By Topic

Communications, IEEE Transactions on

Issue 5 • Date May 1984

Filter Results

Displaying Results 1 - 23 of 23
  • [Front cover and table of contents]

    Page(s): 0
    Save to Project icon | Request Permissions | PDF file iconPDF (212 KB)  
    Freely Available from IEEE
  • [Back cover]

    Page(s): 0
    Save to Project icon | Request Permissions | PDF file iconPDF (194 KB)  
    Freely Available from IEEE
  • Spectral Analysis of Line Regenerator Time Jitter

    Page(s): 561 - 566
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    A closed form expression for the spectral density of the time jitter produced in a line regenerator in the presence of a general polynomial nonlinear circuit, band-limited baseband pulses, and an arbitrary tuned filter is developed. The method applies to a PAM digital signal with mutually independent symbols but with an arbitrary number of levels and symbol probabilities. As an example of the method, the spectrum of the time jitter produced in the presence of a fourth power law nonlinear circuit is reported. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Message Delays for TDMA Scheme Under a Nonpreemptive Priority Discipline

    Page(s): 583 - 588
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    A TDMA access-control scheme operating under a nonpreemptive message-based priority discipline is considered and analyzed. The moment generating function (MGF) of the message waiting-time is obtained, at an arbitrary station of the network, under the assumptions of a Poisson message arrival stream and random message lengths governed by a general distribution, for each priority class. Using these results, explicit formulas for any moment of the message delay can be obtained. In particular, expressions for the average and standard deviation of the message waiting-time are presented, for the case when short (e.g., interactive) messages have priority over longer (e.g., batch) messages. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Error Probability Bounds and Approximations for DS Spread-Spectrum Communication Systems with Mutiple Tone or Multiple Access Interference

    Page(s): 493 - 502
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    Upper and lower bounds on the average probability of error of direct sequence (DS) spread-spectrum communication systems operating in the presence of either multiple tone or multiple access interference are presented. The bounds are quite tight and can be used without the restriction that the peak level of the interference be less than the desired signal level. A simple method for evaluating approximations to the bounds for multiple access systems, in which the peak interference does indeed exceed the desired signal level, is presented as well. The tightness of both the bounds and the approximations are illustrated with numerical results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The Effect of High-Level Acknowledgment Traffic on the Throughput of ALOHA Channels

    Page(s): 640 - 642
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    The behavior of the throughput of an ALOHA channel is investigated, taking into account the effect of acknowledgment traffic when the acknowledgment mechanism is provided by high-level protocols. It is shown that the use of redundant ACK packets slightly increases the channel throughput. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High-Level Modulation and Coding for Nonlinear Satellite Channels

    Page(s): 616 - 626
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1040 KB)  

    Currently, 4-PSK is the prevalent modulation format in use for digital satellite communications. To improve bandwidth efficiency, 8PSK could be used instead, but a higher power would be needed; to improve power efficiency, error-correcting codes could be used, but at the expense of a larger bandwidth. Recently, Ungerboeck [1] has proposed a class of codes in which a constellation of2Msignals is used to transmit information at the rate oflog_{2} Mbits per symbol, and has shown that coding gains of up to several decibels can be achieved on the additive white Gaussian noise (AWGN) channel with no increase in bandwidth occupancy and a relatively small added complexity. Thus, these codes seem to be particularly attractive for application in the band-limited environment typical of satellite communication systems, provided that the performance gain that they provide on the AWGN channel is not lost over a satellite channel. The goal of this work is to assess the performance of this class of codes when used to transmit 3 information bits per symbol on a band-limited, nonlinear satellite channel. Three modulation formats are considered, namely 16-PSK, 16-QAM, and a 16-ary amplitude-phase keying scheme with two amplitude levels. It is found that 16-PSK outperforms the two other modulation formats, and that the use of these codes can provide a substantial performance improvement even on a satellite channel. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multipath Outage Performance of Digital Radio Receivers Using Finite-Tap Adaptive Equalizers

    Page(s): 597 - 608
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB)  

    Recent analysis/simulation studies have quantified the multipath outage statistics of digital radio systems using ideal adaptive equalization. In this paper, we consider the use of finite-tap delay line equalizers, with the aim of determining how many taps are needed to approximate ideal performance. To this end, we assume anM-level QAM system using cosine rolloff spectral shaping and an adaptive equalizer with either fractionally spaced or synchronously spaced taps. We invoke a widely used statistical model for the fading channel and computer-simulate thousands of responses from its ensemble. For each trial, we compute a detection signal-to-distortion measure, suitably maximized with respect to the tap gains. We can thereby obtain probability distributions of this measure for specified combinations of system parameters. These distributions, in turn, can be interpreted as outage probabilities (or outage seconds) versus the number of modulation levels. A major finding of this study is that, for the assumed multipath fading model, very few taps (the order of five) are needed to approximate the performance of an ideal infinite-tap equalizer. We also find that a simple, suboptimal form of timing recovery is generally quite adequate, and that fractionally spaced equalizers are more advantageous than synchronously spaced equalizers with the same number of taps. This advantage is minor for rolloff factors of 0.5 and larger but increases dramatically as the rolloff factor approaches zero. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Partial Correlation Effects in Direct-Sequence Spread-Spectrum Multiple-Access Communication Systems

