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Communication Systems (communication + system)
Kinds of Communication Systems Terms modified by Communication Systems Selected AbstractsMASKING INTERFERENCE AND THE EVOLUTION OF THE ACOUSTIC COMMUNICATION SYSTEM IN THE AMAZONIAN DENDROBATID FROG ALLOBATES FEMORALISEVOLUTION, Issue 9 2006Adolfo Amézquita Abstract The efficacy of communication relies on detection of species-specific signals against the background noise. Features affecting signal detection are thus expected to evolve under selective pressures represented by masking noise. Spectral partitioning between the auditory signals of co-occurring species has been interpreted as the outcome of the selective effects of masking interference. However, masking interference depends not only on signal's frequency but on receiver's range of frequency sensitivity; moreover, selection on signal frequency can be confounded by selection on body size, because these traits are often correlated. To know whether geographic variation in communication traits agrees with predictions about masking interference effects, we tested the hypothesis that variation in the male-male communication system of the Amazonian frog, Allobates femoralis, is correlated with the occurrence of a single species calling within an overlapping frequency range, Epipedobates trivittatus. We studied frogs at eight sites, four where both species co-occur and four where A. femoralis occurs but E. trivittatus does not. To study the sender component of the communication system of A. femoralis and to describe the use of the spectral range, we analyzed the signal's spectral features of all coactive species at each site. To study the receiver component, we derived frequency-response curves from playback experiments conducted on territorial males of A. femoralis under natural conditions. Most geographic variation in studied traits was correlated with either call frequency or with response frequency range. The occurrence of E. trivittatus significantly predicted narrower and asymmetric frequency-response curves in A. femoralis, without concomitant differences in the call or in body size. The number of acoustically coactive species did not significantly predict variation in any of the studied traits. Our results strongly support that the receiver but not the sender component of the communication system changed due to masking interference by a single species. [source] ADVERTISEMENT-CALL PREFERENCES IN DIPLOID-TETRAPLOID TREEFROGS (HYLA CHRYSOSCELIS AND HYLA VERSICOLOR): IMPLICATIONS FOR MATE CHOICE AND THE EVOLUTION OF COMMUNICATION SYSTEMSEVOLUTION, Issue 2 2005H. Carl Gerhardt Abstract Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. T o-alternative playback experiments using synthetic calls that differed in fine-scale temporal properties identified the receiver criteria in females of the treefrog Hyla chrysoscelis for comparison with female criteria in a cryptic tetraploid species (H. versicolor); detailed preference functions were also generated for both species based on natural patterns of variation in temporal properties. The species were similar in three respects: (1) pulses of constant frequency were as attractive as the frequency-modulated pulses typical of conspecific calls; (2) changes in preferences with temperature paralleled temperature-dependent changes in male calls; and (3) preference functions were unimodal, with weakly defined peaks estimated at values slightly higher than the estimated means in conspecific calls. There were also species differences: (1) preference function slopes were steeper in H. chrysoscelis than in H. versicolor; (2) preferences were more intensity independent in H. chrysoscelis than in H. versicolor; (3) a synergistic effect of differences in pulse rate and shape on preference strength occurred in H. versicolor but not in H. chrysoscelis; and (4) a preference for the pulse shape typical of conspecific calls was expressed at the species-typical pulse duration in H. versicolor but not in H. chrysoscelis. However, females of H. chrysoscelis did express a preference based on pulse shape when tested with longer-than-average pulses, suggesting a hypothesis that could account for some examples of nonparallel coevolution. Namely, preferences can be hidden or revealed depending on the direction of quantitative change in a signal property relative to the threshold for resolving differences in that property. The results of the experiments reported here also predict patterns of mate choice within and between contemporary populations. First, intraspecific mate choice in both species is expected to be strongly influenced by variation in temperature among calling males. Second, simultaneous differences in pulse rate and pulse shape are required for effective species discrimination by females of H. versicolor but not by females of H. chrysoscelis. Third, there is greater potential for sexual selection within populations and for discrimination against calls produced by males in other geographically remote populations in H. chrysoscelis than in H. versicolor. [source] Predictors and Effects of Training on an Online Health Education and Support System for Women with Breast CancerJOURNAL OF COMPUTER-MEDIATED COMMUNICATION, Issue 3 2010Helene McDowell