| 1. |
- Athanasiou, George, et al.
(författare)
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Dynamic Frequency Management in 802.11-based Multi-Radio Wireless Networks
- 2014
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Ingår i: European transactions on telecommunications. - : Wiley. - 1124-318X .- 2161-3915. ; 25:7, s. 752-768
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Tidskriftsartikel (refereegranskat)abstract
- Efficient channel selection is essential in 802.11 mesh deployments, for minimising contention and interference among co-channel devices and thereby supporting a plurality of quality of service (QoS)-sensitive applications. A few protocols have been proposed for frequency allocation in such networks; however, they do not address the problem end-to-end. In this paper, we present a general formulation of the channel selection problem, taking into account the performance of both mesh access and mesh backhaul. Moreover, we propose a routing-aware channel selection protocol for wireless mesh networks (ARACHNE). ARACHNE is distributed in nature and motivated by our measurements on a wireless testbed. The main novelty of our protocol comes from adopting a metric that captures the end-to-end link loads across different routes in the network. ARACHNE prioritises the assignment of low-interference channels to links that (i) need to serve high-load aggregate traffic and/or (ii) already suffer significant levels of contention and interference. Our protocol takes into account the number of potential interfaces (radios) per device and allocates these interfaces in a manner that efficiently utilises the available channel capacity. We evaluate ARACHNE through extensive, trace-driven simulations, and we show the approaches to the optimal channel selection. We observe that our protocol improves the total network throughput, as compared to three other representative channel allocation approaches in literature.
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| 2. |
- Bergfeldt, Erik, et al.
(författare)
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Real-time bandwidth measurements over mobile connections
- 2011
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Ingår i: European transactions on telecommunications. - : John Wiley and Sons. - 1124-318X .- 2161-3915. ; 22:6, s. 255-267
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Tidskriftsartikel (refereegranskat)abstract
- The first study that investigates the characteristics of received probe packets and the reliability of bandwidth estimates when actively measuring the available bandwidth over radio interfaces in mobile communication networks is presented. Knowledge of available bandwidth is very useful in various contexts, e. g. in network management and adaptive streaming applications. Bandwidth measuring tools have so far primarily been designed for and evaluated in wired networks. However, such tools should also be examined in wireless networks since the use of, e. g., mobile broadband is rapidly increasing. The properties of wired and wireless links differ substantially, which affect the performance of the tools. We have made active-probing experiments over a high-speed downlink shared channel, which is used for High-Speed Downlink Packet Access (HSDPA) in the mobile communication technology UMTS, and over a forward traffic channel in CDMA2000 1xEV-DO. Both experiments were performed over commercial networks. They show that one cannot always expect uniform per-packet processing over the radio channel in mobile networks, which is expected by many probing tools. This reduces the reliability of the available-bandwidth estimates, however we suggest how this can be handled. Finally, the mobile-network measurements are compared to experiments performed in an IEEE 802.11 wireless LAN, where the radio channel does not create the same packet-processing behaviour. We also discuss the possibility of using the probe traffic for the purpose of identifying the communication technology at the bottleneck of the network path, assumed this is a wireless broadband link, by mapping specifications of standardised communication technologies to observed probe-traffic characteristics.
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| 3. |
- Bohge, Mathias, et al.
(författare)
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Optimal Soft Frequency Reuse and Dynamic Sub-carrier Assignments in Cellular OFDMA Networks
- 2010
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Ingår i: European transactions on telecommunications. - : Wiley. - 1124-318X .- 2161-3915. ; 21:8, s. 704-713
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Tidskriftsartikel (refereegranskat)abstract
- Soft frequency reuse (SFR) is a common technique for co-channel interference (CCI) mitigation in cellular OFDMA networks. The performance of such networks significantly depends on the configuration of the power profiles that implement the soft frequency reuse patterns. In this paper, we investigate the performance of static soft frequency reuse by comparing it against the optimal case, in which a central entity optimally distributes power among the users of the network. It is shown that there is a significant performance gap between both approaches, which needs to be filled by adaptive SFR mechanisms. Moreover, we show that the achievable gain of static SFR is small in a system that is able to optimally decide on terminal/sub-carrier assignments.
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| 4. |
- Charalambous, Themistoklis, et al.
(författare)
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On the Minimum Latency Transmission Scheduling in Wireless Networks with Power Control under SINR Constraints
- 2013
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Ingår i: European transactions on telecommunications. - : Wiley. - 1124-318X .- 2161-3915. ; 26:3, s. 367--379
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Tidskriftsartikel (refereegranskat)abstract
- In order to alleviate interference and contention in a wireless network, we may exploit the existence of multiple orthogonal channels or time slots, thus achieving a substantial improvement in performance. In this paper, we study a joint transmission scheduling and power control problem that arises in wireless networks. The goal is to assign channels (or time slots) and transmitting powers to communication links such that all communication requests are processed correctly, specified quality-of-service requirements are met, and the number of required time slots is minimised. First, we formulate the problem as a mixed-integer linear programming. Then, we show that the problem considered is non-deterministic polynomial-time hard, and subsequently, we propose non-trivial bounding techniques to solve it. Optimisation methods are also discussed, including a column generation approach, specifically designed to find bounds for the transmission scheduling problem. Moreover, we develop optimisation techniques in which the bounding techniques are integrated in order to derive the optimal solution to the problem faster. We close with an extensive computational study, which shows that despite the complexity of the problem, the proposed methodology scales to problems of non-trivial size. Our algorithms can therefore be used for static wireless networks where propagation conditions are almost constant and a centralised agent is available (e.g. cellular networks where the base station can act as a centralised agent or wireless mesh networks), and they can also serve as a benchmark for the performance evaluation of heuristic, approximation or distributed algorithms that aim to find near-optimal solutions without information about the whole network.
