Sung-Hwan Bae

Algorithms for service differentiation in MAC layer over MANETs

Currently, the IETF group is working on service differentiation in the Internet. However, in wireless environments such as ad hoc networks, where channel conditions are variable and bandwidth is scarce, the Internet differentiated services are suboptimal without lower layers’ support. The IEEE 802.11 standard for Wireless LANs is the most widely used WLAN standard today. It has a mode of operation that can be used to provide service differentiation, but it has been shown to perform badly. In this paper, a new scheme of service differentiation to support QoS in the wireless IEEE 802.11 is proposed. It is based on a multiple queuing system to provide priority of user’s flow. Compared with the original IEEE 802.11b protocol, the proposed scheme increases overall throughput in the MAC layer.

Area Efficient and Low Power Pipelined IIR Filter Design for Intelligent Integrated Photonic System

An angle and radius constrained IIR filter design approach using modified Remez exchange algorithm and least squares algorithm is designed to avoid tight pole-crowding in pipelined filters, resulting in improved frequency responses and reduced coefficient sensitivities. Experimental results demonstrate that our proposed method leads to chip area reduction by 33% and low power by 45% against the conventional method.

A New Scheduling Algorithm for Performance Improvement of GFR Service

Guaranteed Frame Rate (GFR) service category is one of the most recent ATM service categories. The GFR specification was recently finalized by the ATM Forum and is expected to become an important service category which can efficiently support TCP/IP traffic in ATM network. In GFR switch implementation, it is important to guarantee MCR (minimum cell rate) and improve fairness. In this paper, we propose a new scheduling algorithm for the GFR service. Proposed algorithm provides priority to VC (virtual circuit)s and high Priority given to a VC which has fewer untagged cells in buffer. High priority VCs are serviced before low priority VCs. Proposed algorithm can guarantee MCR and improve fair sharing of the remaining bandwidth between GFR VCs. From computer simulation results, we demonstrate the proposed scheduling algorithm provide much better performance in TCP goodput and fairness than previous schemes.