CiteULike: dcastro's algorithm

Superresolution algorithms for detecting overlapped paths in DS-CDMA systems with long codes

ES Lohan — 2008-06-13T10:16:09-00:00

Personal, Indoor and Mobile Radio Communications, 2002. The 13th IEEE International Symposium on, Vol. 4 (2002), pp. 1919-1923 vol.4.

The problem of closely-spaced paths in DS-CDMA systems is a challenging task at the baseband receiver for applications such as mobile location and RAKE receivers. Previously, we introduced a method based on Teager-Kaiser (1990) operator for resolving paths spaced at less than one chip distance. We compare the performance of TK operator with that of the subspace based MUSIC (multiple signal classification) algorithm. In order to make a fair comparison, an extension of MUSIC algorithm to the systems with long codes is derived and the performance of both algorithms is assessed via simulations.

Investigation of Simulated annealing, ant-colony optimization, and genetic algorithms for self-structuring antennas

CM Coleman — 2008-06-11T20:22:20-00:00

Antennas and Propagation, IEEE Transactions on, Vol. 52, No. 4. (2004), pp. 1007-1014.

A self-structuring antenna (SSA) is capable of arranging itself into a large number of configurations. Because the properties of the configurations are generally unknown at the onset of operation, efficient search algorithms are required to find suitable configurations for a given set of environmental and operational conditions. This paper investigates the use of ant-colony optimization, simulated annealing, and genetic algorithms for finding suitable antenna states. The implementation of each algorithm for SSA searches is described, and the performance of each algorithm is compared to a random search.

The complex LMS adaptive algorithm--Transient weight mean and covariance with applications to the ALE

B Fisher — 2008-06-11T20:21:42-00:00

Acoustics, Speech, and Signal Processing [see also IEEE Transactions on Signal Processing], IEEE Transactions on, Vol. 31, No. 1. (1983), pp. 34-44.

The transient and steady-state mean and covariance of the complex-valued LMS adaptive element weights are investigated when the inputs are samples from circularly normal processes. It is shown that the data covariance diagonalizing matrix also diagonalizes the weight covariance matrix. This result permits describing the complete transient behavior of the adaptive line enhancer (ALE) weight covariance matrix in closed form for the case of multiple, equal power, narrow-band, statistically independent, orthogonal, Rayleigh fading sinusoids in broad-band noise. Based on these transient covariance results, it is shown that for any stage of adaptation, there exists an optimum ALE gain constant that minimizes the excess mean squared prediction error. This result is of particular significance when processing time-limited data.

An introduction to genetic algorithms for electromagnetics

RL Haupt — 2008-06-09T19:36:24-00:00

Antennas and Propagation Magazine, IEEE, Vol. 37, No. 2. (1995), pp. 7-15.

This article is a tutorial on using genetic algorithms to optimize antenna and scattering patterns. Genetic algorithms are “global” numerical-optimization methods, patterned after the natural processes of genetic recombination and evolution. The algorithms encode each parameter into binary sequences, called a gene, and a set of genes is a chromosome. These chromosomes undergo natural selection, mating, and mutation, to arrive at the final optimal solution. After providing a detailed explanation of how a genetic algorithm works, and a listing of a MATLAB code, the article presents three examples. These examples demonstrate how to optimize antenna patterns and backscattering radar-cross-section patterns. Finally, additional details about algorithm design are given

Genetic algorithms in engineering electromagnetics

JM Johnson — 2008-06-09T19:36:22-00:00

Antennas and Propagation Magazine, IEEE, Vol. 39, No. 4. (1997), pp. 7-21.

This paper presents a tutorial and overview of genetic algorithms for electromagnetic optimization. Genetic-algorithm (GA) optimizers are robust, stochastic search methods modeled on the concepts of natural selection and evolution. The relationship between traditional optimization techniques and the GA is discussed. Step-by-step implementation aspects of the GA are detailed, through an example with the objective of providing useful guidelines for the potential user. Extensive use is made of sidebars and graphical presentation to facilitate understanding. The tutorial is followed by a discussion of several electromagnetic applications in which the GA has proven useful. The applications discussed include the design of lightweight, broadband microwave absorbers, the reduction of array sidelobes in thinned arrays, the design of shaped-beam antenna arrays, the extraction of natural resonance modes of radar targets from backscattered response data, and the design of broadband patch antennas. Genetic-algorithm optimization is shown to be suitable for optimizing a broad class of problems of interest to the electromagnetic community. A comprehensive list of key references, organized by application category, is also provided

A comparative study of initial downlink channel estimation algorithms for mobile WiMAX

T Yucek — 2008-06-09T14:33:18-00:00

Mobile WiMAX Symposium, 2007. IEEE (2007), pp. 32-37.

