arXiv subjects

Sung Whan Yoon

Publications and source records attributed to Sung Whan Yoon.

21 records · Page 2Linked to original sources

arXiv2017

Secure Clustered Distributed Storage Against Eavesdroppers

This paper considers the security issue of practical distributed storage systems (DSSs) which consist of multiple clusters of storage nodes. Noticing that actual storage nodes constituting a DSS are distributed in multiple clusters, two novel eavesdropper models - the node-restricted model and the cluster-restricted model - are suggested which reflect the clustered nature of DSSs. In the node-restricted model, an eavesdropper cannot access the individual nodes, but can eavesdrop incoming/outgoing data for $L_c$ compromised clusters. In the cluster-restricted model, an eavesdropper can access a total of $l$ individual nodes but the number of accessible clusters is limited to $L_c$. We provide an upper bound on the securely storable data for each model, while a specific network coding scheme which achieves the upper bound is obtained for the node-restricted model, given some mild condition on the node storage size.

cs.IT↗

arXiv2017

Capacity of Clustered Distributed Storage

A new system model reflecting the clustered structure of distributed storage is suggested to investigate bandwidth requirements for repairing failed storage nodes. Large data centers with multiple racks/disks or local networks of storage devices (e.g. sensor network) are good applications of the suggested clustered model. In realistic scenarios involving clustered storage structures, repairing storage nodes using intact nodes residing in other clusters is more bandwidth-consuming than restoring nodes based on information from intra-cluster nodes. Therefore, it is important to differentiate between intra-cluster repair bandwidth and cross-cluster repair bandwidth in modeling distributed storage. Capacity of the suggested model is obtained as a function of fundamental resources of distributed storage systems, namely, storage capacity, intra-cluster repair bandwidth and cross-cluster repair bandwidth. Based on the capacity expression, feasible sets of required resources which enable reliable storage are analyzed. It is shown that the cross-cluster traffic can be minimized to zero (i.e., intra-cluster local repair becomes possible) by allowing extra resources on storage capacity and intra-cluster repair bandwidth, according to a law specified in a closed-form. Moreover, trade-off between cross-cluster traffic and intra-cluster traffic is observed for sufficiently large storage capacity.

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arXiv2015

When Pilots Should Not Be Reused Across Interfering Cells in Massive MIMO

The pilot reuse issue in massive multi-input multi-output (MIMO) antenna systems with interfering cells is closely examined. This paper considers scenarios where the ratio of the channel coherence time to the number of users in a cell may be sufficiently large. One such practical scenario arises when the number of users per unit coverage area cannot grow freely while user mobility is low, as in indoor networks. Another important scenario is when the service provider is interested in maximizing the sum rate over a fixed, selected number of users rather than the sum rate over all users in the cell. A sum-rate comparison analysis shows that in such scenarios less aggressive reuse of pilots involving allocation of additional pilots for interfering users yields significant performance advantage relative to the case where all cells reuse the same pilot set. For a given ratio of the normalized coherence time interval to the number of users per cell, the optimal pilot assignment strategy is revealed via a closed-form solution and the resulting net sum-rate is compared with that of the full pilot reuse.

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