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Communications, IEEE Transactions on

Issue 1 • Date Jan 1992

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Displaying Results 1 - 24 of 24
  • Analysis of an antijam FH acquisition scheme

    Page(s): 160 - 170
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (820 KB)  

    An easily implemented matched filter scheme for acquiring hopping code synchronization of incoming frequency-hopping (FH) signals is analyzed, and its performance is evaluated for two types of jamming: partial-band noise jamming and partial-band multitone jamming. The system is designed to reduce jammer-induced false alarms. The system's matched filter output is compared to an adaptive threshold that is derived from a measurement of the number of acquisition channels being jammed. Example performance calculations are given for the frequency coverage of the jamming either fixed over the entire acquisition period or hopped, that is, changed for each acquisition pulse. It is shown that the jammer's optimum strategy (the worst case) is to maximize the false alarm probability without regard for the effect on detection probability, for both partial-band noise and multitone jamming. It is also shown that a significantly lower probability of false acquisition results from using an adaptive matched filter threshold, demonstrating that the strategy studied here is superior to conventional nonadaptive threshold schemes View full abstract»

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  • Performance of a nonblocking space-division packet switch with correlated input traffic

    Page(s): 97 - 108
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1016 KB)  

    This work studies the performance of a nonblocking space-division packet switch in a correlated input traffic environment. In constructing the input traffic model, the author considers that each input is a time division multiaccess (TDM) link connecting to multiple sources. Every source on a link supports one call at a time. Each call experiences the alternation of ON and OFF periods, and generates packets periodically while in ON period. The stochastic property of each call does not have to be identical. Packets from each individual call are destined to the same output. The output address of each call is assumed to be uniformly assigned at random. The author derives both upper and lower bounds of the maximum throughput at system saturation. His study indicates that, if the source access rate is substantially lower than the link transmission rate, the effect of input traffic correlation on the output contentions can generally be ignored. Also, the analysis of each input queue becomes separable from the rest of the switch. The same study is carried out with nonuniform call address assignment View full abstract»

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  • Analysis of the error performance of trellis-coded modulations in Rayleigh-fading channels

    Page(s): 74 - 83
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (836 KB)  

    This work presents an exact expression for the pairwise error event probability of trellis-coded modulation (TCM) transmitted over Rayleigh-fading channels. It includes phase shift keying (PSK) and multilevel quadrature amplitude modulation (QAM) codes, as well as coherent and partially coherent (e.g. differential, pilot tone, etc.) detection. Due to the form of the exact pairwise error event probabilities, this calculation technique cannot be used with the transfer function technique to obtain an upper (union) bound on the overall bit error probability. For this reason, the authors estimate the bit error probability by considering only a small number of short error events. Through simulations, they found that the estimation is usually very accurate at high signal-to-noise ratios but not as accurate at lower signal-to-noise ratios. They study several coded modulation schemes this way. Among the results are the fact that TCM provides significant improvement in the error floor when detected differentially, and an asymmetry in the pairwise error event probability for 16 QAM View full abstract»

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  • A model of reservation systems

    Page(s): 109 - 118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    The author considers the performance evaluation of an advanced capacity reservation system using the CCITT defined reserved call establishment mode. A simple model for the traffic process is introduced: calls are assumed to be offered uniformly to the reservation book. The state of the system can then be described statistically in terms of the population of various types of islands of free time slots. The limit where the length of the reservation book tends to infinity is, in particular, considered. For single-server systems with a deterministic holding time of one or two time slots, a closed-form solution is found. For a general holding time distribution, an asymptotic analytical solution is derived and corrections to this asymptotic solution are calculated numerically. For multiserver systems with geometric holding time distribution, the author presents numerical results obtained by simulations. An interpolation formula valid for all traffic intensities is developed. A procedure is given to extrapolate the results to larger systems than were actually simulated View full abstract»

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  • Efficient communications using the meteor-burst channel

