Browsing by Author "Li, Yang, 1982-"
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Item Classification of human movements using Micro Doppler features in foliage environments.(2017-07-25) Troy, Willis Scott. 1982-; Li, Yang, 1982-; Thompson, Michael Wayne.The focus of this work is measuring and classifying human motion in foliaged environments. A baseline study is performed using a vector network analyzer in open-space and foliaged environments for a variety of frequencies, activities, and formations. The results serve as a justification for a radar prototype’s parameters and a metric to gauge the prototype’s accuracy. The prototype is developed at 2.45 GHz to serve as a low cost and portable alternative to commercially available radars and to the vector network analyzer. Experimentation is repeated in open space and foliaged environments for a more thorough activity list and more participants. Data is post-processed to extract Doppler features and for classification. Results indicate that a low cost radar is capable of distinguishing human motion via human backscatter despite the attenuation, multipath, and blockage due to foliage.Item Design and implementation of a synthetic aperture radar (SAR) imaging system using an ultra-wideband (UWB) radar sensor.(2016-04-14) Ernzen, Brian Thomas.; Li, Yang, 1982-This thesis documents the design and implementation of a radar imaging system. A rail system was constructed to control the location of an off-the-shelf ultra-wideband (UWB) radar along a linear path. Range imaging, cross-range imaging, and synthetic aperture radar (SAR) imaging algorithms were implemented in Matlab based on the data from the radar. Results are presented for a variety of target scenes. The radar imaging system can be used for future research of radar imaging algorithms as well as for classroom demonstration for a radar course at Baylor University.Item Investigation of wave propagation and antenna radiation in forested environments(2011-05) Li, Yang, 1982-; Ling, Hao; Pearce, John; Yilmaz, Ali; Alu, Andrea; Torres-Verdin, Carlos; Shvets, GennadyRecently, there is emerging interests in deploying wireless sensor networks in forests for applications such as forest fire detection, environmental monitoring and remote surveillance. One challenge in the design of such networks is to ensure reliable communication between sensors located near the ground and over short distances. However, the propagation mechanisms in this type of scenario are complex and not well understood. Furthermore, the design of antennas that can exploit the resulting propagation mechanisms for optimal power transfer remains an open question. The objective of this dissertation is to understand wave propagation and antenna radiation in forested environments in the HF/VHF frequency range. To achieve this objective, several forest scaled models are introduced. The first scaled forest model is a periodic metal cut-wire array. The transmission data inside the cut-wire array are simulated and measured. The propagation mechanisms inside the array are extracted. Several interesting propagation phenomena associated with surface waves and leaky waves are observed and explained. Next, a dielectric rod array consisting of water-filled straws is investigated as a more realistic forest model. Water is chosen since its dielectric constant in the microwave range is close to that of tree trunks in the HF/VHF frequencies. The propagation mechanisms in the water rod array are investigated through scaled model measurements in the laboratory, numerical simulations and an effective medium theory. Randomization effects due to rod spacing and rod height on the propagation mechanisms are also studied. Finally, the transmission data in a real forest are collected in the HF/VHF frequency range to corroborate the findings from the models. The measurement site is located at Bastrop, Texas. For comparison, the transmission data are also measured in an open field. The transmission data are processed and the resulting propagation mechanisms are extracted and compared with the model predictions. As an extension of the propagation study, the potential to achieve directive antenna radiations in a forest is explored. A simple metal cut-wire array environment is considered for ease in modeling. For the case when both the transmit antenna and the receive antenna are embedded inside the array, two design ideas are presented. The first design tries to couple the antenna radiation into the dominant propagation mechanism through phase matching and the second design uses a closely spaced Yagi array to decouple the antenna from its surrounding medium. For the case when the transmit antenna is embedded inside the array and the receive antenna is located outside the array, the leaky wave mechanism is explored to achieve directive radiation. These designs are verified through theoretical predictions, numerical simulations and prototype measurements.Item Wireless propagation channel modeling and antenna design for on-body applications.(2017-01-26) Xue, Dong, 1990- 1990-; Li, Yang, 1982-The Wireless Body Area Networks (WBAN) is promising in a variety of applications such as remote health monitoring and assisted living. A typical WBAN consists of wearable body sensor units (BSU) and a body control unit (BCU). The BCU can receive physiological signal data from the BSUs and relay them to a remote access point regarding impending emergencies. One important issue in implementing a WBAN is to ensure reliable and efficient wireless communication links on a human body. This is particularly challenging since the human body represents a difficult propagation environment where body tissues introduce high loss to electromagnetic waves propagating along, around and through the body. The antenna radiation performance may also be affected due to the presence of the human body. Extensive research involving on-body propagations have been conducted over the past decade through experiments, simulations and theories. However, most studies focus only on signal strength attenuation loss of on-body waves at a single frequency on a non-moving human body. Wearable antennas have been designed for on-body applications, but most designs concentrate on optimizing conventional antenna performance on human body. It remains to be studied how to design compact antennas which can couple on-body wave mechanisms efficiently over a broad range of frequencies. In this dissertation electromagnetic wave propagations over a broad frequency band (300 MHz- 3GHz) and within short ranges (<50 cm) are investigated for on-body wireless channel communications. Experimental, simulation and theoretical methods are used to examine two scenarios: along and around the body surface. The study is conducted on both non-moving and moving human bodies. Both signal strength and phase delay are studied. Dominant propagation mechanisms are extracted and analyzed. An electrically-small wearable antenna as well as directive array are designed for on-body applications, and human body effects on antenna performance are discussed.