By Topic

Communications, IEEE Transactions on

Issue 7 • Date Jul 1995

Filter Results

Displaying Results 1 - 14 of 14
  • Simultaneous clock phase and frequency offset estimation

    Publication Year: 1995 , Page(s): 2263 - 2270
    Cited by:  Papers (35)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    Residual frequency offsets may often result in poor functioning of a digital receiver. This is particularly true in a frequency selective environment where an adaptive equalizer may be required. In this paper, a frequency offset estimation algorithm is presented which is based on applying a nonlinear operation on the received sampled baseband signal. Tones at multiples of the clock frequency are produced and the phases of these tones provide both the desired frequency offset and clock phase information. This algorithm is intended to operate without knowledge of the pulse shape and therefore may be suitable for frequency selective environments. Additionally, the clock phase may be estimated with very little overhead. Simulations with AWGN, flat and frequency selective fading channels are included View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On a class of Banyan networks and tandem Banyan switching fabrics

    Publication Year: 1995 , Page(s): 2231 - 2240
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    This paper examines the operating characteristics of a class of tandem Banyan switching fabrics (TBSF's) built using bi-delta networks. We use the functional equivalence between bi-delta networks to induce an equivalence between TBSF's. A weaker form of equivalence guaranteeing identical performance under conditions of symmetric traffic is studied, and a sufficient condition for weak equivalence between functionally distinct TBSF's is established. These results hold for a variety of conflict resolution policies (CRP's) in addition to the one studied by Tobagi et al. (see IEEE J. Select. Areas Commun., vol.9, p.1173, 1991). Simulations indicate that a TBSF constructed by cascading omega networks, (or in fact any other TBSF in its weak equivalence class), performs better than the two TBSF's studied by Tobagi et al., and converges rapidly to a theoretical lower bound on the loss rate, in the region of interest. It is also shown that this loss rate is almost independent of the size of such a TBSF in the region of interest View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Extension of the normalized two-ray transfer-function model to a space-diversity line-of-sight link

    Publication Year: 1995 , Page(s): 2271 - 2280
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (820 KB)  

    Many methods for the prediction of multipath effects on the availability of a digital microwave line-of-sight link use a mathematical and statistical modeling of the propagation channel transfer function. Such a method, making use of the normalized two-ray model and adapted to a nonprotected hop, has been presented in a previous paper. In this paper we investigate the possibility to extend this model to a diversity channel, while keeping the statistical representation of the channel as simple as possible. Two theoretical possibilities, each leading to only one new statistical coefficient, are presented and validated on experimental data. From this result, a simple extension of the availability prediction method to a diversity channel seems to be feasible. Some problems remain to be solved however, which are discussed in the concluding section View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptive nondisruptive measurement of harmonic distortion for voiceband data transmission

    Publication Year: 1995 , Page(s): 2184 - 2200
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1392 KB)  

    Volterra functional expansions are power series with memory that explicitly characterize the input/output relationship of a finite-memory single-valued nonlinear black box whenever the latter is time-invariant and stable. The purpose of this paper is to introduce and report on the strengths and weaknesses of two distinct Volterra-series-type classes of adaptive nonlinear techniques for the quantitative measurement of second- and third-order harmonic distortion present in the communications channel of a, possibly signal space coded, QAM data communication system. Our investigation was originated as part of a request for new nondisruptive impairment measurement algorithms that would reliably characterize in real-time the performance of voiceband modems over both D1 conditioned private lines and the direct-distance-dialing (DDD) public switched network. Though, contrary to earlier studies, we do not contemplate nonlinear distortion compensator design, experimental evidence obtained by implementing the simplest of our nondisruptive algorithms on a digital signal processor chip verifies that over a certain range of signal-to-second- and third-order intermodulation distortion ratios our measurements are consistent with those obtained via the disruptive digital four tone test under a variety of voiceband telephone channel impairment conditions. Unfortunately, our experiments also indicate that neither the digital four-tone test nor any of our nondisruptive techniques have chances to prove useful for greater than 5% of the existing voiceband channels. However, this is entirely due to the special nature of the telephone channel environment and is not likely to dilute the importance of our proposal for other types of nonlinear environments such as radio channels or satellite links View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance of packet-switched fiber-optic frequency-hopping multiple-access networks

