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Communications, IEEE Transactions on

Issue 4 • Date April 2002

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Displaying Results 1 - 25 of 25
  • Impact of clustering in statistical indoor propagation models on link capacity

    Publication Year: 2002 , Page(s): 521 - 523
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (193 KB) |  | HTML iconHTML  

    Explicit clustering in a statistical indoor propagation model is found to have significant effects on the capacity of an array-to-array link or matrix channel. Effects of antenna spacing, Poisson homogeneity, block size, and transmit power allocation strategies are also considered. View full abstract»

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  • Corrections to "scheduling broadcasts in multihop radio networks"

    Publication Year: 2002 , Page(s): 686
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB)  

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  • Abstract of forthcoming manuscripts

    Publication Year: 2002 , Page(s): 687
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  • Corrections to "design of node configuration for all-optical multi-fiber networks"

    Publication Year: 2002 , Page(s): 686
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB)  

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  • Noncoherent MMSE interference suppression for DS-CDMA

    Publication Year: 2002 , Page(s): 577 - 587
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (483 KB) |  | HTML iconHTML  

    A novel robust noncoherent receiver for minimum mean-squared error (MMSE) interference suppression for direct-sequence code-division multiple access (DS-CDMA) is proposed. The receiver consists of a linear MMSE filter and a decision-feedback differential detector (DF-DD). The performance of the proposed scheme is investigated analytically and by computer simulations. It is shown that the loss compared to coherent MMSE interference suppression is limited and can be made arbitrarily small by increasing the observation window used for calculation of the reference symbol of the DF-DD. Hence, the regarded noncoherent receiver is near-far resistant. For adjustment of the MMSE filter coefficients three noncoherent adaptive algorithms are proposed. In contrast to coherent adaptive algorithms, these noncoherent algorithms have the important advantage that they also converge if the channel phase is time-variant View full abstract»

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  • Symbol time offset estimation in coherent OFDM systems

    Publication Year: 2002 , Page(s): 545 - 549
    Cited by:  Papers (36)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB) |  | HTML iconHTML  

    This paper presents a symbol time offset estimator for coherent orthogonal frequency division multiplexing (OFDM) systems. The estimator exploits both the redundancy in the cyclic prefix and available pilot symbols used for channel estimation. The estimator is robust against frequency offsets and is suitable for use in dispersive channels. We base the estimator on the maximum-likelihood estimator for the additive white Gaussian noise channel. Simulations for an example system indicate a system performance as close as 0.6 dB to a perfectly synchronized system View full abstract»

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  • On the outage probability of optimum combining and maximal ratio combining schemes in an interference-limited Rice fading channel

    Publication Year: 2002 , Page(s): 532 - 535
    Cited by:  Papers (44)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (210 KB) |  | HTML iconHTML  

    In this letter, we study the performance of optimum combining (OC) and maximal ratio combining (MRC) diversity schemes in wireless digital communication systems with Rice fading and cochannel interference. New simplified closed-form expressions are derived for the probability density function (pdf) as well as the outage probability for OC and MRC when the desired signal has a line of sight and the interferers are assumed to be scattered and further away from the receiver. It is assumed that the interferers have equal powers and their number (L) is larger than the diversity order (M), i.e., L>M View full abstract»

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  • Optimization of baud-rate timing recovery for equalization

    Publication Year: 2002 , Page(s): 550 - 552
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    This paper suggests the use of a prefilter before baud-rate timing recovery (Mueller and Muller 1976). It is shown that the timing phase of the baud-rate timing synchronizer can be set to a desirable timing phase, at which point a digital equalizer performs best, by proper prefiltering. The procedure for the optimal design of such a prefilter is developed under the assumption that the channel impulse response and desirable timing phase for equalization are known. Application of the proposed scheme to the gigabit Ethernet system demonstrated that prefiltering can improve receiver performance View full abstract»

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  • On the capture performance of smart antennas in a multicellular environment

