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We developed a new scanning positron microbeam for spatially resolved (coincident) Doppler broadening spectroscopy ((C)DBS) at the neutron induced positron source Munich (NEPOMUC). For this purpose, positrons are moderated three times: First, positrons generated by pair production are self-moderated in annealed polycrystalline Pt foils inside the beam tube housing the positron source NEPOMUC. Then, the brightness of the primary 1 keV positron beam with 109 moderated positrons per second is enhanced by a W(100) single crystal remoderator operated in back reflection geometry. Finally, in the upgraded CDB spectrometer we apply a 100 nm thin Ni(100) foil acting as transmission remoderator to generate a positron microbeam with a minimum beam diameter of 33 µm. We demonstrate the potential of laterally resolved DBS by imaging the defect distribution around a laser beam weld of the high-strength age-hardenable Al alloy AlCu6Mn. CDBS was applied with unprecedented spatial resolution to reveal the dissolution of Cu rich precipitates and the formation of Al-vacancy-Cu-complexes.We developed a new scanning positron microbeam for spatially resolved (coincident) Doppler broadening spectroscopy ((C)DBS) at the neutron induced positron source Munich (NEPOMUC). For this purpose, positrons are moderated three times: First, positrons generated by pair production are self-moderated in annealed polycrystalline Pt foils inside the beam tube housing the positron source NEPOMUC. Then, the brightness of the primary 1 keV positron beam with 109 moderated positrons per second is enhanced by a W(100) single crystal remoderator operated in back reflection geometry. Finally, in the upgraded CDB spectrometer we apply a 100 nm thin Ni(100) foil acting as transmission remoderator to generate a positron microbeam with a minimum beam diameter of 33 µm. We demonstrate the potential of laterally resolved DBS by imaging the defect distribution around a laser beam weld of the high-strength age-hardenable Al alloy AlCu6Mn. CDBS was applied with unprecedented spatial resolution to reveal the dissolution of C...

This paper presents channel measurements for short range radar applications in a frequency range from 5 GHz up to 7.5 GHz. For these measurements antennas with a half power beam width of 80° and circular polarization were provided by Maxim Integrated. The measured scenarios included a 28 mm copper pipe, a 26 cm × 28 cm aluminium plate, a bicycle and a 75 mm polokal plastic pipe. All measurements were conducted on flat concrete and grass. Through comparison with the radar equation and radar cross section calculations for the far field, it could be shown, that the size of the reflecting objects has to be used for the calculation of the near field (Fraunhofer Region) to far field transition. The measurements show that the radar cross section of an object declines the farther it comes into the near field.

We present an extension of an existing outdoor UWB scatterer detection algorithm [1], [2], making it usable for indoor scenarios. The algorithm is extended with the capability to find virtual sources, which can explain reflections from extended, plane surfaces. The extension thus removes the restriction to just single-bounce signal paths. Single-bounce scatterers, as well as virtual sources extracted from the channel impulse response, are assigned to positions in 2-dimensional space and can be matched to given floor plan information. The functionality is demonstrated with indoor measurement data obtained in a large office environment that represents a challenging dense multipath scenario. Results show that estimated locations of virtual sources and scatterers fit very well with the expected locations.

Realistic simulation of Ultra-Wideband (UWB) positioning and tracking is a tough and challenging task. Lots of parameters have a significant impact on the final performance of the positioning system, such as parameters of the transmitted waveform, radio regulations, channel, receiver, ranging-, positioning-, and tracking-algorithm, and finally the geometric setup. A realistic simulation framework is needed to develop and optimize UWB methods and algorithms. This work proposes a novel framework for realistic UWB positioning simulations. All stages of influence have been modelled carefully. While ray-tracing simulators focus on a given user defined scenario, our approach uses statistically defined environments. Random processes are used to select channel impulse responses from a measurement database, according to an algorithm that introduces realistic large and small-scale variability with space. In particular, line-of-sight (LOS) and non-LOS (NLOS) channels are used at a defined ratio. In this work the application of the simulation framework is demonstrated to compare the performance of a least-squares (LS) positioning algorithm to a standard and an extended Kalman filter (SKF and EKF) tracking algorithm in environments with a large fraction of NLOS range measurements. The IEEE 802.15.4a standard is analyzed with respect to its positioning performance. It is shown that the localization accuracy and reliability can be improved significantly with the tracking algorithms, but their performance drop significantly with increasing probability of NLOS links.

We present a novel UWB indoor localization concept that performs the position estimation with a set of virtual anchor nodes, generated from a single physical anchor and floor plan information. Using range estimates to the virtual anchors, we perform multilateration to estimate the position of an agent. Previous work has shown the general applicability of this concept. In this contribution, we use a moving agent to exploit the correlation in successive positions using state-space concepts. A motion model for the agent and the measurement likelihood function allow for the use of the powerful framework of Bayesian state estimation. With this concept, we can propagate prior information on the agent position from one time step to the next. The statistical model for the ranging to the virtual anchors accounts for several imperfections, which lead to multimodal and heavy-tailed measurement distributions. We show how modified versions of the Kalman filter as well as a particle filter can account for these imperfections and yield accurate and robust position estimates. In a typical indoor pedestrian motion scenario, we can achieve an accuracy of about 45 cm for 90% of the estimates.

