Browsing by Subject "Wireless networks"

Now showing 1 - 18 of 18

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
Aging wireless bandits: regret analysis and order-optimal learning algorithm
(IEEE, 2021-11-13) Atay, Eray Unsal; Kadota, Igor; Modiano, Eytan
We consider a single-hop wireless network with sources transmitting time-sensitive information to the destination over multiple unreliable channels. Packets from each source are generated according to a stochastic process with known statistics and the state of each wireless channel (ON/OFF) varies according to a stochastic process with unknown statistics. The reliability of the wireless channels is to be learned through observation. At every time-slot, the learning algorithm selects a single pair (source, channel) and the selected source attempts to transmit its packet via the selected channel. The probability of a successful transmission to the destination depends on the reliability of the selected channel. The goal of the learning algorithm is to minimize the Age-of-Information (AoI) in the network over T time-slots. To analyze its performance, we introduce the notion of AoI-regret, which is the difference between the expected cumulative AoI of the learning algorithm under consideration and the expected cumulative AoI of a genie algorithm that knows the reliability of the channels a priori. The AoI-regret captures the penalty incurred by having to learn the statistics of the channels over the T time-slots. The results are two-fold: first, we consider learning algorithms that employ well-known solutions to the stochastic multi-armed bandit problem (such as ϵ-Greedy, Upper Confidence Bound, and Thompson Sampling) and show that their AoI-regret scales as Θ(log T); second, we develop a novel learning algorithm and show that it has O(1) regret. To the best of our knowledge, this is the first learning algorithm with bounded AoI-regret.
Open Access
Bluetooth or 802.15.4 technologies to optimise lifetime of wireless sensor networks: Numerical comparison under a common framework
(IEEE, 2008-04) Buratti, C.; Körpeoğlu, İbrahim; Karasan, Ezhan; Verdone, R.
This paper aims at comparing through simulations the network lifetime of a wireless sensor network using Bluetooth-enabled or IEEE802.15.4 compliant devices. The evaluation is performed under a common reference framework, namely the EMORANS scenario for wireless sensor networks. Since the two enabling technologies rely on different MAC paradigms, suitable definition of the performance metrics is needed, in order to make the comparison meaningful. Thus, the paper has also a methodological objective. In particular, three different definitions of network lifetime are introduced, and a comparison of performance obtained by applying the different definitions is provided. Then, the comparison between the two standards is introduced: it is shown that there are no orders of magnitude of difference in network lifetime when the two technologies are used and the choice of the technology depends on the application requirements.
Open Access
Computing localized power-efficient data aggregation trees for sensor networks
(Institute of Electrical and Electronics Engineers, 2011) Tan, H. O.; Korpeoglu, I.; Stojmenovic, I.
We propose localized, self organizing, robust, and energy-efficient data aggregation tree approaches for sensor networks, which we call Localized Power-Efficient Data Aggregation Protocols (L-PEDAPs). They are based on topologies, such as LMST and RNG, that can approximate minimum spanning tree and canbeefficiently computed using only position or distance information ofone-hop neighbors. The actual routing tree is constructed over these topologies. We also consider different parent selection strategies while constructing a routing tree. We compare each topology and parent selection strategy and conclude that the best among them is the shortest path strategy over LMST structure. Our solution also involves route maintenance procedures that will beexecuted whenasensor node fails ora new node is added to the network. The proposed solution is also adapted to consider the remaining power levels ofnodes in orderto increase the network lifetime. Our simulation results show that byusing our power-aware localized approach, we can almost have the same performance of a centralized solution in terms of network lifetime, and close to 90 percent of an upper bound derived here. © 2011 IEEE.
Open Access
Energy harvesting and wireless power transfer enabled wireless networks
(Elsevier, 2020) Duman, Tolga M.; Zhao, N.; Nallanathan, A.; Chen, Y.; Pan, M.
