| 1. |
- Ahani, Ghafour, et al.
(författare)
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Accounting for Information Freshness in Scheduling of Content Caching
- 2020
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Ingår i: ICC 2020. - 9781728150895 - 9781728150901
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Konferensbidrag (refereegranskat)abstract
- In this paper, we study the problem of optimal scheduling of content placement along time in a base station with limited cache capacity, taking into account jointly the offloading effect and freshness of information. We model offloading based on popularity in terms of the number of requests and information freshness based on the notion of age of information (AoI). The objective is to reduce the load of backhaul links as well as the AoI of contents in the cache via a joint cost function. For the resulting optimization problem, we prove its hardness via a reduction from the Partition problem. Next, via a mathematical reformulation, we derive a solution approach based on column generation and a tailored rounding mechanism. Finally, we provide performance evaluation results showing that our algorithm provides near-optimal solutions.
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| 2. |
- Ahani, Ghafour, et al.
(författare)
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Age-Optimal UAV Scheduling for Data Collection With Battery Recharging
- 2021
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Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 25:4, s. 1254-1258
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Tidskriftsartikel (refereegranskat)abstract
- We study route scheduling of a UAV for data collection from sensor nodes (SNs) with battery recharging. The freshness of the collected information is captured by the metric of age of information (AoI). The objective is to minimize the average AoI cost of all SNs over a scheduling time horizon. We prove that the problem in its general form is NP-hard. Then, for a special case of the problem, we prove that optimum can be computed in polynomial time. Next, we develop an algorithm based on graph labeling. Finally, we show the effectiveness of our algorithm in comparison to greedy scheduling.
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| 3. |
- Ahani, Ghafour, et al.
(författare)
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BS-assisted Task Offloading for D2D Networks with Presence of User Mobility
- 2019
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Ingår i: 2019 IEEE 89TH VEHICULAR TECHNOLOGY CONFERENCE (VTC2019-SPRING). - : IEEE. - 9781728112176
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Konferensbidrag (refereegranskat)abstract
- Task offloading is a key component in mobile edge computing. Offloading a task to a remote server takes communication and networking resources. An alternative is device-to-device (D2D) offloading, where a task of a device is offloaded to some device having computational resource available. The latter requires that the devices are within the range of each other, first for task collection, and later for result gathering. Hence, in mobility scenarios, the performance of D2D offloading will suffer if the contact rates between the devices are low. We enhance the setup to base station (BS) assisted D2D offloading, namely, a BS can act as a relay for task distribution or result collection. However, this would imply additional consumption of wireless resources. The associated cost and the improvement in completion time of task offloading compose a fundamental trade-off. For the resulting optimization problem, we mathematically prove the complexity, and propose an algorithm using Lagrangian duality. The simulation results demonstrate not only that the algorithm has close-to-optimal performance, but also provide structural insights of the optimal trade-off.
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| 4. |
- Ahani, Ghafour, et al.
(författare)
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On optimal proactive and retention-aware caching with user mobility
- 2018
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Ingår i: 2018 IEEE 88th Vehicular Technology Conference (VTC-Fall). - : IEEE. - 9781538663585
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Konferensbidrag (refereegranskat)abstract
- Caching popular contents at edge devices is an effective solution to alleviate the burden of the backhaul networks. Earlier investigations commonly neglected the storage cost in caching. More recently, retention-aware caching, where both the downloading cost and storage cost are accounted for, is attracting attention. Motivated by this, we address proactive and retention-aware caching problem with the presence of user mobility, optimizing the sum of the two types of costs. More precisely, a cost-optimal caching problem for vehicle-to-vehicle networks is formulated with joint consideration of the impact of the number of vehicles, cache size, storage cost, and content request probability. This is a combinatorial optimization problem. However, we derive a stream of analytical results and they together lead to an algorithm that guarantees global optimum with polynomial-time complexity. Numerical results show significant improvements in comparison to popular caching and random caching.
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| 5. |
- Ahani, Ghafour, et al.