    Page(s): 567 - 573
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    Nearly all previous analytical results on the performance of direct-sequence spread-spectrum multiple-access (DS/SSMA) communication systems are restricted to systems in which the periodpof the signature sequence is equal to the numberNof chips per data symbol. In many applications, however, it is necessary to employ signature sequences whose periodpis much larger thanN. Thus, successiveN-chip segments of the signature sequence are used to phase-code the carrier during the transmission of successive data symbols. The performance of such systems depends on the partial correlation properties of the signature sequences (rather than the aperiodic correlation properties as in the case whenN=p). In this paper, we consider the performance of a DS/SSMA system for arbitrary values ofpandN. As special cases of our results, we delermine the effects of partial correlation in three classes of systems: those for whichN =p, those for whichNandpare relatively prime, and those for whichNis a divisor ofp. We also provide two methods for the design of sequences for systems for whichNis a divisor ofp. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • DPSK Signaling Over Hard Limiting Channel in the Presence of Intersymbol Interference

    Page(s): 503 - 510
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    This paper considers the performance evaluation of binary differentially-phase-shift-keyed signals which have been transmitted through a hard limiting channel in the presence of intersymbol interference and additive Gaussian noise. An expression for the probability of error is derived which is in the form of an infinite series. In the analysis, the effects of Gaussian noise in the uplink and downlink are taken into consideration. The intersymbol interference is assumed to be present in the uplink only. In order to illustrate the applicability of the method, numerical results are computed for a channel which employs a Butterworth filter. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Unified Approach to Serial Search Spread-Spectrum Code Acquisition--Part I: General Theory

    Page(s): 542 - 549
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    The purpose of this two-part paper is threefold: 1) Part I discusses the code-acquistion problem in some depth and 2) also provides a general extension to the approach of analyzing serial-search acquisition techniques via transform-domain flow graphs; 3) Part II illustrates the applicability of the proposed theoretical framework by evaluating a matchedfilter (fast-decision rate) noncoherent acquisition receiver as an example. The theory is formulated in a general manner which allows for significant freedom in the receiver modeling. The statistics of the acquisition time for the single-dwell [2], [3] andN-dwell [5] systems are shown to be special cases of this unified approach. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the Relationship Between Geostationary Orbit Capacity and the Interference Allowance

    Page(s): 627 - 634
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    With the increasing demands being placed upon the geostationary orbit/spectrum resource, there is a need to consider the impact of increasing the intersatellite interference allowance. By increasing the intererence allowance, more satellites can be placed along the geostationary orbit. However, as a result, an individual sateilite's capacity will be reduced. This paper examines the tradeoff between intersatellite interference and total orbit capacity for both digital and analog modulation methods. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Delay Analysis of Packet Switching System with a Satellite Having Processing Capability

    Page(s): 642 - 644
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    This correspondence deals with the satellite packet switching system employing a frame format proposed by Ng and Mark [1], and analyzes the average queueing and scheduling delay without a rough approximation made by Ng and Mark [2]. The numerical results indicate that the delay computed by the proposed algorithms is quite different from that given by Ng and Mark, especially in both the regions of low and high traffic intensities. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the Coding Gain of Linear Binary Block Codes

    Page(s): 635 - 638
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    The coding gain of linear binary block codes on the AWGN channel is studied. Antipodal signaling and hard decision demodulation are assumed. Simple asymptotic expressions for the gain at high and low energy to noise spectral density ratios are derived. Monotonicity of the coding gain is also discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Unified Approach to Serial Search Spread-Spectrum Code Acquisition--Part II: A Matched-Filter Receiver

    Page(s): 550 - 560
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    The unified theory developed in Part I [1] is employed here in the analysis of a noncoherent, matched-filter (fast-decision-rate) code acquisition receiver in a direct-sequence spread-spectrum system. The results illustrate the dynamic dependence of the mean acquisition time on system parameters, such as the predetection signal-to-noise ratio (SNR), the decision threshold settings, and the ratio of the decision rate to the code rate. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptive Equalization for SQPSK and SQPR Over Frequency Selective Microwave LOS Channels

    Page(s): 609 - 615
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    This paper compares the effectiveness of linear and decision feedback equalizers in counteracting the effect of frequency-selective distortion in microwave relay links. A quadratic frequency-selective model of the channel is employed and particular attention is given to channels with a null in the passband. Both staggered QPSK and QPR modems are studied. Performance is studied for error probability and mean squared error. The general conclusion is reached that a decision feedback equalizer is required for robust performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The Detection of Errors After Error-Correction Decoding