Many breast cancer patients currently turn to Internet-based education and support to help them cope with their illness. This study explores the role of training in influencing how patients use a particular Interactive Cancer Communication System (ICCS) over time and also examines what pre-test characteristics predict which people are most likely to opt in or out of training in the first place. With use of pre-test survey and unobtrusive individual records of ICCS system use data (N = 216), nonparametric tests revealed that only having a later stage of cancer predicted whether or not patients participated in training. Results indicated that participating in training was a significant predictor of higher levels of using the CHESS system. In particular, the repeated measures analysis of covariance found the significant interaction as well as main effect of group (i.e., training vs. no training) and time (i.e., individual's CHESS usages at different times) in interactive and information CHESS services, suggesting that 1) the training group has a higher level of usage than the no training group, 2) both of the groups' usage decreased over time, and 3) these joint patterns hold over time. Practical guidelines for future ICCS campaign implementation are discussed. [source] A Comparative Analysis of Political Communication Systems and Voter TurnoutAMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 2 2009Mijeong Baek This article explores how political communication institutions affect cross-national differences in voter turnout in democratic elections. It demonstrates how the structure and means of conveying political messages,gauged by media systems, access to paid political television advertising, and campaign finance laws,explain variations in turnout across 74 countries. Relying on a "mobilization" perspective, I argue that institutional settings that reduce information costs for voters will increase turnout. The major empirical findings are twofold. First, campaign finance systems that allow more money (and electioneering communication) to enter election campaigns are associated with higher levels of voter turnout. Second, broadcasting systems and access to paid political television advertising explain cross-national variation in turnout, but their effects are more complex than initially expected. While public broadcasting clearly promotes higher levels of turnout, it also modifies the effect of paid advertising access on turnout. [source] Electromagnetic 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] An Experimental Study of the Emergence of Human Communication SystemsCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 5 2005Bruno Galantucci Abstract The emergence of human communication systems is typically investigated via 2 approaches with complementary strengths and weaknesses: naturalistic studies and computer simulations. This study was conducted with a method that combines these approaches. Pairs of participants played video games requiring communication. Members of a pair were physically separated but exchanged graphic signals through a medium that prevented the use of standard symbols (e.g., letters). Communication systems emerged and developed rapidly during the games, integrating the use of explicit signs with information implicitly available to players and silent behavior-coordinating procedures. The systems that emerged suggest 3 conclusions: (a) signs originate from different mappings; (b) sign systems develop parsimoniously; (c) sign forms are perceptually distinct, easy to produce, and tolerant to variations. [source] Carcinogenicity study of GSM and DCS wireless communication signals in B6C3F1 miceBIOELECTROMAGNETICS, Issue 3 2007Thomas Tillmann Abstract The purpose of this study using a total of 1170 B6C3F1 mice was to detect and evaluate possible carcinogenic effects in mice exposed to radio-frequency-radiation (RFR) from Global System for Mobile Communication (GSM) and Digital Personal Communications System (DCS) handsets as emitted by handsets operating in the center of the communication band, that is, at 902 MHz (GSM) and 1747 MHz (DCS). Restrained mice were exposed for 2 h per day, 5 days per week over a period of 2 years to three different whole-body averaged specific absorption rate (SAR) levels of 0.4, 1.3, 4.0 mW/g bw (SAR), or were sham exposed. Regarding the organ-related tumor incidence, pairwise Fisher's test did not show any significant increase in the incidence of any particular tumor type in the RF exposed groups as compared to the sham exposed group. Interestingly, while the incidences of hepatocellular carcinomas were similar in EMF and sham exposed groups, in both studies the incidences of liver adenomas in males decreased with increasing dose levels; the incidences in the high dose groups were statistically significantly different from those in the sham exposed groups. Comparison to published tumor rates in untreated mice revealed that the observed tumor rates were within the range of historical control data. In conclusion, the present study produced no evidence that the exposure of male and female B6C3F1 mice to wireless GSM and DCS radio frequency signals at a whole body absorption rate of up to 4.0 W/kg resulted in any adverse health effect or had any cumulative influence