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Communications, IEEE Transactions on

Issue 2 • Date Feb 1993

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Displaying Results 1 - 22 of 22
  • Queueing analysis of buffered switching networks

    Page(s): 412 - 420
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    A method for analyzing the queueing behavior of switching networks constructed from switches that employ shared buffering or parallel bypass input buffering is presented. The queueing models introduced by Y.C. Jenq (1983) and generalized by T. Szymanski and S. Shaikh (1989) are extended to handle these classes of networks. The analysis explicitly models the state of an entire switch and infers information about the distribution of packets associated with particular inputs or outputs when needed. It is shown that the method can be extended to switching systems with input buffering, including systems supporting bypass queueing. Numerical comparisons of the different buffering techniques are included View full abstract»

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  • Optimal selection of Reed-Solomon code rate and the number of frequency slots in asynchronous FHSS-MA networks

    Page(s): 307 - 311
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    The performance of Reed-Solomon codes in an asynchronous frequency-hop spread-spectrum multiple-spectrum (FHSS-MA) network is discussed. When q denotes the number of frequency slots available to the network and r denotes the rate of the Reed-Solomon code, optimal (q,r) pairs that meet a given performance criterion with minimum bandwidth expansion (q/r) for a given number of active users are obtained. It is shown that the optimal code rate rapidly converges to a constant value and the optimum number of slots increases approximately linearly as the number of active users increases. This suggests that one should fix the code rate and increase the number of slots to accommodate the increasing number of users in the network under a given performance criterion with minimum bandwidth expansion View full abstract»

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  • LINC: a common theory of transform and subband coding

    Page(s): 266 - 274
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    A common theory of lapped orthogonal transforms (LOTs) and critically sampled filter banks, called L into N coding (LINC), is presented. The theory includes a unified analysis of both coding methods and identity relations between the transform, inverse transform, analysis filter bank, and synthesis filter bank. A design procedure for LINC analysis/synthesis systems, which satisfy the conditions for perfect reconstruction, is developed. The common LINC theory is used to define an ideal LINC system which is used, together with the power spectral density of the input signal, to calculate theoretical bounds for the coding gain. A generalized overlapping block transform (OBT) with time domain aliasing cancellation (TDAC) is used to approximate the ideal LINC. A generalization of the OBT includes multiple block overlap and additional windowing. A recursive design procedure for windows of arbitrary lengths is presented. The coding gain of the generalized OBT is higher than that of the Karhunen-Loeve transform (KLT) and close to the theoretical bounds for LINC. In the case of image coding, the generalized OBT reduces the blocking effects when compared with the DCT View full abstract»

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  • Bidirectional breadth-first algorithms for the decoding of convolutional codes

    Page(s): 370 - 380
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    Bidirectional multiple-path tree searching algorithms for the decoding of convolutional codes are presented. These suboptimal coding algorithms use a multiple-path breadth-first bidirectional tree exploration procedure and long-memory convolution codes. It is shown that, compared to the usual M-algorithm, the bidirectional exploration considerably reduces the bit error propagation due to correct path loss. Computer simulations using rate-1/2 codes over binary symmetric channels are used to analyze the effect of the number of path extensions, code memory, and frame length on the bit error probability. The results show that with a bit error probability of 10-5, coding gains on the order of 2 dB over the M-algorithm and 1 dB over a Viterbi decoder of equivalent complexity can be achieved View full abstract»

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  • Decision feedback sequence estimation for continuous phase modulation on a linear multipath channel

    Page(s): 280 - 284
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    An approach to reduced-complexity detection of partial response continuous phase modulation (CPM) on a linear multipath channel is presented. The method, referred to as decision feedback sequence estimation (DFSE), is based on a conventional Viterbi algorithm (VA) using a reduced-state trellis combined with decision feedback (DF). By varying the number of states in the VA, the receiver structure can be changed gradually from a DF receiver to the optimal maximum-likelihood sequence estimator (MLSE). In this way different tradeoffs between performance and complexity can be obtained. Results on the receiver performance, based on minimum distance calculations and bit error rate simulations, are given for Gaussian minimum-shift keying modulation on typical mobile radio channels. It is shown that for channels with a long memory, a significant complexity reduction can be achieved at the cost of a moderate degradation in performance View full abstract»

