Robert Marks

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R-Shrink: A Heuristic for Improving Minimum Power Broadcast Trees in Wireless Networks

GLOBECOM '03. IEEE Global Telecommunications Conference (IEEE Cat. No.03CH37489)

Broadcasting in wireless networks, unlike wired networks, inherently reaches several nodes with a... more Broadcasting in wireless networks, unlike wired networks, inherently reaches several nodes with a single transmission. For omni-directional wireless broadcast to a node, all nodes closer will also be reached. This property can be used to compute routing trees which minimize the sum of the transmitter powers. It has been shown that this problem is NP-complete. In this paper, we present the r-shrink procedure, a heuristic for improving the solutions obtained using fast sub-optimal algorithms. Specifically, we focus on the lowcomplexity BIP algorithm and Prim's minimum spanning tree algorithm and show through extensive simulations that better solutions are obtained almost always, with considerably lower tree power, if the proposed procedure is used to improve the trees generated using these algorithms.

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Optimization methods for minimum power multicasting in wireless networks with sectored antennas

2004 IEEE Wireless Communications and Networking Conference (IEEE Cat. No.04TH8733)

We consider the problem of minimum power multicasting in wireless networks with sectored antennas... more We consider the problem of minimum power multicasting in wireless networks with sectored antennas. For omnidirectional wireless broadcast to a node, a transmission from node i to node j will also reach all nodes which are closer to i than j. Depending on the network geometry, this strategy can be highly power efficient. In ideal sectored antenna systems, however, this phenomenon is sector specific; i.e., only those nodes which are located in the same sector as j will receive the transmission implicitly. Though this might seem an apparent disadvantage, the higher gains associated with directional antennas (as opposed to omni-directional antennas) allow for reduced transmission powers without sacrificing the signal-to-interference ratio at the receiver. In this paper, we first develop a mixed integer linear programming model for optimal solution of the minimum power multicast problem with sectored antennas. Subsequently, we discuss a biologically inspired algorithm for solving the problem to near-optimality at a very reasonable computation time. Experiments on randomly generated 10, 20 and 30-node networks indicate that near-optimal solutions can be obtained using the proposed algorithm.

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The bias smith tube: Simultaneous optimization of bias voltage and load impedance in power amplifier design

2016 IEEE Radio and Wireless Symposium (RWS), 2016

Multiple factors must be considered in poweramplifier design for wireless communications and rada... more Multiple factors must be considered in poweramplifier design for wireless communications and radar, including bias voltage, input power, and load impedance. The Bias Smith Tube is presented as a three-dimensional extension of the Smith Chart with bias voltage as the vertical axis. It allows simultaneous visualization of nonlinear output characteristic behaviors over transistor bias voltage and load reflection coefficient. Simulated and measured threedimensional surfaces of constant power-added efficiency (PAE), adjacent channel power ratio (ACPR), and delivered power are shown in the Bias Smith Tube, and a design approach is illustrated that finds the combination of load impedance and bias voltage providing maximum PAE under ACPR and/or delivered power constraints.

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Method and Apparatus for Generating Packet Data to Support Multiple Services in a Wireless Packet Data Communication System

Frequency multiplexing tickle tones to determine harmonic coupling weights in nonlinear systems

78th ARFTG Microwave Measurement Conference, 2011

Obtaining the Jacobian parameters for a nonlinear system, such as in X-parameter or S-function me... more Obtaining the Jacobian parameters for a nonlinear system, such as in X-parameter or S-function measurement, requires excitation of tickle tones either on or slightly off of the main harmonic frequencies. Traditional off-frequency measurements involve simultaneous excitation with tickle tones both slightly above and/or below a single harmonic frequency at a time. This paper describes a multiplexing technique for the excitation of the system with perturbations at all harmonics simultaneously. This technique requires both frequency and cross-frequency noninterference for successful results from the measurements. If these conditions exist for the nonlinear system, the off-frequency multiplexing technique for tickle tones can reduce the measurements necessary to find the Jacobian matrices by a factor equal to the number of harmonics considered in the polyharmonic distortion. These methods provide exact results for memoryless polynomial nonlinearities.

format_quoteFrequency multiplexing enables simultaneous application of perturbations at multiple harmonics, reducing measurement iterations for nonlinear parameters.format_quote

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A new modality for microwave tomographic maging : [electronic resource] transit time tomography /

A new method for tomographic imaging using time delay of microwaves as they pass through objects ... more A new method for tomographic imaging using time delay of microwaves as they pass through objects of varying dielectric is presented. To obtain this delay measurement, recording of transmitted waveforms is performed when broadband microwave signals are sent through objects. The experimental setup consists of a circular table with vertically polarized bi-conic horns as transmitting and receiving antennas, with a Vector Network Analyzer as the excitation and measurement device. By obtaining multiple point tomographic projections at multiple angles, a reconstruction of the classic X-ray Radon transform is possible. Results obtained show accuracy and resolution limits to be within acceptable ranges and offer many new, less expensive possibilities for tomographic imaging. Includes bibliographical references (p. 56 [i.e. 55]). Thesis (M.S.)--Baylor University, 2006. Mode of access: World Wide Web. PDF files require Adobe Acrobat Reader.