on the incidence or severity of neoplastic and non-neoplastic background lesions, and thus the study did not provide any evidence of RF possessing a carcinogenic potential. Bioelectromagnetics 28:173,187, 2007. © 2006 Wiley-Liss, Inc. [source] Critical Success Factors for Radical Technological Innovation: A Five Case StudyCREATIVITY AND INNOVATION MANAGEMENT, Issue 4 2000Pier A. Abetti We analyze the critical success factors for radical technological innovation according to four perspectives: as R&D projects, as technological innovations, as internal ventures, and as changes in corporate strategy. We apply ex-post eleven critical success factors to the pairwaise comparison of three radical innovations: GE Project EHV-UHV (success), GE non-impact printer (failure), and Xerox non-impact printer (success). We then apply ex-ante the same factors to "predict" the failure of Motorola's Iridium satellite communication system and the success of Nokia's cellular phones. [source] New ocular movement detector system as a communication tool in ventilator-assisted Werdnig-Hoffmann diseaseDEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 1 2000Masaya Kubota MD; A non-contact communication system was developed for a ventilator-assisted patient with Werdnig-Hoffmann disease who had lost all voluntary movements except for those of the eye. The system detects the extraocular movements and converts them to either a,yes'signal (produced by one lateral eyeball movement) or a,no'signal (produced by two successive lateral eyeball movements) using a video camera placed outside the patient's visual field. The patient is thus able to concentrate on performing a task without any intrusion from the detection system. Once the setting conditions of the device have been selected, there is no need for any resetting, as the patient is unable to move his body. In addition to playing television games, the child can use the device to select television channels, compose music, and learn written Japanese and Chinese characters. This seems to broaden the patient's daily world and promote mental development. [source] Effective Communication in Environmental ManagementENVIRONMENTAL QUALITY MANAGEMENT, Issue 1 2001Kevin J. Sobnosky Communication is the glue that holds together the elements of an environmental management system. This article offers some practical tips on how to ensure that your environmental communication system is doing the job you want it to. © 2001 John Wiley & Sons, Inc. [source] Naked Mole-Rat is Sensitive to Social Hierarchy Encoded in Antiphonal VocalizationETHOLOGY, Issue 9 2009Shigeto Yosida The maintenance of social relationships is critical for group-dwelling species. Social animals often exhibit behaviors such as antiphonal vocalizations that reduce conflict and maintain affiliations. Naked mole-rats (Heterocephalus glaber) have a complex hierarchical society comparable to that of bees and ants. They are also known for their extensive vocal repertoire, which may have evolved in the absence of visual cues. The most frequent vocalization used by naked mole-rats is the soft chirp (SC). It has an antiphonal nature and may function in rank identification and in maintaining affiliations. Relative body weight differences, which are directly related to social rank, are positively correlated with SC emission rates. SCs are elicited from either physical touch or the SC of another conspecific, and other cues might contribute to SC utterance. In the current study, we examined whether an SC alone was able to elicit SC responses. Specifically, we presented artificial SC-like sounds and determined whether the response rate was modulated by the acoustic properties of the stimulus. An analysis of response latency revealed that animals responded to the audio stimuli, and a single audio stimulus could elicit responses from two animals. Thus, antiphony in naked mole-rats may occur among three or more animals. We also found that animals were able to discriminate the acoustic properties of the stimulus and responded more frequently to audio stimuli resembling SCs from large animals than to those resembling SCs from small animals. Therefore, naked mole-rats may be able to judge social relationships (dominant or subordinate) based solely on SCs. The constraints of subterranean habitats and increased social complexity may have led to the evolution of this communication system. [source] Anti-Predator Signals as Advertisements: Evidence in White-Throated Magpie-JaysETHOLOGY, Issue 6 2009Jesse M. S. Ellis Calls and displays elicited by predators usually function as alarms or to inform predators of their detection. However, predator encounters may afford some individuals the opportunity to demonstrate quality or signal their availability. Here, I report on a class of vocal signals produced in predator-elicited displays that share many characteristics with sexually selected song. White-throated magpie-jays (Calocitta formosa) display at low-threat predators while producing ,loud display calls' (LDCs). I use this term because the calls occur primarily in two display contexts (see below) though occasionally in other contexts as well. Such calls and displays are primarily produced by males, and also occur in one other context, at dawn. Playback experiments showed