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  • Real-time traffic management by a parallel algorithm

    Page(s): 351 - 361
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1020 KB)  

    The joint access-control and routing problem for distributed networks is formulated as an equilibrium programming problem (EPP). The strategy, for an upcoming control period, decreases call blocking and balances network load by maximizing network residual capacity, and fairly rejects at the source the source-destination demands that are expected to exceed network capacity. The EPP formulation allows for both decentralized implementation of the joint access control and routing problem and massive parallelization of the optimization procedure to satisfy real-time requirements. The computational complexity of the algorithm decreases proportionally with the number of processors used. The convergence of the decentralized algorithm to the network-wide optimum is proved. Compared to the case where subnet EPPs are solved independently by each controller, simulation results show significantly better utilization of network resources when subnet controllers jointly solve the network-wide EPP. Performance analysis of the algorithm and numerical studies show that the algorithm is well suited for real-time implementation in large networks or internetworks View full abstract»

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  • Optimal channel allocation policies for access control of circuit-switched traffic in ISDN environments

    Page(s): 338 - 350
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1132 KB)  

    The problem of adaptively managing the transmission bandwidth of an integrated network by implemented optimal partitioning policies for the access control of circuit-switched traffic is studied. Precise formulations within an optimization framework of access control problems, both at an isolated multiplexer level and at the overall network level, are developed. For the simple case of a single multiplexer supporting traffic with identical bandwidth requirements, an iterative scheme with guaranteed fast convergence is presented for the determination of optimal channel allocations. For the more general scenario of a multiplexer supporting traffic with nonidentical bandwidth requirements, a methodology is developed to handle the access control problem by a mixed-integer programming formulation. This methodology is further extended to the network-wide access control scenario, and some implementational issues are discussed. A detailed quantitative evaluation of the proposed algorithm is conducted under different loading conditions, and the corresponding performance and efficiency are compared with those of other known procedures View full abstract»

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  • Design and analysis of multidimensional Manhattan street networks

    Page(s): 295 - 298
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    A class of doubly connected two-dimensional Manhattan street networks (MSN) is extended to a multidimensional MSN (MMSN) by a simple edge division operation. The topology is defined by three simple link equations. An approximate expression for the diameter is obtained and a simple routing scheme for three-dimensional MMSN is introduced. The proposed MMSN is shown to possess better performance parameters than the MSN topology View full abstract»

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  • Decorrelating decision-feedback multiuser detector for synchronous code-division multiple-access channel

    Page(s): 285 - 290
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    A decorrelating decision-feedback detector (DF) for synchronous code-division multiple-access (CDMA) that uses decisions of the stronger users when forming decisions for the weaker ones is described. The complexity of the DF is linear in the number of users, and it requires only one decision per user. It is shown that performance gains with respect to the linear decorrelating detector are more significant for relatively weak users and that the error probability of the weakest user approaches the single-user bound as interferers grow stronger. The error rate of the DF is compared to those of the decorrelator and the two-stage detector View full abstract»

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  • Symbol synchronization using signal samples and interpolation

    Page(s): 318 - 321
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    A method for symbol synchronization using two unsynchronized signal samples per symbol is presented. Signal values between the sample points are calculated by interpolation and then processed digitally to find a suitable strobe point. The interpolated value at the strobe point is used for data detection or input to an equalizer. Simulations show that low variance timing estimates can be made for pulses with raised-cosine spectra degraded by quadratic delay distortion View full abstract»

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  • A new approach to reduce the `blocking effect' of transform coding [image coding]

    Page(s): 299 - 302
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    A combined-transform coding (CTC) scheme to reduce the blocking effect of conventional block transform coding and hence to improve the subjective performance is presented. The scheme is described, and its information-theoretic properties are discussed. Computer simulation results for a chest X-ray image are presented. The CTC scheme, the JPEG baseline scheme, and the conventional discrete Walsh-Hadamard transform (DWHT) are compared to demonstrate the performance improvement for the CTC scheme. The advantages of the CTC scheme include no ringing effect as there is no error propagation across the boundary, no additional computation, and distortion always held within a certain level View full abstract»

