Cross-Coupled Phase-Locked Loop with Closed Loop Amplitude Control

In this work a new version of the cross-coupled phaselocked loop (CCPLL) interference canceller is presented. This detector consists of two phase-locked loop (PLL) demodulators interconnected in such a manner as to permit one PLL to lock onto and track the instantaneous frequency of the stronger received signal, while the other loop tracks and demodulates the weaker of two received signals. In addition, the receiver includes control loops to estimate the instantaneous amplitude of both received signals. This demodulator, therefore, has the capability of detecting both the desired and interfering signals, even though the interferer may be stronger than the desired signal and may share the same frequency band. The defining nonlinear differential equations for the CCPLL structure are derived and transient acquisition responses are obtained using computer-aided analysis. The CCPLL has numerous technological applications in suppressing a wide variety of cochannel and adjacent channel interferers.     

Acquisition Behavior of the Cross-Coupled Phase-Locked Loop FM Demodulator

In this work, the acquisition behavior of a cross-coupled phase-locked loop (CCPLL) FM demodulator capable of suppressing cochannel and adjacent channel interferers is examined. This novel detector consists of two phase-locked loop (PLL) demodulators interconnected in such a manner as to permit one PLL to lock onto and track the stronger received signal, while the other loop tracks and demodulates the weaker of two received signals. The demodulator has two separate outputs, namely, the outputs of each PLL, and thus possesses the capability of demodulating both the stronger as well as the weaker received signals even though they are cochannel and share the same frequency band. The transient response of the CCPLL system is obtained using computer-aided analysis of the defining coupled nonlinear differential equations. From these results, steady-state "stability regions" are derived which reveal that range of loop parameters where successful separation and demodulation of the received cochannel signals is assured. The CCPLL receiver has numerous technological applications in suppressing unintentional or intentional CW, AM, FM, and AM/FM interferers. Experimental results demonstrating such potential are included.     

Trade-off between efficiency and linearity in an RF-power amplifier

RF-power amplifiers are used in a variety of applications including radio and TV transmitters, wireless communications, satellite communication systems and RF-power heating. Power efficiency and amplifier linearity are two key parameters which play a significant role in the design of modern power amplifiers. It is well known that driving the amplifier into its non-linear region, e.g. Class C operation, may improve efficiency, but it will also lead to increased distortion. This article examines the trade-off between efficiency and linearity quantitatively and advances a useful design rule.     

Prospective countywide evaluation of the effects of motor vehicle safety device use on hospital resource use and injury severity

Stress echocardiography is increasingly used for the assessment of coronary artery disease and is valuable in the treatment of patients with known disease as well. Although several studies are available on the accuracy of stress echocardiography in the detection of coronary artery disease and evaluation of its severity, studies on the use of this technique for evaluation of prognosis are just now emerging. Over the past decade, few studies have investigated its prognostic value in different patient populations. The versatility and advantage of stress echocardiography lie in the fact that it provides information on both resting ventricular function and stress-induced ischemia, two important determinants of cardiac events. Exercise echocardiography with the bicycle or posttreadmill approach is used in subjects who can exercise and provides important additional prognostic data from physiologic exercise variables. In patients unable to exercise, pharmacologic stress echocardiography with dobutamine or vasodilators is used. Stress echocardiography has been shown to identify different populations of patients at risk of cardiac events, including those with stable or suspected coronary artery disease, those with acute myocardial infarction, and those scheduled for major noncardiac surgery. In the early postinfarct setting, exercise and vasodilator stress have been used more often, whereas dobutamine echocardiography has been used predominantly at low doses for the assessment of residual myocardial viability. This review focuses on recently published investigations evaluating the prognostic effect of stress echocardiography in patients with stable coronary artery disease or acute myocardial infarction.     

Maximum A Posteriori Estimator for Suppression of Interchannel Interference in FM Receivers

In this paper an FM detector capable of suppressing the degradation in receiver performance due to the presence of an interfering signal is presented. Optimum receiver structures based on maximum-aposteriori estimation procedures are first derived and then a practical demodulator based on the optimum receivers is examined. The receiver consists of two phase-locked loops (PLL) interconnected in a manner to permit one PLL to lock onto and track the Stronger received FM signal while the other loop tracks the weaker of the two received FM signals. The detector has the capability of demodulating both the desired received FM as well as the interferer even for the case when both signals are co-channel. Experimental results demonstrating such capability even in the presence of strong input Gaussian noise are presented.     

On channel estimation and detection for multicarrier signals infast and selective Rayleigh fading channels

Time-domain channel estimation and detection techniques are presented for multicarrier signals in a fast and frequency-selective Rayleigh fading channel. As a consequence of the time-varying channel, the orthogonality between subcarriers is destroyed in conventional frequency-domain approaches, resulting in interchannel interference, which increases an irreducible error floor in proportion to the normalized Doppler frequency. An important feature of the proposed technique is the ability to exploit the time-selective channel as a provider of time diversity. This enables us to achieve performance superior to any other structure without increasing bandwidth or incorporating redundancy, in order to reduce the complexity of the estimator, we apply the theory of optimal low rank approximation to a minimum mean squared error channel estimator and present a theoretical calculation of mean squared error and simulations to confirm that the estimator is robust to changes in channel characteristics     

Wireless communications laboratory

Wireless communications technology is one of the most rapidly growing disciplines and is experiencing unprecedented market growth. The 21st Century will witness the widespread deployment of all kinds of public and private wireless networks. Many graduating seniors and graduate students are finding themselves in careers relating to wireless information technology. In addition, practicing engineers, computer specialists, and managers have to re-educate themselves in the area of wireless technology. Polytechnic University (Brooklyn Poly), Brooklyn, NY, recognized the need to prepare its students for careers in wireless and successfully developed one of the first instructional wireless information networks laboratories. The laboratory has provided more than 800 students during the past decade with the opportunity to acquire both in-depth theoretical understanding and hands-on experience in this rapidly growing discipline. The laboratory experience can play an important role in motivating students and stimulating their interest in a specific discipline such as wireless communication systems. It both complements and supplements the other theoretical courses taken by the students. Reading about signals plus additive white Gaussian noise in a textbook and actually observing such signals in a laboratory oscilloscope can be two very different experiences for many students. This paper describes this instructional laboratory, which is replicable by other universities.