Cemin Zhang

Investigation of High-Accuracy Indoor 3-D Positioning Using UWB Technology

There are many challenges in building an ultra-wideband (UWB) indoor local positioning system for high-accuracy applications. These challenges include reduced accuracy due to multipath interference, sampling rate limitations, tag synchronization, and antenna phase-center variation. Each of these factors must be addressed to achieve millimeter or sub-millimeter accuracy. The developed system architecture is presented where a 300-ps Gaussian pulse modulates an 8-GHz carrier signal and is transmitted through an omni-directional UWB antenna. Receiver-side peak detection, a low-cost subsequential-sampling mixer utilizing a direct digital synthesizer, high fidelity 10-MHz crystals, and Vivaldi phase-center calibration are utilized to mitigate these challenging problems. Synchronized and unsynchronized experimental results validated with a sub-millimeter accurate optical tracking system are presented with a detailed discussion of various system errors.

Real-Time Noncoherent UWB Positioning Radar With Millimeter Range Accuracy: Theory and Experiment

In this paper, we propose a novel architecture for ultra-wideband (UWB) positioning systems, which combines the architectures of carrier-based UWB systems and traditional energy detection-based UWB systems. By implementing the novel architecture, we have successfully developed a standalone noncoherent system for positioning both static and dynamic targets in an indoor environment with approximately 2 and 5 mm of 3-D accuracy, respectively. The results are considered a great milestone in developing such technology. 1-D and 3-D experiments have been carried out and validated using an optical reference system, which provides better than 0.3-mm 3-D accuracy. This type of indoor high-accuracy wireless localization system has many unique applications including robot control, surgical navigation, sensitive material monitoring, and asset tracking.

Development of an ultra-wideband elliptical disc planar monopole antenna with improved omni-directional performance using a modified ground

A planar monopole antenna has many attractive features such as a simple structure, exhibition of ultra-wideband characteristics, and a near omni-directional radiation pattern (J. Liang et al., 2004 - Z.N. Low et al., 2005). However, the ability to sustain an omni-directional pattern over ultra-wide band has not been adequately addressed in the literature up until now. The use of a modified ground plane can aid in providing such a feature

UWB antipodal vivaldi antennas with protruded dielectric rods for higher gain, symmetric patterns and minimal phase center variations

In this paper, the authors proposed a technique to improve the gain, narrow the H-plane beamwidth, and minimize the phase center variations with frequency by utilizing Vivaldi antenna with a protruded dielectric rod. A sample antenna was fabricated and measured, and preliminary measured results are very promising, and in good agreement with the simulation results.

Development of an ultra wideband Vivaldi antenna array

We have developed a 1/spl times/16 sub-array antenna structure for ultra wideband applications such as see-through-walls imaging radar. The utilized single element is a flared-antipodal design and has demonstrated almost constant gain and beamwidth over a broad bandwidth of 5 GHz. A one to sixteen wideband Wilkinson power divider was designed, fabricated and utilized to feed the sub-array. Measured results are in excellent agreement with predicted ones, as a constant 13 dB gain and a 4/spl deg/ 3-dB beamwidth was obtained within the operational band of 8-12 GHz.

High accuracy UWB localization in dense indoor environments

UWB communication and localization systems have many inherent advantages for robust performance in dense, indoor multipath environments. Although UWB systems have been designed for numerous industrial applications, there exists the need for short range (i.e. 5-10 m) UWB localization systems with accuracy an order of magnitude higher (i.e. mm-range) than existing commercial systems. Many system level challenges must be overcome to achieve accuracy on the order of tens of picoseconds, such as high Rx sampling rate, Tx-Rx LO phase noise, Tx-Rx pulse repetition frequency clock phase noise, Rx-induced jitter from sequential sampling, Rx-side calibration of phase offsets in I and Q channels, multipath interference due to dense indoor environments, etc. A detailed system level simulation is setup in order to quantify the contribution of these effects on overall system accuracy. Simulation results are used to highlight these system level errors and show how they can be mitigated.

Performance Enhancement of a Sub-Sampling Circuit for Ultra-Wideband Signal Processing

An ultra-wideband (UWB) sampling mixer has been developed based on utilizing the combined advantages of two known circuit topologies: a wideband balun and a balanced-feed mixer. The developed sampler is integrated with a step-recovery diode strobe-step generator to sub-sample UWB signals. The fabricated sub-sampler demonstrated a 3.5-dB radio frequency to intermediate frequency (RF-IF) conversion loss up to 1 GHz (without the IF amplification), and a wide 3 dB bandwidth that exceeded 3.5-GHz. It has a reduced spurious level of better than -38 dBc, a lower sensitivity to the Schottky diode-placement, an excellent input match, and good isolation.

Real-time noncoherent UWB positioning radar with millimeter range accuracy in a 3D indoor environment

In this work, we have successfully developed a stand-alone system for positioning both static and dynamic targets in an indoor environment with approximately 2 mm and 6 mm of 3-D accuracy, respectively. The results are considered a great milestone in developing such technology. 1D and 3D experiments have been carried out and validated using an optical reference system which provides better than 0.3 mm 3D accuracy. Such a high accuracy wireless localization system should have a great impact on many applications that require such high positioning precision.

A System-Level Simulation Framework for UWB Localization

In this paper we present a comprehensive simulation framework that can accurately simulate our indoor UWB positioning system including the analog front-ends, digital back-ends, and channel effects. Experimental results from our UWB positioning system are compared to simulated results to validate the accuracy of the simulation framework. Simulated results illustrate the design decisions made in optimizing overall system performance. Multiple peak detection algorithms are presented, and the robustness of our leading-edge detection algorithm is shown even in dense multipath environments. Geometric effects are examined by simulating various base station configurations. This comprehensive simulation framework provides an in-depth analysis of our UWB positioning system and also provides a general framework for rapid prototyping and design of complex wireless systems.

Planar antipodal Vivaldi antenna array configuration for low cross-polarization and reduced mutual coupling performance

Investigations of various antipodal Vivaldi antenna array configurations have been carried out. Based on this study, it has been demonstrated that planar arrangement of the Vivaldi elements is preferred over stacked ones and are easier to fabricate as well. Additionally, planar Vivaldi array with mirrored elements placed alternately in E-plane has demonstrated improved cross-polarization as compared to conventional antipodal Vivaldi array configurations.