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Communications, IEEE Transactions on

Issue 10 • Date Oct 1998

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Displaying Results 1 - 19 of 19
  • Joint design of fixed-rate source codes and multiresolution channel codes

    Page(s): 1301 - 1312
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    We propose three new design algorithms for jointly optimizing source and channel codes. Our optimality criterion is to minimize the average end-to-end distortion. For a given channel SNR and transmission rate, our joint source and channel code designs achieve an optimal allocation of bits between the source and channel coders. Our three techniques include a source-optimized channel code, a channel-optimized source code, and an iterative descent technique combining the design strategies of the other two codes. The joint designs use channel-optimized vector quantization (COVQ) for the source code and rate compatible punctured convolutional (RCPC) coding for the channel code. The optimal bit allocation reduces distortion by up to 6 dB over suboptimal allocations and by up to 4 dB relative to standard COVQ for the source data set considered. We find that all three code designs have roughly the same performance when their bit allocations are optimized. This result follows from the fact that at the optimal bit allocation the channel code removes most of the channel errors, in which case the three design techniques are roughly equivalent. We also compare the robustness of the three techniques to channel mismatch. We conclude the paper by relaxing the fixed transmission rate constraint and jointly optimizing the transmission rate, source code, and channel code View full abstract»

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  • Joint optimal power control and beamforming in wireless networks using antenna arrays

    Page(s): 1313 - 1324
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    The interference reduction capability of antenna arrays and the power control algorithms have been considered separately as means to increase the capacity in wireless communication networks. The minimum variance distortionless response beamformer maximizes the signal-to-interference-and-noise ratio (SINR) when it is employed in the receiver of a wireless link. In a system with omnidirectional antennas, power control algorithms are used to maximize the SINR as well. We consider a system with beamforming capabilities in the receiver, and power control. An iterative algorithm is proposed to jointly update the transmission powers and the beamformer weights so that it converges to the jointly optimal beamforming and transmission power vector. The algorithm is distributed and uses only local interference measurements. In an uplink transmission scenario, it is shown how base assignment can be incorporated in addition to beamforming and power control, such that a globally optimum solution is obtained. The network capacity and the saving in mobile power are evaluated through numerical study View full abstract»

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  • Analysis and performance of bidirectional decoding of convolutional codes over fading channels

    Page(s): 1292 - 1300
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    The performance of suboptimal convolutional decoding over fading channels is explored. The suboptimal decoding algorithm used is the bidirectional algorithm. By estimating a “decoder weight spectrum” for the decoder, an “equivalent free distance” may be observed. Furthermore, by using this “decoder weight spectrum”, useful estimations of the error probabilities are obtained and compared to computer-simulation results in the case of very slow and very fast fading. The resultant curves are shown to be very tightly related. Computer-simulation results are also shown for various signal-to-noise ratios, normalized Doppler spreads, and frame length on three typical fading channels: the Rayleigh fading channel with exponential and Bessel autocorrelation functions and the Rician fading channel with exponential autocorrelation function. We show that considerable gains (up to 4 dB) can be obtained with respect to a similar-complexity Viterbi decoder at a frame error probability Pe =10-3 and a slightly smaller gain (up to 1.8 dB) at a bit error probability Pb=10-5 View full abstract»

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  • Forced sequence sequential decoding: a concatenated coding system with iterated sequential inner decoding

    Page(s): 1280 - 1291
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    We describe a new concatenated decoding scheme based on iterations between an inner sequentially decoded convolutional code of rate R=1/4 and memory M=23, and block interleaved outer Reed-Solomon (RS) codes with nonuniform profile. With this scheme decoding with good performance is possible as low as Eb/N0=0.6 dB, which is about 1.25 dB below the signal-to-noise ratio (SNR) that marks the cutoff rate for the full system. Accounting for about 0.45 dB due to the outer codes, sequential decoding takes place at about 1.7 dB below the SNR cutoff rate for the convolutional code. This is possible since the iteration process provides the sequential decoders with side information that allows a smaller average load and minimizes the probability of computational overflow. Analytical results for the probability that the first RS word is decoded after C computations are presented. These results are supported by simulation results that are also extended to other parameters View full abstract»

