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Communications, IEEE Transactions on

Issue 5 • Date May 2000

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

    Page(s): 897
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    Freely Available from IEEE
  • Effects of CW interference on phase-locked loop performance

    Page(s): 886 - 896
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    This paper focuses on the modeling and analysis of phase-locked loops in the presence of continuous wave (CW) interference such that the operating vulnerability to CW jamming and interference can be accessed. The loop phase error is characterized, and the conditions under which the loop remains locked in frequency to the desired carrier are presented. Analysis is conducted for arbitrary offsets of carrier and interferer signal frequencies relative to the quiescent voltage-controlled oscillator (VCO) frequency. The results show that loop performance depends not only on the frequency difference between the desired signal and interferer, but also on the frequency offset between the quiescent VCO oscillation and desired carrier. The vulnerability of the loop to the presence of interference increases if interferer and desired signal spectral locations are in opposite sides of quiescent VCO frequency View full abstract»

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  • Spatio-temporal blind adaptive multiuser detection

    Page(s): 729 - 732
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    We propose blind multiuser detection schemes with antenna arrays, which is based on signal subspace estimation. They are a multichannel extension of the decorrelating and minimum mean-square-error detectors, and therefore they share their immunity to near-far effects. The blind scheme may be seen as an extension of the results in of Wang and Poor (see IEEE Trans. Inform. Theory, vol.44, p.677-90, 1998). However, it is seen that compared with the latter results when spatial diversity is considered, the proposed spatio-temporal detectors offer, with little attendant increase in computational complexity, a better performance. A blind adaptive implementation based on a new orthogonal PAST (projection approximation subspace tracking) algorithm, which is shown to be efficient for subspace tracking, is proposed. Also, we develop a blind estimation of the spatial signature based on the orthogonality between noise and signal subspaces. It is seen that the blind adaptive multiuser detection and blind spatio-temporal signature estimation can he integrated jointly View full abstract»

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  • Multiple-dwell and sequential code acquisition with diversity for FFH/MFSK spread-spectrum systems under band multitone jamming

    Page(s): 841 - 851
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    Pseudonoise code acquisition is investigated for constant hopping rate fast frequency-hopped (FFH)/M-ary frequency-shift keying systems under the effects of white Gaussian noise and band multitone jamming. In particular, serial search acquisition systems based on the traditional multiple-dwell test (up to three dwells) and three novel sequential tests are analyzed and compared. Analytical results show the following in a heavily jammed environment: (1) the inherent time diversity in an FFH system can significantly improve the acquisition performance of the multiple-dwell test and (2) the novel sequential tests can significantly outperform the multiple-dwell test. Our analytical results are verified by computer simulations View full abstract»

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  • Reduced-rank array processing for wireless communications with applications to IS-54/IS-136

    Page(s): 743 - 747
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    We study the application of the eigencanceler, a reduced-rank method based on the eigendecomposition of the estimated covariance matrix, to the wireless communication problem. Simple closed-form bounds are obtained for the bit-error rate of binary phase-shift keying modulation in the presence of cochannel interference in systems using sample matrix inversion (SMI) and the eigencanceler. The application of SMI and the eigencanceler to a flat fading time-division multiple-access system is studied in the context of the IS-54/IS-136 standard. It is shown that adaptive antennas in conjunction with reduced-rank processing can be used to increase capacity of such systems by reducing the frequency reuse factor from 7 to 1 View full abstract»

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  • Suboptimal maximum-likelihood multiuser detection of synchronous CDMA on frequency-selective multipath channels

    Page(s): 875 - 885
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    We propose a signal processing technique, based on the estimate-maximize algorithm, in order to perform multiuser code-division multiple-access (CDMA) detection. This algorithm iteratively seeks for the maximum-likelihood solution. The resulting structure is a successive interference cancellation scheme which can be applied to both synchronous and asynchronous CDMA. Higher performance than similar methods is obtained from using deterministic annealing and multiple stages. A soft output is defined, and the signal-to-noise ratio in the soft output of the detector is measured for predicting performance with an outer code with soft input decoder. The new receiver is applied to the problem whereby in a synchronous CDMA system the orthogonality of the codes is destroyed by a frequency-selective channel, caused by multipath fading. This nonlinear technique is shown to perform much better than the minimum mean-square-error linear solution and several other algorithms. The algorithm lends itself to an efficient DSP or VLSI implementation. We evaluate the performance by simulations with coherent quadrature phase-shift keying modulation, known channel and long random Rayleigh multipath. In most cases, we set the number of users equal to the processing gain for maximal throughput. The results are also presented in the form of outage probabilities for random Rayleigh multipath against required fading margin View full abstract»

