Three-point estimator of sinusoidal signal amplitude

The paper presents an estimator that makes it possible to estimate the amplitude on the basis of three initial sinusoidal signal samples. Such an estimator is called a three-point amplitude estimator. Simulations consisting in generating and acquiring quantised samples of a signal affected by Gaussian noise have been run. To generate and acquire the samples, a MathCAD computer program has been used. An experiment has been conducted consisting in generating and acquiring sine-wave voltage signal samples. To generate the signal, an Agilent 33220A function generator has been applied. To acquire the samples, an Agilent 3458A voltmeter has been applied. Based on the collected samples, the values of a three-point estimator and a four-point estimator proposed by Vizireanu and Halunga have been computed. Maximum errors have been determined on the basis of the errors of the results of signal amplitude estimation. It has been shown that, in comparison with a four-point estimator, a three-point estimator can estimate the signal amplitude with higher accuracy.     

Efficient estimators for the land mobile satellite channel

A novel class of adpative Kalman channel estimators (AKCEs) for low-data-rate signalling via the land mobile satellite (LMS) channel is presented in this paper. The proposed technique is based on a scheme known as the ‘parallel processing algorithm’ and assumes a discrete Gauss–Markov extension of the LMS channel model. Three different approaches compared against the non-adaptive filter show an improved estimation error variance under various environmental conditions. Trading off computational complexity and performance, the derived maximum a posteriori (MAP) approach has been found to be best applicable. © 1998 John Wiley & Sons, Ltd.     

Joint carrier frequency offset and channel estimation for OFDM systems with two receive antennas

Carrier frequency offset (CFO) in OFDM systems results in loss of channel orthogonality and hence degrades the system's performance. In this paper, we propose a new method for joint CFO/channel estimation for OFDM systems with two receive antennas. Our method avoids the complexity of full search methods in one or two dimensions. Using one training OFDM symbol and utilizing the knowledge of the structure of the inter‐channel interference that results from CFO, we develop a two‐stage estimation procedure. The first stage derives an initial CFO/channel estimate based on a one shot minimization step. The second stage refines this joint estimate by conducting a small CFO search in the vicinity of the initial estimate. This procedure provides CFO estimates over a full range of −N /2–N /2, (N : number of subcarriers), as well as the channel estimates. Computer simulations show an excellent performance that is very close to the Cramer–Rao lower bound and superior to some existing methods. The effect of antenna correlation on performance is also investigated through computer simulations, showing small performance degradation even at medium correlation coefficients (0.3–0.6). Copyright © 2015 John Wiley & Sons, Ltd.     

Resource allocation in satellite networks: certainty equivalent approaches versus sensitivity estimation algorithms

In this paper, we consider a resource allocation problem for a satellite network, where variations of fading conditions are added to those of traffic load. Since the capacity of the system is finite and divided in finite discrete portions, the resource allocation problem reveals to be a discrete stochastic programming one, which is typically NP‐hard. We propose a new approach based on the minimization over a discrete constraint set using an estimation of the gradient, obtained through a ‘relaxed continuous extension’ of the performance measure. The computation of the gradient estimation is based on the infinitesimal perturbation analysis technique, applied on a stochastic fluid model of the network. No closed‐forms of the performance measure, nor additional feedback concerning the state of the system, and very mild assumptions on the probabilistic properties about the statistical processes involved in the problem are requested. Such optimization approach is compared with a dynamic programming algorithm that maintains a perfect knowledge about the state of the satellite network (traffic load statistics and fading levels). The comparison shows that the sensitivity estimation capability of the proposed algorithm allows to maintain the optimal resource allocation in dynamic conditions and it is able to provide even better performance than the one reached by employing the dynamic programming approach. Copyright © 2004 John Wiley & Sons, Ltd.     

