55 research outputs found
Longitudinal profiling and tracking stability in the Singapore study of macro-angiopathy and microvascular reactivity in type 2 diabetes cohort
No full textThe Singapore Study of Macro-Angiopathy and microvascular Reactivity in Type 2 Diabetes (SMART2D) is a prospective cohort study which was started in 2011 to investigate the effect of risk factors on vascular function and diabetes-related complications in Asians. We aimed to compare the longitudinal change in risk factors by accounting for batch effect and assess the tracking stability of risk factors over time in patients recruited for SMART2D. In this study, we (1) described batch effect and its extent across a heterogenous range of longitudinal data parameters; (2) mitigated batch effect through statistical approach; and (3) assessed the tracking stability of the risk factors over time.Ministry of Health (MOH)National Medical Research Council (NMRC)Published versionThe SMART2D cohort is supported by the Singapore Ministry of Health’s National Medical Research Council under its CSIRG (MOH-000066). The corresponding author is supported by the Singapore Ministry of Health’s National Medical Research Council under its Clinician Scientist Award (NMRC/CSA-INV/ 0020/2017). The first author is supported by the Singapore Ministry of Health’s National Medical Research Council under its Research Training Fellowship (NMRC/MOH000226)
Performance Analysis of Fast Closed-Loop Power Control For WCDMA Systems
No full textIn this thesis project, the author has carried out a thorough study on the performance of an uplink wideband CDMA (WCDMA) cellular system under fast closed-loop power control. Two study approaches are taken. Firstly, analytical study is carried out over a simplified cellular system. A mathematical model for the received signal power is proposed in terms of the probability density function. A large number of important parameters affecting the system performance have been included. The parameters taken into account include Doppler frequency which is related to mobile station's velocity , number of resolvable multipaths , maximum allowable transmitted power, power control updating frequency , number of pilot symbols per transmission frame, and number of receive diversity antenna branches. A set of analytical expression is then derived for the evaluation of the system performance in terms of bit-error rate (BER). The proposed analytical analysis approach has been verified to give good prediction of the system BER performance through comparison with simulation. The mathematical expression derived allow quick analysis of how various parameters may effect the WCDMA system performance. Next, simulation approach is adopted where most of the assumptions made in the pervious analyses are relaxed. A number of parameters are not taken into account in analytical method, such as number of power control command bits, power adjustment step-size, feedback channel error rate, type of power estimator, and power adjustment step-size control logic due to mathematical complexity. With simulation approach, the study of these parameters can be carried out. The analytical expression derived earlier have helped to serve as a reference for calibrating the simulation program developed.
A new method for estimating the received signal power based on Minimum Mean Square Error (MMSE) criteria is then proposed and is found to outperform the conventional power estimator at high mobile speed. Performance and characteristics of the conventional fixed step-size power control scheme has been examined and optimum step-sizes have been identified. A simple adaptive power adjustment step-size control based on information of current and past power control commands is found to be able to improve system performance at low mobile speed. Another adaptive power adjustment step-size control scheme, which takes into account information of the received signal-to-interference ratio (SIR), mobile speed and effective number of resolvable multipaths, has been shown to perform optimally over a wide range of channel conditions
Association between lower phase angle and chronic kidney disease progression in type 2 diabetes patients
No full textIntroduction: Phase angle (PhA), derived from bioelectrical impedance analysis (BIA), is the angle of vector determined by the body’s resistance and reactance. It indicates cellular integrity and hydration status. Though extracellular volume excess was associated with chronic kidney disease (CKD) progression, the association between PhA and CKD progression is unknown. Matrix metalloproteinase-2 (MMP-2) is a member of zinc-dependent endopeptidase family and promotes renal interstitial fibrosis. We investigated association between PhA and CKD progression, and whether the association was through MMP-2 in patients with type 2 diabetes mellitus (T2DM). Method: We conducted a prospective study on 1,078 patients with T2DM (mean age 58.9±9.1 years). PhA was measured using BIA. CKD progression was defined as ≥25% decrease in estimated glomerular filtration rate (eGFR) from baseline with deterioration across eGFR categories. Multiplex immunoassay was used to quantitate MMP-2. We examined association between PhA and CKD progression using Cox proportional hazards model, adjusting for demographics, clinical parameters and medications. Results: Over 8.6 years of follow-up, 43.7% of participants had CKD progression. Compared to tertile 3 PhA (higher level), tertiles 1 and 2 PhA were associated with higher hazards of