| 1. |
- Bagula, Antoine B.
(författare)
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On achieveing bandwidth-aware LSP/lambda SP multiplexing/separation in multi-layer networks
- 2007
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 25:5, s. 987-1000
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Tidskriftsartikel (refereegranskat)abstract
- We present a new Traffic engineering (TE) model which is based on QoS rerouting and uses hybrid resilience to improve the recovery performance of multi-layer networks where an MPLS network is layered above an MP lambda S network. We formulate the rerouting of the LSPs/lambda SPs as a multi-constrained problem and use its polynomial reduction to find a heuristic solution that can be implemented by standardized constraint-based routing algorithms. This heuristic solution uses a cost-based routing optimization to achieve different network configurations which multiplex/separate bandwidth-aware LSPs/lambda SPs on the network links. We formulate the resilience upon failure as a multi-objective problem consisting of finding a resilience strategy that minimizes recovery operation time and maximizes the LSP/lambda SP restorability. A solution to this problem is proposed where a hybrid resilience framework is used to achieve restoration in the MPLS layer to complement path switching in the MP lambda S layer. We evaluate the performance of the TE model when rerouting the tunnels carrying the traffic offered to a 23- and 31-node networks. Simulation reveals that the hybrid resilience model performs better than classical recovery mechanisms in terms of restorability, quality of rerouting paths and rerouting; stability.
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| 2. |
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| 3. |
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| 4. |
- Gross, James, 1975-, et al.
(författare)
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Performance Analysis of Dynamic OFDMA Systems with Inband Signaling
- 2006
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Ingår i: IEEE Journal on Selected Areas in Communications. - : IEEE Press. - 0733-8716 .- 1558-0008. ; 24:3, s. 427-436
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Tidskriftsartikel (refereegranskat)abstract
- Within the last decade, the orthogonal frequency-division multiplexing (OFDM) transmission scheme has become part of several standards for wireless systems. Today, OFDM is even a candidate for fourth-generation wireless systems. It is well known that dynamic OFDMA systems potentially increase the spectral efficiency. They exploit diversity effects in time, space, and frequency by assigning system resources periodically to terminals. Informing the terminals about new assignments creates a signaling overhead. Up to now, this overhead has not been taken into account in studies on dynamic orthogonal frequency-division multiplexing access (OFDMA) systems. Yet this is crucial for a realistic notion of the performance achieved by dynamic approaches. In this paper, we close this gap. We introduce two forms of representing the signaling information and discuss how these affect system performance. The study of the signaling impact on the performance is conducted for an exemplary dynamic approach. We find that the throughput behavior of dynamic OFDMA systems is significantly influenced by the signaling overhead. In many situations, neglecting the overhead leads to wrong performance conclusions. Also, the performance difference between dynamic and static schemes is now much more sensible to the specific parameter set of the transmission scenario (e.g., frame length, subcarrier number, etc.). This leads to the proposal of access points which should adapt certain system parameters in order to provide optimal performance.
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| 5. |
- Hu, Bin, et al.
(författare)
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A divergence minimization approach to joint multiuser decoding for coded CDMA
- 2008
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 26:3, s. 432-445
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a theoretical framework of divergence minimization (DM) is applied to derive iterative receiver algorithms for coded CDMA systems. The DM receiver obtained performs joint channel estimation, multiuser decoding, and noisecovariance estimation. While its structure is similar to that of many ad-hoc receivers in the literature, the DM receiver is the result of applying a formal framework for optimization without further simplifications,namely the DM approach with a factorizable auxiliary model distribution. The well-known expectation-maximization (EM) algorithm and space-alternating generalized expectation-maximization (SAGE) algorithm are special cases of degenerate model distributions within the DM framework. Furthermore, many ad-hoc receiver structures from literature are shown to represent approximations of the proposed DM receiver. The DM receiver has four interesting properties that all result directly from applying the formal framework: (i) The covariances of all estimates involved are taken into account. (ii) The residual interference after interference cancellation is handled by the noise-covariance estimation as opposed to by LMMSE filters in other receivers. (iii) Posterior probabilities of the code symbols are employed rather than extrinsic probabilities. (iv) The iterative receiver is guaranteed to converge in divergence. The theoretical insights are illustrated by simulation results.
