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Accurate code phase estimation of LOS GPS signal using Compressive Sensing and multipath mitigation using interpolation/MEDLL

Viswa, Chaithanya

Abstract Details

2015, MS, University of Cincinnati, Engineering and Applied Science: Electrical Engineering.
A wide variety of error sources affect accuracy of the basic GPS measurements of pseudorange (also known as code-phase) and integrated Doppler (also known as carrier-phase). Among these are satellite clock and ephemeris errors, ionospheric delay, tropospheric delay, receiver dynamic tracking error, multipath and thermal noise. Multipath is the dominant error source in high precision GPS applications as others sources can be countered with differential measurements. Multipath errors result when the receiver receives the direct or line-of-sight (LOS) satellite signal via multiple paths and processes the combined signal as if it were only the direct. This causes anomalies in determining user’s location and velocity. Large time-delay multipath are easily separated by correlators in a GPS receiver due to easy separation of correlation peaks. Medium and small time-delay multipath are more difficult to detect and separate since the correlation peaks are not separated, but rather distorted from the shape of that of a single path. Many solutions have been proposed to estimate LOS in the presence of multipath, almost all of them require faster sampling than the Nyquist rate. This in turn requires a large bandwidth on the RF frontend, i.e., a large pre-correlation bandwidth. A large bandwidth RF frontend admits more noise, and is also more prone to interference. Therefore a narrowband solution would be more desirable. However, tradeoff is that not enough samples are contained in a correlation peak, making it very difficult, if not impossible, to detect LOS and mitigate multipath. In this thesis we present a novel method to reconstruct high-sampling rate (super-Nyquist rate) correlation functions from low-sampling rate (Nyquist-rate) correlation functions using the new signal processing paradigm of compressive sampling or compressive sensing (CS). Since the correlation function of GPS signals is sparse, with only a few high peaks, it is suitable to apply the CS theory so that the above reconstruction can be achieved with almost probability one. We use a narrowband RF frontend, e.g., of a 2 MHz bandwidth as in a typical C/A code GPS receiver. With the aid of the CS, we are able to reconstruct super-Nyquist rate correlation functions of, e.g., 16 MSPS with a CS reconstruction ratio of 4. Also, an attempt was made to mitigate multipath in GPS applications by using interpolation based methods. A standard interpolation method based on linear or nearest neighbor solution is used to generate super Nyquist rate samples and cross correlation functions are obtained. The output of the interpolation method is passed onto a maximum likelihood estimator based method such as MEDLL that enables us to separate multipath with time separations of only one or two such super-Nyquist rate samples (i.e., at 0.1 chip time or less.). This method works well for estimating the multipath delays and amplitudes even in the presence of short and medium multipath delays.
H. Howard Fan, Ph.D. (Committee Chair)
Eric T. Vinande, Ph.D. (Committee Member)
Xuefu Zhou, Ph.D. (Committee Member)
85 p.

Recommended Citations

Citations

  • Viswa, C. (2015). Accurate code phase estimation of LOS GPS signal using Compressive Sensing and multipath mitigation using interpolation/MEDLL [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439282162

    APA Style (7th edition)

  • Viswa, Chaithanya. Accurate code phase estimation of LOS GPS signal using Compressive Sensing and multipath mitigation using interpolation/MEDLL. 2015. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439282162.

    MLA Style (8th edition)

  • Viswa, Chaithanya. "Accurate code phase estimation of LOS GPS signal using Compressive Sensing and multipath mitigation using interpolation/MEDLL." Master's thesis, University of Cincinnati, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439282162

    Chicago Manual of Style (17th edition)