Mark G. Petovello

Benefits of Combined GPS/GLONASS with Low-Cost MEMS IMUs for Vehicular Urban Navigation

The integration of Global Navigation Satellite Systems (GNSS) with Inertial Navigation Systems (INS) has been very actively researched for many years due to the complementary nature of the two systems. In particular, during the last few years the integration with micro-electromechanical system (MEMS) inertial measurement units (IMUs) has been investigated. In fact, recent advances in MEMS technology have made possible the development of a new generation of low cost inertial sensors characterized by small size and light weight, which represents an attractive option for mass-market applications such as vehicular and pedestrian navigation. However, whereas there has been much interest in the integration of GPS with a MEMS-based INS, few research studies have been conducted on expanding this application to the revitalized GLONASS system. This paper looks at the benefits of adding GLONASS to existing GPS/INS(MEMS) systems using loose and tight integration strategies. The relative benefits of various constraints are also assessed. Results show that when satellite visibility is poor (approximately 50% solution availability) the benefits of GLONASS are only seen with tight integration algorithms. For more benign environments, a loosely coupled GPS/GLONASS/INS system offers performance comparable to that of a tightly coupled GPS/INS system, but with reduced complexity and development time.

Measuring GNSS Multipath Distributions in Urban Canyon Environments

In general, standalone global navigation satellite systems (GNSS) receiver architectures cannot provide a position accuracy suitable for use in vehicular applications in urban canyon scenarios. Specifically, GNSS signals are affected by the surrounding objects, such as high buildings, trees, and so on, which introduces multipath errors. Multipath arises from the reception of reflected or diffracted signals, possibly in addition to the line-of-sight signal, and is one of the most detrimental error sources in GNSS positioning applications. Multipath distributions in the urban canyon area are measured and characterized in this paper. In particular, the Doppler and code phase delay under different conditions are assessed as a function of vehicle speed and signal power, which are different from previous calibration metrics. Specifically, multipath directional-dependence phenomenon (i.e., the variation resulting from the direction of travel of the user) is observed during this process, and the multipath maximum Doppler offset and minimum Doppler offset are derived and verified by the real data. The multipath distribution will eventually affect the search strategy (i.e., search space size, coherent integration time) utilized in the high sensitivity receiver.

Measuring Aircraft Carrier Flexure in Support of Autonomous Aircraft Landings

This paper quantifies the experimental measurements of aircraft carrier flexure (deformation) at sea in support of the United States Department of Defense sea-based Joint Precision Approach and Landing System (JPALS) that aims to deliver automatic landing capabilities to inbound aircraft aboard aircraft carriers. The methodology for measuring ship flexure using the Global Positioning System (GPS) and inertial sensors is described. Results indicate that flexure on the aircraft carrier used for testing has a standard deviation of approximately 1-2 cm. For the ship tested, the most significant flexure effects are in the port/starboard direction and correlate best with roll or lateral acceleration.

Use of High Sensitivity GNSS Receiver Doppler Measurements for Indoor Pedestrian Dead Reckoning

Dead-reckoning (DR) algorithms, which use self-contained inertial sensors combined with gait analysis, have proven to be effective for pedestrian navigation purposes. In such DR systems, the primary error is often due to accumulated heading drifts. By tightly integrating global navigation satellite system (GNSS) Doppler measurements with DR, such accumulated heading errors can usually be accurately compensated. Under weak signal conditions, high sensitivity GNSS (HSGNSS) receivers with block processing techniques are often used, however, the Doppler quality of such receivers is relatively poor due to multipath, fading and signal attenuation. This often limits the benefits of integrating HSGNSS Doppler with DR. This paper investigates the benefits of using Doppler measurements from a novel direct vector HSGNSS receiver with pedestrian dead-reckoning (PDR) for indoor navigation. An indoor signal and multipath model is introduced which explains how conventional HSGNSS Doppler measurements are affected by indoor multipath. Velocity and Doppler estimated by using direct vector receivers are introduced and discussed. Real experimental data is processed and analyzed to assess the veracity of proposed method. It is shown when integrating HSGNSS Doppler with PDR algorithm, the proposed direct vector method are more helpful than conventional block processing method for the indoor environments considered herein.

