A Multipath Mitigation Tracking Architecture Using Adaptive Path Estimator for GPS System
Date Issued
2007
Date
2007
Author(s)
Du, Jiun-Shian
DOI
zh-TW
Abstract
The global positioning system (GPS) provides accurate positioning and timing information useful in many applications. The GPS satellites broadcast ranging codes and navigation data with the technique of direct sequence spread spectrum (DS-SS). A wide variety of error sources affect the GPS measurement of pseudorange (also known as code-phase) and integrated Doppler (also known as carrier-phase). Among these are satellite user range error, ionospheric delay, tropospheric delay, receiver dynamic tracking error, multipah and thermal noise. The use of differential techniques theoretically eliminates all error sources which are common to both receivers. The error which remains is multipath, and it becomes the dominant error source in high precision GPS applications.
Multipath errors are not identical to the GPS reference station and remote receivers. Thus, it becomes the significant error source in differential GPS. In this research, a multipath mitigation tracking system is presented for dynamic GPS applications. It is comprised of four function blocks, those being (1) adaptive path estimator (APE), (2) multipath interference reproducer (MPIR), (3) Rake-based delay locked loop (RB-DLL), and (4) Rake-based phase locked loop (RB-PLL). Only the short delay condition with delay less than 1.5 PN chip is considered here, because GPS pseudorange error envelope decreases to zero for delay time greater than 1.5 PN chip. In order to estimate reflection profile in the correlation domain, the FFT-based circular correlation and block average method (BAM) are utilized to offer significant savings in computational complexity. The APE estimates the delayed profiles and coefficients of the reflection signals. With the path parameters from APE, the corresponding multipath arms are activated to accomplish the multipath reproduction. These replica profiles are used for subtracting the reflection components from carrier and code discriminators before sending it into the Rake-based carrier/code tracking loops.
In this thesis, we first introduce the characteristic of GPS spread-spectrum signal and multipath effect. Then, we design the APE and estimate the short-delay path parameters to perform multipath interference cancellation in the RB-DLL. The simulation results of the multipath mitigation system are obtained by using Matlab tool to verify the performances. In outdoor condition, the received signal power is assumed to be -154.6 dBW, because the minimum received signal power is about this value by using a typical GPS antenna with right-hand circular polarization and a hemispherical pattern. The noise power is assumed to be -138.5 dBW in a 2-MHz IF bandwidth, because a typical effective noise temperature for a GPS receiver is 513K. The reflection delay estimation and steady-state tracking error are conducted at different IF band SNR environments (i.e., different IF bandwidth) via extensive simulation to demonstrate the performances of our proposed adaptive rake-based multipath technique.
Subjects
全球定位系統機收機
可適性路徑估測器
多路徑干擾重建器
耙式碼延遲鎖相迴路
耙式載波相位鎖相迴路
Global Positioning System (GPS) Receiver
adaptive path estimator (APE)
multipath interference reproducer (MPIR)
Rake-based delay locked loop (RB-DLL)
Rake-based phase locked loop (RB-PLL)
Type
thesis
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