    Publication Year: 1995 , Page(s): 2241 - 2253
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1140 KB)  

    A packet-switched frequency-hopping multiple-access (FO-FHMA) communication system based on bus topology is proposed and investigated. In this arrangement, access to the optical medium for the network subscribers is provided via frequency-hopping (FH). The proposed FH technique in this analysis takes advantage of the Reed-Solomon (RS) codes to encode information packets and, consequently, to combat possible burst errors at the receiver. At user locations, encoded subpackets are frequency-hopped with the aid of a phase modulator, using a preassigned FH pattern for transmission over the optical medium. At the receiver site, a balanced phase discriminator/detection device followed by a frequency-dehopping receiver is used to recover the desired information. An alternative receiver structure, where the received signal is heterodyned prior to dehopping, is also proposed. The implications of this coherent detection are consequently discussed. Performance measures in terms of throughput and probability of incorrect decoding for chip synchronous model with asynchronous transmission characteristic in the absence of side information are obtained to assess the viability of the proposed packet-switched fiber-optic multiple-access communication system. Numerical results are presented when short RS codes are utilized as FH assignment codes View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Pilot symbol assisted modulation and differential detection in fading and delay spread

    Publication Year: 1995 , Page(s): 2206 - 2212
    Cited by:  Papers (21)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    Pilot symbol assisted modulation (PSAM) has previously been shown to give good performance in flat fading, noise and cochannel interference. The present paper analyzes its performance in ISI due to frequency selective fading, and provides a similar analysis of differential detection for comparison. The paper also introduces a method for performing the formidable average over transmitted data patterns simply, and with an analytical result, PSAM is shown to be sensitive to RMS delay spread, though it always gives better performance than differential detection View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A lower bound on the mean square error of symbol timing recovery for NRZ rectangular signals

    Publication Year: 1995
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (64 KB)  

    In this paper which is based on previous work (see ibid., vol.40, p.1635, 1992), a closed-form lower bound on the mean square error of symbol timing recovery is reported for NRZ rectangular pulse sequences. The bound is a function of the fundamental parameters Eb the symbol energy and N0 the noise power spectral density View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spur-reduced digital sinusoid synthesis

    Publication Year: 1995 , Page(s): 2254 - 2262
    Cited by:  Papers (35)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (772 KB)  

    This paper presents and analyzes a technique for reducing the spurious signal content in digital sinusoid synthesis. Spur reduction is accomplished through dithering amplitude and phase values prior to wordlength reduction. The analytical approach developed for analog quantization is used to produce new bounds on spur performance in these dithered systems. Amplitude dithering allows output wordlength reduction without introducing additional spurs. Effects of periodic dither similar to that produced by a pseudo-noise (PN) generator are analyzed. This phase dithering method provides a spur reduction of 6(M+1) dB per phase bit when the dither consists of M uniform variates. While the spur reduction is at the expense of an increase in system noise, the noise can be made white, making the noise power spectral density small. This technique permits the use of a smaller number of phase bits addressing sinusoid look-up tables, resulting in an exponential decrease in system complexity. Amplitude dithering allows the use of less complicated multipliers and narrower data paths in purely digital applications, as well as the use of coarse-resolution, highly-linear digital-to-analog converters (DAC's) to obtain spur performance limited by the DAC linearity rather than its resolution View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Image compression using VQ-BTC