Development of wireless communication networks, connected devices, and improvement of Internet of Things (IoT) will deeply impact in every aspect of human life. In future mobile systems, a tremendous number of low-power wireless devices will exist within the densely deployed heterogeneous networks. One key challenge from the growing demand in wireless applications is a sufficient and flexible energy supply. Hence, a natural spin from the traditional and limited energy sources to alternative energy sources is a natural step to supply the exponential growth of energy demand of the mankind. Recently, energy harvesting (EH) has emerged as an important method to provide a power supply for green self-sufficient wireless nodes, in which the energy captured from intentional or ambient sources can be collected to replenish the batteries. Besides, EH has been investigated as a promising technology to overcome the energy scarcity problem in energy constrained wireless communication systems, especially for wireless networks with fixed energy supplies. Compared with conventional EH sources such as solar, wind, vibration, thermoelectric effects or other physical phenomena, which rely on external energy sources that are not components of communication networks, a new operation of EH which collects energy from ambient radio-frequency (RF) signals has been proposed. As RF signals are commonly used as a vehicle for transmitting information in wireless networks, simultaneous wireless information and power transfer (SWIPT) has become an emerging technique attracting great attention from both academia and industry. Towards this end, this special issue includes a collection of 24 papers, and we aim to disseminate the latest research and innovations on energy harvesting and wireless power transfer enabled wireless networks.
Open Access
Interference mitigation and awareness for improved reliability
(Cambridge University Press, 2011) Arslan, H.; Yarkan S.; Şahin, M. E.; Gezici, Sinan
Wireless systems are commonly affected by interference from various sources. For example, a number of users that operate in the same wireless network can result in multiple-access interference (MAI). In addition, for ultrawideband (UWB) systems, which operate at very low power spectral densities, strong narrowband interference (NBI) can have significant effects on the communications reliability. Therefore, interference mitigation and awareness are crucial in order to realize reliable communications systems. In this chapter, pulse-based UWB systems are considered, and the mitigation of MAI is investigated first. Then, NBI avoidance and cancelation are studied for UWB systems. Finally, interference awareness is discussed for short-rate communications, next-generation wireless networks, and cognitive radios.Mitigation of multiple-access interference (MAI)In an impulse radio ultrawideband (IR-UWB) communications system, pulses with very short durations, commonly less than one nanosecond, are transmitted with a low-duty cycle, and information is carried by the positions or the polarities of pulses [1-5]. Each pulse resides in an interval called frame, and the positions of pulses within frames are determined according to time-hopping (TH) sequences specific to each user. The low-duty cycle structure together with TH sequences provide a multiple-access capability for IR-UWB systems [6].Although IR-UWB systems can theoretically accommodate a large number of users in a multiple-access environment [2, 4], advanced signal processing techniques are necessary in practice in order to mitigate the effects of interfering users on the detection of information symbols efficiently [6]. © Cambridge University Press 2011.
Open Access
A non-atochastic learning approach to energy efficient mobility management
(Institute of Electrical and Electronics Engineers Inc., 2016) Shen, C.; Tekin, C.; Van Der Schaar, M.
Energy efficient mobility management is an important problem in modern wireless networks with heterogeneous cell sizes and increased nodes densities. We show that optimization-based mobility protocols cannot achieve long-Term optimal energy consumption, particularly for ultra-dense networks (UDNs). To address the complex dynamics of UDN, we propose a non-stochastic online-learning approach, which does not make any assumption on the statistical behavior of the small base station (SBS) activities. In addition, we introduce handover cost to the overall energy consumption, which forces the resulting solution to explicitly minimize frequent handovers. The proposed batched randomization with exponential weighting (BREW) algorithm relies on batching to explore in bulk, and hence reduces unnecessary handovers. We prove that the regret of BREW is sublinear in time, thus guaranteeing its convergence to the optimal SBS selection. We further study the robustness of the BREW algorithm to delayed or missing feedback. Moreover, we study the setting where SBSs can be dynamically turned ON and OFF. We prove that sublinear regret is impossible with respect to arbitrary SBS ON/OFF, and then develop a novel learning strategy, called ranking expert (RE), that simultaneously takes into account the handover cost and the availability of SBS. To address the high complexity of RE, we propose a contextual ranking expert (CRE) algorithm that only assigns experts in a given context. Rigorous regret bounds are proved for both RE and CRE with respect to the best expert. Simulations show that not only do the proposed mobility algorithms greatly reduce the system energy consumption, but they are also robust to various dynamics which are common in practical ultra-dense wireless networks.
Open Access
On the Queuing Model of the energy-delay tradeoff in wireless links with power control and link adaptation
(IEEE, 2019-05) Gamgam, Ege Orkun; Tunç, Çağlar; Akar, Nail
A transmission profile refers to a transmission power and a modulation and coding scheme to be used for packet transmissions over a wireless link. The goal of this paper is to develop transmission profile selection policies so as to minimize the average power consumption on a wireless link while satisfying a certain delay constraint given in terms of a delay violation probability. Toward the assessment of profile selection policies, a multi-regime Markov fluid queue model is proposed to obtain the average power consumption and the queue waiting time distribution which allows one to analyze the energy-delay tradeoff in queuing systems for which the packet transmission duration is allowed to depend on the delay experienced by the packet until the beginning of service. Numerical examples are presented with transmission profiles obtained from realistic LTE simulations. Several transmission profile selection policies are proposed and subsequently compared using the analytical model.
