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Communications, IEEE Transactions on

Issue 2 • Date Feb. 1996

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Displaying Results 1 - 23 of 23
  • Abstracts of forthcoming manuscripts

    Publication Year: 1996
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    Freely Available from IEEE
  • Blind equalization of constant modulus signals using an adaptive observer approach

    Publication Year: 1996 , Page(s): 134 - 136
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    The paper addresses the problem of blind equalization of constant modulus signals which are degraded by frequency selective multipath propagation and additive white noise. An adaptive observer is used to update the weights of an FIR equalizer in order to restore the signal's constant modulus property. The observer gain is selected using fake algebraic Riccati methods in order to guarantee local stability. The performance of this method is compared to the constant modulus algorithm for simulated FM-FDM signals and exhibits significantly better convergence properties, particularly for heavy-tailed noise View full abstract»

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  • Performance of multicarrier DS CDMA systems

    Publication Year: 1996 , Page(s): 238 - 246
    Cited by:  Papers (343)  |  Patents (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    In this paper, we apply a multicarrier signaling technique to a direct-sequence CDMA system, where a data sequence multiplied by a spreading sequence modulates multiple carriers, rather than a single carrier. The receiver provides a correlator for each carrier, and the outputs of the correlators are combined with a maximal-ratio combiner. This type of signaling has the desirable properties of exhibiting a narrowband interference suppression effect, along with robustness to fading, without requiring the use of either an explicit RAKE structure or an interference suppression filter. We use bandlimited spreading waveforms to prevent self-interference, and we evaluate system performance over a frequency selective Rayleigh channel in the presence of partial band interference; we also compare system performance with that of a single-carrier RAKE system View full abstract»

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  • Analysis of the effect of impulse noise on multicarrier and single carrier QAM systems

    Publication Year: 1996 , Page(s): 145 - 147
    Cited by:  Papers (133)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    The paper first shows the equivalence of the Bernoulli-Gaussian impulse noise model in the discrete time domain to the continuous-time model of Poisson arriving delta functions with random area distributed according to the power Rayleigh probability density function. This equivalence is then used to develop a closed form expression for the probability of error for single carrier QAM that is easily evaluated. Furthermore, the performance of multicarrier modulation (MCM) is also analyzed using the same impulse noise model and it is shown that in most cases MCM performs better than single carrier systems, specifically when the probability of an impulse is not too high and the impulse power is moderate View full abstract»

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  • Capacity and power control in spread spectrum macrodiversity radio networks

    Publication Year: 1996 , Page(s): 247 - 256
    Cited by:  Papers (63)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB)  

    What is the capacity of the uplink of a radio network of receivers? We consider a spread spectrum model in which each user is decoded by all the receivers in the network (macrodiversity). We use a carrier-to-interference performance criterion that we derive from Shannon theory; each user must find the right transmitter power level to satisfy its carrier-to interference constraint. Satisfying this requirement for all users is equivalent to solving a fixed point problem. We use this power control problem to derive the network capacity region and find that the feasibility of a configuration of users is independent of their positions in the network; each user can be assigned a bandwidth that is independent of the user's position in the network. Our capacity region is an upper bound over all schemes that treat the interference of other users as pure noise. To show that the capacity can be realized in practice, we propose a decentralized power adaptation algorithm and prove global convergence to the fixed point via a monotonicity argument View full abstract»

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  • Optimum bandwidth-distance performance in partial response CPM systems

    Publication Year: 1996 , Page(s): 148 - 151
    Cited by:  Papers (5)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    The problem of optimizing the baseband pulse shape in order to obtain the minimum effective bandwidth for a prescribed value of minimum Euclidean distance is treated for partial response CPM. Some comparisons with standard pulses are performed and the results are presented in the form of bandwidth-distance and spectral density plots View full abstract»

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  • Performance analysis of frequency hopped/coherent MPSK in the presence of multitone jamming

    Publication Year: 1996 , Page(s): 152 - 155
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    This paper studies the performance of frequency hopped/coherent M-ary PSK signals in the presence of partial-band multitone jamming. The probability density function for the jammed received signal phase is found and utilized in obtaining a probability of error expression. The analytical expressions to assess the performance under worst case multitone jamming are provided View full abstract»

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  • Squeezing the most out of ATM

    Publication Year: 1996 , Page(s): 203 - 217
    Cited by:  Papers (79)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1548 KB)  

