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  • 1.
    Azari, Amin
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Energy-efficient scheduling and grouping for machine-type communications over cellular networks2016In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 43, p. 16-29Article in journal (Refereed)
    Abstract [en]

    In this paper, energy-efficient scheduling for grouped machine-type devices deployed in cellular networks isinvestigated. We introduce a scheduling-based cooperation incentivescheme which enables machine nodes to organize themselveslocally, create machine groups, and communicate through grouprepresentatives to the base station. This scheme benefits from anovel scheduler design which takes into account the cooperationlevel of each node, reimburses the extra energy consumptionsof group representatives, and maximizes the network lifetime.As reusing cellular uplink resources for communications insidethe groups degrades the Quality of Service (QoS) of theprimary users, analytical results are provided which present atradeoff between maximum allowable number of simultaneouslyactive machine groups in a given cell and QoS of the primaryusers. Furthermore, we extend our derived solutions for theexisting cellular networks, propose a cooperation-incentive LTEscheduler, and present our simulation results in the context ofLTE. The simulation results show that the proposed solutionssignificantly prolong the network lifetime. Also, it is shown thatunder certain circumstances, reusing uplink resource by machinedevices can degrade the outage performance of the primary userssignificantly, and hence, coexistence management of machinedevices and cellular users is of paramount importance for nextgenerations of cellular networks in order to enable group-basedmachine-type communications while guaranteeing QoS for theprimary users.

  • 2.
    Charalambous, Themistoklis
    et al.
    Aalto Univ, Dept Elect Engn & Automat, Espoo, Finland..
    Kim, Su Min
    Korea Polytech Univ, Dept Elect Engn, Shihung, South Korea..
    Nomikos, Nikolaos
    Univ Aegean, Dept Informat & Commun Syst Engn, Samos, Greece..
    Bengtsson, Mats
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Johansson, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Relay-pair selection in buffer-aided successive opportunistic relaying using a multi-antenna source2019In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 84, p. 29-41Article in journal (Refereed)
    Abstract [en]

    We study a cooperative network with a buffer-aided multi-antenna source, multiple half-duplex (HD) buffer-aided relays and a single destination. Such a setup could represent a cellular downlink scenario, in which the source can be a more powerful wireless device with a buffer and multiple antennas, while a set of intermediate less powerful devices are used as relays to reach the destination. The main target is to recover the multiplexing loss of the network by having the source and a relay to simultaneously transmit their information to another relay and the destination, respectively. Successive transmissions in such a cooperative network, however, cause inter-relay interference (IRI). First, by assuming global channel state information (CSI), we show that the detrimental effect of IRI can be alleviated by precoding at the source, mitigating or even fully cancelling the interference. A cooperative relaying policy is proposed that employs a joint precoding design and relay-pair selection. Note that both fixed rate and adaptive rate transmissions can be considered. For the case when channel state information is only available at the receiver side (CSIR), we propose a relay selection policy that employs a phase alignment technique to reduce the IRI. The performance of the two proposed relay pair selection policies are evaluated and compared with other state-of-the-art relaying schemes in terms of outage and throughput. The results show that the use of a powerful source can provide considerable performance improvements.

  • 3.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vizcaino Luna, Alexandre
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Papadopouli, Maria
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. University of Crete, Heraklion, Greece.
    Closing the gap between traffic workload and channel occupancy models for 802.11 networks2014In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 21, p. 60-83Article in journal (Refereed)
    Abstract [en]

    The modeling of wireless network traffic is necessary to evaluate the possible gains of spectrum sharing and to support the design of new cognitive protocols that can use spectrum efficiently in network environments where diverse technologies coexist. In this paper we focus on IEEE 802.11 wireless local area networks and close the gap between two popular levels of modeling, macroscopic traffic workload modeling and microscopic channel occupancy modeling. We consider traffic streams generated by established traffic workload models and characterize the networking scenarios where a simple, semi-Markovian channel occupancy model accurately predicts the wireless channel usage. Our results demonstrate that the proposed channel occupancy model can capture the channel idle time distribution in most of the scenarios, while the Markovian assumption cannot be validated in all cases.

