Jongtack Kim

Downlink scheduling with fairness and optimal antenna assignment for MIMO cellular systems

A bandwidth-limited wireless channel can considerably improve its performance by exploiting multiple-input-multiple-output (MIMO) antennas. Combining spatial multiplexing with multiuser diversity, we develop an optimal cross-layer scheduling mechanism that executes fair scheduling at the upper layer and optimal antenna assignment at the physical layer. For fair scheduling, we propose a framework that achieves the objective of maximum capacity and proportional fairness. For optimal antenna assignment, we consider the Hungarian algorithm that maximally utilizes the characteristics of MIMO systems by adopting the graph theoretical approach. Through simulations, we demonstrate the performance of the optimal scheduling.

Design of certification authority using secret redistribution and multicast routing in wireless mesh networks

Wireless mesh networks (WMNs) should provide authentication and key management without a trusted third party because of their self-organizing and self-configuring characteristics. Several solutions to this problem have been proposed in mobile ad hoc networks (MANETs). But they are not optimal for WMNs because WMNs are with stationary mesh routers (MRs) that do not suffer from the limited power problem. In this paper, we design an architecture of mesh certification authority (MeCA) for WMNs. In MeCA, the secret key and functions of certification authority (CA) are distributed over several MRs. For secret sharing and redistribution, we develop the fast verifiable share redistribution (FVSR) scheme, which works for threshold cryptography and minimizes the possibility of secret disclosure when some shareholders are compromised by adversaries. MeCA adopts the multicasting based on Ruiz tree, which is optimal in reducing the operation overhead. It can update, revoke, and verify certificates of WMN nodes in a secure and efficient manner. Simulation results show that MeCA does not disclose its secret key even under severe attacks while incurring low overhead compared to other existing schemes in MANETs.

PECAN: Peer cache adaptation for peer-to-peer video-on-demand streaming

To meet the increased demand of video-on-demand (VoD) services, peer-to-peer (P2P) mesh-based multiple video approaches have been recently proposed, where each peer is able to find a video segment interested without resort to the video server. However, they have not considered the constraint of the servers upload bandwidth and the fairness between upload and download amounts at each peer. In this paper, we propose a novel P2P VoD streaming system, named peer cache adaptation (PECAN) where each peer adjusts its cache capacity adaptively to meet the servers upload bandwidth constraint and achieve the fairness. For doing so, we first propose a new cache replacement algorithm that designs the number of caches for a segment to be proportional to its popularity. Second, we mathematically prove that if the cache capacity of a peer is proportional to its segment request rate, the fairness between upload and download amounts at each peer can be achieved. Third, we propose a method that determines each peers cache capacity adaptively according to the constraint of the servers upload bandwidth. Against the proposed design objective, some selfish peers may not follow our protocol to increase their payoff. To detect such peers, we design a simple distributed reputation and monitoring system. Through simulations, we show that PECAN meets the server upload bandwidth constraint, and achieves the fairness well at each peer. We finally verify that the control overhead in PECAN caused by the search, reputation, and monitoring systems is very small, which is an important factor for real deployment.

Adaptive Peer Caching for P2P Video-on-Demand Streaming

In this paper, we propose a novel P2P VoD streaming system, named PECAN where each peer adjusts its cache capacity adaptively to meet the servers upload bandwidth constraint and achieve the fairness. For doing so, we first propose a new cache replacement algorithm that designs the number of caches for a segment to be proportional to its popularity. Second, we mathematically prove that if the cache capacity of a peer is proportional to its segment request rate, the fairness between upload and download amounts at each peer can be achieved. Third, we propose a method that determines each peers cache capacity adaptively according to the constraint of the servers upload bandwidth. Through simulations, we show that PECAN meets the server upload bandwidth constraint, and achieves the fairness well at each peer.