Low-field current transport mechanisms in rf magnetron sputter deposited boron carbide (B5C)/p-type crystalline silicon junctions in the dark

Measurements of the forward and reverse currents in an undoped rf magnetron sputter deposited boron carbide (B₅C)/p-type Si(111) junction have been made in the dark in the temperature range 120–300K at low-bias voltages (0–0.3V). A diode-like behaviour of the junction current has been observed in this low-bias region at all temperatures but with a rather large reverse (leakage) current I _R, particularly at high temperatures (I _R≈2 μA at V = ?0:3V and T = 290 K). The forward ‘voltage factor’ A (T) was found to decrease with increasing temperature as A (T)≈q/ηk _B T, with relatively high values of the ‘ideality factor’ η(about 3.5–4), probably due to the existence of an interfacial layer. The temperature dependence of the measured junction current (forward and reverse) flowing at low bias voltages and of the forward ‘current factor’ I _0F can be described satisfactorily by a model of the tunnelling of thermally excited carriers, including tunnelling via impurity localized levels, of the form I (T) ∝ exp [?C/T ^1/3] over the entire temperature range studied (120–300K). A high density of ‘localized’ energy states as large as 10¹⁸ cm^?3 eV^?1 was estimated, which can be attributed in part to ‘extrinsic’ interface states that could have been formed throughout the fabrication procedures of the rf sputter deposited B₅C/p-crystalline silicon junction studied. Another possible cause of such large concentration of ‘localized’ states is the ‘intrinsic’ interface states produced by the lattice mismatch between the polycrystalline boron carbide and crystalline silicon semiconductors as well as of the high intrinsic defect concentration caused by structural imperfections that often exist in boron carbide compounds.     

Frequency-Azimuth-Elevation Determination with a Single Acoustic Vector-Sensor Involved in a Reflecting Boundary

The temporally regularized multiresolution ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) algorithm is proposed to exploit the second-order information present in the superposition of incidence of direct and reflected monochromatic acoustic waves for uni-vector-sensor direction finding in the presence of a reflecting boundary. The data are organized such that the phase shifts for frequency estimation of each signal corresponding to two distinct sampling rates are separately embedded in the modulus and argument of the ESPRIT eigenvalue, whereas the direction cosines for azimuth-elevation direction-of-arrival (DOA) estimation dwell in the associated ESPRIT eigenvector, and thus the matching procedure for aligning the output of multidimensional and multi-invariant data manipulation is avoided. The temporal multiresolution herein realized is iteration free and needs merely one lower-dimensional eigendecomposition. The simplified version of the presented method offers a similar performance while requiring only two time-delayed data sets and thus has a comparable computational complexity with the traditional single resolution ESPRIT. This ESPRIT-type method is also blind to the reflection coefficient which generally depends on the boundary nature, medium property, and signal parameters still to be estimated, viz. DOAs and signal frequencies. Simulation results are included to validate the proposed algorithm.     

A novel compressed sensing ultra‐wideband channel estimation method based on non‐convex optimization

Due to the low power spectral density and complicated transfer propagation of ultra‐wideband (UWB) signal, it is important to estimate UWB channel accurately. But it is difficult to sample UWB signals directly due to their wider band width. However, compressed sensing (CS) theory provides a feasible way through lower sampling speed. Common CS‐UWB channel estimation methods adopt convex optimization, non‐sparse or non‐restricted form. In order to strengthen the restriction on sparsity of the reconstructed channel vector, a non‐convex optimization method is proposed in this paper to estimate UWB channel. Proposed method sets the objective function as a non‐convex optimization model using l_p–norm. This model is combined as a convex function to approximate the objective function and reconstruct the UWB channel vector iteratively. Because l_p–norm is closer to l₀–norm than l₁ and l₂–norm, its restriction on sparsity of objective vector is stricter. The simulation results show that this method can enhance reconstruction performance compared with existing CS‐UWB channel estimation methods. Copyright © 2013 John Wiley & Sons, Ltd.     

Blind equalization of multilevel turbo coded‐continuous phase frequency shift keying over MIMO channels

In this paper, multilevel turbo coded‐continuous phase frequency shift keying (MLTC‐CPFSK) is introduced and its bit error performance in multiple input multiple output (MIMO) fading channels are investigated considering a blind maximum likelihood channel estimation. Multilevel turbo coded signals with continuous phase modulation (CPM) provides low spectral occupancy and is suitable for power and bandwidth‐limited channels. Besides, antenna diversity is one of the best method to combat with multipath fading effects. The performance of 2LTC for 4‐ary CPFSK over AWGN, Rician (for Rician channel parameter K=10 dB) and Rayleigh channels are given for 1Tx–1Rx, 2Tx–1Rx and 2Tx–2Rx antenna configurations. Channel capacities of 2LTC‐4CPFSK signals are obtained as ?5.26, ?7.65 and ?7.14 dB for 1Tx–1Rx, 2Tx–1Rx and 2Tx–2Rx antenna configurations, respectively. Baum–Welch (BW) algorithm is used to estimate the channel parameters. Bit error probabilities of 2 level turbo coded 4 CPFSK (2LTC‐4CPFSK) are drawn in the cases of no channel state information (CSI), BW estimation, and perfect CSI. Approximately 0.1 and 0.75 dB gains in E_s/N₀ are obtained using BW channel estimator for Rician and Rayleigh channels, respectively. Therefore, MLTC‐CPFSK with BW channel estimator has excellent performance in MIMO fading channels. Copyright © 2006 John Wiley & Sons, Ltd.     