  • 4.
    Jin, Hongyu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Papadimitratos, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    DoS-resilient cooperative beacon verification for vehicular communication systems2019In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 90, article id UNSP 101775Article in journal (Refereed)
    Abstract [en]

    Authenticated safety beacons in Vehicular Communication (VC) systems ensure awareness among neighboring vehicles. However, the verification of beacon signatures introduces significant processing overhead for resource-constrained vehicular On-Board Units (OBUs). Even worse in dense neighborhood or when a clogging Denial of Service (DoS) attack is mounted. The OBU would fail to verify for all received (authentic or fictitious) beacons. This could significantly delay the verifications of authentic beacons or even affect the awareness of neighboring vehicle status. In this paper, we propose an efficient cooperative beacon verification scheme leveraging efficient symmetric key based authentication on top of pseudonymous authentication (based on traditional public key cryptography), providing efficient discovery of authentic beacons among a pool of received authentic and fictitious beacons, and can significantly decrease waiting times of beacons in queue before their validations. We show with simulation results that our scheme can guarantee low waiting times for received beacons even in high neighbor density situations and under DoS attacks, under which a traditional scheme would not be workable. rights reserved.

  • 5. Milioris, Dimitris
    et al.
    Tzagkarakis, George
    Papakonstantinou, Artemis
    Papadopouli, Maria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tsakalides, Panagiotis
    Low-dimensional signal-strength fingerprint-based positioning in wireless LANs2014In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 12, no 1, p. 100-114Article in journal (Refereed)
    Abstract [en]

    Accurate location awareness is of paramount importance in most ubiquitous and pervasive computing applications. Numerous solutions for indoor localization based on IEEE802.11, bluetooth, ultrasonic and vision technologies have been proposed. This paper introduces a suite of novel indoor positioning techniques utilizing signal-strength (SS) fingerprints collected from access points (APs). Our first approach employs a statistical representation of the received SS measurements by means of a multivariate Gaussian model by considering a discretized grid-like form of the indoor environment and by computing probability distribution signatures at each cell of the grid. At run time, the system compares the signature at the unknown position with the signature of each cell by using the Kullback-Leibler Divergence (KLD) between their corresponding probability densities. Our second approach applies compressive sensing (CS) to perform sparsity-based accurate indoor localization, while reducing significantly the amount of information transmitted from a wireless device, possessing limited power, storage, and processing capabilities, to a central server. The performance evaluation which was conducted at the premises of a research laboratory and an aquarium under real-life conditions, reveals that the proposed statistical fingerprinting and CS-based localization techniques achieve a substantial localization accuracy.

  • 6. Nayebi, Abbas
    et al.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Sarbazi-Azad, Hamid
    Evaluation and design of beaconing in mobile wireless networks2011In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 9, no 3, p. 368-386Article in journal (Refereed)
    Abstract [en]

    One of the intrinsic problems of mobility in wireless networks is the discovery of mobile nodes. A widely used solution for this problem is to use different variations of beacons, such as hello packets. Although a poorly designed beaconing scheme may lead to unnecessary energy usage or poor throughput, a systematic approach to analyze and select beaconing parameters is not provided in the literature. Here, we propose a model to study the beaconing efficiency using some measures such as the link lifetime, the probability of link establishment, and the delay to discover a new neighbor. The model is general and does not adhere to any particular mobility model; the only input from the mobility is the distribution of physical link durations, which not only abstracts away the mobility details but also all effects that contribute to the link stability such as non-perfectly omni-directional antennas and the path loss exponents. Among our results, we prove that the periodic beaconing (which is widely used owing to its simplicity) is the best in terms of beacon hits; we compare one-way and two-way beaconing schemes and study beaconing energy optimization. Finally, the model is applied to three cases of ad hoc, delay-tolerant, and sensor networks, and a simple rule of thumb is proposed to efficiently adjust the beacon interval. (C) 2010 Elsevier B.V. All rights reserved.

  • 7.
    Papadimitratos, Panagiotis
    et al.
    Cornell University, USA.
    Haas, Zygmunt
    Secure message transmission in mobile ad hoc networks2003In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 1, no 1, p. 193-209Article in journal (Refereed)
    Abstract [en]

    The vision of nomadic computing with its ubiquitous access has stimulated much interest in the mobile ad hoc networking (MANET) technology. However, its proliferation strongly depends on the availability of security provisions, among other factors. In the open, collaborative MANET environment, practically any node can maliciously or selfishly disrupt and deny communication of other nodes. In this paper, we propose the secure message transmission (SMT) protocol to safeguard the data transmission against arbitrary malicious behavior of network nodes. SMT is a lightweight, yet very effective, protocol that can operate solely in an end-to-end manner. It exploits the redundancy of multi-path routing and adapts its operation to remain efficient and effective even in highly adverse environments. SMT is capable of delivering up to 83% more data messages than a protocol that does not secure the data transmission. Moreover, SMT achieves up to 65% lower end-to-end delays and up to 80% lower delay variability, compared with an alternative single-path protocol - a secure data forwarding protocol, which we term secure single path (SSP) protocol. Thus, SMT is better suited to support quality of service for real-time communications in the ad hoc networking environment. The security of data transmission is achieved without restrictive assumptions on the network nodes' trust and network membership, without the use of intrusion detection schemes, and at the expense of moderate multi-path transmission overhead only.