that despite being elicited by predators, males were more likely than females to respond to LDCs, and more likely to respond when their mate was fertile. Over 134 different call types were produced in over 200 displays by 34 males; the largest minimum repertoire size was 67. Presentations of taxidermic raptor mounts elicited some LDCs, but fewer calls and lower diversity than at dawn or in predator approach displays. The male bias and high diversity suggest that LDCs are an outcome of intersexual selection, while their elicitation by predators suggests an alarm function. I propose that male magpie-jays use predator encounters as opportunities to advertise their presence and availability as mates; they use LDCs as songs. Such a communication system seems to have been favored by the unusual social system of magpie-jays, in which female groups defend territories and males have little opportunity to defend resources for mate attraction, forcing them to advertise when females are paying the most attention, during predator encounters. [source] Joint data detection and estimation of time-varying multipath rayleigh fading channels in asynchronous DS-CDMA systems with long spreading sequences,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2007Pei Xiao In this paper, we present a joint approach to data detection and channel estimation for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing orthogonal signaling formats and long scrambling codes. Our emphasis is placed on different channel estimation algorithms since the performance of a communication system depends largely on its ability to retrieve an accurate measurement of the underlying channel. We investigate channel estimation algorithms under different conditions. The estimated channel information is used to enable coherent data detection to combat the detrimental effect of the multiuser interference and the multipath propagation of the transmitted signal. In the considered multiuser detector, we mainly use interference cancellation techniques, which are suitable for long-code CDMA systems. Interference cancellation and channel estimation using soft estimates of the transmitted signal is also proposed in this paper. Different channel estimation schemes are evaluated and compared in terms of mean square error (MSE) of channel estimation and bit error rate (BER) performance. Based on our analysis and numerical results, some recommendations are made on how to choose appropriate channel estimators in practical systems. Copyright © 2006 AEIT [source] Graphical models for coded data transmission over inter-symbol interference channelsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2004Michael Tüchler We derive graphical models for coded data transmission over channels introducing inter-symbol interference. These models are factor graph descriptions of the transmitter section of the communication system, which serve at the same time as a framework to define the corresponding receiver. The graph structure governs the complexity and nature (e.g. non-iterative, iterative) of the receiver algorithm. A particular graph yields several algorithms optimizing various cost functions depending on the choice of messages communicated along the edges of the graph. We study these different outcomes of message passing and how the corresponding receiver algorithms are related to existing ones. We also devise strategies to find suitable graphs for communication problems of interest. Copyright © 2004 AEI [source] Experiences from the Implementation and Use of Multimedia Synchronization MechanismsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2000Theodoros H. Bozios This paper presents experiences from the implementation of Multimedia Synchronization Mechanisms related to the support of the many-to-one inter-media synchronization and describes the proposed Synchronization Architecture and its Design Objectives. The main goal of the communication system in the proposed architecture is to maintain the asynchrony levels between the media streams belonging in a Synchronization Group between the levels specitied by the Multimcdia Application. This is achieved through appropriate Synchronization Primitives related to the management and monitoring of the synchronization. The pilper emphasizes on the implementation issues and problems, and the solutions adopted. concluding to the lirst experiences from the use of the synchronization. [source] MASKING INTERFERENCE AND THE EVOLUTION OF THE ACOUSTIC COMMUNICATION SYSTEM IN THE AMAZONIAN DENDROBATID FROG ALLOBATES FEMORALISEVOLUTION, Issue 9 2006Adolfo Amézquita Abstract The efficacy of communication relies on detection of species-specific signals against the background noise. Features affecting signal detection are thus expected to evolve under selective pressures represented by masking noise. Spectral partitioning between the auditory signals of co-occurring species has been interpreted as the outcome of the selective effects of masking interference. However, masking interference depends not only on signal's frequency but on receiver's range of frequency sensitivity; moreover, selection on signal frequency can be confounded by selection on body size, because these traits are often correlated. To know whether geographic variation in communication