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  • Generalized concatenation of encoded tamed frequency modulation

    Page(s): 1337 - 1345
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    A novel construction for encoded tamed frequency modulation (TFM) is introduced which is based on the principles of generalized concatenation. The inner TFM is partitioned into nested subsystems which increases the free Euclidean distances. In order to obtain a large distance among the nested TFM subsystems, the scrambler matrices have to be computed which transfer the original TFM into the equivalent TFM with better partitioning properties. Then outer convolutional codes with different error-correcting capabilities are used to protect the partitioning. The new concatenated and generalized concatenated constructions were simulated in an additive white Gaussian noise channel. A multistep decoding algorithm based on soft-output demodulation was used. We present various simulation results which show a significant coding gain in comparison with the best known trellis codes having the same trellis state complexity View full abstract»

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  • Transmitter precoding in synchronous multiuser communications

    Page(s): 1346 - 1355
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A synchronous multiuser system operating in an additive white Gaussian noise channel, with or without multipath fading, is considered. It is shown that when either a conventional single user receiver or the RAKE receiver is employed, both multiple access and intersymbol interference can be eliminated by means of a suitable transmitter precoding scheme. Transmitter precoding represents a linear transformation of transmitted signals, such that the mean squared errors at all receivers are minimized. Precoding, with both conventional single user receiver and with the RAKE receiver, results in near-far resistant performance and outperforms considerably the respective schemes without precoding. The crucial assumption, in the multipath case, is that the transmitter knows the multipath characteristics of all channels and that channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over the block of precoded bits View full abstract»

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  • Joint design of a channel-optimized quantizer and multicarrier modulation

    Page(s): 1254 - 1257
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB)  

    We present an algorithm for design of a joint source-channel coder using a channel-optimized quantizer and multicarrier modulation. By changing the power of each subchannel in the multicarrier modulation system, different degrees of error protection can be provided for different bits according to their importance. The algorithm converges to a locally optimum system design. Compared to a Lloyd-Max scalar quantizer or a LBG vector quantizer using single-channel transmission, our optimized code can yield substantial performance improvements. The performance improvements are most pronounced at low channel signal-to-noise ratios View full abstract»

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  • Cramer-Rao bounds in the parametric estimation of fading radiotransmission channels

    Page(s): 1390 - 1398
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    The context of this paper is parameter estimation for linearly modulated digital data signals observed on a frequency-flat time-selective fading channel affected by additive white Gaussian noise. The aim is the derivation of Cramer-Rao lower bounds for the joint estimation of all those channel parameters that impact signal detection, namely, carrier phase, carrier frequency offset (Doppler shift), frequency rate of change (Doppler rate), signal amplitude, fading power, and Gaussian noise power. Time-selective frequency-flat fading is modeled as a low-pass autoregressive multiplicative distortion process. In particular, the important case of “slow” fading, with the multiplicative process remaining constant over the whole data burst, is specifically discussed. Asymptotic expressions of the bounds, valid for a large observed sample or for high signal-to-noise ratio (SNR), are also derived in closed form. A few charts with numerical results are finally reported to highlight the dependence of the bounds on channel status (SNR, fading bandwidth, etc.) View full abstract»

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  • Analysis of MFSK frequency-hopped spread-spectrum multiple-access over a Rayleigh fading channel

    Page(s): 1271 - 1274
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    An explicit expression for the symbol error probability for a system using frequency-hopped spread-spectrum multiple-access with M-ary frequency shift keying (M-ary FSK) is given when the channel is undergoing Rayleigh fading. Using this expression, the performance of binary BCH codes, nonbinary BCH codes and RS codes are compared, and the best choices of code and modulation format are determined for different channel conditions. Depending on the required codeword error probability, different choices of code and modulation format are found to give the best result. Some attention is also paid to the sometimes used assumption of a noiseless channel, which in many cases is found to give inaccurate results View full abstract»

