| 1. |
- Farjam, Tahmoores, et al.
(författare)
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A timer-based distributed channel access mechanism in networked control systems
- 2018
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Ingår i: IEEE Transactions on Circuits and Systems II: Express Briefs. - 1549-7747 .- 1558-3791. ; 65:5, s. 652-656
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Tidskriftsartikel (refereegranskat)abstract
- We consider a system consisting of multiple heterogeneous control subsystems sharing a common communication resource for accomplishing their control tasks. Despite the numerous advantages that such networked control systems (NCSs) offer, their implementation is limited in practice due to the limited communication resources. We propose a novel distributed approach for the resource allocation problem in NCSs by which the subsystems can coordinate to access the network. More specifically, we develop a deterministic distributed scheme with which the subsystem with the highest cost is selected, based only on local information without requiring explicit communication between the subsystems. The efficiency of our scheme is demonstrated via simulations and it is compared with a centralized approach and other relevant approaches.
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| 2. |
- Farjam, Tahmoores, et al.
(författare)
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Distributed Channel Access for Control Over Known and Unknown Gilbert-Elliott Channels
- 2023
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 68:12, s. 7405-7419
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Tidskriftsartikel (refereegranskat)abstract
- We consider the distributed channel access problem for a system consisting of multiple control subsystems that close their loop over a shared wireless network with multiple channels subject to Markovian packet dropouts. Provided that an acknowledgement/negative-acknowledgement feedback mechanism is in place, we show that this problem can be formulated as a Markov decision process. We then transform this problem to a form that enables distributed control-aware channel access. More specifically, we show that the control objective can be minimized without requiring information exchange between subsystems as long as the channel parameters are known. The objective is attained by adopting a priority-based deterministic channel access method and the stability of the system under the resulting scheme is analyzed. Next, we consider a practical scenario in which the channel parameters are unknown and adopt a learning method based on Bayesian inference which is compatible with distributed implementation. We propose a heuristic posterior sampling algorithm which is shown to significantly improve performance via simulations.
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| 3. |
- Farjam, Tahmoores, et al.
(författare)
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Distributed Channel Access for Control over Unknown Memoryless Communication Channels
- 2022
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 67:12, s. 6445-6459
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Tidskriftsartikel (refereegranskat)abstract
- We consider the distributed channel access problem for a system consisting of multiple control subsystems that close their loop over a shared wireless network. We propose a distributed method for providing deterministic channel access without requiring explicit information exchange between the subsystems. This is achieved by utilizing timers for prioritizing channel access with respect to a local cost which we derive by transforming the control objective cost to a form that allows its local computation. This property is then exploited for developing our distributed deterministic channel access scheme. A framework to verify the stability of the system under the resulting scheme is then proposed. Next, we consider a practical scenario in which the channel statistics are unknown. We propose learning algorithms for learning the parameters of imperfect communication links for estimating the channel quality and, hence, define the local cost as a function of this estimation and control performance. We establish that our learning approach results in collision-free channel access. The behavior of the overall system is exemplified via a proof-of-concept illustrative example, and the efficacy of this mechanism is evaluated for large-scale networks via simulations.
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| 4. |
- Farjam, Tahmoores, 1990, et al.
(författare)
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Timer-Based Distributed Channel Access for Control Over Unknown Unreliable Time-Varying Communication Channels
- 2019
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Ingår i: 2019 18th European Control Conference, ECC 2019. ; June 2019, s. 2975-2982
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Konferensbidrag (refereegranskat)abstract
- We consider the resource allocation problem for a system consisting of multiple control subsystems that share an unknown unreliable time-varying wireless channel. We propose a novel method for granting channel access deterministically without requiring information exchange between subsystems, based on local timers for prioritizing channel access with respect to a local cost that takes into account the (initially unknown) channel conditions. We propose a novel setup which has the capability of learning the parameters of imperfect communication links while ensuring distributed collision-free implementation. More specifically, we adopt learning algorithms for estimating the channel quality and, hence, define the local cost as a function of this estimation and control performance. The efficacy of this mechanism is evaluated via simulations.
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| 5. |
- Farjam, Tahmoores, et al.
(författare)
-
Timer-Based Distributed Channel Access in Networked Control Systems over Known and Unknown Gilbert-Elliott Channels
- 2019
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Ingår i: 2019 18th European Control Conference, ECC 2019. ; , s. 2983-2989
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Konferensbidrag (refereegranskat)abstract
- In this paper, we consider a system consisting of multiple (possibly heterogeneous) decoupled control subsystems which aim at communicating with their corresponding controllers via shared (possibly) time-varying wireless channels. To address the resource allocation problem in a distributed fashion, we propose a timer-based channel access mechanism in which the subsystem with the smallest timer value, in a channel, claims the slot for transmission in that specific channel. The value of the timer is inversely proportional to a cost which is a function of the temporal correlation in the channel variation and the subsystem state. This cost can be calculated individually and does not require explicit communication between the subsystems, since it is based on locally available information only. The temporal correlation in the channel variation may be unknown and, in such cases, each subsystem tries to deduce it via machine learning techniques. The performance of our proposed mechanism is demonstrated via simulations.
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