    Although ATM seems to be the wave of the future, one analysis requires that the utilization of the network be quite low. That analysis is based on asymptotic decay rates of steady-state distributions used to develop a concept of effective bandwidths for connection admission control. The present authors have developed an exact numerical algorithm that shows that the effective-bandwidth approximation can overestimate the target small blocking probabilities by several orders of magnitude when there are many sources that are more bursty than Poisson. The bad news is that the appealing simple connection admission control algorithm using effective bandwidths based solely on tail-probability asymptotic decay rates may actually not be as effective as many have hoped. The good news is that the statistical multiplexing gain on ATM networks may actually be higher than some have feared. For one example, thought to be realistic, the analysis indicates that the network actually can support twice as many sources as predicted by the effective-bandwidth approximation. The authors also show that the effective bandwidth approximation is not always conservative. Specifically, for sources less bursty than Poisson, the asymptotic constant grows exponentially in the number of sources (when they are scaled as above) and the effective-bandwidth approximation can greatly underestimate the target blocking probabilities. Finally, they develop new approximations that work much better than the pure effective-bandwidth approximation View full abstract»

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  • Two-dimensional spatial signature patterns

    Publication Year: 1996 , Page(s): 184 - 191
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    An optical orthogonal signature pattern code (OOSPC) is a collection of (0,1) two-dimensional (2-D) patterns with good correlation properties (i.e., high autocorrelation peaks with low sidelobes, and low cross-correlation functions). Such codes find applications, for example, to parallelly transmit and access images in “multicore-fiber” code-division multiple-access (CDMA) networks. Up to now all work on OOSPCs has been based on an assumption that at most one pulse per column or one pulse per row and column is allowed in each two-dimensional pattern. However, this restriction may not be required in such multiple-access networks if timing information can be extracted from other means, rather than from the autocorrelation function. A new class of OOSPCs is constructed without the restriction. The relationships between two-dimensional binary discrete auto- and cross-correlation arrays and their corresponding “sets” for OOSPCs are first developed. In addition, new bounds on the size of this special class of OOSPCs are derived. Afterwards, four algebraic techniques for constructing these new codes are investigated. Among these constructions, some of them achieve the upper bounds with equality and are thus optimal. Finally, the codes generated from some constructions satisfy the restriction of at most one pulse per row or column and hence can be used in applications requiring, for example, frequency-hopping patterns View full abstract»

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  • Per-survivor processing and tentative decisions: what is in between?

    Publication Year: 1996 , Page(s): 127 - 129
    Cited by:  Papers (20)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    In per-survivor processing (PSP), the number of parameter estimators equals the number of retained hypothetical data sequences (survivors). The authors propose an algorithm which uses an arbitrary number of parameter estimators and compromises between the two extremes of tentative decisions (one parameter estimator) and PSP. Specific applications to reduced state sequence estimation (RSSE) and maximum likelihood sequence estimation (MLSE) with adaptive tracking of a fading channel are considered View full abstract»

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  • Noncoherent coded modulation

    Publication Year: 1996 , Page(s): 172 - 183
    Cited by:  Papers (64)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1108 KB)  

    Trellis coded modulation with two or multidimensional signal constellations, together with coherent maximum-likelihood detection, is considered an attractive solution for communications over the additive white Gaussian noise (AWGN) channel. In this paper a new noncoherent communication system is introduced called noncoherent coded modulation (NCM) as an alternative to coherent coded modulation. NCM achieves almost the same power efficiency, without bandwidth expansion or an extensive increase in complexity. As a noncoherent system, the method does not need carrier phase estimation. Nonetheless, differential encoding is not required. High performance noncoherent detection is achieved by using multiple symbol observations. Unlike previous approaches, a sliding window for the observations is used, with each observation covering several branches of the trellis, such that the observations are time-overlapped. We define a new type of noncoherent maximum-likelihood sequence estimator (MLSE), and analyze its performance over the AWGN channel by numerical calculation of the union bound. We perform a computerized search and present new codes for noncoherent detection with their performance. The new codes cover many useful rates and complexities and achieve higher performance than existing codes for noncoherent detection. The method can also be used for multiple symbol demodulation of MDPSK with better results than existing methods View full abstract»

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  • Quadrilevel periodic sequences for fast start-up equalization and channel estimation

    Publication Year: 1996 , Page(s): 143 - 144
    Cited by:  Papers (1)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    A class of four-level periodic sequences derived from the binary m-sequences are presented. These sequences can be used as the training sequences in adaptive channel estimation and equalization with fast start-up for multilevel PAM or QAM transmission. The sequence generator can be implemented by simple hardware View full abstract»

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  • Multisampling receivers for uncoded and coded PSK signal sequences transmitted over Rayleigh frequency-flat fading channels

