Browsing by Subject "Age of information"

Now showing 1 - 10 of 10

Open Access
Age aware power allocation for energy-efficient wireless networks using RSMA
(2023-06) Akyürek, Selin
With the commercial deployments of 5G, research in Beyond 5G (B5G) and 6G networks has started. Within the context of meeting all needs and demands of future generation networks, the predicted usage is envisaged in three cases: massive Machine-Type Communications (MTC), ultra-reliable low-latency communications, and enhanced mobile broadband. This thesis focuses on massive Machine-Type Communications (mMTC). Energy efficiency, under the banner of green communications and networking is one of the branches complementary to the research conducted on MTC. mMTC, industrial and medical Internet of Things (IoT) type technologies will demand not only networking capabilities for massive access, enhanced communications, but also sustainability and power efficiency. Rate Splitting Multiple Access (RSMA) presents a candidate massive access scheme with spectral efficiency, energy efficiency, reliability, Degree-of-Freedom (DoF) and Quality of Service (QoS) enhancements in most of user deployments and network loads over traditional access schemes used in 5G. Within the scope of the thesis, we propose an age-aware power allocation policy for minimizing the network’s Weighted-Sum Average AoI (WSAoI). To our knowledge, this is the first work in the literature which combines the Age of Information (AoI) concept and RSMA framework. For downlink communication, we formulate the network’s WSAoI minimization as a Markov Decision Process (MDP) and investigate an optimal as well as suboptimal policies for the Base Station (BS) to select a scheme among RSMA, Orthogonal Multiple Access (OMA), and Nonorthogonal Multiple Access (NOMA). We prove existence of an optimal policy. Complexity of computation is reduced by using an action elimination technique, and by using a sub-optimal policy with performance close to the optimal. We also investigate the tradeoff between energy and the WSAoI of the network. The adaptive RSMA only scheme outperforms adaptive RSMA/NOMA/OMA and OMA/NOMA on the basis of network’s WSAoI. For example, when RSMA is selected, the performance metric, WSAoI, at 14, 15, and 16 dB SNR values, is on average, respectively 35.8%, 15.7%, and 12.7% less than the NOMA/OMA cases. Overall, it is seen that, the optimum policy becomes more likely to operate in the RSMA mode with an increase in Signal to Noise Ratio (SNR). By using RSMA scheme instead of NOMA/OMA scheme, power consumption can be saved in average 65.8%, 62.3%, and 59.6% for the selected WSAoI values of 4, 3, and 2, respectively.
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 Orkun
In 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.
Open Access
Energy management for age of information control in solar-powered IoT end devices
(Springer, 2021-07) Aydin, A. K.; Akar, Nail
In this paper, we propose several harvesting-aware energy management policies for solar-powered wireless IoT end devices that asynchronously send status updates for their surrounding environments to a network gateway device. For such devices, we aim at minimizing the average age of information (AoI) metric which has recently been investigated extensively for status update systems. The proposed energy management policies are obtained using discrete-time Markov chain-based modeling of the stochastic intra-day variations of the solar energy harvesting process in conjunction with the average reward Markov decision process formulation. With this approach, energy management policies are constructed by using the time of day and month of year information in addition to the instantaneous values of the age of information and the battery level. The effectiveness of the proposed energy management policies in terms of their capability to reduce the average AoI as well as improving upon the tail of the AoI distribution, is validated with empirical data for a wide range of system parameters.
Open Access
Exact distribution of age of information (AoI) and peak AoI in single-source and multi-source status update systems
(2021-07) Doğan, Ozancan
In 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.
Open Access
Finding the exact distribution of (peak) age of information for queues of PH/PH/1/1 and M/PH/1/2 type
(IEEE, 2020) Akar, Nail; Doğan, Ozancan; Atay, Eray Ünsal
Bufferless and single-buffer queueing systems have recently been shown to be effective in coping with escalated Age of Information (AoI) figures arising in single-source status update systems with large buffers and FCFS scheduling. In this paper, for the single-source scenario, we propose a numerical algorithm for obtaining the exact distributions of both the AoI and the peak AoI (PAoI) in (i) the bufferless PH/PH/1/1/P(p) queue with probabilistic preemption with preemption probability p, 0 ≤ p ≤ 1, and (ii) the single buffer M/P H/1/2/R(r) queue with probabilistic replacement of the packet in the queue by the new arrival with replacement probability r, 0 ≤ r ≤ 1. The proposed exact models are based on the well-established theory of Markov Fluid Queues (MFQ) and the numerical algorithms are matrix-analytical and they rely on numerically stable and efficient vector-matrix operations. Moreover, the obtained exact distributions are in matrix exponential form, making it amenable to calculate the tail probabilities and the associated moments straightforwardly. Firstly, we validate the accuracy of the proposed method with simulations, and for sume sub-cases, with existing closed-form results. We then comparatively study the AoI performance of the queueing systems of interest under varying traffic parameters.