Fourth generation (4G) wireless products are expected to be based on worldwide interoperability for microwave access (WiMAX) systems. It is the optimized receiver algorithms that will differentiate competitive products. In this paper, an important receiver algorithm, channel estimation, is studied for mobile WiMAX systems (IEEE 802.16e-2005). Various channel estimation algorithms are studied and compared for initial channel estimation in downlink of IEEE 802.16e-2005. Various methods are analyzed in terms of their computational complexity, mean square error and bit error rate performances under different channel models

Novel noise variance and SNR estimation algorithm for wireless MIMO OFDM systems

S Boumard — 2008-05-19T19:45:22-00:00

Global Telecommunications Conference, 2003. GLOBECOM '03. IEEE, Vol. 3 (2003), pp. 1330-1334 vol.3.

A new noise variance and SNR estimation algorithm for a 2 /spl times/ 2 MIMO wireless OFDM system as defined in the IST-STINGRAY project is presented. The SNR information is used to adapt parameters or reconfigure parts of the transmitter. The noise variance estimation algorithm uses only 2 OFDM training symbols from each transmitting antenna and the FFT output signals at the receiver. It does not require knowledge of the channel coefficients. Then, using the channel coefficient estimates given by a channel estimator and the estimate of the noise variance, the SNR is computed. The algorithm's performance is measured through Monte-Carlo simulations on a variety of channel models and compared to those of an MMSE algorithm using perfect channel estimates. The normalized MSE of the obtained noise variance estimate shows good results as long as the delay spread of the channel is small enough compared to the OFDM symbol period.

ML Time Synchronization Algorithm Joint with Channel Estimation for MIMO-OFDM Systems in Frequency Selective Fading Channel

Amir Saemi — 2008-05-19T19:17:47-00:00

This paper addresses Maximum-Likelihood (ML) time synchronization algorithm joint with channel estimation for MIMO-OFDM systems in frequency selective fading channels. For this purpose a SISO joint Maximum likelihood (ML) synchronization algorithm with channel estimation is extended and generalised to MIMO systems. Timing failure probability is presented as a criterion to illustrate the robustness of the algorithm. The performance of the proposed synchronization approach, in terms of timing failure probability, was compared with SISO systems. Based on simulation results, the performance of the proposed algorithm is quite satisfying

A new approach for microstrip active antennas using modal F.F.T-algorithm

RS N'gongo — 2008-05-09T15:42:30-00:00

Antennas and Propagation Society International Symposium, 1999. IEEE, Vol. 3 (1999), pp. 1700-1703 vol.3.

A full-wave fast wave concept iterative technique is developed to analyze single and stacked microstrip active antennas with arbitrary shape. The wave concept is developed to express the boundary conditions on the radiating surfaces in term of the waves, which are solved using the iterative technique. With the help of the modal FFT-algorithm an efficient code is developed which allows a rapid and accurate characterization of arbitrary shaped antennas embedded in single and multilayered dielectric without the trial functions usually used in the conventional integral method. The time saving factor is about 20 compared to the conventional numerical integral methods. Field distribution and input admittance are derived

Evolutionary Algorithms Applied to Microstrip Antennas Design

Juliano Brianeze — 2008-05-08T06:41:00-00:00

Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on (2007), pp. 1-8.

This work presents and compares three evolutionary algorithms (EAs), each one from three of the main trends in literature: Genetic Algorithm (GA), Evolutionary Programming (EP), and Evolutionary Strategies (ES). They are validated and applied to optimize microstrip antennas (MSA) design in single and multiobjective approaches. The effect of random numbers with different distributions (Uniform, Gaussian, Cauchy and Hybrid Gaussian-Cauchy) used by genetic operators is analysed. A CAD Model based on Cavity Method is used to assess MSAs. Standing wave ratio (SWR), bandwidth (BW), and radiation efficiency (er) are optimized parameters. Average maximum values for fitness are obtained and compared fore each case. Through the multiobjective approach, each EA generates the Pareto Frontier for the problem. Finally, the ability of each algorithm to find dominants individuals is compared, what allows the assessment or their efficiency.

