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Selected Areas in Communications, IEEE Journal on

Issue 9 • Date Sept. 2001

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Displaying Results 1 - 16 of 16
  • Guest editorial - the turbo principle: from theory to practice II

    Publication Year: 2001 , Page(s): 1657 - 1661
    Cited by:  Papers (8)
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    Freely Available from IEEE
  • Joint source-channel turbo decoding of entropy-coded sources

    Publication Year: 2001 , Page(s): 1680 - 1696
    Cited by:  Papers (50)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    We analyze the dependencies between the variables involved in the source and channel coding chain. This analysis is carried out in the framework of Bayesian networks, which provide both an intuitive representation for the global model of the coding chain and a way of deriving joint (soft) decoding algorithms. Three sources of dependencies are involved in the chain: (1) the source model, a Markov chain of symbols; (2) the source coder model, based on a variable length code (VLC), for example a Huffman code; and (3) the channel coder, based on a convolutional error correcting code. Joint decoding relying on the hidden Markov model (HMM) of the global coding chain is intractable, except in trivial cases. We advocate instead an iterative procedure inspired from serial turbo codes, in which the three models of the coding chain are used alternately. This idea of using separately each factor of a big product model inside an iterative procedure usually requires the presence of an interleaver between successive components. We show that only one interleaver is necessary here, placed between the source coder and the channel coder. The decoding scheme we propose can be viewed as a turbo algorithm using alternately the intersymbol correlation due to the Markov source and the redundancy introduced by the channel code. The intermediary element, the source coder model, is used as a translator of soft information from the bit clock to the symbol clock View full abstract»

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  • Joint iterative channel estimation and decoding in flat correlated Rayleigh fading

    Publication Year: 2001 , Page(s): 1706 - 1717
    Cited by:  Papers (70)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB) |  | HTML iconHTML  

    This paper addresses the design and performance evaluation with respect to capacity of M-PSK turbo-coded systems operating in frequency-flat time-selective Rayleigh fading. The receiver jointly performs channel estimation and turbo decoding, allowing the two processes to benefit from each other. To this end, we introduce a suitable Markov model with a finite number of states, designed to approximate both the values and the statistical properties of the correlated flat fading channel phase, which poses a more severe challenge to PSK transmission than amplitude hiding. Then, the forward-backward algorithm determines both the maximum a posteriori probability (MAP) value for each symbol in the data sequence and the MAP channel phase in each iteration. Simulations show good performance in standard correlated Rayleigh fading channels. A sequence of progressively tighter upper bounds to the capacity of a simplified Markov-phase channel is derived, and performance of a turbo code with joint iterative channel estimation and decoding is demonstrated to approach these capacity bounds View full abstract»

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  • Iterative multiuser detection for asynchronous CDMA with concatenated convolutional coding

    Publication Year: 2001 , Page(s): 1784 - 1792
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    We propose iterative multiuser detectors for asynchronous code-division multiple-access with parallel-concatenated convolutional codes (turbo codes) and with serially concatenated convolutional codes (SCCC). At each iteration we update and exchange the extrinsic information from the multiuser detector and channel decoders and regenerate soft information between constituent convolutional decoders. Simulation results show that with the proposed structure, near-single-user performance can be achieved. We also propose two reduced-complexity techniques, i.e., the reduced-state iterative multiuser detector based on the T-MAP algorithm and the iterative interference canceler based on a noise-whitening filter. Simulation results show a small performance degradation for these two techniques, particularly for the T-MAP receiver View full abstract»

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  • Turbo equalization for GMSK signaling over multipath channels based on the Gibbs sampler

