| 1. |
- Dediu, V., et al.
(författare)
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Room-temperature spintronic effects in Alq3 -based hybrid devices
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:11
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Tidskriftsartikel (refereegranskat)abstract
- We report on efficient spin polarized injection and transport in long (102 nm) channels of Alq3 organic semiconductor. We employ vertical spin valve devices with a direct interface between the bottom manganite electrode and Alq3, while the top-electrode geometry consists of an insulating tunnel barrier placed between the "soft" organic semiconductor and the top Co electrode. This solution reduces the ubiquitous problem of the so-called ill-defined layer caused by metal penetration, which extends into the organic layer up to distances of about 50-100 nm and prevents the realization of devices with well-defined geometry. For our devices the thickness is defined with an accuracy of about 2.5 nm, which is near the Alq3 molecular size. We demonstrate efficient spin injection at both interfaces in devices with 100- and 200-nm-thick channels. We solve one of the most controversial problems of organic spintronics: the temperature limitations for spin transport in Alq3 -based devices. We clarify this issue by achieving room-temperature spin valve operation through the improvement of spin injection properties of both ferromagnetic/ Alq3 interfaces. In addition, we discuss the nature of the inverse sign of the spin valve effect in such devices proposing a mechanism for spin transport. © 2008 The American Physical Society.
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| 2. |
- Di Paolo, L., et al.
(författare)
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Performance analysis of distributed source coding and packet aggregation in wireless sensor networks
- 2006
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Ingår i: GLOBECOM - IEEE Global Telecommunications Conference. - 9781424403578 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a theoretical setup for evaluation of energy efficiency of wireless sensor networks (WSNs) with distributed source coding (DSC) algorithms and packet aggregation (PA). We consider four topologies for DSC and three alternatives for PA, and the system model includes a realistic network architecture with multi-hop communication, automatic repeat request protocol (ARQ), and packet losses. The analysis is carried out in two steps. Firstly we derive the packet loss probability, and then evaluate the average number of packets transmitted throughout the network. This second performance index can then be mapped onto an energy efficiency indicator. The proposed model is specifically adopted for performance comparison of the different coding strategies and aggregation schemes in terms of energy efficiency. Numerical results show that packet overheads have a relevant influence on performance, while the ARQ protocol introduces negligible effects on the energy consumption. Furthermore, DSC topologies with masterslave approach and fragmentation of packets exhibit better performance.
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| 3. |
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| 4. |
- Fischione, Carlo, et al.
(författare)
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Distributed cooperative processing and control over wireless sensor networks
- 2006
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Ingår i: IWCMC 2006 - Proceedings of the 2006 International Wireless Communications and Mobile Computing Conference. - New York, NY, USA : ACM. - 9781595933065 ; , s. 1311-1316
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An overview of some recent advances in distributed information processing for control over wireless sensor networks is presented in this paper. Firstly, a taxonomy of fundamental control and communication schemes for these systems is introduced. Next, specific research issues are proposed and discussed with three prominent examples on distributed source coding with packet aggregation, distributed cooperative diversity and distributed cooperative localization. In regard to these examples, it is argued about some open research problems and suggestions for further investigations on joint control and communication design for distributed processing and control over wireless sensor networks.
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| 5. |
- Fischione, Carlo, et al.
(författare)
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Reliability and Efficiency Analysis of Distributed Source Coding in Wireless Sensor Networks
- 2009
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Ingår i: 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS. ; , s. 324-329
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Konferensbidrag (refereegranskat)abstract
- We propose a comprehensive theoretical framework to evaluate reliability and energy consumption of distributed source coding (DSC) in wireless sensor networks (WSNs) applications. Energy efficiency and the amount of measurements that can be successfully decoded in tree-based WSNs employing DSC in the presence of different coding topologies and packet aggregation schemes (PA) are accurately characterized. The system model includes a realistic network architecture with multi-hop communication, automatic repeat request protocol (ARQ), packet losses due to channel impairments and collisions, and correlation properties of the sensed phenomena. Four DSC topologies and three alternatives of PA are considered. The analysis is carried out by evaluating the expressions of reliability of DSC in terms of probability of measurements that cannot be decoded (loss factor), and the efficiency in terms of average energy consumption of the network. Numerical results show that the best choice of DSC topology and packet aggregation depends highly on the network parameters and source characteristics. Therefore, the analysis developed in this paper can be used as an effective mean to optimize network operations.
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| 6. |
- Möller, Niels, et al.
(författare)
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Modeling and control of IP transport in cellular radio links
- 2005
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Konferensbidrag (refereegranskat)abstract
- A fundamental assumption of the TCP protocol is that packet losses indicate congestion on the network. This is a problem when using TCP over wireless links, because a noisy radio transmission may erroneously indicate congestion and thereby reduce the TCP sending rate. Two partial solutions, which improve the quality of the radio link, are power control and link-layer retransmissions. We consider a radio channel with multiple users and traffic classes, and investigate how parameters in the radio model influences TCP-related quality measures, such as the average delay and the probability of spurious timeout. The results indicate that the outer loop power control is robust to uncertainties in the radio model. This robustness property supports separation between the radio layer design and the IP and TCP layers.
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| 7. |
- Möller, N., et al.
(författare)
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Modelling and control of IP transport in cellular radio links
- 2005
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Konferensbidrag (refereegranskat)abstract
- A fundamental assumption of the TCP protocol is that packet losses indicate congestion on the network. This is a problem when using TCP over wireless links, because a noisy radio transmission may erroneously indicate congestion and thereby reduce the TCP sending rate. Two partial solutions, which improve the quality of the radio link, are power control and link-layer retransmissions. We consider a radio channel with multiple users and traffic classes, and investigate how parameters in the radio model influences TCP-related quality measures, such as the average delay and the probability of spurious timeout. The results indicate that the outer loop power control is robust to uncertainties in the radio model. This robustness property supports separation between the radio layer design and the ip and TCP layers.
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