A Comparison of Frequency Offset Synchronization Algorithms for WiMAX OFDM Systems

Javier Gonzalez-Bayon — 2008-04-23T17:53:08-00:00

EUROCON, 2007. The International Conference on "Computer as a Tool" (2007), pp. 997-1004.

Synchronization of the carrier frequency offset (CFO) is a crucial issue in the implementation of orthogonal frequency division multiplexing (OFDM) systems. Several estimation techniques for frequency offset have been proposed in the literature but varied test conditions make comparison difficult. This paper compares different synchronization algorithms for the wireless communication standard IEEE 802.16 (WiMAX) with a QPSK signal constellation in a Rayleigh channel. Furthermore, two of the synchronization techniques compared are novel schemes proposed in this paper. Bit error rate (BER) results of different data-aided and non-data-aided synchronization schemes in frequency and time domain are shown and compared. Acquisition is always based on the properties of the short or long preambles defined in WiMAX. Tracking is based on either the pilot tones included in a WiMAX OFDM symbol, or decision-directed algorithms. Results show that synchronization schemes with decision-directed tracking improve the BER with respect the pilot-aided tracking technique at the cost of increased complexity. Furthemore, non-data-aided synchronization schemes maintain the BER within 10% of the value obtained from an offset free system.

An adaptive subchannel allocation algorithm for OFDM-based wireless home networks

Jian Zhu — 2008-03-26T08:27:30-00:00

Consumer Communications and Networking Conference, 2004. CCNC 2004. First IEEE (2004), pp. 352-356.

We present a novel, adaptive subchannel allocation algorithm for the downlink channel of a multiuser, OFDM-based wireless home network. Since channel resources are not adaptively allocated in a traditional OFDM system, some of the users with fixed frequency channel allocation may experience deep fading in a frequency-selective multipath environment. This problem can be mitigated using an adaptive algorithm, which can be modeled as an optimization problem that allocates the proper number of subchannels to achieve maximum channel capacity. We employ the classical bipartite matching algorithm to achieve optimal OFDM subchannel allocation. Simulation results show that the total capacity increases remarkably, and that higher channel capacity is achieved when the number of users is increased. In a wireless environment, the reallocation overhead can be large. As such, we propose a hybrid method for subchannel allocation to support more users while reducing the reallocation overhead. We simulated the performance of the hybrid algorithm and compared it with the matching-only algorithm.

Adaptive OFDM synchronization algorithms based on discrete stochastic approximation

V Krishnamurthy — 2008-02-25T19:19:01-00:00

Signal Processing, IEEE Transactions on [see also Acoustics, Speech, and Signal Processing, IEEE Transactions on], Vol. 53, No. 4. (2005), pp. 1561-1574.

This paper presents discrete stochastic approximation algorithms (DSA) for time synchronization in orthogonal frequency division multiplexing (OFDM) systems. It is shown that the discrete stochastic approximation algorithms can be effectively used to achieve a significant reduction in computational complexity compared to brute force maximum-likelihood (ML) methods for OFDM synchronization. The most important property of the proposed algorithms is their recursive self-learning capability-most of the computational effort is spent at the global or a local optimizer of the objective function. The convergence of the algorithms is analyzed. An adaptive version of the discrete stochastic approximation algorithm is also presented for tracking time-varying time delays and frequency offsets in time-selective fading channels. Detailed numerical examples illustrate the performance gains of these DSA-based synchronization algorithms.

A fast algorithm for bidimensional EMD

C Damerval — 2008-02-25T18:14:57-00:00

Signal Processing Letters, IEEE, Vol. 12, No. 10. (2005), pp. 701-704.

In this letter, we describe a new method for bidimensional empirical mode decomposition (EMD). This decomposition is based on Delaunay triangulation and on piecewise cubic polynomial interpolation. Particular attention is devoted to boundary conditions that are crucial for the feasibility of the bidimensional EMD. The study of the behavior of the decomposition on a different kind of image shows its efficiency in terms of computational cost, and the decomposition of Gaussian white noises leads to bidimensional selective filter banks.

Performance Analysis of Adaptive Threshold Acquisition Algorithm in DS-UWB with Multi-path Environment

Jun Chen — 2008-02-25T15:00:17-00:00

Communications and Networking in China, 2006. ChinaCom '06. First International Conference on (2006), pp. 1-5.