    Publication Year: 2001 , Page(s): 1753 - 1763
    Cited by:  Papers (2)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    We consider the problem of Bayesian data restoration for Gaussian minimum shift keying (GMSK) signals over unknown multipath channels. As an alternative to the linear approximation method employed in the conventional finite impulse response (FIR) model, we develop a nonlinear signal model for this system. A Bayesian equalizer based on the Gibbs sampler, a Markov chain Monte Carlo (MCMC) procedure, is developed for estimating the a posteriori symbol probability in the GMSK system without explicit channel estimation. The basic idea of this technique is to generate ergodic random samples from the joint posterior distribution of all unknowns, and then to average the appropriate samples to obtain the estimates of the unknown quantities. Being soft-input soft-output in nature, the proposed Bayesian equalization technique is well suited for iterative processing in a coded system, which allows the Bayesian equalizer to successively refine its processing based on the information from the decoding stage, and vice versa View full abstract»

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  • On the iterative approximation of optimal joint source-channel decoding

    Publication Year: 2001 , Page(s): 1662 - 1670
    Cited by:  Papers (46)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    Joint source-channel decoding is formulated as an estimation problem. The optimal solution is stated and it is shown that it is not feasible in many practical systems due to its complexity. Therefore, a novel iterative procedure for the approximation of the optimal solution is introduced, which is based on the principle of iterative decoding of turbo codes. New analytical expressions for different types of information in the optimal algorithm are used to derive the iterative approximation. A direct comparison of the performance of the optimal algorithm and its iterative approximation is given for a simple transmission system with “short” channel codewords. Furthermore, the performance of iterative joint source-channel decoding is investigated for a more realistic system View full abstract»

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  • A low-complexity iterative multiuser receiver for turbo-coded DS-CDMA systems

    Publication Year: 2001 , Page(s): 1775 - 1783
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    Optimal joint multiuser detection and decoding for direct-sequence code-division multiple-access (DS-CDMA) systems with forward error correction normally requires prohibitively high computational complexity. A suboptimal solution with low complexity is therefore appealing for use in practical applications. We propose a low-complexity iterative multiuser receiver for turbo-coded DS-CDMA systems. The proposed approach consists of a modified decorrelating decision-feedback detector (MDDFD) and K single-user turbo decoders, where K is the number of users in the DS-CDMA system. The MDDFD is derived on the basis of maximizing a likelihood probability and has a feature that it can use the reliability information from the turbo decoders' output. In addition, the MDDFD can deliver interference-cancelled soft outputs to the turbo decoders where the calculation of transition metrics is modified appropriately. Both performance analysis and computer simulation results have indicated that the reliability information from the turbo decoders' output can enhance the multiuser detection capability of the MDDFD. Computer simulations have also shown that the proposed iterative multiuser receiver outperforms the conventional DDFD-based multiuser receiver in terms of the bit-error probability View full abstract»

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  • Blind and nonblind turbo estimation for fast fading GSM channels

    Publication Year: 2001 , Page(s): 1718 - 1728
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    Wireless communication systems such as global system for mobile (GSM) communications are playing a growing role for data transmission. In order to ensure reliable transmission, the channel impulse response has to be estimated accurately. This is a difficult task particularly for fast fading channels caused by high-speed mobile units. We deal with the application of nonblind and blind channel estimation approaches to identify the full rate data Traffic CHannel (TCHF9.6) of GSM. We present a new iterative channel estimation scheme leading to a significant performance improvement especially for high-speed propagation with Doppler frequencies up to 500 Hz. Furthermore, it is shown that blind channel estimation schemes could be as efficient as nonblind methods when regarding bit error rates (BERs) after channel decoding in terms of the E¯b/N0 ratio. Moreover, a solution for the scalar ambiguity inherent in all blind estimation approaches is suggested View full abstract»

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  • Joint turbo decoding and estimation of hidden Markov sources