traits agrees with predictions about masking interference effects, we tested the hypothesis that variation in the male-male communication system of the Amazonian frog, Allobates femoralis, is correlated with the occurrence of a single species calling within an overlapping frequency range, Epipedobates trivittatus. We studied frogs at eight sites, four where both species co-occur and four where A. femoralis occurs but E. trivittatus does not. To study the sender component of the communication system of A. femoralis and to describe the use of the spectral range, we analyzed the signal's spectral features of all coactive species at each site. To study the receiver component, we derived frequency-response curves from playback experiments conducted on territorial males of A. femoralis under natural conditions. Most geographic variation in studied traits was correlated with either call frequency or with response frequency range. The occurrence of E. trivittatus significantly predicted narrower and asymmetric frequency-response curves in A. femoralis, without concomitant differences in the call or in body size. The number of acoustically coactive species did not significantly predict variation in any of the studied traits. Our results strongly support that the receiver but not the sender component of the communication system changed due to masking interference by a single species. [source] Lymphotoxin and LIGHT signaling pathways and target genesIMMUNOLOGICAL REVIEWS, Issue 1 2004Kirsten Schneider Summary:, Lymphotoxins (LT, and LT,), LIGHT [homologous to LT, inducible expression, competes with herpes simplex virus (HSV) glycoprotein D for HSV entry mediator (HVEM), a receptor expressed on T lymphocytes], tumor necrosis factor (TNF), and their specific receptors LT,R, HVEM, and TNF receptor 1 (TNFR1) and TNFR2, form the immediate family of the larger TNF superfamily. These cytokines establish a critical communication system required for the development of secondary lymphoid tissues; however, knowledge of the target genes activated by these signaling pathways is limited. Target genes regulated by the LT,,-LT,R pathway include the tissue-organizing chemokines, CXCL13, CCL19, and CCL21, which establish cytokine circuits that regulate LT expression on lymphocytes, leading to organized lymphoid tissue. Infectious disease models have revealed that LT,, pathways are also important for innate and adaptive immune responses involved in host defense. Here, regulation of interferon-, by LT,R and TNFR signaling may play a crucial role in certain viral infections. Regulation of autoimmune regulator in the thymus via LT,R implicates LT/LIGHT involvement in central tolerance. Dysregulated expression of LIGHT overrides peripheral tolerance leading to T-cell-driven autoimmune disease. Blockade of TNF/LT/LIGHT pathways as an intervention in controlling autoimmune diseases is attractive, but such therapy may have risks. Thus, identifying and understanding the target genes may offer an opportunity to fine-tune inhibitory interventions. [source] Adaptive synchronization for nonlinear FitzHugh,Nagumo neurons in external electrical stimulationINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 9 2008Chung-Wen Lai Abstract This paper investigates the synchronization problem for FitzHugh,Nagumo (FHN) neurons in external electrical stimulations. Using the sliding mode control technique, an adaptive control law is established that guarantees synchronization even when the parameters of the master and slave FHN neurons are fully unknown. A proportional-integral switching surface is introduced to simplify the task of assigning the stability of the closed-loop error system in the sliding mode. Furthermore, the proposed synchronization scheme is then applied to a secure communication system. Computer simulations are provided to verify the effectiveness of the proposed adaptive synchronization scheme. Copyright © 2007 John Wiley & Sons, Ltd. [source] A utility-based capacity optimization framework for achieving cooperative diversity in the hierarchical converged heterogeneous wireless networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 12 2008Mugen Peng Abstract A hierarchical convergence mechanism for the heterogeneous wireless communication system via the heterogeneous cooperative relay node is presented in this paper, in which the techniques of cooperative communication and wireless relay are utilized to improve performances of the individual user and the overall converged networks. In order to evaluate the benefits of the proposal, a utility-based capacity optimization framework for achieving the heterogeneous cooperative diversity gain is proposed. The heterogeneous cooperative capacity, relay selection and power allocation theoretical models are derived individually. The joint optimization model for relay selection and power allocation is presented as well. Owing to the computation complexity, the sub-optimal cooperative relay selection algorithm, the sub-optimal power allocation algorithm and the sub-optimal joint algorithm are determined to approach the maximum overall networks' spectrum efficiency. These proposed algorithms are designed in conformance to guarantee the equivalent transmission rates of the different wireless access networks. The