Synchronization process is essential especially in UWB communication system owes to its extremely short transmitted pulse shape and the ultra dense multi-path interference. Acquisition performance decreased rapidly own to serious inter-symbol interference (ISI) caused by those complex channel with relatively large delay spread. An interference resistant adaptive threshold acquisition algorithm (IR-ATAA) for DS-UWB systems proposed here has the feature that the decision threshold changes automatically adapting to the signal to noise ratio (SNR) at time of comparison. The performance analysis mainly focus on the probability of correct acquisition (P<sub>ACQ</sub>) and estimation error of timing delay (MSE) with IEEE defined standard channel models and in the presents of multi-access interference (MAI) which is assumed as an additive white Gaussian noise. The simulation results also indicate the superiority of IR-ATAA over the fixed threshold acquisition algorithm

Optimisation of modified Mueller and Muller algorithm

GR Danesfahani — 2008-02-25T08:20:45-00:00

Electronics Letters, Vol. 31, No. 13. (1995), pp. 1032-1033.

Optimisation of the modified Mueller and Muller (mM&M) timing error detection algorithm by cancelling its self-noise is presented. Simulation results show that not only is the new algorithm self-noise free, but there are also no symbol slips at medium to high SNR. Short acquisition time, operation on only one sample per symbol to estimate the timing error, and a low complexity are other features of the new algorithm

Experimental and theoretical comparison of some algorithms for beamforming in single receiver adaptive arrays

BG Wahlberg — 2008-02-24T13:45:23-00:00

Antennas and Propagation, IEEE Transactions on, Vol. 39, No. 1. (1991), pp. 21-28.

Adaptive null steering in single receiver adaptive arrays is discussed. The single receiver structure allows only output power for a given set of weights to be measured. The problem, then, is to adaptively adjust the weights of the antenna array based on output power measurements only so as to reject interference signals while maintaining a fixed response in a given look direction. The authors determine the optimal beamformer weights in a single step, by estimating the covariance matrix of the array sensor outputs using a weight perturbation technique. Based on this covariance matrix estimate, three different approaches for finding the beamformer weights are studied. The first corresponds to a sample matrix inversion scheme, with the sample covariance matrix replaced by the one obtained from the perturbation estimation method, while in the second approach the weights are determined using an eigenvalue decomposition of the covariance matrix estimate. In the third approach the directions-of-arrival (DOAs) of the incoming wavefronts are first estimated, and then, in a second step, the beamformer weights are calculated from the DOA estimates. The advantage of the third approach is that this method is not affected by correlation between the different sources

Symbol synchronization algorithms for M-PSK operating at one sample per symbol

S Bellini — 2008-02-22T08:13:38-00:00

Communications, 1993. ICC 93. Geneva. Technical Program, Conference Record, IEEE International Conference on, Vol. 2 (1993), pp. 794-798 vol.2.

Carrier-dependent and carrier-independent clock synchronization algorithms requiring only one sample per symbol are considered. The connection between symbol synchronization and "blind identification" of the impulse response of a discrete-time channel, driven by an unknown independent identically distributed (i.i.d.) data sequence, is analyzed. It is shown that this approach leads to a couple of algorithms already proposed. As carrier-independent synchronizers (for M>2) are twice as noisy as carrier-dependent ones, the interaction between an algorithm for carrier phase estimation, well suited to digital receiver implementation, and carrier-dependent symbol synchronization is analyzed. Much of the loss can be recovered, for all values of M, without harmful interaction between the clock and phase estimators

Time and Frequency Synchronization for OFDMA Uplink System using the SAGE Algorithm

Jong-Ho Lee — 2008-02-14T13:55:58-00:00

Wireless Communications, IEEE Transactions on, Vol. 6, No. 4. (2007), pp. 1176-1181.

Software radio architecture with smart antennas: a tutorial on algorithms and complexity

J Razavilar — 2008-02-09T01:17:47-00:00

Selected Areas in Communications, IEEE Journal on, Vol. 17, No. 4. (1999), pp. 662-676.