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  • Coding CPFSK for differential demodulation

    Page(s): 721 - 724
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    A model is developed for finding codes for differentially demodulated continuous phase frequency-shift keying with modulation index h=1/M, where M is the size of the symbol alphabet. The results of codes searches show that there is very little loss in squared Euclidean distance when comparing differential codes with coherent codes View full abstract»

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  • MAP decoding in channels with memory

    Page(s): 757 - 763
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    The expectation-maximization (EM) algorithm is popular in estimating the parameters of various statistical models. We consider applications of the EM algorithm to the maximum a posteriori (MAP) sequence decoding assuming that sources and channels are described by hidden Markov models (HMMs). The HMMs can accurately approximate a large variety of communication channels with memory and, in particular, wireless fading channels with noise. The direct maximization of the a posteriori probability (APP) is too complex. The EM algorithm allows us to obtain the MAP sequence estimation iteratively. Since each step of the EM algorithm increases the APP, the algorithm can improve the performance of any decoding procedure View full abstract»

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  • Multilevel coded modulation for unequal error protection and multistage decoding. II. Asymmetric constellations

    Page(s): 774 - 786
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    In this paper, multilevel coded asymmetric modulation with multistage decoding and unequal error protection (UEP) is discussed. These results further emphasize the fact that unconventional signal set partitionings are more promising than traditional (Ungerboeck-type) partitionings, to achieve UEP capabilities with multilevel coding and multistage decoding. Three types of unconventional partitionings are analyzed for asymmetric 8-PSK and 16-QAM constellations over the additive white Gaussian noise channel to introduce design guidelines. Generalizations to other PSK and QAM type constellations follow the same lines. Upper bounds on the bit-error probability based on union bound arguments are first derived. In some cases, these bounds become loose due to the large overlappings of decision regions associated with asymmetric constellations and unconventional partitionings. To overcome this problem, simpler and tighter approximated bounds are derived. Based on these bounds, it is shown that additional refinements can be achieved in the construction of multilevel UEP codes, by introducing asymmetries in PSK and QAM signal constellations View full abstract»

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  • Adaptive detection in asynchronous code-division multiple-access system in multipath fading channels

    Page(s): 863 - 874
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    In code-division multiple-access systems transmitting data over time-varying multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) arise. In this paper, we address interference suppression, multipath diversity and processing gain protection for multiuser detection with less noise enhancement by using a parallel cancelling scheme. The proposed detector consists of a RAKE filter, forward filter, and feedback filter with different functions for each filter. The RAKE filter increases the signal-to-noise ratio by taking the advantage of multipath and code diversities. The forward filter is proposed, in combination with the feedback filter, to remove the effects of MAI and ISI by parallel cancellation. In order to avoid performance deterioration due to unreliable initial estimation in the parallel cancellation, a cost function with proper weighting is introduced to improve the performance of the proposed detector. In the proposed design method, a recursive least square algorithm is employed to update the tap-coefficients of all filters for MAI and ISI cancellation. Finally, the performance of the proposed detector is analyzed and compared with other detectors View full abstract»

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  • An asynchronous multirate decorrelator

    Page(s): 739 - 742
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    This paper examines truncated window decorrelators for an asynchronous direct-sequence code-division multiple-access system supporting users transmitting at different bit rates. We decode a user by extending the observation window over a sufficient number of its bits. To characterize practical window sizes, simple upper and lower bounds for the asymptotic efficiency of both the truncated window and infinite window decorrelators are developed. Empirical results show that as the length of the observation window increases, the bounds converge rapidly to the asymptotic efficiency of the infinite window decorrelator. The complexity of the receiver depends strongly on the ratio of the maximum to minimum bit rates View full abstract»

