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Communications, IEEE Transactions on

Issue 12 • Date Dec. 1998

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Displaying Results 1 - 24 of 24
  • List of reviewers

    Page(s): 1701 - 1705
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    Freely Available from IEEE
  • Author index

    Page(s): 1 - 7
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    Freely Available from IEEE
  • Subject index

    Page(s): 7 - 32
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    Freely Available from IEEE
  • System capacity of F-TDMA cellular systems

    Page(s): 1649 - 1661
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    We study the system capacity of cellular systems with time-division multiple access, slow time-frequency hopping (F-TDMA), and conventional single-user processing at the receivers. System capacity is formally defined as the maximum of the product of the number of users per cell times the user spectral efficiency for a given maximum outage probability. We adopt an information-theoretic definition of outage as the event that the mutual information of the block-interference channel resulting from a finite number of signal bursts spanned by the transmission of a user code word falls below the actual code rate, because of fading, shadowing, and interference. Starting from this definition, we develop a general framework which naturally takes into account many different aspects of F-TDMA cellular systems like channel reuse, channel utilization, waveform design, time-frequency hopping, voice activity exploitation, handoff, and power control strategies. Most importantly, our analysis does not rely on the choice of a particular coding scheme and can be applied to a very large class of systems in order to find guidelines for capacity-maximizing system design. A numerical example based on a typical urban mobile environment shows that there is a considerable capacity gap between actual F-TDMA systems and the limits predicted by our analysis. However, this gap can be filled by carefully designed (practical) systems, which make use of conventional single-user processing and simple coded modulation schemes View full abstract»

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  • Spatial distribution of traffic density in ALOHA with capture

    Page(s): 1669 - 1674
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    We demonstrate how to calculate the packet traffic density as a function of distance from a central receiver in an ALOHA network with capture parameter α>1. Given a general function for the desired throughput density inside a circle of radius ρ and boundary conditions, the packet traffic density is derived at all radii less than ρ. The packet traffic density is first obtained in an annulus between radii ρ and ρ/α, and then is found in each of a number of successive inner annuli in terms of the solution in the adjacent outer annulus. Applications of this method are illustrated for a few throughput densities, boundary conditions, and capture parameters. Restriction of a class of throughput densities to a region of radius ρ is shown to be necessary in order to obtain a finite packet traffic density, and an upper bound on ρ is found in this case View full abstract»

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  • Optimal and suboptimal symbol-by-symbol demodulation of continuous phase modulated signals

    Page(s): 1662 - 1668
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    In applications requiring soft-decision metrics, e.g., systems with interleaved coded modulation, symbol-by-symbol detection is preferred to sequence detection. This paper develops the optimum soft-output algorithm (OSA) for the demodulation of continuous phase modulated (CPM) signals. Since this optimum detector is computationally complex, a class of suboptimum symbol-by-symbol detectors, called the reduced state soft-output algorithm (RS-SOA) is developed. By varying certain parameters, the RS-SOA offers an effective tradeoff between performance and complexity, as measured by arithmetic operation count and the number of integrators required. Additionally, some simple complexity reduction schemes can be used in conjunction with the OSA and the RS-SOA. The properties of the OSA and the RS-SOA, and the various complexity reduction schemes are explored in an extensive simulation study View full abstract»

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  • Error-trellises for convolutional codes .I. Construction

    Page(s): 1592 - 1601
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    An error-trellis is a directed graph that represents all the sequences belonging to the coset which contains the symbol-by-symbol detected version of a given received sequence. A modular construction of error-trellises for an (n,k) convolutional code over GF(q) is presented. The trellis is designed on the basis of partitioning the scalar check matrix of the code into submatrices of l rows, accompanied with a corresponding segmentation of the syndrome. The value of the design parameter l is an essentially unconstrained multiple of n-k. For all the cosets of the code, the sections of the error-trellis are drawn from a collection of only ql modules; the module for each section is determined by the value of the associated syndrome segment. In case the construction is based on a basic polynomial check matrix, either canonical or noncanonical, then the error-trellis is minimal in the sense that σ⩽μ, where σ is the dimension of the state space of the trellis and μ is the constraint length of a canonical generator matrix for the code. For basic check matrices with delay-free columns, the inequality reduces to σ=μ View full abstract»