There has been considerable interest in using antenna arrays in wireless communication networks to increase the capacity and decrease the cochannel interference. Adaptive beamforming with smart antennas at the receiver increases the carrier-to-interference ratio (CIR) in a wireless link. This paper considers a wireless network with beamforming capabilities at the receiver which allows two or more transmitters to share the same channel to communicate with the base station. The concrete computational complexity and algorithm structure of a base station are considered in terms of a software radio system model, initially with an omnidirectional antenna. The software radio computational model is then expanded to characterize a network with smart antennas. The application of the software radio smart antenna is demonstrated through two examples. First, traffic improvement in a network with a smart antenna is considered, and the implementation of a hand-off algorithm in the software radio is presented. The blocking probabilities of the calls and total carried traffic in the system under different traffic policies are derived. The analytical and numerical results show that adaptive beamforming at the receiver reduces the probability of blocking and forced termination of the calls and increases the total carried traffic in the system. Then, a joint beamforming and power control algorithm is implemented in a software radio smart antenna in a CDMA network. This shows that, by using smart antennas, each user can transmit with much lower power, and therefore the system capacity increases significantly

A maximum likelihood CDMA receiver using the EM algorithm and the discrete wavelet transform

I Sharfer — 2008-02-09T00:58:29-00:00

Acoustics, Speech, and Signal Processing, 1996. ICASSP-96. Conference Proceedings., 1996 IEEE International Conference on, Vol. 5 (1996), pp. 2654-2657 vol. 5.

A maximum likelihood (ML) method for joint estimation of amplitude, phase, time delay, and data demodulation in a single-user direct sequence spread spectrum communication system is developed. The likelihood function is analytically intractable, so a recursive estimation algorithm is considered. The expectation maximization (EM) algorithm has been used in similar problems, however, in this case it is not computationally efficient. A variant of the EM algorithm, called space alternating generalized EM (SAGE), has been derived. We apply the SAGE algorithm to the sequence estimation problem in a way which results in simple sequential updates of all the estimated parameters. An important feature of the proposed algorithm is the use of a discrete wavelet decomposition of the received signal as a sufficient statistic. The consequence is that all the information is still available to the receiver, while the complicated estimation problem is considerably simplified. Computer simulations of a single user system were performed. It is shown that the algorithm has a fast convergence, and essentially achieves optimal performance

A robust PN code tracking algorithm for frequency selective Rayleigh-fading channels

M El-Tarhuni — 2008-02-09T00:47:47-00:00

Wireless Communications, IEEE Transactions on, Vol. 3, No. 4. (2004), pp. 1018-1023.

In this letter, we propose a new tracking scheme that is robust against multipath fading for pseudonoise (PN) code tracking in direct-sequence-spread spectrum systems. The proposed scheme employs an adaptive filter whose taps are adapted using a block least-mean square algorithm and it results in minimizing the effect of multipath interference on the tracking performance. We show that the mean-squared tracking error performance of the proposed scheme is not affected by the presence of closely spaced paths (e.g., one to three chips), unlike that of conventional delay locked loops. We also show that the tap-weight distribution of the filter provides accurate estimates of the multipath delays. For example, at E/sub b//N/sub 0/=5 dB, 98% of the time the path estimates lie within one sample (1/5 of a chip) from the actual delays. Furthermore, simulation results suggest that multipath delays over a wide range of terminal speeds can be tracked successfully. The proposed scheme is well suited for wideband code-division multiple-access systems where a large number of closely-spaced multipath components need to be tracked and used in RAKE combining.

A Viterbi algorithm with soft-decision outputs and its applications

J Hagenauer — 2006-08-15T21:50:13-00:00

Global Telecommunications Conference, 1989, and Exhibition. 'Communications Technology for the 1990s and Beyond'. GLOBECOM '89., IEEE (1989), pp. 1680-1686 vol.3.

The Viterbi algorithm (VA) is modified to deliver the most likely path sequence in a finite-state Markov chain, as well as either the a posteriori probability for each bit or a reliability value. With this reliability indicator the modified VA produces soft decisions to be used in the decoding of outer codes. The inner software output Viterbi algorithm (SOVA) accepts and delivers soft sample values and can be regraded as a device for improving the signal-to-noise ratio, similar to an FM demodulator. Several applications are investigated to show the gain over the conventional hard-deciding VA, including concatenated convolutional codes, concatenation of trellis-coded modulation with convolutional FEC (forward error correcting) codes, and coded Viterbi equalization. For these applications additional gains of 1-4 dB as compared to the classical hard-deciding algorithms were found. For comparison, the more complex symbol-to-symbol MAP, whose optimal a posteriori probabilities can be transformed into soft outputs, was investigated

A soft decision 16-QAM demodulation algorithm for multipath affected DVB-T systems

SL Linfoot — 2008-01-23T08:51:53-00:00

Consumer Electronics, IEEE Transactions on, Vol. 51, No. 4. (2005), pp. 1121-1128.

