김치하 교수

Cognitive radio networks need to utilize available spectrum in a dynamic and opportunistic fashion without causing interference to co-located primary nodes. Before data transmission begins, secondary nodes must establish a link on a channel which is not occupied by primary nodes. Unfortunately, in cognitive radio networks, the set of available channels can be different for each node, since it is determined by the relative locations of nodes to primary nodes. We are the first to present a distrib

A Mobile Ad Hoc Network (MANET) is a self-configuring network of mobile devices connected by a wireless link. In MANETs, the data packet may fail to be delivered for various reasons including nodes movement, packet collision and bad channel condition. Because re-route recovery of traditional on-demand routing protocols has high latency, several ideas have been proposed to solve this problems. AODV-BR and AODV-ABR schemes improve the AODV routing protocol by supplying multiple backup routes, but

A new hybrid multiple access coordination scheme (HMAC) that increases channel utilization for orthogonal frequency-division multiple access wireless local area network is presented. This scheme is based on a mixture of centralized access control and distributed random access to maximize channel utilization. Remarkably, HMAC allows two schemes to function at the same time, not alternatively. Performance evaluation results show notable improvement on channel utilization, which is mainly based on

Solutions to the total ordering problem can be used to maintain consistency in distributed system applications such as replicated databases. We propose a total ordering protocol based on a dynamic token-passing scheme which determines the next token holder dynamically, not in predetermined order. The proposed protocol provides fast stability time, uses a small buffer, and distributes evenly the load of ordering messages to accomplish a total message ordering. We present simulation results to ill

A full-duplex radio allows packets to be transmitted and received simultaneously using self-interference cancellation technologies. Thus, it can double the channel capacity compared with the half-duplex radio. Since conventional medium access control (MAC) protocols were designed for the half-duplex radio, the potential capacity of the full-duplex radio cannot be utilized. In this letter, we propose a full-duplex MAC protocol using frequency domain coordination to fully utilize the full-duplex r

As full duplex radio communication is introduced, it is expected to double the throughput theoretically over full duplex radio for one-to-one communication. However, in the practical environment, it is hard to find such an application that demands the same amount of traffic in the both directions at the same time. To enhance the throughput as much as possible, we need to arrange medium accesses in a different way, not like the contention-based MAC. In this paper, we propose an efficient MAC prot

It is important to design an energy efficient data gathering tree structure for wireless sensor networks. As for the energy efficiency, network's overall energy consumption and per-node fairness have been studied. Note that the minimum degree spanning tree (MDST) is optimal in the sense of per-node fairness. We believe that the per-node fairness is of practical interest and that the delay bound associated with it must be investigated. Unfortunately, no such efforts have been made so far. In this