Hyeopgeon Lee

An efficient slotted CSMA/CA algorithm for the IEEE 802.15.4 LR-WPAN

The wireless sensor networks is a network technique for the implementation of Ubiquitous computing environment. The nodes use the CSMA/CA for the communication. However, the number of nodes which are joined from the PAN coordinator is more increasing, also the competition and the overhead are more increasing. Therefore, the performance of current standard is decrease. In this paper, we design an efficient slotted CSMA/CA algorithm for the IEEE 802.15.4 LR-WPAN. The proposal algorithm using the EBE (Efficient Backoff Exponent) variable decreases the network output load, the energy consumption and the dropped packet, so the data transmission is more efficient than the current standard.

Retransmission Algorithm for Channel Allocation in IEEE 802.15.4 LR-WPAN

IEEE 802.15.4 was developed for simple, low-power and low-cost wireless communication. It employs the slotted carrier sense multiple access with collision avoidance (CSMA/CA) for the contention mechanism. The blind backoff process in the slotted CSMA/CA will cause lower channel utilization. Sensor node performs backoff process immediately when the clear channel assessment (CCA) detecting busy channel. If a collision occurs, CSMA/CA algorithm executes retransmission operation. If packet retransmission fails for three times, this packet is dropped. However if this dropped packet has emergency information, the reliability of data transmission and Quality of Service (QoS) are reduce. In this paper, we design a retransmission algorithm for channel allocation in IEEE 802.15.4 LR-WPAN. To conduct performance analysis, we used an OPNET network simulator. A performance analysis shows that the proposed algorithm reduces the dropped packet and throughput, so proposed algorithm improves the reliability of data transmission and Quality of Service (QoS).

An Enhanced Key Distribution Scheme for the Energy Consumption and the Security in the Wireless Sensor Networks

The ZigBee which is a type of the sensor networks defines a role of the Trust Center, so it securely communicates through the key distribution. But the key distribution through the Trust Center concentrates all traffic from the Trust Center, so it occurs a delay and an overhead. In this paper, we design a key distribution scheme for secure communication in the wireless sensor networks. It is designed to the Trust Center to Trust Center, the Trust Center to node and the node to node in the proposal scheme. Specially, the proposal scheme through a key distribution between the Trust Centers by reuse the key information improves an energy consumption and a security.

A secure information flow architecture for public web service

Cyber hacking has been increased every year and it has resulted in severe damages and losses to companies to the extent that it may lose whole business. Recent trend of hacking shows that aims of hacking is to get personal information profile as many as possible, such as ID, residential registration number, password, etc, and to use it for other purposed. The prominent target of hacking is the database of company. This thesis aims to suggest one way data transmission method as one of network partition solutions for the purpose of protecting database where critical information is stored, even when server is attacked and damaged by hacking. The suggested architecture reduced transmission time for data exchange, a problem in existing architectures, for example between web server and Database, to enable real-time safe transmission of even large-scale data.