A receiver autonomous integrity monitoring (RAIM) algorithm is presented for extended Kalman filter (EKF)-based global navigation satellite system receivers. To this end, a novel method to bound the EKF mean position error is developed under the assumption of step and ascending ramp fault profiles. The calculated mean position error bound is subsequently used to determine EKF protection levels. Simulation results show that the EKF RAIM algorithm offers performance comparable to that of the traditional weighted least squares RAIM. Although performance gains may not be achieved, the proposed approach lays the foundation for efficient, real-time computation of protection levels for range residual-based RAIM with EKF. Thus, it has important extensions to advanced EKF-based navigation algorithms, such as vector tracking receivers.
This paper develops parametric models from the existing vector architecture equations to explain the performance benefits of vector tracking loops. A theoretical analysis of the parametric models which are validated with simulation studies shows that internal aiding among loops is the key to the superior performance of the vector tracking architecture. A systematic methodology for comparing scalar and vector architectures with similar design parameters is also presented. From this, the conditions under which both architectures can perform comparably are identified. The analysis results presented in the paper lead to the following important conclusions. First, internal aiding, in addition to being responsible for vector loops' superior performance, allows easy propagation of errors among loops and, therefore, affects the fault tolerance capability of the vector tracking architecture. Second, well designed scalar tracking loops with external Doppler aiding can offer similar performance improvements while avoiding the complexity of the vector architecture.
Background:Spinal anesthesia is the technique of choice in transurethral resection of prostate (TURP). The major complication of spinal technique is risk of hypotension. Saddle block paralyzed pelvic muscles and sacral nerve roots and hemodynamic derangement is less.Aims and objectives:To compare the hemodynamic changes and adequate surgical condition between saddle block and subarachnoid block for TURP.Material and methods:Ninety patients of aged between 50 to 70 years of ASA-PS I, II scheduled for TURP were randomly allocated into 2 groups of 45 in each group. Group A patients were received spinal (2 ml of hyperbaric bupivacaine) and Group B were received saddle block (2 ml of hyperbaric bupivacaine). Baseline systolic, diastolic and mean arterial pressure, heart rate, oxygen saturation were recorded and measured subsequently. The height of block was noted in both groups. Hypotension was corrected by administration of phenylephrine 50 mcg bolus and total requirement of vasopressor was noted. Complications (volume overload, TURP syndrome etc.) were noted.Results:Incidence of hypotension and vasopressor requirement was less (P < 0.01) in Gr B patients. Adequate surgical condition was achieved in both groups. There was no incidence of volume overload, TURP syndrome, and bladder perforation.Conclusion:TURP can be safely performed under saddle block without hypotension and less vasopressor requirement.
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