    Publication Year: 2002 , Page(s): 536 - 539
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (214 KB) |  | HTML iconHTML  

    In this letter, we present a study of the signal-to-interference-plus-noise ratio (SINR) and throughput efficiency achievable on the uplink of a multicellular environment in the presence of smart antennas at the base station receivers. Both intracell and intercell interferers are explicitly taken into account, as is the SINR gain yielded by optimal beamforming. Different cases are compared, and in particular the tradeoff involved in choosing the frequency reuse plan is considered. It is seen that the system operates most efficiently with full frequency reuse, even though this requires intercell synchronization View full abstract»

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  • Turbo multiuser detection with unknown interferers

    Publication Year: 2002 , Page(s): 616 - 622
    Cited by:  Papers (18)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (345 KB) |  | HTML iconHTML  

    We consider the problem of turbo multiuser detection for synchronous and asynchronous code-division multiple-access (CDMA) in the presence of unknown users. Turbo multiuser detectors, as previously developed, typically require knowledge of the signature waveforms of all of the users in the system and ignore users whose signature sequences are unknown, e.g., users outside the cell. We develop turbo multiuser detection for CDMA uplink systems and other environments in which the receiver has knowledge of the signature waveforms of only K˘⩽ K users. Subspace techniques are used to estimate the interference from the unknown-users and the interference estimate is subtracted from the received signal. We see that the new receiver significantly outperforms the conventional turbo multiuser receiver for moderate and high signal-to-noise ratios. It is also seen that the traditional turbo receiver provides little gain through iteration when unknown users are present View full abstract»

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  • Systematic design of space-time codes employing multiple trellis coded modulation

    Publication Year: 2002 , Page(s): 608 - 615
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    The design of space-time (ST) codes employing multiple trellis coded modulation (MTCM) is considered. This structure is shown to be necessary for achieving maximum transmit diversity gain when using trellis codes with parallel paths. Systematic code search procedures with low complexity are described based on the properties of ST-MTCM codes. It is illustrated that, if the trellis branches are properly labeled, the overall coding gain can be made larger than that achieved by conventional ST codes with the same transmission rate and the same number of states View full abstract»

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  • Coded continuous phase modulation with low-complexity noncoherent reception

    Publication Year: 2002 , Page(s): 517 - 520
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    Coded continuous phase modulation based on a feedback-free modulator with noncoherent detection is discussed. Low-complexity receiver processing is achieved by using only two or three linear filters for demodulation and applying noncoherent sequence estimation with reduced-state Viterbi decoding and simple branch metric calculation. Overall, the proposed noncoherent receiver provides significant advantages over previously presented approaches View full abstract»

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  • Digital communications channel equalization using the Kernel Adaline

    Publication Year: 2002 , Page(s): 571 - 576
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (265 KB) |  | HTML iconHTML  

    For transmission of digital data over a linear channel with additive white noise, it can be shown that the optimal symbol-decision equalizer is nonlinear. The Kernel Adaline algorithm, a nonlinear generalization of Widrow's and Hoff's (1960) Adaline, is capable of learning arbitrary nonlinear decision boundaries while retaining the desirable convergence properties of the linear Adaline. This work investigates the use of the Kernel Adaline as an equalizer for such transmission channels. We show that the performance of the Kernel Adaline approaches that of the optimal symbol-decision equalizer given by Bayes theory and further, still produces useful results when the additive noise is nonwhite. A description and preliminary results of an adaptive version of the Kernel Adaline are also presented View full abstract»

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  • A multipath model for the powerline channel

    Publication Year: 2002 , Page(s): 553 - 559
    Cited by:  Papers (408)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB) |  | HTML iconHTML  

    The development of powerline communication (PLC) systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the mains network suitable for performance analysis by simulation. This paper presents an analytic model describing complex transfer functions of typical powerline networks using only a small set of parameters. The model is based on physical signal propagation effects in mains networks including numerous branches and impedance mismatching. Besides multipath propagation accompanied by frequency-selective fading, signal attenuation of typical power cables increasing with length and frequency is considered. A verification of the model at a test network, as well as its use for definition of attenuation profiles and reference channels, demonstrate the practical value of the proposed model View full abstract»

