Mean-square deviation analysis of the zero-attracting variable step-size LMS algorithm

The well-known variable step-size least-mean-square (VSSLMS) algorithm provides faster convergence rate while maintaining lower mean-square error than the conventional LMS algorithm. The performance of the VSSLMS algorithm can be improved further in a channel estimation problem if the impulse response of the channel is sparse. Recently, a zero-attracting (ZA)-VSSLMS algorithm was proposed to exploit the sparsity of a channel. This was done by imposing an \(\ell _1\)-norm penalty to the original cost function of the VSSLMS algorithm which utilizes the sparsity in the filter taps during the adaptation process. In this paper, we present the mean-square deviation (MSD) analysis of the ZA-VSSLMS algorithm. A steady-state MSD expression for the ZA-VSSLMS algorithm is derived. An upper bound of the zero-attractor controller (\(\rho \)) that provides the minimum MSD is also provided. Moreover, the effect of the noise distribution on the MSD performance is shown theoretically. It is shown that the theoretical and simulation results of the algorithm are in good agreement with a wide range of parameters, different channel, input signal, and noise types.     

GPS spoofer countermeasure effectiveness based on signal strength,noise power,and C/N0 measurements

Spoofing sources can effectively disrupt a GPS receiver during the acquisition phase by generating multiple false correlation peaks and increasing the noise floor. Such deceptive correlation peaks can mislead the GPS receiver into acquiring the spoofer generated signals rather than the authentic signals. Also, the spoofer can increase the receiver noise floor to bury the authentic signals in the noise and at the same time generate correlation peaks with amplitudes commensurate with reasonable C/N₀ expectations. The main focus of this paper is on assessment of the reduced effectiveness of the GPS spoofer countermeasure during acquisition where the GPS receiver utilizes C/N₀ discrimination. As shown, whereas the C/N₀ discrimination is of limited effectiveness, with a modest circuit modification, the receiver can measure the absolute power of the correlation peaks, which is an effective means of detecting and discriminating spoofer sources. It will be shown that employing absolute power monitoring technique considerably reduces the vulnerability region of the receiver compared with the C/N₀ monitoring techniques. Copyright © 2012 John Wiley & Sons, Ltd.     

A lumped parameter mathematical model to analyze the effects of tachycardia and bradycardia on the cardiovascular system

In this study, the cardiovascular system and heart hemodynamic performance are modeled using lumped method (electrical analogy) to evaluate the effects of abnormal heartbeats on the cardiovascular system performance. Lumped method (voltage–current relations of an electrical circuit) is able to simulate the cardiovascular (CV) system behavior in various physiological conditions. CV system consists of 42 compartments, including artery, vein, capillary set, and heart chambers. Each blood circulatory subsystem (compartment) is modeled using electrical elements, such as resistor, capacitor, and inductor. In this study, by utilizing lumped model, CV system is simulated in matlab software (SIMULINK environment). There are two major types of irregular heart rates. In tachycardia, the heartbeats are too quick: over 100 beats per minute. In bradycardia, the heart beat is too slow: less than 60 beats per minute. Healthy blood circulation and heart performance are modeled (heartbeat: 75 beat/minute), and the results such as left atrium outflow‐time graph and pressure‐time diagram of aorta artery and pulmonary circulation are obtained. The present results are found to be in agreement with numerical and experimental studies. Then, by increasing and decreasing the heartbeat, the abnormality (150 and 50 beat/minute representing tachycardia and bradycardia, respectively) is simulated. The results show that the tachycardia leads to a significant reduction of capillary blood flow into less than 100 ml/s, while it exceeds 100 ml/s when heart has normal function. The results of the present study have clinical implications for detailed diagnosis of CV diseases when experimental studies have limitation. Copyright © 2014 John Wiley & Sons, Ltd.