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Communications, IEEE Transactions on

Issue 5 • Date May 1990

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Displaying Results 1 - 23 of 23
  • Analysis of a coherent frequency-hopped spread-spectrum receiver in the presence of jamming

    Publication Year: 1990 , Page(s): 715 - 726
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1069 KB)  

    A digital phase/timing tracking loop for a coherent frequency-hopped spread-spectrum receiver is analyzed. A training period is introduced to aid the system in entering the tracking mode; once in this latter mode, decision-directed measurements are used. The S-curve, the conditional variance of the phase estimator, and the linear model of the loop are derived. Then, under minor assumptions, the phase error is modeled as a homogeneous finite Markov chain. Based on this model, the length of the training period and the approximate probability of entering the tracking range are obtained; in the tracking mode, the steady-state average probability of error and the mean-time to loss-of-lock are obtained. By limiting the maximum output magnitude of the phase estimator, it is shown that the tracking performance is close to that of coherent binary phase-shift keying (BPSK) in the absence of jamming, or that assuming perfect synchronization, in the presence of partial-band jamming. The mean-time to loss-of-lock is shown to be several orders of magnitude larger than the expected length of training period. The effects of a cubic channel phase response and a constant RF phase error are presented View full abstract»

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  • On the error probability of coded frequency-hopped spread-spectrum multiple-access systems

    Publication Year: 1990 , Page(s): 571 - 573
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    A simple, exact calculation is presented of the probability distribution of the number of hits in a block of n symbols in a frequency-hopped, spread-spectrum, multiple-access communication system. While the sequence of hits is not Markovian, there is an underlying Markovian structure that allows the probability distribution of the number of hits to be calculated in a recursive fashion. Knowing the probability distribution of the number of hits makes it possible to calculate the probability of error for a system employing error correcting codes for several different types of receivers, including receivers with both errors and erasures. The numerical results show that both the approximation obtained by assuming the actual sequence of hits is Markovian and the approximation obtained by assuming the hits are independent are very good. When the number of frequency slots is not too small (less than five), calculations show that assuming the independence of hits gives an error probability accurate to within 1% of the actual error probability. Assuming the hits are Markovian gives error probabilities which are accurate to within 0.001% View full abstract»

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  • Analysis of a delay-dependent priority discipline in an integrated multiclass traffic fast packet switch

    Publication Year: 1990 , Page(s): 659 - 665
    Cited by:  Papers (25)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    A dynamic packet transmission priority discipline, head-of-the-line with priority jumps, is proposed and analyzed for a packet switch serving multiple classes of delay-sensitive traffic. It is shown that, under realistic traffic conditions, the discipline can make the tail probabilities of the delay distributions for the different classes of traffic, in excess of their respective delay requirements, approximately the same, thus resulting in fairness of service and minimization of the maximum tail probability among the different classes. Implementation of the discipline is considered to be relatively simple, and involved processing overhead is minimal View full abstract»

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  • Spread-spectrum multiple-access performance of orthogonal codes for indoor radio communications

    Publication Year: 1990 , Page(s): 574 - 577
    Cited by:  Papers (44)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    Direct-sequence spread spectrum, with its inherent resistance to multipath, is a promising technique for indoor wireless communication. To allow multiple users within a limited bandwidth, code division multiple access (CDMA) is needed. The bandwidth efficiency of M-ary CDMA systems in fading multipath indoor radio channels is analyzed. It is shown that M-ary signaling improves the bandwidth efficiency significantly when compared to binary signaling View full abstract»

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  • Sufficient conditions on trellis-coded modulation for code-independent synchronizer performance

    Publication Year: 1990 , Page(s): 595 - 601
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    The carrier synchronization and symbol timing recovery for two-dimensional trellis-code modulated signals are considered. For many popular carrier and clock synchronizers, and tracking and cycle-slipping performance depends on the trellis code only through the second- and fourth-order moments of the coded channel symbols. For three successively more complicated classes of coded symbol alphabets, simple conditions on the trellis code are derived which are sufficient to yield the same second- and fourth-order moments as for uncoded symbols. For trellis codes satisfying these conditions, the synchronizer performance does not depend on the specific code, and is the same as for uncoded symbols. These sufficient conditions are fulfilled by many codes which have been presented in the literature, some of which are discussed View full abstract»

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  • The optimum combination of block codes and receivers for arbitrary channels

    Publication Year: 1990 , Page(s): 615 - 621
    Cited by:  Papers (36)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    A determination is made of the combinations of transmitted block codewords and matching receiver filters that maximize the signal-to-noise ratio at the detector with arbitrary channel impulse response and arbitrary noise spectrum. This permits representing the channel as a set of parallel, uncoupled subchannels with uncorrelated noise; the representation is used to calculate the capacity of an arbitrary block coded, time discrete channel. It is shown that substantial coding gains, compared to symbol-by-symbol processing, can be achieved. The block code used can be concatenated with trellis-coded modulation so that the two coding gains are additive View full abstract»