simulation results demonstrate that the utility-based capacity model is available for the heterogeneous cooperative wireless communication system, and the proposed algorithms can improve performances by achieving the cooperative gain and taking full advantage of the cross-layer design. Copyright © 2008 John Wiley & Sons, Ltd. [source] Closed-form expression for the BER of m-QAM-OFDM systems over time- and frequency-selective wireless channelsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2006F. Castells Abstract The broadcast DVB-T system is an m-QAM-OFDM communication system that includes pilot-symbol-assisted modulation (PSAM) in order to enhance channel estimation at the receiver. This characteristic makes DVB-T suitable for a mobile reception, over time- and frequency-selective wireless channels. In this work, a closed-form expression for the BER as a function of the transmission system, channel model and the channel estimation strategy employed at the receiver is derived. In addition, adjacent channel interference due to Doppler effects is also considered. The results are focused on the DVB-T system under different scenarios. The channel estimation at the receiver has been shown to be very critical, and the impact of channel estimation errors on the BER is analysed in detail. Copyright © 2005 John Wiley & Sons, Ltd. [source] Parallel combinatory multiple-subcarrier optical wireless communication systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2005Norio Kitamoto Abstract We analyse the performance of parallel combinatory multiple-subcarrier (PC-MS) optical wireless communication system. The PC-MS system can transmit more information at each symbol interval than conventional MS systems with the same subcarriers. In addition the PC-MS system can decrease the bias that must be added to the MS electrical signal, because the number of subcarriers other than null subcarriers is smaller than that in the conventional MS systems and thus the minimum power becomes larger. Therefore, the PC-MS system can decrease the required energy per bit. Copyright © 2005 John Wiley & Sons, Ltd. [source] Experimental studies of direction of arrivals using a smart antenna testbed in wireless communication systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2003Shiann-Shiun Jeng Abstract This paper presents some preliminary results from experimental studies on space-division-multiple-access (SDMA) for wireless communications. A smart antenna system utilizing direction-of-arrival (DOA)-based beamforming techniques can enhance signal quality by reducing co-channel interference from mobiles located at angles spatially distinct from the base station. Adopting both smart uplink and downlink beamforming, a communication system with an antenna array can increase the cell coverage of a base station and significantly boost capacity compared with conventional antenna systems. However, successful implementation of DOA-based beamforming techniques depends on the DOA characteristics. This paper presented the feasibility of direction finding and DOA variation with respect to frequency. Furthermore, the angle spread was studied for selected environments. The results demonstrate the feasibility of applying proposed smart antenna system utilizing DOA-based beamforming algorithm for increasing channel capacity and improving system performance in frequency-division-duplex (FDD) wireless communication systems. Copyright © 2003 John Wiley & Sons, Ltd. [source] Adaptive coding and modulation scheme for satellite-UMTS TDD systems based on a photogrammetric channel estimation methodINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 1 2006Hsin-Piao Lin Abstract The conventional wireless communication systems are designed to overcome the worst-case channel, using the huge amount of redundant bits to assure communications performance and quality of services. Those systems cannot achieve the optimum spectrum and power efficiency. This paper presents an adaptive coding and modulation scheme used in the user terminals of the third-generation satellite communication system. A three-state photogrammetric channel estimation method is introduced for tracing the variations of large-scale environments. The mobile user terminal dynamically switches the suitable coding and modulation schemes according to the result of photogrammetric channel estimator in order to maximize the power efficiency and data throughput. The real measurement data were used to validate our proposed method. The results show that the proposed method not only reduces the system complexity, but also mitigates the power control requirements and increases the data throughput for the land mobile satellite personal communication systems. Copyright © 2006 John Wiley & Sons, Ltd. [source] Short-scale diversity in a dynamic rain fade environmentINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2005Cristina Enjamio Abstract This article is concerned with using time-varying uniformly spaced rainfall data to investigate the concept and values of instantaneous diversity gain. This has been obtained on a minute-by-minute basis in order to illustrate the behaviour of a VSAT communication system which switches to the most reliable link every minute. The simulations have been carried out using a whole