In 1998, the United Kingdom started the world's first commercial digital terrestrial television service. The system used was the European digital video broadcast-terrestrial (DVB-T) but due to technological constraints at the time, the system chosen was the 2K system - a system that uses 1705 carriers to convey the digital television services through a hostile terrestrial environment. Today, these constraints are no longer applicable but in order to maintain backwards compatibility to the older set top boxes, the 2K system is still used. The 2K system has the disadvantage of excluding the possibility of employing a single frequency network (SFN) - something that can help minimize the required bandwidth for television services. This paper demonstrates an observed phenomenon that explains why DVB-T fails to meet the required BER criteria and also shows how this phenomenon can be used in a computationally inexpensive technique for estimating the relative path attenuation of a multipath signal and how it can be used to estimate the parameters required for a soft decision QAM demapper.

Efficient subcarrier and bit allocation algorithm for OFDMA system with adaptive modulation

Ho Kim — 2007-12-07T09:53:34-00:00

Vehicular Technology Conference, 2004. VTC 2004-Spring. 2004 IEEE 59th, Vol. 3 (2004), pp. 1816-1820 Vol.3.

This paper investigates the adaptive subcarrier and bit allocation algorithm for OFDMA systems. To minimize overall transmit power, we propose a novel adaptive subcarrier and bit allocation algorithm based on channel state information, Moreover, the block-wise method is considered based on channel variation for adaptive subcarrier and bit allocation. It is shown that a near optimal solution is obtained by the proposed algorithm which has low complexity compared to that of other conventional algorithms. Also, it is shown that the block-wise method significantly reduces the complexity and the feedback or side information though has a slight transmit power increase.

List Viterbi decoding algorithms with applications

N Seshadri — 2007-12-06T16:55:11-00:00

Communications, IEEE Transactions on, Vol. 42, No. 234. (1994), pp. 313-323.

A list Viterbi decoding algorithm (LVA) produces a rank ordered list of the L globally best candidates after a trellis search. The authors present two such algorithms, (i) a parallel LVA that simultaneously produces the L best candidates and (ii) a serial LVA that iteratively produces the k<sup>th</sup> best candidate based on knowledge of the previously found k-1 best paths. The application of LVA to a concatenated communication system consisting of an inner convolutional code and an outer error detecting code is considered in detail. Analysis as well as simulation results show that significant improvement in error performance is obtained when the inner decoder, which is conventionally based on the Viterbi algorithm (VA), is replaced by the LVA. An improvement of up to 3 dB is obtained for the additive white Gaussian noise (AWGN) channel due to an increase in the minimum Euclidean distance. Ever larger gains are obtained for the Rayleigh fading channel due to an increase in the time diversity. It is also shown that a 10% improvement in throughput is obtained along with significantly reduced probability of a decoding failure for a hybrid FEC/ARQ scheme with the inner code being a rate compatible punctured convolutional (RCPC) code

A genetic algorithm tutorial

Darrell Whitley — 2007-07-11T14:44:39-00:00

Statistics and Computing, Vol. 4, No. 2. (1 June 1994), pp. 65-85.

This tutorial covers the canonical genetic algorithm as well as more experimental forms of genetic algorithms, including parallel island models and parallel cellular genetic algorithms. The tutorial also illustrates genetic search by hyperplane sampling. The theoretical foundations of genetic algorithms are reviewed, include the schema theorem as well as recently developed exact models of the canonical genetic algorithm.

Channel parameter estimation in mobile radio environments using the SAGE algorithm

BH Fleury — 2007-11-28T10:32:38-00:00

Selected Areas in Communications, IEEE Journal on, Vol. 17, No. 3. (1999), pp. 434-450.

