By Topic

Communications, IEEE Transactions on

Issue 2 • Date Feb. 2003

Filter Results

Displaying Results 1 - 23 of 23
  • Comments on "Combined turbo codes and interleaver design"

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB)  

    The authors comment that in the paper of Yuan, Vucetic and Feng (see ibid., vol.47, p.484-87, Apr. 1999), the optimum distance spectrum (ODS) code found for memory order v=5, is actually v=3 convolutional code. The ODS code with h/sub 0/=43/sub s/ and h /sub 1/=55/sub s/ is actually v=3 code, because the feedback polynomial h/sub 0/, and feedforward polynomial h/sub 1/ are not relatively prime polynomials. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Diversity combining for DS/SS systems with time-varying, correlated fading branches

    Page(s): 284 - 295
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (791 KB) |  | HTML iconHTML  

    Diversity combining of multiple time varying and correlated fading branches is investigated for direct-sequence spread-spectrum systems. The correlated branches are modeled and estimated jointly as a vector autoregressive (VAR) process. The joint estimation is shown to provide performance gain over separate estimation of the fading branches. The parameter matrices of the VAR model are estimated via the method of expectation maximization (EM) with two algorithms. The first algorithm, using results from Kalman smoothing, provides a closed-form solution to the maximization problem in the iterative EM procedure. However, the iterative EM-Kalman algorithm operates repeatedly on a batch of training data and results in large storage requirements and long processing delays. To overcome these disadvantages, a new algorithm with only forward-time recursions is proposed that approximates the iterative EM solution and efficiently adapts to slowly changing Doppler spreads. As a result, the new algorithm significantly reduces memory and training sequence requirements. Through computer simulations, a near ideal bit-error rate performance is found for both algorithms, and the efficacy of the new adaptive algorithm for channels with changing Doppler spreads is demonstrated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Iterative data detection and channel estimation for advanced TDMA systems

    Page(s): 141 - 144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (346 KB) |  | HTML iconHTML  

    This letter presents a new receiver for Q-ary transmission, where all receiver blocks are embedded in an iterative structure. Packet data transmission in Global Systems for Mobile communications (GSM) and Enhanced Data rates for Global Evolution (EDGE) are considered as examples. A low-complexity soft-in-soft-out detector for EDGE is introduced and its modification suitable for iterative detection is derived. Application of iterative detection and channel estimation techniques in GSM/EDGE shows a significant performance enhancement. Additional improvement may be obtained if the iterative processing is applied to packet retransmission schemes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Polynomial-complexity noncoherent symbol-by-symbol detection with application to adaptive iterative decoding of turbo-like codes

    Page(s): 197 - 207
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (705 KB) |  | HTML iconHTML  

    The problem of generating symbol-by-symbol soft decision metrics (SbSSDMs) in the presence of unknown channel parameters is considered. The motivation for this work lies in its application to iterative decoding of high-performance turbo-like codes, transmitted over channels that introduce unknown parameters in addition to Gaussian noise. Traditional methods for the exact evaluation of SbSSDMs involve exponential complexity in the sequence length. A class of problems is identified for which the SbSSDMs can be exactly evaluated with only polynomial complexity with respect to the sequence length. Utilizing the close connection between symbol-by-symbol and sequence detection, it is also shown that for the aforementioned class of problems, detection of an uncoded data sequence in the presence of unknown parameters can be performed with polynomial complexity. The applicability of this technique is demonstrated by considering the problem of iterative detection of low-density parity-check codes in the presence of unknown and time-varying carrier-phase offset. Finally, based on the proposed exact schemes, an ultra-fast approximate algorithm for performing joint iterative decoding and phase estimation is derived that is well suited for hardware implementation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • MIMO MAP equalization and turbo decoding in interleaved space-time coded systems

    Page(s): 155 - 160
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (454 KB) |  | HTML iconHTML  

    Decoding of space-time codes in frequency-selective fading channels is considered. The approach is based on iterative soft-in soft-out equalization and decoding. It is applicable to space-time coded systems that deploy symbol/bit interleavers. We focus on the equalization stage by extending the Ungerboeck equalizer formulation to a multiple-input multiple-output time-variant channel. The resulting structure comprises a bank of matched filters, followed by an a posteriori probabilities calculator that runs the Bahl-Cocke-Jelinek-Raviv/maximum a posteriori algorithm with an appropriate metric. Simulation results are reported for space-time bit-interleaved codes designed over the enhanced data rates for GSM evolution (EDGE) air interface. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiple-symbol differential detection with interference suppression

    Page(s): 208 - 217
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (707 KB) |  | HTML iconHTML  

