Browsing by Subject "RTK"
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Item Advanced techniques for centimeter-accurate GNSS positioning on low-cost mobile platforms(2015-12) Pesyna, Kenneth Mark Jr.; Humphreys, Todd Edwin; Heath, Robert W., Jr, 1973-; Vikalo, Haris; York, Johnathan; Sanghavi, SujayOver the past decade, GPS and other Global Navigation Satellite System (GNSS) chipsets have become smaller, cheaper, and more energy efficient, so much so that they now come standard in most smartphones and tablets. Under good multipath conditions, one can expect 2-to-3-meter-accurate positioning with these chipsets, under adverse multipath, accuracy degrades to 10 meters or worse. Outside the mainstream of consumer GNSS receivers, however, centimeter---even millimeter---accurate GNSS receivers are used routinely in geodesy, agriculture, and surveying. The key to their accuracy is a radically different approach to positioning in which the standard code-phase (or pseudorange) positioning technique is replaced by differential carrier-phase positioning. Adopting this high-precision carrier-phase-based technique for consumer-grade mobile devices is possible, but comes with significant challenges. This dissertation identifies and addresses the challenges to performing centimeter accurate carrier-phase differential GNSS (CDGNSS) positioning on low-cost mobile devices. To this end, this dissertation makes three primary contributions. First, this dissertation develops a carrier phase reconstruction technique to address the high power consumption of current CDGNSS algorithms. The reconstruction technique enables a continuous and unambiguous phase time history to be reconstructed from intermittent phase measurements, permitting aggressive duty cycling of the mobile device's internal GNSS chip, decreasing energy consumption. Second, this dissertation demonstrates that a centimeter-accurate positioning solution is possible based on GNSS data collected using a smartphone, a first in the open literature. It is identified that the primary impediment to performing CDGNSS on smartphones lies not in the commodity GNSS chipset within the phone, but instead in the antenna, whose chief failing is its poor multipath suppression, resulting in long initialization times. It is demonstrated that wavelength-scale random antenna motion can be used to decorrelate multipath errors and reduce the initialization period---the so-called time-to-ambiguity-resolution (TAR)---of smartphones employing CDGNSS to obtain centimeter-level positioning fix. Finally, this dissertation develops a framework that tightly fuses smartphone camera image measurements with GNSS carrier phase measurements to reduce CDGNSS initialization times beyond what is achievable using antenna motion alone. The framework augments the traditional bundle-adjustment- (BA-)-based structure from motion (SFM) algorithm with the carrier phase differential GNSS (CDGNSS) algorithm in a way that preserves the key features of both algorithms, namely the sparseness of the matrices in BA and the integer structure of the ambiguities in CDGNSS. The framework is shown to produce a faster, more robust, and more accurate positioning solution than achievable with existing techniques.Item Advanced techniques for safety-of-life carrier phase differential GNSS positioning with applications to triplex architectures(2018-01-24) Green, Gary Nathan; Humphreys, Todd Edwin; Andrews, Jeffrey; de Veciana, Gustavo; Vikalo, Haris; York, JohnathanSafety-of-life Carrier phase Differential Global Navigation Satellite System (CDGNSS) positioning systems must provide guarantees that their position estimates have errors that are smaller than specified levels, called alert limits (AL). These guarantees are specified as an allowable probability, called integrity risk (IR), that the error exceeds its AL. Typical values of IR are between 10⁻⁹ and 10⁻⁷, per hour of operation. CDGNSS positioning has been demonstrated to provide centimeter-accurate estimates of a vehicle's location when the so-called integer ambiguities are resolved; however, in safety-of-life applications, the probability of incorrectly resolving the integer ambiguities frequently exceeds the allowable IR. To address this limitation, existing algorithms bound the positioning error caused by incorrectly resolved ambiguities. If such bounds satisfy the AL, then the integer-resolved, or fixed, solution can be used. Unfortunately, the positioning error from incorrect fixing can exceed several meters, which fails to satisfy the most demanding ALs for autonomous vehicles. This dissertation offers three