SwePub - search: WFRF:(Moltafet Mohammad)

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1.	Jahandideh, Mojtaba, et al. (author) Low Complexity Sparse Channel Estimation for Wideband mmWave Systems: Multi-Stage Approach 2019 In: 2019 IEEE WIRELESS COMMUNICATIONS AND NETWORKING CONFERENCE (WCNC). - : IEEE. - 9781538676462 Conference paper (peer-reviewed)abstract We consider the problem of channel estimation in hybrid transceiver architectures operating in millimeter wave (mmWave) band. Due to the dynamic features of the environment and the sensitivity of mmWave bands to blockage and deafness, it is important to estimate mmWave channels with a low complexity and high performance algorithm. In this regard, we exploit the sparse structure of the frequency-selective mmWave channels and formulate the channel estimation problem as a sparse signal reconstruction in frequency domain. In order to solve the estimation problem, we propose a multi-stage based low complexity algorithm. Simulation results show that the proposed algorithm significantly reduces the computational complexity while preserving the quality of the estimation.
2.	Moltafet, Mohammad, et al. (author) An Approximate Expression for the Average AoI in a Multi-Source M/G/1 Queueing Model 2020 In: 2020 2ND 6G WIRELESS SUMMIT (6G SUMMIT). - : IEEE. - 9781728160474 - 9781728160481 Conference paper (peer-reviewed)abstract Freshness of status update packets is essential for wide range of real-time Internet of things applications. In this paper, we study the information freshness of a single-server multi-source queueing model under a first-come first-served (FCFS) serving policy. In the considered model, each source independently generates status update packets according to a Poisson process. The information freshness of the status updates of each source is evaluated by the average age of information (AoI). We derive an approximate expression for the average AoI for a multi-source M/G/1 queueing model having a general service time distribution. Simulation results are provided to validate and assess the tightness of the proposed approximate expression for the average AoI in the M/G/1 queueing model where the service time follows a gamma distribution.
3.	Moltafet, Mohammad, et al. (author) An Exact Expression for the Average AoI in a Multi-Source M/M/1 Queueing Model 2020 In: 2020 IEEE 31ST ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS (IEEE PIMRC). - : IEEE. - 9781728144900 Conference paper (peer-reviewed)abstract Information freshness is crucial in a wide range of wireless applications where a destination needs the most recent measurements of a remotely observed random process. In this paper, we study the information freshness of a single-server multi-source M/M/1 queueing model under a first-come first-served (FCFS) serving policy. The information freshness of the status updates of each source is evaluated by the average age of information (AoI). We derive an exact expression for the average AoI for the multi-source M/M/1 queueing model. Simulation results are provided to validate the derived exact expression for the average AoI.
4.	Moltafet, Mohammad, et al. (author) Average Age of Information for a Multi-Source M/M/1 Queueing Model with Packet Management and Self-Preemption in Service 2020 In: 2020 18TH INTERNATIONAL SYMPOSIUM ON MODELING AND OPTIMIZATION IN MOBILE, AD HOC, AND WIRELESS NETWORKS (WIOPT). - : IEEE. - 9783903176294 ; , s. 1765-1769 Conference paper (peer-reviewed)abstract We consider an M/M/1 status update system consisting of two independent sources and one server. We derive the average age of information (AoI) of each source using the stochastic hybrid systems (SHS) technique under the following packet management with self-preemptive serving policy. The system can contain at most two packets with different source indexes at the same time, i.e., one packet under service and one packet in the queue. When the system is empty, any arriving packet immediately enters the server. When the server is busy at an arrival of a packet, the possible packet of the same source in the system (either waiting in the queue or being served) is replaced by the fresh packet. Numerical results illustrate the effectiveness of the proposed packet management with self-preemptive serving policy compared to several baseline policies.
