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Base Stations (base + stations)
Selected AbstractsDS/CDMA throughput of a multi-hop sensor network in a Rayleigh fading underwater acoustic channelCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 8 2007Choong Hock Mar Abstract Asynchronous half-duplex Direct-Sequence Code-Division Multiple-Access (DS/CDMA) is a suitable candidate for the MAC protocol design of underwater acoustic (UWA) sensor networks owing to its many attractive features. Our ad-hoc multi-hop network is infrastructureless in that it is without centralized base stations or power control. Hence, we develop an asynchronous distributed half-duplex control protocol to regulate between the transmitting and receiving phases of transmissions. Furthermore, multi-hop communications are very sensitive to the time variability of the received signal strength in the fading channel and the ambient noise dominated by snapping shrimp in harsh underwater environments, because a broken link in the multi-hop path is enough to disrupt communications and initiate new route searches. In our configuration, we use the Ad hoc On-demand Distance Vector (AODV) routing protocol optimized for UWA networks. Empirical studies show that we can model the channel as a slow-varying frequency non-selective Rayleigh fading channel. We theoretically analyze the throughput of our configuration by considering three salient features: the ability of the receiver to demodulate the data, the effect of our control protocol and the effect of disconnections on the generation of routing packets. The throughput under various operating conditions is then examined. It is observed that at optimal node separation, the throughput is improved by a factor of 10. Copyright © 2007 John Wiley & Sons, Ltd. [source] Inter-cell coordination in wireless data networksEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2006Thomas Bonald Over the past few years, the design and performance of channel-aware scheduling strategies have attracted huge interest. In the present paper, we examine a somewhat different notion of scheduling, namely coordination of transmissions among base stations, which has received little attention so far. The inter-cell coordination comprises two key elements: (i) interference avoidance and (ii) load balancing. The interference avoidance involves coordinating the activity phases of interfering base stations so as to increase transmission rates. The load balancing aims at diverting traffic from heavily loaded cells to lightly loaded cells. Numerical experiments demonstrate that inter-cell scheduling may provide significant capacity gains. Copyright © 2006 AEIT [source] Exploiting the short,term and long,term channel properties in space and time: Eigenbeamforming concepts for the BS in WCDMAEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2001Christopher Brunner The deployment of adaptive antennas at base stations considerably increases the spectral efficiency of wireless communication systems. To reduce the computational complexity and increase performance of space,time (ST) processing, processing may take place in reduced dimension, i. e., pre,filtering takes place which is related to linear estimation theory based on second order statistics. To this end, long,term and short,term channel estimates are integrated into specific Tx/Rx systems. In this article, we present a new ST rake structure for uplink reception in WCDMA which operates in reduced dimension. Accordingly, our approach combines short,term and long,term spatial and temporal channel properties using an eigenanalysis. By choosing dominant eigenbeams in time and space, the algorithm enhances interference suppression as well as spatial and temporal receive diversity. In contrast to previously introduced well,known receiver structures, the ST eigenrake inherently adapts to different propagation environments and achieves higher spectral efficiency than other receivers. This is illustrated by Monte,Carlo simulations. Then we extend the proposed concept to the downlink. The downlink eigenbeamformer improves closed,loop downlink diversity compared to other proposals in standardization (3GPP) which only exploit short,term channel properties. Even though the short,term feedback rate remains unchanged, additional antenna elements can be included to increase antenna and diversity gain. We also present a tracking solution to the downlink eigenbeamforming in WCDMA. To this end, we propose a distributed implementation of the eigenspace/,beam tracking at the mobile terminal and base station (BS), respectively. Moreover, the specific nature of the deployed tracking scheme offers an advantageous feedback signalling. [source] WTCP: an efficient mechanism for improving wireless access to TCP servicesINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2003Karunaharan Ratnam Abstract The transmission control protocol (TCP) has been mainly designed assuming a relatively reliable wireline network. It is known to perform poorly in the presence of wireless links because of its basic assumption that any loss of a data segment is due to congestion and consequently it invokes congestion control measures. However, on wireless access links, a large number of segment losses will occur more often because of wireless link errors or host mobility. For this reason, many proposals have recently appeared to improve TCP performance in such environment. They usually rely on the wireless access points (base stations) to locally retransmit the data in order to hide wireless losses from TCP. In this paper, we present Wireless-TCP (WTCP), a