This study investigates the application potential of the SAGE (space-alternating generalized expectation-maximization) algorithm to jointly estimate the relative delay, incidence azimuth, Doppler frequency, and complex amplitude of impinging waves in mobile radio environments. The performance, i.e., high-resolution ability, accuracy, and convergence rate of the scheme, is assessed in synthetic and real macro- and pico-cellular channels. The results indicate that the scheme overcomes the resolution limitation inherent to classical techniques like the Fourier or beam-forming methods. In particular, it is shown that waves which exhibit an arbitrarily small difference in azimuth can be easily separated as long as their delays or Doppler frequencies differ by a fraction of the intrinsic resolution of the measurement equipment. Two waves are claimed to be separated when the mean-squared estimation errors (MSEEs) of the estimates of their parameters are close to the corresponding Cramer-Rao lower bounds (CRLBs) derived in a scenario where only a single wave is impinging. The adverb easily means that the MSEEs rapidly approach the CLRBs, i.e., within less than 20 iteration cycles. Convergence of the log-likelihood sequence is achieved after approximately ten iteration cycles when the scheme is applied in real channels. In this use, the estimated dominant waves can be related to a scatterer/reflector in the propagation environment. The investigations demonstrate that the SAGE algorithm is a powerful high-resolution tool that can be successfully applied for parameter extraction from extensive channel measurement data, especially for the purpose of channel modeling

Error bounds for convolutional codes and an asymptotically optimum decoding algorithm

A Viterbi — 2007-05-30T22:12:50-00:00

Information Theory, IEEE Transactions on, Vol. 13, No. 2. (1967), pp. 260-269.

The probability of error in decoding an optimal convolutional code transmitted over a memoryless channel is bounded from above and below as a function of the constraint length of the code. For all but pathological channels the bounds are asymptotically (exponentially) tight for rates above<tex>R_0</tex>, the computational cutoff rate of sequential decoding. As a function of constraint length the performance of optimal convolutional codes is shown to be superior to that of block codes of the same length, the relative improvement increasing with rate. The upper bound is obtained for a specific probabilistic nonsequential decoding algorithm which is shown to be asymptotically optimum for rates above<tex>R_0</tex>and whose performance bears certain similarities to that of sequential decoding algorithms.

On a simple algorithm to calculate the `energy' of a signal

JF Kaiser — 2007-11-14T19:17:45-00:00

Acoustics, Speech, and Signal Processing, 1990. ICASSP-90., 1990 International Conference on (1990), pp. 381-384 vol.1.

A simple algorithm is derived that permits on-the-fly calculation of the energy required to generate, in a certain sense, a signal. The results of applying this algorithm to a number of well-known signals are shown. Some of the invariance and noise properties of the algorithm are derived and verified by simulation. The implementation of the algorithm and its application to speech processing are briefly discussed

A practical discrete multitone transceiver loading algorithm for data transmission over spectrally shaped channels

PS Chow — 2007-11-11T16:37:03-00:00

Communications, IEEE Transactions on, Vol. 43, No. 234. (1995), pp. 773-775.

In this paper, we present a finite-granularity, loading algorithm for a discrete multitone (DMT) modulation system. The proposed algorithm offers significant implementational advantages over the well-known water-pouring method and the earlier Hughes-Hartogs algorithm, while typically suffering only negligible performance degradation relative to the optimal solution. We also present simulation results of this loading algorithm applied to the newly proposed asymmetric digital subscriber lines (ADSL) service

Novel efficient bit-loading algorithms for peak-energy-limited ADSL-type multicarrier systems

E Baccarelli — 2007-11-11T16:36:27-00:00

Signal Processing, IEEE Transactions on [see also Acoustics, Speech, and Signal Processing, IEEE Transactions on], Vol. 50, No. 5. (2002), pp. 1237-1247.

We develop solutions for the loading of digital subscriber loop (DSL) multicarrier (MC) systems that present constraints both on overall available energy and maximum energy per carrier. In the emerging G.DMT-based systems planned for high-throughput multimedia applications, the constraint on the peak-energy arises from spectral compatibility issues. However, until today, optimal solutions for loading peak-energy constrained MC systems do not seem explicitly developed in the literature. Hence, starting from suitable applications of the Kuhn-Tucker conditions, we present the analytical relationships characterizing the optimal solution of the peak-energy-limited loading for the general case of concave "rate-functions", and then, we apply them in the context of the so-called "gap analysis". Thus, a low-complexity iterative algorithm implementing this solution is also developed, and its performance is numerically tested on several ANSI-standard asymmetric DSL (ADSL)-type loops impaired by crosstalk. Furthermore, a version of the presented loading algorithm that guarantees integer bit rates with low computational effort is also presented, and its performance is tested. The carried-out performance comparisons allow us to evaluate the throughput loss induced by peak-energy constraints in emerging ADSL-like services

A blind OFDM synchronization algorithm based on cyclic correlation

Byungjoon Park — 2007-11-11T15:43:34-00:00

Global Telecommunications Conference, 2001. GLOBECOM '01. IEEE, Vol. 5 (2001), pp. 3116-3119 vol.5.