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  • On the convergence of blind adaptive equalizers for constant modulus signals

    Page(s): 795 - 803
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    This paper studies the behavior of the error sequence of stop-anti-go variants of two adaptive blind equalizers, namely CMA2-2 and Sato's (1975) algorithm. It is shown that for transmitted signals with constant modulus γ, the equalizer output can be made to lie within the circle of radius γ√c infinitely often, for some value of c that is only slightly larger than one View full abstract»

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  • CMA-based code acquisition scheme for DS-CDMA systems

    Page(s): 852 - 862
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    In direct-sequence code-division multiple access, a code synchronization must take place before the multiuser detector. As the initial synchronization stage, a code acquisition scheme is used to estimate the relative timing phase for the desired transmission within one chip interval. In this paper, a blind code acquisition scheme using adaptive linear filtering based on a linearly constrained constant modulus algorithm (CMA) is proposed. The uncertainty of a desired user's delay is initially discretized and translated into a number of hypotheses. The lock convergence property of CMA is exploited, where the filter at the steady state can lock onto the desired user while nulling all other interfering users (i.e., a decorrelator). For each delay hypothesis, the filter is initialized as the corresponding shifted spreading sequence of the desired user. It is shown that lock convergence always occurs for the correct hypothesis, while all incorrect hypotheses will be hovered around some saddle regions, given sufficiently small step sizes. Then, the correct hypothesis is the one which has the converged filter to yield the maximum lock onto the desired user, or a maximum output energy View full abstract»

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  • Decision-feedback MAP receiver for time-selective fading CDMA channels

    Page(s): 829 - 840
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    A decision-feedback maximum a posteriori (MAP) receiver is proposed for code-division multiple-access channels with time-selective fading. The receiver consists of a sequence-matched filter and a MAP demodulator. Output samples (more than one per symbol) from the matched filter are fed into the MAP demodulator. The MAP demodulator exploits the channel memory by delaying the decision and using a sequence of observations. This receiver also rejects multiple-access interference and estimates channel fading coefficients implicitly to give good demodulation decisions. Moreover, computer simulations are performed to evaluate the bit-error rate performance of the receiver under various channel conditions View full abstract»

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  • Multiuser detectors with disjoint Kalman channel estimators for synchronous CDMA mobile radio channels

    Page(s): 752 - 756
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    We compare performance of several multiuser detectors for differentially encoded data combined with simple, disjoint, decision-directed Kalman channel estimators over flat Rayleigh fading channels. Simpler detectors with noncoherent differential detection are also compared. Different performance trends relative to the case of perfect channel estimation are observed. We find that in the presence of channel mismatch, the linear decorrelator is the most robust detector in terms of the bit-error rate and the near-far resistance. Parameter adjustment for fading channel modeling and estimation in the decision-directed mode are also discussed View full abstract»

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  • Power control for an asynchronous multirate decorrelator

    Page(s): 804 - 812
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    For code-division multiple-access (CDMA) wireless systems employing multiuser detection, the varied bit-error rate (BER) requirements of multimedia traffic dictate the use of transmitted power control. Using a decorrelator in an asynchronous multirate direct-sequence CDMA system, it may be necessary for different users to combat the noise enhancement and the propagation losses to varying degrees depending on individual requirements. In this context, we propose a power control algorithm for a multirate decorrelator that is suitable for a class of BER-based link quality objectives. If the uplink channel gain of the desired user is known, then it is straightforward for each user to choose the transmitted power needed to meet its target BER objective. In practice, however, the uplink channel gain is often difficult to measure. To avoid this measurement, we employ stochastic approximation methods to develop a simple iterative power control algorithm. In this algorithm, each mobile uses the output of its own decorrelator to update its transmitted power in order to achieve its BER objective. We show that when a user's bits have nonzero asymptotic efficiencies, the power control algorithm converges quickly in the mean square sense to the minimum power at which a user achieves its quality-of-service objective View full abstract»

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  • A systematic approach to detecting OFDM signals in a fading channel

    Page(s): 725 - 728
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    We derive the maximum a posteriori probability (MAP) receiver for orthogonal frequency-division multiplexed signals in a fading channel. As the complexity of the MAP receiver is high, we obtain a low-complexity, suboptimal receiver and evaluate its performance View full abstract»

