Direction of Arrival Estimation Using a Multiple-Input-Multiple-Output Radar with Applications to Automobiles
نویسنده
چکیده
The thesis at hand investigates the direction of arrival (DOA) estimation using a Multiple-InputMultiple-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 Chapter 2 we introduce the basics of radar systems, which are important for this thesis. First we present three different kinds of radars, the pulse Doppler radar, the frequency modulated continuous wave (FMCW) radar, and the chirp sequence radar. After that, the performance measures of a radar system, which are used in the following chapters, are introduced. For that purpose, the concept of parameter estimators are presented. Thereafter, the accuracy is defined and a definition for the resolution is given. Chapter 3 gives an overview on the two types of MIMO radars: The MIMO radar with widely separated antennas and the colocated MIMO radar. A survey on the research already done on MIMO radars is presented. Thereafter, the different multiplexing techniques are discussed, which can be used in a MIMO radar to separate the signals of the different Tx antennas. The last part of Chapter 3 focuses on the application of MIMO radars in automobiles. It shows why TDM MIMO radars are suitable for the use in automotive applications. In Chapter 4 we study the DOA estimation for stationary targets, i. e. the targets are not moving relative to the radar. We investigate SIMO and MIMO radars and compute the deterministic CramerRao Bound (CRB) of the DOA for both types of systems. With these results we can determine the maximal achievable DOA accuracy. We compare both CRBs and show under which conditions
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