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Communications, IEEE Transactions on

Issue 3 • Date March 1999

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Displaying Results 1 - 21 of 21
  • Performance of slotted asynchronous CDMA using controlled time of arrival

    Publication Year: 1999 , Page(s): 454 - 463
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (501 KB)  

    A slotted asynchronous (SA) code-division multiple-access communication scheme controlling the time of arrival is proposed for distributed spread-spectrum packet radio networks where the transmission range is limited as in an indoor wireless system. In this scheme, each terminal can send its packet randomly at any one of N/sub w/, possible time instants, equally spaced over one period of direct-sequence spread-spectrum signals. Such transmissions initiated at different time instants can be resolved because of the high time resolution of wide-band signals if the channel delays associated with multipath are small due to limited transmission range. Quasi-synchronous distributed networks are considered to allow timing drift among terminals and also reflect wireless multiple-access channels, in which common-transmitter-based (C-T) and receiver-transmitter-based (R-T) spreading code assignments are adopted to permit a contention mode only for the header portion. The throughput is evaluated under the spread ALOHA assumption on collision events and also by reflecting the effect of the MAI in the header detection process. Theoretical results show that the combination of the SA scheme with C-T assignment results in more significant improvement than the case of R-T assignment, and also the former provides the benefit of the efficient usage of spreading codes in a code-limited environment. View full abstract»

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  • Abstracts of forthcoming manuscripts

    Publication Year: 1999 , Page(s): 476
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    Freely Available from IEEE
  • Extended Hamming and BCH soft decision decoders for mobile data applications

    Publication Year: 1999 , Page(s): 333 - 337
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (132 KB)  

    A methodology is presented for the design and development of efficient trellis-based soft decision decoders for extended Hamming and BCH codes. A new metric for noncoherent discriminator detection is proposed that substantially improves the performance of trellis-based decoders over additive white Gaussian noise (AWGN) channels. Minimal edge trellises are then presented for the class of extended Hamming codes and the (32, 21) extended BCH code. The latter is in extensive use in narrow-band wireless data systems. An automatic request (ARQ) protocol is described that allows the soft decision decoders to outperform their hard decision counterparts in both reliability and throughput View full abstract»

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  • Iterative maximum-likelihood trellis decoding for block codes

    Publication Year: 1999 , Page(s): 338 - 342
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    An iterative trellis search technique is described for the maximum-likelihood (ML) soft decision decoding of block codes. The proposed technique derives its motivation from the fact that a given block code may be a subcode for a parent code whose associated trellis has substantially fewer edges. Through the use of list-Viterbi (1967) decoding and an iterative algorithm, the proposed technique allows for the use of a trellis for the parent code in the ML decoding of the desired subcode. Complexity and performance analyses, as well as details of potential implementations, indicate a substantial reduction in decoding complexity for linear block codes of practical length while achieving ML or near-ML soft decision performance View full abstract»

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  • Interference suppression for DS/CDMA

    Publication Year: 1999 , Page(s): 446 - 453
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    A direct-sequence spread spectrum (DS/SS) receiver for suppressing multiple-access interference in direct-sequence code-division multiple-access (DS/CDMA) communication systems is introduced. The proposed receiver does not require knowledge of other users' spreading codes, timing, or phase information. Moreover, the receiver allows the number of taps to be chosen independently of the processing gain and, hence, is easily applicable to CDMA systems employing either a small or a large processing gain. Performance analysis, including average probability of error and signal-to-noise ratio, is provided, and results are presented for systems varying from lightly loaded (for example, eight user/255 chip) to heavily loaded (for example, 50 user/200 chip). Performance results indicate that the proposed receiver outperforms the linear correlation receiver and, in many cases, it does so by a considerable margin View full abstract»

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  • Equalization of digital radio channels with large multipath delay for cellular land mobile applications

    Publication Year: 1999 , Page(s): 348 - 351
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    A new maximum a posteriori (MAP) equalizer is proposed for digital radio links affected by large multipath delays. The “sparse” nature of the channel, where a few nonzero powerful taps are spaced by many negligible taps, is exploited to achieve a complexity proportional to the number of nonzero taps. When the channel is time-varying, an efficient nonlinear Kalman like channel estimator is employed to track only the nonzero taps View full abstract»