    Publication Year: 1995 , Page(s): 2177 - 2182
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Vector quantization (VQ) and block truncation coding (BTC) are successful image compression techniques. However, a reproduced image using VQ or BTC suffers from edge degradation. A new technique that combines the advantages of both VQ and BTC to combat this degradation is presented and is referred to as VQ-BTC. In VQ-BTC, a low-detail block is encoded using VQ. For a high-detail block, a modification of BTC is used to determine the locations of the relatively lighter and relatively darker pixels inside the block and VQ is then used to encode each. VQ-BTC provides improved edge reproduction and much lower bit rates than those obtained by BTC View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A new adaptive hybrid ARQ scheme

    Publication Year: 1995 , Page(s): 2169 - 2171
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    First Page of the Article
    View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Variable rate QAM for mobile radio

    Publication Year: 1995 , Page(s): 2223 - 2230
    Cited by:  Papers (184)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Quadrature amplitude modulation (QAM) schemes which vary the number of modulation levels in accordance with the mobile radio fading channel variations are investigated. Important parameters considered are the fading rate and the block size used. We describe how the adaptive QAM modems can be employed and consider their use in a DECT-like TDD packet structure. System performance in the presence of cochannel interference is also considered. Simulations show that the variable rate system has about 5 dB improvement in channel SNR over a fixed 16-level QAM system for BER's between 10-2 and 10-5 and channel SNR's between 25 and 40 dB View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A multirate acoustic echo canceler structure

    Publication Year: 1995 , Page(s): 2172 - 2176
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    A new subband echo canceler (SBEC) structure is proposed to reduce the transmission delay introduced by conventional SBEC structures, without distorting the near-end signal. The proposed structure is based on computing two output errors, one for using during single-talk and the other one for using during double-talk periods. With the SBEC structure we propose a double-talk detector with a subband configuration which allows a fast and accurate detection of double-talk periods, enabling the SBEC algorithm to track changes in the echo path impulse response when the near-end signal is absent. Computer simulations using actual speech signals, and subjective evaluation tests are given to show the convergence performance, tracking and double-talk detection ability, of the proposed scheme View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimum transmission ranges in multihop packet radio networks in the presence of fading

    Publication Year: 1995 , Page(s): 2201 - 2205
    Cited by:  Papers (51)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    The evaluation of optimum transmission ranges in a packet radio network in a fading and shadowing environment is considered. It is shown that the optimal probability of transmission of each user is independent of the system model and is po≃0.271. The optimum range should be chosen so that on the average there are χ(G/b)2η/ terminals closer to the transmitter than the receiver, where G is the spread spectrum processing gain, b is the outage signal-to-noise ratio threshold, η is the power loss factor and χ depends on the system parameters and the propagation model. The performance index is given in terms of the optimal normalized expected progress per slot, given by ϑ(G/b)1η/ where ϑ is proportional to the square root of χ. A comparison with the results obtained by using deterministic propagation models shows, for typical values of fading and shadowing parameters, a reduction up to 40% of the performance index View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Blind equalization by direct examination of the input sequences

    Publication Year: 1995 , Page(s): 2213 - 2222
    Cited by:  Papers (20)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    This paper presents a novel approach to blind equalization (deconvolution), which is based on direct examination of possible input sequences. In contrast to many other approaches, it does not rely on a model of the approximative inverse of the channel dynamics. To start with, the blind equalization identifiability problem for a noise-free finite impulse response channel model is investigated. A necessary condition for the input, which is algorithm independent, for blind deconvolution is derived. This condition is expressed in an information measure of the input sequence. A sufficient condition for identifiability is also inferred, which imposes a constraint on the true channel dynamics. The analysis motivates a recursive algorithm where all permissible input sequences are examined. The exact solution is guaranteed to be found as soon as it is possible. An upper bound on the computational complexity of the algorithm is given. This algorithm is then generalized to cope with time-varying infinite impulse response channel models with additive noise. The estimated sequence is an arbitrary good approximation of the maximum a posteriori estimate. The proposed method is evaluated on a Rayleigh fading communication channel. The simulation results indicate fast convergence properties and good tracking abilities 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