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  • Analysis and optimization of adaptive multicopy transmission ARQ protocols for time-varying channels

    Page(s): 1356 - 1368
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    This paper outlines an efficient method to concurrently optimize a multiplicity of design variables for continuous selective-repeat (SR) and go-back-N (GBN) automatic repeat request (ARQ) strategies, both in noiseless and noisy feedback channels. For these ARQ protocols, we adapt either the number of identical message blocks sent in each transmission (in the case of GBN scheme) or the number of copies of a block retransmitted to handle a NACKed codeword (for the SR protocol) dynamically to the estimated channel condition. The channel state information is obtained by counting the contiguous acknowledgment (ACK or NACK) messages. Exploiting the asymptotic properties of the steady state probability expressions, we show analytically that the optimum solution indeed lies in the infinite space. Subsequently, a simple expression to estimate the suboptimal design parameters is suggested. Our approach of minimizing the mean-square error function yields to a quantitative study of the appropriateness of the selected parameters. Exact analytical expressions that allows us to compute the throughput crossover probability between any two arbitrary multicopy transmission modes are derived. The results provide fundamental insights into how these key parameters interact and determine the system performance View full abstract»

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  • A universal analytic model for photonic Banyan networks

    Page(s): 1381 - 1389
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    One of the important considerations in designing waveguide-based photonic switching networks is to avoid crosstalk. Two approaches have been proposed which dilate a network in the space and time domains, respectively, to establish crosstalk-free connections. The space-domain dilation uses more hardware, representing cost in space, while the time-domain dilation uses more rounds (or time slots), representing cost in time. In order to evaluate the space-time tradeoffs involved in these two approaches, an analytical model is developed. We describe a recursive procedure which calculates the probability that a new connection can be established without crosstalk in a Banyan (or dilated Banyan) network by taking into consideration the dependency between traffic distributions at different stages. A Markov process based on such probabilities is then used to determine the average number of rounds needed for a set of one-to-one random connections. The model is applicable to both Banyan and dilated Banyan networks, with either stage or individual control. Simulation results are also obtained and compared to the analytic results. We show that the time-domain approach can achieve better space-time tradeoffs than the space-domain approach. One of the practical implications of this result is that a multiplane Banyan network may be more cost-effective than a dilated Banyan in avoiding crosstalk View full abstract»

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  • A partitioned adaptive approach to nonlinear channel equalization

    Page(s): 1325 - 1336
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    The problem of identifying digital transmitted symbols over nonlinear communication channels is addressed. The equalization scenario is considered from the decision point of view, and constitutes a joint identification and estimation situation due to incomplete knowledge of the system model. A new class of multilinearization algorithms for nonlinear systems is derived according to partitioning theory concepts. The procedure targets on adaptively selecting the best reference points for linearization from an ensemble of generated trajectories that span the whole state space of the desired signal. In the various simulations examined, the partitioned-based equalizer is found superior to the classical extended Kalman filter View full abstract»

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  • Coupled estimators for equalization of fast-fading mobile channels

    Page(s): 1262 - 1265
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    This letter presents a new method for identification of fast-fading mobile channels (for which combinations of vehicle speed and carrier frequency give rise to significant fading). Our new algorithm estimates both the channel statistics and the time-varying channel impulse response on-line. Simulation studies demonstrate the performance of the new estimator which couples an augmented Kalman filter with a recursive least squares algorithm View full abstract»

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  • A comparison of trellis modules for binary convolutional codes

    Page(s): 1245 - 1249
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    A convolutional code can be represented by the conventional trellis module or the “minimal” trellis module based on the BCJR trellis for block codes. For many convolutional codes, the trellis complexity (TC) of the minimal module is significantly less than the TC of the conventional module. An alternative representation, consisting of an extended BCJR trellis module and a pruned version of the conventional module, was previously introduced. We prove that the overall TC of the two new modules is less than the TC of the conventional module for infinitely many codes. Furthermore, we show that the overall TC of the new modules is smaller than the TC of the minimal module for many codes considered in the literature View full abstract»

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  • Finding cyclic redundancy check polynomials for multilevel systems

    Page(s): 1250 - 1253
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    This letter describes a technique for finding cyclic redundancy check polynomials for systems for transmission over symmetric channels which encode information in multiple voltage levels, so that the resulting redundancy check gives good error protection and is efficient to implement. The codes which we construct have a Hamming distance of 3 or 4. We discuss a way to reduce burst error in parallel transmissions and some tricks for efficient implementation of the shift register for these polynomials. We illustrate our techniques by discussing a particular example where the number of levels is 9, but they are applicable in general View full abstract»

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  • Adaptive symbol-by-symbol reception of MPSK on the Gaussian channel with unknown carrier phase characteristics

    Page(s): 1275 - 1279
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    An adaptive version of the optimum, decision-aided, symbol-by-symbol receiver obtained in our previous works for M-ary phase shift keying over the Gaussian channel with unknown carrier phase characteristics is considered. It uses a first-order adaptive filter for carrier reference tracking, and the filter gain is adapted on-line based on the observed signal samples using a least-mean-square-error criterion. The phase tracking performance of the filter in the steady-state tracking mode is analyzed using a linearized model. The phase tracking error variance is minimized due to the risk function used in designing the filter gain adaptation algorithm. The bit-error probability for quadrature phase shift-keying is obtained, both analytically and via computer simulations View full abstract»

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  • Performance bounds and cutoff rates for data channels affected by correlated randomly time-variant multipath fading

    Page(s): 1258 - 1261
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    The symmetric cutoff rate is derived for quadrature-amplitude-modulated (QAM) block-coded data transmissions over noisy links affected by time-correlated multipath-phenomena which introduce intersymbol interference (ISI) in the received signal. Maximum likelihood (ML) decoding supported by perfect channel-state information (CSI) is assumed. Due to the presence of time-correlated ISI phenomena, the resulting transmission link constitutes an example of a continuous-state channel with memory View full abstract»

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  • Performance analysis of an improved MMSE multiuser receiver for mismatched delay channels

    Page(s): 1369 - 1380
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    Motivated by the fact that time delays in a practical direct-sequence code-division multiple-access (DS-CDMA) system can never be perfectly estimated, an improved minimum-mean squared-error (MMSE)-based receiver is proposed and analyzed. Via the simple assumption of a probability distribution for the delay estimation errors, the proposed receiver can achieve a performance superior to that of the conventional MMSE (CMMSE) receiver. The performances of this improved receiver and the CMMSE receiver are compared in terms of the mean squared error (MSE), probability of error, and asymptotic multiuser efficiency (AME). As the original definition of AME does not consider mismatched channels, the behavior of three single-user receivers bearing imperfect delay estimation is also investigated. These single-user receivers are employed to define a more appropriate AME. Finally, an efficient update mechanism to accommodate dynamic channel statistics, and thus practical implementation, is proposed View full abstract»

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  • Noncoherent detection of preamble-signal-assisted differentially phase-encoded APSK signals

    Page(s): 1266 - 1270
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    A noncoherent detection scheme for differentially encoded amplitude- and phase-shift-keyed data transmission, assisted with differentially phase-shift-keyed preamble signals, is presented and analyzed for an additive white Gaussian noise channel. It is analytically shown that, despite a controllable reduction in bandwidth efficiency, the proposed scheme yields an error performance approaching that of the quadrature amplitude modulation scheme with ideal coherent detection within a loss of approximately 1 dB 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