5.	Moltafet, Mohammad, et al. (author) Average Age of Information in a Multi-Source M/M/1 Queueing Model with LCFS Prioritized Packet Management 2020 In: IEEE INFOCOM 2020 - IEEE CONFERENCE ON COMPUTER COMMUNICATIONS WORKSHOPS (INFOCOM WKSHPS). - : IEEE. - 9781728186955 ; , s. 303-308 Conference paper (peer-reviewed)abstract In this paper, we consider an M/M/1 status update system consisting of two independent sources, one server, and one sink. We consider the following last-come first-served (LCFS) prioritized packet management policy. When the system is empty, any arriving packet immediately enters the server; when the server is busy, a packet of a source waiting in the queue is replaced if a new packet of the same source arrives and the fresh packet goes at the head of the queue. We derive the average age of information (AoI) of the considered M/M/1 queueing model by using the stochastic hybrid systems (SHS) technique. Numerical results illustrate the effectiveness of the proposed packet management policy compared to several baseline policies.
6.	Moltafet, Mohammad, et al. (author) Average AoI in Multi-Source Systems With Source-Aware Packet Management 2021 In: IEEE Transactions on Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0090-6778 .- 1558-0857. ; 69:2, s. 1121-1133 Journal article (peer-reviewed)abstract We study the information freshness under three different source aware packet management policies in a status update system consisting of two independent sources and one server. The packets of each source are generated according to the Poisson process and the packets are served according to an exponentially distributed service time. We derive the average age of information (AoI) of each source using the stochastic hybrid systems (SHS) technique for each packet management policy. In Policy 1, the queue can contain at most two waiting packets at the same time (in addition to the packet under service), one packet of source 1 and one packet of source 2. When the server is busy at an arrival of a packet, the possible packet of the same source waiting in the queue (hence, source-aware) is replaced by the arrived fresh packet. In Policy 2, the system (i.e., the waiting queue and the server) can contain at most two packets, one from each source. When the server is busy at an arrival of a packet, the possible packet of the same source in the system is replaced by the fresh packet. Policy 3 is similar to Policy 2 but it does not permit preemption in service, i.e., while a packet is under service all new arrivals from the same source are blocked and cleared. Numerical results are provided to assess the fairness between sources and the sum average AoI of the proposed policies.
7.	Moltafet, Mohammad, et al. (author) Closed-Form Expression for the Average Age of Information in a Multi-Source M/G/1 Queueing Model 2019 In: 2019 IEEE INFORMATION THEORY WORKSHOP (ITW). - : IEEE. - 9781538669006 - 9781538669013 ; , s. 599-603 Conference paper (peer-reviewed)abstract In the context of the next generation wireless networks, freshness of status update packets is essential for enabling the services where a destination needs the most recent measurements of various sensors. In this paper, we study the information freshness of a multi-source M/G/1 first-come first-served (FCFS) queueing model, where each source independently generates status update packets according to a Poisson process. The information freshness of the status updates of each source is evaluated using the average age of information (AoI). To this end, we derive a closed-form expression for the average AoI of each source. As particular cases of our general expressions, we also derive closed-form expressions of the average AoI for both multi-source M/M/1 and single-source M/G/1 queueing models.
8.	Moltafet, Mohammad, et al. (author) Moment Generating Function of Age of Information in Multisource M/G/1/1 Queueing Systems 2022 In: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 70:10, s. 6503-6516 Journal article (peer-reviewed)abstract We consider a multi-source status update system, where each source generates status update packets according to a Poisson process which are then served according to a generally distributed service time. For this multi-source M/G/1/1 queueing model, we consider a self-preemptive packet management policy and derive the moment generating functions (MGFs) of the age of information (AoI) and peak AoI of each source. According to the policy, an arriving fresh packet preempts the possible packet of the same source in the system. Furthermore, we derive the MGFs of the AoI and peak AoI for the globally preemptive and non-preemptive policies, for which only the average AoI and peak AoI have been derived earlier. Finally, we use the MGFs to derive the average AoI and peak AoI in a two-source M/G/1/1 queueing model under each policy. Numerical results show the effect of the service time distribution parameters on the average AoI. The results also highlight the importance of higher moments of the AoI.