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  • Model-based channel estimation for OFDM signals in Rayleigh fading

    Publication Year: 2002 , Page(s): 540 - 544
    Cited by:  Papers (55)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (333 KB) |  | HTML iconHTML  

    This paper proposes a robust pilot-assisted channel estimation method for orthogonal frequency division multiplexing (OFDM) signals in Rayleigh fading. Our estimation method is based on nonlinear regression channel models. Unlike the linear minimum mean-squared error (LMMSE) channel estimate, the method proposed does not have to know or estimate channel statistics like the channel correlation matrix and the average signal-to-noise ratio (SNR) per bit. Numerical results indicate that the performance of the proposed channel estimator is very close to the theoretical bit error propagation lower bound that is obtained by a receiver with perfect channel response information View full abstract»

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  • Noncoherent sequential PN code acquisition using sliding correlation for chip-asynchronous direct-sequence spread-spectrum communications

    Publication Year: 2002 , Page(s): 664 - 676
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (527 KB) |  | HTML iconHTML  

    Noncoherent sequential pseudonoise (PN) code acquisition using sliding correlation is proposed in this paper. Noncoherent detection and chip asynchronization should be taken care of to handle a severely noisy environment, while frequency offset and data modulation effects can be simultaneously dealt with in the proposed technique. To realize sequential detection, the cross-correlation sequences at the output end of the integrate/dump (LID) filter under out-of-lock conditions have to be modeled as either a Gaussian random sequence for chip-asynchronous applications or as their upper bound for chip-synchronous applications in order to avoid significantly high probabilities of false alarm caused by the conventional zero-sequence model. Meanwhile, the in-lock sequence also has to be modified by taking the frequency offset and chip-asynchronization effects into account in order to avoid the occurrence of high probabilities of miss. Extensive computer simulation results indicate that the proposed technique can achieve low probabilities of false alarm and miss and can outperform its fixed-sample-size (FSS) counterparts by roughly 2~4 dB. This superiority, furthermore, increases with decreasing SNRs and/or decreasing desired error probabilities View full abstract»

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  • Iterative packet combining schemes for intersymbol interference channels

    Publication Year: 2002 , Page(s): 560 - 570
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB) |  | HTML iconHTML  

    We study packet combining techniques for retransmission schemes over intersymbol interference (ISI) channels. Two types of combining schemes are investigated, namely, maximum-likelihood combining (MLC) and iterative combining (IC). By first employing a precoding technique and then by interpreting the ISI channel as a trellis code, the transmissions of the same data packet at different times through the channel can be treated as the parallel concatenation of recursive trellis codes. If interleavers are used in between retransmissions, "turbo" coding gains can be achieved by iterative equalization. It is shown that IC provides excellent performance and outperforms other forms of combining in terms of frame error rate performance both analytically and through simulations View full abstract»

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  • Network-assisted diversity multiple access in dispersive channels

    Publication Year: 2002 , Page(s): 623 - 632
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB) |  | HTML iconHTML  

    Network-assisted diversity multiple access (NDMA) is a novel random medium access method, which provides impressive throughput efficiency for multiplexing variable-bit-rate data sources. We study the implementation of the NDMA scheme in the presence of multipath channels. A transceiver architecture and random access strategies are proposed, which are able to detect and resolve collisions in the presence of unknown propagation channels. The performance issues are studied both analytically and numerically View full abstract»

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  • Low-complexity maximum-likelihood detection of coded signals sent over finite-state Markov channels

    Publication Year: 2002 , Page(s): 524 - 531
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB) |  | HTML iconHTML  