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  • Reliability performances of optical ATM switches based on different routing and buffering schemes

    Publication Year: 1999 , Page(s): 472 - 475
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB)  

    Reliability performances of seven equal-capacity optical asynchronous transfer mode switches based on different routing and buffering schemes are compared. Calculations are based on available reliability data for commercial components as well as expected life lengths for new components and systems. In general, for switching systems, the average downtime is required to be held below 3 min/year. However, our results indicate that the average downtime for the proposed configurations is much longer than requested, over ten times longer for the best case and over 1500 times longer for the worst case. Therefore, the multiplane structures (i.e., multiplying of the entire systems) have to be provided for the switching systems investigated here in order to satisfy reliability requirements View full abstract»

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  • Properties of the single-bit single-user MMSE receiver for DS-CDMA systems

    Publication Year: 1999 , Page(s): 416 - 425
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    The single-bit single-user minimum mean-squared error (MMSE) receiver for direct-sequence code-division multiple access systems is studied in great detail. It is shown that the MMSE receiver is near-far resistant and asymptotically optimum as the interference or noise disappear (i.e., in interference or noise dominated scenarios). It is experimentally shown that the popular Gaussian approximation of the error probability is reasonable for the MMSE receiver over a broad range of operating conditions-i.e., signal-to-noise ratios and interference situations-even though this may not be the case for the standard matched-filter receiver. The concept of dimension reduction is introduced to reduce the complexity of the adaptive part of the receiver and the optimum dimension reduction transform is derived. Unfortunately, the optimum transform is dependent on unknown side-information and is, therefore, of limited practical use. However, several practical schemes are proposed (one which is asymptotically optimum). The schemes are shown to outperform previously known methods View full abstract»

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  • Error probabilities of two-dimensional M-ary signaling in fading

    Publication Year: 1999 , Page(s): 352 - 355
    Cited by:  Papers (36)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    A new exact method for computing the average symbol error probability of two-dimensional M-ary signaling in slow fading is presented. The method is generally applicable to polygonal decision regions. The exact average symbol error rate of coherent 16-star-QAM is obtained and compared to that of 16-rectangular-QAM. New results for optimum ring ratios of 16-star-QAM in additive white Gaussian noise (AWGN) and in slow fading are also given View full abstract»

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  • Edge decision assisted decorrelators for asynchronous CDMA channels

    Publication Year: 1999 , Page(s): 438 - 445
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    Asynchronous decorrelating detector is a linear multiuser detector in code-division multiple-access (CDMA) environment. It has relatively good performance and low-computational complexity. However, the ideal asynchronous decorrelating detector requires the observation of the entire input bit sequence. Implementation of this ideal detector based on a long bit sequence results in long delays and high computational complexity. In fact, if the observed window does not cover the entire data sequence, the classical asynchronous decorrelating detector is no longer near-far resistant. In this paper, we propose a method using initial decisions on bits for both edges of the finite observed window. These initial decisions are used to assist subsequent decisions of the whole sequence inside the observed window based on the decorrelating method. This new edge decision assisted decorrelator (EDAD) method is shown to be near-far resistant View full abstract»

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  • Architecture for restorable call allocation and fast VP restoration in mesh ATM networks

    Publication Year: 1999 , Page(s): 397 - 403
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (84 KB)  

    This paper presents an architecture for restorable call allocation and fast virtual path (VP) restoration in mesh ATM networks. In this architecture, virtual working and spare capacities needed for call allocation and restoration are reserved and released dynamically on a call-by-call basis at the time of call admission and termination. This obviates the need for advance assignment of spare and working capacities. To shorten the call processing delay, this is done in a parallel-distributed fashion. To provide restorable call allocation, parallel-distributed call processing algorithms of sender-chooser type are suggested. The algorithms integrate, on the call level, virtual bandwidth allocation, virtual spare-capacity assignment, and fixed, alternate, or state-dependent routing. Each routing scheme leads to a particular tradeoff between call processing complexity, call setup delay, and bandwidth efficiency. For each pair of nodes, two sets of VPs are provisioned. The first, working VP (WVP) set, is used for call allocation during the normal operation. The second, spare VP (SVP) set, is used for WVP restoration in the event of failures of network elements. Each SVP protects a preassigned subset of the node pair's WVPs. Each SVP is selected to be link/node disjoint from the WVPs that it is assigned to protect. This assures a protection of the WVP set by a small number of SVPs. Since SVPs are preset and appropriate virtual spare capacities are reserved in advance, the architecture guarantees full restorability and provides very fast restoration. The restoration is done on the VP level in a self-healing manner. The suggested architecture requires only local information to be maintained at each node View full abstract»

