Sunmyeng Kim

Deterministic Priority Channel Access Scheme for QoS Support in IEEE 802.11e Wireless LANs

The enhanced distributed channel access (EDCA) of IEEE 802.11e has been standardized to support quality of service (QoS) in wireless local area networks (LANs). The EDCA statistically supports the QoS by differentiating the probability of channel access among different priority traffic and does not provide the deterministically prioritized channel access for high-priority traffic, such as voice or real-time video. Therefore, lower priority traffic still affects the performance of higher priority traffic. In this paper, we propose a simple and effective scheme called deterministic priority channel access (DPCA) to improve the QoS performance of the EDCA mechanism. To provide guaranteed channel access to multimedia applications, the proposed scheme uses a busy tone to limit the transmissions of lower priority traffic when higher priority traffic has packets to send. Performance evaluation is conducted using both numerical analysis and simulation and shows that the proposed scheme significantly outperforms the EDCA in terms of throughput, delay, delay jitter, and packet drop ratio under a wide range of contention level.

Admission control scheme based on priority access for wireless LANs

In order to support the quality of service (QoS) requirements at the medium access control (MAC) layer, the enhanced distributed channel access (EDCA) has been developed in IEEE 802.11e standard. However, it cannot guarantee the stringent real-time constraints of multimedia applications such as voice and video without an efficient method of controlling network loads. In this paper, we propose a measurement-based admission control scheme, which is made up of two parts: priority access and admission control. First, in order to measure the channel status per traffic type, we propose a priority access mechanism in which each priority traffic is distinguished by a busy tone, and separately performs its own packet transmission operation. Then, admission control mechanism protects existing flows from new ones, and maintains the QoS of the admitted flows based on the measured channel status information. Performance of the proposed scheme is evaluated by simulation. Our results show that the proposed scheme is very effective in guaranteeing the QoS of multimedia applications as well as in avoiding the performance starvation of low priority traffics.

An improved self routing scheme by using parent-child relationship and beacon-only period for WSNs

The IEEE Standard 802.15.4 for wireless personal area networks shows promise of bringing ubiquitous sensor networking into reality, at least technically. In this paper, a beacon-based self routing (BSR) scheme of a beacon-only period (BOP) mode is presented. The proposed scheme, BSR routes packets from sensor nodes to sink based on the parent-child relationships and from the sink to sensor nodes by BOP formation. Simulation results using TOSSIM (TinyOS SIMulator) and experimental results with Mica-Z show that the BSR scheme outperforms well in comparison to the conventional AODV routing scheme over the parameters such as: average throughput, number of collisions, number of network commands and delivery ratio. Since this work considers utilising beacon payload for routing information delivery in contrast to the previously published in-band conveying approach like AODV, it is concluded that this algorithm could provide better optimisation during the commercialising phase with regard to the level of expectations.

Busy tone based multi-slot allocation protocol for improving performance in IEEE WLANs

In order to improve the performance of the EDCA mechanism, an efficient collision resolution protocol must be used. To this end, many collision reduction protocols have been proposed. However, there remain still many problems. In this paper, we propose a novel multi-slot allocation protocol to resolve the collisions. The proposed protocol uses short-duration busy-tone signals to avoid collisions and not to waste channel time. Based on the busy-tone signals and new control packets, the proposed protocol allocates time slots for data transmissions. Simulation results show that the proposed protocol works well and improves network performance.

Privacy Protection of Medical Imagery Using Reversible Watermarking

This paper addresses a high capacity and quality reversible watermarking algorithm for medical imagery which is directly applicable in medical scanners or PACS systems. After the characteristics of medical imagery are analyzed, a reversible watermarking algorithm using difference histogram shifting is modified. The watermark that is private information is inserted into the original image by modifying the difference histogram of adjacent pixels. After the watermark is extracted from the watermarked image, the original image is perfectly restored. The inherent overflow and underflow issues are solved by applying an error compensation technique. In experiments using various medical imagery such as MRI, CT and X-Ray, the performance is analyzed in aspect of capacity, perceptual quality and the reconstruction rates. Results show that the algorithm performs well for medical imagery.

Cooperative Communication Protocol Based on EDCA in IEEE 802.11e WLANs

The IEEE 802.11 standard provides multiple transmission rates. When using multiple transmission rates, the capacity of wireless LAN improves, but the performance anomaly problem may occur. Cooperative communications were introduced to alleviate the performance anomaly problem with the help of relay nodes with higher transmission rates. Previous cooperative communications protocols are based on the IEEE 802.11 DCF MAC protocol. In this paper, we apply the IEEE 802.11e EDCA features such as TXOP and block ACK for cooperative communications. Simulation results show that the proposed protocol works well and improves network performance.

Distributed TXOP Allocation Scheme in IEEE 802.11e Wireless LANs

Multimedia traffic is expected to be one of the most important traffic types in wireless LANs. However, multimedia traffic is very sensitive to delay so that the traffic has to be transmitted to receivers within its delay bound. The IEEE 802.11e EDCA (Enhanced Distributed Channel Access) defines a TXOP (Transmission Opportunity) parameter to provide service differentiation and QoS (Quality of Service) of the traffic. A station can continuously transmit multiple packets for the duration of a TXOP. When stations support multimedia applications with different QoS requirements, fairness problem occurs. In order to alleviate the fairness problem, we propose a distributed TXOP allocation scheme based on the delay bound. In the proposed scheme, a station checks the delay bound of each data packet in the queue, and allocates its TXOP value to guarantee the delay bounds of all the packets in the queue. Simulation results show that the proposed scheme outperforms other TXOP allocation schemes.

Photomosaic Algorithm with Adaptive Tilting and Block Matching

Mosaic is to make a big image by gathering lots of small materials having various colors. With advance of digital imaging techniques, photomosaic techniques using photos are widely used. In this paper, we presents an automatic photomosaic algorithm based on adaptive tiling and block matching. The proposed algorithm is composed of two processes: photo database generation and photomosaic generation. Photo database is a set of photos (or tiles) used for mosaic, where a tile is divided into regions and the average RGB value of each region is the feature of the tile. Photomosaic generation is composed of 4 steps: feature extraction, adaptive tiling, block matching, and intensity adjustment. In feature extraction, the feature of each block is calculated after the image is splitted into the preset size of blocks. In adaptive tiling, the blocks having similar similarities are merged. Then, the blocks are compared with tiles in photo database by comparing euclidean distance as a similarity measure in block matching. Finally, in intensity adjustment, the intensity of the matched tile is replaced as that of the block to increase the similarity between the tile and the block. Also, a tile redundancy minimization scheme of adjacent blocks is applied to enhance the quality of mosaic photos. In comparison with Andrea mosaic software, the proposed algorithm outperforms in quantitative and qualitative analysis.