new mechanism for improving wireless access to TCP services. We use extensive simulations to evaluate TCP performance in the presence of congestion and wireless losses when the base station employs WTCP, and the well-known Snoop proposal (A comparison of mechanisms for improving TCP performance in wireless networks. In ACM SIGCOMM Symposium on Communication, Architectures and Protocols, August 1996). Our results show that WTCP significantly improves the throughput of TCP connections due to its unique feature of hiding the time spent by the base station to locally recover from wireless link errors so that TCPs round trip time estimation at the source is not affected. This proved to be critical since otherwise the ability of the source to effectively detect congestion in the fixed wireline network is hindered. Copyright © 2003 John Wiley & Sons, Ltd. [source] Virtual base stations for wireless mobile ad hoc communications: an infrastructure for the infrastructure-lessINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2001Hossam Hassanein Abstract In this paper, we propose a new protocol for wireless mobile ad hoc networks, which establishes a dynamic wireless mobile infrastructure. The proposed protocol, namely, the virtual base stations (VBS) protocol, mimics and maintains the operation of the conventional fixed infrastructure in cellular networks. In the VBS protocol, a mobile node is elected from a set of nominees to act as a temporary base station within its zone. We provide proofs for the correctness of the VBS protocol, and show lower and upper bounds for its global convergence time. Likewise, we study the characteristics and performance of VBS by means of simulation. It is shown that VBS scales well to large networks of mobile stations, and that it outperforms other infrastructure-formation protocols in terms of stability. The VBS protocol would facilitate the development of a comprehensive and promising framework for quality of service (QoS) management in wireless mobile ad hoc networks once the proper integration of the MAC protocol with the routing and call admission control mechanisms is established. The VBS architecture lays the groundwork for assigning bandwidth, and/or implementing priorities, and hence for QoS-based routing by conveying the quality of a path prior to call setup. Copyright © 2001 John Wiley & Sons, Ltd. [source] The EMF uncertainty problem related to mobile phones: where do consumers place their trust?INTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 2 2010Lisbet Berg Abstract This paper addresses the uncertainty problem, i.e. cases characterized by lack of knowledge or scientific uncertainty. In such situations, it can be hard for consumers to ,voice' or practise consumer power. One field characterized by the uncertainty problem is electromagnetic radiation. An explicit goal of this study has been to articulate Norwegian consumers' practices, attitudes and beliefs regarding electromagnetic radiation from mobile phones to public authorities and consumer policy makers. The study was based on 1000 telephone interviews collected in 2008. Today, experts disagree on the potential health effects of radiation from electromagnetic fields (EMF), as well as standards for safe limits of exposure to mobile phones, base stations and wireless telecommunication systems. In addition, complicated technology and extremely rapid product development and diffusion leave consumers' security considerations to their own beliefs and trust. Whether or not electromagnetic radiation from mobile phones constitutes a health hazard will not be addressed in this paper. Rather, it will focus on how consumers react to this situation of uncertainty. The material reveals four main ways in which consumers can solve what we have named the EMF uncertainty problem: the confident and comfortable way, the sceptical and cautious way, the responsible and good citizen way, and finally, the neglecting way. The paper also discusses the precautionary principle related to EMF. Who should be precautionary: the public authorities, the mobile phone industry or the consumers themselves? We believe that a consistent governmental precautionary policy in combination with consumers taking their own precautionary measures is a viable solution. In this way, all consumers would be addressed and aided when navigating this field of uncertainty. [source] Pre-handover signalling for QoS aware mobility managementINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 6 2004Hakima Chaouchi In this paper we present a new approach to provide fast handover in Mobile IP. A new Pre-Handover Signalling (PHS) protocol is proposed to allow the network to achieve accurate handover decisions considering different constraints such as QoS, load balancing in the base stations, the user profile, the mobile node service requirements, etc. In addition we propose to minimize the time discovery of the new base station in order to minimize the handover latency. We propose to start the PHS as soon as the mobile node crosses a predefined critical zone area in its current location, this signalling will provide a list of candidate cells to the mobile node with corresponding priorities; the mobile node will select the highest priority base station as soon as the layer two handover occurs. We propose in the current work to use an extension of COPS (Common Open Policy Service) to support the proposed PHS mechanism and overcome the blind handover decisions of Mobile IP and improve the handover performance.,Copyright © 2004 John Wiley & Sons, Ltd. [source] The STRokE DOC trial technique: ,video clip, drip, and/or