Kenneth M. Pesyna

Tightly-Coupled Opportunistic Navigation for Deep Urban and Indoor Positioning

A strategy is presented for exploiting the frequency stability, transmit location, and timing information of ambient radio-frequency “signals of opportunity” for the purpose of navigating in deep urban and indoor environments. The strategy, referred to as tightly-coupled opportunistic navigation (TCON), involves a receiver continually searching for signals from which to extract navigation and timing information. The receiver begins by characterizing these signals, whether downloading characterizations from a collaborative online database or performing characterizations on-the-fly. Signal observables are subsequently combined within a central estimator to produce an optimal estimate of position and time. A simple demonstration of the TCON strategy focused on timing shows that a TCONenabled receiver can characterize and use CDMA cellular signals to correct its local clock variations, allowing it to coherently integrate GNSS signals beyond 100 seconds.

Centimeter Positioning with a Smartphone-Quality GNSS Antenna

This paper demonstrates for the first time that centimeteraccurate positioning is possible based on data sampled from a smartphone-quality Global Navigation Satellite System (GNSS) antenna. Centimeter-accurate smartphone positioning will enable a host of new applications such as globally-registered fiduciary-marker-free augmented reality and location-based contextual advertising, both of which have been hampered by the several-meterlevel errors in traditional GNSS positioning. An empirical analysis of data collected from a smartphone-grade GNSS antenna reveals the antenna to be the primary impediment to fast and reliable resolution of the integer ambiguities which arise when solving for a centimeter-accurate carrierphase differential position. The antenna’s poor multipath suppression and irregular gain pattern result in large timecorrelated phase errors which significantly increase the time to integer ambiguity resolution as compared to even a low-quality stand-alone patch antenna. The time to integer resolution—and to a centimeter-accurate fix—is significantly reduced when more GNSS signals are tracked or when the smartphone experiences gentle wavelength-scale random motion.

Constructing a continuous phase time history from TDMA signals for opportunistic navigation

A technique is developed for reconstructing a continuous phase time history from the noncontinuous phase bursts of time division multiple access (TDMA) signals. A continuous phase time history facilitates exploitation of TDMA signals as signals of opportunity (SOPs) within an opportunistic navigation framework. Because of their widespread use and availability in todays wireless communication market, TDMA signals are attractive candidate SOPs for opportunistic navigation. The phase reconstruction technique presented here combines an integer least squares technique for estimating phase ambiguities at the beginning of each TDMA phase burst with a Kalman filter and smoother for removing these ambiguities and optimally “stitching” the bursts together. A Monte-Carlo-type simulation and test environment has been developed to investigate the sensitivity of the proposed phase reconstruction technique to various system parameters, namely, carrier-to-noise ratio, receiver clock quality, TDMA transmitter clock quality, line-of-sight acceleration uncertainty, and TDMA burst structure. Simulation results indicate that successful carrier phase reconstruction is most strongly dependent on the TDMA burst period and on the combined phase random walk effect of the receiver and transmitter clocks, the propagation effects, and the range errors.

Collaborative Opportunistic Navigation

Despite the extraordinary advances in global navigation satellite systems (GNSS), the inherent limitation of the weakness of their space-based signals makes such signals easy to block intentionally or accidentally. This makes GNSS insufficient for reliable anytime, anywhere navigation, particularly in GNSS-challenged environments, such as indoors, deep urban canyons, and GNSS-denied environments experiencing intentional jamming [1]. Several approaches have been proposed to address this inherent limitation of GNSS-based navigation, most notably augmenting GNSS receivers with deadreckoning systems. This approach typically fuses the outputs of a fixed number of well-modeled heterogeneous sensors, particularly, GNSS receivers, inertial navigation systems, and digital map databases, with specialized signal processing algorithms. Motivated by the plenitude of ambient radio frequency signals in GNSS-challenged environments, a new paradigm to overcome the limitations of GNSSbased navigation is proposed. This paradigm, termed opportunistic navigation (OpNav), aims to extract positioning and timing information from ambient radio frequency signals of opportunity (SOPs). OpNav radio receivers continuously search for opportune signals from which to draw navigation and timing

Extending the reach of GPS-assisted femtocell synchronization and localization through Tightly-Coupled Opportunistic Navigation

A strategy known as Tightly-Coupled Opportunistic Navigation (TCON) is proposed for extending the penetration of GPS-assisted femtocells in weak-signal indoor environments. Standards and regulatory agencies impose strict time, frequency, and location requirements on femtocells. These can be met with GPS aiding to unparalleled time and positioning accuracies, but GPS signals are extremely weak and thus difficult to acquire indoors. The results of this paper suggest that a TCON solution fusing GPS with CDMA cellular signals offers significant sensitivity gains over state-of-the-art assisted-GPS receivers, allowing GPS-synchronized femtocells to be deployed in 90% of all residences.

