Kate A. Remley

Improving the accuracy of ray-tracing techniques for indoor propagation modeling

Problems with the use of ray-tracing techniques in indoor propagation environments are identified, and a new set of widely applicable diffraction coefficients is developed. The limitations on the accuracy of the ray-tracing method in indoor propagation environments are first assessed. The effects of scatterers with dimensions approaching the wavelength of operation and of scatterers with finite conductivity are considered. The accuracy of ray tracing is quantified by comparison to a full-wave simulation technique, which combines the finite-difference time-domain method with a spatial transformation technique, the Kirchhoff surface integral formulation. Simulation results demonstrate that when the magnitude and phase of the received signal components are properly accounted for, the ray-tracing solution may be accurate down to a fraction of a wavelength. A new set of diffraction coefficients is presented for calculations involving obstacles with finite conductivity. The new coefficients eliminate an artificial dip in the diffracted field strength, which is often encountered when currently available techniques are used. Validation is provided by comparison with full-wave simulations and measurements. Improved accuracy in both the illuminated and shadowed regions is demonstrated.

Compensation of Random and Systematic Timing Errors in Sampling Oscilloscopes

In this paper, a method of correcting both random and systematic timebase errors using measurements of only two quadrature sinusoids made simultaneously with a waveform of interest is described. The authors estimate the fundamental limits to the procedure due to additive noise and sampler jitter and demonstrate the procedure with some actual measurements

Linearization of large-signal scattering functions

We describe a linearization of large-signal scattering functions describing weakly nonlinear device behavior. The linearization takes on a convenient form similar to scattering parameters that clearly illustrates the role of phase-conjugated mixing products in the theory. We develop rules for the evolution of the linearization with time. We illustrate the theory with transistor measurements and apply the theory to the characterization of the reflection coefficients of a microwave source in its large-signal operating state.

Designing and Testing Software-Defined Radios

This article reviews the main parts of a software-defined radio (SDR) to emphasize several possible implementations of both receivers and transmitters. We describe solutions for testing and characterizing these types of devices. SDRs typically operate in both the analog and the digital domains, thus mixed-domain instrumentation is necessary to carry out testing. We first give a short overview of several architectures for SDR receiver front ends. Then, several possible architectures for transmitter front ends are described. We discuss methods that can be used to improve amplifier efficiency. Instrumentation currently available in the commercial market that allows the characterization of such types of transceivers is presented.

Multisine excitation for ACPR measurements

We use a simulator to compare adjacent-channel power ratio (ACPR) measurements of a nonlinear device excited with various multisine signals to ACPR measurements of the same device excited with pseudorandom digital modulation. We examine four common types of multisine excitation, each with identical numbers of tones, tone-spacings, and nominal power levels, but with different magnitude and phase relationships between tones. We show that use of some common multisines may result in significant overestimation of the actual ACPR from the digitally modulated nonlinear device.

Phase detrending for measured multisine signals

We develop a method to detrend the phases of measured multisine signals. We find a time reference that removes the linear component of the measured phases and aligns them, within a precision specified by the user, to their expected values. An initial guess is provided by a closed-form expression. We then find the global minimum of a user-specified error function. The simple postprocessing algorithm is general and can be implemented in many software packages.

Reverberation Chamber Measurement Correlation

This contribution evaluates the utility of several different metrics for studying correlation between reverberation chamber measurements collected at different stirrer positions. Metrics considered are the autocovariance, the correlation matrix, and two metrics based upon the entropy of the data correlation matrix: 1) the effective number of uncorrelated measurements and 2) the measurement efficiency. The different metrics are shown to be useful for different correlation analyses. Application of these metrics reveals that the correlation between reverberation chamber measurements is strongly affected by stirring methodology, loading configuration, and measurement frequency.

Multisine signals for wireless system test and design [Application Notes]

Multisine signals are used in the laboratory and in the field to provide a periodic, well-characterized waveform that can simulate complex modulated radio frequency (RF) signals. In the field of wireless telecommunications, multisines are often used to provide realistic test signals that have statistics similar to various types of digitally modulated signals. It is concluded that the multisine approach is well suited for evaluating a nonlinear system excited by real communication signals. Multisine signals enable to gather important information about the in-band distortion and to excite long-term memory effects by generating baseband components. They are periodic and straightforward to characterize, making them ideal for identifying both magnitude and phase distortion during test and verification. Using multisines to simulate standard wireless system excitations and figures of merit allows for very good laboratory nonlinear distortion measurement setups.

Reverberation-Chamber Test Environment for Outdoor Urban Wireless Propagation Studies

We introduce a test environment to replicate the well-known clustering of reflections in power delay profiles arising from late-time delays and reflections. Urban wireless propagation environments are known to exhibit such clustering. The test setup combines discrete reflections generated by a fading simulator with the continuous distribution of reflections created in a reverberation chamber. We describe measurements made in an urban environment in Denver, CO, that illustrate these multiple distributions of reflections. Our comparison of measurements made in the urban environment to those made in the new test environment shows good agreement.

Electromagnetic Measurements for Counterfeit Detection of Radio Frequency Identification Cards

We investigate a technique for counterfeit detection of high-frequency radio frequency identification (RFID) cards based on the electromagnetic characteristics of the cards rather than the digital information that they transmit. We describe a method of quantifying the electromagnetic signature of an RFID card and identify a small set of features that is sufficient to correctly classify a test set of cards. Furthermore, we show that our measurements indicate that the features most useful for distinguishing cards are contained within the reader inquiry rather than the card response, a reflection of the near-field coupling nature of the RFID transactions in ISO 14443.