Richard Klukas

Using WLAN Infrastructure for Angle-of-Arrival Indoor User Location

This paper investigates the potential for future multiple antenna wireless local area network technologies such as 802.11n to perform indoor network-based positioning using angle of arrival (AOA) estimation. A multiple-input multiple-output (MIMO) channel measurement system is used to determine the statistical accuracy of the indoor AOA estimation when performed at an 802.11n wireless access point (AP). Two different channel parameter estimation algorithms are used to perform AOA estimation; a simple maximum-likelihood (ML) scheme and the space-alternating generalized expectation-maximization (SAGE) technique. Results indicate that general channel parameter estimation algorithms, such as SAGE, are ill suited to estimate AOA for positioning purposes. However, results show that with the use of a specialized channel parameter estimation algorithm, such as the simple ML algorithm, quality AOA estimates for positioning might be achieved with low computational complexity. A positioning simulation that incorporates the AOA estimates from the simple ML algorithm achieves a positioning accuracy of 1.7 m with the help of an extended Kalman filter.

A Nonline-of-Sight Error-Mitigation Method for TOA Measurements

In wireless location, nonline-of-sight (NLOS) errors are a major error source. To improve positional performance, these errors should be identified and mitigated before measurements are used in position computations. A novel NLOS mitigation algorithm is proposed in this paper. Employing system redundancy, the algorithm derives from the distribution function of hyperbolic intersections, which is an intermediate mobile location. Cost functions based on the intermediate position are then created for each time-of-arrival measurement. NLOS errors are detected and mitigated via hypothesis tests performed on the cost functions. Simulation tests are presented in this paper, and the results verify the effectiveness of this NLOS-error-mitigation method. This paper also demonstrates that algorithm performance depends closely on receiver noise. Reducing receiver noise or providing the intermediate mobile location via external aiding can improve performance

Wireless Indoor Optical Positioning With a Differential Photosensor

An indoor optical positioning technique using a differential photosensor device is presented. The method is based on angle of arrival information estimated by the differential photosensor in an indoor environment with fixed optical beacons. A photocurrent is generated by each of the three photodiodes in the photosensor by incident light from the optical beacons. The amplitudes of these photocurrents are a function of the incident angle of the light. Previously derived equations that express photocurrent amplitudes as a function of the azimuthal arrival angle, φ, and the polar arrival angle, θ, are modeled with second- and third-order polynomials, respectively, to determine the φ and θ angles from measured photocurrents. Testing with optical beacons in various positions with respect to a fixed photosensor resulted in a root mean squared error for all estimated angles φ and θ of 2.8°. A positioning accuracy of better than 4 cm is achieved.

Tightly-coupled GPS/UWB Integration

Ultra-wideband (UWB) ranging radios, an emerging technology that offers precise, short distance range measurements are investigated as a method to augment carrier-phase GPS positioning. A commercially available UWB ranging system is used in a tightly-coupled GPS and UWB real-time kinematic (RTK) system. The performance of the tightly-coupled system is evaluated in static and kinematic testing. This work demonstrates that UWB errors can be successfully estimated in a real-time filter. The results of static testing show that the integrated solution provides better accuracy, better ability to resolve integer ambiguities and enhanced fixed ambiguity solution availability compared with GPS alone. In kinematic testing in a degraded GPS environment, sub-decimetre accuracy was maintained.

Ultra-wideband ranging precision and accuracy

This paper provides an overview of ultra-wideband (UWB) in the context of ranging applications and assesses the precision and accuracy of UWB ranging from both a theoretical perspective and a practical perspective using real data. The paper begins with a brief history of UWB technology and the most current definition of what constitutes an UWB signal. The potential precision of UWB ranging is assessed using Cramer?Rao lower bound analysis. UWB ranging methods are described and potential error sources are discussed. Two types of commercially available UWB ranging radios are introduced which are used in testing. Actual ranging accuracy is assessed from line-of-sight testing under benign signal conditions by comparison to high-accuracy electronic distance measurements and to ranges derived from GPS real-time kinematic positioning. Range measurements obtained in outdoor testing with line-of-sight obstructions and strong reflection sources are compared to ranges derived from classically surveyed positions. The paper concludes with a discussion of the potential applications for UWB ranging.