(författare)
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On SC-FDMA Resource Allocation with Power Control
- 2016
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Ingår i: 2016 IEEE 21ST INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD). - : IEEE. - 9781509025589 ; , s. 112-116
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Konferensbidrag (refereegranskat)abstract
- In this paper, single-carrier frequency division multiple accesses (SC-FDMA) is discussed. In particular, minimum stun power, subject to meeting users demand is considered. There are two channel allocation schemes, localized and interleaved. In localized scheme, a block of convective channels in the spectrum is allocated to each user. In interleaved scheme, channels will be spread out over the spectrum and will be distributed equidistantly. It has been previously assumed that when a block of channels is assigned to a user, the same amount of power will be allocated to each channel. However, the power could be used more efficiently without this assumption We show that the resulting power allocation problem can be solved in linear time and propose an optimal power allocation procedure. Next, the effect of this new power optimization procedure is investigated numerically. In the next part of paper, we prove that for the interleaved scheme, Minimum sum power problem with or without this new power optimization is polynomial solvable. Finally, we numerically compare localized and interleaved SC-FDMA with and without power optimization The results show that the localized scheme with the new power optimization yields the best performance
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| 6. |
- Ahani, Ghafour, et al.
(författare)
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Optimal Content Caching and Recommendation With Age of Information
- 2024
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Ingår i: IEEE Transactions on Mobile Computing. - : IEEE Computer Society. - 1536-1233 .- 1558-0660. ; 23:1, s. 689-704
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Tidskriftsartikel (refereegranskat)abstract
- Content caching at the network edge is an effective way of mitigating backhaul load and improving user experience. Caching efficiency can be enhanced by content recommendation and by keeping the information fresh. By content recommendation, a requested content that is not in the cache can be alternatively satisfied by a related cached content recommended by the system. Information freshness can be quantified by age of information (AoI). This article has the following contributions. First, we address optimal scheduling of cache updates for a time-slotted system accounting for content recommendation and AoI, and to the best of our knowledge, there is no work that has jointly taken into account these aspects. Next, we rigorously prove the problem's NP-hardness. Then, we derive an integer linear formulation, by which the optimal solution can be obtained for small-scale scenarios. On the algorithmic side, our contributions include the development of an effective algorithm based on Lagrangian decomposition, and efficient algorithms for solving the resulting subproblems. Our algorithm computes a bound that can be used to evaluate the performance of any suboptimal solution. We conduct simulations to show the effectiveness of our algorithm.
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| 7. |
- Ahani, Ghafour
(författare)
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Optimal Scheduling for Timely Information in Communication Systems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The explosive growth of data in information society poses significant challenges in the timely delivery of information in the context of communication networks. Hence, optimal utilization of scarce network resources is crucial. This dissertation contributes to several aspects related to the timely delivery of information, including scheduling of data flows between sources and destinations in a network, scheduling of content caching in a base station of mobile networks, and scheduling of information collection. Two important metrics, namely, delivery deadline and information freshness, are accounted for. Mathematical models and tailored solution approaches are developed via tools from optimization.Five research papers are included in the dissertation. Paper I studies a flow routing and scheduling problem with delivery deadline. This type of problem arises in many applications such as data exchange in scientific projects or data replication in data centers where large amounts of data need to be timely distributed across the globe. Papers II, III, and IV investigate content caching along time in a base station. Content caching at the network’s edge has recently been considered a costefficient way of providing users with their requested information. In Paper II, the schedule for updating the cache is optimized with respect to the content requests of users and the popularity of contents over time. Paper III, as an extension of Paper II, addresses the question of how to keep the cache information fresh, as all contents can not be updated due to the limited capacity of the backhaul link. The freshness of information is quantified via the notion of age of information (AoI). Paper IV investigates joint optimization of content caching as well as recommendation; the latter contributes to satisfying content requests in case of a cache miss. Paper V studies optimal scheduling of information collection from a set of sensor nodes via an unmanned aerial vehicle. The objective is to keep the overall AoI as small as possible.In these studies, analysis of problem complexity is provided, and timeefficient solution algorithms based on column generation, Lagrangian decomposition, and graph labeling are developed. The algorithms also yield a bound of global optimum, that can be used to assess the performance of any given solution. The effectiveness of the algorithms in obtaining nearoptimal solutions is demonstrated via extensive simulations.