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  • Timing recovery in high bit-rate transmission systems over copper pairs

    Page(s): 1583 - 1586
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    This letter proposes a timing recovery scheme for transmission systems with baud-rate sampling allowing the use of an all digital phase-locked loop. The impact of the numerically controlled oscillator on the attainable signal-to-noise ratio and jitter under conditions of the European Telecommunications Standardization Institute (ETSI) HDSL standard is discussed View full abstract»

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  • Bounds on the pairwise error probability of coded DS/SSMA communication systems in Rayleigh fading channels

    Page(s): 1685 - 1692
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    Arbitrarily tight upper and lower bounds on the pairwise error probability (PEP) of a trellis-coded or convolutional-coded direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system over a Rayleigh fading channel are derived. A new set of probability density functions (PDFs) and cumulative distribution functions (CDFs) of the multiple-access interference (MAI) statistic is derived, and a modified bounding technique is proposed to obtain the bounds. The upper bounds and lower bounds together specify the accuracy of the resulting estimation of the PEP, and give an indication of the system error performance. Several suboptimum decoding schemes are proposed and their performances are compared to that of the optimum decoding scheme by the average pairwise error probability (APEP) values. The approach can be used to accurately study the multiple-access capability of the coded DS/SSMA system without numerical integrations View full abstract»

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  • Peak power and bandwidth efficient linear modulation

    Page(s): 1639 - 1648
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    In portable wireless communication systems, power consumption is of major concern. Traditional modulation and coding schemes have been designed from the standpoint of minimizing average power. However, for linear power amplifiers needed for spectrally efficient modulation formats, amplifier efficiency and hence power consumption are determined by the peak power of the transmitted signal. This paper looks into modulation formats which minimize peak power and retain high spectral efficiency. Peak power is broken into a sum (in terms of decibels) of average power and a peak-to-average power ratio, and a variety of modulation formats are evaluated in terms of peak power efficiency in both a Gaussian noise and Rayleigh fading channel. A generalized phase shift keying (PSK) modulation format is developed and shown to offer superior peak power efficiency relative to that of commonly used linear modulation formats. Two schemes are presented for reducing the peak-to-average power ratio of various modulation formats. First, data translation codes are used to avoid data sequences which cause large peaks in the transmitted signal. This approach was found to be most productive in quadrature amplitude modulation (QAM) formats. Finally, an adaptive peak suppression algorithm is presented which further reduces the peak-to-average power ratios of the PSK and generalized PSK formats. The peak suppression algorithm is also applicable to π/4-QPSK and was found to improve peak power efficiency of that format by about 1.25 dB over a Rayleigh fading channel View full abstract»

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  • Maximum-likelihood diversity combining in partial-band noise

    Page(s): 1569 - 1574
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    Maximum-likelihood diversity combining is investigated for an FFH/MFSK spread spectrum system in partial-band noise (PBN). The structure of maximum-likelihood diversity reception in PBN plus white Gaussian noise is derived. It is shown that signal-to-noise ratio and the noise variance at each hop have to be known to implement this optimum diversity combiner. Several suboptimum diversity combining schemes are also considered. The performance of the optimum combining scheme is evaluated. It is shown that adaptive gain control diversity combining actually achieves the optimum performance when interference is not very weak View full abstract»

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  • Complex scaled tangent rotations (CSTAR) for fast space-time adaptive equalization of wireless TDMA

    Page(s): 1587 - 1591
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    A new update algorithm for space-time equalization of wireless time-division multiple access signals is presented. The method is based on a modified QR factorization that reduces the computational complexity of the traditional QR-decomposition based recursive least squares method and maintains numerical stability. Square roots operations are avoided due to the use of an approximately orthogonal transformation, defined complex scaled tangent rotation View full abstract»

