Christian Waldschmidt

Complete RF system model for analysis of compact MIMO arrays

A framework to analyze compact arrays for multiple-input-multiple-output (MIMO) is presented. Many handheld devices require very compact arrays. Small spacings between the antennas lead to mutual coupling, which decreases the efficiency of the antennas and therefor the signal-to-noise ratio and leads to correlated signals at the antennas. Both effects are completely taken into account in this framework; thus, it allows for a fair comparison of different antenna arrays for MIMO. It is distinguished between MIMO systems for multiplex transmission or pure beamforming, which have different requirements for the antennas. Different compact array configurations, which exploit spatial, polarization, and pattern diversity, are discussed and compared. For practical purposes, it is also shown how to connect this framework to standard path-based channel models.

Compact wide-band multimode antennas for MIMO and diversity

This paper presents broadband multimode antennas for multiple-input multiple-output (MIMO) and diversity applications. The antenna system is not based on spatial diversity, as usual MIMO systems, but on a combination of pattern and polarization diversity. Different modes of self-complementary, thus extremely broadband, spiral and sinuous antennas are used to decorrelate the signals. It is shown that only one antenna is necessary to receive three uncorrelated signals, thus the space required to place the MIMO antenna is very small. Simulation results and measurements of a typical indoor scenario are given.

Automotive radar gridmap representations

In robotic applications gridmaps are a common representation of the environment. For the automotive field, radar as sensing technology is suitable due to its robustness. This paper presents two radar-based grid-mapping algorithms for automotive applications like self-localization. These algorithms involve first an amplitude-based approach, which gains information about the RCS of all targets, and second an occupancy grid-mapping approach with an adapted inverse sensor measurement model. Experiments show that both gridmapping algorithms result in adequate representations of the environment.

Reliable Orientation Estimation of Vehicles in High-Resolution Radar Images

With new generations of high-resolution imaging radars, the orientation of vehicles can be estimated without temporal filtering. This enables time-critical systems to respond even faster. Based on a large data set, this paper compares three generic algorithms for the orientation estimation of a vehicle. An experimental MIMO imaging radar is used to highlight the requirements of a robust algorithm. The well-known orientated bounding box and the so-called L-fit are adapted for radar measurements and compared with a brute-force approach. A quality function selects the best fitted model and is a key factor to minimize alignment errors. Moreover, the reliability of the estimation is evaluated with respect to the aspect angle, the distance to the target, and the number of sensors. An approach to estimate the reliability of the current orientation estimation is introduced. It is shown that the root mean square error of the orientation estimation is 9.77° and 38% smaller compared with the common algorithm. In 50% of the evaluated measurements the orientation estimation error is smaller than 3.73°.

Active transmitarray submodule for K/Ka Band Satcom applications

A novel concept for an active transmitarray architecture for K/Ka Band Satcom applications is presented. The highly-integrated antenna system is based on planar multilayer arrangement covering both Satcom frequency bands for uplink at 30 GHz and downlink at 20 GHz. To verify the proposed manifold approach, the individual components and a first active dual-band transmitarray submodule enhanced by a multi-functional SiGe BiCMOS MMIC have been realized and measured successfully.

Compact bistatic 160 GHz transceiver MMIC with phase noise optimized synthesizer for FMCW radar

This paper presents an ultra compact bistatic FMCW radar transceiver MMIC at 160 GHz with a mixer-based synthesizer concept. The integrated mixer converts a ramp signal with a stabilized local oscillator (SLO) signal to the RF output signal. The usage of a mixer reduces the frequency multiplication factor of the ramp signal and hence improves the phase noise at 160 GHz. The fixed frequency local oscillator for the up-conversion has a comparably small phase noise level compared to the ramp input signal and does not contribute significantly to the total phase noise level at 160 GHz. Apart from the synthesizer, the MMIC also includes a power amplifier with a maximum output power of 2 dBm, two efficient integrated antennas with a wide radiation pattern, and an IQ-receiver. Two FMCW radar responses recorded with a bandwidth of 20 GHz show the dynamic range of this sensor and its near range behavior. The compact SiGe MMIC requires only a chip area of 1.4mm × 1.0mm and consumes 285mW from a 3V power supply.

MMIC-to-waveguide transition at 160 GHz with galvanic isolation

In this paper a new approach for a monolithic microwave integrated circuit (MMIC) to rectangular waveguide transition is presented, which has no need for a specific package. The transition uses a partly integrated antenna with a patch radiator and a tapered dielectric waveguide to guide the wave into a widened metallic waveguide. Due to the usage of the dielectric waveguide the ground potentials of the MMIC and the metallic waveguide are galvanically isolated. The proposed transition was characterized in back-to-back measurements without probe-tips. A minimum insertion loss of 3 dB was measured. To the authors knowledge, this is the first approach of a galvanically isolated MMIC to metallic waveguide transition.

RCS measurements of a human hand for radar-based gesture recognition at E-band

This paper presents monostatic radar cross section (RCS) measurements of a human hand in the frequency range from 60GHz to 90 GHz. These values are important parameters for system designs in the emerging field of radar-based gesture recognition. The measurement procedure is described in detail and results of four gestures at three different distances are depicted and analysed.

Analytical and Experimental Investigations on Mitigation of Interference in a DBF MIMO Radar

As driver assistance systems and autonomous driving are on the rise, radar sensors become a common device for automobiles. The high sensor density leads to the occurrence of interference, which decreases the detection capabilities. Here, digital beamforming (DBF) is applied to mitigate such interference. A DBF system requires a calibration of the different receiving channels. It is shown how this calibration completely changes the DBF beam pattern required to cancel interferences, if the system has no IQ receiver. Afterward, the application of DBF on a multiple-input multiple-output (MIMO) radar is investigated. It is shown that only the real aperture and not the virtual one can be used for interference suppression, leading to wide notches in the pattern. However, for any target the large virtual aperture can be exploited, even if interferers are blinded out. Moreover, the wide notches for interference suppression of the real aperture appear narrow in the virtual aperture for target localization. The results are verified by measurements with time-multiplexing MIMO radar.

Wireless channel-based message authentication

Inter-vehicle communication has attracted a lot of attention in the past. A major concern is the security and especially the integrity and authenticity of messages. Current standards and proposals in literature leverage asymmetric cryptographic mechanisms to achieve this, which is costly both in terms of consumed computational power, bandwidth, and introduced delay. We present a novel idea to use physical characteristics of the wireless channel to verify subsequent messages after initial trust in a first message has been established cryptographically. In this paper, we sketch the concept and provide a first evaluation on its potential for saving named resources.