Combining Pilot-Symbol-Aided Techniques for Fading Estimation and Diversity Reception in Multipath Fading Channels

A novel pilot-symbol-aided (PSA) fading estimation technique that combines the estimates from a conventional PSA technique and a bandwidth-efficient PSA technique to achieve better performances is proposed for digital signals in multipath fading channels. The conventional technique has better performances at low signal-to-noise ratios (SNRs), while the bandwidth-efficient technique is superior at high SNRs. Monte Carlo computer simulation has been used to assess the effects of the proposed combining technique on the bit-error-rate (BER) performances of 16-ary quadrature-amplitude-modulation (16QAM), with and without two-branch diversity reception, in a flat Rayleigh fading channel. Results have shown that the combining technique has the advantages of both of the conventional technique and the bandwidth-efficient technique and is more preferred for use with diversity reception. Man-Hung Ng received a BSc degree in Computer Studies from City University of Hong Kong in 1991. He worked as a computer programmer in Hong Kong from 1991 to 1995. In 1996, he obtained a MSc degree in Communication and Radio Engineering from King's College London. He joined the University of Hong Kong as a research assistant in 1997, and completed a PhD degree in mobile communications in 2001. He joined Lucent Technologies N.S. UK in 2001 and is now a principal standards engineer. Sing-Wai Cheung received the BSc degree in Electrical and Electronic Engineering from Middlesex University, U.K. in 1982 and the PhD degree from Loughborough University of Technology, U.K. in 1986. From 1986–1988, he was a post-doctorate research assistant in the Communications Research Group of King's College, London University. During 1988–1990, he was with the Radio and Satellite Communications Division in British Telecom Research Laboratories (now British Telecom Laboratories). He joined the Department of Electrical and Electronic Engineering at the University of Hong Kong in 1990 and is now an Associate Professor. He contributes regularly courses on mobile and satellite communications systems. His current research interests include modulation, coding, fading compensation and diversity and MIMO for mobile and satellite communications systems.     

2-D DOA estimation employing L-shape array without estimation failure and pair matching failure

To remove estimation failure problems and pair matching failure problems in two-dimensional direction-of-arrival estimation, we propose a novel method employing a special L-shape array in this study. Two cross-correlated matrices can be used to complete two one-dimensional direction-of-arrival estimations. Based on array configuration and the definitions of azimuth and elevation angles, estimation in each dimension is completely independent. In this way, the estimation failure problems can be removed. Then, we calculate the estimation matrix and construct the expansion matrix of the steering matrix. Both the estimation matrix and the expansion matrix contain the ‘generalised’ permutation matrices. We use pair matching employing these ‘generalised’ permutation matrices instead of the ‘beamforming-like’ method. Simulation results verify that this algorithm can remove these problems and can also significantly improve performance without additional computational loads.     

Healable,Stable and Stiff Hydrogels: Combining Conflicting Properties Using Dynamic and Selective Three‐Component Recognition with Reinforcing Cellulose Nanorods

Nanocomposite hydrogels are prepared combining polymer brush‐modified ‘hard’ cellulose nanocrystals (CNC) and ‘soft’ polymeric domains, and bound together by cucurbit[8]uril (CB[8]) supramolecular crosslinks, which allow dynamic host–guest interactions as well as selective and simultaneous binding of two guests, i.e., methyl viologen (the first guest) and naphthyl units (the second guest). CNCs are mechanically strong colloidal rods with nanometer‐scale lateral dimensions, which are functionalized by surface‐initiated atom transfer radical polymerization to yield a dense set of methacrylate polymer brushes bearing naphthyl units. They can then be non‐covalently cross‐linked through simple addition of poly(vinyl alcohol) polymers containing pendant viologen units as well as CB[8]s in aqueous media. The resulting supramolecular nanocomposite hydrogels combine three important criteria: high storage modulus (G′ > 10 kPa), rapid sol–gel transition (<6 s), and rapid self‐healing even upon aging for several months, as driven by balanced colloidal reinforcement as well as the selectivity and dynamics of the CB[8] three‐component supramolecular interactions. Such a new combination of properties for stiff and self‐healing hydrogel materials suggests new approaches for advanced dynamic materials from renewable sources.     