    Publication Year: 2001 , Page(s): 1671 - 1679
    Cited by:  Papers (49)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    We describe a joint source-channel scheme for modifying a turbo decoder in order to exploit the statistical characteristics of hidden Markov sources. The basic idea is to treat the trellis describing the hidden Markov source as another constituent decoder which exchanges information with the other constituent decoder blocks. The source block uses as extrinsic information the probability of the input bits that is provided by the constituent decoder blocks. On the other hand, it produces a new estimation of such a probability which will be used as extrinsic information by the constituent turbo decoders. The proposed joint source-channel decoding technique leads to significantly improved performance relative to systems in which source statistics are not exploited and avoids the need to perform any explicit source coding prior to transmission. Lack of a priori knowledge of the source parameters does not degrade the performance of the system, since these parameters can be jointly estimated with turbo decoding View full abstract»

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  • Iterative channel estimation and decoding of pilot symbol assisted turbo codes over flat-fading channels

    Publication Year: 2001 , Page(s): 1697 - 1705
    Cited by:  Papers (152)  |  Patents (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    A method for coherently detecting and decoding turbo-coded binary phase shift keying (BPSK) signals transmitted over frequency-flat fading channels is discussed. Estimates of the complex channel gain and variance of the additive noise are derived first from known pilot symbols and an estimation filter. After each iteration of turbo decoding, the channel estimates are refined using information fed back from the decoder. Both hard-decision and soft-decision feedback are considered and compared with three baseline turbo-coded systems: (1) a BPSK system that has perfect channel estimates; (2) a system that uses differential phase shift keying and hence needs no estimates; and (3) a system that performs channel estimation using pilot symbols but has no feedback path from decoder to estimator. Performance can be further improved by borrowing channel estimates from the previously decoded frame. Simulation results show the influence of pilot symbol spacing, estimation filter size and type, and fade rate. Performance within 0.49 and 1.16 dB of turbo-coded BPSK with perfect coherent detection is observed at a bit-error rate of 10-4 for normalized fade rates of fdTs=0.005 and fdTs=0.02, respectively View full abstract»

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  • Performance of a turbo coded multicarrier DS/CDMA system with nonuniform repetition coding

    Publication Year: 2001 , Page(s): 1764 - 1774
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    This paper presents a turbo coded multicarrier direct sequence code division multiple access (DS/CDMA) system, where the outputs of a turbo encoder are repetition coded at multiple rates and transmitted in parallel over a number of subchannels. A performance bound useful in the so-called error floor region is obtained for Rayleigh fading channels when different diversity orders are given to each turbo code symbol. Simulation results are also provided for the low signal-to-noise ratio (SNR) region where the bound is not applicable. It is observed that the error floor can be lowered, with some performance loss in the low SNR region, by applying nonuniform repetition coding to the turbo code symbols View full abstract»

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  • Combined MMSE interference suppression and turbo coding for a coherent DS-CDMA system

    Publication Year: 2001 , Page(s): 1793 - 1803
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    The performance of a turbo-coded code division multiaccess system with a minimum mean-square error (MMSE) receiver for interference suppression is analyzed on a Rayleigh fading channel. In order to accurately estimate the performance of the turbo coding, two improvements are proposed on the conventional union bounds: the information of the minimum distance of a particular turbo interleaver is used to modify the average weight spectra, and the tangential bound is extended to the Rayleigh fading channel. Theoretical results are derived based on the optimum tap weights of the MMSE receiver and maximum-likelihood decoding. Simulation results incorporating iterative decoding, RLS adaptation, and the effects of finite interleaving are also presented. The results show that in the majority of the scenarios that we are concerned with, the MMSE receiver with a rate-1/2 turbo code will outperform a rate-1/4 turbo code. They also show that, for a bit error rate lower than 10-3, the capacity of the system is increased by using turbo codes over convolutional codes, even with small block sizes View full abstract»

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  • Turbo equalization: adaptive equalization and channel decoding jointly optimized

    Publication Year: 2001 , Page(s): 1744 - 1752
    Cited by:  Papers (113)  |  Patents (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    This paper deals with a receiver scheme where adaptive equalization and channel decoding are jointly optimized in an iterative process. This receiver scheme is well suited for transmissions over a frequency-selective channel with large delay spread and for high spectral efficiency modulations. A low-complexity soft-input soft-output M-ary channel decoder is proposed. Turbo equalization allows intersymbol interference to be reduced drastically. For most time-invariant discrete channels, the turbo-equalizer performance is close to the coded Gaussian channel performance, even for low signal-to-noise ratios. Finally, results over a time-varying frequency-selective channel proves the excellent behavior of the turbo equalizer View full abstract»