    Page(s): 119 - 128
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    This work presents the results of a theoretical study of the meteor-burst channel which illustrates its time-varying bursty nature. In addition, the authors describe an innovative approach to data transmission over meteor-burst systems, i.e. the use of the feedback adaptive variable rate (FAVR) system which allows the maximum amount of information to be transmitted over each meteor-burst channel. For underdense meteor channels the FAVR performance is compared to an optimum system, i.e. a system capable of changing its bit rate instantaneously to channel conditions so as to maintain a constant SNR in each bit, and to a constant optimum rate/burst system. It is shown that when compared to an optimum rate per burst system, FAVR can result in a throughput increase exceeding a factor of 10. It is also shown that FAVR can approach the optimum system performance, although for practical purposes, it appears that 83-88% of optimum is attainable View full abstract»

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  • A random-access algorithm for data networks carrying high-priority traffic

    Page(s): 84 - 96
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1004 KB)  

    The authors consider data networks carrying mixed traffic, partially low and partially high priority. For such networks, they propose a synchronous limited sensing random access algorithm per channel, which gives a delay advantage to the high-priority traffic. The algorithm basically consists of two dynamically coupled window algorithms, one for the high and one for the low-priority packets. Assuming limit Poisson user models for both the traffic classes, the authors optimize the windows of the mixed algorithm for: (a) throughput maximization under no specific delay constraints, and (b) throughput maximization subject to expected delay constraints for the high-priority traffic. For cases (a) and (b), they study the delay characteristics of the algorithm, for the two classes of data traffic. With appropriate selection of the two window sizes, the algorithm can attain relatively high throughput, while it simultaneously maintains low expected per high-priority packet delays, whose values are only slightly affected by the total traffic rate View full abstract»

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  • Design and analysis of a new self-routing network

    Page(s): 171 - 177
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A new self-routing network constructed from the sorting and the routing cells is proposed. The complexity of the new network is roughly twice as much as that of a pure banyan network. The new network can be viewed as an implementation of the load-sharing network which requires a very simple management. Its performance under uniform and nonuniform traffic models is analyzed for the unbuffered case. It is found that a higher degree of nonuniformity results in a better performance for certain forms of nonuniform traffic matrices. Simulations are performed to obtain the normalized throughputs and mean packet delays for the single-buffered case. Different from single-buffered pure banyan networks, the mean delay of high-traffic packets is smaller than that of low-traffic packets for a particular form of nonuniform traffic matrices. In addition to performance improvement, the new network is easy to diagnose. Some variations of the proposed network are also studied View full abstract»

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  • Analysis and testing of application layer protocols with an application to FTAM

    Page(s): 7 - 11
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    An experience with formal specification, analysis, and testing of an application layer protocol is presented. The ISO file, transfer, access, and management (FTAM) protocol is chosen due to its potential for widespread use. The specification language used was the ISO standard Estelle. This tool generates control and dataflow graphs of the specification and derives unparameterized test sequences for each function identified by the user. The authors describe formal specification of application layer protocols in Estelle and translation of ASN.1 data definitions into Estelle data types. The test design tool is used to obtain functional decomposition of the control and dataflow graphs. This way unparameterized test sequences are obtained. These sequences lead to a complete test suite obtained by parameterization which must be the next step. Analysis of the control and dataflow graphs leads to the derivation of several properties that most of the application layer protocols must possess. The identified properties are shown to simplify the test design process View full abstract»

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  • Low-delay vector excitation coding of speech at 16 kb/s

    Page(s): 129 - 139
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1044 KB)  

    The need for a 16-kb/s speech coding algorithm that has very low coding delay while achieving essentially the same high quality as the 32-kb/s adaptive differential pulse code modulation (ADPCM) standard G.721 is addressed. The authors describe low-delay vector excitation coding (LD-VXC), a new coding algorithm which provides high quality with less than 2 ms of coding delay and is robust to transmission errors. The algorithm combines techniques such as vector quantization, analysis-by-synthesis, and perceptual weighting together with backward adaptive linear predictive encoding, and uses a novel long-term predictor employing backward adaptive pitch tracking. Perceptually based nose shaping and postfiltering contribute to the masking of audible quantization noise View full abstract»