Channel Estimation Method with Improved Performance for the UMTS-TDD Mode

Channel estimation is an essential building block for UTRA-TDD high performance receivers. Once the performance of the channel estimator algorithm proposed by 3GPP is highly dependent on the time spreading between consecutive multi-path components, a Successive Multi-path channel Estimation Technique (SMET) that improves the time resolution is proposed in this paper. A SMET based maximum likelihood approach for vectorial channel estimation, to include the estimation of the direction-of-arrival, is also proposed. This algorithm solves efficiently the complex problem of DOA estimation of multiple users in a multi path propagation environment even when the number of required DOA's exceeds the number of antenna array elements. Another property of the proposed algorithm is its ability to resolve signals from different users arriving from the same direction. This is due to processing in both time and space dimensions. The performance of these algorithms is assessed by resorting to simulations in multi-path environments using the UMTS-TDD specifications, and also by comparing the rms estimation errors against the Crámer-Rao Bound. The effect of imperfect channel estimation on the performance of RAKE and Hard-Decision Parallel Interference Canceller receivers is also analysed. The results show that a good performance can be achieved with SMET, from low to high values of Eb/n ₀.     

An efficient MAC protocol for multi‐channel mobile ad hoc networks based on location information

This paper considers the channel assignment problem in a multi‐channel MANET environment. We propose a scheme called GRID, by which a mobile host can easily determine which channel to use based on its current location. In fact, following the GSM style, our GRID spends no communication cost to allocate channels to mobile hosts since channel assignment is purely determined by hosts' physical locations. We show that this can improve the channel reuse ratio. We then propose a multi‐channel MAC protocol, which integrates GRID. Our protocol is characterized by the following features: (i) it follows an ‘on‐demand’ style to access the medium and thus a mobile host will occupy a channel only when necessary, (ii) the number of channels required is independent of the network topology, and (iii) no form of clock synchronization is required. On the other hand, most existing protocols assign channels to a host statically even if it has no intention to transmit [IEEE/ACM Trans. Networks 1995; 3 (4):441–449; 1993; 1 (6): 668–677; IEEE J. Selected Areas Commun. 1999; 17 (8):1345–1352], require a number of channels which is a function of the maximum connectivity [IEEE/ACM Trans. Networks 1995; 3 (4):441–449; 1993; 1 (6): 668–677; Proceedings of IEEE MILCOM'97, November 1997; IEEE J. Selected Areas Commun. 1999; 17 (8):1345–1352], or necessitate a clock synchronization among all hosts in the MANET [IEEE J. Selected Areas Commun. 1999; 17 (8):1345–1352; Proceedings of IEEE INFOCOM'99, October 1999]. Through simulations, we demonstrate the advantages of our protocol. Copyright © 2005 John Wiley & Sons, Ltd.     

Estimation of multi‐junction solar cell parameters

The paper deals with the parameter estimation of InGaP/GaAs/Ge multi‐junction solar cell and is based on minimizing the difference between the measured I–V and the theoretical I–V characteristics—the objective function. The parameter estimation was first performed on a multi‐junction solar cell represented by a single‐diode model containing eight parameters: five conventional parameters and three additional parameters for the negative diode breakdown voltage. An extended model is also presented for detailed analysis of the multi‐junction cell containing three subcells connected in series. In this model, each subcell is represented by eight parameters, and therefore a total of 24 parameters describe the cell. The parameter estimation procedure requires derivatives of the first and the second order of an objective function, filtering of noisy measurements, iteration algorithm, guessing of initial parameters, zero finding, and stopping criteria. The paper presents a mathematical method and a procedure for extracting solar cell parameters based on I–V measured data. The parameters' values may be used for analysis of the current mismatch of the subcells, the power loss, the output power of the multi‐junction cell for different environmental conditions, and to some extent, for cell fabrication. Copyright © 2012 John Wiley & Sons, Ltd.     