  • 8. Redondi, Alessandro
    et al.
    Cesana, Matteo
    Tagliasacchi, Marco
    Filippini, Ilario
    Dan, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Cooperative image analysis in visual sensor networks2015In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 28, p. 38-51Article in journal (Refereed)
    Abstract [en]

    This work addresses the problem of enabling resource-constrained sensor nodes to perform visual analysis tasks. The focus is on visual analysis tasks that require the extraction of local visual features, which form a succinct and distinctive representation of the visual content of still images or videos. The extracted features are then matched against a feature data set to support applications such as object recognition, face recognition and image retrieval. Motivated by the fact that the processing burden imposed by common algorithms for feature extraction may be prohibitive for a single, resource-constrained sensor node, this paper proposes cooperative schemes to minimize the processing time of the feature extraction algorithms by offloading the visual processing task to neighboring sensor nodes. The optimal offloading strategy is formally characterized under different networking and communication paradigms. The performance of the proposed offloading schemes is evaluated using simulations and is validated through experiments carried out on a real wireless sensor network testbed. The results show that the proposed offloading schemes allow to reduce the feature extraction time up to a factor of 3 in the reference scenario.

  • 9.
    Vukadinovic, Vladimir
    et al.
    Disney Research Zurich.
    Glaropoulos, Ioannis
    Disney Research Zurich.
    Mangold, Stefan
    Disney Research Zurich.
    Enhanced Power Saving Mode for Low-Latency Communication in Multi-Hop 802.11 Networks2014In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 23, no December 2014, p. 18-33Article in journal (Refereed)
    Abstract [en]

    The Future Internet of Things (IoT) will connect billions of battery-powered radio-enabled devices. Some of them may need to communicate with each other and with Internet gateways (border routers) over multi-hop links. While most IoT scenarios assume that for this purpose devices use energy-efficient IEEE 802.15.4 radios, there are use cases where IEEE 802.11 is preferred despite its potentially higher energy consumption. We extend the IEEE 802.11 power saving mode (PSM), which allows WLAN devices to enter a low-power doze state to save energy, with a traffic announcement scheme that facilitates multi-hop communication. The scheme propagates traffic announcements along multi-hop paths to ensure that all intermediate nodes remain awake to receive and forward the pending data frames with minimum latency. Our simulation results show that the proposed Multi-Hop PSM (MH-PSM) improves both end-to-end delay and doze time compared to the standard PSM; therefore, it may optimize WLAN to meet the networking requirements of IoT devices. MH-PSM is practical and software-implementable since it does not require changes to the parts of the IEEE 802.11 medium access control that are typically implemented on-chip. We implemented MH-PSM as a part of a WLAN driver for Contiki OS, which is an operating system for resource-constrained IoT devices, and we demonstrated its efficiency experimentally.

  • 10.
    Zeng, Ming
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering.
    Fodor, Viktória
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering.
    Energy minimization for delay constrained mobile edge computing with orthogonal and non-orthogonal multiple access2020In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 98, article id 102060Article in journal (Refereed)
    Abstract [en]

    Mobile edge computing (MEC) is envisioned as a promising technology for enhancing the computation capacities and prolonging the lifespan of mobile devices, by enabling mobile devices to offload computation-intensive tasks to servers in close proximity. For wireless communication, MEC introduces a new scenario, where computations are performed directly at the receiving side of the wireless links. Our objective is therefore to evaluate the importance of joint radio-and-computational resource allocation and spectral efficiency enhancing techniques in this new scenario. We formulate the resource allocation problem to minimize the energy consumption of computation offloading of delay sensitive tasks and propose near-optimal solutions for both orthogonal and non-orthogonal multiple access schemes, with the optimal joint allocation of computing resources and transmission power. Our numerical results demonstrate the superiority of non-orthogonal multiple access over its orthogonal counterpart and the importance of joint resource allocation, especially in scenarios with strict delay limits, where both the transmission and the computational resources are scarce.

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