Byungcheol Kang

A-MPDU using fragmented MPDUs for IEEE 802.11ac MU-MIMO WLANs

In this paper, we propose an Aggregated Medium Access Control Protocol Data Unit (A-MPDU) using fragmented MPDUs with a Very High Throughput (VHT) Compressed Block Ack mechanism for use in IEEE 802.11ac Multi-User Multi-Input Multi-Output (MU-MIMO) Wireless Local Area Networks (WLANs). By allowing the use of fragmentation with the A-MPDU, the waste of medium resources in terms of meaningless A-MPDU pads can be eliminated. Using our proposed method, a fragmented MPDU-instead of A-MPDU pads-can be added to fill the length of A-MPDU boundary in Enhanced Distributed Channel Access (EDCA) Transmission Opportunity (TXOP) sharing mode, enhancing multi-user throughput owing to the increased number of frames that can be transmitted within the A-MPDU boundaries. To acknowledge the fragmented MPDUs in the A-MPDU frame, the VHT Compressed Block Ack mechanism is also newly defined. Simulation results show that the proposed method improves multi-user throughput, over 28% at low data rates and by up to 3% at high data rates.

Low complexity multi-point 4-channel FFT processor for IEEE 802.11n MIMO-OFDM WLAN system

This paper proposes an energy and area efficient structure and hardware architecture of FFT processor for 4×4 MIMO-OFDM WLAN systems with four transmit and four receive antennas. Since the basic scheme of MIMO-OFDM system is multiple data transmission, conventional FFT processor for SISO-OFDM system is not suitable for MIMO-OFDM systems. The proposed FFT processor has multi-channel structure to support multiple data path. Multi-channel structure enables to processor several FFT operation with just single processor. Also, by the mixed radix algorithm, the number of non-trivial multiplications of the FFT processor is decreased. The proposed FFT processor reduces the logic gates about 25% over a 4-channel R4MDC FFT processor. Therefore, the proposed FFT processor will contribute improvement to the low power and low complexity design of MIMO-OFDM systems, since the MIMO-OFDM FFT processor is one of the largest modules in the systems, in which the low complexity design is a very important issue.

A energy-efficient system by reducing beacon listening for periodic vital sign monitoring

This paper presents a new energy-efficient system by reducing beacon listening for periodic vital sign monitoring in wireless body area networks (WBANs). The node can reduce energy consumption by not waking up to listen to an unnecessary beacon when the data of the beacon frame rarely change. In proposed scheme, the node decides whether it wakes up or not for beacon listening according by previous received acknowledge (ACK) frame from the hub. The system is compatible with the IEEE 802.15 TG6 draft, which attracts attention as WBAN protocol. The results show that proposed scheme saves the power consumption to 14.7% when there is no network transition and 13.2% when network transition occurs at average of 2 seconds compared with that of the existing scheme.

Throughput enhancemnet with optimal fragmented MSDU size for fragmentation and aggregation scheme in WLANs

The fragmentation and aggregation (F&A) algorithm improves the throughput while ensuring the reliability in the MAC layer. To determining the optimal fragment size is a key issue of effectively operating the F&A algorithm. In this paper, the proposed method selects the optimal fragmented frame size and uses aggregation scheme based on various channel conditions. As a result the throughput can be further increased.

High reliable broadcasting protocol in WLAN using retransmission

In this paper, high reliable broadcasting protocol in WLAN using retransmission is proposed. Broadcast in conventional WLAN has advantage of high efficient use of wireless resource, but has disadvantage of low reliability and data rate. Broadcasting frame includes the sequence indicating which nodes send ACK frame first. If some nodes fail to receive the frame, the node which success to receive the frame retransmits the frame with broadcasting. By these broadcasting with relay retransmission algorithm, the probability of transmission increase when the channel is better between the nodes.