Christoph Degen - Academia.edu (original) (raw)

Papers by Christoph Degen

Efficient antenna development involves precise electromagnetic (EM) simulation of the antenna and... more Efficient antenna development involves precise electromagnetic (EM) simulation of the antenna and all surroundings. Most accurate results can be obtained by using CAD data of all parts belonging to the antenna and objects in its vicinity. However, depending on size and number of parts involved this can lead to a huge amount of data which can not be handled by current EM simulation tools anymore. Thus, usually a trade-off between simulation accuracy and object size needs to be found. In this paper, simplification algorithms for automatically reducing CAD data of a Galileo II satellite are introduced and tested.

For driver assistance systems, range and velocity measurement using radar is of high importance. ... more For driver assistance systems, range and velocity measurement using radar is of high importance. Usually, such assistance systems are applied to cars. However, vulnerable road users such as pedelecs also offer the opportunity to increase safety by using assistance systems based on radars, cameras etc. In this paper, Kalman filtering for object tracking using radar is reviewed briefly. Then, a metric for measuring the hazardousness of crossing traffic is given. For this, a radar mounted on a pedelec is simulated. A measured pedelec trajectory is used to demonstrate effects arising from driving on a wiggly line. That is, the radar suffers from an angular motion, which is different compared to standard automotive applications.

2022 16th European Conference on Antennas and Propagation (EuCAP), Mar 27, 2022

The objective of this paper is to provide a throughout complex-valued treatment of different aspe... more The objective of this paper is to provide a throughout complex-valued treatment of different aspects in backscatter modulation. Such modulation is a key aspect in radio-frequency identification (RFID) communication. The main point in this paper is the introduction of a complex radar cross section that describes amplitude and phase effects of any reflecting object but especially of RFID tag antennas. Then, the efficiency of sideband modulation is derived based on switching between different complex radar cross section values. Finally, the modulation efficiency is illustrated in an example scenario with a tag antenna placed in front of a metal plate.

Direction-of-arrival (DoA) estimation is an essential means for localization issues in various ap... more Direction-of-arrival (DoA) estimation is an essential means for localization issues in various applications. DoA estimation can be extended, for example, to source triangulation. Many approaches in this field, such as beamforming, exploit the knowledge of all signal amplitudes and phases of an antenna array. That is, as many receivers and analog-to-digital converters as antenna elements are required, followed by array signal processing. In contrast to that, Doppler-based DoA estimation typically involves switching between circularly arranged antenna elements and further processing of the resulting signal stream. In this paper, a novel Doppler-based DoA scheme is presented which makes use of the same hardware set-up as classical beamforming approaches on the one hand. On the other hand, very simple signal processing in analogy to Doppler direction finding is applied. This results in the advantage of having a common hardware that now can be used for a wider range of DoA algorithms. Also, the proposed scheme as well as the well-known MUSIC algorithm have been implemented using software-defined-radio (SDR) modules. Measurement results for validation and comparison are presented in this paper.

2022 44th Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), Jul 11, 2022

2021 18th European Radar Conference (EuRAD), Apr 5, 2022

Advances in Science, Technology and Engineering Systems Journal, May 1, 2023

In this paper we present a measurement system that is able to evaluate radar algorithms for vital... more In this paper we present a measurement system that is able to evaluate radar algorithms for vital signs sensing applications. For such medical applications, it is crucial to develop robust and reliable algorithms that are tested in a laboratory environment. The presented measurement system generates reproducible vital sign micro movement and dynamic clutter using loudspeakers to replicate realistic scenarios with two moving objects. It is described how realistic vital sign movement patterns are prepared using signal synthesis or recorded measurements, e.g. from a published dataset. The capability of the system to evaluate radar algorithms is demonstrated by investigating the impact of a beamforming algorithm on dynamic clutter. During the measurements presented in this paper, one loudspeaker replicates different vital sign movement patterns and the other loudspeaker creates dynamic clutter. It is shown that a digital beamforming improves the dynamic clutter rejection and leads to a better quality of the radar phase signal.

There are many algorithms for direction-of-arrival (DoA) estimation in array signal processing. M... more There are many algorithms for direction-of-arrival (DoA) estimation in array signal processing. Most of the work is carried out in scenarios with a large number of available snapshots. That is, received signals are sampled for a certain time duration. This paper focuses on worst case scenarios of having only one signal snapshot available, while trying to resolve several target signal sources. Such scenarios might occur in automotive radar applications, with small number of available snapshots being available. Moreover, other difficult propagation channels with correlated signals might reduce the possibility to exploit an increased number of signal snapshots. This paper elaborates on improved signal covariance matrix estimation based on averaging in space instead of taking time-averaged samples.

2015 9th European Conference on Antennas and Propagation (EuCAP), 2015

Car-to-car (C2C) communications requires reliable connectivity at moderate data rates. This is es... more Car-to-car (C2C) communications requires reliable connectivity at moderate data rates. This is essential for safety-related applications. The development of such communication systems needs to cope with time-variant propagation channels and rich multipath environments. Moreover, the choice of the antennas and their position in/on the car highly influences the overall propagation channel. This paper proposes a measurement method by means of software-defined radio systems. That is, USRP N210 modules are used for implementation of IEEE 802.11p physical layer aspects at 5.9 GHz. Moreover, this standard is extended for using spatial diversity at transmitter and receiver side. For this, Alamouti space-time coding is implemented for exploitation of transmit diversity in combination of maximum ratio combining at the receiver side. Thus, four USRP modules are used in a 2×2 communication system while placing two transmit and two receive antennas at different positions on the car.