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  • Iterative multiuser detection for turbo-coded FHMA communications

    Publication Year: 2001 , Page(s): 1810 - 1819
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    An iterative receiver structure Is proposed for turbo-coded frequency-hop multiple access (FHMA) systems. In FHMA systems, the adjacent channel interference (ACI) is the major contributor of multiple access interference (MAI) if orthogonal hopping patterns are used. The ACI is a function of the tone spacings of the adjacent subchannels and the rolloff factor of the pulse-shaping filter. The calculation of the ACI for a square-root raised-cosine pulse-shaping filter in an FHMA system is presented in this paper. In addition, a low complexity iterative multiuser detector is developed to mitigate the degradation caused by ACI in the FHMA systems. The iterative receiver structure is based on a modified turbo decoding algorithm which makes use of the a posteriori log-likelihood ratio (LLR) information of the systematic bits to obtain the a posteriori information of the turbo-encoded parity bits. Iterations of the receiver/decoder are used as the mechanism to estimate and mitigate the MAI in the FHMA system. The properties of both soft and hard interference suppressors based on the modified turbo decoding algorithm are examined and an efficient recursive implementation is derived. Compared to maximum-likelihood multiuser detection, the proposed system is more practical and its complexity is only a linear function of the number of users. Simulation results show that the proposed iterative receiver structure offers significant performance gain in bandwidth efficiency and the required signal-to-noise ratio (SNR) for a target bit-error rate (BER) over the noniterative receiver structure. Moreover, the single user performance can be achieved when imperfect power control exists View full abstract»

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  • Iterative decoding of convolutionally encoded signals over multipath Rayleigh fading channels

    Publication Year: 2001 , Page(s): 1729 - 1743
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB) |  | HTML iconHTML  

    We analyze and compare several strategies for iteratively decoding trellis-encoded signals over channels with memory. Soft-in/soft-out extensions of reduced-complexity trellis search algorithms such as delayed decision-feedback sequence estimating (DDFSE) or parallel decision-feedback decoding (PDFD) algorithms are used instead of conventional BCJR and min-log-BCJR algorithms. It has been shown that for long channel impulse responses and/or high modulation orders where the BCJR algorithm becomes prohibitively complex, the proposed algorithms offer very good performance with low complexity. The problem of channel estimation in practical implementation of turbo detection schemes is studied in the second part. Two methods of channel reestimation are proposed: one based on the expectation-maximization (EM) algorithm and the second on a simple Bootstrap technique. Both algorithms are shown to dramatically improve the performance of the classical pseudo inverse channel estimation performed initially on a training sequence View full abstract»

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  • Soft Bayesian recursive interference cancellation and turbo decoding for TDD-CDMA receivers

    Publication Year: 2001 , Page(s): 1804 - 1809
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    A novel receiver is proposed for CDMA links with recursive turbo coding, based on a soft-input soft-output multistage interference canceler (IC) and an iterative turbo decoder (TD). After performing IC and TD a first time, the coder state estimates available from the two soft-output Viterbi algorithms in the last TD iteration are exploited to calculate the data bits and the redundancy bits. These are employed for preliminary hard cancellation in the first iteration of a supplementary IC run, and then the TD is run again. An alternative solution with soft feedback is obtained by approximating the reliabilities of the redundancy bits with those of the coder state estimates, and using them for preliminary soft cancellation. Simulation results show the effectiveness of the proposed solutions View full abstract»

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Aims & Scope

IEEE Journal on Selected Areas in Communications focuses on all telecommunications, including telephone, telegraphy, facsimile, and point-to-point television, by electromagnetic propagation.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Muriel Médard
MIT