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  • Super-resolution of pulsed multipath channels for delay spread characterization

    Publication Year: 1999 , Page(s): 343 - 347
    Cited by:  Papers (27)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB)  

    Frequency selective channels can be measured by either a continuous wave frequency sweep, which gives directly the transfer function, or by sounding the channel with pulses, which results in the impulse response. When the sounding pulse becomes a chirp-type waveform, the two approaches become similar. Simple rectangular pulses can be used for partial, but usually sufficient, channel characterization. In this paper, the process is described for resolving impulse response components into bins smaller than the duration of the sounding pulse and smaller than the reciprocal of the channel bandwidth. From such “super-resolution”, the delay spread of the propagation channel can be established accurately even when it is much less than the sounding pulse duration, allowing longer, higher energy pulses to be used for channel characterization. The process is demonstrated using subtractive deconvolution where a loop gain of unity is shown to be stable; and a modified inverse filter technique, in which the modification caters for the spectral zeros of the sounding pulse View full abstract»

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  • A robust receiver structure for time-varying, frequency-flat, Rayleigh fading channels

    Publication Year: 1999 , Page(s): 360 - 364
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    A receiver structure for unknown time-varying, frequency-flat, Rayleigh fading channels is proposed. Unlike the maximum-likelihood receiver structure, this receiver does not need any knowledge of the channel autocovariance or the received signal-to-noise ratio, and yet analytic and simulation results show, that its bit-error rate performance is close to the optimal structure. The receiver is applicable to signals with constant or approximately constant envelopes or to linearly modulated signals using Nyquist pulses View full abstract»

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  • Congestion measures in DS-CDMA networks

    Publication Year: 1999 , Page(s): 426 - 437
    Cited by:  Papers (33)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    We investigate the notion of “congestion” in spread spectrum wireless networks, such as those employing direct-sequence code-division multiple access. We find “congestion” to be multidimensional in nature, but two features emerge: (1) when congestion occurs, transmit powers and cell site interference levels increase and (2) capacity constraints are approached. Among other measures, we focus on a particular measure, λ, which is immediately of interest, since λ<1 is the condition for network feasibility. We relate λ both to the “power warfare” that arises as “capacity limits” are approached, and to the level of traffic in the network, where we consider traffic in regions ranging from local (single cells) to global (the whole network) View full abstract»

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  • Probability density functions for analyzing multi-amplitude constellations in Rayleigh and Ricean channels

    Publication Year: 1999 , Page(s): 380 - 386
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    This paper derives probability density functions (PDFs) to describe the behavior of data demodulated with imperfect channel estimation. The PDFs apply to cases of flat Rayleigh-fading, multiple-diversity reception Rayleigh-fading, and flat Ricean-fading. These PDFs can be used to determine analytically both the symbol error rate and bit error rate for multi-amplitude constellations with in-phase and quadrature components, thus avoiding the need for extensive computer simulation View full abstract»

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  • Multi-user performance of direct-sequence CDMA using combined binary PPM/orthogonal modulation

    Publication Year: 1999 , Page(s): 404 - 415
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    A new modulation format is proposed for cellular code-division multiple-access (CDMA) communications where binary pulse position modulation (PPM) is embedded in the chip waveform and combined with orthogonal modulation using Walsh/Hadamard codes. Compared to the conventional CDMA using orthogonal codes, this scheme allows reduction in receiver complexity by lowering the modulation level for the second-stage orthogonal modulation. The staggered (half-chip) quadrature direct-sequence signaling is adopted to uniformly distribute the transmit power and allow noncoherent detection at the receiver because carrier phase tracking is not feasible because of the binary PPM, suitable for the reverse link in cellular networks. Statistics of inter-user interferences are characterized, and then derive the symbol error probability for the proposed M-ary modulation format. It is shown that the advantage in view of receiver complexity can be achieved without deteriorating the multi-user performance in terms of the number of users affordable at a specified error rate View full abstract»

