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Communications, IEEE Transactions on

Issue 4 • Date Apr 1990

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Displaying Results 1 - 22 of 22
  • Directional signal modulation by means of switched spaced antennas

    Publication Year: 1990 , Page(s): 399 - 403
    Cited by:  Papers (11)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    The theory of modulation by hopping or by commutation among a number of spaced antennas is presented. The theory brings out the important considerations and criteria for determining the separation of discrete antennas in time and/or space that produces a desired modulation. In addition, antenna hopping and commutation are proposed for generating direction-dependent spread spectrum to enhance receiving system anti-interference processing gain and/or transmitted signal camouflage and LPI, as well as to provide an effective means for channel monitoring and analytical probing View full abstract»

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  • Multichannel signal processing for data communications in the presence of crosstalk

    Publication Year: 1990 , Page(s): 551 - 558
    Cited by:  Papers (35)  |  Patents (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    Transceiver designs for multiple coupled channels typically treat the crosstalk between adjacent twisted pairs as random noise uncorrelated with the transmitted signal. The authors propose a transmitter/receiver pair that compensates for crosstalk by treating an entire bundle of twisted pairs as a single multi-input/multi-output channel with a (slowly varying) matrix transfer function. The proposed transceiver uses multichannel adaptive FIR filters to cancel near- and far-end crosstalk, and to pre- and postprocess the input/output of the channel. Linear pre- and postprocessors that minimize mean squared error between the received and transmitted signal in the presence of both near- and far-end crosstalk are derived. The performance of an adaptive near-end crosstalk canceller using the stochastic gradient (least-mean-square) transversal algorithm is illustrated by numerical simulation. Plots of mean squared error versus time and eye diagrams are presented, assuming a standard transmission line model for the channel. A signal design algorithm that maps a vector input bit stream to a stream of channel symbol vectors is also presented and illustrated explicitly for s simple model of two coupled channels View full abstract»

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  • Double-loop sigma-delta modulation with DC input

    Publication Year: 1990 , Page(s): 487 - 495
    Cited by:  Papers (41)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    A discrete-time model having a two-bit (2-b) quantizer is analyzed exactly, and an analytical expression for the quantizer noise sequence is found. Rigorous answers are then provided to two fundamental questions for a double-loop sigma-delta modulation system with DC input: (1) What is the long-term statistical behavior of the internal quantizer noise? (2) How does the asymptotic mean square sigma-delta quantization error vary as a function of the oversampling ratio? View full abstract»

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  • Bipartite graph design principle for photonic switching systems

    Publication Year: 1990 , Page(s): 529 - 538
    Cited by:  Papers (36)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    Several attributes of a bipartite graph are exploited in designing switching systems. First, in a network based on bipartite graphs, no two paths are allowed to intersect at a vertex. This attribute is used to design a directional coupler-based photonic switching network with very low crosstalk. Since crosstalk is the most limiting factor in constructing a large directional-coupler-based photonic switching network, crosstalk reduction on the device and architecture levels is an important design issue. Secondly, broadcast, which is an intrinsic property of a bipartite graph (the same is always true with a crossbar representation), is used in designing multiconnection switching networks. Thirdly, it is shown that the nonplanar nature of bipartite graphs makes them well suited for designing three-dimensional free-space-transmission photonic switching systems View full abstract»

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  • Convergence and steady-state behavior of a phase-splitting fractionally spaced equalizer

    Publication Year: 1990 , Page(s): 418 - 425
    Cited by:  Papers (15)  |  Patents (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    The eigenstructure, the initial convergence, and the steady-state behavior of a phase-splitting fractionally spaced equalizer (PS-FSE) are analyzed. It is shown that the initial convergence rate of a T/3 or, in general, a T/M, PS-FSE employing the least-mean-square (LMS) stochastic gradient adaptive algorithm is half that of a symbol rate equalizer (SRE) or a complex fractionally spaced equalizer (CFSE) with the same time span. It is also shown that the LMS adaptive PS-FSE with symbol rate update converges to a Hilbert transformer followed by a matched filter in cascade with an optimal SRE, and thus forms an optional receiver structure. The LMS PS-FSE is computationally more efficient and introduces less system delay than the CFSE View full abstract»

