By Topic

Communications, IEEE Transactions on

Issue 4 • Date Apr 1998

Filter Results

Displaying Results 1 - 22 of 22
  • Performance of FH SS radio networks with interference modeled as a mixture of Gaussian and alpha-stable noise

    Page(s): 509 - 520
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    We consider the performance of frequency-hopping spread spectrum (FH SS) radio networks in a Poisson field of interfering terminals using the same modulation and power. The problem is relevant to wireless random-access communication systems where little information about transmitters requires stochastic modeling of their positions. Assuming that the signal strength is attenuated over distance r on average as 1/r m, we show that the interference in the network could be modeled as a mixture of Gaussian and α-stable noise. Based on this modeling, we derive expressions for the probability of error (Pe ) for systems with M-ary frequency shift keying (FSK) which use conventional envelope detectors. Because conventional envelope detectors are optimum only in Gaussian noise and are suboptimum in the noise considered, we also investigate noncoherent detectors which offer improved performance. We examine receivers with limiting nonlinearities and detectors which are optimal in Cauchy noise. Numerical calculations and Monte Carlo simulations are provided to confirm the accuracy of the analysis presented. The results obtained are useful in the performance evaluation of multiple-access radio networks in environments varying from urban settings to office buildings with deterministic and stochastic propagation laws such as lognormal shadowing and Rayleigh fading View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • New results about analysis and design of TCM for ISI channels and combined equalization/decoding

    Page(s): 417 - 420
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    New upper bounds for the performance of the optimum combined symbol-by-symbol (SbS) Abend-Fritchman-like equalizer and decoder are presented, and a related criterion for the actual design of good trellis-coded-modulated (TCM) schemes effectively matched to the distortion introduced by the intersymbol interference (ISI)-corrupted transmission channel is developed. The actual application of the proposed design criterion is also addressed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Detection of errors recovered by decoders for signal quality estimation on rain-faded AWGN satellite channels

    Page(s): 446 - 449
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    We describe a method for estimating satellite link quality for use with rain fade countermeasures. The method applies to convolutionally encoded bit streams. It is based on the measurement of the uncoded data bit-error rate (BER) which is estimated by monitoring the errors recovered by a Viterbi decoder. Using a previously developed attenuation model, the measurement time intervals are optimized for a simple application, and the performance of the estimator is shown View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Combined channel estimation and data detection using soft statistics for frequency-selective fast-fading digital links

    Page(s): 424 - 427
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    A novel adaptive nonlinear equalizer for fast time-varying multipath channels that combines the channel estimation and data detection tasks is presented. The a posteriori probabilities (APPs) of the states of the intersymbol interference (ISI) channel are recursively computed from the received data by a symbol-by-symbol (SbS) detector and are then employed by a Kalman-type nonlinear channel estimator. Robust channel tracking and good data-detection performance are obtained, with a reasonable receiver complexity View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Differential detection of GMSK signals with low BtT using the SOVA

    Page(s): 428 - 430
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB)  

    A noncoherent Gaussian minimum phase-shift keying (GMSK) detector using differential phase detection combined with the soft-output Viterbi algorithm (SOVA) is presented. This approach overcomes the severe intersymbol interference (ISI) of GMSK signals with low BtT. Unlike conventional detectors the SOVA produces soft-decision bits resulting in larger coding gains in subsequent convolutional decoders View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Algorithms for automatic modulation recognition of communication signals

    Page(s): 431 - 436
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    This paper introduces two algorithms for analog and digital modulations recognition. The first algorithm utilizes the decision-theoretic approach in which a set of decision criteria for identifying different types of modulations is developed. In the second algorithm the artificial neural network (ANN) is used as a new approach for the modulation recognition process. Computer simulations of different types of band-limited analog and digitally modulated signals corrupted by band-limited Gaussian noise sequences have been carried out to measure the performance of the developed algorithms. In the decision-theoretic algorithm it is found that the overall success rate is over 94% at the signal-to-noise ratio (SNR) of 15 dB, while in the ANN algorithm the overall success rate is over 96% at the SNR of 15 dB View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Choosing the best logk(N, m, P) strictly nonblocking networks