Unicast probing techniques for estimation of shared loss rate

The paper introduces two new unicast active end‐to‐end measurement techniques, called the single–double unicast probing (SDUP) and the delay‐based unicast probing (DUP), to estimate the rate of losses which occurs on the shared network path of two flows. A comprehensive performance evaluation and a comparison between these two techniques and an existing one having the same objective, the striped unicast probing (SUP) (Proceedings of the INFOCOM 2001—The IEEE Conference on Computer Communications, No. 2, Anchorage, Alaska, U.S.A., 2001; 915–923), were carried out. We demonstrate that our proposed SDUP technique provides even better estimation accuracy compared to that of the SUP while it requires only one piece of measurement equipment at only one receiver instead of deploying units to both receivers. Furthermore, with only one sender and receiver pair we can measure not only one shared path, but any partial path that begins at the sender and is located on the sender–receiver path. We also show that while the DUP have the same accuracy as the SUP in the case of Drop‐Tail buffer management, the DUP is capable of measuring loss rates of RED buffers, which the other techniques do not work with. The SDUP and the DUP are less intrusive and cause less bursty traffic compared to the SUP. Finally, the adaptation of these techniques into passive measurements is also considered. Copyright © 2006 John Wiley & Sons, Ltd.     

Position‐based adaptive quantization for target location estimation in wireless sensor networks using one‐bit data

The problem of target location estimation in a wireless sensor network is considered, where due to the bandwidth and power constraints, each sensor only transmits one‐bit information to its fusion center. To improve the performance of estimation, a position‐based adaptive quantization scheme for target location estimation in wireless sensor networks is proposed to make a good choice of quantizer' thresholds. By the proposed scheme, each sensor node dynamically adjusts its quantization threshold according to a kind of position‐based information sequences and then sends its one‐bit quantized version of the original observation to a fusion center. The signal intensity received at local sensors is modeled as an isotropic signal intensity attenuation model. The position‐based maximum likelihood estimator as well as its corresponding position‐based Cramér–Rao lower bound are derived. Numerical results show that the position‐based maximum likelihood estimator is more accurate than the classical fixed‐quantization maximum likelihood estimator and the position‐based Cramér–Rao lower bound is less than its fixed‐quantization Cramér‐Rao lower bound. Copyright © 2015 John Wiley & Sons, Ltd.     

Recursive maximum likelihood estimation of time‐varying carrier frequency offset for orthogonal frequency‐division multiplexing systems

A recursive maximum likelihood carrier frequency offset (CFO) estimator is proposed in this work, where redundancy information contained in the cyclic prefix of multiple consecutive orthogonal frequency‐division multiplexing (OFDM) symbols is exploited in an efficient recursive fashion. Because the estimator is based on multiple OFDM symbols, the time‐varying CFO must be considered. We investigate the effect of time‐varying CFO on the performance of the estimator and the trade‐off between fast tracking ability and low estimation variance. We show that, without channel noise, the mean squared error (MSE) of estimation due to CFO estimation variation increases approximately quadratically with n, where n is the number of OFDM symbols used for CFO estimation (estimation window size), whereas the MSE due to channel noise decreases proportionally to 1/n (approximately) if the CFO is constant. A closed‐form expression of the optimal estimation window size (approximately) is derived by minimizing the MSE caused by both time‐varying CFO and channel noise. For wireless systems with time‐varying rate of change for CFO, the proposed estimator can be implemented adaptively. In addition, typical optimal estimation window sizes for WiMAX, DVB‐SH and MediaFLO systems are evaluated as an example. Copyright © 2011 John Wiley & Sons, Ltd.     

Reply to comment on 'Active simulation of grounded inductors with CCII+ s and grounded passive elements'

A reply to comments made by Abuelma'atti (2000, International Journal of Electronics, 87, 177–181) regarding ‘Active simulation of grounded inductors with CCII+ s and grounded passive elements’ (1998, International Journal of Electronics, 85, 455–462).     

Improved coherent DOA estimation algorithm for uniform linear arrays

An improved algorithm on coherent direction-of-arrival (DOA) estimation is presented in this article, with the objective to overcome the unsatisfactory performances of estimation of signal parameter via rotational invariance techniques (ESPRIT)-like algorithms (Han and Zhang, IEEE Antennas and Wireless Propagation Letters 2005;4:443–446). On the basis of trilinear model by reconstructing a series of Toeplitz matrix from the co-variance matrix of array output, our proposed algorithm is to resolve the DOAs of coherent signals, which not only has much better DOA estimation performance than algorithms of ESPRIT-like and multi-invariance ESPRIT but also identifies more DOAs than ESPRIT-like algorithm. Simulation results demonstrate its validity.