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  • The fast packet ring switch: a high-performance efficient architecture with multicast capability

    Publication Year: 1990 , Page(s): 539 - 545
    Cited by:  Papers (3)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    An architecture is presented for the packet switching of integrated traffic. It is based on the asynchronous routing of packets of varying size through regularly recurring dedicated time slots provided by a simple slotted-ring system. The architecture implements the distributed buffering and processing of packets, is data driven, and is designed to exploit fully the limited bandwidth of the ring system. Thus, switch modules of reasonable size and throughput are made feasible. The switch modules can be easily interconnected to achieve sufficient throughput for networking of services such as voice, data, image, and videoconferencing. The architecture provides a simple modular switching structure which does not suffer from the topological complexities and bottlenecks of those that use the staged Banyan-type networks for the switching of packets. Quasicircuit-switching can easily be achieved through selected ports with a peak bit-rate bandwidth allocation strategy in the switch control. Multicasting in particular is made simple and efficient in the current architecture. Moreover, it provides for the selective queueing of packets in the transmit ports View full abstract»

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  • Design and characterization of an error-correcting code for the SONET STS-1 tributary

    Publication Year: 1990 , Page(s): 467 - 476
    Cited by:  Papers (11)  |  Patents (43)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1008 KB)  

    The authors have designed and characterized a single-error-correcting (SEC), double-error-detecting (DED) code applicable to the STS-1 SONET format. They show that if two of the presently unallocated bytes in the path overhead field of STS-1 are assigned for error-correction coding (ECC), a {6208, 6195} shortened extended Hamming code can be implemented using as few as 660 gates plus a 1-kbyte RAM IC, achieving (O8.6×10-3 P 22) BER reduction with 139 μs of signal delay. The authors explain how the existing BIP-8 error-monitoring byte of the STS-1 format could be integrated with the proposed ECC so that a net allocation of only one new STS-1 overhead byte is required for both error monitoring and error correction. The implementation method is such that all path, line, and section overhead functions in SONET can be performed at intermediate sites without requiring ECC decoding. The authors consider application alternatives and describe the forward-error-correction (FEC) circuit design and trial results. System issues are covered, including network delay, effects of error extension on BER, addition of double-error detection, performance monitoring, and options for intelligent network control and management of FEC functions. Codes related to their path-level design that are applicable to a number of other strategies for applying FEC in SONET are presented View full abstract»

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  • Message delays at packet-switching nodes serving multiple classes

    Publication Year: 1990 , Page(s): 447 - 455
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    A packet-switching node is modeled as a single-server queueing system. Messages in class c have Jc packets, each of which has a length which may be drawn from a general service time distribution prescribed on the basis of the packet's position in the message. All of the messages' packets arrive at the instant of message arrival; each packet within the message has a preassigned priority. The first packet of the message joins a transmission queue at the message arrival instant, there being one queue for each distinct priority. Upon completion of transmission of a given packet within a message, its successor packet joins the queue of appropriate priority. Packets which are waiting in the queues are serviced by the trunk under a nonpreemptive priority discipline. A method is presented for finding average message system times for the service discipline just described. This class of service disciplines includes several service disciplines which have been reported in the literature including the PR+RR, the HOL, and HOLP, the RR, and others that are discussed herein. Some numerical examples are presented View full abstract»

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  • A practical reliability metric for block codes used on binary-input channels