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| 5. |
- Nomikos, Nikos, et al.
(författare)
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Joint relay-pair selection for buffer-aided successive opportunistic relaying
- 2014
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Ingår i: European transactions on telecommunications. - : Wiley. - 1124-318X .- 2161-3915. ; 25:8, s. 823-834
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a buffer-aided successive opportunistic relaying scheme that aims at improving the average capacity of the network when inter-relay interference arises between relays that are selected for simultaneous transmission and reception. We propose a relay selection policy that, by exploiting the benefits of buffering at the relays, decouples the receiving relay at the previous time slot to be the transmitting relay at the next slot. Furthermore, we impose an interference cancellation threshold allowing the relay that is selected for reception to decode and subtract the inter-relay interference. The proposed relaying scheme selects the relaying pair that maximises the average capacity of the relay network. Its performance is evaluated through simulations and comparisons with other state-of-the-art half-duplex and full-duplex relay selection schemes, in terms of outage probability, average capacity and average delay. The results reveal that a trade-off has to be made between improving the outage at the cost of reduced capacity and increased delay and vice versa. Finally, conclusions are drawn and future directions are discussed, including the need for a hybrid scheme incorporating both half-duplex and full-duplex characteristics.
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| 6. |
- You, Lei, et al.
(författare)
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Cross-layer optimisation for uplink transmission in OFDMA cellular networks with fixed relays
- 2011
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Ingår i: European transactions on telecommunications. - : John Wiley & Sons. - 1124-318X .- 2161-3915. ; 22:6, s. 296-314
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we consider a cross-layer design aimed to enhance performance for uplink transmission in an orthogonal frequency division multiple-access (OFDMA)-based cellular network with fixed relay stations. Because mobile stations (MSs) spend most of the power on the uplink transmission, power efficiency resource allocation becomes very important to MSs. We develop a cross-layer optimisation framework for two types of uplink flows (inelastic and elastic flows) that have different quality-of-service requirements. For inelastic flows with fixed-rate requirement, we formulate the cross-layer optimisation problem as the minimisation of the sum transmission power of MSs under the constraints of flow conservation law, subcarrier assignment, relaying path selection and power allocation. For elastic flows with flexible-service-rate requirement, we consider the cross-layer trade-off between uplink service rate and power consumption of MSs and pose the optimisation problem as the maximisation of a linear combination of utility (of service rates) and power consumption (of MSs). Different trade-offs can be achieved by varying the weighting parameters. Dual decomposition and subgradient methods are used to solve the problems optimally with reduced computational complexity. The simulation results show that, through the proposed cross-layer resource optimisation framework and algorithms, significant benefits of deployment of multiple fixed relays in an OFDMA cellular network can be fully obtained such as reduction in power consumption, increase in service rate and energy savings in the uplink transmission of MSs.
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| 7. |
- Athanasiou, George, et al.
(författare)
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Design and Implementation of Distributed Resource Management Mechanisms for Wireless Mesh Networks
- 2012
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Ingår i: Transactions on Emerging Telecommunications Technologies. - : Wiley. - 2161-3915.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we design and implement a resource management scheme based on cooperative association, where the STAs can share useful information in order to improve the performance of the association/handoff procedures. The cooperative association mechanism is inspired by the rapidly designed cooperative protocols in the field of wireless networks. Furthermore, we introduce a load balancing mechanism that operates in a cross-layer manner taking into account uplink and downlink channel conditions, routing performance and congestion control. The iterative heuristic algorithms that we propose, control the communication load of each mesh AP in a distributed manner. We evaluate the performance of our mechanisms through OPNET simulations and testbed experiments.
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| 8. |
- Fei, Zesong, et al.
(författare)
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Improved Luby transform codes in low overhead regions for binary erasure channels
- 2014
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Ingår i: Transaction on Emerging Telecommunications Technologies. - : Wiley-Blackwell. - 2161-3915.
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Tidskriftsartikel (refereegranskat)abstract
- We study improved degree distribution for Luby transform (LT) codes, which exhibits improved bit error rates particularly in low overhead regions. We construct the degree distribution by modifying robust soliton distribution. The performance of our proposed LT codes is evaluated and compared with the conventional LT codes via And-Or tree analysis. Then we propose a transmission scheme based on our proposed degree distribution to improve the frame error rate in full recovery regions. Furthermore, the improved degree distribution is applied to distributed multi-source relay networks and unequal error protection. It is shown that our schemes achieve better performance and reduced complexity especially in low overhead regions, compared with conventional schemes.
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| 9. |
- Obregon, Evanny, et al.
(författare)
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On the Feasibility of Indoor BroadbandSecondary Access to the 960-1215 MHz Aeronautical Spectrum
- 2013
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Ingår i: Transactions on Emerging Telecommunications Technologies. - : John Wiley & Sons. - 2161-3915. ; 24:7-8, s. 724-733
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we analyse the feasibility of indoor broadband service provisioning using secondary spectrum access to the 960–1215 MHz band, primarily allocated to the distance measuring equipment (DME) system for aeronautical navigation. We propose a practical secondary sharing scheme customised to the characteristics of the DME. Because the primary system performs a safety-of-life functionality, protection from harmful interference becomes extremely critical. The proposed scheme controls aggregate interference by imposing an individual interference threshold on the secondary users. We examine the feasibility of large scale secondary access in terms of the transmission probability of the secondary users that keeps the probability of harmful interference below a given limit. Uncertainties in the estimation of propagation loss and DME location affect the feasibility of the secondary access. Numerical results show that a large number of secondary users are able to operate in adjacent DME channels without harming the primary system even with limited accuracy on the estimation of the propagation loss.
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