Browsing by Subject "Status update systems"
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Item Open Access Age of information-oriented comparative evaluation of channel access mechanisms in multi-rate wireless lans(2023-08) Erdem, Umut UtkuDelay-sensitive applications have recently garnered significant attention because of the increasing demand for real-time data and time-critical information. In delay-sensitive systems, the timeliness of the delivered information is crucial to guarantee a reliable operation. A performance metric called Age of Information (AoI) is introduced in the literature to measure the freshness of information. In this study, various channel access methods are comparatively evaluated for stations transmitting age-sensitive status update packets over a multi-rate IEEE 802.11 WLAN. For wireless networks carrying conventional data traffic, the legacy channel access mechanism imposed by the Distributed Coordination Function (DCF) allows sources to access the channel equally. This mechanism results in a throughput-fair bandwidth allocation which is also known as a performance anomaly in the literature. Airtime-fair channel access methods have been proposed in the literature for multirate wireless LANs to mitigate this anomaly. Recently, there has been a surge of interest in status update systems with the emergence of performance criteria called age of information. Age-based performance metrics (AoI, peak AoI) are more effective to satisfy the requirements of the carried age-sensitive traffic as opposed to using conventional performance metrics (throughput, delay, or loss). In this study, we propose a novel channel access mechanism for age-sensitive traffic which is devised to lessen the mean Peak AoI (PAoI) averaged over all the sources in the network, which is termed as the system PAoI. The proposed channel access mechanism effectively reduces the system PAoI compared to LCA and PFCA. Although system PAoI performance improvement depends on the system configuration, i.e. packet size, the multi-rate mixture of the network etc., system PAoI can be reduced up to 12.04% and 27.44% compared to the legacy channel access and airtime-fair channel access, respectively, for the considered system configurations in this study. Although the proposed channel access mechanism outperforms legacy and airtime-fair channel access mechanisms in terms of system PAoI, it may lead to a reduction in the overall throughput of the system compared to airtime-fair channel access.Item Open Access Distribution of age of information in status update systems with heterogeneous information sources: an absorbing markov chain-based approach(Institute of Electrical and Electronics Engineers, 2023-05-31) Akar, Nail; Gamgam, Ege OrkunIn this letter, we obtain the exact distributions of the Age of Information (AoI) and Peak AoI (PAoI) in a non-preemptive multi-source status update system for (i) Generate-At-Will (GAW) servers with probabilistic transmissions (ii) Random Arrival with Single Buffer (RA-SB) servers employing probabilistic buffer management, using absorbing Continuous-Time Markov Chains (CTMC). For both servers, the information sources are allowed to have different relative urgencies, phase-type service time distributions, and transmission error probabilities, for the sake of generality. Numerical examples are presented to validate the proposed analytical model.Item Open Access Exact distribution of age of information (AoI) and peak AoI in single-source and multi-source status update systems(2021-07) Doğan, OzancanIn this thesis, we first study bufferless and single-buffer single-source queueing models of a status update system with various accompanying buffer manage-ment schemes. Next, we study the bufferless multi-source queueing model of a status-update system with probabilistic preemption. For both single-source and multi-source queueing models, we obtain the exact distributions of the associ-ated Age of Information (AoI) and Peak Age of Information (PAoI) processes. For this purpose, we propose a Markov Fluid Queue (MFQ) model for both scenarios out of which the exact AoI distributions are derived. The numerical so-lution obtained from the proposed model provides the distributional expressions in matrix-exponential form out of which one can easily obtain their high order moments. We validate the accuracy of our proposed algorithm by comparing our results with simulations and also existing results in the literature in certain sub-cases. Numerical results are presented to provide engineering insight on how state update systems need to be configured and operated.Item Open Access Is proportional fair scheduling suitable for age-sensitive traffic?(Elsevier, 2023-05) Akar, Nail; Karaşan, EzhanProportional Fair (PF) scheduling with successful deployments in various cellular wireless networks and wireless LANs, aims at maximizing the sum of the logarithms of user throughputs. PF scheduling is known to strike an appropriate balance between fairness and throughput, for conventional data traffic. On the other hand, there has recently been a surge of interest in status update networks carrying age-sensitive traffic for which information freshness is crucial and therefore network performance metrics driven by Age of Information (AoI) are instrumental, as opposed to conventional performance metrics such as delay, loss, or throughput, used for conventional data traffic. This paper studies the scheduling problem for the downlink of a cellular wireless network with a transmitter sending age-sensitive status update packets from multiple information sources to users with the goal of keeping the information as fresh as possible for the users. For this purpose, under the generate-at-will scenario, an age-agnostic model-free scheduler is proposed with the goal of minimizing the weighted sum peak AoI of the network, which is the performance metric used in this paper for quantifying information freshness. With numerical examples, the proposed scheduler is compared and contrasted with weighted PF scheduling in terms of implementation and performance, in both non-opportunistic and opportunistic scenarios.Item Open Access Scheduling and queue management for information freshness in multi-source status update systems(2023-09) Gamgam, Ege OrkunTimely delivery of information to its intended destination is essential in many ex-isting and emerging time-sensitive applications. While conventional performance metrics like delay, throughput, or loss have been extensively studied in the literature, research concerning the management of age-sensitive traffic is relatively immature. Recently, a number of information freshness metrics have been intro-duced for quantifying the timeliness of information in networked systems carrying age-sensitive traffic, primarily the Age of Information (AoI) and peak AoI (PAoI) metrics as well as their alternatives including Age of Synchronization (AoS), ver-sion age, binary freshness, etc. The focus of this thesis is the development and performance modeling of age-agnostic scheduling and queue management policies in various multi-source status update systems carrying age-sensitive traffic, using the recently introduced information freshness metrics. In this thesis, first, the exact distributions of the AoI and PAoI for the probabilistic Generate-At-Will (GAW) and Random Arrival with Single Buffer (RA-SB) servers are studied with general number of heterogeneous information sources with phase-type (PH-type) service time distributions for which an absorbing Continuous-Time Markov Chains (CTMC) based analytical modeling method, namely AMC (Absorbing Markov Chains) method, is proposed. Secondly, a homogeneous multi-source status update system with Poisson information packet arrivals and exponentially distributed service times is studied for which the server is equipped with a queue holding the freshest packet from each source referred to as Single Buffer Per-Source Queueing (SBPSQ). For this case, two SBPSQ-based scheduling policies are studied, namely First Source First Serve (FSFS) and the Earliest Served First Serve (ESFS) policies, using the AMC method, and it is shown that ESFS presents a promising scheduler for this special setting. Third, a general status update system with two heterogeneous information sources is studied, i.e., sources have different priorities and generally distributed service times, for Deterministic GAW (D-GAW) and Deterministic RA-SB (D-RA-SB) servers. The aim in both servers is to minimize the system AoI/AoS that is time-averaged and weighted across the two sources. For the D-GAW server, the optimal update policy is obtained in closed form. A packet replacement policy, referred to as Pattern-based Replacement (PR) policy, is then proposed for the D-RA-SB server based on the optimal policy structure of the D-GAW server. Finally, scheduling in a cache update system is investigated where a remote server delivers time-varying contents of multiple items with heterogeneous popularities and service times to a local cache so as to maximize the weighted sum binary freshness of the system, and the server is equipped with a queue that holds the most up-to-date content for each item. A Water-filling based Scheduling (WFS) policy and its extension, namely Extended WFS (E-WFS) policy, are proposed based on convex optimization applied to a relaxation of the original system, with low computational complexity and near optimal weighted sum binary freshness performance.