    Publication Year: 1990 , Page(s): 405 - 408
    Cited by:  Papers (2)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    A reliability metric (RM) for a block code is defined to be a function that operates on both the decoder input (a block of channel output) and the decoder output (the codeword estimate) and produces a real number as a measure of the reliability of the decoder decision. The best RM has the disadvantage of depending on the codeword probabilities. Thus, the ideal RM is defined as the value that would be computed for equally likely codewords. The implementation of the ideal RM is too costly for most applications. The author proposes an easily implemented RM for binary-input memoryless channels (for state-observable channels with a freely evolving state such as some fading channels) when the codewords consist of n 2m-ary symbols, each of which is transmitted serially by m uses of the channel. Simulation results for some BCH codes and some Reed-Solomon codes used in a simple ARQ system show that the proposed RM performs nearly as well as the ideal RM and much better than a previously proposed practical RM View full abstract»

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  • Channel coding with quadrature-quadrature phase shift-keying (Q2PSK) signals

    Publication Year: 1990 , Page(s): 409 - 417
    Cited by:  Papers (13)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (796 KB)  

    Channel coding due to trellis modulation has been proved to be useful for bandlimited channels. However, these modulations, mostly designed with n-use of 2D signals, are primarily aimed at coding gain only. It is pointed out that utilization of all available signal dimensions, which is limited by the time-bandwidth product, may improve the bandwidth efficiency and simultaneously bring an additional coding gain. Trellis coding with a spectrally efficient 4D signal set based on Q2PSK is addressed. Without any expansion of the Q 2PSK signal set, a simple hand-designed 16-state trellis code provides a coding gain of 6.02 dB. With the same number of states in G. Ungergoeck's (1982) 8-PSK trellis, the gain is 4.1 dB. In low intersymbol interference situations, the bandwidth efficiency of this coded Q2PSK is twice that of coded 8-PSK; if both operate at 2 b/s Hz and Pb(E)=10-5, the coded Q2PSK provides a saving of about 4 dB over the coded 8-PSK. Some fully connected trellises with an expanded signal due to 2-use of Q2PSK signals are also presented. Two such codes ar rate-7/8 achieve a gain of 5.45 dB with only eight states View full abstract»

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  • A composite importance sampling technique for digital communication system simulation

    Publication Year: 1990 , Page(s): 393 - 396
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    A new composite importance sampling technique is presented and investigated. An exact analysis is used to optimize the sample size saving and to investigate its robustness with respect to threshold settings. The composite technique offers a sample size savings of ~2.5 compared to the translation technique of D. Lu and K. Yao (1988) for memoryless systems. Applications as well as some questions for further research are discussed View full abstract»

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  • Toward alternative high-speed network concepts: the SWIFT architecture

    Publication Year: 1990 , Page(s): 431 - 439
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    An approach to communication architectures for high-speed networks which provides efficient, adaptive communication for any traffic distribution is presented. It is based on a concept of dynamic sharing of communication resources which is obtained from the following three-tier SWIFT architecture. At the physical layer the high-speed communication system is based on the use of several lower speed channels or frequencies. At the data link layer, driven by hardware simplicity considerations, the SWIFT architecture uses a fixed time-slotted allocation of subchannels, in which each node is required to transmit or receive over only a single, predetermined, subchannel at a time. To provide adaptive channel access control, while preserving the data link hardware simplicity, a network layer is added. This layer introduces multihop adaptive channel (frequency) routing on the inherently broadcast communication medium. The routing concept provides dynamic sharing of communication channels and buffers, leading to a fully distributed adaptive bandwidth control. An analytic model for analyzing the performance of the multilayered architecture is developed. It shows that for homogeneous or heterogeneous traffic requirements the approach provides throughput/delay performance superior to that found in existing communication systems View full abstract»

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  • Maximum likelihood carrier phase recovery for coherently orthogonal CPFSK signals