    Page(s): 454 - 455
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    We extend the log2 (N, m, P) network proposed by Shyy and Lea (1991) to base k. We give a unifying proof (instead of three separate cases as done by Shyy and Lea) for the condition of being strictly nonblocking, and a simpler expression of the result. We compare the number of crosspoints for logk(N, m, p) over various k View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Iterative implementation of linear multiuser detection for dynamic asynchronous CDMA systems

    Page(s): 503 - 508
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    Several linear multiuser detectors for code-division multiple access (CDMA) systems can be characterized as an inverse of some form of correlation matrices. If the correlations change, the detectors must be redesigned. An ideal computation of the decorrelating or the linear minimum mean-squared-error (LMMSE) detector requires order K3 flops, where K is the number of users. To alleviate the computational complexity, iterative decorrelating and LMMSE detectors are proposed. The iterative detectors use steepest descent (SD), conjugate gradient (CG), and preconditioned conjugate gradient (PCG) algorithms, and require order K2 flops per iteration. Their main advantages are the reduced number of flops and their suitability to highly parallel implementations. The correlation coefficient computation can also be embedded into the CG algorithm, which is an advantage with time-varying signature waveforms. The performance of the iterative algorithms is studied via computer simulations View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance analysis of optimum combining in wireless communications with Rayleigh fading and cochannel interference

    Page(s): 473 - 479
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    Optimum combining for space diversity reception is studied in digital cellular mobile radio communication systems with Rayleigh fading and multiple cochannel interferers. This paper considers binary phase-shift keying (BPSK) modulation in a flat Rayleigh-fading environment when the number of interferences L is no less than the number of antenna elements N(L⩾N). The approach of this paper and its main contribution is to carry out the analysis in a multivariate framework. Using this approach and with the assumption of equal-power interferers, it is shown that the probability density function of the maximum signal-to-interference ratio (SIR) at the output of the optimum combiner has a Hotelling T2 distribution. Closed form expressions using hypergeometric functions are derived for the outage probability and the average probability of bit error. Theoretical results are demonstrated by Monte Carlo simulations View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Joint delay-power capture in spread-spectrum packet radio networks

    Page(s): 450 - 453
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    Capture phenomena in slotted ALOHA packet radio networks employing spread-spectrum modulation is considered. Probability of capture with both delay and power capture mechanisms are derived and compared with power- and delay-only capture models. Significant improvements in the capture probability is observed. The improvement over the delay-only capture model increases with decreasing arrival-time randomization overhead View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Throughput performance of an FHMA system with variable rate coding

    Page(s): 521 - 532
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    We compare throughput bounds for a frequency-hopped multiple-access (FHMA) system employing variable rate as well as fixed rate coding (FRC). Nonfading as well as Rayleigh-fading channels are explored. The throughput bounds for the variable rate coding (VRC) schemes are based on the assumption that the number of active users in the system, m, is known at any time while the bounds for the FRC scheme assumes that the fixed code rate is optimized for the user population mean, λ, where the population is assumed to be Poisson distributed. We present bounds for theoretical “perfect” codes which achieve the capacity as well as bounds for Reed-Solomon (RS) codes of practical block lengths. Finally, we show the dependence of a VRC scheme upon the accuracy of the estimates of m and present a general comparison of the gains of using VRC versus a realistic FRC scheme View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Matched filter bound for multipath Rician-fading channels

    Page(s): 441 - 445
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    This paper derives an infinite series and an integral for computing matched filter bounds for binary phase-shift keying (BPSK) communications over a multipath Rician-fading channel of discrete or continuous dispersion. Based on the derived bound we compare intrinsic frequency diversity (IFD) gains for channels of different Rician factors View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The performance of continuous-phase-coded DS/SSMA communications