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  • Adaptive linear equalization combined with noncoherent detection for MDPSK signals

    Page(s): 733 - 738
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    A novel noncoherent receiver for M-ary differential phase-shift keying signals transmitted over intersymbol interference channels is presented. The noncoherent receiver consists of a linear equalizer and a decision-feedback differential detector. A significant performance gain over a previously proposed noncoherent receiver can be observed. For an infinite number of feedback symbols, the optimum equalizer coefficients can be calculated analytically, and the performance of the proposed receiver approaches that of a coherent linear minimum mean-squared-error equalizer. Moreover, a modified least mean square and a modified recursive least squares algorithm for adaptation of the equalizer coefficients are discussed View full abstract»

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  • Multilevel coded CPFSK systems for AWGN and fading channels

    Page(s): 764 - 773
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    In this paper, we introduce multilevel coded continuous-phase frequency-shift keying (CPFSK) systems for both additive white Gaussian noise and fading channels based on multilevel coding and multistage decoding techniques. These schemes are designed under the constraint M⩾2P for M-ary CPFSK with modulation index J/P. In order to maintain the phase continuity property after multilevel coding, we use some specific set partitioning rules. We construct examples to show that the proposed systems outperform the corresponding conventional one-level schemes. For the fading case, we consider an ideal fading channel where adjacent fading symbols are assumed to be independent and a correlated fading channel where bit interleavers are needed at each coding level. The computer simulation results show that the proposed systems have bit-error performance and decoder complexity advantages over the corresponding reference codes taken from the literature. It is also shown that there is only a slight degradation on the bit-error performance for correlated fading, compared to the ideal fading case View full abstract»

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  • Joint source/channel coding for variable length codes

    Page(s): 787 - 794
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    When using entropy coding over a noisy channel, it is customary to protect the highly vulnerable bitstream with an error correcting code. In this paper, we propose a technique which utilizes the residual redundancy at the output of the source coder to provide error protection for entropy coded systems View full abstract»

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  • Adaptive lattice filters for CDMA overlay

    Page(s): 820 - 828
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    This paper presents the behavior of reflection coefficients of a stochastic gradient lattice (SGL) filter applied to a code division multiple-access overlay system. Analytic expressions for coefficients for a two-stage filter are derived in a Rayleigh fading channel with the presence of narrow-band interference and additive white Gaussian noise. It is shown that the coefficients of the lattice filter exhibit separate tracking and convergent properties, and that compared to an LMS filter, the lattice filter provides fast rate of convergence, while having good capability of narrow-hand interference suppression View full abstract»

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  • Improved image compression using S-tree and shading approach

    Page(s): 748 - 751
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    Distasi et al. (see ibid., vol.45, p.1095-1100, 1997), presented a storage-saving image compression method called the B-tree triangular coding (BTTC) method. Based on the modified S-tree data structure and the Gouraud shading method, this paper presents an improved image compression method railed the S-tree compression (STC) method. Experimental results illustrate that the bit rates and the image quality of the proposed STC method are quite competitive with the BTTC method, Due to the simple geometrical decomposition in the STC method, the ratio of the execution time or the proposed method over the BTTC method is less than 1/2 View full abstract»

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  • Extremal shape-controlled traffic patterns in high-speed networks

    Page(s): 813 - 819
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    We consider a variable bit-rate connection with a deterministically shaped random traffic process, as specified by communications networking standards. Regarding randomness, we assume no restricted model other than the natural requirement that the process be stationary and ergodic. Given only the shape parameters, we consider the open problem of determining the maximum service bandwidth required to achieve a given bound on the probability that the packet-transfer delay exceeds a certain threshold. The shape parameters together with a probabilistic bound on the packet-transfer delay define a variable bit-rate “channel”; an equivalent problem is to determine the “capacity” of this channel. To this end, we consider a queue with a constant service rate and a shaped arrival process and obtain tight bounds on queue occupancy and queueing delay. In particular, we describe that traffic pattern (among all stationary-ergodic and deterministically constrained arrival processes) which achieves the probabilistic bound 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