In this paper, MIMO techniques for suppression of ISI and MAI in frequency-selective fading chann... more In this paper, MIMO techniques for suppression of ISI and MAI in frequency-selective fading channels are evaluated analytically and by means of link level computer simulation in a UTRA-TDD like system. Equalization of the spatio-temporal channel matrix is either performed at the transmitter via joint predistortion (JP), at the receiver via zero-forcing block linear equalization (ZF-BLE) combined with symbol cancellation (ZF-B-BLAST), or balanced at both sites of the channel via space-time vector coding (STVC). The computational complexity of all presented approaches is reduced by the introduction of blocked block-circulant system matrices

2019 20th International Radar Symposium (IRS), 2019

Driver assistance systems in cars are standard nowadays, using a wide range of sensors and approp... more Driver assistance systems in cars are standard nowadays, using a wide range of sensors and appropriate signal processing for sensor fusion. Radar systems play a major role within such systems, being combined with cameras and further sensors. This paper elaborates on transferring such systems to pedelecs or e-bikes in order to support mainly elderly people in challenging traffic situations. The concept as well as first results with a prototype are described, focusing on sensor fusion between radar and camera. Moreover, power consumption is an important issue for this pedelec application, so that power saving concepts are highlighted in this paper.

EURASIP Journal on Wireless Communications and Networking, 2021

This paper gives an overview of optimizing wireless power transfer systems using magnetic couplin... more This paper gives an overview of optimizing wireless power transfer systems using magnetic coupling. Optimization aims to maximize either the power transfer efficiency or the transferred power. The resulting load calculation and matching strategies are revisited. Moreover, the coupling system is described, starting with its equivalent circuit and scattering parameters. In addition to wireless power transfer, communication in RFID and NFC systems and its frequency characteristics and bandwidth issues are highlighted. The focus in this paper is on load modulation for data transfer between a tag and reader. For this purpose, subcarrier voltages are derived using time-domain as well as frequency-domain signal analysis.

10th International Conference on Telecommunications, 2003. ICT 2003.

It has been shown, that exploifing the radio channel in mo-bile communications systems in a multi... more It has been shown, that exploifing the radio channel in mo-bile communications systems in a multiple-input multiple-output (MIMO) manner highly increases system capaciiy. The access to such a MIMO channel usually involves spa-tially separated antennas of the same ...

European Transactions on Telecommunications, 2006

In multiuser multiple-input multiple-output (MIMO) systems the performance of joint detection and... more In multiuser multiple-input multiple-output (MIMO) systems the performance of joint detection and joint predistortion techniques highly depends on the quality of radio-frequency (RF) components. Therefore, the focus of this paper is on front-end imperfections. We demonstrate the influence of erroneous calibration (which is essential for downlink predistortion), phase noise and nonlinear amplifiers. For all issues we elaborate on the different disturbances that arise, analyse the impact on symbol estimation and evaluate system performance in terms of coded bit error ratio (BER). A general result for all examined front-end imperfections is that their influence increases with the number of spatially multiplexed data streams culminating in unacceptable performance degradation in fully loaded systems. Moreover, Wiener-based detection and predistortion reduces the degradation due to front-end imperfections in low SNR regimes compared to zero forcing. Copyright # 2006 AEIT.

Electronics Letters, 2002

The access to multiple-input multiple-output channels usually involves spatially separated antenn... more The access to multiple-input multiple-output channels usually involves spatially separated antennas of the same polarisation at the transmitter and the receiver side. The potential of dual-polarised antennas in mobile radio systems, which avoid undesired antenna spacings and promise increased system performance for certain environments, is considered.

EURASIP Journal on Advances in Signal Processing, 2006

The growing demand for high data rates for wireless communication systems leads to the developmen... more The growing demand for high data rates for wireless communication systems leads to the development of new technologies to increase the channel capacity thus increasing the data rate. MIMO (multiple-input multiple-output) systems are best qualified for these applications. In this paper, we present a MIMO test environment for high data rate transmissions in frequency-selective environments. An overview of the testbed is given, including the analyzed algorithms, the digital signal processing with a new highly parallel processor to perform the algorithms in real time, as well as the analog front-ends. A brief overview of the influence of polarization on the channel capacity is given as well.

European Transactions on Telecommunications, 2003

ABSTRACT In this paper multiuser detection in OFDM systems is examined. The separation of concurr... more ABSTRACT In this paper multiuser detection in OFDM systems is examined. The separation of concurrently transmitted signals is based on space division and code division multiple access (SD/CDMA). The achievable bit error ratio and the peak to average power ratio (PAPR) are evaluated for different spreading strategies. A novel time domain spreading technique for OFDM systems is proposed for which the PAPR is independent of the processing gain. The examined OFDM techniques are compared with single-carrier transmission using equalization in the frequency domain (SC/FDE), which shows strong similarities to OFDM systems.

Pimrc, 2004

ABSTRACT Instantaneous channel state information at a transmitting access point can be efficientl... more ABSTRACT Instantaneous channel state information at a transmitting access point can be efficiently used by joint predistortion techniques (JP). The required channel state information can be obtained at the access point from a preceding reception time slot in time division duplex (TDD) systems. During the succeeding transmission time slot, transmit filters predistort data signals using multiple transmit antennas and spreading sequences in order to compensate for the channel influence. The separation of simultaneously transmitted users' signals is based on combined space and code division multiple access (SD/CDMA). In this paper, linear predistortion techniques for single-carrier and orthogonal frequency division multiplexing (OFDM) transmission systems with frequency domain filtering are presented using either zero forcing or Wiener optimization. For OFDM transmission, different frequency and time domain spreading strategies are analyzed. In general, we focus on direct reuse of uplink filter coefficients for downlink transmission instead of just using uplink channel state information in order to avoid additional matrix inversions. The achievable uncoded and coded bit error ratio of the presented schemes is presented as well as peak-to-average power ratio (PAPR).