    Page(s): 533 - 543
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    A class of spread-spectrum systems with continuous-phase spreading signals is proposed. We present a characterization of the spectral-spreading signals that allows computation of various measures of the system performance, such as the signal-to-noise ratio (SNR), spectral density, and average bit-error probability. The error probability can be evaluated if the distributions of the multiple-access interferences (MAIs) are available. We obtain the conditional distributions of random variables that characterize the MAI given the time delays. These conditional distributions are used to compute vectors, allowing the average bit-error probability to be computed with arbitrary accuracy. Since most of the computations only involve array additions and multiplications, these operations can be performed efficiently on array processors View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • PLL FM demodulator performance under Gaussian modulation

    Page(s): 437 - 440
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB)  

    A widespread test of the phase-locked loop (PLL) FM demodulator under Gaussian modulation is simulated using the Monte Carlo method. Unified noise-free and noise performance analyses of the PLL FM demodulator are presented. Substantial reduction of the modulation limit by the input bandpass filter is reported in the region of the input bandwidth of practical interest. Bessel bandpass filters of order greater than two are shown to compare favorably with Butterworth filters in front of the PLL FM demodulator relative to the intermodulation (IM) distortion. A lower bound on the loop noise bandwidth is found by minimizing the output click rate for given IM distortion specifications. FM threshold of 4 and 7 dB for the root-mean-square (RMS) frequency deviation-to-message bandwidth ratio 0.1 and 1.0, respectively, is reported on the worst-case IM distortion of 45 dB View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Asynchronous classification of MFSK signals using the higher order correlation domain

    Page(s): 480 - 493
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    The problem of asynchronous classification of M-ary frequency-shift keying (MFSK) signals when contaminated by additive white Gaussian noise (AWGN) is addressed. Two approaches are adopted. The first is based on the classical likelihood-ratio theory, which provides performance that is optimal, but sensitive to unknown frequency offsets. The second completely eliminates the fixed-frequency structure and instead utilizes measurements made strictly in the higher order correlation (HOC) domain. Assessed are the sensitivity gaps in performance incurred by the synchronous rules when the unknown signal time of arrival or epoch offsets are introduced. This sensitivity is ameliorated by averaging over a reduced-uncertainty epoch model. Fairly satisfactory results are reported with a small number of the discretized epoch uncertainty levels View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A statistical basis for lognormal shadowing effects in multipath fading channels

    Page(s): 494 - 502
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    Empirical justifications for the lognormal, Rayleigh and Suzuki (1977) probability density functions in multipath fading channels are examined by quantifying the rates of convergence of the central limit theorem (CLT) for the addition and multiplication of random variables. The accuracy of modeling the distribution of rays which experience multiple reflections/diffractions between transmitter and receiver as lognormal is quantified. In addition, it is shown that the vector sum of lognormal rays, such as in a narrow-band signal envelope, may best be approximated as being either Rayleigh, lognormal or Suzuki distributed depending on the fading channel conditions. These conditions are defined statistically View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The effect of carrier phase jitter on the performance of orthogonal frequency-division multiple-access systems

    Page(s): 456 - 459
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB)  

    We investigate the sensitivity to carrier phase jitter of an orthogonal frequency-division multiple-access (OFDMA) system. When all OFDMA carriers have the same power level and jitter spectrum, the degradation caused by the jitter is shown to be equal to the degradation of an OFDM system. Also, traditional FDMA is found to be slightly more robust than OFDMA View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiple-symbol detection of MPSK in narrow-band interference and AWGN

    Page(s): 460 - 463
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    We propose a new technique for rejection of narrow-band interference (NBI) based on multiple-symbol detection of coherent or differential phase-shift keying (DPSK). We first show that the direct use of multiple-symbol detection offers poor performance when NBI is dominant. Our proposed technique employs a special signaling or coding scheme which is shown to be robust against NBI. The evaluation of bit-error rate (BER) shows significant performance improvement in NBI vis-a-vis direct multiple-symbol detection. When viewed as a coding scheme, the proposed signaling scheme is significantly simpler for achieving the same coding gain than conventional error correction codes View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Unification of MLSE receivers and extension to time-varying channels