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| 8. |
- Ahani, Ghafour, et al.
(författare)
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Optimal Scheduling of Age-centric Caching : Tractability and Computation
- 2022
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Ingår i: IEEE Transactions on Mobile Computing. - : IEEE. - 1536-1233 .- 1558-0660 .- 2161-9875. ; 21, s. 2939-2954
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Tidskriftsartikel (refereegranskat)abstract
- The notion of age of information (AoI) has become an important performance metric in network and control systems. Information freshness, represented by AoI, naturally arises in the context of caching. We address optimal scheduling of cache updates for a time-slotted system where the contents vary in size. There is limited capacity for the cache for making updates. Each content is associated with a utility function that depends on the AoI and the time duration of absence from the cache. For this combinatorial optimization problem, we present the following contributions. First, we provide theoretical results of problem tractability. Whereas the problem is NP-hard, we prove solution tractability in polynomial time for a special case with uniform content size, by a reformulation using network flows. Second, we derive an integer linear formulation for the problem, of which the optimal solution can be obtained for small-scale scenarios. Next, via a mathematical reformulation, we derive a scalable optimization algorithm using repeated column generation. In addition, the algorithm computes a bound of global optimum, that can be used to assess the performance of any scheduling solution. Performance evaluation of large-scale scenarios demonstrates the strengths of the algorithm in comparison to a greedy schedule. Finally, we extend the applicability of our work to cyclic scheduling.
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| 9. |
- Ahani, Ghafour, et al.
(författare)
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Optimal scheduling of content caching subject to deadline
- 2020
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Ingår i: IEEE Open Journal of the Communications Society. - : IEEE. - 2644-125X. ; 1, s. 293-307
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Tidskriftsartikel (refereegranskat)abstract
- Content caching at the edge of network is a promising technique to alleviate the burden of backhaul networks. In this paper, we consider content caching along time in a base station with limited cache capacity. As the popularity of contents may vary over time, the contents of cache need to be updated accordingly. In addition, a requested content may have a delivery deadline within which the content needs to be obtained. Motivated by these, we address optimal scheduling of content caching in a time-slotted system under delivery deadline and cache capacity constraints. The objective is to minimize a cost function that captures the load of backhaul links. For our optimization problem, we prove its NP-hardness via a reduction from the Partition problem. For problem solving, via a mathematical reformulation, we develop a solution approach based on repeatedly applying a column generation algorithm and a problem-tailored rounding algorithm. In addition, two greedy algorithms are developed based on existing algorithms from the literature. Finally, we present extensive simulations that verify the effectiveness of our solution approach in obtaining near-to-optimal solutions in comparison to the greedy algorithms. The solutions obtained from our solution approach are within 1.6% from global optimality.
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| 10. |
- Ahani, Ghafour, et al.
(författare)
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Optimal Scheduling of Content Caching with recommendation and Freshness of Information
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Tidskriftsartikel (refereegranskat)abstract
- Content caching at the network edge has been considered an effective way of mitigating backhaul load and improving user experience. Caching efficiency can be enhanced by content recommendation and by keeping the information as fresh as possible. To the best of our knowledge, there is no work that jointly takes into account both these aspects in content caching. By content recommendation, a requested content that is not in the cache can be alternatively satisfied by a related cached content recommended by the system. Informationfreshness, arising naturally in content caching can be quantified by age of information (AoI). We address, optimal scheduling of cache updates for a time-slotted system accounting for both content recommendation and AoI, subject to cache capacity as well as backhaul capacity for updating the cache. For each content, there are requests that need to be satisfied and there is a cost function capturing the freshness of information which is monotonically increasing in the AoI. We present the following contributions. First, we prove that the problem is NP-hard even with contents of uniform size. Second, we derive an integer linear formulation for the problem, by which the optimal solution can be obtained for small-scale scenarios. Third, we develop an algorithm based on Lagrangian decomposition. Fourth, we develop efficient algorithms for solving the resulting subproblems. In addition, our algorithm computes a bound that can be used to evaluate the performance of any suboptimal solution. Finally, we conduct simulations to show the effectiveness of our algorithm in comparison to a greedy schedule.
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