| 1. |
- Angelakis, Vangelis, et al.
(författare)
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Adjacent Channel Interference in 802.11a Is Harmful: Testbed Validation of a Simple Quantification Model
- 2011
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Ingår i: IEEE COMMUNICATIONS MAGAZINE. - : IEEE Institute of Electrical and Electronics. - 0163-6804. ; 49:3, s. 160-166
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Tidskriftsartikel (refereegranskat)abstract
- Wireless LAN radio interfaces based on the IEEE 802.11a standard have lately found widespread use in many wireless applications. A key reason for this was that although the predecessor, IEEE 802.11b/ g, had a poor channelization scheme, which resulted in strangling adjacent channel interference (ACI), 802.11a was widely believed to be ACI-free due to a better channelization combined with OFDM transmission. We show that this is not the case. ACI does exist in 802.11a, and we can quantify its magnitude and predict its results. For this, we present minor modifications of a simple model originally introduced by [1] that allow us to calculate bounding values of the 802.11a ACI, which can be used in link budget calculations. Using a laboratory testbed, we verify the estimations of the model, performing experiments designed to isolate the affected 802.11 mechanisms. This isolation was enabled by not using the wireless medium, and emulating it over cables and attenuators. Our results show clear throughput degradation because of ACI in 802.11a, the magnitude of which depends on the interfering data rates, packet sizes, and utilization of the medium.
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| 2. |
- Angelakis, Vangelis, et al.
(författare)
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Security and Resilience in Cognitive Radio Networks
- 2011
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Ingår i: European Research Consortium for Informatics and Mathematics Magazine. - 0926-4981. ; :85, s. 48-49
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Tidskriftsartikel (refereegranskat)abstract
- After more than a decade of research, system securityand resilience is now the major technological barrier forthe Cognitive Radio (CR) to be adopted by the telecommunication industry. New ideas are required tomake CR networks secure and robust against attacks taking advantage the inherent characteristics of the CR functionality. This work explores key points that urgentlyneed to be addressed.
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| 3. |
- Papadimitriou, Georgios, et al.
(författare)
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Network-level performance evaluation of a two-relay cooperative random access wireless system
- 2015
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Ingår i: Computer Networks. - : Elsevier. - 1389-1286 .- 1872-7069. ; 88, s. 187-201
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Tidskriftsartikel (refereegranskat)abstract
- In wireless networks relay nodes can be used to assist the users transmissions to reach their destination. Work on relay cooperation, from a physical layer perspective, has up to now yielded well-known results. This paper takes a different stance focusing on network-level cooperation. Extending previous results for a single relay, we investigate here the benefits from the deployment of a second one. We assume that the two relays do not generate packets of their own and the system employs random access to the medium; we further consider slotted time and that the users have saturated queues. We obtain analytical expressions for the arrival and service rates of the queues of the two relays and the stability conditions. We investigate a model of the system, in which the users are divided into clusters, each being served by one relay, and show its advantages in terms of aggregate and throughput per user. We quantify the above, analytically for the case of the collision channel and through simulations for the case of multi-packet reception (MPR), and we provide insight on when the deployment of a second relay in the system can yield significant advantages.
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| 4. |
- Pappas, Nikolaos, et al.
(författare)
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Effect of Energy Harvesting on Stable Throughput in Cooperative Relay Systems
- 2016
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Ingår i: Journal of Communications and Networks. - : KOREAN INST COMMUNICATIONS SCIENCES (K I C S). - 1229-2370 .- 1976-5541. ; 18:2, s. 261-269
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the impact of energy constraints on a two hop network with a source, a relay and a destination under random medium access is studied. A collision channel with erasures is considered, and the source and the relay nodes have energy harvesting capabilities and an unlimited battery to store the harvested energy. Additionally, the source and the relay node have external traffic arrivals and the relay forwards a fraction of the source nodes traffic to the destination; the cooperation is performed at the network level. An inner and an outer bound of the stability region for a given transmission probability vector are obtained. Then, the closure of the inner and the outer bound is obtained separately and they turn out to be identical. This work is not only a step in connecting information theory and networking, by studying the maximum stable throughput region metric but also it taps the relatively unexplored and important domain of energy harvesting and assesses the effect of that on this important measure.
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| 5. |
- Pappas, Nikolaos, et al.
(författare)
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Relay-Assisted Multiple Access With Full-Duplex Multi-Packet Reception
- 2015
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Ingår i: IEEE Transactions on Wireless Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1536-1276 .- 1558-2248. ; 14:7, s. 3544-3558
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Tidskriftsartikel (refereegranskat)abstract
- The effect of full-duplex cooperative relaying in a random access multiuser network is investigated here. First, we model the self-interference incurred due to full-duplex operation, assuming multi-packet reception capabilities for both the relay and the destination node. Traffic at the source nodes is considered saturated and the cooperative relay, which does not have packets of its own, stores a source packet that it receives successfully in its queue when the transmission to the destination has failed. We obtain analytical expressions for key performance metrics at the relay, such as arrival and service rates, stability conditions, and average queue length, as functions of the transmission probabilities, the self interference coefficient, and the links outage probabilities. Furthermore, we study the impact of the relay node and the self-interference coefficient on the per-user and aggregate throughput, and the average delay per packet. We show that perfect self-interference cancelation plays a crucial role when the SINR threshold is small, since it may result to worse performance in throughput and delay comparing with the half-duplex case. This is because perfect self-interference cancelation can cause an unstable queue at the relay under some conditions.
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| 6. |
- Pappas, Nikolaos, 1982-, et al.