    Page(s): 511 - 517
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    In data transmission and storage systems, combined error correction and detection procedures are often used to provide high reliability. This paper considers the use of separate concatenated codesCandDfor error correction and detection, respectively. It examines the error detection performance of codeDto determine how the probability of undetected error depends on the choice ofCandD. A comparison is made of the probability of undetected error achievable by codeDwith and without error correction, respectively. Asymptotic bounds for low bit error rates are developed which provide criteria to be considered when choosing codesCandD. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Frequency Hopping with Multiple Frequency-Shift Keying and Hard Decisions

    Page(s): 574 - 582
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (744 KB)  

    The performance of frequency-hopping systems with multiple frequency-shift keying and hard decisions is determined for operation against optimal partial-band jamming. A receiver that eliminates the potential advantage of optimally placed jamming tones is proposed. The effects of Reed-Solomon, binary block, and convolutional codes are analyzed. Concatenated codes with hard and soft decisions available to the outer decoder are examined. Continuous-phase frequency-shift keying with limiter-discriminator demodulation is shown to offer potentially improved performance in frequency-hopping systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Node Synchronization for the Viterbi Decoder

    Page(s): 524 - 531
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    Motivated by the needs of NASA's Voyager 2 mission, in this paper we describe an algorithm which detects and corrects losses of node synchronization in convolutionally encoded data. This algorithm, which would be implemented as a hardware device external to a Viterbi decoder, makes statistical decisions about node synch based on the hard-quantized undecoded data stream. We will show that in a worst-case Voyager environment, our method will detect and correct a true loss of synch (thought to be a very rare event) within several hundred bits; many of the resulting outages will be corrected by the outer Reed-Solomon code. At the same time, the mean time between false alarms is on the order of several years, independent of the signal-to-noise ratio. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bandwidth Efficient Quadrature Overlapped Modulation

    Page(s): 638 - 640
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    This correspondence describes modified QORC (MQORC) modulation. The power spectral density of MQORC is shown to take on the form of the product of the QPSK and SFSK spectra, which attains good spectral characteristics. We show that the bandpass hard-limited staggered MQORC tends to keep its sidelobes suppressed, and therefore, its sidelobes drop off faster compared to staggered QORC. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Recent Results on the Use of Concatenated Reed-Solomon/Viterbi Channel Coding and Data Compression for Space Communications

    Page(s): 518 - 523
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    The development of sophisticated adaptive source coding algorithms together with inherent error sensitivity problems fostered the need for efficient space communication at very low bit error probilbilities(leq 10^{-6}). This led to the specification and implementation of a concatenated coding system using an interleaved Reed-Solomon code as the outer code and a Viterbi-decoded convolutionai code as the inner code. This paper presents the experimental results of this channel coding system under an emulatedS-band uplink andX-band downlink two-way space communication channel, where both uplink and downlink have strong carrier power. Test results verify that at a bit error probability of 10-6or less, this concatenated coding system does provide a coding gain of 2.5 dB or more over the viterbi-decoded convolutional-only coding system. These tests also show that a desirable interleaving depth for the Reed-Solomon outer code is 8 or more. The imptict of this "virtually" error-free space communication link on the transmission of images is discussed and examples of Simulation results are given. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Coding for a Multiple-Access Frequency-Hopping System

    Page(s): 589 - 597
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    A multiuser system employing on-off FSK modulation in conjunction with frequency hopping is examined for digital transmission. The receiver consists of a bank of bandpass noncoherent detectors followed by a message decoder. An analysis is presented for a transmission channel characterized by Rayleigh fading and additive Gaussian noise. The main source of impairment is interference between users. An upper limit on the number of simultaneous system users for acceptable transmission quality is derived. An example of a system with (one-way) bandwidth of 20 MHz and transmission rate of 32 kbits/s per user shows a maximum of 169 users at an average SNR on the channel of 25 dB and a bit error probability not exceeding 10-3. The effect of applying error correcting codes to the system is evaluated. It is shown how Reed-Solomon codes can be used to generate both user identification and message coding. Such coding increases the number of users the system can accommodate in the example above to 212. Convolutional codes are shown to be even more effective. Such a code of constraint length 2 results in 285 simultaneous users in the example, which is an increase of 70 percent over an uncoded system. The drawback of coding is an increased complexity of the receiver. The amount of computation needed for the decoding of block and convolutional codes is estimated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The Output Distribution of Median Type Filters

    Page(s): 532 - 541
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    The distribution of the output of the one-dimensional median filter is derived for several cases including thekth-order output distribution with any input distribution. This is then used in several illustrative examples of median filtering a signal plus white noise. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia