GPS Adaptive Array Phase Compensation using a Software Radio Architecture

Global Navigation Satellite System raw measurements from Android smart devices make accurate positioning possible with advanced techniques, e.g., precise point positioning (PPP). To achieve the sub-meter-level positioning accuracy with low-cost smart devices, the PPP algorithm developed for geodetic receivers is adapted and an approach named Smart-PPP is proposed in this contribution. In Smart-PPP, the uncombined PPP model is applied for the unified processing of single- and dual-frequency measurements from tracked satellites. The receiver clock terms are parameterized independently for the code and carrier phase measurements of each tracking signal for handling the inconsistency between the code and carrier phases measured by smart devices. The ionospheric pseudo-observations are adopted to provide absolute constraints on the estimation of slant ionospheric delays and to strengthen the uncombined PPP model. A modified stochastic model is employed to weight code and carrier phase measurements by considering the high correlation between the measurement errors and the signal strengths for smart devices. Additionally, an application software based on the Android platform is developed for realizing Smart-PPP in smart devices. The positioning performance of Smart-PPP is validated in both static and kinematic cases. Results show that the positioning errors of Smart-PPP solutions can converge to below 1.0 m within a few minutes in static mode and the converged solutions can achieve an accuracy of about 0.2 m of root mean square (RMS) both for the east, north and up components. For the kinematic test, the RMS values of Smart-PPP positioning errors are 0.65, 0.54 and 1.09 m in the east, north and up components, respectively. Static and kinematic tests both show that the Smart-PPP solutions outperform the internal results provided by the experimental smart devices.

This study proposed a Controlled Reception Pattern Antenna (CRPA) array for digital beam forming in Global Navigation Satellite System (GNSS) applications. The proposed array antenna was designed to receive signals in both the GPS L1 (1.57542 GHz) and GLONASS L1 (1.602 GHz) bands. To accommodate a specific platform, it featured eight antenna elements arranged in a circular pattern on a 9-inch circular plate. The array elements were fed using a low-temperature co-fired ceramic (LTCC) hybrid coupler that provided a 90° phase difference and two indirectly fed probes to achieve circular polarization. The proposed antenna was optimized and fabricated using three-dimensional electromagnetic (3D EM) simulation tools, and its performance was evaluated through measurements conducted using a network analyzer and in an anechoic chamber. The measured voltage standing wave ratio (VSWR) of the antenna array averaged below 1.7:1, and the average gain exceeded 0 dBic. The antenna was also tested under real-world outdoor conditions using a commercial satellite receiver, successfully verifying its ability to reliably receive satellite signals within the designed frequency bands.

A new TWSTFT modem was developed for both time and frequency transfer. The code and carrier phase measurements become available by it. We evaluated the performance in a common-clock and non common-clock measurements. The results encourage us to widely spread the use of the new modem.

The expected positioning accuracies of civil users utilizing modernized GPS and Galileo are derived using the error analysis in this paper. Since, in general, the performance of DLL, PLL and FLL is proportional to chip lengths and wavelengths, the positioning accuracies from various measurements of modernized GPS and Galileo are derived as function of chip length and wavelength. These results are compared with that from GPS Ll measurement. In absolute positioning, compared to GPS C/A code only case, more than 17 times performance improvement is expected when all civil code signals of modernized GPS and Galileo (L1, L2, L5, E1, E5A and E5B) are used. In relative positioning, compared to GPS L1 carrier phase only case, more than 2 times performance improvement is expected when all civil signals of modernized GPS and Calileo are used. Furthermore, the relationship between GDOP and RGDOP in single frequency case is expanded to general case where multiple frequencies and both code and carrier phase measurements are used.