    We propose a decision-feedback decoder for coded signals transmitted over finite-state Markov channels. The decoder achieves maximum-likelihood sequence detection (in the absence of feedback errors) with very low complexity by exploiting previous bit decisions and the Markov structure of the channel. We also propose a similar decoder, the output-feedback decoder, that does not use previous bit decisions and therefore does not suffer from error propagation. The decoder performance is determined using a new sliding window analysis technique as well as by simulation. Both decoders exhibit excellent bit error rate performance with a relatively low complexity that is independent of the channel decorrelation time View full abstract»

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  • Methods of summing crosstalk from mixed sources .II. Performance results

    Publication Year: 2002 , Page(s): 600 - 607
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (269 KB) |  | HTML iconHTML  

    For pt.I see ibid., vol.50, p.453-61, (Mar. 2002). In a companion paper, the problem of summing crosstalk from mixed sources has been deeply analyzed. The problem of determining a good model for the summation of mixed crosstalk is becoming more important now that many digital subscriber line (DSL) services are being deployed in the field. The straightforward application of the usual 1% worst-case model for only one kind of disturber to all the individual worst-case contributions is overly pessimistic. The most well-known methods of summing mixed crosstalk, the FSAN and the Mean PSD methods, are less pessimistic. Also, the two new summation methods presented previously, the Minkowski-bound and the Holder-bound methods, are less pessimistic and offer the appealing feature of choosing the level of pessimism or optimism through a parameter. However, the accuracy of these methods has never been quantified in the past. As more and more types of DSLs are deployed by multiple service providers, it is imperative to gain confidence in the methods of modeling worst-case mixed crosstalk and to understand their limitations. In this paper, the problem of defining an accurate statistical modeling of the pair-to-pair crosstalk power coupling losses is addressed first. This has been accomplished by exploiting a large measurement campaign performed on real cables. The results of a large simulation campaign that compares the accuracy of known and newly proposed methods of summing mixed crosstalk are then presented. In addition, it is proposed here to use the signal-to-noise ratio (SNR) as the metric for determining the actual system performance in the presence of mixed crosstalk. A Monte Carlo simulation is run that assigns randomly each disturber to a pair-to-pair NEXT coupling which matches the statistics of measured cables. The Monte Carlo method accurately determines the I % worst-case impact on the SNR of DSL systems affected by mixed crosstalk. ISDN, HDSL, HDSL2, T1 and ADSL are each simulated with many different numbers and types of mixed crosstalk View full abstract»

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  • Initial synchronization of DS-CDMA via bursty pilot signals

    Publication Year: 2002 , Page(s): 677 - 685
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (429 KB) |  | HTML iconHTML  

    We consider initial timing acquisition in discrete-sequence code-division multiple-access (DS-CDMA) when propagation is affected by multipath and fading, and where the base-station broadcasts a synchronization pilot signal in the form of bursts of modulated chips transmitted periodically and separated by long silent intervals. Subject to certain simplifying assumptions, we derive the maximum-likelihood (ML) estimator by solving a constrained maximization problem. Our ML timing estimator has constant complexity per observation sample. The relation to other estimation methods is addressed, and performance comparisons are provided by simulation. The proposed estimator yields good performance independently of the multipath-intensity profile of the channel, provided that the delay spread is not larger than a given maximum spread. Moreover, our estimator is fairly robust to the mismatch in the fading Doppler spectrum and provides good performance for both fast and slow fading View full abstract»

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  • Specular coherent and noncoherent optimal detection for unresolved multipath Ricean fading channels

    Publication Year: 2002 , Page(s): 588 - 599
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (539 KB) |  | HTML iconHTML  

