Research On IR-UWB Signal Through-the-wall Propagation Characteristics Modeling And Detection Techniques

The Impulse Radio Ultra Wideband (IR-UWB) signal provides the advantages of fine time resolution, good penetration capability, and excellent anti-jamming as well as anti-multipath characteristics. It is an excellent alternative for target detection and data communications in complex environments. Based on the needs of through-the-wall detection and communication applications, this dissertation investigates the modeling of IR-UWB through-the-wall propagation and target detection, and hence would offer strong theoretical supports for the IR-UWB and the relevant system designs.The following topics on IR-UWB signal through-the-wall propagation characteristics modeling are studied:Ⅰ. Taking advantage of the IR-UWB signal properties, an efficient time domain ray tracing (TD-Ray) technique for fast accurate computation of large-scale structures (e.g. walls) is developed. Combining the TD-Ray and finite-difference time-domain (FDTD), this dissertation also proposes a hybrid method for modeling mixed-scale structures, which obtains a good balance among the computational complexity, accuracy and efficiency.Ⅱ. The ultra-wideband frequency-domain measurement and signal processing are performed to acquire the electromagnetic properties and key electrical parameters of typical building materials. Moreover, the through-the-wall path loss is also extracted. And on that basis, two through-the-wall propagation numerical models are established by the TD-Ray and the FDTD, respectively. Furthermore, their correction accuracy and computation efficiency for wall refraction calibration are analyzed and compared in detail.Ⅲ. By the through-the-wall time-domain measurement, the statistical impulse response models for through-the-wall channel are presented. The Bit Error Rates (BER) calculated according to the proposed model and802.15.SG3a model are compared with experimental data. The results demonstrate that our model agrees better with the physical truth.Ⅳ. The FDTD technique is utilized to compute the electromagnetic scattering from a human body model referring to some relevant papers. And the Radar Cross-Section (RCS) of human is analyzed for both the free space and behind the wall by FDTD and the hybrid method respectively. The comparisons with the actual measurements show that the RCS simulation results of our model are satisfactory.Ⅴ. From the above-mentioned numerical results, the parameters of multiple scattering centers for human body are extracted. On the basis of the transient scattering mechanism, an IR-UWB human-target multi-scatter centers model is established. Based on the matching degree between the re-constructed echo and original echo, a valuable conclusion can be reached that the human target echo can be modeled precisely with only few strong scatter centers. Therefore, the complexity of modeling human-target echoes can be greatly reduced.The following topics about IR-UWB signal detection are studied:Ⅰ. According to the non-stationary behavior of the wall clutter, the wanted target echoes are extracted and enhanced using the empirical mode decomposition (EMD) method. Furthermore, a wall clutter suppression method is proposed based on the independent component analysis (ICA). Both simulation and experimental results show that the proposed method improves the detection ability of static human target.Ⅱ. In order to analyze the effect of the finite-level quantization on IR-UWB detection, the detection capabilities of two types of generalized likelihood ratio tests (GLRT) are systematically analyzed. The analysis provides a theoretical basis in applying the high-speed low-bit resolution quantization technique in IR-UWB radar system and reduces the system complexity.