    A multiple-symbol differential detector is formulated for M-ary differential phase-shift keying modulation where the channel state information is unknown to the receiver. The maximum-likelihood decision statistic is derived for the detector, and its performance is demonstrated by analysis and simulation. Under the Gaussian assumption for the aggregate interference plus noise, an exact expression for the symbol pairwise error probability is developed for M-ary differential phase-shift keying modulation over a diversity, slow-fading Rayleigh channel in the presence of an interference source. A simpler expression of the pairwise error probability is developed for the asymptotic case of large signal-to-noise ratio and small signal-to-interference ratio. It is shown that with an increasing observation interval, the performance of the differential detector over an unknown channel approaches that of optimum combining with known channel. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dynamic rate adaptation based on multidimensional multicode DS-CDMA in cellular wireless networks

    Page(s): 247 - 260
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (850 KB) |  | HTML iconHTML  

    Dynamic rate adaptation for uplink data transmission in a cellular multidimensional multicode (MDMC) direct-sequence code-division multiple-access packet data network is modeled and analyzed. An analytical framework is developed to evaluate the performances of radio link level dynamic rate adaptation schemes under multipath fading and log-normal shadowing. The radio link level throughput under optimal dynamic rate adaptation (having exponential computational complexity) and different heuristic-based suboptimal rate adaptation schemes can be assessed under the presented analytical framework. The performance of MDMC signaling is compared with that of the single-code variable spreading factor (VSF) signaling. To this end, based on an equilibrium point analysis of the system in steady-state, a base station-assisted and mobile-controlled dynamic rate adaptation scheme is presented. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • VLSI architectures for the MAP algorithm

    Page(s): 175 - 185
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (729 KB) |  | HTML iconHTML  

    This paper presents several techniques for the very large-scale integration (VLSI) implementation of the maximum a posteriori (MAP) algorithm. In general, knowledge about the implementation of the Viterbi (1967) algorithm can be applied to the MAP algorithm. Bounds are derived for the dynamic range of the state metrics which enable the designer to optimize the word length. The computational kernel of the algorithm is the add-MAX* operation, which is the add-compare-select operation of the Viterbi algorithm with an added offset. We show that the critical path of the algorithm can be reduced if the add-MAX* operation is reordered into an offset-add-compare-select operation by adjusting the location of registers. A general scheduling for the MAP algorithm is presented which gives the tradeoffs between computational complexity, latency, and memory size. Some of these architectures eliminate the need for RAM blocks with unusual form factors or can replace the RAM with registers. These architectures are suited to VLSI implementation of turbo decoders. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Blind FSR-LPTV equalization and interference rejection

    Page(s): 145 - 150
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB) |  | HTML iconHTML  

    We address the problem of synthesizing blind channel identification and equalization methods for digital communications systems, aimed at counteracting the presence of cochannel or adjacent-channel interference. Owing to the presence of the interfering signal, the minimum mean-square error equalizer turns out to be linear periodically time-varying, which is implemented by resorting to its Fourier series representation. Moreover, by exploiting the cyclic conjugate second-order statistics of the channel output, we propose a new weighted subspace-based channel identification method, which is asymptotically immune to the presence of high-level interference. Computer simulation results confirm the effectiveness of the proposed identification/equalization technique. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A new bound and algorithm for Star 16-QAM carrier phase estimation

    Page(s): 161 - 165
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (362 KB) |  | HTML iconHTML  

    The true Cramer-Rao lower bound (CRLB) is derived and evaluated for the estimation of carrier phase of Star 16-quadrature amplitude modulation (QAM) and can be simply applied to carrier frequency estimation. Different geometries are investigated by varying the ring ratio (RR). For signal-to-noise ratios (SNRs) between 6-15 dB, the CRLB with RR=3 is lower than that of Square 16-QAM. A modified phase estimator is presented, which closely follows the new CRLB. Investigation of symbol error performance in short packet length reveals Star 16-QAM to be superior to Square 16-QAM for SNR<13 dB, which is a reasonable operating range for a coded system. Although Square 16-QAM and Star RR=1.8 are optimum for a perfect receiver, when the effect of phase estimation is considered, we find Star RR=3 to be better for SNR below 10 dB. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Nonparametric trellis equalization in the presence of non-Gaussian interference

    Page(s): 229 - 239
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (747 KB) |  | HTML iconHTML  

    We consider the problem of trellis equalization of the intersymbol interference channel in the presence of thermal noise and cochannel interference (CCI). Conventional maximum-likelihood sequence estimation (MLSE) and maximum a posteriori probability (MAP) trellis equalizers treat the sum of noise and interference as additive white Gaussian noise, while CCI is generally a colored non-Gaussian process. We propose a novel nonparametric approach based on the estimation of the probability density function of the noise-plus-interference. Given the availability of a limited volume of data, the density is estimated by kernel-smoothing techniques. The use of a whitening filter in the presence of temporally colored disturbance is also addressed. Simulation results are provided for the global system for mobile communications (GSM), showing a significant performance improvement with respect to the equalizer based on the Gaussian assumption. Major advantages of the proposed strategy are its intrinsic robustness and general applicability to those cases where accurate modeling of the interference is difficult or a model is not available. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A two-dimensional impulse noise model and error probability of QAM in DSL