    This paper considers specular coherent and noncoherent optimal detection for unresolved multipath Ricean fading channels with known delays. The focus is on receiver structures and performance. Specular coherent detection employs the carrier phase of the Ricean specular component, while noncoherent detection does not. Therefore, a specular coherent detector must be augmented with a carrier phase estimator for the specular component. The structures considered are generalization of the well-known RAKE receiver to the unresolved multipath case. It is shown that both optimal structures perform a decorrelation operation before combining, which is essential to eliminating error floors under multipath unresolvability conditions. Furthermore, the noncoherent optimal receiver includes an inherent estimator for the specular component phasor. It is shown that the specular coherent and noncoherent structures converge at high SNR. This result is confirmed through analytical and numerical performance evaluation. Little performance gains can be obtained by the use of specular coherent detection for orthogonal frequency-shift keying and to a lesser extent for differential phase-shift keying over mixed mode Ricean/Rayleigh fading channels, making noncoherent demodulation attractive in these cases View full abstract»

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  • Digital multi-carrier spread spectrum versus direct sequence spread spectrum for resistance to jamming and multipath

    Publication Year: 2002 , Page(s): 643 - 655
    Cited by:  Papers (20)  |  Patents (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB) |  | HTML iconHTML  

    We compare single user digital multi-carrier spread spectrum (MC-SS) modulation with direct sequence (DS) SS (with a modified implementation) in the presence of narrowband interference (NBI) and multipath fading. We derive closed-form expressions for the symbol error probability for both the linear MMSE receiver as well as the conventional matched-filter receiver under different scenarios: additive white Gaussian noise (AWGN) channel with NBI, multipath channel with or without NBI. We show that DS-SS can achieve the same performance as MC-SS if the spreading code is carefully designed to have perfect periodic autocorrelation function (PACF). On the other hand, MC-SS is more robust to narrowband interference and multipath fading than is DS-SS with the widely used spreading codes that do not possess perfect PACE. Our analysis reveals that the performance improvement of MC-SS is precisely due to the implicit construction of an equivalent spreading code having nonconstant amplitude but possessing perfect periodic autocorrelation View full abstract»

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  • A simple and accurate method of probability of bit error analysis for asynchronous band-limited DS-CDMA systems

    Publication Year: 2002 , Page(s): 656 - 663
    Cited by:  Papers (42)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (354 KB) |  | HTML iconHTML  

    This paper considers probability of bit error (Pe) analysis in asynchronous band-limited direct-sequence code-division multiple-access (DS-CDMA) systems. It presents a simple and accurate method of Pe analysis. The proposed method can serve as an attractive alternative to the only two techniques currently available for band-limited systems: the standard Gaussian approximation (SGA) and the characteristic function method. The former is prone to inaccuracy while the latter, large computational complexity. The method generalizes the simplified improved Gaussian approximation (SIGA) derived previously for rectangular pulses. This paper also outlines a generalization of another method referred to as the improved Gaussian approximation (IGA). Numerical examples demonstrate the far greater accuracy of the generalized SIGA with respect to the SGA. The examples consider the IS-95 and square-root raised cosine (Sqrt-RC) pulses as well as uniform and nonuniform received power conditions View full abstract»

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  • An application of Markovian arrival process (MAP) to modeling superposed ATM cell streams

    Publication Year: 2002 , Page(s): 633 - 642
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (337 KB) |  | HTML iconHTML  

    First, we propose a new modeling method for superposed ATM traffic by the MMPP(2), which is a special case of the MAP(2). In this new method, we measure the mean and autocorrelation of cell interarrival times, and the histogram of the number of arrivals during measurement windows of fixed size. The MMPP(2) has interarrival times with a second-order hyper-exponential distribution with coefficient of variation cν > 1. However, superposed traffic is often observed to have cν < 1. To cover this situation, we extend the MMPP(2) to a MAP(3) by adding a new state with inter-state transition accompanied by an arrival. For the MAP(3) model, we take into account the second moment of the interarrival times. From numerical examples, we observe that both the proposed MMPP(2) and MAP(3) yields very good estimation of the cell loss ratio (CLR) for usual superpositions of voice and/or VBR video sources. However, when we have superpositions from CBR video sources together with other VBR sources, c ν. is much less than 1, and the MAP(3) outperform the MMPP(2), as expected. The proposed MAP(3) well characterizes the cell scale component as well as the burst scale component of superposed traffic streams 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