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  • The behavior of a Costas loop in the presence of space telemetry signals

    Page(s): 190 - 198
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    When the Costas loop is operated in the presence of a residual carrier space telemetry signal, the loop reconstructs its carrier reference from an input signal whose carrier component is not completely suppressed. The telemetry signal investigated in this work is generated by phase shift-keying the data onto a subcarrier and then phase modulating onto the sinusoidal carrier. The telemetry modulation index, telemetry bit rate, subcarrier waveform, and subcarrier frequency are shown to be the key system parameters that contribute to the performance degradation of a Costas loop. Furthermore, the effect of Doppler shift on the loop is also investigated in this work View full abstract»

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  • Selective-repeat-ARQ schemes for broadcast links

    Page(s): 12 - 19
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    The authors propose retransmission error control schemes for broadcast channels. In their selective-repeat-ARQ (automatic repeat request) method, they incorporate some aspects of implementation that they believe were ignored by all the previous work. Based on this protocol, they also propose a type-2 hybrid ARQ scheme that uses parity retransmission. They apply the dynamic programming optimization technique of Wang and Silvester (1987), with some modification, to their schemes. Analysis shows that their schemes outperform all the existing schemes. As special cases of their proposed schemes, the authors can obtain point-to-point ARQ schemes which also outperform all the existing point-to-point schemes. Thus, their schemes extend the useful range of retransmission error control schemes for these channels View full abstract»

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  • Digital transmission performance of standard analog filters

    Page(s): 42 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    This work analyzes the performances of Bessel, Gaussian, Butterworth, and Chebyshev (0.1-dB ripple) filters for synchronous baseband digital transmission. Numerical results showing the effects of system parameters such as signal rate, filter bandwidth, filter order, and pulse duty-cycle are presented. For rectangular inputs, linear phase filters perform better than those with nonlinear phase, from the viewpoint of the Nyquist 1 criterion. In terms of the Nyquist 2 criterion, linear phase filters perform better when the input duty-cycle is unity. For lower duty-cycles, there are symbol rate ranges over which nonlinear phase filters perform better. From the viewpoint of symbol time synchronization, the performances of the two types of filter are essentially the same. Linear phase filters are more robust to sampling clock jitter than nonlinear ones when the symbol rate is higher than the bandwidth. Furthermore, it is shown that for linear phase filters it is possible to increase the transmitting rate while keeping the filter bandwidth constant and with only a minor increase in degradation, by using low duty-cycle inputs View full abstract»

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  • A full-duplex DLC protocol on two links

    Page(s): 210 - 222
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    The authors consider a special case of multilink protocol, namely, a system consisting of two half-duplex parallel links that carry data in opposite directions between two nodes. They construct a protocol that simulates a full-duplex reliable link between the two nodes. Synchronization is achieved without resorting to the use of serial numbers. A validation proof of the protocol is provided. The design of the protocol exhibits an instance of the value of correctness proofs in the design process, as several successive protocols, discussed in the paper, were only found to be incorrect through the effort to prove them otherwise View full abstract»

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  • Signal interception: performance advantages of cyclic-feature detectors

    Page(s): 149 - 159
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    The problem of detecting the presence of spread-spectrum phase-shift-keyed signals in variable noise and interference backgrounds is considered, and the performances of four detectors are evaluated and compared. The detectors include the optimum radiometer, the optimum modified radiometer that jointly estimates the noise level and detects the signal, and the maximum-SNR spectral-line regenerator for spectral-line frequencies equal to the chip rate and the doubled carrier frequency. It is concluded that the spectral-line regenerators can outperform both types of radiometers by a wide margin. The performance advantages are quantified in terms of receiver operating characteristics for several noise and interference environments and receiver collection times View full abstract»