    Page(s): 129 - 134
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (393 KB) |  | HTML iconHTML  

    In this letter, we extend the baseband impulse noise modeling over the subscriber loop conducted over the German Telephone Network to the passband scenario. We apply an in-phase (I) and quadrature (Q) resolution of the passband impulse noise and model these components as a generalized error distribution. We use simulation to verify our postulation. Closed-form symbol error rate (SER) expressions for M-ary quadrature amplitude modulation over this passband impulse noise channel are then derived. From the computed SER results, we conclude that the system performance is not sensitive to the dependency factor between the I and Q noise components. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the Monte Carlo simulation of digital communication systems in Gaussian noise

    Page(s): 267 - 274
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (519 KB) |  | HTML iconHTML  

    We consider the general problem of the simulation of highly reliable systems operating in the presence of Gaussian noise. Our methodology uses importance sampling which has been shown to be a particularly effective method in the general discipline of rare-event simulation. The methods we propose are optimal in a certain sense, i.e., they are efficient. We also give a new class of simulation distributions that are universally efficient in the sense that they depend only on a single scalar parameter, regardless of the dimensionality of the underlying system or of the error sets to be simulated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bounds and approximations for optimum combining of signals in the presence of multiple cochannel interferers and thermal noise

    Page(s): 296 - 307
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (947 KB) |  | HTML iconHTML  

    We derive an upper bound and investigate some approximations on the symbol error probability (SEP) for coherent detection of M-ary phase-shift keying, using an array of antennas with optimum combining in wireless systems in the presence of multiple uncorrelated equal-power cochannel interferers and thermal noise in a Rayleigh fading environment. Our results are general and valid for an arbitrary number of antenna elements as well as an arbitrary number of interferers. In particular, the exact SEP is derived for an arbitrary number of antennas and interferers; the computational complexity of the exact solution depends on the minimum number of antennas and interferers. Moreover, closed-form approximations are provided for the cases of dual optimum combining with an arbitrary number of interferers, and of two interferers with an arbitrary number of antenna elements. We show that our bounds and approximations are close to Monte Carlo simulation results for all cases considered in this paper. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fast estimation of BER in PAR-limited DMT systems using noise injection method

    Page(s): 170 - 174
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (310 KB) |  | HTML iconHTML  

    A high peak-to-average power ratio is a major problem that is inherent in all multicarrier communication systems. Clipping the high-peak power samples introduces (extra) clipping noise, which degrades the system performance in terms of bit-error rate (BER). Measuring the BER usually requires a very long simulation time, as clipping occurs very rarely. We propose a method called clipping noise injection, which allows BER estimation (due to clipping) in discrete multitone-based systems in a fast and quite precise way. Savings of as great as 90% or more are observed in some simulations that are reported. Higher savings are expected when lower BER cases have to be studied. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • CA-CDMA: channel-adapted CDMA for MAI/ISI-free burst transmission

    Page(s): 275 - 283
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    This paper proposes a precoding technique for the complete elimination of both multiple-access interference and intersymbol interference in the uplink of a code-division multiple-access system based on burst transmission, with reduction of the minimum mean-square error joint detector to a simple filter matched to the total impulse responses. If the received power is fixed, this system minimizes the variance of the symbol estimation error. An infinity of solutions exists to orthogonalize the system. Two objectives are added: a possible progression in the number of users and a minimization of the average emitted power. In an ideal progressive system, users can enter or leave the system easily without recomputing the codes of the other users. The minimization of the emitted power is a complex optimization problem. An approximate solution is proposed. It is shown that the system introduced in this paper outperforms burst systems using a conventional set of codes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Maximum-likelihood detection of nonlinearly distorted multicarrier symbols by iterative decoding

    Page(s): 218 - 228
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (719 KB) |  | HTML iconHTML  

    This paper proposes a new method for decoding multicarrier symbols with severe nonlinear distortion. The first part evaluates mutual information expressions for practical nonlinear models and shows the performance bounds for commonly used receiver structures. Then, we derive the maximum-likelihood (ML) sequence estimator, which unfortunately has an exponential complexity due to the nonlinear distortion. This extremely large complexity can be reduced with a simple algorithm that iteratively estimates the nonlinear distortion, thereby reducing the exponential ML to the standard ML without nonlinear distortion. The proposed method can be used to reduce the peak-to-average power ratio of multicarrier signals by clipping the transmit sequence. It can also be used to correct any nonlinear distortion present in transmitter/receiver amplifiers that are operating close to saturation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On generalized optimal scheduling of high data-rate bursts in CDMA systems

