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Communications, IEEE Transactions on

Issue 10 • Date Oct. 2005

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Displaying Results 1 - 25 of 33
  • Table of contents

    Publication Year: 2005 , Page(s): c1 - c4
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    Freely Available from IEEE
  • IEEE Transactions on Communications publication information

    Publication Year: 2005 , Page(s): c2
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  • Iterative decoding and channel parameter estimation algorithms for repeat-accumulate codes

    Publication Year: 2005 , Page(s): 1597 - 1602
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    The sensitivity of the iterative decoder for repeat-accumulate (RA) codes to carrier phase and channel signal-to-noise ratio estimation errors is investigated, and efficient algorithms to estimate and correct these errors are developed. The behavior of RA codes with imperfect channel estimation is different from that of turbo codes, and correction algorithms specific to RA codes must be formulated. The proposed algorithms use the soft information generated within the iterative decoder, and thus, are not only hardware-efficient, but also offer excellent performance. View full abstract»

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  • A soft decoding scheme for vector quantization over a CDMA channel

    Publication Year: 2005 , Page(s): 1603 - 1608
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    The optimal decoding of vector quantization (VQ) over a code-division multiple-access (CDMA) channel is too complicated for systems with a medium-to-large number of users. This paper presents a low-complexity, suboptimal decoder for VQ over a CDMA channel. The proposed decoder is built from a soft-output multiuser detector, a soft bit estimator, and the optimal soft VQ decoding of an individual user. Simulation results obtained over both additive white Gaussian noise and flat Rayleigh fading channels show that with a lower complexity and good performance, the proposed decoding scheme is an attractive alternative to the more complicated optimal decoder. View full abstract»

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  • Combined equalization for uplink MC-CDMA in Rayleigh fading channels

    Publication Year: 2005 , Page(s): 1609 - 1614
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    In this letter, we propose the concept of combined equalization for uplink multicarrier code-division multiple access (MC-CDMA) and perform a theoretical analysis which shows that better single-user bounds than the classical matched-filter bounds are achieved with this new concept. Moreover, we illustrate how to properly design an uplink MC-CDMA transmitter and receiver for combined equalization, and show by Monte Carlo simulations that the improved single-user bounds are closely approached, even in the case of a fully loaded system. View full abstract»

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  • Generalized APP detection of continuous phase modulation over unknown ISI channels

    Publication Year: 2005 , Page(s): 1615 - 1619
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    Techniques for computing soft information in the presence of unknown intersymbol interference are presented, with a particular focus on iterative detection of serially concatenated continuous phase modulation. The techniques are centered around the recursive least-squares algorithm, thus enabling unsupervised detection. In particular, we employ bidirectional estimation. View full abstract»

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  • Capacity and coverage increase with repeaters in UMTS urban cellular mobile communication environment

    Publication Year: 2005 , Page(s): 1620 - 1624
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    In this letter, we propose to use repeaters to increase system information capacity in urban areas, where path loss exponents are higher (as much as 3.4 or more). There is at least a 10% increase in coverage area when repeaters are placed in every cell within the network to increase system capacity. The overall system information capacity is doubled at propagation exponent 3.7-3.9. View full abstract»

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  • Noncooperative power-control game and throughput game over wireless networks

    Publication Year: 2005 , Page(s): 1625 - 1629
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    Resource allocation is an important means to increase system performance in wireless networks. In this letter, a game-theory approach for distributed resource allocation is proposed. Observing the bilinear matrix inequality nature of resource allocation, we construct two interrelated games: a power-control game at the user level, and a throughput game at the system level, respectively, to avoid local optima. An optimal complex centralized algorithm is developed as a performance bound. The simulations show that the proposed games have near-optimal system performance. View full abstract»

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  • Turbo codes with rate-m/(m+1) constituent convolutional codes

    Publication Year: 2005 , Page(s): 1630 - 1638
    Cited by:  Papers (78)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    The original turbo codes (TCs), presented in 1993 by Berrou et al., consist of the parallel concatenation of two rate-1/2 binary recursive systematic convolutional (RSC) codes. This paper explains how replacing rate-1/2 binary component codes by rate-m/(m+1) binary RSC codes can lead to better global performance. The encoding scheme can be designed so that decoding can be achieved closer to the theoretical limit, while showing better performance in the region of low error rates. These results are illustrated with some examples based on double-binary (m=2) 8-state and 16-state TCs, easily adaptable to a large range of data block sizes and coding rates. The double-binary 8-state code has already been adopted in several telecommunication standards. View full abstract»