9.	Moltafet, Mohammad, et al. (author) Moment Generating Function of the AoI in a Two-Source System With Packet Management 2021 In: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 10:4, s. 882-886 Journal article (peer-reviewed)abstract We consider a status update system consisting of two independent sources and one server in which packets of each source are generated according to the Poisson process and packets are served according to an exponentially distributed service time. We derive the moment generating function (MGF) of the age of information (AoI) for each source in the system by using the stochastic hybrid systems (SHS) under two existing source-aware packet management policies which we term self-preemptive and non-preemptive policies. In the both policies, the system (i.e., the waiting queue and the server) can contain at most two packets, one packet of each source; when the server is busy and a new packet arrives, the possible packet of the same source in the waiting queue is replaced by the fresh packet. The main difference between the policies is that in the self-preemptive policy, the packet under service is replaced upon the arrival of a new packet from the same source, whereas in the non-preemptive policy, this new arriving packet is blocked and cleared. We use the derived MGF to find the first and second moments of the AoI and show the importance of higher moments.
10.	Moltafet, Mohammad, et al. (author) Moment Generating Function of the AoI in Multi-Source Systems with Computation-Intensive Status Updates 2021 In: 2021 IEEE INFORMATION THEORY WORKSHOP (ITW). - : IEEE. - 9781665403122 Conference paper (peer-reviewed)abstract We consider a multi-source status update system in which status updates are transmitted as packets containing the measured value of the monitored process and a time stamp representing the time when the sample was generated. The packets of each source are generated according to a Poisson process and served according to an exponentially distributed service time. We assume that the received status update packets need further processing before being used (hence, computation-intensive). This is mathematically modeled by an additional server at the sink. The sink server serves the packets according to an exponentially distributed service time. We introduce two packet management policies, a preemptive policy and a blocking policy, and derive the moment generating function (MGF) of the AoI of each source under the both policies. In the both policies, the system can contain at most two packets, one at the transmitter server and one at the sink server. In the preemptive policy, a new arriving packet preempts any possible packet that is currently under service regardless of the packets source index. In the blocking policy, when a server is busy at the arrival instant of a packet, the arriving packet is blocked and cleared. We assume that the same preemptive/blocking policy is employed in both the transmitter and sink server. Numerical results are provided to assess the results.
11.	Moltafet, Mohammad, et al. (author) On the Age of Information in Multi-Source Queueing Models 2020 In: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 68:8, s. 5003-5017 Journal article (peer-reviewed)abstract Freshness of status update packets is essential for enabling services where a destination needs the most recent measurements of various sensors. In this paper, we study the information freshness of single-server multi-source queueing models under a first-come first-served (FCFS) serving policy. In the considered model, each source independently generates status update packets according to a Poisson process. The information freshness of the status updates of each source is evaluated by the average age of information (AoI). We derive an exact expression for the average AoI for the case with exponentially distributed service time, i.e., for a multi-source M/M/1 queueing model. Moreover, we derive three approximate expressions for the average AoI for a multi-source M/G/1 queueing model having a general service time distribution. Simulation results are provided to validate the derived exact average AoI expression, to assess the tightness of the proposed approximations, and to demonstrate the AoI behavior for different system parameters.
12.	Moltafet, Mohammad, et al. (author) Power Minimization for Age of Information Constrained Dynamic Control in Wireless Sensor Networks 2022 In: IEEE Transactions on Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0090-6778 .- 1558-0857. ; 70:1, s. 419-432 Journal article (peer-reviewed)abstract We consider a status update system where multiple sensors communicate timely information about various random processes to a sink. The sensors share orthogonal sub-channels to transmit such information in the form of status update packets. A central controller can control the sampling actions of the sensors to trade-off between the transmit power consumption and information freshness which is quantified by the Age of Information (AoI). We jointly optimize the sampling action of each sensor, the transmit power allocation, and the sub-channel assignment to minimize the average total transmit power of all sensors, subject to a maximum average AoI constraint for each sensor. To solve the problem, we develop a dynamic control algorithm using the Lyapunov drift-plus-penalty method and provide optimality analysis of the algorithm. According to the Lyapunov drift-plus-penalty method, to solve the main problem, we need to solve an optimization problem in each time slot which is a mixed integer non-convex optimization problem. We propose a low-complexity sub-optimal solution for this per-slot optimization problem that provides near-optimal performance and we evaluate the computational complexity of the solution. Numerical results illustrate the performance of the proposed dynamic control algorithm and the performance of the sub-optimal solution for the per-slot optimization problem versus the different parameters of the system. The results show that the proposed dynamic control algorithm achieves more than 60 % saving in the average total transmit power compared to a baseline policy.