    Publication Year: 1990 , Page(s): 397 - 398
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    ML estimation of carrier phase for coherently orthogonal continuous-phase frequency-shift-keying (COCPFSK) signals is considered. Although the estimator, in general is nonimplementable, its high and low signal-to-noise-ratio approximations both lead to linear readily implementable receiver structures. The high SNR approximation yields a DA receiver, whereas the low SNR approximation yields an NDA receiver. The performance of both receivers in term of bit error probability is analyzed. The existence of an unmodulated component in the sufficient statistical representation of a COCPFSK signal is pointed out, and it is shown how this component enters directly into maximum-like carrier recovery. This leads to interpretation of the NDA receiver as a generalization of the conventional matched-filter envelope-detector receiver. The insights gained here are useful to the problem of ML carrier recovery for Viterbi decoding of continuous phase modulation signals View full abstract»

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  • Statistical properties of timing jitter due to data echo in digital modem receivers

    Publication Year: 1990 , Page(s): 546 - 550
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    Consideration is given to the influence of the noise and data sequences present in the received data signal on a nondecision-aided timing recovery scheme in digital modem receivers, It is known that white noise is not particularly disturbing for timing recovery, whereas data signals such as local echo (or residual echo) introduce a bias, called jitter, into the sampling recovered phase. It is shown that when the disturbing data signal has power P less than the power S of the useful signal (whose timing must be recovered), the jitter is sinusoidal with amplitude proportional to the ratio P/S. In the opposite situation, the bias increases indefinitely with time View full abstract»

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  • An extended least-hop distributed routing algorithm

    Publication Year: 1990 , Page(s): 520 - 528
    Cited by:  Papers (6)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    A routing strategy called NELHNET has been developed for networks with multiprecedence traffic and operating under dynamic traffic and topological conditions. An adaptive distributed algorithm that uses least-hop and least-hop-plus-1 routes in a table of routing vectors, as opposed to the usual table of routing scalars, is described. Current delays are passed backward and forward with the packets to allow development of expected delays to each node via all acceptable routes. The route then selected is the acceptable route with the least expected delay. For speedier recovery, a node returning to service receives the current network status from an adjoining node as soon as the link connecting them is operational. The resultant algorithms show far greater than the marginal improvements originally expected over Arpanet simulations. NELHENET strategies also permit the network to function stably under more heavily loaded conditions than do the Arpanet strategies View full abstract»

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  • Near-far resistance of multiuser detectors in asynchronous channels

    Publication Year: 1990 , Page(s): 496 - 508
    Cited by:  Papers (598)  |  Patents (87)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1036 KB)  

    Consideration is given to an asynchronous code-division multiple-access environment in which receiver has knowledge of the signature waveforms of all the users. Under the assumption of white Gaussian background noise, the authors compare detectors by their worst case bit error rate in a near-far environment with low background noise, where the received energies of the users are unknown to the receiver and are not necessarily similar. Conventional single-user detection in a multiuser channel is not near-far resistant, and the substantially higher performance of the optimum multiuser detector requires exponential complexity in the number of users. The authors explore suboptimal demodulation schemes which exhibit a low order of complexity while not exhibiting the impairment of the conventional single-user detector. It is shown that there exists a linear detector whose bit-error-rate is independent of the energy of the interfering users. It is also shown that the near-far resistance of optimum multiuser detection can be achieved by a linear detector. The optimum linear detector for worst-case energies is found, along with existence conditions, which are always satisfied in the models of practical interest View full abstract»

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  • A technique for extrapolating the end-to-end performance of HDLC links for a range of lost packet rates

    Publication Year: 1990 , Page(s): 461 - 466
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    A technique based on importance sampling is presented for extrapolating the end-to-end delay performance of a high-level data link control (HDLC) network. The lost packets can arise from bit errors or discarding due to network congestion. The technique works well for a substantial range of loads, as long as the desired performance is at an error rate less than the observed rate (the environment most frequently encountered). It is applicable across a range of error rates. The technique was tested on a simple HDLC link but would generalize to other link-level protocols. The extrapolation technique can be based on simulation or measurement. Simulation results are presented to demonstrate its effectiveness View full abstract»

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  • A study of the ground illumination footprint of meteor scatter communication