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  • The ERPC: an efficient error-resilient technique for encoding positional information or sparse data

    Page(s): 140 - 148
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3840 KB)  

    In many source and data compression schemes, information relating to positions of high-energy samples or areas of importance often needs to be relayed to the decoder. The error resilient positional code (ERPC) is an efficient fixed-rate coding scheme for encoding such positional information, or, equivalently, sparse binary data patterns. It has also been designed with good channel error robustness properties, such that the decoded data quality degrades gracefully with worsening channel conditions, without the possibility of catastrophic breakdown or loss of sync. In this work, the coding efficiency of the ERPC is compared to a few other standard schemes. It is found to be efficient and its error extension in terms of the expected number of samples corrupted per bit error is reported and shown to be low and noncatastrophic. The ERPC is applied to an image coding example based on subband coding and vector quantization. It results in an efficient adaptive codec capable of operating in harsh channel conditions, without the aid of error correction or detection techniques View full abstract»

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  • Data-aided synchronization of coherent CPM-receivers

    Page(s): 178 - 189
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (920 KB)  

    By means of a signal representation in a signal space spanned by a few time-limited exponential basis-functions, and data-aided maximum-likelihood techniques, novel methods for the joint and nonjoint estimation of carrier-phase and symbol-timing for general coherent CPM (continuous phase modulation) receivers are proposed. The estimators are quite simple, especially in obtaining symbol-timing. Simulation results show that synchronizers using such estimation structures exhibit an excellent steady-state behavior. Whereas a fast acquisition of the carrier-phase is always possible, joint synchronizer loops tend to hang up for CPM-schemes with partial response signaling. Several ways to overcome the hang-up problem are discussed View full abstract»

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  • Reduced-state sequence detection of multilevel partial-response signals

    Page(s): 3 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    This work is concerned with the problem of designing reduced-complexity Viterbi decoders for the transmission of digital data over intersymbol interference channels. First, optimal state-grouping for constructing reduced-state trellises is presented and illustrative examples are given for multilevel transmission over partial-response channels of the type 1±Dn, (1+D)2, (1+D) 2(1-D), and (1+D)3(1-D). Then, the quaternary 1-D type partial-response channel is considered in more detail and a difference-matric algorithm employing state-reduction is derived and shown to result in a simple decoding scheme View full abstract»

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  • Burst error statistics of simulated Viterbi decoded BPSK on fading and scintillating channels

    Page(s): 34 - 41
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    The author presents and analyzes burst error statistics of a soft-decision Viterbi decoder when the transmitted signal is encoded with the 313 (3, 1/2) or 31123 (5, 1/2) convolutional codes, modulated via coherent binary phase-shift keying (BPSK) for the additive white Gaussian noise (AWGN) channel, and subjected to slow and nonselective scintillation/fading modeled by the Nakagami-m distribution. These statistics were generated by Monte-Carlo simulations, and presented in terms of burst error length average and quantile (90 and 99%) statistics versus SNR (Eb/N0) parameterized by the fading intensity parameter m. The results indicate how Viterbi decoder burst error statistics vary with the fading/scintillation intensity m for Nakagami-m channels, and, consequently, provide information important to the design of interleaved or noninterleaved concatenated coding schemes for such channel environments View full abstract»

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  • Multireception probabilities for FH/SSMA communications

    Page(s): 223 - 233
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (700 KB)  

    Exact expressions for the probabilities P(l,m-l/k) of l correct packet receptions and m-l erroneous ones, out of total k packets contending in a slot, are presented for the case of frequency-hopped spread-spectrum random-access slotted networks employing random frequency hopping patterns. These expressions are difficult to evaluate numerically for values of m>3. However, their numerical analysis indicates that under light traffic conditions these probability values are very close to the ones provided by the independent receiver operation assumption, under which the distribution of multireception obeys the binomial law View full abstract»