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  • A lattice vector quantization using a geometric decomposition

    Publication Year: 1990 , Page(s): 704 - 714
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB)  

    An efficient lattice vector quantization design and the associated fast coding algorithm are proposed for high-bit-rate, high-quality data compression applications. The codewords are uniformly distributed and densely packed as 2n-dimensional lattice points, based on a geometric lattice decomposition technique. The maximum quantization error has been chosen as the design criterion. For high-rate applications, it has the following advantages: (1) simple vector codeword generation; (2) no codewords need to be stored and only predetermined rules are used at encoder and decoder ends; (3) highly regular code structure, so that encoding is done via an inverse tree-search suitable for fast parallel processing, and decoding is done similar to a scalar quantizer; (4) high coding quality capability, viz. the maximum quantization distortion can be prespecified to a desired value and the entire hyper-region is covered uniformly; and (5) dimensionality saving can be easily predicted and it can be achieved using fixed-length codes View full abstract»

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  • Word timing recovery in direct detection optical PPM communication systems with avalanche photodiodes using a phase lock loop

    Publication Year: 1990 , Page(s): 666 - 673
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    A technique for word timing recovery in a direct detection optical pulse position modulation (PPM) communication system is described. It tracks on back-to-back pulse pairs in the received random PPM data sequences with the use of a phase locked loop. The experimental system consisted of an AlGaAs laser diode transmitter (λ=833 nm) and a silicon avalanche photodiode photodetector, and its used Q=4 PPM signaling at a source data rate of 25 Mb/s. The mathematical model developed to characterize system performance is shown to be in good agreement with the experimental measurements. Use of this recovered PPM word clock, along with a slot clock recovery system described previously, caused no measurable penalty in receiver sensitivity when compared to a receiver which used common transmitter/receiver clocks. The completely self-synchronized receiver was capable of acquiring and maintaining both slot and word synchronizations for input optical signal levels as low as 20 average detected photons per information bit. The receiver achieved a bit error probability of 10-6 at less than 60 average detected photons per information bit View full abstract»

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  • Performance improvements using synchronous code correction in ADPCM/PCM tandem connections

    Publication Year: 1990 , Page(s): 561 - 564
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    A sufficient condition for the existence of tandem distortion accumulation is described. The distortion for a sample time at which the sufficient condition is satisfied is studied. It is shown that the transcoding distortion is greater than the adaptive differential pulse code modulation (ADPCM) distortion when synchronous code correction is not used and less than the ADPCM distortion when synchronous code correction is used. These results are combined to show that when synchronous code correction is used, the upper bound of the single transcoding distortion is determined by the single transcoding distortion when synchronous code correction is not used. This bound cannot be generalized for multiple tandem cases View full abstract»

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  • Multiuser signal detection using sequential decoding

    Publication Year: 1990 , Page(s): 578 - 583
    Cited by:  Papers (66)  |  Patents (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The application of sequential decoding to the detection of data transmitted over the additive white Gaussian noise channel by K asynchronous transmitters using direct-sequence spread-spectrum multiple access (DS/SSMA) is considered. A modification of R.M. Fano's (1963) sequential-decoding metric, allowing the messages from a given user to be safely decoded if its Eb/N0 exceeds -1.6 dB, is presented. Computer simulation is used to evaluate the performance of a sequential decoder that uses this metric in conjunction with the stack algorithm. In many circumstances, the sequential decoder achieves results comparable to those obtained using the much more complicated optimal receiver View full abstract»

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  • On the least squares tap adjustment algorithm in adaptive digital echo cancellers

    Publication Year: 1990 , Page(s): 622 - 628
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    Fast recursive algorithms for updating coefficients in digital echo cancellers can be derived from the well-known method of least squares. Unless zero initial conditions are assumed, the exact initialization of these algorithms is yet unknown. For random data of more than twice the order of the filter, the existence of a unique least squares solution is proven. A constructive recursive procedure in time and order for computing the pseudoinverse solution for the initial steps is derived. Since the data matrix is composed of integers, this technique facilitates the implementation of stable tap-update algorithms View full abstract»

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  • Demand assignment in the ACTS LBR system