(författare)
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Wireless Network-Level Partial Relay Cooperation: A Stable Throughput Analysis
- 2018
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Ingår i: Journal of Communications and Networks. - 1229-2370 .- 1976-5541. ; 20:1, s. 93-101
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we study the benefit of partial relay cooperation. We consider a two-node system consisting of one source and one relay node transmitting information to a common destination. The source and the relay have external traffic and in addition, the relay is equipped with a flow controller to regulate the incoming traffic from the source node. The cooperation is performed at the network level. A collision channel with erasures is considered. We provide an exact characterization of the stability region of the system and we also prove that the system with partial cooperation is always better or at least equal to the system without the flow controller.
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| 7. |
- Ploumidis, Manolis, et al.
(författare)
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Flow Allocation for Maximum Throughput and Bounded Delay on Multiple Disjoint Paths for Random Access Wireless Multihop Networks
- 2017
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Ingår i: IEEE Transactions on Vehicular Technology. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9545 .- 1939-9359. ; 66:1, s. 720-733
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we consider random-access wireless networks, withmultipacket reception capabilities, where multiple flows are forwarded to the gateways through node disjoint paths. We explore the issue of allocating flow on multiple paths, exhibiting both intra-and interpath interference, in order to maximize average aggregate flow throughput (AAT) and provide bounded packet delay. A distributed flow allocation scheme is proposed where allocation of flow on paths is formulated as an optimization problem. Through an illustrative topology, it is shown that the corresponding problem is nonconvex. Furthermore, a simple but accurate model is employed for the AAT achieved by all flows, which captures both intra-and interpath interference through the signal-to-interference-plus-noise ratio (SINR) model. The proposed scheme is evaluated through Ns2 simulations of several random wireless scenarios. Simulation results reveal that the model employed accurately captures the AAT observed in the simulated scenarios, even when the assumption of saturated queues is removed. Simulation results also show that the proposed scheme achieves significantly higher AAT for the vast majority of the wireless scenarios explored than for the following flow allocation schemes: one that assigns flows on paths on a round-robin fashion, one that optimally utilizes the best path (BP) only, and another one that assigns the maximum possible flow on each path. Finally, a variant of the proposed scheme is explored, where interference for each link is approximated by considering its dominant interfering nodes only.
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| 8. |
- Ploumidis, Manolis, et al.
(författare)
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On the delay of a throughput optimal flow allocation scheme for random access WMNs
- 2014
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Ingår i: 2014 IEEE 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD). - : IEEE. - 9781479957255 ; , s. 218-223
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Konferensbidrag (refereegranskat)abstract
- In this paper we consider random access wireless mesh networks with multi-packet reception capabilities where multiple flows are forwarded to the gateways through node disjoint paths. We address the issue of aggregate throughput optimal flow rate allocation with bounded delay guarantees for flows exhibiting both intra- and inter-path interference. In our prior work we have suggested a distributed flow allocation scheme that maximizes the average aggregate throughput of all flows also providing bounded delay guarantees. In this work we evaluate this scheme in terms of delay and compare its performance with the following schemes: a scheme that utilizes paths on a round-robin fashion, one that optimally utilizes the best path only and another one that assigns the maximum possible flow on each path. For the evaluation process Ns2 simulations of several random wireless scenarios are employed.
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| 9. |
- Ploumidis, Manolis, et al.
(författare)
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On the performance of network coding and forwarding schemes with different degrees of redundancy for wireless mesh networks
- 2015
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Ingår i: Computer Communications. - : ELSEVIER SCIENCE BV. - 0140-3664 .- 1873-703X. ; 72, s. 49-62
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Tidskriftsartikel (refereegranskat)abstract
- This work explores the throughput and delay that can be achieved by various forwarding schemes, employing multiple paths and different degrees of redundancy, focusing on linear network coding. The key contribution of the study is an analytical framework for modeling the throughput and delay forvarious schemes, considering wireless mesh networks where unicast traffic is forwarded and hop-by-hop retransmissions are employed for achieving reliability. The analytical framework is generalized for an arbitrary number of paths and hops per path. Another key contribution of the study is the evaluation and extension of the numerical results, drawn from the analysis, through system-level simulations. Our results show that, in scenarios with significant interference, the best throughput-delay tradeoff is achieved by single path forwarding. Moreover, when significant interference is present and network coding employs the larger packet generation size, it experiences higher delay than the other schemes. This is due to the inter-arrival times aggregating over all coded packets required to decode a packet generation. (C) 2015 Elsevier B.V. All rights reserved.
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| 10. |
- Ploumidis, Manolis, et al.
(författare)
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Performance of Flow Allocation with Successive Interference Cancelation for Random Access WMNs
- 2015
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Ingår i: 2015 IEEE Globecom Workshops (GC Wkshps). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467395267 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- In this study we explore the gain that can be achieved by jointly allocating flow on multiple paths and employing successive interference cancelation (SIC), for random access wireless mesh networks with multi-packet reception capabilities. More precisely, we explore a distributed flow allocation scheme aimed at maximizing average aggregate flow throughput, while also providing bounded delay, when SIC is employed. Simulation results derived from three illustrative topologies show that the gain over treating interference as noise (IAN) for this scheme can be up to 15.2%, for an SINR threshold value equal to 0.5. For SINR threshold values as high as 2.0 however, SIC does not always result in higher throughput. In some scenarios explored, the gain of SIC over IAN is insignificant, while in some others treating interference as noise proves better. The reason is that, although SIC improves the throughput on a specific link, it also increases the interference imposed on neighbouring receivers. We also show that, the gain of applying SIC is more profound in cases of a large degree of asymmetry among interfering links.
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