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RF Channels (rf + channel)
Selected AbstractsCapacity analysis for underlaying CDMA microcell/macrocell systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2001Jen-Kung Chung Abstract The CDMA system can provide more capacity than the conventional AMPS system and the hierarchical layer of cells is required for system design in the future. However, the problem is whether the same RF channels used in a CDMA underlaying macrocell/microcell structure also obtain high capacity as in the homogeneous structure. This paper investigates the interference of uplink and downlink from both the microcell and macrocell in a hierarchical structure. Downlink power control is also considered. The results show that the capacity of microcell in a hierarchical structure is 23 per cent less than in homogeneous cells. The capacity of macrocell in a hierarchical structure decreases dramatically in proportion to the number of microcells. The capacities of the microcell and macrocell are limited in downlink, and uplink, respectively. In addition, more efforts for microcell should be made, such as more power is transmitted by microcell basestation if the same RF channel is used in a hierarchical structure. The results suggest that different RF channels are used in a two-tier cellular environment. Copyright © 2001 John Wiley & Sons, Ltd. [source] High temporal resolution SSFP cine MRI for estimation of left ventricular diastolic parametersJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2010Ramkumar Krishnamurthy MS Abstract Purpose: To obtain high temporal resolution (HTR) magnetic resonance (MR) steady-state free-precession (SSFP) cine cardiac images by using multichannel radiofrequency (RF) hardware and parallel imaging techniques; to study the effect of temporal resolution; and to compare the derived left ventricular (LV) diastolic filling parameters with echocardiographic results. Materials and Methods: HTR images were acquired in 13 healthy volunteers using a 1.5 T scanner with 32 RF channels and sensitivity encoding (SENSE) and k-t broad-use linear-acquisition speedup technique (k-t BLAST) imaging techniques. LV diastolic parameters were calculated and compared to conventional echocardiographic indices such as the isovolumic relaxation time (IVRT) and E/A ratio. The need for HTR was assessed and the MR results were compared with echocardiographic results. Results: The HTR (,6-ms) images yielded higher peak filling rates, peak ejection rates, and peak atrial filling rates. A progressive decline in filling and ejection rates was observed with worsening temporal resolution. The IVRTs and E/A ratios measured with MR versus echocardiography were in broad agreement. Also, SENSE and k-t BLAST yielded similar diastolic functional parameters. Conclusion: With SENSE or k-t BLAST and modern hardware, HTR cine images can be obtained. The lower temporal resolutions (30,50 ms) used in clinical practice reduce LV filling rates by ,30% and may hinder characterization of transient phenomena such as the IVRT. J. Magn. Reson. Imaging 2010;31:872,880. ©2010 Wiley-Liss, Inc. [source] CNR enhancement using Mach Zehnder filter (MZF) with tunable phase shifter in a digital/RF optical-transmission linkMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2005Sang-Hoon Lee Abstract We experimentally demonstrate a digital/RF WDM-link system, which transmits a 1.25-Gb/s digital data stream and 1.8-GHz RF signals over a single-mode fiber, and simultaneously detect the signals using a single photodiode. We propose a novel suppression scheme employing a Mach,Zehnder filter (MZF) to improve the CNR of the RF signal for the case where the digital and RF channels are located close to each other. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 531,533, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20870 [source] | ||||||||||