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Communications, IEEE Transactions on

Issue 1 • Date Jan 1991

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Displaying Results 1 - 21 of 21
  • GMSK with limiter discriminator detection in satellite mobile channel

    Publication Year: 1991 , Page(s): 94 - 101
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    Formulas are derived to find the error probability of partial-response frequency-shift keying with limiter discriminator detection, with and without decision feedback, for a satellite-mobile channel. The special cases of a Gaussian channel and a land-mobile channel are discussed. The formulas are applied to Gaussian minimum shift keying, and the error probability is computed as a function of energy-to-noise ratio, Gaussian filter bandwidth, Doppler frequency, maximum Doppler frequency, the ratio of powers in the specular and diffuse signal components, and the time delay between specular diffuse components View full abstract»

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  • Comparative evaluations of randomized and dynamic routing strategies for circuit-switched networks

    Publication Year: 1991 , Page(s): 102 - 116
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1132 KB)  

    The performances of two classes of routing algorithms, randomized and deterministic, are evaluated and compared in terms of revenue generated and link failures. The randomized algorithm evaluated is dynamic alternate routing, and for the deterministic algorithm, attempts to carry a call are made in a specific precomputed order. The design of the routing sequences depends upon analytic approximations based on fixed-point equations to evaluate network performance and heuristics for the complicated problem of network revenue maximization. The control mechanism of trunk reservations is shown to play an important role in all cases. The performances of the algorithms were evaluated on a fully connected six-node network, the data for which were extracted from a realistic network. The design tools, time constants of various algorithms, and hybrid algorithms developed using the evaluation results are described View full abstract»

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  • Block division carrier slot setting for satellite SCPC systems

    Publication Year: 1991 , Page(s): 21 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    A carrier slot setting plan is proposed to reduce intermodulation (IM) effects for satellite single-channel-per-carrier (SCPC) systems. Carrier slots are divided into blocks and slight frequency gaps are set among blocks. This setting introduces frequency offset between the center frequencies of carrier slots and the center frequencies of the IM components. A method of deriving optimum division in order to derive the upper bound of improvement of the C/IM ratio in the worst channel is developed. The results show that the setting plan achieves significant improvement of IM effects at a cost of only slight bandwidth expansion, even in fully loaded SCPC systems View full abstract»

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  • Analysis of self-noise in a fourth-power clock regenerator

    Publication Year: 1991 , Page(s): 133 - 140
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    A method for computing the power spectra of the in-phase and quadrature components of self-noise in a fourth-power clock recovery scheme is presented. This method is shown to be effective if the symbol waveform is time-limited or can be so approximated. The method applies to baseband signaling schemes such as pulse-amplitude modulation and to modulated carrier schemes such as quadrature-amplitude modulation. Comparison is made with the squaring-type recovery technique using cosine rolloff Nyquist pulses on the binary-phase-shift-keyed mode, at several excess bandwidth factors (α). It is shown that when α is less than 0.4, the fourth-power circuit gives less time jitter than the squarer for a noiseless channel. The method for self-noise spectrum calculation is verified by computer simulation. A prefilter that completely eliminates time jitter in the fourth-power clock recovery circuit is described View full abstract»

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  • Performance study of an input queueing packet switch with two priority classes

    Publication Year: 1991 , Page(s): 117 - 126
    Cited by:  Papers (17)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    An N×N nonblocking packet switch with input queues and two priority classes that can be used to support traffic with different requirements is described. The switch operation is slotted and, at each time slot, fixed-size packets arrive at the inputs with distinct Bernoulli distributions for both the high- and low-priority classes. Two policies are discussed. In the first policy, packets of both priority classes are queued when waiting for service. In the second policy, only low-priority packets are queued, and high-priority packets not delivered at the first attempt are dropped from the system. Under both policies, high-priority packets prevail over low-priority packets at the inputs as well as the outputs. An approximate analysis that is based on independence assumptions and uses an equivalent queueing system to estimate the service capability seen be each input is presented. Using this approach, an expression for the input queue length distribution is obtained. The maximum system throughput is derived and shown to exceed that of a single priority switch. Numerical results are compared to simulations and are found to agree View full abstract»

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  • Distributed scheduling of CDMA networks with minimal information