CKD progression, with corresponding unadjusted hazard ratios (HRs) of 2.27 (95% confidence interval [CI] 1.80–2.87, P<0.001) and 1.57 (95% CI 1.24–2.01, P<0.001). The positive association between tertiles 1 and 2 PhA with CKD progression persisted in the fully adjusted model with corresponding HRs of 1.71 (95% CI 1.30–2.26, P<0.001) and 1.46 (95% CI 1.13–1.88, P=0.004). MMP-2 accounted for 14.7% of association between tertile 1 PhA and CKD progression. Conclusion: Our findings revealed a previously unobserved association between BIA-derived lower PhA and CKD progression through MMP-2 in patients with T2DM.Ministry of Health (MOH)National Medical Research Council (NMRC)Published versionThis study was supported by the Singapore Ministry of Health’s (MOH) National Medical Research Council (NMRC) under its Clinician Scientist-Individual Research Grant (MOH-000066). The corresponding author is supported by NMRC under its Clinician Scientist Award (NMRC/CSA-INV/0020/2017). The first author is supported by NMRC under its Research Training Fellowship (NMRC/MOH000226)
Closed-loop power control algorithms for cellular mobile CDMA systems
No full textIn this thesis, the author carried out a thorough study on the performance of a reverse link DS/CDMA system with various fast closed-loop power control algorithms. The algorithms studied include the Conventional single and multiple step-size, and two newly proposed alternatives, i.e., Adaptive step-size, and Predictive power control algorithms. Major parameters affecting the system performance were identified. The relationships between each of these parameters and system performance were examined. Finally, the optimum values for control variables associated with each power control algorithm were obtained or recommended.Master of Engineerin
Broadband access device and user interface design for ubiquitous computing: Perspective from a service provider
No full textPAR Reduction in Space-Time Coded OFDM via Modified Active Constellation Extension
No full textHigh peak-to-average ratio (PAR) is one of the main problems in Orthogonal Frequency Division Multiplexing (OFDM) systems. This problem becomes more complicated when Space-time codes (STC) are employed as any PAR reduction method should not destroy the relationships among STC encoded OFDM symbols. There are existing PAR reduction methods for STC-OFDM systems. However, these methods do not provide sufficient performance of PAR reduction without complex receivers. In this paper, we propose Modified Active Constellation Extension (Modified ACE) method for STC encoded OFDM systems to provide 3.5dB of PAR improvement at a 10(-3) complementary cumulative density function (CCDF) of PAR. Most importantly, Modified ACE does not require any complex receivers or side information
Predictive call admission control algorithm for power-controlled wireless systems
No full textIn wireless communication systems, a conventional call admission control (CAC) mechanism determines whether a node can be admitted to the network by firstly monitoring the received interference plus noise and estimate the achievable signal-to-interference-plus-noise ratio (SINR). However, in the presence of power control, the SINR may vary over time, thus, rendering the conventional CAC inaccurate. The maximum achievable SINR for a new node in a general wireless system depends on the link gains amongst all the co-channel interfering nodes involved. Thus, one of the challenges of CAC in a power-controlled wireless system is the estimation of maximum achievable SINR when information about global link gains is not available. By ignoring the white noise factor, we present a predictor for the maximum achievable signal-to-interference ratio (SIR) of a new node trying to gain access to the medium. Using the SIR predictor we then calculate an optimal active link protection margin, which together with a SIR threshold would constitute an enhanced threshold value for the new node to attain. By doing so current active communication links would be protected from performance degradation should the maximum achievable SIR value common to all the nodes be lower than the SIR threshold. The accuracy of the predictor is evaluated by means of simulation in terms of mean error and root-mean-square error. Together with finding the corresponding optimal active link protection margin, efficient CAC mechanism to ensure stability of the feasible system can be maintained over a wide range of operating SIR values
A dynamic channel assignment strategy via power control for ad-hoc network systems
No full textThe increasing demand for wireless network services have resulted a plethora of studies on the efficient management of radio resources to improve network capacity. As radio spectrum is a scarce resource, sharing of radio frequency has to be considered among wireless network nodes and by doing so introduces interference among users, which in turn limit the network capacity. Our study addresses the problem of dynamically assigning channels in ad-hoc wireless networks via power control in order to satisfy their minimum QoS requirements. The objective then is to maximize the number of co-channel links subject to some stability conditions. In order to assign the optimal number of co-channel nodes that can co-exist over a wide range of operating SINR values, we propose two novel ways to find the optimal combination of co-channel links so that a feasible power vector can be found within its power limits
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