Diversity Gain For MIMO-OTH Radar Under Complicated Environment

Multiple-input multiple-output(MIMO) system exploits spatial diversity gain by employing dispersed multiple transmit and receive antennas, which can be used to confront channel fading. Due to the special working mode, skywave over-the-horizon( OTH) radar can provide air and surface situational awareness over vast regions of land and sea. This dissertation considers the implementation of the MIMO radar concepts to the OTH radar, called MIMO-OTH radar, and studies the diversity gain for MIMO-OTH radar target detection under complicated ionosphere environment. The impact of the radar system parameters and the multipath propagation on the detection performance is also analyzed.According to the working mode of the OTH radar and the propagation features of the OTH radar signals over the ionosphere, with the structural features of MIMO radar, the received signal model of the MIMO-OTH radar is developed, which can reflect the propagation characteristics of radar signals under complicated ionosphere environment and the influence of the multipath propagation. Considering the additive complex white Gaussian noise and clutter, the Gaussian detector under Neyman-Pearson(NP) criterion is investigated, based on the received signal model of the MIMO-OTH radar.This thesis studies the miss probability of the MIMO-OTH radar under NP criterion and derives the diversity gain for MIMO-OTH radar target detection, which is proposed to be an evaluation index for the detection performance. Assume that the transmitted signals are reflected once off the target and twice by the ionosphere before arriving at the receive end, and any of these three reflections can be either categorized as being complex Gaussian or deterministic.Further, two different complicated scenarios(complex double Gaussian channel reflection and complex triple Gaussian channel reflection) are considered to derive the diversity gain for the MIMO-OTH radar target detection. Consider a MIMO-OTH radar system with M transmit and N receive antennas, the signal from the m th transmit antenna reaches the target after being reflected by the ionosphere via mQ ray paths. Each of these multipath signals bounce off the target and reach the n th receiver after being reflected by the ionosphere again via mnH ray paths. The largest possible diversity gain for the MIMO-OTH radar system target detection is upper bounded by1 1min{, }N Mn m mn md NM H Q= =￡ ? ?.It is shown that the diversity gain is decided by the number of antennas and the number of multipaths. Under certain conditions, increasing the number of antennas or the number of multipaths can increase the diversity gain, which is beneficial to improve radar detection performance. Also, it is proved that the skywave MIMO-OTH radar has better detection performance than the traditional OTH radar.In the end, the detection probabilities of MIMO-OTH radar target detection for different cases are shown by numerical results. Meanwhile, the influence of different radar parameters,different channel reflection and different multipath propagation on the diversity gain is presented. The simulation results also validate the correctness of the theory.