    Publication Year: 1990 , Page(s): 684 - 692
    Cited by:  Papers (7)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    The advanced communications technology satellite (ACTS) is an experimental communications satellite being developed by NASA's Lewis Research Center. Low burst rate (LBR) traffic stations will access the ACTS multibeam communications package (MCP) through two hopping beams that can be directed at certain cities and areas in the continental United States. An onboard baseband processor (BBP) demodulates uplink traffic received via two up-link (30 GHz) hopping beams, switches the traffic between uplink and downlink beams at baseband, and then remodulates the traffic for retransmission at 20 GHz via two downlink hopping beams. This study concentrates on the demand assigned operation of the ACTS LBR system where the onboard switch is remote from both the traffic stations and the centralized master control station (MCS). Network control uses inbound and outbound orderwire channels and a BBP control channel thereby allowing the MCS to coordinate assignment of individual 64-kb/s channels in the spacecraft. Models are developed to simulate the dynamics of the demand assignment process in order to verify call blocking behavior, to predict control channel loads, and to evaluate alternative algorithms for burst time plan rearrangement that becomes necessary to minimize blocking under conditions of high-traffic intensity View full abstract»

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  • Congestion control for packet voice by selective packet discarding

    Publication Year: 1990 , Page(s): 674 - 683
    Cited by:  Papers (89)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    In order to reduce the time delays as well as multiplexer memory requirements in packet voice systems, a family of congestion control schemes is proposed. They are all based on the selective discarding of packets whose loss will produce the least degradation in quality of the reconstructed voice signal. A mathematical model of the system is analyzed and queue length distributions are derived. These are used to compute performance measures, including mean waiting time and fractional packet loss. Performance curves for some typical systems are presented, and it is shown that the control procedures can achieve significant improvement over uncontrolled systems, reducing the mean waiting time and total packet loss (at transmitting and receiving ends). Congestion control with a resume level is also analyzed, showing that without increasing the fractional packet loss, the mean and variance of the queue can be reduced by selecting an appropriate resume level. The performance improvements are confirmed by the results of some informal subjective testing View full abstract»

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  • Hybrid trellis-coded 8/4-PSK modulation systems

    Publication Year: 1990 , Page(s): 602 - 614
    Cited by:  Papers (8)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1040 KB)  

    By using codes of rate 2/3 followed by 8-PSK modulation, a gain of 3-6 dB is obtained over uncoded 4-PSK, for an ideal coherent transmission on the white Gaussian channel. In the presence of carrier phase offset, it has been shown that trellis-coded 8-PSK systems are more sensitive than uncoded 4-PSK. A more robust performance can be achieved by using rate 2/3 trellis-coded 8-PSK signals and 4-PSK signals in a time-varying manner. Only the mapper from the output of the binary convolutional code to the signal point number to be transmitted has to be periodically time-varying. In its simplest form, trellis-coded 8-PSK and 4-PSK signals alternate in time. An examination has also been made of systems where the mixture of 8-PSK and 4-PSK signals varies, with a short periodic sequence of time-varying mapping rules. The distance spectra and error probability are evaluated with and without phase offset. Simulation results of bit error rate (BER) and performance of the recovery loop (S curve) are presented. It is concluded that systems which are more robust against jitter can be achieved by means of time-varying hybrid trellis-coded 8/4-PSK systems View full abstract»

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  • Adaptive cosine transform image coding with constant block distortion

    Publication Year: 1990 , Page(s): 698 - 703
    Cited by:  Papers (16)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (788 KB)  

    An adaptive block discrete-cosine transform (DCT) coding scheme is implemented with the same average distortion designated for each block. This constant distortion designation not only has perceptual advantages, but also allows the rate to vary, adjusting to the changing spectral characteristics among the blocks. The successful execution of this scheme requires a different spectral estimate for each block. To keep overhead and computation within limits, a novel technique is introduced by which a two-dimensional block spectrum is characterized by a one-dimensional autoregressive model. Simulations with images of natural scenes and medical radiology provide reconstructions with nearly uniform block distortion and very high visual and measurable quality at low rates View full abstract»

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  • Comparison of coherent and differential detection of BPSK and QPSK in a quasistatic fading channel

    Publication Year: 1990 , Page(s): 565 - 567
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    The advantage of coherent detection over differential detection for quadrature phase-shift keying (QPSK) and binary phase-shift keying (BPSK) in a flat-fading channel is evaluated based on receiver-sensitivity analysis using three performance criteria. QPSK is concentrated upon to perform simulations for a frequency-selective fading channel. Spectral efficiency improvement due to better frequency reuse for the more sensitive coherent detection is evaluated with a combination of analysis and simulation. It is found that coherent detection with perfect carrier recovery is superior to differential detection by at least 2.4 dB, which converts to about a 30% improvement in spectral efficiency in a two-dimensional, frequency reuse system with a fourth-power propagation exponent. This advantage is preserved even if diversity selection is used to mitigate fading View full abstract»

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  • Further results on a new combined strategy based on the SRPT-principle