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| 6. |
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| 7. |
- Karlsson, Gunnar, et al.
(författare)
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Delay and disruption tolerant wireless communication
- 2008
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Ingår i: IEEE Journal on Selected Areas in Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0733-8716 .- 1558-0008. ; 26:5, s. 745-747
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Kim, Thanh Tung, et al.
(författare)
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On Cooperative Source Transmission with Partial Rate and Power Control
- 2008
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Ingår i: IEEE Journal on Selected Areas in Communications. - : IEEE Communications Society. - 0733-8716 .- 1558-0008. ; 26:8, s. 1408-1418
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Tidskriftsartikel (refereegranskat)abstract
- The problem of transmitting a Gaussian source over a half-duplex fading relay channel with limited channel state feedback is studied. It is shown that under a short-term power constraint, combining a simple feedback scheme with separate source and channel coding outperforms the best known no-feedback strategies even with only a few bits of feedback information. Partial power control is shown to be instrumental in achieving a very fast decaying average distortion, especially in the regime of high bandwidth ratios. Performance limitation due to the lack of full channel state information at the destination is also investigated, where the degradation in terms of the distortion exponent is shown to be significant. However, even in such restrictive scenarios, using partial feedback still yields distortion exponents superior to any no-feedback schemes.
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| 9. |
- Larsson, Erik G., et al.
(författare)
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Competition Versus Cooperation on the MISO Interference Channel
- 2008
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 26:7, s. 1059-1069
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Tidskriftsartikel (refereegranskat)abstract
- We consider the problem of coordinating two competingmultiple-antenna wireless systems (operators) that operatein the same spectral band. We formulate a rate region whichis achievable by scalar coding followed by power allocationand beamforming. We show that all interesting points on thePareto boundary correspond to transmit strategies where bothsystems use the maximum available power. We then argue thatthere is a fundamental need for base station cooperation whenperforming spectrum sharing with multiple transmit antennas.More precisely, we show that if the systems do not cooperate,there is a unique Nash equilibrium which is inefficient in the sensethat the achievable rate is bounded by a constant, regardless ofthe available transmit power. An extension of this result to thecase where the receivers use successive interference cancellation(SIC) is also provided.Next we model the problem of agreeing on beamformingvectors as a non-transferable utility (NTU) cooperative gametheoreticproblem, with the two operators as players. Specificallywe compute numerically the Nash bargaining solution, which isa likely resolution of the resource conflict assuming that theplayers are rational. Numerical experiments indicate that selfishbut cooperating operators may achieve a performance which isclose to the maximum-sum-rate bound.
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| 10. |
- Papadimitratos, Panagiotis, et al.
(författare)
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Secure Data Communication in Mobile Ad Hoc Networks
- 2006
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 24:2, s. 343-356
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Tidskriftsartikel (refereegranskat)abstract
- We address the problem of secure and fault-tolerant communication in the presence of adversaries across a multihop wireless network with frequently changing topology. To effectively cope with arbitrary malicious disruption of data transmissions, we propose and evaluate the secure message transmission (SMT) protocol and its alternative, the secure single-path (SSP) protocol. Among the salient features of SMT and SSP is their ability to operate solely in an end-to-end manner and without restrictive assumptions on the network trust and security associations. As a result, the protocols are applicable to a wide range of network architectures. We demonstrate that highly reliable communication can be sustained with small delay and small delay variability, even when a substantial portion of the network nodes systematically or intermittently disrupt communication. SMT and SSP robustly detect transmission failures and continuously configure their operation to avoid and tolerate data loss, and to ensure the availability of communication. This is achieved at the expense of moderate transmission and routing overhead, which can be traded off for delay. Overall, the ability of the protocols to mitigate both malicious and benign faults allows fast and reliable data transport even in highly adverse network environments.
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