Advanced Multipath Mitigation Techniques for Satellite-Based Positioning Applications

Abstract

Multipath remains a dominant source of ranging errors in Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS) or the future European satellite navigation system Galileo. Multipath is generally considered undesirable in the context of GNSS, since the reception of multipath can make significant distortion to the shape of the correlation function used for time delay estimation. However, some wireless communications techniques exploit multipath in order to provide signal diversity though in GNSS, the major challenge is to effectively mitigate the multipath, since we are interested only in the satellitereceiver transit time offset of the Line-Of-Sight (LOS) signal for the receiver's position estimate. Therefore, the multipath problem has been approached from several directions in order to mitigate the impact of multipath on navigation receivers, including the development of novel signal processing techniques. In this paper, we propose a maximum likelihood-based technique, namely, the Reduced Search Space Maximum Likelihood (RSSML) delay estimator, which is capable of mitigating the multipath effects reasonably well at the expense of increased complexity. The proposed RSSML attempts to compensate the multipath error contribution by performing a nonlinear curve fit on the input correlation function, which finds a perfect match from a set of ideal reference correlation functions with certain amplitude(s), phase(s), and delay(s) of the multipath signal. It also incorporates a threshold-based peak detection method, which eventually reduces the code-delay search space significantly. However, the downfall of RSSML is the memory requirement which it uses to store the reference correlation functions. The multipath performance of other delay-tracking methods previously studied for Binary Phase Shift Keying-(BPSK-) and Sine Binary Offset Carrier-(SinBOC-) modulated signals is also analyzed in closed loop model with the new Composite BOC (CBOC) modulation chosen for Galileo E1 signal. The simulation results show that the RSSML achieves the best multipath mitigation performance in a uniformly distributed two-to-four paths Rayleigh fading channel model for all three modulated signals.

RETRACTED ARTICLE: Likelihood-based GNSS positioning using LOS/NLOS predictions from 3D mapping and pseudoranges

“…The term ''multipath'' is often used to describe NLOS reception. However, this is misleading as the two phenomena have different characteristics and can require different mitigation approaches (Groves 2013a, b;Bhuiyan and Lohan 2012). 3D-mapping-aided (3DMA) GNSS techniques largely compensate for the effects of NLOS reception.…”

Wavelet Thresholding Method based on Hypotheses Testing and Noise Estimation for Multipath Mitigation in GPS Receivers

“…In detail, the noise level is estimated by taking the standard deviation of the correlation values out-of-1-chip early with respect to the correlation peak in the prompt correlator. Since the multipath components are delayed with respect to the LOS component, the correlation values for out-of-1-chip early time delays are not affected any multipath components [13]. This concept is explained by Fig.…”

A Novel Hearability Enhancement Method for Forward-Link Multilateration Using OFDM Signal

“…In dense multipath environment, the performance of interference cancellation technique is degraded, thus multipath mitigation method is needed. Multipath can be mitigated by estimating the channel [26], using a correlator technique in the tracking system [28], or by implementing a cancellation technique similar to interference cancellation [29]. Because most of the existing multipath mitigation and interference cancellation techniques for cellular system have been developed for data decoding, they usually do not estimate propagation time, which is essential for geo-location.…”

“…While interference cancellation methods in [26][27][28][29] are applicable to W-CDMA or CDMA2000 cellular systems, they are not suited for OFDM signals, which it is complexvalued. Interference cancellation methods for orthogonal frequency-division multiplex (OFDM) communication systems have been proposed previously.…”