    Publication Year: 1990 , Page(s): 568 - 570
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    The method used for analyzing the combined shortest remaining processing time first/round robin (SRPT/RR) strategy is briefly introduced, and it is shown that this combined strategy preserves the essential advantages of the SRPT principle. In data communications, this strategy potentially may be applied to the packet switching process. The packet length corresponds to the time slice, and overhead corresponds mainly to the packet frame because most of the operations needed to organize the queue can be performed in parallel. In networks with virtual or static routing, this strategy selects the next packet of the message with the least number of remaining packets; for an equal number of remaining packets, the message with the shortest last packet is chosen. The first in, first out (FIFO) rule is used to resolve any remaining ambiguity. Local area networks are a special area of application for this strategy View full abstract»

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  • Performance of buffered banyan networks under nonuniform traffic patterns

    Publication Year: 1990 , Page(s): 648 - 658
    Cited by:  Papers (43)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (920 KB)  

    An analytical method of evaluating the performance of the buffered banyan packet-switching network under nonuniform traffic patterns is presented. It is shown that nonuniform traffic can have a detrimental effect on the performance of the network. The analytical model is extended to evaluate the performance of multibuffer and parallel banyan networks. These modified networks are shown to have better throughput capacity and delay performance than the single-buffer banyan network View full abstract»

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  • On the capacity of binary and Gaussian channels with run-length-limited inputs

    Publication Year: 1990 , Page(s): 584 - 594
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    Bounds on the capacity of binary symmetric channels and additive Gaussian channels with run-length-limited two-level (binary, bipolar) inputs are presented, and their tightness is demonstrated for some cases. Stationary input sequences, which do not degrade capacity, are considered when deriving the bounds. Lower bounds on the magnetic recording density for a simple continuous-time recording model incorporating a minimal intertransition constraint are evaluated for soft and hard decisions. A superiority of about 1.5 dB in signal-to-noise ratio is observed for the soft-decision scheme View full abstract»

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  • Design and performance of block-coded modulation for digital microwave radio systems

    Publication Year: 1990 , Page(s): 727 - 733
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    Two block-coded modulation (BCM) families particularly suited for high-capacity digital microwave radio systems are presented. The first family is based on one-step partitioning, and the second family is based on two-step partitioning of the signal constellation. The alphabet expansion is a decreasing function of the block length, and the constellation is constructed in such a way as to minimize both the average and peak signal powers. Using short block lengths, specific modulation schemes are described that transmit 4, 6, and 8 information bits per symbol. The asymptotic coding gain is only on the order of 2 dB in the first family, and of 3 dB in the second family, but their detection simplicity makes the presented BCM schemes particularly attractive for high-speed applications where trellis-coded modulation (TCM) decoders may be difficult to implement View full abstract»

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  • On optimum and suboptimum biasing procedures for importance sampling in communication simulation

    Publication Year: 1990 , Page(s): 639 - 647
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    Importance sampling can significantly reduce simulation run time in estimating the bit error probability of digital systems if a suitable procedure is used. Various aspects of optimum and suboptimum biasing procedures are considered. It is shown that the strict optimum does not lead to a realistic procedure. An examination is made of the suboptimal variations that can be implemented reasonably; in one variation, it is found that for a linear system, the biasing scheme should have a time-varying mean proportional to the impulse response. Aspects of implementation are also discussed View full abstract»

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  • A fast echo canceller initialization method for the CCITT V.32 modem

    Publication Year: 1990 , Page(s): 629 - 638
    Cited by:  Papers (27)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (948 KB)  

    An investigation is conducted of the use of a fast-converging frequency-domain adjustment method for the echo canceller that conforms to the CCITT V.32 standard. The method requires no additional processor cycles (or cost increase) over that already required during steady-state operation of the V.32 modem, and reduces the training period to a maximum of 7.5 s, and nominally about 2.5 s. The presence of intermediate echoes can be detected naturally with the presented methods. Simple modifications of the new method are also introduced to accommodate special situations where intermediate echoes and/or frequency offset are present View full abstract»

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  • Digital transmission through a land mobile satellite channel

    Publication Year: 1990 , Page(s): 693 - 697
    Cited by:  Papers (28)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    An analytical derivation of the probability of bit error noncoherent frequency-shift keying (FSK) and coherent phase-shift keying (PSK) signals transmitted through a land-mobile satellite channel is described. The channel characteristics used in the analysis are based on a recently developed model which includes the combined effects of fading and shadowing. Analytical expressions for the probability of bit error of FSK and coherent phase-shift keying (CPSK) signals are obtained. The results show that large amounts of signal-to-noise ratio (SNR) are required to compensate for the combined effect of fading and shadowing. An analytical expression for the irreducible probability of bit error of a CPSK signal due to phase variations caused by fading and shadowing is derived. The results described should be useful in the design of land mobile satellite communication 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