    Publication Year: 1991 , Page(s): 17 - 20
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    An algorithm which produces conflict-free communication schedules in mobility multihop radio networks is presented. These schedules are produced in a completely distributed manner. The algorithm is based on a globally known permutation on the nodes of the network. As a result the only knowledge needed on the part of individual nodes is the number of nodes in the network. This permutation guarantees that conflict-free schedules can be produced in a distributed manner. Two extensions to the basic permutation are discussed. The first enables neighboring nodes to enhance their communication schedules in a fast, robust, distributed manner. The second extension allows the algorithm to operate in the presence of secondary conflicts View full abstract»

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  • Uniform distance and error probability properties of TCM schemes

    Publication Year: 1991 , Page(s): 41 - 53
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    The class of uniform trellis-coded modulation (TCM) techniques is defined, and simple explicit conditions for uniformity are derived. Uniformity is shown to depend on the metric properties of the two subconstellations resulting from the first step in set partitioning, as well as on the assignment of binary labels to channel symbols. The uniform distance property and uniform error property, which are both derived from uniformity but are not equivalent, are discussed. The derived concepts are extended to encompass transmission over a (not necessarily Gaussian) memoryless channel in which the metric used for detection may not be maximum likelihood. An appropriate distance measure is defined that generalizes the Euclidean distance. It is proved that uniformity of a TCM scheme can also be defined under this new distance. The results obtained are shown to hold for channels with phase offset or independent, amplitude-only fading. Examples are included to illustrate the applicability of the results View full abstract»

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  • A metropolitan area radio system using scanning pencil beams

    Publication Year: 1991 , Page(s): 141 - 151
    Cited by:  Papers (7)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    A metropolitan-area radio system that, from a centrally located base station, provides continuously 360° coverage over a large service region is proposed. The base station blankets the service region with a raster of very narrow pencil beams that can be rapidly scanned to any position in synchronism with the switching sequences of a time-division-multiple-access (TDMA) assignment. By deploying multiple scanning spot beams, the allocated spectrum can be reused many times. A centralized network controller, executing an efficient TDMA assignment algorithm, dynamically allocates the resources of a small transceiver pool among the far larger number of beam positions in response to real-time requests for service. By varying the dwell time at each beam position in response to the traffic intensity of the position, highly efficient resource utilization is provided. The high antenna gain of the base station antenna provides adequate arain fade margin to permit operation in the uncongested portion of the ratio spectrum above 20 GHz. The system is particularly well suited to emerging, direct-to-end-user wideband digital service offerings View full abstract»

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  • A new method for phase synchronization and automatic gain control of linearly modulated signals on frequency-flat fading channels

    Publication Year: 1991 , Page(s): 25 - 29
    Cited by:  Papers (54)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    An optimal phase synchronization and automatic gain control (AGC) scheme for coherent reception of linearly modulated signals on frequency-flat mobile fading channels is presented. The channel model and receiver performance are described. It is shown that using the technique allows the irreducible error floors (due to random FM) known from the noncoherent methods to be practically eliminated. Depending on the fastness of the fading, large power gains over the noncoherent methods are achieved. Unfavorable analog signal processing and/or the high bandwidth inefficiency of the FDM-pilot coherent methods are also avoided View full abstract»

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  • Constrained-storage quantization of multiple vector sources by codebook sharing

    Publication Year: 1991 , Page(s): 11 - 13
    Cited by:  Papers (28)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    A codebook sharing technique, called constrained storage vector quantization (CSVQ), is introduced. This technique offers a convenient and optimal way of trading off performance against storage. The technique can be used in conjunction with tree-structured vector quantization (VQ) and other structured VQ techniques that alleviate the search complexity obstacle. The effectiveness of CSVQ is illustrated for coding transform coefficients of audio signals with multistage VQ View full abstract»

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  • The expectation-maximization algorithm for symbol unsynchronized sequence detection

    Publication Year: 1991 , Page(s): 54 - 61
    Cited by:  Papers (47)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    The expectation-maximization (EM) algorithm for maximizing likelihood functions, combined with the Viterbi algorithm, is applied to the problem of sequence detection when symbol timing information is not present. Although the EM algorithm is noncausal, results obtained using the algorithm on the problem of nonsynchronized sequence detection indicate that it converges most of the time in three iterations, making it both of theoretical and of practical interest. A practical algorithm based on the EM algorithm is introduced. It reduces the computational burden and improves performance by making use of timing estimates in previous observation windows View full abstract»