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  • Time-division versus superposition coded modulation schemes for unequal error protection

    Publication Year: 1999 , Page(s): 370 - 379
    Cited by:  Papers (17)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    This paper is concerned with the design problem of coded modulation schemes which provide unequal error protection (UEP) against Gaussian noise. Starting with the case of two bit streams, we consider two classes of UEP schemes: time-division coded modulation (TDCM) and superposition coded modulation (SCM). The early result of Bergmanns and Cover (1974) ensures the asymptotic superiority of SCM. However, accounting for the fact that practical channel codes do not achieve capacity, we show that the validity of this result depends on the prescribed degree of inequality in protection of the streams. To complement the straightforward design and use of TDCM schemes, we propose methods to decode and design SCM schemes. The design examples substantiate the conclusions obtained from performance analysis. We extend the results to the case of UEP of multiple (more than two) bit streams, where a hybrid of SCM and TDCM must also be considered. We show that, for a large range of unequal protection levels, the hybrid scheme outperforms both SCM and TDCM View full abstract»

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  • Analysis of new and existing methods of reducing intercarrier interference due to carrier frequency offset in OFDM

    Publication Year: 1999 , Page(s): 365 - 369
    Cited by:  Papers (230)  |  Patents (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    Orthogonal frequency division multiplexing (OFDM) is very sensitive to frequency errors caused by frequency differences between transmitter and receiver local oscillators. This sensitivity is analyzed in terms of the complex weighting coefficients which give the contribution of each transmitter subcarrier to each demodulated subcarrier. Previously described windowing and self intercarrier interference (ICI) cancellation methods are analyzed in terms of these weighting coefficients. New ICI cancellation schemes with very much improved performance are described. A condition for orthogonality of windowing schemes is derived in terms of the discrete Fourier transform (DFT) of the windowing function View full abstract»

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  • Performance of multiuser diversity reception in Rayleigh fading CDMA channels

    Publication Year: 1999 , Page(s): 356 - 359
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB)  

    Error probability of an adaptive multiuser diversity receiver is evaluated in terms of channel fading rate and the number of code-division multiple access users. Fading-induced performance loss, which leads to the error probability floor, is established for the proposed coherent combining scheme and compared to that of the differentially coherent receiver with equal-gain combining View full abstract»

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  • Blind adaptive signal reception for MC-CDMA systems in Rayleigh fading channels

    Publication Year: 1999 , Page(s): 464 - 471
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    We consider signal reception in multicarrier code-division multiple-access (MC-CDMA) systems. A blind adaptive algorithm is proposed to determine a weight vector which optimally combines the desired signal contributions from different carriers while suppressing noise and interference. No knowledge of the channel conditions (fading coefficients, signature sequences and timing of interferers, statistics of other noises, etc.) nor any training sequence is required. The performance is examined for Rayleigh fading channels. Results show that the proposed algorithm performs well and is robust to the near-far problem. Hence, the results show that MC-CDMA systems are attractive candidates for future CDMA systems View full abstract»

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  • Locally optimum Bayes detection in nonadditive first-order Markov noise

    Publication Year: 1999 , Page(s): 387 - 396
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    The purpose of this paper is to extend the recent formulation of locally optimum Bayes (LOB) detection in nonadditive non-Gaussian noise with independent sampling to the case where dependence between the noise samples is modeled via an ergodic first-order Markov discrete-time process. Moreover, unlike previous related work, numerical results are provided which are based on an empirically derived second-order transition density, the marginal PDF of which is Middleton's (1993) Class A noise, an experimentally verifiable and widely applicable non-Gaussian model. Canonical, in signal waveform and noise statistics, asymptotically and LOB detectors in both coherent and incoherent modes are derived and their statistics are computed under both “signal present” and “signal absent” hypotheses. Performance measures are thus obtained together with the correlation gain G(M.P.), which is used for systems comparison. Explicit forms for the transition density and and the nonlinearities involved, as well as numerical values of the noise indices, are calculated from a generalized observation model containing multiplicative and additive Markov noise components. It is shown that significant performance gains over the case with independent sampling can be achieved, depending upon the degree of correlation between the noise samples 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