Mathias Grudén

Accurate and reliable soldier and first responder indoor positioning: multisensor systems and cooperative localization

A robust, accurate positioning system with seamless outdoor and indoor coverage is a highly needed tool for increasing safety in emergency response and military urban operations. It must be lightweight, small, inexpensive, and power efficient, and still provide meter-level accuracy during extended operations. GPS receivers, inertial sensors, and local radio-based ranging are natural choices for a multisensor positioning system. Inertial navigation with foot-mounted sensors is suitable as the core system in GPS denied environments, since it can yield meter-level accuracies for a few minutes. However, there is still a need for additional supporting sensors to keep the accuracy at acceptable levels during the duration of typical soldier and first responder operations. Suitable aiding sensors are three-axis magnetometers, barometers, imaging sensors, Doppler radars, and ultrasonic sensors. Further more, cooperative positioning, where first responders exchange position and error estimates in conjunction with performing radio based ranging, is deemed a key technology. This article provides a survey on technologies and concepts for high accuracy soldier and first responder positioning systems, with an emphasis on indoor positioning.

Evaluation of a microplasma source based on a stripline split-ring resonator

In this paper, a stripline split-ring resonator microwave-induced plasma source, aimed for integration in complex systems, is presented and compared with a traditional microstrip design. Devices based on the two designs are evaluated using a plasma breakdown test setup for measuring the power required to ignite plasmas at different pressures. Moreover, the radiation efficiency of the devices is investigated with a Wheeler cap, and their electromagnetic compatibility is investigated in a variable electrical environment emulating an application. Finally, the basic properties of the plasma in the two designs are investigated in terms of electron temperature, plasma potential and ion density. The study shows that, with a minor increase in plasma ignition power, the stripline design provides a more isolated and easy-to-integrate alternative to the conventional microstrip design. Moreover, the stripline devices showed a decreased antenna efficiency as compared with their microstrip counterparts, which is beneficial for plasma sources. Furthermore, the investigated stripline devices exhibited virtually no frequency shift in a varying electromagnetic environment, whereas the resonance frequency of their microstrip counterparts shifted up to 17.5%. With regard to the plasma parameters, the different designs showed only minor differences in electron temperature, whereas the ion density was higher with the stripline design.

Sample-Selection Method for Arbitrary Fading Emulation Using Mode-Stirred Chambers

Mode-stirred chambers (MSCs) consist of one or more resonant cavities coupled in some way in order to allow the measurement of different antenna parameters such as antenna efficiency, correlation, diversity gain, or multiple-input multiple-output (MIMO) capacity, among others. In a single-cavity MSC, also known as a reverberation chamber (RC), the environment is isotropic and the amplitude of the signal is Rayleigh distributed. Real environments, however, rarely follow an isotropic Rayleigh-fading scenario. Previous results have shown that a Rician-fading emulation can be obtained via hardware modification using an RC. The different methods lack from an accurate emulation performance and are strongly dependent upon chamber size and antenna configurations. With the innate complexity of more-than-one-cavity MSC, the coupling structure generates sample sets that are complex enough so as to contain different clusters with diverse fading characteristics. This letter presents a novel method to accurately emulate a more realistic Rician-fading distribution from a Rayleigh-fading distribution by selecting parts of the sample set that forms different statistical ensembles using a complex two-cavity multi-iris-coupled MSC. Sample selection is performed using a genetic algorithm. Results demonstrate the potential of MSCs for versatile MIMO fading emulation and over-the-air (OTA) testing. The method is patent protected by EMITE Ing., Murcia, Spain.

Field operational testing for safety improvement of freight trains using wireless monitoring by sensor network

Today, the majority of wagon failures on railroad systems are because of the poor maintenance of ball bearings, which causes emergent stops and delays. The existing stationary detectors, lack in predicting failures which cause troubles in scheduling maintenance. During the fall of 2011, a trial was performed by applying a wireless sensor network (WSN) aboard a train wagon with the objective to demonstrate a proof of concept for monitoring the temperature of ball bearings aboard the train wagon. This trial investigates several key aspects when applying sensor networks such as radio wave propagation, energy scavenging and performance of the WSN aboard the wagon. Two wireless links were used in the WSN. The aboard network communicates at 2.45 GHz, and the external communication is an 868 MHz radio frequency identification radio link. Since the energy in the WSN node is limited, appropriate energy scavenging devices are also presented and evaluated in a lab environment. Effort has been made to overcome these problems. The energy consumption in the network is still a problem; the most promising energy scavenging technique is piezoelectric harvesting by vibrations, which in the experiments scavenged 2.32 mW.