    Publication Year: 1996 , Page(s): 130 - 133
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    An algorithm, based on previous work [Vitetta and Taylor 1994, 1995], for the detection of coded and uncoded PSK sequences transmitted on a frequency-flat fading channel is investigated. It is based on the Viterbi algorithm and processes more than one signal sample per signaling interval. Its performance is evaluated by means of computer simulations for both uncoded and coded systems View full abstract»

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  • The effects of sequence selection on DS spread spectrum with selective fading and Rake reception

    Publication Year: 1996 , Page(s): 229 - 237
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (912 KB)  

    Error probabilities are evaluated for direct-sequence spread-spectrum communications and Rake reception over channels with doubly selective fading. The error probability for such a system depends on the spreading sequence, the autocorrelation function of the fading process, the received signal-to-noise ratio, and the number of taps in the Rake receiver. The focus of the paper is on the effect of the spreading sequence on the performance of each of two systems. One system employs noncoherent detection of differentially-encoded binary direct-sequence spread-spectrum signals and a post-detection diversity-combining Rake receiver which uses equal-gain combining. The other system employs coherent detection of binary direct-sequence spread-spectrum signals and a post-detection diversity-combining Rake receiver with perfect gain estimates for the channel. A simple sequence selection criterion is introduced, and the sensitivity of the performance of the system to the choice of the spreading sequence is examined. It is shown that significant performance differences result from different choices of the spreading sequence. It is also shown that, given a moderate range of delay spreads, sequences can be found that yield low bit error probabilities over that range. These are found to be robust with respect to the delay spectrum for the channel, the number of taps in the Rake receiver, the Doppler spread, and the signal-to-noise ratio View full abstract»

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  • Performance study of high-speed asymmetric digital subscriber lines technology

    Publication Year: 1996 , Page(s): 156 - 157
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    Computer simulation results are presented for the loop range coverage of an asymmetric digital subscriber lines (ADSL) system that uses the quadrature amplitude modulation (QAM) signaling scheme, ADSL performance is evaluated in the presence of background additive white Gaussian noise (AWGN), and crosstalk noise from existing services in the local telephone loop plant. It is shown that coverage of the extreme carrier serving area (CSA) is possible at transmission rates that are well above the existing T1 rate View full abstract»

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  • A saturation analysis of error-spectrum shaping quantizers

    Publication Year: 1996 , Page(s): 218 - 228
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    Error spectrum shaping (ESS) quantizers are analyzed in the context of realistic FIR reconstruction filters and nonzero probability of saturation. Conditions for stable operation are derived, and a suboptimal but effective and computationally efficient design method is proposed. Excellent agreement is obtained between the analysis and simulations. Even under these more stringent constraints, ESS quantizers are shown to achieve significant signal-to-quantization-noise ratio (SQNR) gains when quantizing oversampled Gaussian sources View full abstract»

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  • Cost-based scheduling and dropping algorithms to support integrated services

    Publication Year: 1996 , Page(s): 192 - 202
    Cited by:  Papers (11)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1212 KB)  

    Applications with diverse performance objectives must be supported on a single packet-switched network. The efficiency of such networks can be greatly improved through the use of sophisticated scheduling and dropping algorithms within the queues that form at the network access points and in switches throughout the network. In the present approach, arbitrary performance objectives are expressed in the form of cost functions, which map the queueing delay experienced by each packet to a cost incurred. The heuristic algorithms, cost-based scheduling (CBS) and cost-based dropping (CBD), then attempt to optimize network performance as perceived by the applications by minimizing the total cost incurred by all packets. Appropriate cost functions are presented for common applications. Scheduling and dropping algorithms are defined from these cost functions. It is demonstrated that network performance is better when these algorithms are used as opposed to the common alternatives. Also, contrary to conventional wisdom, some evidence is presented indicating that sophisticated scheduling may be preferable to sophisticated dropping as a means of adjusting loss rates View full abstract»

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  • A new architecture for the Viterbi decoder for code rate k/n

    Publication Year: 1996 , Page(s): 158 - 164
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    A novel VLSI architecture is proposed for implementing a long constraint length Viterbi decoder (VD) for code rate k/n. This architecture is based on the encoding structure where k input bits are shifted into k shift registers in each cycle. The architecture is designed in a hierarchical manner by breaking the system into several levels and designing each level independently. The tasks in the design of each level range from determining the number of computation units, and the interconnection between the units, to the allocation and scheduling of operations. Additional design issues such as in-place storage of accumulated path metrics and trace back implementation of the survivor memory have also been addressed. The resulting architecture is regular, has a foldable global topology and is very flexible. It also achieves a better than linear trade-off between hardware complexity and computation time View full abstract»

