Seung-Chur Yang

Association information management using MAC subnet addressing in Wireless Mesh Networks

Station association information, such as an associated mesh router is required to support communication between legacy stations in Wireless Mesh Networks (WMN). Current IEEE 802.11s draft standard specifies two mechanisms to maintain the station association information: Proxy Registration Procedure (PRP) and Association Discovery Protocol (ADP). Each of them has structural limitations in that mesh routers always maintain a station association information table. Consequently, the more the number of station and mobility increases, the more management overhead increases. In this paper, we propose the method of station association information and forwarding frame using MAC subnet addressing without a station association information table. According to simulations, we results in significant improvement in terms of management frame overhead and frame transmission delay.

Implementation of a Multi-radio, Multi-hop Wireless Mesh Network Using Dynamic WDS Based Link Layer Routing

In this paper, we introduce a Linux-based implementation of a WLAN mesh system which can be used to construct multi-radio, multi-hop wireless mesh networks. We found that most wireless mesh system implementations from the research community are built by combining some existing Linux networking packages. While this approach enables fast and easy development, it shows weak points in supporting or reflecting link layer characteristics. For example, many implementations do not support dynamic link set-up between nodes and do not take advantage of multi-channel feature of WLAN. As a result, most existing implementations suffer from inflexibility in network configuration and low network performance in multi-hop paths. The main design goal of our system is to fully exploit link layer characteristics to enhance configuration flexibility and network performance. To achieve this, we develop our own networking components by modifying existing Linux modules or adding new ones. The contributions of this paper are implementation platform for a WLAM mesh networks which enables dynamic link set-up using Dynamic WDS and multi-channel paths selection. According to our experimental results, our system supports fast autonomous network configuration and shows high network performance by making use of multi-channel paths.

Design and Implementation of a Smartphone-Based Reliable Real-Time Wi-Fi Broadcast System

In recent years, the demand for real-time multi-media service in WLAN environment rapidly increases due to the Wi-Fi smart phone user growth. In order to transmit real-time multimedia to many users, broadcast transmission is more efficient than unicast transmission. However, broadcast transmission without retransmissions leads to the higher loss rate in real wireless environments. In this paper, we propose a smart phone-based reliable multimedia transmission system with packet-level forward error correction scheme using Reed-Solomon code. According to our experimental results, the system shows the average packet delivery ratio between 90% and 95% regardless of interference strength.

Design and Implementation of WLAN-Based Automatic Vehicle Identification

In this paper, we present a WLAN-based automatic vehicle identification (AVI) technique. AVI, typically used for electronic toll collection, is a basic functional requirement for a smart car. The development of this technique is a subtask of building a WLAN-based multi-purpose vehicular terminal device providing various functions, such as AVI, car-to-car communication and vehicular internet access. The design and implementation of our WLAN-based AVI system was based on reducing the identification time in order to cover high-speed cars. As time is required to establish a network connection between a roadside access point and a car station, identifying a high-speed car by communicating through that network connection is not feasible. We utilize IEEE 802.11 management frame such as probe request frame in order to identify a station without establishing a network connection. We also control the timing of the scanning procedure in order to generate enough frames for reliable identification of high speed-cars. Based on the experimental results, our WLAN-based AVI system achieves an identification ratio of nearly 100% for various car speeds ranging from 40km/h to 100km/h, whereas, active RFID, one of the representative technologies for AVI, does not show reliable identification performance, especially at high-speeds.

A hybrid measurement approach to medium occupied time for radio resource management in IEEE 802.11 networks

The wireless resources required by users have increased in parallel with and above improvements in WLAN technology, requiring even more accurate and practical resource management. Research on medium utilization, which is fundamental to resource management, has supplied insufficient evidence to apply it in real environments. This paper proposes a hybrid measurement approach to medium utilization using both a signal-level register monitor and a frame-level frame parser. We redefine medium utilization in terms of Medium Occupied Time (MOT) to describe the status of the medium in more detail. The proposed approach enables us to measure the classified MOT occupied by 802.11 frames, wireless interference, and a MAC protocol. We implement our approach by modifying a Linux device driver of an off-the-shelf 802.11n NIC. In addition, an indoor test bed is built to verify the approachs support for various traffic patterns, quantitative measurement of wireless interference, and backoff time estimation. We conclude that our hybrid measurement approach is accurate and deployable in a real environment.

Design and Implementation of Multi-Rate Broadcast Based Link Quality Measurement for Wireless Mesh Network

capture link quality more accurately than the existing techniques.

Design and Implementation of Multi-rate Broadcast based Link Quality Measurement for WLAN Mesh Network

We propose MBAP (Multi-rate Broadcast Active Probing) technique to get the right measurements for link quality in Wireless Mesh Network (WMN). Most routing protocols for WMN make use of link quality-aware routing metrics, such as ETX(Expected Transmission Count) and ETT(Expected Transmission Time), while the hop count is usually used in MANET (Mobile Ad-hoc NETwork). A broadcast based active proving technique is adopted in the previous studies to get the ETX or ETT of a link. However this technique does not reflect the multi-rate feature of WLAN because it uses a single fixed transmission rate for broadcast which usually differs from the actual rate used in data transmissions. MBAP overcomes this shortage by exploiting various rate broadcast frames for probing. We implement MBAP on linux system by modifying WLAN driver and related kernel sub-systems. Experimental results show that MBAP can capture link quality more accurately than the existing techniques.