In this contribution, a novel opto-acoustic indoor navigation system for linear distance measurement is presented. The novelty consists in the simultaneous use of envelope time-of-flight (ETF) and carrier phase (CPH) measurements. In particular, we establish a two-channel link consisting of an ultrasound and infrared channel, the latter using a carrier frequency equal to the ultrasound frequency. In order to render the system extendible for multiple transmitters and receivers, code-division-multiple-access using Gold codes is employed, as all ultrasound and infrared signals share the same carrier frequency. This is also beneficial for multipath scattering suppression. The time difference between the carrier phase of the received ultrasound and infrared signals offers a high resolution but ambiguous distance signal. On the other hand, correlation of the received signals yields a coarse but unique distance signal. Experimental results show that a measurement resolution in the submillimeter range is feasible.

In this paper we show that the judicious use of all the information available from C/A code can provide results better than the reported accuracy of P code with much lower cost. This performance however, is limited to low-dynamic, low-jamming environments which are typical of civilian applications. The elegance of P-code is primarily manifested in high dynamic vehicles (jets and missiles) and in jamming environments. Results are provided in stationary and low-dynamic cases based on code-phase, carrier-phase, doppler, and integrated doppler measurements from TRIMBLE 4000 receivers. In particular, it is shown that the relative or differential accuracy of better than 10 centimeters can be achieved in low-dynamic applications. Position fixes are obtained every second. after a short time of initial calibration and tracking. The improved accuracy is based on aiding the code phase measurements with integrated doppler. Each one second position fix. which is provided in both polar and cartisian coordinates is based on a complete and independent set of measured data, with no hypothetical modeling, interpolation, or extrapolation. INDEX TERMS: GLOBAL POSITIONING SYSTEM, GPS DOPPLER PROCESSING. TRIMBLE 4000A LOCATOR. INTRODUCTION Even a brief survey of the growing body of GPS literature, leaves little doubt that GPS will indeed replace all existing positioning and timing systems in the near future. The attractiveness of GPS is not only due to its technical superiority, but also to economic considerations. It is interesting to observe that, even in this early stage of the GPS program, production of low cost GPS receivers is a reality. Today C/A code GPS receivers can be manufactured, in large volumes, at a lower cost than LORAN receivers [1]. Of the two classes of GPS signals, C/A and P code, only C/A code will be available for civilian applications [2]. This restriction might lead one to conclude that the precision positioning and timing capabilities of GPS will not be available to civilian users. This is a false conclusion. Judicious use of all the information available from C/A code can provide results equivalent to P code, with much lower cost. In this paper we prove this claim by providing results based on code phase, doppler, integrated doppler and carrier phase measurements from TRIMBLE C/A code receivers. It is our belief that even if P code was available for civilian applications it adds very little, if any, to the precision that is available from C/A code. The elegance of P code is mostly manifested in military applications such as in high dynamic vehicles (jets and missiles) and in jamming environments. In this paper we distinguish between four levels of accuracy that can be obtained from the C/A code system:LEVEL A: Accuracy of about 10 meters,LEVEL B: Accuracy of about 1 meter,LEVEL C: Accuracy of about 10 centimeters,LEVEL D: Accuracy of about 1 centimeter, Each one of these accuracy levels can be achieved with a different type of C/A code information processing, and with a different operational requirement.

The radar AESA technology is evolving towards two main directions. First, the digital Transmit/Receive Modules will allow to avoid the use of analog RF Beam Forming Networks and to exploit the Digital Beam Forming technique. Second, the use of Gallium Nitride High Power Amplifiers will allow to increase the antenna MTBF Virtualabs developed a module, called VBR, of 16 TRMs, fully digital, working in the S band. Each TRM is fully controlled in digital form, thanks to the use of System On Chips (SoCs). Gallium Nitride High Power Amplifiers (HPA) are used for final RF amplification. The echo received by each TRM is immediately transformed in digital data in the SoCs, allowing an easy Digital Beam Forming (DBF) in the FPGA that controls the SoCs. DBF is used also in transmission, in fact the waveform is generated directly in the VBR and converted to analog in the SoCs. More VBRs can be synchronized using a synchronization board, and the digital echoes provided by more VBRs can be combined by Digital Beam Forming Network boards. With such architecture, any type of radar AESA antenna can be designed by combining different numbers of VBRs (modular architecture). The FPGA inside the VBR has enough computational power to allow to perform tests on a digital phase compensation technique to keep the beam pointed correctly also in case of LFM pulses with bandwidth up to 200 MHz. Experimental results achieved with the realized VBR are presented.