    Page(s): 464 - 472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    Forney (1972) and Ungerboeck (1974) have each developed maximum-likelihood sequence estimation (MLSE) receivers for intersymbol interference (ISI) channels. The Forney receiver uses a whitened matched filter, followed by a sequence estimation algorithm using the Euclidean distance metric. The Ungerboeck receiver uses a matched filter, followed by a sequence estimation algorithm using a modified metric. A unified development of both receivers is given, in which each receiver is derived from the other. By deriving the Ungerboeck receiver from the Forney receiver, we show that the whitening operation is cancelled in the Euclidean distance metric, leaving the modified metric. In addition, the Ungerboeck receiver is extended to the case of a time-varying known channel. When the channel is unknown, decision-directed channel estimation is assumed, which requires channel prediction to account for the decision delay. It is shown that the Ungerboeck receiver requires additional channel prediction, degrading performance due to prediction uncertainty. To solve this problem, two alternative receiver forms are developed which do not require additional prediction, though the computational complexity is increased. Performance and complexity of the receiver forms are compared for the IS-136 digital cellular time-division multiple-access (TDMA) standard View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • SNR mismatch and online estimation in turbo decoding

    Page(s): 421 - 423
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (76 KB)  

    Iterative decoding of turbo codes, as well as other concatenated coding schemes of similar nature, requires knowledge of the signal-to-noise ratio (SNR) of the channel so that proper blending of the a posteriori information of the separate decoders is achieved. We study the sensitivity of decoder performance to misestimation of the SNR, and propose a simple online scheme that estimates the unknown SNR from each code block, prior to decoding. We show that this scheme is sufficiently adequate in accuracy to not appreciably degrade the performance View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The effect of diversity on a burst-mode carrier-frequency estimator in the frequency-selective multipath channel

    Page(s): 553 - 560
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    This paper describes a carrier-frequency offset estimator derived using maximum-likelihood techniques. The estimator is designed for a digital space-diversity receiver, operating in a wide-band frequency-selective multipath fading channel. The estimator is suited to a burst-mode time-division-multiple-access system, because the estimate is formed in an open-loop manner, and relies on a training sequence normally used in burst-mode systems. The main advantage is that it does not require channel state information; rather, it only requires knowledge of the auto-correlation of the channel. Simulation results show the estimator to be unbiased over a wide frequency range. The normalized error standard deviation is shown to be 0.0015 across the frequency offset range for a receiver with four diversity branches, when the normalized channel delay spread is 0.1, the signal-to-noise ratio (SNR) is 10 dB, and the training sequence length is 23 symbols. It is found that, for most parameter configurations, there is approximately a factor of two improvement in the estimate error standard deviation when the antenna diversity is doubled View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance comparison of a slotted ALOHA DS/SSMA network and a multichannel narrow-band slotted ALOHA network

    Page(s): 544 - 552
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    Throughput, delay, and stability for two slotted ALOHA packet radio systems are compared. One system is a slotted direct-sequence spread-spectrum multiple-access (DS/SSMA) network where each user employs a newly chosen random signature sequence for each bit in a transmitted packet. The other system is a multiple-channel slotted narrow-band ALOHA network where each packet is transmitted over a randomly selected channel. Accurate packet success probabilities for the code-division multiple-access (CDMA) system are computed using an improved Gaussian approximation technique which accounts for bit-to-bit error dependencies. Average throughput and delay results are obtained for the multiple-channel slotted ALOHA system and CDMA systems with block error correction. The first exit time (FET) is computed for both systems and used as a measure of the network stability. The CDMA system is shown to have better performance than the multiple-channel ALOHA system in all three areas 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