Empirical Tests of Wireless Sensor Network in Jet Engine Including Characterization of Radio Wave Propagation and Fading

This letter describes how to replace a wired telemetry system for structural health monitoring (SHM) in jet engines with a wireless sensor network (WSN). With a WSN, the time required for engine preparation can be reduced from several months to only a few weeks. The WSN is tested in a military jet engine used in the Swedish jet fighter JAS 39 Gripen. Also, the wave propagation is characterized in the real engine and a half-scale engine with both linear- and circular-polarized antennas. The measurements are analyzed by using K-factor and path loss. Finally, the complete system is tested in a full-scale test with a running engine. The intended WSN will operate in the 2.45-GHz ISM band. The K-factor for the real engine ranges from about 2 to 8 and for the half-scale engine from about 1 to 15. The use of circularly polarized antennas does not always reduce the fading. The complete system measured the bit error rate (BER) and temperature. The performed tests were successful, and the BER were 2.8%-10.5% during the test. The practical test also showed the possibility of using a WSN as a monitoring system in jet engines.

Measurements and Simulations of Wave Propagation for Wireless Sensor Networks in Jet Engine Turbines

In this letter, measurements and simulations of wave propagation inside a jet engine fan have been performed. The investigation was done using both EM simulations of different cases of propagation inside the engine and by measuring the corresponding cases inside a half-scale model of a jet engine fan. The average path loss was calculated, and the shapes of the fading distributions were extracted. The time between two consecutive fading dips was measured in the empirical part. Measurements were performed with engine speeds of both 30 and 60 rpm and were shown to be linearly scalable from 60 rpm to full speed of 10 000 rpm. The results showed an average path loss of about 55 dB. When scaling the measurements from 60 rpm to full-speed rotation of about 10 000 rpm, the fading was so severe that the time slot between consecutive fading dips was limited to 290 μs.

Sample Selection Algorithms for Enhanced MIMO Antenna Measurements Using Mode-Stirred Reverberation Chambers

Mode-stirred reverberation chambers (MSRCs) are a useful tool for measuring several wireless-related MIMO antenna parameters. In a conventional single-cavity MSRC, the emulated fading environment is isotropic and the amplitude of the signal is Rayleigh distributed. Previous contributions have enhanced the emulation capabilities of MSRCs so as to include the ability to emulate Rician- and non-isotropic fading environments. In this contribution, arbitrary amplitude probability density functions (PDF) emulation using a MSRC is presented by selecting parts of the sample set that forms different statistical ensembles. Several algorithms are presented and compared in terms of computation time and power accuracy using simulated as well as measured data from different MSRCs to obtain Rician, on-body and amplitude PDFs of standardized models. The technique is patent-protected by EMITE.

Large Ad Hoc Shielded Room with Removable Mode Stirrer for Mobile Phone Antenna Tests

Reverberation chambers (RC) are widely used for measuring antenna performance and parameters for MIMO systems. RCs for mobile phone antenna tests are often specially designed for this purpose. The lowest frequency of operation of an RC is decided by its size. With a trend of lower frequency bands being allocated for mobile phones, the minimum size of RCs for mobile phone antenna tests increases, and is approaching the size of a normal room. At the same time, many large shielded rooms are already in use for various electrical measurements. In this paper, a standard shielded room designed for EMC testing is used as an RC for mobile phone antenna tests. To complete the RC, a large mode stirrer is built. The fact that the room is also used for other tests requires a detachable, foldable, and lightweight stirrer design. Therefore, metal meshes are evaluated for the design of the mode stirrer. The performance of the used room is verified by standard tests for RCs, and it is verified that it is possible to measure antennas from about 400 MHz up to 4 GHz with good accuracy. The size of the room also enables measurements including humans carrying mobile phones or body area networks.

Diversity Techniques for Robustness and Power Awareness in Wireless Sensor Systems for Railroad Transport Applications

Diversity Techniques for Robustness and Power Awareness in Wireless Sensor Systems for Railroad Transport Applications

Broadband Space-Time Measurements in Reverberation Chamber Including Comparison With Real Environment

Spatial variations of the broadband time-domain impulse response in a reverberation chamber are studied experimentally. The goal is to introduce the technique as a means for characterizing reverberation chambers and to demonstrate typical results and the information that can be extracted. Similar measurements are performed in a lab room for comparison. The results provide new insights regarding the signal environment inside a reverberation chamber and how it compares to real-life environments. The minimum number of signal paths in the chamber is calculated based on the spatial and temporal resolutions used in the characterization.