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  • A semiclassical analysis of optical code division multiple access

    Publication Year: 1991 , Page(s): 85 - 93
    Cited by:  Papers (30)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (956 KB)  

    A model noncoherent, optical, asynchronous, CDMA system is described. The error rate for a single-user matched-filter receiver that is valid for arbitrary photomultipliers and signature sequence sets, adheres to the semiclassical model of light, and does not depend on approximations for large user groups, strong received optical fields, or chip synchronism is analyzed. The exact minimum probability of error and optimal threshold are compared to those obtained with user-synchronism and multiple-access interference (MAI) distribution approximations. For the special case of unity-gain photodetectors and prime sequences, it is shown that the approximation of chip synchronism yields a weak upper bound on the exact error rate. It is demonstrated that the approximations of perfect optical-to-electrical conversion and Gaussian-distributed MAI yield a poor approximation to the minimum error rate and an underestimate of the optimal threshold. Arbitrarily tight bounds are developed on the error rate for unequal energies per bit. In the case when the signal energies coincide, these bounding expressions are considerably easier to compute than the exact error rate View full abstract»

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  • An improvement of dynamic Huffman coding with a simple repetition finder

    Publication Year: 1991 , Page(s): 8 - 10
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    A mixed-mode file compression scheme that incorporates interval encoding for finding duplicate occurrences of strings without storing or parsing the past sequence and a one-pass scheme for dynamic Huffman codes is presented. Results from experiments performed on various types of files are discussed. The proposed method runs in linear time, and the memory requirement depends only on the alphabet size. The code efficiency is compared experimentally to that of other schemes View full abstract»

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  • A buffered two-node packet radio network with product form solution

    Publication Year: 1991 , Page(s): 62 - 75
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1068 KB)  

    A packet radio network with two nodes, both of which access a single radio channel using the slotted ALOHA protocol, is discussed. This model results in a network of two interfering queues. Networks of interfering nodes normally do not have partial balance and thus seldom have product-form solution (PFSs). However, when certain assumptions are made on the network parameters, PFS-controls can be found that yield a PFS for the interfering two-node network. Three such cases are described. In the first two cases, PFS controls are found that control the new packet arrival rate. When operating under these PFS controls, the two-mode network has a simple, closed-form solution of the equilibrium probabilities, the expected throughput, and the expected packet delay. The throughput-delay performance closely approximates that of an exact two-node packet radio model. In the third case, a PFS control is found on one node's transmission probabilities. When operating under this PFS control, the transmission probabilities approach asymptotic values as the packet backlog increases. The network tends to adjust its transmission probabilities to reduce large unequal packet backlogs View full abstract»

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  • Generalization of the ECCS method to the multihour case

    Publication Year: 1991 , Page(s): 76 - 84
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    The classical ECCS method for dimensioning hierarchical telephone networks is extended to the multihour case. The problem is reformulated as a nonlinear optimization method, and the Kuhn-Tucker equations are derived. It is shown why the ECCS method cannot solve this multihour case. The ECCS method is presented as a solution technique for the Lagrangian relaxation of the multihour problem in which subgradient techniques are used for the solution of the dual. A numerical algorithm implementing these ideas is described that can handle networks with arbitrary hierarchies and allows time-of-day routing changes. Preliminary numerical results of the method are presented, showing that the multihour algorithm can reduce a network's cost when compared to currently used methods View full abstract»

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  • Symbol synchronization using baud-rate sampling and data-sequence-dependent signal processing

    Publication Year: 1991 , Page(s): 127 - 132
    Cited by:  Papers (6)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    An algorithm for symbol timing recovery using baud-rate sampling is presented. Using this algorithm, the decoded data sequence is scanned for particular data patterns that yield samples which need only to be added or subtracted to give an estimate of the required timing function. The statistics of occurrence of these data patterns are calculated for random binary data. The variance of the timing function estimates is calculated for pulses with raised-cosine spectra that have been degraded by quadratic delay distortion and is shown to be lower, in most cases, than for other synchronizers using baud-rate sampling View full abstract»