Open Access
A peer-to-peer file search and download protocol for wireless ad-hoc networks
(Elsevier BV, 2009-01) Sözer, H.; Tekkalmaz, M.; Korpeoglu, I.
Deployment of traditional peer-to-peer file sharing systems on a wireless ad-hoc network introduces several challenges. Information and workload distribution as well as routing are major problems for members of a wireless ad-hoc network, which are only aware of their immediate neighborhood. In this paper, we propose a file sharing system that is able to answer location queries, and also discover and maintain the routing information that is used to transfer files from a source peer to another peer. We present a cross-layer design, where the lookup and routing functionality are unified. The system works according to peer-to-peer principles, distributes the location information of the shared files among the members of the network. The paper includes a sample scenario to make the operations of the system clearer. The performance of the system is evaluated using simulation results and analysis is provided for comparing our approach with a flooding-based, unstructured approach. © 2008 Elsevier B.V. All rights reserved.
Open Access
Performance modeling and analysis of the interplay among Tcp, active queue management and wireless link adaptation
(2015-09) Öztürk, Onur
We propose a novel workload-dependent queuing model of a wireless router link which employs active queue management and is offered with a number of persistent TCP flows. As opposed to existing work that focus only on the average queue occupancy as the performance metric of interest, the proposed analytical method obtains the more informative steady-state queue occupancy distribution of the wireless link. With the intention of maximizing TCP throughput, this analytical method is used to study traffic agnostic link adaptation schemes with and without hybrid ARQ. Moreover, a novel cross-layer queue-aware link adaptation scheme is proposed to improve the TCP throughput relative to the case where adaptive modulation and coding decisions are made based solely on the physical layer parameters. A fixed-point analytical model is proposed to obtain the aggregate TCP throughput attained at wireless links employing active queue management and queue-aware link adaptation. Allowing packet retransmissions and generalizing the scope from a single link to a network of such links, we propose an energy efficient queue-aware link adaptation scheme with hybrid ARQ which jointly adapts the transmission power and rate of the wireless links based on the queue occupancy levels and the channel conditions. Furthermore, we provide a fixed-point analytical method for such networks.
Open Access
Power-source-aware backbone routing in wireless sensor networks
(IEEE, 2010-11) Tekkalmaz, Metin; Körpeoğlu, İbrahim
Due to the limited energy-source and mostly unattended nature of the wireless sensor networks, efficient use of energy has a critical importance on the lifetime of the applications accomplished by such networks. Although in most of the cases sensor nodes are battery-powered, there are application scenarios in which battery- and mains-powered nodes coexist. In this paper, we present an approach and algorithms based on this approach that increase the lifetime of wireless sensor networks in such heterogeneous deployment cases. In the proposed approach, a backbone, which is composed of mains-powered nodes, sink, and battery-powered nodes if required, is constructed to relay the data packets. Simulation results show that, the proposed approach is able to increase the network lifetime up to more than a factor of two, compared to the case in which battery- and mains-powered nodes are not distinguished.
Open Access
Routing in delay tolerant networks with periodic connections
(SpringerOpen, 2015) Mergenci, C.; Korpeoglu, I.
In delay tolerant networks (DTNs), the network may not be fully connected at any instant of time, but connections occurring between nodes at different times make the network connected through the entire time continuum. In such a case, traditional routing methods fail to operate because there are no contemporaneous end-to-end paths between sources and destinations. This study examines the routing in DTNs where connections arise in a periodic nature. We analyze various levels of periodicity in order to meet the requirements of different network models. We propose different routing algorithms for different kinds of periodic connections. Our proposed routing methods guarantee the earliest delivery time and minimum hop-count, simultaneously. We evaluate our routing schemes via extensive simulation experiments and compare them to some other popular routing approaches proposed for DTNs. Our evaluations show the feasibility and effectiveness of our schemes as viable routing methods for delay tolerant networks.