Current cooperative positioning with global navigation satellite system (GNSS) for connected vehicle application mainly uses pseudorange measurements. However, the positioning accuracy offered cannot meet the requirements for lane-level positioning, collision avoidance and future automatic driving, which needs real-time positioning accuracy of better than 0.5 m. Furthermore, there is an apparent lack of research into the integrity issue for these new applications under emerging driverless vehicle applications. In order to overcome those problems, a new extended Kalman filter (EKF) and a multi-failure diagnosis algorithm are developed to process both GNSS pseudorange and carrier phase measurements. We first introduce a new closed-loop EKF with partial ambiguity resolution as feedback to address the low accuracy issue. Then a multi-failure diagnosis algorithm is proposed to improve integrity and reliability. The core of this new algorithm includes using Carrier phase-based Receiver Autonomous Integrity Monitoring method for failure detection, and the double extended w test detectors to identify failure. A cooperative positioning experiment was carried out to validate the proposed method. The results show that the proposed closed-loop EKF can provide highly accurate positioning, and the multi-failure diagnosis method is effective in detecting and identifying failures for both code and carrier phase measurements.

Alternative positioning techniques, such as those using ambient signals-of-opportunity, have been increasingly developed for global navigation satellite system (GNSS)-challenging urban and indoor environments. For instance, cellular long-term evolution (LTE) network supports a variety of positioning methods based on signal measurements such as received signal strength or time-of-arrival (TOA). Carrier phase measurement extracted from LTE signals has also received substantial attention due to its potential high ranging accuracy. This paper presents a closed-loop (CL) carrier phase tracking architecture for positioning in LTE networks with robustness to the channel fading effects. The pilot cell-specific reference signal (CRS) is exploited for generating the channel estimation results, which are inputs for the carrier phase discriminator to measure the carrier phase error. The undesired bias corrupting the phase discriminator output for multipath channels is analytically derived. Then, the state-space model of LTE carrier signal tracking in light of the specific CRS time-frequency domain pattern is established and the state estimator gain matrix is derived based on the proportional integral filter deign. Simulation assessment of the proposed carrier phase tracking architecture is performed in a single path Rician fading channel under different Rician factors and signal powers. The impact of loop parameters, e.g., loop bandwidth and updating interval, is investigated. Real collected LTE data in a multipath fading channel is also used to comparatively analyze the performances of the existing open-loop and proposed CL carrier tracking methods combined with three LTE signal TOA estimators. The proposed algorithm in conjunction with the multipath estimating delay lock loop is shown to provide accurate and robust carrier phase measurements against multipath fading effects compared to other considered tracking schemes.

A general expression is derived for the eye pattern boundaries of a multilevel class-4 partial-response (PR) signal after single-sideband amplitude-modulation (SSBAM) transmission with a carrier phase error. From the expression particular results are obtained for the horizontal and vertical eye openings of the signal. Expressions are derived for the tap settings of a linear transversal equalizer using the minimum mean-square error (MMSE) criterion when the class-4 PR signal is distorted by a carrier phase error and sampled with timing error. The values of the tap settings can be used to reduce the carrier and timing phase errors. Finally, an expression for the vertical eye opening of the equalized signal is derived as a function of the carrier phase and the number of stages in the equalizer.

Apart from communications, the Fifth Generation (5G) technology is also motivated by positioning requirements down to the sub-meter level across industry verticals. In this work, we utilize Universal Software Radio Peripheral to transmit and receive the 5G New Radio signals. The obtained samples are then processed by the proposed 5G code and carrier phase software defined receiver. In this process, the dedicated 5G Positioning Reference Signal (PRS) is adopted to obtain time of arrival estimates using more accurate carrier phase measure-ments instead of code phase measurements. The continuously transmitted 5G PRSs over time enable accurate carrier phase tracking and avoid ambiguity problems during the tracking stage in line-of-sight environments. Furthermore, a roadside unit is set up to observe the same signals and cancel out the measurement error introduced by the clock offset between two transmitters. Finally, some field experiments are carried out, and the experimental results indicate that using 5G double-difference carrier phase measurements from only four transmitters, a position root mean square error of 0.790m is achievable.