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  • Analysis of a new bit tracking loop-SCCL

    Page(s): 199 - 209
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    The authors propose a new bit tracking loop for biphase signals which is implemented like the maximum a posteriori probability (MAP) optimal bit synchronizer by the sample-correlate choose-largest algorithm except that the estimator is sampled and moved at most one sample each bit time. A mathematical Markovian model for analysis is used. The performance of the bit tracking loop, the mean square error of the jitter and the average acquisition time, are theoretically derived. The numerical results of performance analysis for various signal-to-noise ratios are found through computer evaluations. The data obtained illustrate that this new structure is a very effective bit synchronizer for digital communications systems applying digital signal processing techniques View full abstract»

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  • Performance of coded systems over fading dispersive channels

    Page(s): 51 - 59
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    The authors consider a number of topics concerned with coding schemes over fading dispersive channels. They begin with comparing the performance of the energy receiver with the optimum and envelope receivers. Different coding schemes are used to improve the performance. The effect of channel spread on the performance of single-state Reed-Solomon (RS) codes is investigated. Channel information (CI) is discussed as a means for further improvement. The simple erasure criterion used is suboptimal, but gives a measure of the gain that can be achieved by using CI. Of special interest is the use of a concatenated coding technique for forming codes of large distance. Concatenated codes using short RS codes with CI as inner codes and RS outer codes are compared. It has been shown that the improvement obtained by concatenation is significant for overspread channels. This is attributed to the implicit diversity introduced by the channel. Furthermore, a concatenated system using convolutional codes as inner codes performs better than the system using RS inner codes View full abstract»

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  • Exact analysis of the outage probability in multiple-user mobile radio

    Page(s): 20 - 23
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    A novel mathematical method is presented to express the outage probability for a desired radio signal received from a mobile transmitter in the presence of multiple interfering signals with combined log-normal and Rayleigh fading. In contrast to previously reported analyses, this exact method avoids approximation of the PDF of the received powers of the various signals. This is useful in determining the spectrum efficiency and performance of (interference-limited) radio networks for high-capacity cellular telephony, two-way paging, packet radio and other mobile data networks View full abstract»

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  • Six-dimensional trellis-coding with QAM signal sets

    Page(s): 24 - 33
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    A family of 6-D trellis-coded modulation (TCM) schemes which involve a 2-step partitioning of the constituent QAM signal alphabet is presented. With infinite constellations without shaping, the asymptotic coding gain is 3 dB for the 2-state code, 4 dB for the 4- and 8-state codes, and 5 dB for the 16- and 32-state codes which involve a smaller alphabet expansion. The authors also describe a rotationally invariant 16-state code that achieves the same asymptotic gain as its linear counterpart. Practical signal constellations are described for 6-D TCM with the spectral efficiency of uncoded 64-QAM, and the performance of these schemes is studied by means of computer simulations. It was found that they achieve an additional coding gain of 0.2-0.3 dB over infinite hypercube-type constellations. The performance of the presented schemes at practical signal-to-noise ratio values is evaluated using transfer function techniques View full abstract»

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  • Variable-rate hybrid ARQ for meteor-burst communications

    Page(s): 60 - 73
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    The authors introduce a form of automatic repeat request (ARQ), referred to as variable-rate type-I hybrid ARQ, in which the code rate varies in response to the fluctuations in the power received from a meteor trail. For one implementation, the source or the destination periodically obtains estimates of the signal power at the destination, and the source uses these estimates to select the rate of the code. For an alternative approach, the code rate is determined completely by the decoding successes and failures during previous transmissions. The performance measure is the throughput per trail, which is defined as the expected number of information bits received correctly for a given meteor trail. Numerical results for Reed-Solomon codes are included to illustrate the relative performance of the various schemes. It is shown that the throughput is larger for both implementations of variable-rate type-I hybrid ARQ than for fixed-rate type-I hybrid ARQ and ARQ without forward error correction 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