Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 4 Articles
The well-known Space-Alternating Generalized Expectation Maximisation (SAGE) algorithm has been recently considered for\r\nmultipath mitigation in Global Navigation Satellite System (GNSS) receivers. However, the implementation of SAGE in a GNSS\r\nreceiver is a challenging issue due to the numerous number or parameters to be estimated and the important size of the data to\r\nbe processed. A new implementation of the SAGE algorithm is proposed in this paper in order to reach the same efficiency with a\r\nreduced complexity. This paper focuses on the trade-off between complexity and performance thanks to the Cramer Rao bound\r\nderivation. Moreover, this paper shows how the proposed algorithm can be integrated with a classical GNSS tracking loop. This\r\nsolution is thus a very promising approach for multipath mitigation....
A simple approach to gyro and accelerometer bias estimation is proposed. It does not involve Kalman filtering or similar formal\r\ntechniques. Instead, it is based on physical intuition and exploits a duality between gimbaled and strapdown inertial systems. The\r\nestimation problem is decoupled into two separate stages. At the first stage, inertial system attitude errors are corrected by means\r\nof a feedback from an external aid. In the presence of uncompensated biases, the steady-state feedback rebalances those biases and\r\ncan be used to estimate them. At the second stage, the desired bias estimates are expressed in a closed formin terms of the feedback\r\nsignal. The estimator has only three tunable parameters and is easy to implement and use. The tests proved the feasibility of the\r\nproposed approach for the estimation of low-cost MEMS inertial sensor biases on a moving land vehicle....
Vehicle-to-vehicle relative navigation of a network of vehicles travelling in an urban canyon is assessed using least-squares and\r\nKalman filtering covariance simulation techniques. Between-vehicle differential GPS is compared with differential GPS augmented\r\nwith between-vehicle ultrawideband range and bearing measurements. The three measurement types are combined using both\r\nleast-squares and Kalman filtering to estimate the horizontal positions of a network of vehicles travelling in the same direction on\r\na road in a simulated urban canyon. The number of vehicles participating in the network is varied between two and nine while the\r\nseverity of the urban canyon was varied from15-to 65-degree elevation mask angles.Theeffect of each vehicle�s azimuth being known\r\na priori, or unknown is assessed.The resulting relative positions in the network of vehicles are then analysed in terms of horizontal\r\naccuracy and statistical reliability of the solution. The addition of both range and bearing measurements provides protection levels\r\non the order of 2m at almost all times where DGPS alone only rarely has observation redundancy and often exhibits estimated\r\naccuracies worse than 200 m. Reliability is further improved when the vehicle azimuth is assumed to be known a priori....
Multiconstellation satellite navigation is critical in signal-degraded environments where signals are strongly corrupted. In this\r\ncase, the use of a single GNSS system does not guarantee an accurate and continuous positioning. A possible approach to solve\r\nthis problem is the use of multiconstellation receivers that provide additional measurements and allows robust reliability testing;\r\nin this work, a GPS/GLONASS combination is considered. In urban scenario, a modification of the classical RAIM technique\r\nis necessary taking into account frequent multiple blunders. The FDE schemes analysed are the ââ?¬Å?Observation Subset Testing,ââ?¬Â\r\nââ?¬Å?Forward-BackwardMethod,ââ?¬Â and ââ?¬Å?DanishMethodââ?¬Â; they are obtained by combining different basic statistical tests.Theconsidered\r\nFDEmethods aremodified to optimize their behaviour in urban scenario. Specifically a preliminary check is implemented to screen\r\nout bad geometries.Moreover, a large blunder could causemultiple test failures; hence, a separability index is implemented to avoid\r\nthe incorrect exclusion of blunder-free measurements. Testing the RAIM algorithms of GPS/GLONASS combination to verify the\r\nbenefits relative to GPS only case is a main target of this work too. The performance of these methods is compared in terms of RMS\r\nand maximum error for the horizontal and vertical components of position and velocity....
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