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  • Iterative multiuser detection for CDMA with FEC: near-single-user performance

    Page(s): 1693 - 1699
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    This paper introduces an iterative multiuser receiver for direct sequence code-division multiple access (DS-CDMA) with forward error control (FEC) coding. The receiver is derived from the maximum a posteriori (MAP) criterion for the joint received signal, but uses only single-user decoders. Iterations of the system are used to improve performance, with dramatic effects. Single-user turbo code decoders are utilized as the FEC system and a complexity study is presented. Simulation results show that the performance approaches single-user performance even for moderate signal-to-noise ratios View full abstract»

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  • Pilot symbol assisted BPSK on Rayleigh fading channels with diversity: performance analysis and parameter optimization

    Page(s): 1560 - 1563
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    The loss due to imperfect channel estimation is derived for pilot symbol assisted binary phase-shift keying (BPSK) on fading channels with diversity. The presented approach, which holds for both narrow-band and spread spectrum communication, further provides an analytical optimization of pilot symbol spacing. The loss due to channel estimation is demonstrated to be low if the maximum Doppler frequency is significantly less than the bit rate View full abstract»

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  • Concatenated coding performance for FSK modulation on time-correlated Rician fading channels

    Page(s): 1610 - 1618
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    We present an analytical method for evaluating the performance of noninterleaved concatenated codes over channels modeled as a nonfrequency selective correlated Rician fading channel with a known power spectral density. The main idea is to model the communication system from the modulator input to the demodulator output as a finite state channel (FSC) model, and apply powerful enumeration techniques to such a discrete channel in order to gain useful information on the system performance. The concatenated scheme makes use of two codes; Reed-Solomon codes are employed for the outer code, and binary block codes are used as the inner code. Next, the method is extended to study the effect on the performance when an interleaving with finite depth is incorporated into the communication system. A comparison between symbol and bit interleaving is made. Finally, we study the potential gain produced when channel information is passed on to the outer decoder in the form of an erasure symbol. In all cases, analytical expressions for the probability of the number of error symbols produced by the FSC model were obtained in terms of a coefficient in a formal power series. This is an interesting alternative approach with respect to computer simulations View full abstract»

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  • Adaptive threshold control scheme for packet acquisition

    Page(s): 1580 - 1582
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    An adaptive threshold control scheme for packet acquisition is described. The threshold control is done adaptively by setting the threshold proportional to the maximum likelihood estimate of the noise power View full abstract»

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  • Noncoherent decorrelative detection for nonorthogonal multipulse modulation over the multiuser Gaussian channel

    Page(s): 1675 - 1684
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    This paper introduces the problem of noncoherent detection for nonorthogonal multipulse modulation in the context of the synchronous multiuser Gaussian channel. Each user sends an M-ary information symbol by transmitting one of M possibly nonorthogonal waveforms. Furthermore, the M signals of one user are allowed to be correlated with the signals of all other users. A key idea proposed here is that of a noncoherent decorrelative receiver front end. Like its counterpart in single-pulse modulation, this front end eliminates multiuser interference. It therefore reduces the multiuser detection problem into decoupled single-user problems over equivalent noise-enhanced single-user channels. Each equivalent single-user channel is rather general and can be described as one where the waveforms employed are not only correlated, but are also of unequal energies. Several new results pertaining to the design and analysis of optimum and suboptimum noncoherent detectors for this single-user channel are obtained. In the multiuser channel, these detectors constitute the post-decorrelative processing units for each user View full abstract»

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  • On Viterbi detector path metric differences

    Page(s): 1549 - 1554
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    This letter continues the investigation of methods for computing exact bounds on the path metric differences in maximum-likelihood sequence detectors based upon the Viterbi algorithm. New upper and lower estimates for these bounds are presented and recast in terms of a collection of linear programming problems. These estimates improve upon previously proposed linear programming bounds. The estimates are applied to derive exact bounds or provably close to exact bounds for several Viterbi detectors corresponding to coded and uncoded partial-response channels of practical interest in digital magnetic and optical recording View full abstract»

