Multipath Error Envelope Research Articles

Multipath error mitigation using self‐encoded spread spectrum for binary‐offset‐carrier signals

Self-encoded spread spectrum (SESS) incorporated with binary-offset-carrier modulation can significantly improve the navigation accuracy exploiting the inherent temporal diversity of iterative detection (ID). ID is the natural realisation of the detection scheme based on the unique SESS spreading sequence that comes from the data source itself. The enhanced precision is presented in terms of multipath error envelope, running average error and root-mean-square error for early-minus-late and elary/late slope. SESS is a promising technology that can substantially mitigate detrimental effects of multipath on tracking error for position location or navigation. The accuracy of SESS with ID is superior to other conventional correlation detection schemes with a similar or minimally increased computational complexity.

Performance evaluation of MSK and OFDM modulations for future GNSS signals

The objective of this work is to investigate the performances of orthogonal frequency division multiplexing (OFDM) and minimum frequency shift keying (MSK) modulations as potential future global navigation satellite systems (GNSS) signal modulation schemes. MSK is used in global system for mobile communications because of its spectral efficiency, while OFDM is used in WLAN and digital video broadcast-terrestrial because of its multipath mitigation capability. These advantages of MSK and OFDM modulations render them as promising modulation candidates for future GNSS signals to offer enhanced performances in challenging environments. Gabor bandwidth and multipath error envelopes of these two modulations were computed and compared with those of the current global positioning system (GPS), Galileo, and Beidou signal modulations. The results show that OFDM modulation demonstrated promises as a viable future GNSS modulation, especially for signals that require pre-filtering bandwidths larger than 2 MHz, while MSK modulation is more desirable for pre-filtering bandwidth below 2 MHz where it exhibits the largest Gabor bandwidth.

Adaptive multipath mitigation tracking system for GPS receiver

Multipath effects are the major source of error in GPS differential positioning. In this paper, an adaptive multipath mitigation tracking system is presented for 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. By using 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. Simulation results show that our proposed method provides a better performance in terms of multipath error envelope and carrier-phase error.

합성 이진 옵셋 반송파 신호 추적을 위한 새로운 비모호 상관함수

In this paper, we propose a novel unambiguous correlation function for composite binary offset carrier (CBOC) signal tracking. First, we observe that a sub-carrier of CBOC signal is seen as a sum of four partial sub-carriers, and generate four partial-correlations composing the CBOC autocorrelation. Then, we obtain an unambiguous correlation function with a sharp main-peak by re-combining the partial correlations. From numerical results, we confirm that the proposed unambiguous correlation function offers a better tracking performance than the conventional correlation functions in terms of the tracking error standard deviation and multipath error envelope.

TMBOC과 CBOC 신호에 적합한 모호성이 낮은 다중경로 오차완화 기법

One of the most significant errors in the pseudo-range measurement performance of GNSSes (Global Navigation Satellite Systems) is their multipath error for high-precision applications. Several schemes to mitigate this error have been studied. Most of them, however, have been focused on the GPS (Global Positioning System) L1 C/A (Coarse/Acquisition) signal that was designed in the 1970s and is still being used for civil navigation. Recently, several modernized signals that were especially conceived to more significantly mitigate multipath errors have been introduced, such as Time Multiplexed and Composite Binary Offset Carrier (TMBOC and CBOC, respectively) signals. Despite this advantage, however, a problem remains with the use of TMBOC and CBOC modulations: the ambiguity of BOC (Binary Offset Carrier)-modulated signal tracking. In this paper, a novel unambiguous multipath error mitigation scheme for these modernized signals is proposed. The proposed scheme has the same complexity as HRCs (High Resolution Correlators) but with low ambiguity. The simulation results showed that the proposed scheme outperformed or performed at par with the HRC in terms of their multipath error envelopes and running averages in the static and statistical channel models. The ranging error derived by the mean multipath error of the proposed scheme was below 1.8 meters in an urban area in the statistical channel model.

Combination of squared correlators for multipath mitigation in safety-of-life global navigation satellite systems receivers

This study presents a novel solution of DLL discrimination function for multiband global navigation satellite systems (GNSS) receivers, designed to cope with a multipath-prone environment in safety-of-life (SoL) applications. The solution is based on a combination of squared correlators (CSC) outputs, following an approach similar to that driving to the well-known, and patented, Strobe TM discriminator. The proposed CSC discriminator features the novelty with respect to other `double-delta` architectures, usually covered by patents, still maintaining a light implementation (four correlators per channel, plus the prompt one); this comes at the cost of sub-optimal performance with respect to the classic Strobe TM discriminator. The study presents the definition of the CSC solution in the context of a SoL receiver architecture, discusses the motivations for its design choices and shows an analysis of performance both in open-loop, basically employing the discriminator S -curve and the multipath error envelope, and in closed-loop, measuring the variance of estimated code phase and the statistics of the multipath-induced phase error. Performance of the proposed function are evaluated for the typical modulations of the GPS L 1 and Galileo E 1 systems, namely BPSK(1), BOC(1,1) and CBOC(6,1,1/11).

Analysis of Galileo E5 and E5ab code tracking

The world of global navigation satellite systems has been enhanced with several new or improved signals in space aiming to optimize accuracy, reliability, navigation solution, and interoperability between different constellations. However, such developments bring various challenges to the receivers’ designers. For example, acquisition and tracking stages turn into more complex processes while handling the increasing bandwidth requires additional processing power. In this context, we study the code tracking of Galileo E5ab in a full band or of only one of its components, i.e., either E5a or E5b. More specifically, an architecture for tracking the E5 pilot channel as an AltBOC(15,10) or BPSK(10) modulation is introduced, and the performance of well-known discriminator types is analyzed using analytical derivations and simulations of linearity and stability regions, thermal noise tracking errors, multipath error envelopes and tracking thresholds. Different parameters, such as the front-end filter bandwidth, the early/late chip spacing, un-normalized and normalized discriminators, are taken into consideration. The results obtained are used to illustrate the main advantages and drawbacks of tracking the E5 signal as well as to help defining the main tracking loop parameters for an enhanced performance.

Definition and Analysis of WAAS Receiver Multipath Error Envelopes

: Multipath is the primary range error constraining the accuracy of differential GPS systems. This has been an important motivating factor in the development of receiver and antenna technologies to mitigate multipath errors. This paper describes the results of a study of GPS receiver multipath error envelopes, measured employing a high-resolution technique for use with laboratory-environment GPS signal simulators, and their consistency with multipath errors observed at the Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) reference sites. Using the WAAS reference receiver, the effects of receiver bandwidth, correlator spacing, very short or extended multipath delays, autocorrelation function sidelobes, and multiple specular reflections were explored. Test results showed good agreement among theoretical, experimental, and field-observed multipath error estimates, and illustrated the characteristics and impact of the variety of multipath mitigating receiver technologies employed in the WAAS receiver. The results are widely applicable to GPS receiver designs in general, and to other differential systems, such as the FAA's Local Area Augmentation System. Results confirmed that measurements from the WAAS reference sites are dominated by close-in multipath and multiple reflections. New multipath mitigation techniques, such as ultra-narrow correlator spacing and refined receiver algorithms, coupled with new antenna designs, have the potential for further reducing multipath errors at differential reference sites.