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  • DC-free error-control block codes

    Publication Year: 2005 , Page(s): 1639 - 1647
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    DC-free codes and error-control (EC) codes are widely used in digital transmission and storage systems. To improve system performance in terms of code rate, bit-error rate (BER), and low-frequency suppression, and to provide a flexible tradeoff between these parameters, this paper introduces a new class of codes with both dc-control and EC capability. The new codes integrate dc-free encoding and EC encoding, and are decoded by first applying standard EC decoding techniques prior to dc-free decoding, thereby avoiding the drawbacks that arise when dc-free decoding precedes EC decoding. The dc-free code property is introduced into standard EC codes through multimode coding techniques, at the cost of minor loss in BER performance on the additive white Gaussian noise channel, and some increase in implementation complexity, particularly at the encoder. This paper demonstrates that a wide variety of EC block codes can be integrated into this dc-free coding structure, including binary cyclic codes, binary primitive BCH codes, Reed-Solomon codes, Reed-Muller codes, and some capacity-approaching EC block codes, such as low-density parity-check codes and product codes with iterative decoding. Performance of the new dc-free EC block codes is presented. View full abstract»

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  • Joint source/channel coding for multiple images

    Publication Year: 2005 , Page(s): 1648 - 1654
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    A joint source/channel coding algorithm is proposed for the transmission of multiple image sources over memoryless channels. The proposed algorithm uses a quality scalable image coder to optimally allocate a limited bit budget among all the sources to achieve the optimal overall distortion reduction for the multiple reconstructed images. In addition to the conventional un gain, it provides channel multiplexing gain, which can be much more significant. Furthermore, an extended scheme is proposed to provide flexibility between the optimization performance and complexity. View full abstract»

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  • Diversity combining with imperfect channel estimation

    Publication Year: 2005 , Page(s): 1655 - 1662
    Cited by:  Papers (14)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    The optimal diversity-combining technique is investigated for a multipath Rayleigh fading channel with imperfect channel state information at the receiver. Applying minimum mean-square error channel estimation, the channel state can be decomposed into the channel estimator spanned by channel observation, and the estimation error orthogonal to channel observation. The optimal combining weight is obtained from the first principle of maximum a posteriori detection, taking into consideration the imperfect channel estimation. The bit-error performance using the optimal diversity combining is derived and compared with that of the suboptimal application of maximal ratio combining. Numerical results are presented for specific channel models and estimation methods to illustrate the combined effect of channel estimation and detection on bit-error rate performance. View full abstract»

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  • Rate-adaptive transmission over correlated fading channels

    Publication Year: 2005 , Page(s): 1663 - 1670
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    In this paper, we investigate link adaptation and incremental redundancy (IR) retransmission schemes over correlated wireless channels. While computer simulations have been used to study the performance of these techniques, a numerically tractable analytical approach is more desirable to analyze generic protocols, and to reveal insights into the performance tradeoffs. An error-recursion approach is developed in this paper to mathematically analyze the throughput, delay, and energy efficiency of rate-adaptation techniques over fading channels with arbitrary correlations between retransmissions. Using Reed-Solomon codes as an example, we quantitatively predict the performance tradeoff of throughput and latency for IR schemes and the performance dependency on the channel correlation. Numerical results also show that reactive rate-adaptation schemes with IR retransmission outperform proactive rate-adaptive schemes, even with perfect channel side information, in terms of throughput and energy efficiency. View full abstract»

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  • The expectation-maximization Viterbi algorithm for blind adaptive channel equalization

    Publication Year: 2005 , Page(s): 1671 - 1678
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    A blind maximum-likelihood equalization algorithm is described and its convergence behavior is analyzed. Since the algorithm employs the Viterbi algorithm (VA) to execute the expectation step of the expectation-maximization (EM) iteration, we call it the expectation-maximization Viterbi algorithm (EMVA). An EMVA-based blind channel-acquisition technique which achieves a high global convergence probability is developed. The performance of the method is evaluated via numerical simulations under static and fading channel conditions. View full abstract»