Angle-of-arrival reception for optical wireless location technology

An optical wireless location (OWL) system is introduced for indoor positioning. The OWL system makes use of a mobile photoreceiver that facilitates triangulation by measuring angle-of-arrival (AOA) bearings from LEDs in an optical beacon grid. The photoreceiver has three photodiodes (PDs), arranged in a corner-cube, to facilitate differential photocurrent sensing of the incident light AOA, by way of azimuthal ϕ and polar θ angles. The AOA error for indoor positioning is characterized empirically. Optical AOA positioning is shown to have a fundamental advantage over known optical received signal strength (RSS) positioning, as AOA estimation is insensitive to power and alignment imbalances of the optical beacon grid. The OWL system is built, and a performance comparison is carried out between optical AOA and RSS positioning. It is shown that optical AOA positioning can achieve a mean 3-D positioning error of only 5 cm. Experimental design and future prospects of optical AOA positioning are discussed.

Microlenses with tuned focal characteristics for optical wireless imaging

Microlenses are fabricated and investigated for integrated imaging applications. The microlenses are fabricated by an in situ polymer electro-dispensing technique that enables user-controlled microlens sizes and shapes, by direct-dispensing and voltage-tuning with a metal micro-needle tip in a filler solution. Theoretical and experimental analyses are carried out for three limiting-cases of electro-dispensed microlenses: an acute-angle microlens with a 30° contact angle, a right-angle microlens with a 90° contact angle, and an obtuse-angle microlens with a 120° contact angle. It is found that the right-angle microlens, with a 500 μm diameter, yields an especially short focal length (700 μm) and exceedingly large numerical aperture (0.533). These characteristics can meet the needs of emerging applications, such as optical wireless devices, which demand compact device integration and broad field-of-view imaging. The microlenses are tested in optical wireless imaging receivers, for signal-to-noise ratio perf...

Controlled GPS Signal Simulation for Indoors

For certain applications such as E911/E999/E112, GPS chipset receiver manufacturers will possibly have to test their products to ensure these fulfill mandated performance specifications for a variety of outdoor and indoor conditions. As opposed to testing in the field, laboratory testing is totally repeatable and controllable, and may be less costly. Hardware GPS signal simulators are now able to simulate signals under a variety of attenuation and multipath conditions. In indoor environments, GPS signals suffer not only from severe attenuation and multipath but from complex variations thereof. A method to simulate indoor GPS signals such that the stochastic characteristics of the simulated signals match those of actual GPS signals received in situ by a high sensitivity GPS receiver in various indoor environments is presented. Probability density functions and correlation coefficients are used to demonstrate the similarity between field and simulated data in terms of signal power fading and estimated pseudorange error. The results clearly demonstrate the feasibility of the approach.

Indoor positioning through integration of optical angles of arrival with an inertial measurement unit

A novel indoor positioning solution (IPS) is proposed in this paper. An inertial navigation system (INS) is integrated with optical angles of arrival (OAOA) measurements to yield a smoother, more accurate, and robust positioning solution for indoor environments. An extended Kalman filter (EKF) is used to integrate the INS and OAOA measurement. In this paper, both loosely coupled and tightly coupled integration strategies are explored for INS and OAOA integration. The tightly coupled strategy results in an average error of 1.67 cm while the loosely coupled strategy has a larger average error of 2.34 cm for the same experimental environment. However, the performance improvement of the tightly coupled system comes with an increased computational cost.

Reliable jump detection for snow sports with low-cost MEMS inertial sensors

Body-mounted devices, incorporating low-cost micro-electromechanical systems (MEMS) Inertial Measurement Units (IMUs), for real-time sports performance feedback are commercially available. In sports such as skiing, snowboarding, and mountain biking, aerial jumps can be detected with these devices and performance variables including air time and jump drop can be calculated real-time. However, the performance of currently used real-time athletic jump detection algorithms using MEMS IMUs is unsatisfactory in terms of accuracy, power efficiency, and reliability. In this paper, a novel algorithm for jump detection with a head-mounted MEMS IMU is proposed. Two novel methods used in this algorithm, namely Windowed Mean Canceled Multiplication and Preceding and Following Acceleration Difference, are introduced. Field experiments are conducted and the results of the proposed algorithm are compared with those of algorithms used in two state-of-the-art sport performance measurement devices. Results demonstrate that the proposed jump detection algorithm comprehensively outperforms these commercial algorithms.