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  • A soft decision-directed LMS algorithm for blind equalization

    Page(s): 275 - 279
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    An adaptation algorithm for equalizers operating on very distorted channels is presented. The algorithm is based on the idea of adjusting the equalizer tap gains to maximize the likelihood that the equalizer outputs would be generated by a mixture of two Gaussians with known means. The decision-directed least-mean-square algorithm is shown to be an approximation to maximizing the likelihood that the equalizer outputs come from such an independently and identically distributed source. The algorithm is developed in the context of a binary pulse-amplitude-modulation channel, and simulations demonstrate that the algorithm converges in channels for which the decision-directed LMS algorithms does not converge View full abstract»

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  • State-dependent routing on symmetric loss networks with trunk reservations. I

    Page(s): 400 - 411
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (892 KB)  

    The aggregated-least-busy-alternative (ALBA), a distributed, state-dependent, dynamic routing strategy for circuit-switched loss networks is discussed. The networks considered are symmetric and fully connected. The offered calls form Poisson streams, and routes have at most two links. In ALBA(K), the states of each link are lumped into K (K⩾2) aggregates, and the route of each call is determined by local information on the aggregate states of the links of the alternate routes at the time of the call's arrival. The last aggregate is always the set of states reserved for direct traffic. A fixed-point model for ALBA(K) for general K is presented. The particular case of ALBA in which there is no aggregation is least busy alternative (LBA); ALBA(2) represents the other extreme of aggregation. Simulation and analytic results for LBA are compared. An asymptotic scaling based on the fixed-point models is also discussed. It is shown that there is a dichotomy in network behavior: if the offered traffic is below a threshold, then the network loss probability decreases exponentially with increasing network size, and above the threshold, performance is poor View full abstract»

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  • Nonblocking multirate distribution networks

    Page(s): 362 - 369
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    Results for nonblocking distribution networks are generalized for the multirate environment in which different user connections share a switch's internal data paths for arbitrary fractions of the total capacity. Conditions under which network proposed by Y.P. Ofman (1965), C.D. Thompson (1978), and N. Pippenger (1973) lead to multirate distribution networks are derived. The results include both rearrangement and wide-sense nonblocking networks. The complexity of the rearrangement multirate network exceeds that of the corresponding space-division network by a log log factor, while the complexity of the wide-sense nonblocking network is within a factor of two of the corresponding space-division network View full abstract»

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  • Sequential sequence estimation for multiple-channel systems with intersymbol and interchannel interference

    Page(s): 322 - 331
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    A vector sequential sequence estimator is proposed for multiple-channel systems with both intersymbol interference (ISI) and interchannel interference (ICI). Both finite ISI-ICI and infinite ISI-ICI are considered. The estimator consists of a multiple-dimensional whitened matched filter and a vector sequential decoder. The metric of the sequential algorithm is derived, and the algorithm's performance is analyzed. Computer simulation results for a two-dimensional finite ISI-ICI channel and a two-dimensional infinite ISI-ICI channel are presented. Analysis and simulation show that the symbol error probability of the vector sequential algorithm is essentially the same as for maximum-likelihood sequence estimation using the vector Viterbi algorithm, while its average computational complexity is much less, although computation per symbol is a random variable with the Pareto distribution. There exists a signal-to-noise ratio above which the ensemble average computation is bounded. An upper bound on this ratio is found View full abstract»

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  • Block adaptive quantization of images

    Page(s): 303 - 306
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    Results on block adaptive quantization of images using the adaptive dynamic range coding (ADRC) method are presented. In this method, the minimum and maximum intensities for each block are determined, and the pixels in the block are quantized with a uniform quantizer covering this range. The minimum and maximum values are transformed to midpoint and range values and then quantized and coded for transmission as side information. In order to reduce the visibility of blocking effects, ADRC can be applied to a subband decomposition of the image. This extension is called SADRC. Experimental results are presented for ADRC applied to the original image, as well as for four-band SADRC View full abstract»

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  • Performance of the IEEE 802.2 type-2 logical link protocol with selective retransmission