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  • Multirate modulation: a bandwidth- and power-efficient modulation scheme

    Publication Year: 2005 , Page(s): 1679 - 1687
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    Multirate (MR) modulation resembles block-coded modulation (BCM), since matrices are being used to transform binary input vectors to multilevel output vectors (blocks) of length K. Unlike BCM, attention is given to the spectral shaping of the signal to be transmitted. Hence, the encoding matrices are designed to provide simultaneous spectral shaping and Euclidean distance. The encoding matrices can be implemented by using MR digital filters of low complexity. MR modulation also resembles partial response (PR) modulation since, in both cases, a transmitter and receiver filter is used with an overall duobinary impulse response. It will be shown that MR modulation has a number of significant advantages compared with PR modulation. Thus, for example, with MR modulation, loss of synchronization or gain control, as can occur with PR modulation, cannot happen in the receiver. Furthermore, computer simulations for an additive white Gaussian noise channel demonstrate that, for a bit-error rate of 10-6, MR modulation (with K=10) gives a gain of 1.5 dB, compared with PR modulation and symbol-by-symbol detection. However, MR modulation requires a slightly higher bandwidth. It is also explained how, for block lengths K≥10, MR modulation gives a larger bandwidth efficiency than M-ary pulse-amplitude modulation with raised-cosine pulses and a rolloff factor α≥0.1. View full abstract»

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  • A new performance bound for PAM-based CPM detectors

    Publication Year: 2005 , Page(s): 1688 - 1696
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB) |  | HTML iconHTML  

    It is well understood that the pulse amplitude modulation (PAM) representation of continuous phase modulation (CPM) can lead to reduced-complexity detectors with near optimum performance. It has recently been shown that the PAM representation also extends to CPM schemes with multiple modulation indexes (multi-h CPM). In this paper, we present a detector for multi-h CPM which is based on the PAM representation. We also give an exact expression for the pairwise error probability for the entire class of PAM-based CPM detectors (single- and multi-h, optimal, and reduced-complexity) over the additive white Gaussian noise (AWGN) channel and show that this bound is tighter than the previously published bound for approximate PAM-based detectors. In arriving at this expression, we show that PAM-based detectors for CPM are a special case of the broad class of mismatched CPM detectors. We also show that the metrics for PAM-based detectors accumulate distance in a different manner than metrics for other CPM detectors. These distance properties are especially useful in applications with greatly reduced trellis sizes. We give thorough examples of the analysis for different single- and multi-h signaling schemes. We also apply the new bound in comparing the performance of PAM-based detectors with other reduced-complexity detectors for CPM. View full abstract»

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  • Design of turbo-coded modulation for the AWGN channel with Tikhonov phase error

    Publication Year: 2005 , Page(s): 1697 - 1707
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB) |  | HTML iconHTML  

    We design 1-b/symbol/Hz parallel concatenated turbo-coded modulation (PCTCM) for the additive white Gaussian noise (AWGN) channel with Tikhonov phase error. Constituent recursive convolutional codes are optimized so that the turbo codes have low error floors and low convergence thresholds. The pairwise error probability based on the maximum-likelihood decoding metric is used to select codes with low error floors. We also present a Gaussian approximation method that accurately predicts convergence thresholds for PCTCM codes on the AWGN/Tikhonov channel. Simulation results show that the selected codes perform within 0.6 dB of constellation constrained capacity, and have no detectable error floor down to bit-error rates of 10-6. View full abstract»

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  • Adaptive opportunistic fair scheduling over multiuser spatial channels

    Publication Year: 2005 , Page(s): 1708 - 1717
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB) |  | HTML iconHTML  