Open Access
Sabit genişbantlı telsiz uygulamalarında ÇGÇÇ-DFBÇ için kanal kestirimi
(IEEE, 2006-04) Karakaya, B.; Çırpan, H. A.; Panayırcı, Erdal
Systems employing multiple transmit and receive antennas, known as multiple input multiple output (MIMO) systems can be used with OFDM to improve the resistance to channel impairments. Thus the technologies of OFDM and MIMO are equipped in fixed wireless applications with attractive features, including high data rates and robust performance. However, since different signals are transmitted from different antennas simultaneously, the received signal is the superposition of these signals, which implies new challenges for channel estimation. In this paper we propose a time domain MMSE based channel estimation approach for MIMO-OFDM systems. The proposed approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and finds MMSE estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MMSE estimator. Also the performance of the proposed approach is studied through the evaluation of minimum Bayesian MSE. © 2006 IEEE.
Open Access
Sequential churn prediction and analysis of cellular network users-a multi-class, multi-label perspective
(IEEE, 2017) Khan, Farhan; Kozat, Süleyman Serdar
We investigate the problem of churn detection and prediction using sequential cellular network data. We introduce a cleaning and preprocessing of the dataset that makes it suitable for the analysis. We draw a comparison of the churn prediction results from the-state-of-the-art algorithms such as the Gradient Boosting Trees, Random Forests, basic Long Short-Term Memory (LSTM) and Support Vector Machines (SVM). We achieve significant performance boost by incorporating the sequential nature of the data, imputing missing information and analyzing the effects of various features. This in turns makes the classifier rigorous enough to give highly accurate results. We emphasize on the sequential nature of the problem and seek algorithms that can track the variations in the data. We test and compare the performance of proposed algorithms using performance measures on real life cellular network data for churn detection.
Open Access
Static positioning using UWB range measurements
(IEEE, 2010) Gholami, M.R.; Ström, E.G.; Sottile F.; Dardari, D.; Conti, A.; Gezici, Sinan; Rydström, M.; Spirito, M.A.
The performance of several existing and partly new algorithms for positioning of sensor node based on distance estimate is compared when the distance estimates are obtained from a measurement campaign. The distance estimates are based on time-of-arrival measurements done by ultrawideband devices in an indoor office environment. Two different positioning techniques are compared: statistical and geometrical. In statistical category, distributed weighted-multidimensional scaling (dwMDS), least squares, and sum product algorithm are evaluated and in geometrical technique projections approach and outer approximation (OA) method are investigated. No method shows the best performance in all cases, while in many situations, sum product algorithm, dwMDS, nonlinear least square, projection approach, OA, and weighted least square work well. Copyright © The authors.
Open Access
Throughput modeling of single hop CSMA networks with non-negligible propagation delay
(IEEE, 2013) Koseoglu, M.; Karasan, E.
We analyze the performance of the CSMA protocol under propagation delays that are comparable with packet transmission times. We propose a semi-Markov model for the 2-node CSMA channel. For the 2-node case, the capacity reduces to 40% of the zero-delay capacity when the one-way propagation delay is 10% of the packet transmission time. We then extend this model and obtain the optimum symmetric probing rate that achieves the maximum network throughput as a function of the average propagation delay, d, and the number of nodes sharing the channel, N. The proposed model predicts that the total capacity decreases with d-1 as N goes to infinity when all nodes probe the channel at the optimum rate. The optimum probing rate for each node decreases with 1/N and the total optimum probing rate decreases faster than d-1 as N goes to infinity. We investigate how the short-term unfairness problem in CSMA worsens as the propagation delay increases and propose a back-off mechanism to mitigate this issue. The theoretical results presented in this paper can be used as a benchmark for the performance improvements provided by algorithms that have already been developed.
Open Access
A two-level temporal fair scheduler for multi-cell wireless networks
(Department of Electrical and Electronics Engineers, 2015) Shahsavari, S.; Akar, N.
We propose a two-level scheduler for a frequency reuse-1 multi-cell wireless network satisfying inter-and intra-cell weighted temporal fairness constraints. As opposed to hard partitioning of the entire frequency band to different cell patterns in frequency reuse-M systems (M>1), we propose sharing this band opportunistically in time by these patterns. Through numerical examples, we show notable gains in overall network throughput due to improved multi-user diversity in comparison with a conventional frequency reuse-3 system. © 2012 IEEE.
Open Access
Wireless ATA: A new data
(2005) Özler, Serdar; Körpeoğlu, İbrahim
This paper introduces a new data transport architecture and protocol for storage that is implemented on wireless devices and that can be accessed through a short-range wireless access technology such as Bluetooth or 802.11. We call the protocol WATA (Wireless ATA), as its architecture is similar to current ATA and ATA-based technologies. In this paper, we give basic technical details of the protocol and discuss its main advantages and disadvantages over the current protocols, and talk about our decisions to implement a prototype system to see an actual implementation of the architecture.