The IEEE 802.15.4a standard for wireless sensor networks is designed for highly accurate ranging with impulse radio Ultra Wideband (UWB) signals. The standard is designed for coherent and non-coherent (energy detector) receivers, thus the choice of complexity is left to the implementer. In this paper, the maximal operating distance is analyzed for ranging, using a coherent receiver and an energy detector under FCC/EC regulations. The analysis is based on the working points of the receivers and a link budget calculation. The preamble of the standard is defined by several parameters, which influence the allowed FCC transmit power, the free space losses and thus the maximal operating distance. It is shown which code and channel combinations achieve the largest operating distance. The best performance is achieved by using long spreaded codes, where coherent receivers can achieve a maximal operating distance up to several thousand meters and energy detectors up to several hundred meters.

Real time locating systems (RTLS) and wireless sensor networks are currently a hot and challenging research topic. Ultra wideband (UWB) shows promising properties for these systems, such as low-power transmitter designs and highly accurate ranging, where cm-level accuracy is achievable even in multipath intensive environments. A high-performance reference receiver architecture based on coherent processing is presented in this paper. It is used to define quality metrics of the received signals, as for example peak signal to noise ratio (PSNR) and line-of-sight signal to noise ratio (LSNR) for ranging, and Eb/N0 for communication. These metrics are used to evaluate the experimental data in their quality and their ranging performance. Furthermore, performance trade-offs w.r.t. system parameter and receiver architecture choices, in particular for non-coherent receivers, can be analyzed. In this work, the reference receiver is verified experimentally using IEEE 802.15.4a compliant signals. The ranging performance is correlated to the signal-to-noise ratios for an indoor line-of-sight measurement campaign.

The IEEE 802.15.4a standard for wireless sensor networks is designed for highly accurate ranging with impulse radio Ultra Wideband (UWB) signals. The standard allows a large number of different system parameters for the preamble, which are analyzed in detail for energy detectors. Energy detectors have low complexity and promise low cost and low energy consumption. The focus of this work is on statistical modeling of inter-pulse interference (IPI), noise terms and correlation properties of two despreading methods. One method shows perfect crosscorrelation properties and the other one shows a zero-mean noise floor. An IPI intensive LOS industrial environment was chosen to verify the theoretical results and to evaluate both despreading methods for different system settings. It is shown that the first method performs better if IPI is the limiting factor and the other one is suitable if noise is dominant.

In this contribution we present a modular IEEE 802.15.4a UWB demonstrator platform. The demonstrator supports a one-way communication link and allows for ranging and communication experiments.

In this contribution we design and analyze pulse shaping filters for use in IEEE 802.15.4a transmitters. They are developed and evaluated for Channels 1-4 in the low band. We analyze the minimum requirements for IEEE 802.15.4a standard compliance and design passive filters which shape a given input pulse stream at baseband. Further, we simulate these filters by using S-parameter models of available components and optimize the resulting designs for standard compliance of the baseband transmit pulse with an iterative method. Finally, we compare the simulations with measurement results and evaluate our design by means of an IEEE 802.15.4a transmitter application.

A chip manufacturing process requires extensive support of CAD-tools in order to predict the behavior of the embedded circuitry and to ensure the intended system functionality. Past experience shows that the overall performance of UHF RFID systems is mainly limited by multipath propagation and detuning. In this context, system-level simulations are vital to assess the overall performance and improve the embedded circuit. We present a simulator framework capable of handling chip-level tag models, fading MIMO radio channels, and interrogator building blocks on signal level. It is based on highly flexible behavioral tag-models instead of highly accurate but static ASIC models. In contrast to other UHF RFID simulators, it is explicitly designed to handle wideband signals, fading channels, nonlinearities, and detuning effects. The simulator is currently used to develop and evaluate the performance of ranging and realtime channel estimation systems. The presented results emphasize the feasibility of our framework in the evaluation of a range estimation approach between a standard UHF RFID transponder and an interrogator.

At NEPOMUC, four different experiments are installed permanently and one beam port is open for positron experiments provided by external users. To match the different demands of these experiments on the phase space density of the positron beam, the established NEPOMUC remoderator was relocated and two novel beam switches were installed to provide the primary high-intensity beam or the remoderated high-brightness beam within short switching times. At the present state, the remoderated beam has a mean diameter of 1.85(35) mm and an intensity of 3.0(3) 107 e+/s. For the transformation of the longitudinal phase space density a new buncher setup was developed which converts the continuous positron beam into a pulsed beam.

A new high resolution coincidence Doppler spectrometer is under development at the positron beam facility NEPOMUC at the research neutron source FRM II. A Ni(100) re-moderation foil will be installed at the new spectrometer in transmission geometry for producing a positron beam with high brightness. Therefore, a magnetic lens for focusing the positrons onto the re-moderator and an electrostatic lens system for focusing the beam onto the sample have to be designed and simulated. The aim is to reach a beam diameter below 10 μm at the sample position for high resolution experiments. The current status of the project will be described and presented.