    We consider the problem of opportunistic fair scheduling (OFS) of multiple users in downlink time-division multiple-access (TDMA) systems employing multiple transmit antennas and beamforming. OFS is an important technique in wireless networks to achieve fair bandwidth usage among users, which is performed on a per-frame basis at the media access control layer. Multiple-transmit-antenna beamforming provides TDMA systems with the capability of supporting multiple concurrent transmissions, i.e., multiple spatial channels at the physical layer. Given a particular subset of users and their channel conditions, the optimal beamforming scheme can be calculated. The multiuser opportunistic scheduling problem then refers to the selection of the optimal subset of users for transmission at each time instant to maximize the total throughput of the system subject to a certain fairness constraint on each individual user's throughput. We propose discrete stochastic approximation algorithms to adaptively select a better subset of users. We also consider scenarios of time-varying channels for which the scheduling algorithm can track the time-varying optimal user subset. We present simulation results to demonstrate the performance of the proposed scheduling algorithms in terms of both throughput and fairness, their fast convergence, and the excellent tracking capability in time-varying environments. View full abstract»

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  • Systolic array implementation of a real-time symbol-optimum multiuser detection algorithm

    Publication Year: 2005 , Page(s): 1718 - 1728
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB) |  | HTML iconHTML  

    This paper presents the systolic array implementation of a real-time symbol-optimum multiuser detection (MUD) algorithm for a direct-sequence code-division multiple-access system by truncating the backward recursions in the generalized forward/backward schedule. Simulation results show that the real-time algorithm provides negligible performance loss compared to the original symbol-optimum detection algorithm. The systolic array implementation is derived in this paper through the factor graph language of the real-time algorithm in order to exploit the suitability of the algorithm for parallel signal processing. View full abstract»

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  • An overlay architecture for managing lightpaths in optically routed networks

    Publication Year: 2005 , Page(s): 1729 - 1737
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    Existing solutions for optically routed networks (ORNs) lack certain key management functions available to electronically routed networks. In particular, ORNs have extremely limited capabilities to trace the path of an optical signal through the network. In this paper, we present a method for embedding path identification and other management information into the transport stream in such a way that the management information can be read by a low-bandwidth, low-cost receiver, without having to terminate or decode the full-rate payload stream. We outline a method for embedding such management information, using a digital coding process at the transmitter, and two distinct digital decoding processes for receiving the management and payload data streams, respectively. Feasibility of the method is demonstrated by computing the bit-error performance of example codes under realistic operating conditions, including multiple management streams in multiwavelength systems. View full abstract»

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  • Multiple-subcarrier optical communication systems with subcarrier signal-point sequence

    Publication Year: 2005 , Page(s): 1738 - 1743
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB) |  | HTML iconHTML  

    We propose a multiple-subcarrier (MS) optical communication system with subcarrier signal-point sequence (SSPS). We use the SSPSs having a large minimum value and large Euclidean distances, so that the required dc bias is minimized and the error-rate performance is improved. Note that in the proposed system, the signal points having the larger minimum value are selected, while the signal points having a lower peak-to-mean-envelope-power ratio (PMEPR) are selected in orthogonal frequency-division multiplexing (OFDM) systems. Therefore, the SSPSs good for OFDM with phase shifting by π rad are not necessarily effective for MS optical communication systems. The main contributions of our paper are: 1) we derive transmit sequences having a large minimum value and large Euclidean distances by using 8-phase-shift keying and (8+1)-amplitude phase-shift keying; and 2) since designing optimal sequences would be prohibitively complex, we introduce a reasonable procedure for suboptimal sequence design, obtaining good results. We show that the normalized power requirements and normalized bandwidth requirements of the MS systems with SSPS are smaller than those of the conventional MS systems. View full abstract»

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  • On the tradeoff between two types of processing gains

    Publication Year: 2005 , Page(s): 1744 - 1753
    Cited by:  Papers (37)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    One of the features characterizing almost every multiple-access (MA) communication system is the processing gain. Through the use of spreading sequences, the processing gain of random code-division multiple-access (RCDMA) systems, or any other code-division multiple-access (CDMA) systems, is devoted to both bandwidth expansion and orthogonalization of the signals transmitted by different users. Another type of MA system is impulse radio (IR). IR systems promise to deliver high data rates over ultra-wideband channels with low-complexity transmitters and receivers. In many aspects, IR systems are similar to time-division MA systems, and the processing gain of IR systems represents the ratio between the actual transmission time and the total time between two consecutive transmissions (on-plus-off-to-on ratio). While CDMA systems, which constantly excite the channel, rely on spreading sequences to orthogonalize the signals transmitted by different users, IR systems transmit a series of short pulses, and the orthogonalization between the signals transmitted by different users is achieved by the fact that most of the pulses do not collide with each other at the receiver. In this paper, a general class of MA communication systems that use both types of processing gain is presented, and both IR and RCDMA systems are demonstrated to be two special cases of this more general class of systems. The bit-error rate of several receivers as a function of the ratio between the two types of processing gain is analyzed and compared, under the constraint that the total processing gain of the system is large and fixed. It is demonstrated that in non-intersymbol interference (ISI) channels, there is no tradeoff between the two types of processing gain. However, in ISI channels, a tradeoff between the two types of processing gain exists. In addition, the suboptimality of RCDMA systems in frequency-selective channels is established. View full abstract»

