Current Issue : January - March Volume : 2014 Issue Number : 1 Articles : 5 Articles
Recent advances in MEMS IMUs give the potential to develop affordable low-end GNSS/INS systems for land vehicles navigation\r\n(LVN). To improve the performance of low-end GNSS/INS systems, we made detailed quantitative analysis to the computation\r\nterms of the INS navigation equation in regard to accuracy impacts and computation loads and then proposed a simplified INS\r\nalgorithm and adjusted the corresponding Kalman filter of GPS/INS integration. Comprehensive analysis was made to get the\r\nquantitative impacts of each simplified term. Results of road test have shown that the degradation of the navigation accuracy caused\r\nby the algorithmsimplification wasmuch less than that caused by the sensors errors of theMEMSIMU.Meanwhile, the computation\r\nload could be reduced by 70%with the simplified algorithm, and the reduction can go further to reach nearly 95% by downsampling\r\nIMU data rate simultaneously. Therefore, it is feasible to simplify the INS algorithm without losing accuracy and get benefits of\r\nreducing the computation load, which can further enhance the real-time performance of the navigation. The work has special\r\nsignificance for the applications that have limited processor resource and request strict real-time response, such as a deeply coupled\r\nGPS/INS receiver....
Small portable Global Navigation Satellite System (GNSS) receivers have revolutionized personal navigation through providing\r\nreal-time location information for mobile users. Nonetheless, signal fading due to multipath remains a formidable limitation\r\nand compromises the performance of GNSS receivers. Antenna diversity techniques, including spatial and polarization diversity,\r\ncan be used to mitigate multipath fading; however, the relatively large size of the spatially distributed antenna system required is\r\nincompatible with the small physical size constraints of a GNSS handheld receiver. User mobility inevitably results in motion of the\r\nhandset that can be exploited to achieve diversity gain through forming a spatially distributed synthetic array. Traditionally, such\r\nmotion has been construed as detrimental as it decorrelates the received signal undermining the coherent integration processing\r\ngain generally necessary for acquiring weak faded GNSS signals. In this paper the processing gain enhancement resulting from a\r\ndual-polarized synthetic array antenna, compatible with size constraints of a small handset that takes advantage of any user imposed\r\nmotion, is explored. ?eoretical analysis and experimental veri??cations attest the effectiveness of the proposed dual-polarized\r\nsynthetic array technique by demonstrating an improvement in the processing gain of the GNSS signal acquisition operation....
This paper presents an extended Kalman filter-based hybrid indoor position estimation technique which is based on integration\r\nof fingerprinting and trilateration approach. In this paper, Euclidian distance formula is used for the first time instead of radio\r\npropagation model to convert the received signal to distance estimates. This technique combines the features of fingerprinting and\r\ntrilateration approach in a more simple and robust way. The proposed hybrid technique works in two stages. In the first stage, it\r\nuses an online phase of fingerprinting and calculates nearest neighbors (NN) of the target node, while in the second stage it uses\r\ntrilateration approach to estimate the coordinate without the use of radio propagation model.The distance between calculated NN\r\nand detective access points (AP) is estimated using Euclidian distance formula.Thus, distance between NN and APs provides radii\r\nfor trilateration approach. Therefore, the position estimation accuracy compared to the lateration approach is better. Kalman filter\r\nis used to further enhance the accuracy of the estimated position. Simulation and experimental results validate the performance\r\nof proposed hybrid technique and improve the accuracy up to 53.64% and 25.58% compared to lateration and fingerprinting\r\napproaches, respectively....
The paper focuses on a navigation facility, relying on commercial-off-the-shelf (COTS) technology, developed to generate highaccuracy\r\nattitude and trajectory measurements in postprocessing. Target performance is cm-level positioning with tenth of degree\r\nattitude accuracy. The facility is based on the concept of GPS-aided inertial navigation but comprises carrier-phase differential\r\nGPS (CDGPS) processing and attitude estimation based on multiantenna GPS configurations. Expected applications of the system\r\ninclude: (a) performance assessment of integrated navigation systems, developed for general aviation aircraft and medium size\r\nunmanned aircraft systems (UAS); (b) generation of reference measurements to evaluate the flight performance of airborne sensors\r\n(e.g., radar or laser); and (c) generation of reference trajectory and attitude for improving imaging quality of airborne remote sensing\r\ndata.The paper describes system architecture, selected algorithms for data processing and integration, and theoretical performance\r\nevaluation. Experimental results are also presented confirming the effectiveness of the implemented approach.\r\n1. Introduction\r\nField test refers to the testing of a device or sensor in the\r\nconditions under which it will be actually used. Field testing\r\nbecomes necessary when numerical and indoor testing may\r\nfail, that is, in all the cases in which the operative conditions\r\nare difficult to be reproduced with high fidelity by software or\r\nlaboratory simulations.\r\nA typical example is the performance assessment of integrated\r\nnavigation systems for airborne applications. In this\r\ncase several factorsmust be taken into account, including but\r\nnot limited to: (a) the intrinsic dynamical and statisticalmodels\r\nof sensor and systems, (b) the selected data fusion strategy,\r\nand (c) the typical and the worst case manoeuvres that must\r\nbe considered to determine a trustworthy dynamicalmodel of\r\nthe aircraft where the system is installed. Indeed, high performance\r\nheading and attitude determination units are needed\r\nboth in general aviation and in unmanned aircraft systems\r\n(UAS) applications to attain an adequate control performance.\r\nUAS are more demanding in terms of attitude determination\r\nperformance than manned aircraft for a series of\r\nissues. First, the absence of a human pilot onboard prevents\r\nthe aircraft from using the human senses such...
The time model of Beidou satellite clocks is analyzed. The general relations of satellite clocks with the system time are studied.\r\nThe error sources of two-way radio time transfer between satellites and uplink stations are analyzed.The uncertainty of type A is\r\nabout 0.3 ns in Beidou system. All the satellite clocks in orbit of Beidou satellite navigation system are evaluated by the clock offsets\r\nobserved by the two-way radio time transfer.The frequency stabilities at a sample time of 10000 s and 1 day for all the satellite clocks\r\nare better than 1.0 Ã?â?? 10-13. It means that the performance of Beidou satellite clocks in orbit is consistent with the ground test, and\r\nthe results in orbit are a little better than those in ground vacuum....
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