Generalised ambiguity function for MIMO radar systems

In this work a generalised signal model is presented to accommodate both narrowband and wideband signals in a multi-input multi-output (MIMO) sensor system scenarios. The derived model is then used to define a MIMO ambiguity function (AF) based on the Kullback-Leibler divergence (KLD). Moreover, the proposed formulation is parametrised using the signal and channel correlation matrices to account for different waveform and sensor placement designs, thereby allowing a flexible modelling approach. A comparison between the proposed definition and the more conventional approach of summing the squared matched filter outputs is presented for different sensors and waveforms configurations

Some contributions on MIMO radar

Motivated by recent advances in Multiple Input Multiple Output (MIMO) wireless communications, this dissertation aims at exploring the potential of MIMO approaches in the radar context. In communications, MIMO systems combat the fading effects of the multi-path channel with spatial diversity. Further, the scattering environment can be used by such systems to achieve spatial multiplexing. In radar, a complex target consisting of several scatterers takes the place of the multi-path channel of the communication problem. A target\u27s radar cross section (RCS), which determines the amount of returned power, greatly varies with the considered aspect. Those variations significantly impair the detection and estimation performance of conventional radar employing closely spaced arrays on transmit and receive sides. In contrast, by widely separating the transmit and receive elements, MIMO radar systems observe a target simultaneously from different aspects resulting in spatial diversity. This diversity overcomes the fluctuations in received power. Similar to the multiplexing gain in communications, the simultaneous observation of a target from several perspectives enables resolving its features with an accuracy beyond the one supported by the bandwidth. The dissertation studies the MIMO concept in radar in the following manner. First, angle of arrival estimation is explored for a system applying transmit diversity on the transmit side. Due to the target\u27s RCS fluctuations, the notion of ergodic and outage Cramer Rao bounds is introduced. Both bounds are compared with simulation results revealing the diversity potentials of MIMO radar. Afterwards, the detection of targets in white Gaussian noise is discussed including geometric considerations due to the wide separation between the system elements. The detection performance of MIMO radar is then compared to the one achieved by conventional phased array radar systems. The discussion is extended to include returns from homogeneous clutter. A Doppler processing based moving target detector for MIMO radar is developed in this context. Based on this detector, the moving target detection capabilities of MIMO radar are evaluated and compared to the ones of phased array and multi-static radar systems. It is shown, that MIMO radar is capable of reliably detecting targets moving in an arbitrary direction. The advantage of using several transmitters is illustrated and the constant false alarm rate (CFAR) property of adaptive MIMO moving target detectors is demonstrated. Finally, the high resolution capabilities of MIMO radar are explored. As noted above, the several individual scatterers constituting a target result in its fluctuating RCS. The high resolution mode is aimed at resolving those scatterers. With Cramer Rao bounds and simulation results, it is explored how observing a single isotropic scatterer from several aspects enhances the accuracy of estimating the location of this scatterer. In this context a new, two-dimensional ambiguity function is introduced. This ambiguity function is used to illustrate that several scatterers can be resolved within a conventional resolution cell defined by the bandwidth. The effect of different system parameters on this ambiguity function is discussed

Direction of arrival estimation using a multiple-input-multiple-output radar with applications to automobiles

The thesis at hand investigates the direction of arrival (DOA) estimation using a Multiple-Input-Multiple-Output (MIMO) radar system. The application of MIMO radars in automobiles is studied. A MIMO radar consists of several transmitting (Tx) and receiving (Rx) antennas. We focus on a time division multiplexed (TDM) MIMO radar with colocated Tx and Rx antennas. The motivation is the use of a radar as a security system in automotive applications, e.g. to identify a dangerous situation and react automatically. Security systems must be very reliable. Hence, besides a good estimation of the distance and velocity, a high performance in DOA estimation is necessary. This is a demanding task, since only a small number of antennas is used and the radar is limited to a small geometrical size. Compared to the corresponding Single-Input-Multiple-Output (SIMO) radar, a MIMO radar with colocated antennas can achieve a higher accuracy in DOA estimation due to its larger virtual aperture. Therefore it is a promising technique for the use in automobiles. The obtained results of this thesis enable us to find optimal TDM schemes which yield a very high DOA accuracy for targets which are stationary as well as for targets which are moving relative to the radar system. The results are not confined to MIMO radars in automobiles, but can be used in other applications as well.In der vorliegenden Arbeit wird die Winkelschätzung (auch Einfallsrichtung genannt, engl. Direction of Arrival (DOA)) mit Hilfe eines Multiple-Input-Multiple-Output (MIMO) Radars untersucht. Darüber hinaus wird die Verwendung eines MIMO Radars in automobilien Anwendungen betrachtet. Ein MIMO Radar besteht aus mehreren Sende- (Tx) und Empfangsantennen (Rx). Wir betrachten insbesondere MIMO Radare die im Zeitmultiplexverfahren (engl. time division multiplex (TDM)) betrieben werden und geometrisch nahe beieinander liegende Antennen (engl. colocated) besitzen. Die Motivation dieser Untersuchungen ist die Verwendung von Radarsystemen als Sicherheitssysteme in Fahrzeugen, z.B. um eine gefährliche Situation zu detektieren und darauf automatisch zu reagieren. Sicherheitssysteme müssen sehr zuverlässig sein. Daher ist neben einer genauen Abstands- und Geschwindigkeitsschätzung auch eine hohe Performance in der Winkelschätzung nötig. Dies ist eine anspruchsvolle Aufgabe, da nur eine geringe Anzahl an Antennen zur Verfügung steht und das Radarsystem nur eine kleine geometrische Größe aufweisen darf. Im Vergleich zu einem entsprechenden Single-Input-Multiple-Output (SIMO) Radar kann ein colocated MIMO Radar aufgrund seiner größeren virtuellen Apertur eine höhere Winkelgenauigkeit erreichen. Daher ist es eine vielversprechende Technik für die Anwendung in Fahrzeugen. Die Ergebnisse dieser Arbeit ermöglichen uns optimale Zeitmultiplexverfahren zu finden, welche sowohl für stationäre Objekte als auch für Objekte die sich relativ zum Radar bewegen, eine hohe Winkelgenauigkeit erreichen. Die Ergebnisse beschränken sich nicht nur auf Radare in Fahrzeugen, sondern können auch in anderen Anwendungen verwendet werden