The article is intended for specialists in the field of radar, radio engineering and telecommunications. It considers the problem of forming virtual receiving channels in a car MIMO radar to increase the antenna aperture in the horizontal plane. The case is investigated when two cars fall into the main beam of the radar antenna pattern, and therefore, the application of super-resolution methods in azimuth is required. In modern vehicles, this option is required for vehicle collision avoidance and driver assistance systems. The use of MIMO technology makes it possible to form a larger antenna array (AR) for reception, the so-called virtual AR. This becomes possible due to a special choice of the topologies of the location of the transmitting and receiving channels, as well as due to the multiplication of the probing signals in each transmitting channel by an individual code. As a result, the resolving power of the AR increases in the direction finding of the target. A radar with “short” sounding chirp pulses is considered, in which the range is measured by the frequency method. The parameters of the signal in the radar are chosen so that the contribution of the terms associated with the speed of the target on the pulse duration to the beat frequency on the receiving side is negligible. Analytical expressions are obtained for the received signals under conditions of the Doppler frequency shift and “short” probing pulses. A method for generating signals in virtual receiving channels using an encoder only on the transmitting side and without a decoder on the receiving side is proposed. The use of various codes is investigated and their effectiveness is compared. For direction finding of targets, the method of the minimum polynomial of the correlation matrix of the received signals is applied. The method involves assessing the degree of the minimum polynomial of the correlation matrix of the input process in the AR based on a statistically valid root-mean-square criterion. This method allows adaptive estimation of the number of signal sources and has a super-resolution function. In contrast to the known works, the main attention is paid to the case of a short sample of the input process, when the number of samples is less than the dimension of the virtual AR. In this case, the sample correlation matrix is degenerate. The results of numerical modeling are given for the accuracy of azimuth measurement and the probability of correct resolution of two targets. A natural experiment was carried out. The presented results demonstrate the efficiency of the proposed concept, high accuracy of azimuth measurements, and the possibility of super resolution of two targets in the case of a short sample.
DIRECTION FINDING FOR BISTATIC MIMO RADAR USING EM MAXIMUM LIKELIHOOD ALGORITHM