Fundamentals of Fourier Analysis and Stochastic Processes

Springer Texts in Electrical Engineering, 1991

The sampling theorem is traditionally expressed in the language of Fourier analysis. Stochastic p... more The sampling theorem is traditionally expressed in the language of Fourier analysis. Stochastic processes are used to analyze the effects of uncertainty on the interpolation process and, in certain cases, are used as signal models. This chapter contains a brief overview of the fundamentals of Fourier analysis and stochastic processes. The material in this chapter is prerequisite for material in the remainder of the book. Except for an isolated application in Section 3.5, however, stochastic processes are not used until Chapter 5.

The Sampling Theorem in Higher Dimensions

Springer Texts in Electrical Engineering, 1991

The first generalization of the Shannon sampling theorem to two and more dimensions was done by P... more The first generalization of the Shannon sampling theorem to two and more dimensions was done by Peterson and Middleton. Multidimensional signals include black and white images, which can be depicted as two dimensional functions with zero corresponding to black and one as white. Intermediate grey levels are classified between these limits.

Generalizations of the Sampling Theorem

Springer Texts in Electrical Engineering, 1991

There have been numerous interesting and useful generalizations of the sampling theorem. Some are... more There have been numerous interesting and useful generalizations of the sampling theorem. Some are straightforward variations on the fundamental cardinal series. Oversampling, for example, results in dependent samples and allows much greater flexibility in the choice of interpolation functions. In Chapter 7, we will see that it can also result in better performance in the presence of sample data noise. Bandlimited signal restoration from samples of various filtered versions of the signal is the topic addressed in Papoulis’ generalization [1086, 1087] of the sampling theorem. Included as special cases are recurrent nonuniform sampling and simultaneously sampling a signal and one or more of its derivatives. Kramer [772] generalized the sampling theorem to signals that were bandlimited in other than the Fourier sense. We also demonstrate that the cardinal series is a special case of Lagrangian polynomial interpolation. Sampling in two or more dimensions is the topic of Section 8.9. There are a number of functions other than the sinc which can be used to weight a signal’s samples in such a manner as to uniquely characterize the signal. Use of these generalized interpolation functions allows greater flexibility in dealing with sampling theorem type characterizations. If a bandlimited signal has bandwidth B, then it can also be considered to have bandwidthW ≥ B.

Inversion of feedforward neural networks: algorithms and applications

Proceedings of the IEEE, 1999

Direct algorithm for the Pareto load-pull optimisation of power-added efficiency and adjacent-channel power ratio

IET Radar, Sonar & Navigation, 2014

Adaptive radar systems will be required to operate in different frequency bands with spectrum req... more Adaptive radar systems will be required to operate in different frequency bands with spectrum requirements that will likely change both in time and with geographic region. A new algorithm is presented that allows direct optimisation of an amplifier's load reflection coefficient to find a Pareto optimum between the power-added efficiency (PAE) and adjacent-channel power ratio. Comparisons of simulation and measurement results are presented. The new algorithm's results compare well with traditionally acquired data and show consistency between the optimum values for PAE that are obtained from different starting points. Measurement comparison is performed with the previous optimisation algorithm reported by the authors, and results show that up to a 50% reduction in the number of measured experimental queries can be obtained. This translates into a significant time savings in reconfiguring a radar transmitter power amplifier.

Fuzzy and extra crisp alternating projection onto convex sets (POCS)

Proceedings of 1995 IEEE International Conference on Fuzzy Systems. The International Joint Conference of the Fourth IEEE International Conference on Fuzzy Systems and The Second International Fuzzy Engineering Symposium, 1995

Alternating projections onto convex sets (POCS) is a powerful tool for signal and image restorati... more Alternating projections onto convex sets (POCS) is a powerful tool for signal and image restoration and synthesis. Convex sets of signals obeying desired constraints are first specified. Then, by repeated projection onto these sets, convergence is to a signal obeying all desired constraints. The method assumes, however, that there is a nonempty intersection of the sets. If the intersection is

Fuzzy parameter adaptation in neural systems

[Proceedings 1992] IJCNN International Joint Conference on Neural Networks

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Time scale discrete Fourier transforms

2010 42nd Southeastern Symposium on System Theory (SSST 2010), 2010

The discrete and continuous Fourier transforms are applicable to discrete and continuous time sig... more The discrete and continuous Fourier transforms are applicable to discrete and continuous time signals respectively. Time scales allows generalization to to any closed set of points on the real line. Discrete and continuous time are special cases. Using the Hilger exponential from time scale calculus, the discrete Fourier transform (DFT) is extended to signals on a set of points with arbitrary spacing. A time scale consisting of points in time is shown to impose a time scale (more appropriately dubbed a frequency scale), , in the Fourier domain The time scale DFT's (TS-DFT's) are shown to share familiar properties of the DFT, including the derivative theorem and the power theorem. Shifting on a time scale is accomplished through a boxminus and boxplus operators. The shifting allows formulation of time scale convolution and correlation which, as is the case with the DFT, correspond to multiplication in the frequency domain.