Blind synchronization algorithm is developed for estimating jointly timing and frequency offset of OFDM signals transmitted through a frequency-selective fading channel. The proposed estimator exploits the second-order cyclostationarity of received signals. As a blind estimator, the information of impulse response of channel is not required. The performance of the estimator is evaluated through computer simulations

A novel OFDM time and frequency synchronization algorithm

Ma Zhangyong — 2007-11-11T15:35:40-00:00

Communication Technology Proceedings, 2003. ICCT 2003. International Conference on, Vol. 2 (2003), pp. 1114-1118 vol.2.

OFDM system performance is more sensitive to frequency offset and timing error than single-carrier systems. In this paper, the integer frequency offset is estimated based on the special pilot symbols; the timing error estimation value is obtained by the correlation characteristics of the pseudo noise sequence (PN-sequence); then the fractional frequency offset can be estimated grounded on the correlation of pilots. In order to improve the accuracy of the estimator, oversampling technology is adopted. The simulation shows that the good performance is gained, the results approach the modified Cramer-Rao lower bound (MCRLB).

A low complexity timing and frequency synchronization algorithm for OFDM systems

CRN Athaudage — 2007-11-11T15:35:11-00:00

Global Telecommunications Conference, 2002. GLOBECOM '02. IEEE, Vol. 1 (2002), pp. 244-248 vol.1.

The paper presents a low complexity discrete stochastic approximation algorithm for time and frequency synchronization in OFDM systems. The proposed technique can track the conditions of a slowly time varying channel where synchronization parameters, namely the symbol timing and frequency offset, vary slowly with time. The most important property of the proposed algorithm is its self-learning capability - it spends most of the computational effort at the global minimizer of the objective function. In particular, we show that the algorithm achieves an /spl epsiv/=(1-/spl rho/)/(1+/spl rho/) reduction in computational cost (in terms of complex multiplications to be performed), where /spl rho/=N/sub cp//N is the ratio between cyclic prefix length (N/sub cp/) and number of subcarriers (N) of the OFDM system (e.g. N=512 and N/sub cp/=64 gives /spl epsiv/=78%). Numerical examples illustrate the synchronization accuracy of the proposed technique in terms of symbol timing and frequency offset estimation errors.

A joint estimation algorithm of symbol timing and carrier offset in OFDM systems

Jun Wu — 2007-11-11T15:32:16-00:00

Vehicular Technology Conference, 2001. VTC 2001 Spring. IEEE VTS 53rd, Vol. 1 (2001), pp. 712-716 vol.1.

An adaptive joint estimation algorithm of carrier frequency, carrier phase and symbol timing offset in OFDM systems is proposed. The synchronization can be divided into three steps. Firstly, the carrier frequency is estimated and corrected based on the cyclic prefix before the OFDM demodulation (FFT). Secondly, carrier phase synchronization and the timing acquisition can be implemented simultaneously based on the pilot symbols after OFDM demodulation. Thirdly, the above coarse timing algorithm acquires synchronization alignment to within several samples, then the fine timing algorithm estimates and corrects this residual timing offset. Simulations show the carrier frequency and phase estimator has a good performance, the timing algorithm can acquire the synchronization position and eliminate the effect of residual timing offset completely. The advantage of this algorithm is simple computation and only a little resource loss due to pilot symbols

Two adaptive algorithms for multipath time delay estimation

PC Ching — 2007-11-02T17:39:39-00:00

Oceanic Engineering, IEEE Journal of, Vol. 19, No. 3. (1994), pp. 458-463.

The problem of time delay estimation (TDE) with multipath transmissions arises often in many sonar and radar systems. Two adaptive algorithms based on a parameter estimation approach are proposed to estimate the difference in arrival times of a signal at two separated sensors in the presence of multipath propagation. The first method uses an adaptive IIR filter to eliminate the multipath signal in each transmission channel prior to applying a constrained delay estimation algorithm to extract the time difference between the two received outputs. The second employs two constrained adaptive FIR filters to perform equalization of the multipath arrivals, and time delay is then derived using a constrained delay estimator similar to that in the first method. Computer simulations are presented to compare and contrast the tracing capability and convergence behavior of these multipath TDE methods