13.	Moltafet, Mohammad, et al. (author) Power Minimization in Wireless Sensor Networks With Constrained AoI Using Stochastic Optimization 2019 In: CONFERENCE RECORD OF THE 2019 FIFTY-THIRD ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS. - : IEEE. - 9781728143002 ; , s. 406-410 Conference paper (peer-reviewed)abstract In this paper, we consider a system where multiple low-power sensors communicate timely information about a random process to a sink. The sensors share orthogonal subchannels to transmit such information in the form of status update packets. Freshness of the sensors information at the sink is characterized by the Age of Information (AoI), and the sensors can control the sampling policy by deciding whether to take a sample or not. We formulate an optimization problem to minimize the time average total transmit power of sensors by jointly optimizing the sampling action of each sensor, the transmit power allocation, and the subchannel assignment under the constraints on the maximum time average AoI and maximum power of each sensor. To solve the optimization problem, we use the Lyapunov drift-plus-penalty method. Numerical results show the performance of the proposed algorithm versus the different parameters of the system.
14.	Moltafet, Mohammad, et al. (author) Status Update Control and Analysis Under Two-Way Delay 2023 In: IEEE/ACM Transactions on Networking. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1063-6692 .- 1558-2566. Journal article (peer-reviewed)abstract We study status updating under two-way delay in a system consisting of a sampler, a sink, and a controller residing at the sink. The controller drives the sampling process by sending request packets to the sampler. Upon receiving a request, the sampler generates a sample and transmits the status update packet to the sink. Transmissions of both request and status update packets encounter random delays. We develop optimal control policies to minimize the average age of information (AoI) using the tools of Markov decision processes in two scenarios. We begin with the system having at most one active request, i.e., a generated request for which the sink has not yet received a status update packet. Then, as the main distinctive feature of this paper, we initiate pipelined-type status updating by studying a system having at most two active requests. Furthermore, we conduct AoI analysis by deriving the average AoI expressions for the Zero-Wait-1, Zero-Wait-2, and Wait-1 policies. According to the Zero-Wait-1 policy, whenever a status update packet is delivered to the sink, a new request packet is inserted into the system. The Zero-Wait-2 policy operates similarly, except that the system can hold two active requests. According to the Wait-1 policy, whenever a status update packet is delivered to the sink, a new request is sent after a waiting time which is a function of the current AoI. Numerical results illustrate the performance of each status updating policy under varying system parameter values.
15.	Moltafet, Mohammad, et al. (author) Timely status updating via packet management in multisource systems 2023 In: Age of information. - Cambridge : Cambridge University Press. - 9781108943321 ; , s. 115-139 Book chapter (other academic/artistic)
16.	Moltafet, Mohammad, et al. (author) Worst Case Age of Information in Wireless Sensor Networks: A Multi-Access Channel 2020 In: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 9:3, s. 321-325 Journal article (peer-reviewed)abstract Freshness of status update packets is essential for enabling a wide range of applications in wireless sensor networks (WSNs). Accordingly, we consider a WSN where sensors communicate status updates to a destination by contending for the channel access based on a carrier sense multiple access (CSMA) method. We analyze the worst case average age of information (AoI) and average peak AoI from the view of one sensor in a system where all the other sensors have a saturated queue. Numerical results illustrate the importance of optimizing the contention window size and the packet arrival rate to maximize the information freshness.