This paper proposed heave estimation using time-differenced GPS carrier phase measurement and compensated barometer measurement with applying error model. The carrier phase measurement makes a precise of the altitude more than code measurement because carrier phase based pseudo range has mm error. But integer ambiguity resolution problem must be solved when carrier phase measurement is used. Time-Differenced(TD) carrier phase measurements can be used to find a relative altitude using single GPS without an integer ambiguity resolution since a time-invariant. Integer ambiguity is removed by TD operation. Barometer error model estimated using Gauss-Morkov process. Output is result of kalman filter using barometer and carrier phase measurement. Performance of implemented system was evaluated through the experiments at various scenarios including static test in rural and urban areas.

GPS time transfer is usually carried out with C/A code measurements using the common-view technique. An uncertainty of a few nanoseconds can be obtained for an integration time of about 1000 seconds when ionospheric measurements and precise orbits are used. This limits the capability of frequency comparison to the level of 3 parts in 10/sup 14/ for an integration time of one day. Recently new frequency standards have been developed that claim an accuracy at or below 1/spl times/10/sup -14/. For existing time transfer techniques it is a challenge to compare their frequency over a sufficiently short interval. Previous studies have already shown the potential of carrier-phase and P-code measurements from geodetic GPS receivers. This paper draws up tentative uncertainty budgets for clock frequency comparisons using phase and code measurements from commercially available dual-frequency and multi-channel GPS receivers. Although the level of noise involved in carrier phase measurements is two or three orders of magnitude lower than that of code measurements in the short term, other error sources such as tropospheric delay of GPS signals, multipath propagation and the phase ambiguity problem lead to a limitation in the accuracy of frequency transfer at the 10/sup -15/ level over an averaging time of one day. Carrier phase measurements, however, provide an improvement over the performance expected from code measurements for all averaging times smaller than one day.

Carrier phase-based ionospheric observables using PPP models

The Expectation-Maximization algorithm is adapted to the extended Kalman filter to multiple GNSS Precise Point Positioning (PPP), named EM-PPP. EM-PPP considers better the compatibility of multiple GNSS data processing and characteristics of receiver motion, targeting to calibrate the process noise matrix Qt and observation matrix Rt, having influence on PPP convergence time and precision, with other parameters. It is possibly a feasible way to estimate a large number of parameters to a certain extent for its simplicity and easy implementation. We also compare EM-algorithm with other methods like least-squares (co)variance component estimation (LS-VCE), maximum likelihood estimation (MLE), showing that EM-algorithm from restricted maximum likelihood (REML) will be identical to LS-VCE if certain weight matrix is chosen for LS-VCE. To assess the performance of the approach, daily observations from a network of 14 globally distributed International GNSS Service (IGS) multi-GNSS stations were processed using ionosphere-free combinations. The stations were assumed to be in kinematic motion with initial random walk noise of 1 mm every 30 s. The initial standard deviations for ionosphere-free code and carrier phase measurements are set to 3 m and 0.03 m, respectively, independent of the satellite elevation angle. It is shown that the calibrated Rt agrees well with observation residuals, reflecting effects of the accuracy of different satellite precise product and receiver-satellite geometry variations, and effectively resisting outliers. The calibrated Qt converges to its true value after about 50 iterations in our case. A kinematic test was also performed to derive 1 Hz GPS displacements, showing the RMSs and STDs w.r.t. real-time kinematic (RTK) are improved and the proper Qt is found out at the same time. According to our analysis despite the criticism that EM-PPP is very time-consuming because a large number of parameters are calculated and the first-order convergence of EM-algorithm, it is a numerically stable and simple approach to consider the temporal nature of state-space model of PPP, in particular when Qt and Rt are not known well, its performance without fixing ambiguities can even parallel to traditional PPP-RTK.