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  • Jitter analysis for two methods of synchronization for external timing injection

    Publication Year: 1996 , Page(s): 269 - 276
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    The jitter generated by two different approaches to synchronization of an external timing source is analyzed. The two approaches are: the use of conventional stuffing and the use of a simpler frame sampling synchronizer. It is shown that these two approaches have the same jitter power density spectrum. The result is obtained using a new time domain method developed in the paper. Exact expressions for the jitter on the synchronized external timing source are obtained. Furthermore, the effect of quantization in the conventional stuffing synchronizer on the jitter expressions obtained is also explored. Jitter generated by the frame sampling synchronizer is also analyzed using the time domain method, which again produces an exact expression. In the case where certain parameters of the two approaches are related, the location of spectral lines in their respective jitter spectra is shown to be identical. It is also shown that both approaches to synchronization introduce the so-called waiting-time jitter View full abstract»

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  • Variable-complexity trellis decoding of binary convolutional codes

    Publication Year: 1996 , Page(s): 121 - 126
    Cited by:  Papers (10)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    Considers trellis decoding of convolutional codes with selectable effort, as measured by decoder complexity. Decoding is described for single parent codes with a variety of complexities, with performance “near” that of the optimal fixed receiver complexity coding system. Effective free distance is examined. Criteria are proposed for ranking parent codes, and some codes found to be best according to the criteria are tabulated, Several codes with effective free distance better than the best code of comparable complexity were found. Asymptotic (high SNR) performance analysis and error propagation are discussed. Simulation results are also provided View full abstract»

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  • An artificial neural net Viterbi decoder

    Publication Year: 1996 , Page(s): 165 - 171
    Cited by:  Papers (20)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    The Viterbi algorithm is a maximum likelihood means for decoding convolutional codes and has thus played an important role in applications ranging from satellite communications to cellular telephony. In the past, Viterbi decoders have usually been implemented using digital circuits. The speed of these digital decoders is directly related to the amount of parallelism in the design. As the constraint length of the code increases, parallelism becomes problematic due to the complexity of the decoder. In this paper an artificial neural network (ANN) Viterbi decoder is presented. The ANN decoder is significantly faster than comparable digital-only designs due to its fully parallel architecture. The fully parallel structure is obtained by implementing most of the Viterbi algorithm using analog neurons as opposed to digital circuits. Several modifications to the ANN decoder are considered, including an analog/digital hybrid design that results in an extremely fast and efficient decoder. The ANN decoder requires one-sixth the number of transistors required by the digital decoder. The connection weights of the ANN decoder are either +1 or -1, so weight considerations in the implementation are eliminated. This, together with the design's modularity and local connectivity, makes the ANN Viterbi decoder a natural fit for VLSI implementation. Simulation results are provided to show that the performance of the ANN decoder matches that of an ideal Viterbi decoder View full abstract»

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  • A new system identification method for fast echo canceler initialization

    Publication Year: 1996 , Page(s): 137 - 142
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    Proposes a new recursive version of an earlier technique for fast initialization of data-driven echo cancelers (DDECs). The speed of convergence and the covariance of the estimate of the proposed technique are comparable to the recursive least squares (RLS) algorithm, however, the computational complexity is no greater than the least mean square (LMS) algorithm. Analysis of computational complexity and the estimation error is also provided. Simulation results based on both floating-point and fixed-point arithmetic illustrate a remarkable improvement in terms of speed of convergence and steady-state error over the computationally comparable LMS algorithm View full abstract»

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  • Analysis of an adaptive decorrelating detector for synchronous CDMA channels

    Publication Year: 1996 , Page(s): 257 - 268
    Cited by:  Papers (26)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1196 KB)  

    Multiuser detection allows for the efficient use of bandwidth in code-division multiple-access (CDMA) channels through mitigation of near-far effects and multiple-access noise limitations. The decorrelating detector, developed by Lupas and Verdu (1989), is a linear multiuser detector that is asymptotically optimal in terms of near-far resistance when certain communication parameters are completely known to the detector. In this paper, a simple adaptive decorrelating detector is developed by placing constraints on the set of spreading codes to be used by the active users. This adaptive detector has two modules: it first decorrelates the existing users, and then it determines the spreading code of a new user entering the network with or without the use of a training sequence. Maximum likelihood detection is proposed for determining the new user's spreading code. The performance of this algorithm is studied by investigating the probability of making an error in determining the new user's spreading code as a function of the number of samples used to make the determination, the number of users transmitting, and the signal to noise ratio of the new user with respect to the ambient Gaussian noise 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