Hyo-Sun Hwang

Throughput enhancement of IEEE 802.11 WLAN via frame aggregation

The popular IEEE 802.11 WLAN is known to achieve relatively small throughput performance compared to the underlying physical layer (PHY) transmission rate. This is due mainly to the large overheads composed of medium access control (MAC) header, PHY preamble/header, backoff time, acknowledgement (ACK) transmission, and some inter-frame spaces (IFSs). Since these overheads are added to each frame transmission, the throughput degradation is relatively high with small-size frames. In this paper, we present a frame aggregation (FA) scheme, which can improve the throughput performance. By aggregating small-size frames into a large frame, we can reduce these overheads relatively. We propose a simple method to implement the FA into the real testbed using off-the-shelf products via device driver modifications. The performance of the FA is evaluated by both numerical analysis and actual measurements from the real testbed. According to the measurement results, the FA can improve the throughput performance by 2 to 3 Mbps, when multiple frames are aggregated.

Optimal Handover Decision Algorithm for Throughput Enhancement in Cooperative Cellular Networks

In fourth generation wireless communication standards, the throughput enhancement for cell edge users is a main issue so that various inter-cell interference (ICI) coordination techniques have been suggested. Since the coordination between different cells requires the resources of cooperating cell, its use should be determined carefully. In this paper, we consider two basic handover schemes (Fast Cell Selection and Soft Handover) for the ICI coordination and propose a new handover decision algorithm from a viewpoint of the improvement of cell edge throughput. For the proposed algorithm, a new measurement parameter named Interference to other-Interferences-plus-Noise Ratio (IINR) is defined and some practical issues are addressed in the OFDMA-based cellular system. Compared to the legacy SINR-based decision algorithm, the proposed IINR-based decision algorithm improves the cell edge throughput with reduced feedback overhead, because it optimally selects mobile stations that have cooperation gains more than cooperation costs.

Network lifetime improvement by relaying node re-selection in the IEEE 802.15.6 BAN

In this paper, we study a relaying node re-selection problem in the IEEE 802.15.6 body area network (BAN) protocol, which requires to alleviate energy consumption burden of a relaying node and enhance the network life time. To this end, we develop a procedure for wake-up schedule control for a node that can be accommodated in the IEEE 802.15.6 standard. Numerical results show that by allowing a node to re-select its relaying node with our procedure, we can improve the network lifetime.

Quantitative analysis for noise generated from share circuitries within DDR3 DRAM

Correctable errors, almost single bit errors, can be induced from random data transition in DRAM. In the system, most of CEs are corrected by error correction code, but there is intermittent system down. Several literatures have reported that noise generated from share circuitries is regarded as a cause of soft failure. Noisy environments are one of the unavoidable factors in the high speed, high density, and low power DRAM. For the purpose of finding out noise source, we investigated states of share circuitries with random data transition. BLSA, power transistor, power line, and common plate were also researched with DDR3 DRAMs. A simple model was proposed with the quantitative analysis. Results show that the soft failure occurs when unexpected combination of noise factors happen at once, because the revealed erratic bits have similar characteristics of normal bits, except for the influence on noise.