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Lee K.-K.,Korea Advanced Institute of Science and Technology | Ryoo J.-D.,Advanced Communications Research Laboratory | Ryoo J.-D.,Korean University of Science and Technology | Kim S.H.,Korea Advanced Institute of Science and Technology | Kim D.,Korea Advanced Institute of Science and Technology
IEEE Communications Letters | Year: 2012

Ethernet ring protection (ERP), defined in ITU-T recommendation G.8032, is a promising technology to realize the SONET/SDH-grade resilience in carrier Ethernet infrastructures. With its own loop prevention technique to block a link called ring-protection-link (RPL) in an ERP ring, the ERP introduces a new optimization problem named RPL positioning whose objective is to find the optimal RPL location to minimize the required ring capacity for given traffic demands. In this paper, we derive the optimal RPL positioning as an integer linear programming (ILP) problem and additionally propose an optimal RPL positioning algorithm for more effective ring loading. By evaluations, we demonstrate that our proposed algorithm is indeed capable of finding the optimal RPL equal to the results by an exhaustive search emerged in prior works or the formulated ILP model. But, it is more efficient in computing time than the exhaustive search and the ILP model. © 2012 IEEE. Source

Choi Y.,Stanford University | Lee Y.,Korea Advanced Institute of Science and Technology | Chang K.,Advanced Communications Research Laboratory | Chang K.,Simon Fraser University
ETRI Journal | Year: 2012

Carrier aggregation is an essential feature in the Long Term Evolution-Advanced (LTE-A) system, which allows the scalable expansion of the effective bandwidth to be delivered to user equipment (UE) through the concurrent use of radio resources across multiple component carriers (CCs). This system's optimal radio-resource use has received much attention under simultaneous access (SA) scenarios for multiple CCs (m-CCs). This letter establishes how many CCs a UE should simultaneously connect to maintain maximum uplink capacity. Under the m-CC LTE-A system, the spectral efficiency of the m-CC SA scheme (m≥2) is compared with that of CC selection (CCS). Numerical results reveal that the 2-CC SA scheme outperforms CCS and performs almost equally to the m-CC SA scheme (m≥3). © 2012 ETRI. Source

Yu H.,Yeungnam University | Lee S.-K.,Advanced Communications Research Laboratory
ETRI Journal | Year: 2012

A beam design method based on signal-to-leakage-plus-noise ratio (SLNR) has been recently proposed as an effective scheme for multiuser multiple-input multiple-output downlink channels. It is shown that its solution, which maximizes the SLNR at a transmitter, can be simply obtained by the generalized eigenvectors corresponding to the dominant generalized eigenvalues of a pair of covariance matrices of a desired signal and interference leakage plus noise. Under time-varying channels, however, generalized eigendecomposition is required at each time step to design the optimal beam, and its level of complexity is too high to implement in practical systems. To overcome this problem, a predictive beam design method updating the beams according to channel variation is proposed. To this end, the perturbed generalized eigenvectors, which can be obtained by a perturbation theory without any iteration, are used. The performance of the method in terms of SLNR is analyzed and verified using numerical results. © 2012 ETRI. Source

Kang T.-S.,LG Corp | Seo B.,Advanced Communications Research Laboratory
ETRI Journal | Year: 2012

When the number of users is finite, the performance improvement of the orthogonal random beamforming (ORBF) scheme is limited in high signal-to-noise ratio regions. In this paper, to improve the performance of the ORBF scheme, the user set and transmit power allocation are jointly determined to maximize sum rate under the total transmit power constraint. First, the transmit power allocation problem is expressed as a function of a given user set. Based on this expression, the optimal user set with the maximum sum rate is determined. The suboptimal procedure is also presented to reduce the computational complexity, which separates the user set selection procedure and transmit power allocation procedure. © 2012 ETRI. Source

Lee K.-K.,Korea Advanced Institute of Science and Technology | Ryoo J.-D.,Advanced Communications Research Laboratory | Joo B.S.,Advanced Communications Research Laboratory
ETRI Journal | Year: 2012

Self-healing Ethernet rings show promise for realizing the SONET/SDH-grade resilience in Carrier Ethernet infrastructures. However, when a ring is faulty, high-priority protection messages are processed in less time than low-priority data frames are processed. In this situation, any delayed data frames either being queued or traveling through long ring spans will cause the ring nodes to generate incorrect forwarding information. As a result, the data frames spread in the wrong direction, causing the ring to become unstable. To solve this problem, we propose four schemes, that is, dual flush, flush delay timer setting, purge triggering, and priority setting, and evaluate their protection performance under various traffic conditions on a ring based on the Ethernet ring protection (ERP) method. In addition, we develop an absorbing Markov chain model of the ERP protocol to observe how traffic congestion can impact the protection performance of the proposed priority setting scheme. Based on our observations, we propose a more reliable priority setting scheme, which guarantees faultless protection, even in a congested ring. © 2012 ETRI. Source

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