| 1. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Unsourced Multiple Access for Heterogeneous Traffic Requirements
- 2022
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Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; 2022-October, s. 687-691
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Konferensbidrag (refereegranskat)abstract
- We investigate the coexistence of critical and massive Internet of Things (IoT) services in the context of the unsourced multiple access (UMA) framework, introduced by Polyanskiy (2017). We consider the standard UMA setup in which all users employ a common codebook and the receiver returns an unordered list of codewords. To model the critical IoT service, we assume that the users can also communicate a common alarm message. We further assume that the number of active users in each transmission attempt is random and unknown. We derive a random-coding bound for the Gaussian multiple access channel and demonstrate that orthogonal network slicing enables the two traffic types to coexist with high energy efficiency.
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| 2. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Unsourced Multiple Access With Common Alarm Messages: Network Slicing for Massive and Critical IoT
- 2024
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 72:2, s. 907-923
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the coexistence of massive and critical Internet of Things (IoT) services in the context of the unsourced multiple access (UMA) framework introduced by Polyanskiy (2017), where all users employ a common codebook and the receiver returns an unordered list of decoded codewords. This setup is suitably modified to introduce heterogeneous traffic. Specifically, to model the massive IoT service, we assume that a standard message originates independently from each IoT device as in the standard UMA setup. To model the critical IoT service, we assume the generation of alarm messages that are common for all devices. This setup requires a significant redefinition of the error events, i.e., misdetections and false positives. We further assume that the number of active users in each transmission attempt is random and unknown. We derive a random-coding achievability bound on the misdetection and false positive probabilities of both standard and alarm messages on the Gaussian multiple access channel. Using our bound, we demonstrate that orthogonal network slicing enables massive and critical IoT to coexist under the requirement of high energy efficiency. On the contrary, we show that nonorthogonal network slicing is energy inefficient due to the residual interference from the alarm signal when decoding the standard messages.
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| 3. |
- Zanini, A, et al.
(författare)
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Monte Carlo simulation of the photoneutron field in linac radiotherapy treatments with different collimation systems
- 2004
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 49:4, s. 571-582
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Tidskriftsartikel (refereegranskat)abstract
- Bremsstrahlung photon beams produced by linac accelerators are currently the most commonly used method of radiotherapy for tumour treatments. When the photon energy exceeds 10 MeV the patient receives an undesired dose due to photoneutron production in the accelerator head. In the last few decades, new sophisticated techniques such as multileaf collimators have been used for a better definition of the target volume. In this case it is crucial to evaluate the photoneutron dose produced after giant dipole resonance (GDR) excitation of the high Z materials (mainly tungsten and lead) constituting the collimator leaves in view of the optimization of the radiotherapy treatment. A Monte Carlo approach has been used to calculate,the photoneutron dose arising from the GDR reaction during radiotherapy with energetic photon beams. The simulation has been performed using the code MCNP4B-GN which is based on MCNP4B, but includes a new routine GAMMAN to model photoneutron production. Results for the facility at IRCC (Istituto per la Ricerca e la Cura del Cancro) Candiolo (Turin), which is based on 18 MV x-rays from a Varian Clinac 2300 C/D, are presented for a variety of different collimator configurations.
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