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Mobile Communication Systems (mobile + communication_system)
Selected AbstractsElectromagnetic safety of children using wireless phones: A literature reviewBIOELECTROMAGNETICS, Issue S7 2005Luc Martens Abstract In this article, several issues related to the safety of electromagnetic field exposure of children when using wireless devices such as mobile phones are described. The information available in the literature is reviewed and open areas that need to be subject of future research are identified. A lack of proof that dielectric properties change with age and an inconsistency in absorption studies in children is reported. The number of biological studies relevant to children is limited. Only some of the cognitive studies specifically target children and these show no significant effect of exposure. There is also a need to investigate the impact of electromagnetic fields on the developmental process of children. All this makes a definitive answer to the question if children are more sensitive to electromagnetic fields than adults impossible. More consistent research will be needed. This study is part of the European COST281 project "Potential Health Implications from Mobile Communication Systems." Bioelectromagnetics Supplement 7:S133,S137, 2005. © 2005 Wiley-Liss, Inc. [source] A simple approach for optimum channel reservation for hand-over calls in cellular systemsINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 4 2006Mohamed Laith In cellular mobile communication systems, while an active subscriber is moving from one cell to another, the service of his call needs to be handed over to the base station of the new cell. In such a case, cutting the service, due to all channels being busy at the new base station, would be more annoying to subscribers than normal congestion at the first initiation of calls. This paper is concerned with providing a simple approach for choosing the optimum set of channels that need to be reserved for hand-over calls, while maintaining an acceptable overall system performance. The approach evaluates channel reservation at the cell level, taking into account the offered traffic, that is both the newly initiated original traffic and the hand-over traffic. The approach produces a simple mathematical solution based on Erlang-B formula. It uses the concept of ,Combined Failure Rate' to evaluate the required reservation. The approach is supported by a simulation study that verifies its validity. Applications of the approach to illustrate its use are also presented.,Copyright © 2006 John Wiley & Sons, Ltd. [source] Thermal analysis of multi-finger GaInP collector-up heterojunction bipolar transistors with miniature heat-dissipation packaging structuresINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2010Pei-Hsuan Lee Abstract We build up a finite element modeling (FEM) approach to analyze the thermal performance of collector-up (C-up) heterojunction bipolar transistor (HBTs) with a heat-dissipation via configuration. Highly compact heat-dissipation packaging structures of GaInP/GaAs C-up HBTs have been designed and evaluated systematically. In this work, we devise the 2-D and 3-D models to simulate the actual devices and to investigate the temperature distribution behavior. Results from 2-D model indicate that the large heat-dissipation via configuration can be further reduced by 29% to meet the requirement of HBT-based small high-power amplifiers (HPAs) for the cellular phones. Furthermore, the demonstrated results show that the maximum temperature within the collector calculated from 3-D model is lower than that from 2-D model. In the 3-D analysis, it is revealed that the configuration can be reduced by 32%. Therefore, thinning the heat-dissipation via constructed underneath the GaInP/GaAs C-up HBT should be helpful for miniaturization of HBT-based HPAs in future mobile communication systems. Copyright © 2009 John Wiley & Sons, Ltd. [source] Stability analysis of an adaptive packet access scheme for mobile communication systems with high propagation delaysINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2003Giovanni Giambene Abstract In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time-Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot-code resource. This protocol is named Adaptive Time Code-Packet Reservation Multiple Access (ATC-PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)- Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High-Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC-PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC-PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd. [source] A compact inverted double-L antennaMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2006Zhiming Zhuang Abstract A compact inverted double-L antenna (CDLA) fed by a microstrip line and operating at 2.45 GHz is presented in this paper. The linearly polarized CDLA can be constructed using conducting wires mounted on a small PCB board. This antenna maintains a simple structure, low profile, and compact size, which can be very useful for mobile communication systems such as Bluetooth and radio frequency identification (RFID) applications. Simulated and measured results are provided and good agreement between them is observed. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 968,969, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21535 [source] Generic UMTS test signal for RF bioelectromagnetic studiesBIOELECTROMAGNETICS, Issue 6 2004H. Ndoumbč Mbonjo Mbonjo Abstract This report outlines the characteristics of universal mobile telecommunications system (UMTS) signals and discusses the signal parameters with respect to their possible biological relevance in order to define a generic UMTS test signal (GUS) for experiments aiming at the investigation of biological effects of weak electromagnetic fields. The GUS includes features of a real UMTS signal and especially the characteristics of UMTS, which differ from those of already applied second generation mobile communication systems (GSM 900, DCS1800, PCS1900, IS-95). It has been specified on the basis of the recommendations of a working group of the German Forschungsgemeinschaft Funk (FGF) with a focus on the mechanisms of UMTS which are responsible for slow term signal contributions, i.e., low frequency variations of the radio frequency (RF) envelope, since the hypothetical possibility of biological relevance of weak electromagnetic fields is often attributed to time variations of the RF envelope with frequencies close to those of natural processes. In this respect, it is also shown that the mandatory power control loop in UMTS gives rise to very strong 1.5 kHz variations on the air interface. Based upon the concept of the GUS, a UMTS test signal generator (GUS6960S) is described. Bioelectromagnetics 25:415,425, 2004. © 2004 Wiley-Liss, Inc. [source] Cytogenetic damage in human lymphocytes following GMSK phase modulated microwave exposureBIOELECTROMAGNETICS, Issue 1 2002Guglielmo d'Ambrosio Abstract The present study investigated, using in vitro experiments on human lymphocytes, whether exposure to a microwave frequency used for mobile communication, either unmodulated or in presence of phase only modulation, can cause modification of cell proliferation kinetics and/or genotoxic effects, by evaluating the cytokinesis block proliferation index and the micronucleus frequency. In the GSM 1800 mobile communication systems the field is both phase (Gaussian minimum shift keying, GMSK) and amplitude (time domain multiple access, TDMA) modulated. The present study investigated only the effects of phase modulation, and no amplitude modulation was applied. Human peripheral blood cultures were exposed to 1.748 GHz, either continuous wave (CW) or phase only modulated wave (GMSK), for 15 min. The maximum specific absorption rate (,5 W/kg) was higher than that occurring in the head of mobile phone users; however, no changes were found in cell proliferation kinetics after exposure to either CW or GMSK fields. As far as genotoxicity is concerned, the micronucleus frequency result was not affected by CW exposure; however, a statistically significant micronucleus effect was found following exposure to phase modulated field. These results would suggest a genotoxic power of the phase modulation per se. Bioelectromagnetics 23:7,13, 2002. © 2002 Wiley-Liss, Inc. [source] | ||||||||||