year of rain data obtained from the recordings of a dense rain gauge network located in Barcelona. After illustrating the concept of instantaneous diversity gain, this paper shows the results obtained for various site separations and 20 GHz. These results have been plotted together with the values given by some long-term-based models. The comparison shows that such models are not appropriate for dynamic site diversity. This was found to increase the reliability of a VSAT system, especially under severe rain conditions in which the rainfall rates are spatially arranged in rain cells and the attenuation experienced by the two sites is strongly decorrelated. The correlation coefficient between the attenuation series calculated for several separation distances has also been obtained to illustrate this concept. Finally, the paper gives the attenuation distributions calculated for a VSAT system with and without site diversity and for several site separations. Copyright © 2005 John Wiley & Sons, Ltd. [source] Multimedia satellite communications experiments to the international space stationINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 5 2002Carlo Matarasso Abstract In the present concept of the International Space Station ISS, it is planned to provide the communication services between the European Columbus module of the ISS and the ground equipment via the TDRS (tracking and data relay satellite) network provided by the American NASA (National Aeronautics and Space Agency). Especially because of its low uplink data rate, an unacceptable limitation of the communication services with Columbus is to be expected. In order to investigate possible improvements to this situation, the MEDIS proposal studies the feasibility of a 150 Mbps full duplex communication system to the Columbus Module on via two MEO satellites. A mixed topology with optical inter satellite links and Ka-band up/down-links shall be employed. Also possible liaisons with the Artemis mission will be considered. The MEDIS project is a collaboration of Astrium GmbH, which is project manager, Bosch SatCom, GMD-Fokus and the German Aerospace Center (DLR). The preparation phase of the project will investigate the concept of the communications infrastructure and the experiments that could be realized when the MEOs are launched. This stage has been completed in February 2001. An additional study phase followed, which will be completed with a presentation in July 2002. Briefly the following aspects have been studied by DLR in the preparation phase: the overall concept of experimental communication services for Columbus, the system requirements and network topology, the relevant protocol and hardware architectures, useful satellite constellations and link scenarios. Two phases could follow the preparation phase, in phase one the satellite will be launched and the link will be tested. In phase two the satellites will be connected to the ISS. Copyright © 2002 John Wiley & Sons, Ltd. [source] Performance evaluation of adaptive routing algorithms in packet-switched intersatellite link networksINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2002Mihael Mohor Abstract This paper addresses the performance evaluation of adaptive routing algorithms in non-geostationary packet-switched satellite communication systems. The dynamic topology of satellite networks and variable traffic load in satellite coverage areas, due to the motion of satellites in their orbit planes, pose stringent requirements to routing algorithms. We have limited the scope of our interest to routing in the intersatellite link (ISL) segment. In order to analyse the applicability of different routing algorithms used in terrestrial networks, and to evaluate the performance of new algorithms designed for satellite networks, we have built a simulation model of a satellite communication system with intersatellite links. In the paper, we present simulation results considering a network-uniform source/destination distribution model and a uniform source,destination traffic flow, thus showing the inherent routing characteristics of a selected Celestri-like LEO satellite constellation. The updates of the routing tables are centrally calculated according to the Dijkstra shortest path algorithm. Copyright © 2002 John Wiley & Sons, Ltd. [source] Potential of combined spaceborne infrared and microwave radiometry for near real-time rainfall attenuation monitoring along earth-satellite linksINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2001Frank S. Marzano Abstract The objective of this paper is to investigate how spaceborne remote sensors, and their derived products, can be exploited to optimize the performances of a satellite communication system in the presence of precipitating clouds along the path. The complementarity between sun-synchronous microwave (MW) and geo-stationary infrared (IR) radiometry for monitoring the earth's atmosphere is discussed and their potential as a rain detection system within near real-time countermeasure techniques for earth-satellite microwave links is analysed. A general approach, consisting in estimating rainfall intensity and attenuation by polar-orbiting microwave radiometers and temporally tracking the rainfall areas by geo-stationary infrared radiometers, is delineated. Multiple