRBR
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Ding, Z., Cowan, C.F.N. · CentAUR (University of Reading) · 2006
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