Combined Modulation Technique Research Articles

New PWM Strategy to Enable Dual-Mode Operation Capability in Common-Grounded Transformerless Inverters

A novel pulsewidth modulation (PWM) technique has been presented in this article, which enables the converter to operate in the conventional (boost) mode as well as in the buck mode (proposed). The proposed buck PWM method significantly reduces the current stresses of the components compared to the boost mode. Using this combined modulation technique, a dual-mode operation of such a class of inverters is demonstrated to accommodate a wide input voltage variation while maintaining the regulation of the output ac voltage. The proposed modulation technique is simple to implement and has been implemented in some of the conventional Type-I and Type-II inverters to demonstrate a very wide input voltage range (200–400 V dc), while keeping a fixed output voltage of 110 V ac rms. The theoretical analysis, key operating circuit, and waveforms are presented along with the thermal profile of various switches. Experimental results show that Type-I and Type-II inverters rated at 500 VA have around <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$95.5~\pm ~1$ </tex-math></inline-formula> % efficiency for a wide load range with a peak efficiency of 97.3% in buck * invert mode for Type-I and 95.5% for Type-II inverters.

Performance of a resonant fiber-optic gyroscope based on a broadband source.

A resonant fiber-optic gyroscope (RFOG) based on a broadband source can avoid the fundamental drawback of coherence detection processing while possessing the greater sensitivity afforded by the finesse of the fiber-optic ring resonator. In this paper, the basic operation principle is presented and demonstrated in detail, and various noise sources, as well as the temperature effect encountered in this broadband source-driven RFOG, are studied and analyzed. Then a combined modulation technique is proposed to suppress the residual backscattering noise. To further reduce the effect of temperature transience, an asymmetric fiber ring resonator is designed. In the experiment, a bias stability of 0.01°/h is successfully demonstrated with a 100 m-long fiber ring resonator of 8 cm diameter in a laboratory environment without temperature control.

Comparison of Angular and Combined Automatic Tube Current Modulation Techniques with Constant Tube Current CT of the Abdomen and Pelvis

The objective of our study was to compare image quality and radiation dose associated with abdominopelvic CT using combined modulation, angular modulation, and constant tube current. Compared with using a constant tube current to scan the abdomen and pelvis, the use of a combined modulation technique results in a substantial reduction (42-44%) in radiation dose with acceptable image noise and diagnostic acceptability.

Metallic Prosthesis: Technique to Avoid Increase in CT Radiation Dose with Automatic Tube Current Modulation in a Phantom and Patients

The institutional review board approved this Health Insurance Portability and Accountability Act-compliant study protocol, with waiver of informed consent. The purpose of the study was to retrospectively evaluate the combined automatic tube current modulation technique in patients with orthopedic metallic prostheses. Five hundred abdominal-pelvic computed tomographic (CT) studies performed with combined modulation technique were reviewed to identify nine patients with metallic prostheses (mean age, 66 years; range, 35-86 years; male-female ratio, 5:4). On the basis of age and transverse abdominal images, these patients were matched with nine others with no metallic prostheses (mean age, 56 years; range, 36-72 years; male-female ratio, 4:5) who were control patients. Images were graded for extent and severity of streak artifacts (grade 1, streak artifact present but not substantially compromising evaluation of adjacent structures; grade 2, streak artifact present and slightly compromising evaluation of adjacent structures; and grade 3, streak artifact present and severely compromising evaluation of adjacent structures). Student t test was performed for statistical analysis. There was no difference in mean effective tube current-time product between study and control patients (P > .49). With automatic tube current modulation, an increase in CT dose caused by metallic prostheses can be successfully avoided.

Combined photo‐ and wavelength‐modulation spectroscopy of quantum well structures

AbstractA spectroscopic technique that combines photoreflectance (PR) and wavelength‐modulated reflectance (WMR) spectroscopies was developed. This technique, which indeed is a second derivative spectroscopy, is based on measurements of a difference in the WMR with and without illumination of the sample. The combined modulation technique was used to study excitonic transitions and their photomodulation mechanisms in GaAs/AlAs quantum well structures. The enhancement of weak optical features and suppression of background effects as well as the possibility of studying changes in excitonic transitions induced both by modulated and continuous laser illumination are considered to be advantages of proposed modulation spectroscopy method. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Implementation of STARNET: a WDM computer communications network

STARNET is a broadband backbone optical wavelength-division multiplexing (WDM) local area network (LAN). Based on a physical passive star topology, STARNET offers all users two logical subnetworks: a high-speed reconfigurable packet-switched data subnetwork and a moderate-speed fix-tuned packet-switched control subnetwork. Thus, STARNET supports traffic with a wide range of speed and continuity characteristics. We report the analysis and implementation of an entire STARNET two-node network, from the optical to the computer layer, at the Optical Communications Research Laboratory (OCRL) of Stanford University. To implement the two logical subnetworks, we designed and implemented two different techniques: combined modulation and multichannel subcarrier multiplexing (MSCM). OCRL has already demonstrated several combined modulation techniques such as phase shift-keyed and amplitude shift-keyed (PSK/ASK), and differential phase shift-keyed and amplitude shift-keyed (DPSK/ASK), yielding combined ASK/DPSK modulation receiver sensitivities better than -32 dBm. OCRL has designed and implemented a high-speed high-performance packet-switched STARNET computer interface which enables high-throughput transfer to/from host computer, low latency switching, traffic prioritization, and capability of multicasting and broadcasting. With this interface board, OCRL has achieved average transmit and receive throughputs of 685 Mb/s and 571 Mb/s, respectively, out of the 800 Mb/s theoretical maximum of the host computer bus. The incurred packet latency due to the interface for a specified multihop network configuration has been simulated to be 24 /spl mu/s. Using simulation and experimental results, it is shown that STARNET is highly suitable for high-speed multimedia network applications.

On efficient spectrum utilization from the standpoint of communication theory

This paper reviews the concepts of spectrum efficiency, the parameters for assessing system performance, and the techniques for improving spectrum utilization. The rationale of possible bandwidth reduction and power savings by combined modulation techniques is discussed and special attention is given to combined amplitude and phase modulation (APSK) systems. It is believed, based on the available results of several analyses over additive Gaussian noise channels, that certain combined modulation systems can have significant power savings over single-parameter modulation systems when the number of bits per symbol of the signal is large and can achieve more efficient use of the spectrum for signal-to-noise ratios greater than certain levels.