Ultratight GPS/Reduced-IMU Integration for Land Vehicle Navigation

A reduced inertial measurement unit (RIMU) is ultratightly (UT) integrated with a vector-based Global Positioning System (GPS) receiver using two approaches; vector delay and frequency lock loops (VDLL/VFLL), and a VDLL with a cascaded phase lock loop (CaP). A CaP plus a frequency discriminator (CaPF) composite loop is developed to provide reliable Doppler measurements and improves navigation performance by up to 20% compared with other methods using real world data.

GPS/Reduced IMU with a Local Terrain Predictor in Land Vehicle Navigation

In order to reduce the cost and volume of land vehicle navigation (LVN) systems, a “reduced” inertial measurement unit (IMU) consisting of only one vertical gyro and two or three accelerometers is generally used and is often integrated with other sensors. Since there are no horizontal gyros in a reduced IMU, the pitch and roll cannot be calculated or observed directly from the inertial data, and the navigation performance is thus affected by local terrain variations. In this work, a reduced IMU is integrated with global positioning system (GPS) data and a novel local terrain predictor (LTP) algorithm. The latter is used primarily to help estimate the pitch and roll of the reduced IMU system and thus to improve the navigation performance. In this paper, two reduced IMU configurations and two grades of IMUs are investigated using field data. Test results show that the LTP is valid. Specifically, inclusion of the LTP provides more than an 80% horizontal velocity improvement relative to the case when the LTP is not used in a GPS/reduced IMU configuration.

Combined Acquisition and Tracking Methods for GPS L1 C/A and L1C Signals

Article deposited according to Hindawi Publishing Corporation policy in SHERPA/RoMEO, June 15, 2011.

Indoor doppler error characterization for high sensitivity GNSS receivers

Indoor Doppler measurements in high sensitivity receivers are often biased due to the indoor multipath and user dynamics. The work presented here investigates the relationship between Doppler errors and some key channel parameters. A directional multipath channel model is introduced and some essential channel parameters are defined. In nonsymmetric scattering environments, the Doppler biases are shown to be explicitly related with these parameters. Theoretical simulation and experimental data are analyzed and demonstrated to be consistent.

Requirements analysis for bit synchronization and decoding in a standalone high-sensitivity GNSS receiver

In weak GNSS signal environments, extending integration time is paramount to improving the GNSS receivers sensitivity. Furthermore, sufficient coherent integration can help to separate the line-of-sight (LOS) and non LOS (NLOS) signals - primarily in the Doppler domain - for multipath mitigation. However, extending integration time is limited by the presence of the navigation message data bits. The Maximum-Likelihood (ML) estimation method has been shown as the most effective way to estimate the navigation bit boundary locations (i.e., bit synchronization) and subsequently estimate the data bit values (i.e., bit decoding) in the presence of noise alone. This paper further analyzes the performance of ML estimation method as a function of various other parameters by using the successful synchronization rate (SSR) and successful decoding rate (SDR) as the criteria. The parameters considered include the number of data bits required (i.e., integration time) and the Doppler frequency error, and both are evaluated under different signal strength scenarios. The requirements for bit synchronization are analyzed under three SSRs, which are 85%, 90% and 95%. Results indicate that, under the SSR of 90% and the SDR of 90%, bit synchronization and bit decoding are valid for signal strengths of 15 dB-Hz and 20 dB-Hz respectively, and the Doppler frequency errors should not be larger than 24 Hz and 11 Hz respectively.

Collaborative acquisition of weak GPS signals

Signal commonality among local GPS receivers is studied in this paper. More specifically, the GPS signal parameters, carrier Doppler, code phase and carrier to noise power density (C/N0), from different GPS receivers are investigated. It shows that as the antenna spacing is small (<30 meters) the code phase and carrier Doppler are quite in-common. The code phase falls into the same code bin, while the carrier Doppler difference is mainly due to the clock drifts from different receivers. It also shows that the C/N0 difference is within a certain range (more than 90% is less than 8dB). The impacts of imperfection of these parameters on GPS signal acquisition are then studied in terms of probability of detection and probability of false alarm. Based on the field measurements and the theoretical analysis, the potential advantage of collaborative GPS signal acquisition is present.