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  • Closed-form expressions on the geometric tail behavior of statistical multiplexers with heterogeneous traffic

    Page(s): 1575 - 1579
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    We consider a statistical multiplexer fed by heterogeneous on and off sources. We provide closed-form results on the tail behavior of the queue-length distribution for statistical multiplexers, where the tail behavior can be expressed in terms of traffic parameters such as the first and second moments of on and off periods for individual sources. Since our results are of simple closed-form, they can be used to provide a simple and efficient way to predict the tail behavior and the impact of traffic parameters on performance View full abstract»

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  • Low-complexity indexing method for Zn and Dn lattice quantizers

    Page(s): 1602 - 1609
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    Code vector indexing is a key problem in lattice quantization applications. In order to solve this problem, we propose a method based on the idea of a coding table encompassing a set of points as small as possible. Our method works for both spherical and pyramidal code books. It provides a good tradeoff between computational complexity and storage requirements View full abstract»

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  • Modeling of code acquisition process in CDMA networks-quasi-synchronous systems

    Page(s): 1564 - 1568
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    We present a model of serial code acquisition process in code-division multiple-access networks. The difference between this model and the existing work is in using the assumption that in each cell of delay uncertainty region the probability of false alarm, is different. This is caused by the fact that in each cell cross correlations between the local code and the codes used by the other users in the network are different. A closed-form expression for the average acquisition time is derived and discussed View full abstract»

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  • A unified approach to the probability of error for noncoherent and differentially coherent modulations over generalized fading channels

    Page(s): 1625 - 1638
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    We present a unified approach to determine the exact bit error rate (BER) of noncoherent and differentially coherent modulations with single and multichannel reception over additive white Gaussian noise and generalized fading channels. The multichannel reception results assume independent fading in the channels and are applicable to systems that employ post-detection equal gain combining. Our approach relies on an alternate form of the Marcum Q-function and leads to expressions of the BER involving a single finite-range integral which can be readily evaluated numerically. Aside from unifying the past results, the new approach also allows for a more general solution to the problem in that it includes many situations that in the past defied a simple solution. The best example of this occurs for multichannel reception where the fading on each channel need not be identically distributed nor even distributed according to the same family of distributions View full abstract»

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  • Error protection for progressive image transmission over memoryless and fading channels

    Page(s): 1555 - 1559
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    Product channel codes are proposed to protect progressively compressed and packetized images for noisy channels. Within packets, the product code uses the concatenation of a rate-compatible punctured convolutional code and an error detecting parity check code. Across packets, Reed-Solomon codes are used. Benefits include flexible choice of delay, adaptability of error protection level (i.e., unequal error protection), and scalable decoding complexity. The system outperforms the best known image coders for memoryless channels and performs well on fading channels View full abstract»

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  • Upper bounds on the bit-error rate of optimum combining in wireless systems

    Page(s): 1619 - 1624
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    This paper presents upper bounds on the bit-error rate (BER) of optimum combining in wireless systems with multiple cochannel interferers in a Rayleigh fading environment. We present closed-form expressions for the upper bound on the bit-error rate with optimum combining, for any number of antennas and interferers, with coherent detection of BPSK and QAM signals, and differential detection of DPSK. We also present bounds on the performance gain of optimum combining over maximal ratio combining. These bounds are asymptotically tight with decreasing BER, and results show that the asymptotic gain is within 2 dB of the gain as determined by computer simulation for a variety of cases at a 10-3 BER. The closed-form expressions for the bound permit rapid calculation of the improvement with optimum combining for any number of interferers and antennas, as compared with the CPU hours previously required by Monte Carlo simulation. Thus these bounds allow calculation of the performance of optimum combining under a variety of conditions where it was not possible previously, including analysis of the outage probability with shadow fading and the combined effect of adaptive arrays and dynamic channel assignment in mobile radio systems 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