ship'INTERNATIONAL JOURNAL OF STROKE, Issue 4 2007B. C. Meyer Rationale To describe the clinical trial methods of a site-independent telemedicine system used in stroke. Aims A lack of readily available stroke expertise may partly explain the low rate of rt-PA use in acute stroke. Although telemedicine systems can reliably augment expertise available to rural settings, and may increase rt-PA use, point-to-point systems do require fixed base stations. Site-independent systems may minimize delay. The STRokE DOC trial assesses whether site-independent telemedicine effectively and efficiently brings rt-PA to a remote population. Design STRokE DOC is a 5-year, 400-participant, noninvasive trial, comparing two consultative techniques at four remote sites. Participants are randomized to acute ,STRokE DOC telemedicine' or ,telephone' consultations. Treatment decision accuracy is adjudicated at two time points, using three levels of data availability and an independent auditor. Study outcomes The primary outcome measure is whether there was a ,correct decision to treat or not to treat using rt-PA' at each of three adjudication levels (primarily at Level #2). Secondary outcomes include the number of thrombolytic recommendations, intracerebral hemorrhage, and 90-day outcomes. Using the STRokE DOC system (or telephone evaluation), medical history, neurologic scales, CT interpretations, and recommendations have been completed on over 200 participants to date. Of the initial 11, nonrandomized, ,run-in' patients, six (65%) were evaluated wirelessly, and five (45%) were evaluated with a site-independent LAN or cable modem. Three (27%) received rt-PA. The adjudication methodology was able to show both agreements and disagreements in these 11 cases. It is feasible to perform site-independent stroke consultations, and adjudicate those cases, using the STRokE DOC system and trial design. Telemedicine efficacy remains to be proven. [source] Improving the radiation characteristics of a base station antenna array using a particle swarm optimizerMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2007Z. D. Zaharis Abstract A particle swarm optimization based technique is applied on linear antenna arrays used by broadcasting base stations. Both the geometry and the excitation of the antenna array are optimized by a suitable algorithm under the constraints of the maximum possible gain at the desired direction and the desired value of side lobe level. The matching condition of the elements of the antenna array is also required by the algorithm. The technique has been applied to antenna arrays composed of collinear wire dipoles and seems to be very promising for improving radiation patterns of base station antenna arrays in many practical applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1690,1698, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22505 [source] Microstrip antennas for cellular and wireless communication systemsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2002obodzian Abstract The Letter describes problems related to use of microstrip antennas in cellular and wireless telecommunications systems. Because of the unique properties, microstrip technology is nowadays often used to manufacture small internal antennas for portable terminals as well as antenna arrays for base stations. It also seems to be a very promising technology for multisystem antennas, for which there is an ever-growing demand. The Letter also presents a short overview of currently available solutions and ones under development by the authors, along with some key problems related to their design. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 380,384, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10468 [source] A nested benders decomposition approach for telecommunication network planningNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2010Joe Naoum-Sawaya Abstract Despite its ability to result in more effective network plans, the telecommunication network planning problem with signal-to-interference ratio constraints gained less attention than the power-based one because of its complexity. In this article, we provide an exact solution method for this class of problems that combines combinatorial Benders decomposition, classical Benders decomposition, and valid cuts in a nested way. Combinatorial Benders decomposition is first applied, leading to a binary master problem and a mixed integer subproblem. The subproblem is then decomposed using classical Benders decomposition. The algorithm is enhanced using valid cuts that are generated at the classical Benders subproblem and are added to the combinatorial Benders master problem. The valid cuts proved efficient in reducing the number of times the combinatorial Benders master problem is solved and in reducing the overall computational time. More than 120 instances of the W-CDMA network planning problem ranging from 20 demand points and 10 base stations to 140 demand points and 30 base stations are solved to optimality. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Do mobile phone base stations affect sleep of residents?AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2010Results from an experimental double-blind sham-controlled field study Objectives: The aim of the present double-blind, sham-controlled, balanced randomized cross-over study was to disentangle effects of electromagnetic fields (EMF) and non-EMF effects of mobile phone base stations on objective and subjective sleep quality. Methods: In total 397 residents aged 18,81 years (50.9% female) from 10 German sites, where no mobile phone service was available, were exposed to sham and GSM (Global System for Mobile Communications, 900 MHz and 1,800 MHz) base station signals by an experimental base station while their sleep was monitored at their homes during 12 nights. Participants were randomly exposed to real (GSM) or sham exposure for five nights each. Individual measurement of EMF exposure, questionnaires on sleep disorders, overall sleep quality, attitude towards mobile communication, and on subjective sleep quality (morning and evening protocols) as well as objective sleep data (frontal EEG and EOG recordings) were gathered. Results: Analysis of the subjective and objective sleep data did not reveal any significant differences between the real and sham condition. During sham exposure nights, objective and subjective sleep efficiency, wake after sleep onset, and subjective sleep latency were significantly worse in participants with concerns about possible health risks resulting from base stations than in participants who were not concerned. Conclusions: The study did not provide any evidence for short-term physiological effects of EMF emitted by mobile phone base stations on objective and subjective sleep quality. However, the results indicate that mobile phone base stations as such (not the electromagnetic fields) may have a significant negative impact on sleep quality. Am. J. Hum. Biol. 22:613,618, 2010. © 2010 Wiley-Liss, Inc. [source] GaN/AlGaN HEMT hybrid and MMIC microstrip power amplifiers on s.i. SiC substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006R. Quay Abstract This work presents very recent examples for the realization of high-power amplifiers for both communication and solid-state radar applications based on AlGaN/GaN HEMTs on s.i. SiC substrate. Broadband power amplifiers for mobile communication base stations between 0.9 and 2.7 GHz are presented. Microstrip line X-frequency band power amplifiers provide pulsed output power levels of 10 W with 16 dB of gain at 9 GHz. This work further shows improved device reliability results at VDS = 30 V and 200 °C channel temperature for gate lengths of 300 nm. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Enhancement of throughput and fairness in 4G wireless access systems by non-orthogonal signalingBELL LABS TECHNICAL JOURNAL, Issue 4 2009Joerg Schaepperle Besides having significantly enhanced throughput, fourth generation (4G) cellular wireless access systems are expected to be cost efficient and provide sufficient performance even at the cell edge. This paper proposes a new method, called radial space-division multiple access (RDMA) for improving the system's spectral efficiency significantly and providing fairness among users without increasing the number of antennas and without requiring fast backbone communication and synchronization between base stations. The basic idea is to approach the capacity of the multi-user channel under fairness constraints by exploiting not only the angular dimension of space, as in space-division multiple access (SDMA), but also the radial dimension. Non-orthogonal signaling for simultaneous transmission of multiple signals over the same radio resource and joint detection in the receiver are used. Significant throughput gains are achieved with low complexity methods requiring only long term channel statistics and no instantaneous channel state information at the transmitter. Detailed link and first simple systemlevel simulation results in the context of the evolution of IEEE 802.16/Worldwide Interoperability for Microwave Access (WiMAX) systems towards 802.16m show that system throughput can be doubled without requiring more advanced analog hardware or increasing bandwidth or transmit power. © 2009 Alcatel-Lucent. [source] Effects of short-term W-CDMA mobile phone base station exposure on women with or without mobile phone related symptomsBIOELECTROMAGNETICS, Issue 2 2009Toshiaki Furubayashi Abstract To investigate possible health effects of mobile phone use, we conducted a double-blind, cross-over provocation study to confirm whether subjects with mobile phone related symptoms (MPRS) are more susceptible than control subjects to the effect of electromagnetic fields (EMF) emitted from base stations. We sent questionnaires to 5,000 women and obtained 2,472 valid responses from possible candidates; from these, we recruited 11 subjects with MPRS and 43 controls. There were four EMF exposure conditions, each of which lasted 30 min: continuous, intermittent, and sham exposure with and without noise. Subjects were exposed to EMF of 2.14 GHz, 10 V/m (W-CDMA), in a shielded room to simulate whole-body exposure to EMF from base stations, although the exposure strength we used was higher than that commonly received from base stations. We measured several psychological and cognitive parameters pre- and post-exposure, and monitored autonomic functions. Subjects were asked to report on their perception of EMF and level of discomfort during the experiment. The MPRS group did not differ from the controls in their ability to detect exposure to EMF; nevertheless they consistently experienced more discomfort, regardless of whether or not they were actually exposed to EMF, and despite the lack of significant changes in their autonomic functions. Thus, the two groups did not differ in their responses to real or sham EMF exposure according to any psychological, cognitive or autonomic assessment. In conclusion, we found no evidence of any causal link between hypersensitivity symptoms and exposure to EMF from base stations. Bioelectromagnetics 30:100,113, 2009. © 2008 Wiley-Liss, Inc. [source] GSM base stations: Short-term effects on well-being,BIOELECTROMAGNETICS, Issue 1 2009Christoph Augner Abstract The purpose of this study was to examine the effects of short-term GSM (Global System for Mobile Communications) cellular phone base station RF-EMF (radiofrequency electromagnetic fields) exposure on psychological symptoms (good mood, alertness, calmness) as measured by a standardized well-being questionnaire. Fifty-seven participants were selected and randomly assigned to one of three different exposure scenarios. Each of those scenarios subjected participants to five 50-min exposure sessions, with only the first four relevant for the study of psychological symptoms. Three exposure levels were created by shielding devices in a field laboratory, which could be installed or removed during the breaks between sessions such that double-blinded conditions prevailed. The overall median power flux densities were 5.2 µW/m2 during "low," 153.6 µW/m2 during "medium," and 2126.8 µW/m2 during "high" exposure sessions. For scenario HM and MH, the first and third sessions were "low" exposure. The second session was "high" and the fourth was "medium" in scenario HM; and vice versa for scenario MH. Scenario LL had four successive "low" exposure sessions constituting the reference condition. Participants in scenarios HM and MH (high and medium exposure) were significantly calmer during those sessions than participants in scenario LL (low exposure throughout) (P,=,0.042). However, no significant differences between exposure scenarios in the "good mood" or "alertness" factors were obtained. We conclude that short-term exposure to GSM base station signals may have an impact on well-being by reducing psychological arousal. Bioelectromagnetics 30:73,80, 2009. © 2008 Wiley-Liss, Inc. [source] Cognitive function and symptoms in adults and adolescents in relation to rf radiation from UMTS base stationsBIOELECTROMAGNETICS, Issue 4 2008Ingunn S. Riddervold Abstract There is widespread public concern about the potential adverse health effects of mobile phones in general and their associated base stations in particular. This study was designed to investigate the acute effects of radio frequency (RF) electromagnetic fields (EMF) emitted by the Universal Mobile Telecommunication System (UMTS) mobile phone base stations on human cognitive function and symptoms. Forty adolescents (15,16 years) and 40 adults (25,40 years) were exposed to four conditions: (1) sham, (2) a Continuous Wave (CW) at 2140 MHz, (3) a signal at 2140 MHz modulated as UMTS and (4) UMTS at 2140 MHz including all control features in a randomized, double blinded cross-over design. Each exposure lasted 45 min. During exposure the participants performed different cognitive tasks with the Trail Making B (TMB) test as the main outcome and completed a questionnaire measuring self reported subjective symptoms. No statistically significant differences between the UMTS and sham conditions were found for performance on TMB. For the adults, the estimated difference between UMTS and sham was ,3.2% (,9.2%; 2.9%) and for the adolescents 5.5% (,1.1%; 12.2%). No significant changes were found in any of the cognitive tasks. An increase in ,headache rating' was observed when data from the adolescents and adults were combined (P,=,0.027), an effect that may be due to differences at baseline. In conclusion, the primary hypothesis that UMTS radiation reduces general performance in the TMB test was not confirmed. However, we suggest that the hypothesis of subjective symptoms and EMF exposure needs further research. Bioelectromagnetics 29:257,267, 2008. © 2007 Wiley-Liss, Inc. [source] Mobile phone base station-emitted radiation does not induce phosphorylation of Hsp27BIOELECTROMAGNETICS, Issue 2 2007H. Hirose Abstract An in vitro study focusing on the effects of low-level radiofrequency (RF) fields from mobile radio base stations employing the International Mobile Telecommunication 2000 (IMT-2000) cellular system was conducted to test the hypothesis that modulated RF fields act to induce phosphorylation and overexpression of heat shock protein hsp27. First, we evaluated the responses of human cells to microwave exposure at a specific absorption rate (SAR) of 80 mW/kg, which corresponds to the limit of the average whole-body SAR for general public exposure defined as a basic restriction in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. Second, we investigated whether continuous wave (CW) and Wideband Code Division Multiple Access (W-CDMA) modulated signal RF fields at 2.1425 GHz induced activation or gene expression of hsp27 and other heat shock proteins (hsps). Human glioblastoma A172 cells were exposed to W-CDMA radiation at SARs of 80 and 800 mW/kg for 2,48 h, and CW radiation at 80 mW/kg for 24 h. Human IMR-90 fibroblasts from fetal lungs were exposed to W-CDMA at 80 and 800 mW/kg for 2 or 28 h, and CW at 80 mW/kg for 28 h. Under the RF field exposure conditions described above, no significant differences in the expression levels of phosphorylated hsp27 at serine 82 (hsp27[pS82]) were observed between the test groups exposed to W-CDMA or CW signal and the sham-exposed negative controls, as evaluated immediately after the exposure periods by bead-based multiplex assays. Moreover, no noticeable differences in the gene expression of hsps were observed between the test groups and the negative controls by DNA Chip analysis. Our results confirm that exposure to low-level RF field up to 800 mW/kg does not induce phosphorylation of hsp27 or expression of hsp gene family. Bioelectromagnetics © 2006 Wiley-Liss, Inc. [source] | |||||||||||||||||||