RESUMEN
This paper evaluates the performance of an integrity monitoring algorithm of global navigation satellite systems (GNSS) for the Kalman filter (KF), termed KF receiver autonomous integrity monitoring (RAIM). The algorithm checks measurement inconsistencies in the range domain and requires Schmidt KF (SKF) as the navigation processor. First, realistic carrier-smoothed pseudorange measurement error models of GNSS are integrated into KF RAIM, overcoming an important limitation of prior work. More precisely, the error covariance matrix for fault detection is modified to capture the temporal variations of individual errors with different time constants. Uncertainties of the model parameters are also taken into account. Performance of the modified KF RAIM is then analyzed with the simulated signals of the global positioning system and navigation with Indian constellation for different phases of aircraft flight. Weighted least squares (WLS) RAIM used for comparison purposes is shown to have lower protection levels. This work, however, is important because KF-based integrity monitors are required to ensure the reliability of advanced navigation methods, such as multi-sensor integration and vector receivers. A key finding of the performance analyses is as follows. Innovation-based tests with an extended KF navigation processor confuse slow ramp faults with residual measurement errors that the filter estimates, leading to missed detection. RAIM with SKF, on the other hand, can successfully detect such faults. Thus, it offers a promising solution to developing KF integrity monitoring algorithms in the range domain. The modified KF RAIM completes processing in time on a low-end computer. Some salient features are also studied to gain insights into its working principles.
RESUMEN
This paper presents a novel Kalman filter (KF)-based receiver autonomous integrity monitoring (RAIM) algorithm for reliable aircraft positioning with global navigation satellite systems (GNSS). The presented method overcomes major limitations of the authors' previous work, and uses two GNSS, namely, Navigation with Indian Constellation (NavIC) of India and the Global Positioning System (GPS). The algorithm is developed in the range domain and compared with two existing approaches-one each for the weighted least squares navigation filter and KF. Extensive simulations were carried out for an unmanned aircraft flight path over the Indian sub-continent for validation of the new approach. Although both existing methods outperform the new one, the work is significant for the following reasons. KF is an integral part of advanced navigation systems that can address frequent loss of GNSS signals (e.g., vector tracking and multi-sensor integration). Developing KF RAIM algorithms is essential to ensuring their reliability. KF solution separation (or position domain) RAIM offers good performance at the cost of high computational load. Presented range domain KF RAIM, on the other hand, offers satisfactory performance to a certain extent, eliminating a major issue of growing position error bounds over time. It requires moderate computational resources, and hence, shows promise for real-time implementations in avionics. Simulation results also indicate that addition of NavIC alongside GPS can substantially improve RAIM performance, particularly in poor geometries.
RESUMEN
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.
RESUMEN
OBJECTIVES: Pregabalin and clonidine have anti-nociceptive properties. This study assesses their efficacy in prolonging the analgesic effect of spinal anesthesia and post-operative analgesic requirement in patients undergoing vaginal hysterectomy. MATERIALS AND METHODS: A total of 90 females in the age group of 30-60 years were randomly allocated in to three groups of 30 each, to receive either oral clonidine (150 µg) or oral pregabalin (150 mg) or oral multivitamin as placebo 1.5 h before spinal anesthesia with 3ml (15 mg) of 0.5% hyperbaric bupivacaine. Intensity of pain was measured on a visual analog scale (VAS) at the end of operation (0 h) then at 1,2,4,6,12 and 24 h thereafter. Diclofenac sodium intramuscularly 1 mg/kg was provided when the VASscore was >4 in the study period. Sedation was defined by Ramsay sedation scale at 0,6,12 and 24 h. Side-effects such as nausea and vomiting, respiratory depression and dryness of mouth were noted. RESULTS: The VAS scores were significantly less in the pregabalin group compared with the clonidine group at 6,12 and 24 h post-operatively with a P < 0.0001. More sedation was seen in the clonidine group than in the pregabalin group (P < 0.05). Analgesic consumption and VAS scores were lower in clonidine and pregabalin group compared with the placebo group (P < 0.05). CONCLUSION: Oral pregabalin (150 mg) prolongs the post-operative pain relief after spinal anesthesia but produces less sedation compared with oral clonidine (150 µg).