17.	Moltafet, Mohammad, et al. (author) Worst Case Analysis of Age of Information in a Shared-Access Channel 2019 In: 2019 16TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATION SYSTEMS (ISWCS). - : IEEE. - 9781728125275 ; , s. 613-617 Conference paper (peer-reviewed)abstract Freshness of status update packets is essential for enabling a wide range of Internet of Things (IoT) applications. In this paper, we consider a status update system in which various sensors are assigned to transmit status update packets of a physical process to a desired destination. We consider that the sensors share a wireless channel and contend for the channel access based on a carrier sense multiple access (CSMA) method. We study freshness of the status update system at the destination using the age of information (AoI) metric. To this end, we analyze the worst case average AoI for each sensor in the CSMA-based system. Numerical results show that the AoI in the CSMA-based system may dramatically increase when the number of sensors increases. Moreover, we observe that the contention window size and the packet arrival rate must be optimized since they have a critical role in the performance of the system.
18.	Vilni, Saeid Sadeghi, et al. (author) AoI Analysis and Optimization in Systems with Computations-Intensive Updates 2023 In: Journal of Communications and Networks. - : KOREAN INST COMMUNICATIONS SCIENCES (K I C S). - 1229-2370 .- 1976-5541. ; 25:5, s. 585-597 Journal article (peer-reviewed)abstract consider a status update system consisting of a sampler, a controller, a processing unit, a transmitter, and a sink. The sampler generates a sample upon receiving a request from the controller and the sample requires further processing before transmission, hence is computation-intensive. This is mathematically modeled by a server called process server. After processing the sample, the status update packet is generated and sent to the transmitter for delivery to the sink. This is mathematically modeled by a server called transmit server. The service time of each packet at the transmit and process servers follow geometric distributions. Moreover, we consider that the servers serve packets under the blocking policy, i.e., whenever a server is busy at the arrival time of a new packet, the new arriving packet is blocked and discarded. We analyze the average age of information (AoI) for two fixed policies, namely, 1) zero-wait-one policy and 2) zero-wait-blocking policy. According to the former policy, the controller requests sampling when there is no packet in the system. According to the zero-waitblocking policy, the controller requests a sample whenever the process server is idle. Furthermore, we develop an optimal control policy to minimize the average AoI using the tools of Markov decision process (MDP). In numerical results, we evaluate the performance of the policies under different system parameters. Moreover, we analyze the structure of the optimal policy.
19.	Vilni, Saeid Sadeghi, et al. (author) Multi-Source AoI-Constrained Resource Minimization Under HARQ: Heterogeneous Sampling Processes 2024 In: IEEE Transactions on Vehicular Technology. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9545 .- 1939-9359. ; 73:1, s. 1084-1099 Journal article (peer-reviewed)abstract We consider a multi-source hybrid automatic repeat request (HARQ) based system, where a transmitter sends status update packets of random arrival (i.e., uncontrollable sampling) and generate-at-will (i.e., controllable sampling) sources to a destination through an error-prone channel. We develop transmission scheduling policies to minimize the average number of transmissions subject to an average age of information (AoI) constraint. First, we consider known environment (i.e., known system statistics) and develop a near-optimal deterministic transmission policy and a low-complexity dynamic transmission (LC-DT) policy. The former policy is derived by casting the main problem into a constrained Markov decision process (CMDP) problem, which is then solved using the Lagrangian relaxation, relative value iteration algorithm, and bisection. The LC-DT policy is developed via the drift-plus-penalty (DPP) method by transforming the main problem into a sequence of per-slot problems. Finally, we consider unknown environment and devise a learning-based transmission policy by relaxing the CMDP problem into an MDP problem using the DPP method and then adopting the deep Q-learning algorithm. Numerical results show that the proposed policies achieve near-optimal performance and illustrate the benefits of HARQ in status updating.