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Performance Attributes of Generalized Time-Frequency Representations with Double Diamond and Cone Sh

1990 Conference Record Twenty-Fourth Asilomar Conference on Signals, Systems and Computers, 1990.

... li\cmcls Seho Oh and Robert J. Marks I1 Department of Elcctrical Fngr., F&#x27;r-10 Unive... more

Measurement-based radar waveform optimization using the ambiguity function and spectral mask

Texas Symposium on Wireless and Microwave Circuits and Systems, 2014

This paper demonstrates the optimization of a radar waveform based on ambiguity function measurem... more This paper demonstrates the optimization of a radar waveform based on ambiguity function measurements and spectral mask criteria. Compliance with spectral mask criteria is becoming ever-critical in radar systems due to the increased number of devices using the wireless spectrum. The capability of reducing ambiguity at certain range-Doppler combinations is useful in enhancing the detection capability of radar systems. This paper shows the combined optimization for both ambiguity function and spectral mask criteria based on time-domain measurements taken with a high-speed oscilloscope. A benefit of optimizing based on measurements is that the transmitter power amplifier's output waveform can be used, allowing the results of nonlinear distortion to be factored into the optimization process.

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Estimation of multi-component mixture proportions using regression machine analysis of ultra-wideband spectroscopic measurements

2013 IEEE International Conference on Ultra-Wideband (ICUWB), 2013

Ultra-wideband signals are used to examine multiple-constituent fluid mixtures in a semi-open sys... more Ultra-wideband signals are used to examine multiple-constituent fluid mixtures in a semi-open system. A feedforward neural network operates on an array of easily computed signal properties, plus the weight and temperature of the fluid samples, to provide an estimate of the constituent proportions. The average performance of the neural network is tested by artificially increasing the test data sample size and repeatedly training neural networks of the same topology. Networks of differing topologies are compared. Statistical analysis is performed on these results and the 95% confidence interval of the data prediction is shown. The 95% accuracy averages around 6.9 percentage points for both oil and water.

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A spherical dose model for radiosurgery plan optimization

Physics in Medicine and Biology, 1998

Conventional 3D dose calculations for stereotactic radiosurgery involve integration of individual... more Conventional 3D dose calculations for stereotactic radiosurgery involve integration of individual static beams comprising a set of arcs. For iterative optimization of multiple isocentre treatment, which requires repetitive dose calculations at a large number of sample points, the conventional method is too slow. To overcome this problem spherically symmetric dose distributions are assumed. The authors describe a spherical dose model derived from a parametrized convolution of the collimator width and a dose spread kernel. The method is fast and easy to implement requiring just a single empirically derived value. Furthermore, the model is differentiable with respect to the parameters to be optimized. This property is useful when the optimization strategies rely on gradient information.

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Fast cross-projection algorithm for reconstruction of seeds in prostate brachytherapy

Medical Physics, 2002

A fast method of seed matching and reconstruction in prostrate brachytherapy is proposed. Previou... more A fast method of seed matching and reconstruction in prostrate brachytherapy is proposed. Previous approaches have required all seeds to be matched with all other seeds in other projections. The fast cross-projection algorithm for the reconstruction of seeds ͑Fast-CARS͒ allows for matching of a given seed with a subset of seeds in other projections. This subset lies in a proximal region centered about the projection of a line, connecting the seed to its source, onto other projection planes. The proposed technique permits a significant reduction in computational overhead, as measured by the required number of matching tests. The number of multiplications and additions is also vastly reduced at no trade-off in accuracy. Because of its speed, Fast-CARS can be used in applications requiring real-time performance such as intraoperative dosimetry of prostate brachytherapy. Furthermore, the proposed method makes practical the use of a larger number of views as opposed to previous techniques limited to a maximum use of three views.

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Optimization of intensity modulated beams with volume constraints using two methods: Cost function minimization and projections onto convex sets

Medical Physics, 1998

For accurate prediction of normal tissue tolerance, it is important that the volumetric informati... more For accurate prediction of normal tissue tolerance, it is important that the volumetric information of dose distribution be considered. However, in dosimetric optimization of intensity modulated beams, the dose-volume factor is usually neglected. In this paper we describe two methods of volumedependent optimization for intensity modulated beams such as those generated by computercontrolled multileaf collimators. The first method uses a volume sensitive penalty function in which fast simulated annealing is used for cost function minimization ͑CFM͒. The second technique is based on the theory of projections onto convex sets ͑POCS͒ in which the dose-volume constraint is replaced by a limit on integral dose. The ability of the methods to respect the dose-volume relationship was demonstrated by using a prostate example involving partial volume constraints to the bladder and the rectum. The volume sensitive penalty function used in the CFM method can be easily adopted by existing optimization programs. The convex projection method can find solutions in much shorter time with minimal user interaction.

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