    Page(s): 291 - 294
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    The effects on performance of adding the selective retransmission feature to the IEEE 802.2 type-2 logical link protocol are discussed. Simulation results indicate that selective retransmission significantly improves the performance in case of overload and performs as well as an enhancement that was suggested by W. Bux and D. Grillo (see ibid., vol.COM-33, p.1058-65, 1985) View full abstract»

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  • Computational complexity of sequential sequence estimation for intersymbol interference channels

    Page(s): 332 - 337
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    The computational complexity of a sequential algorithm (SA) developed for intersymbol interference (ISI) channels is analyzed. To determine the computational complexity, the finite-state machine that models the channel and white matched filter system, of which the SA is a part, is interpreted as a special convolutional encoder followed by a binary symbol to Q-ary symbol mapping. It follows that the computational distribution is Pareto, and that there exists a computational cutoff rate Rcomp. For the uncoded data considered, the rate is fixed and the Rcomp criterion translates into a signal-to-noise ratio (SNR) criterion. An upper bound on SNRcomp is found analytically by assuming a uniform input distribution. Iteration equations developed by S. Arimoto (1976) are adapted to find the true SNRcomp numerically View full abstract»

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  • Overview and performance of CCITT/ANSI embedded ADPCM algorithms

    Page(s): 391 - 399
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    Embedded adaptive differential pulse coded modulation (ADPCM) algorithms quantize the differences between the input signal and the estimated signal into core bits and enhancement bits. CCITT Recommendation G.727, which describes embedded ADPCM encoding algorithms with 5, 4, 3, and 2 core bits, is virtually identical to the corresponding ANSI standard T1.310. The main features of G.727 and T1.310 and performance results are presented. A formal subjective evaluation of the speech performance of embedded ADPCM algorithms indicates that a midrise quantizer provides better voice transmission performance than its midtread counterpart when two core bits are used. The subjective data also show that the performance of the 40-kb/s midrise ADPCM algorithm with two feedback bits is indistinguishable from that of 64-kb/s pulse code modulation (PCM) for up to four tandem encodings. Embedded algorithms are therefore recommended for flexible congestion control of integrated traffic in multinode networks View full abstract»

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  • Quantization loss in convolutional decoding

    Page(s): 261 - 265
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The loss in quantizing coded symbols in the additive white Gaussian noise (AWGN) channel with binary phase-shift keying (BPSK) or quadrature phase-shift keying (QPSK) modulation is discussed. A quantization scheme and branch metric calculation method are presented. For the uniformly quantized AWGN channel, cutoff rate is used to determine the step size and the smallest number of quantization bits needed for a given bit-signal-to-noise ratio (Eb/N0) loss. A nine-level quantizer is presented, along with 3-b branch metrics for a rate-1/2 code, which causes an Eb/N0 loss of only 0.14 dB. These results also apply to soft-decision decoding of block codes. A tight upper bound is derived for the range of path metrics in a Viterbi decoder. The calculations are verified by simulations of several convolutional codes, including the memory-14, rate-1/4 or -1/6 codes used by the big Viterbi decoders at JPL View full abstract»

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  • An improved time-slot assignment algorithm for TDM hierarchical switching systems

    Page(s): 312 - 317
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    It is shown that any hierarchical switching system can be modeled by a special class of flow networks called unit networks. Using the results available for finding maximum flow through a unit network, a time-slot assignment (TSA) algorithm that runs in O(min(L ,M2)×min(N, √MM2) time is presented. This is an O(max(M/N, √M)) improvement over the TSA algorithm proposed by M.A. Bonucelli (1989) View full abstract»

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  • Channel reassignment algorithm in multiple carrier hopping TDMA systems

    Page(s): 381 - 390
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    Channel reassignment schemes used in multiple carrier hopping time-division multiple access (MCH-TDMA) systems are described. In MCH-TDMA systems channels are identified by two degrees of freedom: carrier frequency and time slot. The overlap-chain concept in which related calls from the same transmitting station to the same receiving station are grouped into contiguous streams is introduced. Using this concept, one channel can always be assigned to a call blocked due to inefficient assignment by reassigning channels to calls in progress within two or three time slots. A channel reassignment algorithm called OVERLAP-CHAINING which provides efficient means to reassign channels to calls in progress is proposed 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