20.	Zakeri, Aholfaz, et al. (author) Minimizing AoI in Resource-Constrained Multi-Source Relaying Systems with Stochastic Arrivals 2021 In: 2021 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM). - : IEEE. - 9781728181042 Conference paper (peer-reviewed)abstract We consider a multi-source relaying system where the sources independently and randomly generate status update packets which are sent to the destination with the aid of a buffer-aided relay through unreliable links. We formulate a stochastic optimization problem aiming to minimize the sum average age of information (AAoI) of sources under per-slot transmission capacity constraints and a long-run average resource constraint. To solve the problem, we recast it as a constrained Markov decision process (CMDP) problem and adopt the Lagrangian method. We analyze the structure of an optimal policy for the resulting MDP problem that possesses a switching-type structure. We propose an algorithm that obtains a stationary deterministic near-optimal policy, establishing a benchmark for the system. Simulation results show the effectiveness of our algorithm compared to benchmark algorithms.
21.	Zakeri, Abolfazl, et al. (author) Minimizing the AoI in Multi-Source Two-Hop Systems under an Average Resource Constraint 2022 In: 2022 IEEE 23RD INTERNATIONAL WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATION (SPAWC). - : IEEE. - 9781665494557 - 9781665494564 Conference paper (peer-reviewed)abstract We develop online scheduling policies to minimize the sum average age of information (AoI) subject to transmission capacity and long-run average resource constraints in a multi-source two-hop system, where independent sources randomly generate status update packets which are sent to the destination via a relay through error-prone links. A stochastic optimization problem is formulated and solved in known and unknown environments. For the known environment, an online nearoptimal low-complexity policy is developed using the drift-plus-penalty method. For the unknown environment, a deep reinforcement learning policy is developed by employing the Lyapunov optimization theory and a dueling double deep Q-network. Simulation results show up to 136% performance improvement of the proposed policy compared to a greedy-based baseline policy.
22.	Zakeri, Abolfazl, et al. (author) Minimizing the AoI in Resource-Constrained Multi-Source Relaying Systems: Dynamic and Learning-Based Scheduling 2024 In: IEEE Transactions on Wireless Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1536-1276 .- 1558-2248. ; 23:1, s. 450-466 Journal article (peer-reviewed)abstract We consider a multi-source relaying system where independent sources randomly generate status update packets which are sent to the destination with the aid of a relay through unreliable links. We develop transmission scheduling policies to minimize the weighted sum average age of information (AoI) subject to transmission capacity and long-run average resource constraints. We formulate a stochastic control optimization problem and solve it using a constrained Markov decision process (CMDP) approach and a drift-plus-penalty method. The CMDP problem is solved by transforming it into an MDP problem using the Lagrangian relaxation method. We theoretically analyze the structure of optimal policies for the MDP problem and subsequently propose a structure-aware algorithm that returns a practical near-optimal policy. Using the drift-plus-penalty method, we devise a near-optimal low-complexity policy that performs the scheduling decisions dynamically. We also develop a model-free deep reinforcement learning policy for which the Lyapunov optimization theory and a dueling double deep Q-network are employed. The complexities of the proposed policies are analyzed. Simulation results are provided to assess the performance of our policies and validate the theoretical results. The results show up to 91% performance improvement compared to a baseline policy.
23.	Zakeri, Abolfazl, et al. (author) Query-Age-Optimal Scheduling Under Sampling and Transmission Constraints 2023 In: IEEE Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1089-7798 .- 1558-2558. ; 27:4, s. 1205-1209 Journal article (peer-reviewed)abstract This letter provides query-age-optimal joint sampling and transmission scheduling policies for a heterogeneous status update system, consisting of a stochastic arrival and a generate-at-will source, with an unreliable channel. Our main goal is to minimize the average query age of information (QAoI) subject to average sampling, average transmission, and per-slot transmission constraints. To this end, an optimization problem is formulated and solved by casting it into a linear program. We also provide a low-complexity near-optimal policy using the notion of weakly-coupled constrained Markov decision processes. The numerical results show up to 32% performance improvement by the proposed policies compared with a benchmark policy.

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