regression algorithms for predicting rainfall attenuation from spaceborne brightness temperatures and from surface rainrate, trained by radiative transfer and cloud models, are illustrated. A maximum likelihood technique is delineated to discriminate stratiform and convective rainfall from spaceborne brightness temperatures. The differences among attenuation estimates derived from layered raining-cloud structures with respect to those obtained from simple rain slabs, as recommended by ITU-R, are also quantified. A test of the proposed attenuation prediction methods is performed using raingage and Italsat data acquired in Spino d'Adda (Italy) during 1994. A description of the statistical method, based on the probability matching technique, adopted to combine MW and IR data for retrieving and tracking precipitating cloud systems in terms of path attenuation and accumulated rain at ground is finally provided together with its application to a case study over the Mediterranean area during October 1998. Copyright © 2001 John Wiley & Sons, Ltd. [source] Improving the coordination efficiency of limited-communication multi,autonomus underwater vehicle operations using a multiagent architectureJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 4 2010Christopher C. Sotzing This research addresses the problem of coordinating multiple autonomous underwater vehicle (AUV) operations. An intelligent mission executive has been created that uses multiagent technology to control and coordinate multiple AUVs in communication-deficient environments. By incorporating real-time vehicle prediction, blackboard-based hierarchical mission plans, mission optimization, and a distributed multiagent,based paradigm in conjunction with a simple broadcast communication system, this research aims to handle the limitations inherent in underwater operations, namely poor communication, and intelligently control multiple vehicles. In this research, efficiency is evaluated and then compared to the current state of the art in multiple AUV control. The research is then validated in real AUV coordination trials. Results will show that compared to the state of the art, the control system developed and implemented in this research coordinates multiple vehicles more efficiently and is able to function in a range of poor communication environments. These findings are supported by in-water validation trials with heterogeneous AUVs. © 2010 Wiley Periodicals, Inc. [source] Introduction of picture archiving and communication system at The Townsville HospitalJOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 4 2005PE Jackson Summary The performance of a medical imaging department (MID) can be judged by the timing and availability of an image and its report to the treating physician, as this can impact on the patient's treatment, as well as the length and cost of a patient's hospitalization. The use of digital imaging has dramatically improved report turnaround time. In October 2001, The Townsville Hospital (TTH) was opened as a 460 bed greenfield site and as part of the installation a picture archiving and communication system, including web distribution of images and reports to wards and clinics, was included. This retrospective analysis of the MID at TTH is the first data on departmental productivity and individual workload and how these have changed since the hospital's opening 2 years ago, with some ideas for further improvement. [source] Urinary chemosignals in giant pandas (Ailuropoda melanoleuca): seasonal and developmental effects on signal discriminationJOURNAL OF ZOOLOGY, Issue 3 2004A. M. White Abstract As a solitary species, giant pandas Ailuropoda melanoleuca have a chemical communication system that allows for avoidance with conspecifics throughout most of the year and facilitates breeding during their brief reproductive period. To date, most studies have focused on adults during the breeding season, but much remains to be learned about developmental and seasonal effects on chemical communication. Here, using odour discrimination methodology, we examine these contextual influences on chemosignalling in giant pandas for the first time. During the breeding season both adult and subadult giant pandas overtly discriminated conspecific sex using chemical cues in urine. Male urine was consistently investigated more than female urine by pandas across all age-sex categories. This preference for male urine was observed for both adult and subadult urine donors, indicating that adult levels of reproductive hormones are not necessary for the production of sex-specific urinary odour cues. By contrast, giant pandas did not overtly discriminate sex during the non-breeding season. This finding underscores that negative results for discrimination studies need to be interpreted with caution, as many contextual factors may influence overt expression of this ability. Evidence points to seasonal changes in motivation, rather than in the availability of sex-specific chemical cues in urine, as the causal factor for changing odour discrimination patterns. These and other findings are discussed in the light of the potential role that discrimination of odour plays in the regulation of competitive and reproductive interactions in nature. [source] | |||||||||||||||||||||||||