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  • An iterative extension of BLAST decoding algorithm for layered space-time signals

    Publication Year: 2005 , Page(s): 1754 - 1761
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB) |  | HTML iconHTML  

    We propose an iterative extension of the Bell Laboratory Layered Space-Time (BLAST) algorithm and its variant, vertical BLAST (VBLAST). A characteristic feature of the BLAST-type algorithm is that symbol decisions with low reliability are fed back to decode other symbols. Both performance analysis based on Gaussian approximation of residual interference, and simulation results demonstrate that error propagation due to unreliable decision feedback can severely limit system performance. The extended algorithm exploits inherent signal diversity in BLAST to mitigate residual interference, thus overcoming the performance bottleneck due to error propagation. It yields an impressive performance gain over BLAST. In particular, the extension of BLAST with zero-forcing interference ing admits a simple QR implementation and exhibits excellent performance with low complexity. View full abstract»

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  • Blind carrier frequency tracking for filterbank multicarrier wireless communications

    Publication Year: 2005 , Page(s): 1762 - 1772
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (776 KB) |  | HTML iconHTML  

    Filterbank multicarrier modulation (FBMCM) is an attractive technology for high-speed twisted-pair transmission and for broadband wireless communications, as well. In wireline applications, signal transmission takes place at baseband, so the issue of carrier acquisition and tracking for coherent demodulation does not apply. In wireless communications, on the contrary, carrier-frequency recovery reveals the Achille's heel of multicarrier modulation, so that robust signal processing algorithms are needed in this respect. In this paper, we derive a nondata-aided carrier-frequency offset recovery method for wireless FBMCM modems. In particular, we illustrate how to derive a low-complexity closed-loop tracker starting from a maximum-likelihood approach. We then show that the proposed simplifications do not entail large performance losses. In this respect, we derive the standard performance metrics of a closed-loop tracker (S-curve, root mean square estimation error, acquisition time) both on the additive white Gaussian noise channel and on a typical static frequency-selective wireless channel. We also demonstrate by simulation good robustness of the frequency tracker with respect to FBMCM symbol-timing errors. View full abstract»

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  • Nonsystematic Turbo Codes

    Publication Year: 2005 , Page(s): 1773
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (36 KB)  

    Nonsystematic Turbo Codes In this paper, we introduce the concept of nonsystematic turbo codes and compare them with classical systematic turbo codes. Nonsystematic turbo codes can achieve lower error floors than systematic turbo codes because of their superior effective free-distance properties. Moreover, they can achieve comparable performance in the waterfall region if the nonsystematic constituent encoder has a lower weight feedforward inverse. A uniform inteleaver analysis is used to show that rate R-12/3 turbo codes using nonsystematic constituent encoders have larger effective free distance than when systematic constituent encoders are used. Also, mutual information-based transfer characteristics and EXIT charts are used to show that rate R = 1/3 turbo codes with nonsystematic constituent encoders having low-weight feedforward inverses achieve convergence thresholds comparable to those achieved with systematic constituent encoders. Catastrophic encoders, which do not possess a feedforward inverse, are shown to be capable of achieving low convergence thresholds by doping the code with a small fraction of systematic bits. Finally, we give tables of good nonsystematic turbo codes and present simulation results comparing the performance of systematic and nonsystematic turbo codes. View full abstract»

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Aims & Scope

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

 

 

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Editor-in-Chief
Robert Schober
University of British Columbia