Open Access
Is proportional fair scheduling suitable for age-sensitive traffic?
(Elsevier, 2023-05) Akar, Nail; Karaşan, Ezhan
Proportional 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.
Open Access
Modeling age of information in a cooperative slotted Aloha network
(Springer, 2023-03-28) Vaezi, Kaveh; Akar, Nail; Karaşan, Ezhan
In this paper, we study a slotted Aloha cooperative network where a source node and a relay node send status updates of two underlying stochastic processes to a common destination. Additionally, the relay node cooperates with the source by accepting its packets for further re-transmissions using probabilistic acceptance and relaying. We obtain the exact steady state distributions of Age of Information (AoI) and Peak AoI sequences of both nodes using Quasi-Birth-Death Markov chains. The analytical model is first validated by simulations and then used to obtain optimal cooperation policies when transmission probabilities are fixed. Subsequently, we study the more general problem of joint optimization of the transmission probabilities and cooperation level between the source and relay, with detailed numerical examples.
Open Access
The multi-source probabilistically preemptive M/PH/1/1 queue with packet errors
(IEEE, 2021-08-20) Doğan, Ozancan; Akar, Nail
Analytical modeling of Age of Information (AoI) and Peak AoI (PAoI) has recently drawn a lot of attention in the context of quantitative assessment of information freshness in status update systems. In this paper, we study a probabilistically preemptive bufferless M/PH/1/1 queue fed with information update packets from N separate information sources for which a new information packet arrival from source- m is allowed to preempt a packet from source- n in service, with a probability depending on n and m . To make the model even more general than the existing ones, we assume a distinct phase-type (PH-type) service time distribution, a distinct packet error and retransmission probability, for each of the information sources. Using sample path arguments and the theory of Markov Fluid Queues (MFQ), the exact distributions of the AoI and PAoI are numerically obtained for each of the sources. Numerical examples are provided to demonstrate the impact of various system parameters on AoI performance. In the context of a two-source system, we present a methodology on how to optimally choose the preemption probabilities and packet generation rates so as to minimize certain AoI-oriented cost functions.
Open Access
Performance analysis of CSMA-based half duplex and full duplex MAC protocols for vehicular networks
(2021-09) Yavuz, Ali Serdar
Beaconing mechanism used in vehicular networks is an essential mechanism to improve the cooperative awareness between vehicles by periodically broadcast-ing vehicle kinematic information and other traÿc entities. Cooperative aware-ness between vehicles a˙ects the performance of safety applications in vehicular networks. Therefore, the Quality of Service (QoS) provided by the beaconing mechanism determines whether the strict timeliness and reliability requirements of safety applications are met. The most important state parameter of the bea-coning mechanism is the beacon generation rate. Even if increasing it increases the cooperative awareness between vehicles, it also increases the channel conges-tion. This trade-o˙ poses a challenge in the MAC protocol design of the beaconing mechanism. Moreover, the broadcast nature of beacon packets prevents the usage of acknowledgement mechanism in the beaconing mechanism, further complicat-ing the problem. In this thesis, we examine the performance of two CSMA-based MAC protocols used for the beaconing mechanism. The first one makes use of Half-Duplex radios (HD-MAC), and it does not support collision detection, whereas the second one makes use of Full-Duplex radios (FD-MAC), and it sup-ports collision detection and retransmission. These protocols are analyzed using Markov Chain based queueing models, taking queue state and beacon generation rate into account. FD-MAC model considers missed and false collision detection occuring due to non-ideal behavior of the self-interference cancellation. Using the Markov Chain models, QoS measures such as successful transmission probabil-ity, throughput, service delay, packet loss probability and age of information are derived. The accuracy of the Markov Chain based models are validated through simulations. It is shown that the FD-MAC protocol is superior to HD-MAC protocol in terms of throughput, packet loss probability, and age of information.
Open Access
Scheduling and queue management for information freshness in multi-source status update systems
(2023-09) Gamgam, Ege Orkun
Timely 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.