    Publication Year: 1990 , Page(s): 426 - 430
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    An examination is made of the ground illumination footprint of meteor trails and its effect on the simultaneous reception of meteor scatter transmissions by multiple receivers. A technique for calculating the ground illumination footprint of individual trails which provides added insight into the physical mechanisms is presented. The probability of adjacent station reception as a function of location on the ground is calculated by computing the ground illumination footprint of individual trails at different locations and orientations within the common volume and weighting each footprint by the number of trails at that location and orientation. Two different models for the spatial arrival pattern of meteor trails are considered: the first model assumes that trails arrive uniformly over the common volume, and the second calculates the number of arrivals from the spatial distribution of meteor orbits, antenna patterns, time of day, and season. The effect of antenna patterns on the ground illumination footprint of meteor scatter communication is examined View full abstract»

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  • A linear solution to queueing analysis of synchronous finite buffer networks

    Publication Year: 1990 , Page(s): 440 - 446
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    An approximate solution to slotted communication systems with finite population and finite buffer capacity is presented. The authors assume symmetric systems and present for the first time a linear solution involving linear equations whose number is a linear function of the total buffer capacity. They show that the model can be applied to existing multiaccess channel protocols in which a single successful transmission can be affected per slot. They further show that, unlike solutions based on existing nonlinear models, the proposed solution can be extended to communication systems in which several successful transmissions can take place in parallel, such as multibus communication networks and multichannel satellite systems View full abstract»

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  • Multistage detection in asynchronous code-division multiple-access communications

    Publication Year: 1990 , Page(s): 509 - 519
    Cited by:  Papers (674)  |  Patents (49)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (952 KB)  

    A multiuser detection strategy for coherent demodulation in an asynchronous code-division multiple-access system is proposed and analyzed. The resulting detectors process the sufficient statistics by means of a multistage algorithm based on a scheme for annihilating successive multiple-access interference. An efficient real-time implementation of the multistage algorithm with a fixed decoding delay is obtained and shown to require a computational complexity per symbol which is linear in the number of users K. Hence, the multistage detector contrasts with the optimum demodulator, which is based on a dynamic programming algorithm, has a variable decoding delay, and has a software complexity per symbol that is exponential in K. An exact expression is obtained and used to compute the probability of error is obtained for the two-stage detector, showing that the two-stage receiver is particularly well suited for near-far situations, approaching performance of single-user communications as the interfering signals become stronger. The near-far problem is therefore alleviated. Significant performance gains over the conventional receiver are obtained even for relatively high-bandwidth-efficiency situations View full abstract»

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  • Scheduling broadcasts in multihop radio networks

    Publication Year: 1990 , Page(s): 456 - 460
    Cited by:  Papers (176)  |  Patents (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    A comprehensive study of the problem of scheduling broadcast transmissions in a multihop, mobile packet radio network is provided that is based on throughput optimization subject to freedom from interference. It is shown that the problem is NP complete. A centralized algorithm that runs in polynomial time and results in efficient (maximal) schedules is proposed. A distributed algorithm that achieves the same schedules is then proposed. The algorithm results in a maximal broadcasting zone in every slot View full abstract»

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  • Tree-structured scene adaptive coder

    Publication Year: 1990 , Page(s): 477 - 486
    Cited by:  Papers (61)  |  Patents (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1184 KB)  

    A new type of scene adaptive coder has been developed. It involves a quadtree mean decomposition of the motion-compensated frame-to-frame difference signal followed by a scalar quantization of the local means. As a fundamental property, the new coding algorithm treats the displacement estimation problem and the quadtree construction problem as a unit. The displacement vector and the related quadtree are jointly optimized in order to minimize the direct frame-to-frame update information rate (in bits), which turns up as a new and more adequate cost function in displacement estimation. This guarantees the highest possible data compression ratio at a given quality threshold. Excellent results have been obtained for coding of color image sequences at a rate of 64 kb/s. The quadtree concept entails a much lower computational complexity compared to the conventional motion-compensated transform coder while achieving a subjective image quality that is as good or better than that of the traditional transform-based counterpart 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