contributions to the science of CDGNSS positioning for safety-of-life applications. First, a novel algorithm is developed that validates the correctness of integer ambiguity estimates. This algorithm, called Generalized Integer Aperture Bootstrapping (GIAB), establishes a rigorous, fixed-missed-detection-rate test that provides a guarantee that the integer ambiguities have been fixed correctly. GIAB also allows for partial fixing, where a subset of the ambiguities are resolved. Partial fixing allows for graceful degradation of positioning when measurement quality is poor. GIAB is derived analytically and validated via Monte Carlo simulation. Its performance is compared with existing ambiguity validation techniques. Second, the probability density function of the positioning estimate resulting from GIAB is derived. This distribution leads to a provable bound on the IR that the estimate has errors exceeding the specified ALs. This bound allows GIAB to be used for safety-of-life application while satisfying ALs of less than a meter. Third, triplex CDGNSS architectures, in which the vehicle position is estimated using three separate navigation systems with mid-level voting (MLV) logic, are analyzed. Such architectures are commonly used since they are robust to single equipment failures, but the integrity benefit of their fault-free performance has not previously been evaluated. It is shown that integer-fixed CDGNSS solutions improve in accuracy performance, but gain no integrity benefit. However, when the integer constraint is not enforced, the so called CDGNSS float solution benefits greatly from MLV in both accuracy and integrity performance.Item Dense RTK: Mass-Market Positioning for Automated Vehicles(2016-09-15) Humphreys, Todd E.; Pesyna, Ken; Shepard, Daniel; Murrian, Matthew; Kerns, AndrewItem The role of JNK2 and JNK1 in breast cancer mediated invasion and metastasis(2010-08) Nasrazadani, Azadeh; Van Den Berg, CarlaReceptor tyrosine kinase (RTK) inhibitors are emerging as an effective therapeutic option for treatment of breast cancer patients overexpressing particular RTKs. However, more patients may benefit from an inhibitor targeting a common effector protein downstream several RTKs. The presented studies herein identify c-Jun N-Terminal Kinase 2 (JNK2), a kinase downstream multiple RTKs, as a novel target to effectively inhibit Phosphatidylinositol 3-kinase/AKT activation and metastasis. Knockdown of JNK2 in the highly metastatic 4T1.2 mammary cancer cells significantly decreased growth factor induced invasion in Boyden chambers, orthotopic tumor growth, and metastatic lesions in lungs and bone. Intra-cardiac introduction of cancer cells is utilized to specifically study the later steps in the metastatic cascade including travel of disseminated cancer cells to a secondary location. Thus, earlier steps such as the process of acquiring a malignant phenotype leading to escape from the primary tumor are bypassed. Survival was prolonged in mice receiving intra-cardiac injection of cells deficient of JNK2 either in the host or in the tumor cells, suggesting a potential role for JNK2 as a therapeutic target for advanced stage breast cancer patients. Using siRNA and inhibitors against Src and PI3K, we determined that JNK2 activity is dependent on Src and PI3K, positioning JNK2 downstream of two critical factors involved in tumor progression. Microarray analysis of JNK2 deficient tumors revealed that JNK2 positively regulates the adaptor protein Grb2 associated binding protein 2 (Gab2). Knockdown of Gab2 in 4T1.2 cells resulted in decreased tumor growth and a trend for decreased lung metastasis. In vitro, stimulation of 4T1.2 shJNK2 or 4T1.2 shGab2 cells with HGF, heregulin, or insulin resulted in impaired AKT activation, suggesting involvement of Gab2 and JNK2 in multiple RTK signaling pathways. Understanding of the intricate mechanisms involved in RTK signal transduction can contribute to drug design geared towards more effective targets, namely JNK2. The secondary goal of this research was to decipher the individual roles of JNK2 and JNK1 in metastatic breast cancer. Survival was significantly shortened in mice injected intra-cardiac with 4T1.2 shJNK1 cells. In congruence, serum Cathepsin K levels were increased and bone lesions observed were higher in mice injected with shJNK1 expressing tumor cells compared to mice injected with control cells. In sharp contrast, jnk1-/- mice displayed dramatically increased survival and fewer bone lesions upon intra-cardiac injections of 4T1.2 cells. Collectively, these data suggest cell and isoform specific roles for JNKs.