Opportunistic Frequency Stability Transfer for Extending the Coherence Time of GNSS Receiver Clocks

A framework is presented for exploiting the frequency stability of non-GNSS signals to extend the coherence time of inexpensive GNSS receiver clocks. This is accomplished by leveraging stable ambient radio frequency signals, called “signals of opportunity,” to compensate for the frequency instability of the reference oscillators typically used in inexpensive handheld GNSS receivers. Adequate compensation for this frequency instability permits the long coherent integration intervals required to acquire and track GNSS signals with low carrier-to-noise ratios. The goal of this work is to push the use of GNSS deeper indoors or into environments where GNSS may be subject to interference.

Exploiting Antenna Motion for Faster Initialization of Centimeter-Accurate GNSS Positioning With Low-Cost Antennas

This paper investigates the effectiveness of multipath-decorrelating antenna motion in reducing the initialization time of global navigation satellite system (GNSS) receivers employing low-cost single-frequency antennas for carrier-phase differential GNSS (CDGNSS) positioning. Fast initialization times with low-cost antennas will encourage the expansion of CDGNSS into the mass market, bringing the benefits of globally referenced centimeter-accurate positioning to many consumer applications, such as augmented reality and autonomous vehicles, that have so far been hampered by the several-meter-level errors of traditional GNSS positioning. Poor multipath suppression common to low-cost antennas results in large and strongly time-correlated phase errors when a receiver is static. Such errors can result in the CDGNSS initialization time, the so-called time to ambiguity resolution (TAR), extending to hundreds of seconds—many times longer than for higher cost survey-grade antennas, which have substantially better multipath suppression. This paper demonstrates that TAR can be significantly reduced through antenna motion, particularly gentle wavelength-scale random antenna motion. Such motion acts to decrease the correlation time of the multipath-induced phase errors. A priori knowledge of the motion profile is shown to further reduce TAR, with the reduction shown to be more pronounced as the initialization scenario is more challenging.

On the feasibility of cm-accurate positioning via a smartphone's antenna and GNSS chip

The feasibility of centimeter-accurate carrier-phase differential GNSS (CDGNSS) positioning using a smartphones internal GNSS antenna and GNSS chip is investigated. Precise positioning on a mass-market platform would significantly influence the world economy, ushering in a host of consumer-focused applications that have so far been hampered by the several-meter-level errors in traditional GNSS positioning. Previous work has shown that GNSS signals received through a mass-market smartphones GNSS antenna can be processed to yield a centimeter-accurate CDGNSS position solution, but this earlier work processed all GNSS signals externally to the smartphone. The question remains whether a smartphones internal oscillator and GNSS chip can produce observables of sufficient quality to support centimeter-accurate carrier-phase-based positioning. This paper answers the question by accessing and processing the raw code- and carrier-phase observables produced by a mass-market smartphone GNSS chip - observables that have heretofore been unavailable to the research community. The phones carrier phase measurements are shown to suffer from five anomalies compared to those from a survey-grade GNSS receiver, four of which are readily fixed in post-processing. The remaining anomaly, an error in the phase measurement that grows approximately linearly with time, currently prevents the phones phase measurements from satisfying the conditions for CDGNSS positioning. But the phones measurements seem otherwise fully capable of supporting cm-accurate carrier-phase differential GNSS positioning. A separate analysis of a smartphones GNSS signal strength dependency on azimuth and elevation reveals that multipath-induced deep fading and large phase errors remain a significant challenge for centimeter-accurate smartphone positioning.

A Phase-Reconstruction Technique for Low-Power Centimeter-Accurate Mobile Positioning

A carrier phase reconstruction technique is presented as an enabler for low-power centimeter-accurate mobile positioning. Reliable carrier phase reconstruction permits the duty cycling of a Global Navigation Satellite System (GNSS) receiver whose outputs are used for precise carrier-phase differential GNSS (CDGNSS) positioning. Existing CDGNSS techniques are power intensive because they require continuous tracking of each GNSS signals carrier phase. By contrast, the less-precise code-ranging technique that is commonly used in mobile devices for 3-to-10-meter-accurate positioning allows for aggressive measurement duty-cycling, which enables low-power implementations. The technique proposed in this paper relaxes the CDGNSS continuous phase tracking requirement by solving a mixed real and integer estimation problem to reconstruct a continuous carrier phase time history from intermittent phase measurement intervals each having an ambiguous initial phase. Theoretical bounds on the probability of successful phase reconstruction, corroborated by Monte-Carlo-type simulation, are used to investigate the sensitivity of the proposed technique to various system parameters, including the time period between successive phase measurement intervals, the duration of each interval, the carrier-to-noise ratio, and the line-of-sight acceleration uncertainty. A demonstration on real data indicates that coupling a GNSS receiver with a consumer-grade inertial measurement unit enables reliable phase reconstruction with phase measurement duty cycles as low as 5%.

WHITEPAPER: ACHIEVING THE CRAMER-RAO LOWER BOUND IN GPS TIME-OF-ARRIVAL ESTIMATION, A FREQUENCY DOMAIN WEIGHTED LEAST-SQUARES ESTIMATOR APPROACH

WHITEPAPER: ACHIEVING THE CRAMER-RAO LOWER BOUND IN GPS TIME-OF-ARRIVAL ESTIMATION, A FREQUENCY DOMAIN WEIGHTED LEAST-SQUARES ESTIMATOR APPROACH