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  • A convolutional single-parity-check concatenated coding scheme for high-data-rate applications

    Publication Year: 1991 , Page(s): 4 - 7
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    The coding scheme uses a set of n convolutional codes multiplexed into an inner code and a (n,n-1) single-parity-check code serving as the outer code. Each of the inner convolutional codes is decoded independently, with maximum-likelihood decoding being achieved using n parallel implementations of the Viterbi algorithm. The Viterbi decoding is followed by additional outer soft-decision single-parity-check decoding. Considering n=12 and the set of short constraint length K=3, rate 1/2 convolutional codes, it is shown that the performance of the concatenated scheme is comparable to the performance of the constraint length K=7, rate 1/2 convolutional code with standard soft-decision Viterbi decoding. Simulation results are presented for the K=3, rate 1/2 as well as for the punctured K=3, rate 2/3 and rate 3/4 inner convolutional codes. The performance of the proposed concatenated scheme using a set of K=7, rate 1/2 inner convolutional codes is given View full abstract»

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  • Two classes of convolutional codes over GF(q) for q -ary orthogonal signaling

    Publication Year: 1991 , Page(s): 30 - 40
    Cited by:  Papers (21)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    Two classes of nonbinary convolutional codes for error control in communication systems employing q-ary orthogonal signaling are discussed. These classes include as special cases, the dual-k codes and the codes treated by B.D. Trumpis (1975). The types of code, extensions of previous bounds on free distance, the noncatastrophic condition for these codes, and conditions for catastrophic error propagation are described. Codes obtained by a computer search, optimal in that the truncated transfer function bound on the probability of symbol error is minimized, are presented. It is shown how good convolutional codes can be constructed from cyclic block codes. The performance of some of these codes over additive white Gaussian noise channels, Rayleigh channels, and partial-band interference channels is also discussed View full abstract»

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  • A new interpretation of the average matched filter for MSK-type receivers

    Publication Year: 1991 , Page(s): 14 - 16
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    The minimum-mean-square-error approximation to a generalized minimum-shift-keying (MSK) signal using an offset quadrature phase-shift keying waveform with an elementary pulse, g(t), is considered. It is shown that the optimum shape of G(t), γ(t), coincides with the average pulse of the generalized MSK signal. Therefore, γ(-t) is the impulse response of the corresponding average matched fiber View full abstract»

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  • An experimental TDMA indoor radio communications system using slow frequency hopping and coding

    Publication Year: 1991 , Page(s): 152 - 162
    Cited by:  Papers (17)  |  Patents (68)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1124 KB)  

    The general principles, implementation, and performance of a 1-Mb/s time-division-multiple-access (TDMA), slow frequency hopping and coding, 1.5-GHz radio communications system for a medium-sized office building are discussed. TDMA is provided for service flexibility and slow frequency hopping and coding for immunity against multipath fading and interference. Measurements show that, with a hallway-mounted distributed antenna system installed on one floor of the building and with the mobile unit transmitting only 1 mW of peak RF power from anywhere on that floor, only a single 384-b frame out of a total of 200000 transmitted frames suffered an unrecoverable error. This kind of performance is comparable to that of wired data modems. Similar performance was obtained from a central antenna covering the same floor. However, the required transmitted power in this case was 100 mW. Implementation issues, such as spectrum allocation, cellular subdivisions, and spectrum efficiency, are also discussed View full abstract»

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  • An effective simplifying scheme for Viterbi decoder

    Publication Year: 1991 , Page(s): 1 - 3
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    A Viterbi decoding algorithm with a scarce-state transition-type circuit configuration, namely the probability selecting states (PSS) mode decoder, is presented. The algorithm has reduced complexity compared to a conventional Viterbi decoder. It is shown that this method has three advantages over the general Viterbi algorithm: it is suitable to the quick look-in code, it applies the optimum decoding in a PSS-type decoder, and it makes full use of the likelihood concentration property. The bit-error-rate (BER) performance of a r=1/2, k=7 (147,135) code and PSS-type Viterbi decoder approximates the optimum performance of the standard Viterbi decoder and reduces the hardware of the conventional Viterbi decoder to about half 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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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia