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Rate Adaptation (rate + adaptation)
Selected AbstractsLetter: Compressed Disparity Information Transmission over Constant Bit Rate ATM ChannelsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2000Dionysis Papadimatos This letter presents a real-time lossless compression/decompression unit for disparity map information used in 3D teleconferencing systems. A lossless compression algorithm is used to compress the disparity map data in real-time, resulting in a variable bit-rate data stream that has to be transmitted through a constant bit-rate channel. The system uses a controlled-data-loss method for data rate adaptation and for minimizing the loss of information. [source] Ka-band link optimization with rate adaptation for Mars and lunar communicationsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2007Jun Sun Abstract On-going development of Ka-band capability for the Deep Space Networks (DSN) will radically increase the bandwidth available to support advanced mission concepts envisioned for future robotic as well as human exploration of Mars and beyond. While Ka-band links can operate at much higher data rate than X-band, they are much more susceptible to fluctuating weather conditions and manifest a significant trade-off between throughput and availability. If the operating point is fixed, the maximum average throughput for deep space Ka-band link is achieved at about 80% availability, i.e. weather-related outages will occur about 20% of the time. Low availability increases the complexity of space mission operation, while higher availability would require additional link margins that lowers the overall throughput. To improve this fundamental throughput-availability trade-off, data rate adaptation based on real-time observation of the channel condition is necessary. In this paper, we model the Ka-band channel using a Markov process to capture the impact of the temporal correlation in weather conditions. We then develop a rate adaptation algorithm to optimize the data rate based on real time feedback on the measured channel conditions. Our algorithm achieves both higher throughput and link availability as compared to the constant rate scheme presently in use. Copyright © 2007 John Wiley & Sons, Ltd. [source] Atrial Fibrillation in the Goat Induces Changes in Monophasic Action Potential and mRNA Expression of Ion Channels Involved in RepolarizationJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 11 2000HUUB M.W. VAN DER VELDEN PH.D. MAP Changes and Ion Channel Expression in Goat AF. Introduction: Sustained atrial fibrillation (AF) is characterized by a marked shortening of the atrial effective refractory period (AKRP) and a decrease or reversal of its physiolonic adaptation to heart rate. The aim of the present study was to investigate whether the AF-induced changes in AKKP in the goat are associated with changes in the atrial monophasic action potential (MAP) and whether an abnormal expression of specific ion channels underlies such changes. Methods and Results: Following thoracotomy, MAPs were recorded from the free wall of the right atrium hoth before induction of AF (control) and after cardioversion of sustained AF (>2 months) in chronically instrumented goats. In control goats. MAP duration at 80% repolarization (MAPD80) shortened (P < 0.01) from 132 ± 4 msec during slow pacing (400-msec interval) to 86 ± 10 msec during fast pacing (180 msec). After cardioversion of sustained AF, the MAPD80, during slow pacing was as short as 67 ± 5 msec (electrical remodeling). Increasing the pacing rate resulted in prolongation (P = 0.02) of the MAPD80 to 91 ± 6 msec. Also. MAPD20 (20% repolarization) shortened (P = 0.05) from 32 ± 4 msec (400 msec) to 14 ± 7 msec (180 msec) in the control goats, whereas it prolonged (P = 0.03) from 20 ± 3 msec (400 msec) to 33 ± 5 msec (180 msec) in sustained AF, mRNA expression of the L-type Ca2+ channel ,1c gene and Kv1.5 potassium channel gene, which underlie Ica, and Ikur respectively, was reduced in sustained.AF compared with sinus rhythm hy 32% (P = 0.01) and 45% (P < 0.01). respectively. No significant changes were found in the mRNA levels of the rapid Na+ channel, the Na+/Ca2+ exchanger, or the Kv4.2/4.3 channels responsible for I10. Conclusion: AF-induced electrical remodeling in the goat comprises shortening of MAPD and reversal of its physiologic rate adaptation. Changes in the time course of reploarization of the action potential are associated with changes in mRNA expression of the , subunit genes of the L.-type Ca2+ channel and the Kvl.5 potassium channel. [source] Impact of Right Ventricular Pacing Sites on Exercise Capacity during Ventricular Rate Regularization in Patients with Permanent Atrial FibrillationPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 12 2009HUNG-FAT TSE M.D., Ph.D. Background:The deleterious effects of right ventricular apical (RVA) pacing may offset the potential benefit of ventricular rate (VR) regularization and rate adaptation during an exercise in patient's atrial fibrillation (AF). Methods:We studied 30 patients with permanent AF and symptomatic bradycardia who receive pacemaker implantation with RVA (n = 15) or right ventricular septal (RVS, n = 15) pacing. All the patients underwent an acute cardiopulmonary exercise testing using VVI-mode (VVI-OFF) and VVI-mode with VR regularization (VRR) algorithm on (VVI-ON). Results:There were no significant differences in the baseline characteristics between the two groups, except pacing QRS duration was significantly shorter during RVS pacing than RVA pacing (138.9 ± 5 vs 158.4 ± 6.1 ms, P = 0.035). Overall, VVI-ON mode increased the peak exercise VR, exercise time, metabolic equivalents (METs), and peak oxygen consumption (VO2max), and decreased the VR variability compared with VVI-OFF mode during exercise (P < 0.05), suggesting that VRR pacing improved exercise capacity during exercise. However, further analysis on the impact of VRR pacing with different pacing sites revealed that only patients with RVS pacing but not patients with RVA pacing had significant increased exercise time, METs, and VO2max during VVI-ON compared with VVI-OFF, despite similar changes in peaked exercise VR and VR variability. Conclusion:In patients with permanent AF, VRR pacing at RVS, but not at RVA, improved exercise capacity during exercise. [source] Dynamics and Rate-Dependence of the Spatial Angle between Ventricular Depolarization and Repolarization Wave Fronts during Exercise ECGANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2010Tuomas Kenttä M.Sc. Background: QRS/T angle and the cosine of the angle between QRS and T-wave vectors (TCRT), measured from standard 12-lead electrocardiogram (ECG), have been used in risk stratification of patients. This study assessed the possible rate dependence of these variables during exercise ECG in healthy subjects. Methods: Forty healthy volunteers, 20 men and 20 women, aged 34.6 ± 3.4, underwent an exercise ECG testing. Twelve-lead ECG was recorded from each test subject and the spatial QRS/T angle and TCRT were automatically analyzed in a beat-to-beat manner with custom-made software. The individual TCRT/RR and QRST/RR patterns were fitted with seven different regression models, including a linear model and six nonlinear models. Results: TCRT and QRS/T angle showed a significant rate dependence, with decreased values at higher heart rates (HR). In individual subjects, the second-degree polynomic model was the best regression model for TCRT/RR and QRST/RR slopes. It provided the best fit for both exercise and recovery. The overall TCRT/RR and QRST/RR slopes were similar between men and women during exercise and recovery. However, women had predominantly higher TCRT and QRS/T values. With respect to time, the dynamics of TCRT differed significantly between men and women; with a steeper exercise slope in women (women, ,0.04/min vs ,0.02/min in men, P < 0.0001). In addition, evident hysteresis was observed in the TCRT/RR slopes; with higher TCRT values during exercise. Conclusions: The individual patterns of TCRT and QRS/T angle are affected by HR and gender. Delayed rate adaptation creates hysteresis in the TCRT/RR slopes. Ann Noninvasive Electrocardiol 2010;15(3):264,275 [source] | |||||||||||||