    Page(s): 261 - 266
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB) |  | HTML iconHTML  

    In a code-division multiple access (CDMA)-based wireless communication system, forward link is power limited and reverse link is interference limited. With power control and statistical multiplexing, voice services can be supported reasonably well. However, for high data-rate services, a more comprehensive scheduling mechanism is needed in order to achieve a high capacity while satisfying the forward and reverse link constraints. We formulate the high data-burst scheduling as a integer programming problem using a generic CDMA system model. We also suggest an optimal algorithm for generating scheduling solutions. With cdma2000 system details plugged in the proposed algorithm, it is found that our algorithm considerably outperforms several fast heuristics, including equal sharing, first-come-first-served, longest delay first, and shortest burst first. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Source-channel rate allocation for progressive transmission of images

    Page(s): 186 - 196
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB) |  | HTML iconHTML  

    Progressive image transmission is difficult in the presence of a noisy channel, mainly due to the propagation of errors during the decoding of a progressive bitstream. Excellent results for this problem are made possible through combined source-channel coding, a method that matches the channel code to the source operational rate distortion as well as channel conditions. This paper focuses on the key component of combined source-channel coding: rate allocation. We develop a parametric methodology for rate allocation in progressive source-channel coding. The key to this technique is an empirical model of decoded bit-error rate as a function of the channel code rate. We investigate several scenarios. In the case of the memoryless channel, we present closed-form expressions. For the fading channel and channels with feedback, where closed-form results are elusive, our analysis leads to low-complexity algorithms. The results presented are applicable to any progressive source code, and any family of channel codes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Packet-error probability analysis for FH-CDMA unslotted packet networks

    Page(s): 151 - 154
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB) |  | HTML iconHTML  

    This letter is concerned with the interference analysis in time-unslotted frequency-hopping code-division multiple-access packet networks with error control coding. We derive, under the conditional independence assumption, a new exact closed-form expression for the packet error probability of a reference packet in the presence of other K interfering packets. In contrast to the previously known results, the computational complexity of the new result is independent of K. We also develop a new tight upper bound on packet error probability relying on mapping the unslotted system into an equivalent slotted one experiencing the same level of short-term average interference. The accuracy of the proposed approximation is demonstrated by some numerical examples and is shown to be tighter than the previously used results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An all-digital clock-smoothing technique - counting-prognostication

    Page(s): 166 - 169
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB) |  | HTML iconHTML  

    This article presents a novel universal all-digital clock-smoothing technique - counting-prognostication. Operation principles, performance analysis, and comparisons are given. Analysis and measurement results show that this technique can efficiently smooth jitter and wander for a wide pull-in range and pull-out range, and jitter accumulation is small. A cycle-varying counting-prognostication method, which decreases pull-in time, is also suggested. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Iterative diversity detection for correlated continuous-time Rayleigh fading channels

    Page(s): 240 - 246
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (425 KB) |  | HTML iconHTML  

    An antenna array is proposed as a means of achieving a space-diversity effect that partly overcomes the severity of continuous-time Rayleigh fading channels. The investigated channel is assumed to be frequency-nonselective with correlated diversity links, where the correlation is related to the array geometry and the spatial and Doppler dispersions. Further, the error performance is improved by bit interleaving and channel coding, where the encoders/channel is viewed as a serially concatenated system: a convolutional code constitutes the outer code, whereas a differential encoder and the fading channel (having truncated memory) form a joint inner code. In order to obtain a practical detector structure it is desirable to perform iterative decoding by applying some a posteriori probability (APP) algorithms. For this purpose, we propose a novel generalization of the well-known Bahl-Cocke-Jelinek-Raviv (1974) algorithm that calculates the APPs over channels having memory. Numerical results indicate that iterative decoding becomes more powerful when the exploited channel memory depth is extended. Also, the error performance is significantly improved by introducing multiple antennas. The interleaver gain is, however, seen to be quite moderate, in contrast to additive white Gaussian noise channels. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A low-complexity ML channel estimator for OFDM

    Page(s): 135 - 140
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    Orthogonal frequency-division multiplexing with cyclic prefix enables low-cost frequency-domain mitigation of multipath distortion. However, to determine the equalizer coefficients, knowledge of the channel frequency response is required. While a straightforward approach is to measure the response to a known pilot symbol sequence, existing literature reports a significant performance gain when exploiting the frequency correlation properties of the channel. Expressing this correlation by the finite delay spread, we build a deterministic model parametrized by the channel impulse response and, based on this model, derive the maximum-likelihood channel estimator. In addition to being optimal (up to the modeling error), this estimator receives an elegant time-frequency interpretation. As a result, it has a significantly lower complexity than previously published methods. 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