Stefan Scheiblhofer

A 77-GHz FMCW MIMO Radar Based on an SiGe Single-Chip Transceiver

This paper describes a novel frequency-modulated continuous-wave radar concept, where methods like nonuniform sparse antenna arrays and multiple-input multiple-output techniques are used to improve the angular resolution of the proposed system. To demonstrate the practical feasibility using standard production techniques, a prototype sensor using a novel four-channel single-chip radar transceiver in combination with differential patch antenna arrays was realized on off-the-shelf RF substrate. Furthermore, to demonstrate its practical applicability, the assembled system was tested in real world measurement scenarios in conjunction with the presented efficient signal processing algorithms.

Performance evaluation of algorithms for SAW-based temperature measurement

Whenever harsh environmental conditions such as high temperatures, accelerations, radiation, etc., prohibit usage of standard temperature sensors, surface acoustic wave-based temperature sensors are the first choice for highly reliable wireless temperature measurement. Interrogation of these sensors is often based on frequency modulated or frequency stepped continuous wave-based radars (FMCW/FSCW). We investigate known algorithms regarding their achievable temperature accuracy and their applicability in practice. Furthermore, some general rules of thumb for FMCW/FSCW radar-based range estimation by means of the Cramer-Rao lower bound (CRLB) for frequency and phase estimation are provided. The theoretical results are verified on both simulated and measured data.

High-Speed FMCW Radar Frequency Synthesizer With DDS Based Linearization

Recently , we introduced a software linearization technique for frequency-modulated continuous-wave (FMCW) radar applications using a nonlinear direct digital synthesizer based frequency source. In this letter, we present a method that uses this unconventional, cost efficient, basically nonlinear synthesizer concept, but is capable of linearizing the frequency chirp directly in hardware by means of defined sweep predistortion. Additionally, the concept is extended for the generation of defined nonlinear frequency courses and verified on measurements with a 2.45-GHz FMCW radar prototype

Signal model and linearization for nonlinear chirps in FMCW Radar SAW-ID tag request

In this paper, we present a frequency-modulated continuous-wave radar interrogation concept, based on direct digital synthesis (DDS), that operates without the commonly necessary high-frequency DDS reference oscillator. As the generated frequency sweeps are nonlinear, standard Fourier transform methods for baseband signal evaluation cannot be applied directly. We show the corresponding signal model, derive a linearization concept on the basis of resampling, and demonstrate the linearization algorithm on simulated data, as well as on real wireless interrogations of surface acoustic-wave sensors.

The Influence of Windowing on Bias and Variance of DFT-Based Frequency and Phase Estimation

In sinusoidal parameter-estimation problems for measurement applications, discrete spectra with high dynamic range are often under investigation. To suppress unwanted interference effects (ldquoleakagerdquo) in the discrete Fourier transform (DFT) spectrum, the application of data windows is common practice. In this paper, the influence of windowing on the bias and variance of the frequency and phase estimates, calculated via the DFT, is investigated. Furthermore, the effect of choosing different sampling start times on both the bias and the variance is discussed.

Identification of SAW ID-tags using an FSCW interrogation unit and model-based evaluation

Surface acoustic wave (SAW) devices are well suited for the application as wireless and completely passive identification (ID)-tag. They operate even under harsh environmental conditions, especially under high temperatures. Interrogation units operate similar to conventional radar systems and therefore, have the same resolution restrictions when an inverse fast Fourier transformation (IFFT) is applied. The application of model-based algorithms to the evaluation of identification tags is presented and enhancements in either improved resolution or reduced system bandwidth are shown. Furthermore, optimizations in the coding scheme for reduced tag sizes are discussed, and measured results obtained by a built interrogation unit and fabricated ID-tags for an identification system are shown.

Precise distance measurement with cooperative FMCW radar units

In many applications the precise distance between different units has to be measured. The proposed measurement system operates with frequency modulated continuous wave (FMCW) radar sensors for distance measurement in a cooperative but unsynchronized way. Due to the missing synchronization a data transfer between the units is performed by means of the radar hardware. On the other hand, this principle could be easily implemented in communication systems. A prototype system in the 5.8-GHz ISM band has been built, and measurement results up to about 780 meters distance with accuracies of few centimeters are shown. Furthermore, the distance can be calculated at both transponder units.

Modeling and performance analysis of SAW reader systems for delay-line sensors

In this contribution, we present a comprehensive modeling approach for delay line-based surface acoustic wave (SAW) sensor reader systems, which provides valuable insight into the interaction of the individual system parameters. A parametric analysis of signal strength, noise, and quantization effects and consideration of important signal processing parameters, such as data windows and averaging, allows prediction of the achievable statistical measurement accuracy by closed-form solutions. The performance and capabilities of the derived model are verified on system design examples as well as multiple practical measurement scenarios, using a prototype 2.45-GHz frequency-stepped continuous-wave SAW reader system.

Sparse antenna array design and combined range and angle estimation for FMCW radar sensors

In this paper the design of sparse antenna arrays and signal processing algorithms for non-parametric high resolution range and angle estimation algorithms for FMCW radar sensor arrays are presented. Since the performance of such systems strongly depends both on the antenna placement as well as the adequate algorithms, the close relation between antenna hardware and signal processing is exploited in the development of the whole system. The theory is verified by measurements utilizing a system operating at 24 GHz and using a four element array with interelement spacings larger than half a wavelength for each array element. The simulations and measurements show promising results which makes the system attractive for applications where only few channels are available and high gain and therefore large array elements are necessary, which would prohibit the use of classical half-wavelength spaced arrays.

Effects of Systematic FMCW Radar Sweep Nonlinearity on Bias and Variance of Target Range Estimation

In linear frequency modulated continuous wave (FMCW) radar systems, the quality of target range estimation is directly associated to the linearity of the transmitted frequency sweep. In this paper we introduce a novel technique for analyzing the effects of systematic sweep nonlinearities on bias and variance of target range estimates, applicable to the commonly used Fourier transform based evaluation methods. A prototype FMCW radar system, capable of generating nonlinear frequency sweeps, is presented and used to verify the theoretical results on real measurement data