Seung Hyong Rhee

An application-aware MAC scheme for IEEE 802.15.3 high-rate WPAN

The emerging high-rate wireless personal area network (WPAN) technology, currently being developed by IEEE 801.15.3 task group, provides a very high-speed short-range transmission capability with quality of service provisions. MPEG-4 bit stream is anticipated to occupy a large portion of the traffic in the WPAN, and its decoding depends on successful transmissions of frame data, which require a low JFR (job failure rate) and a Iow delay variance as well as a high throughput. In this paper, we propose a simple application-aware MAC scheme for the WPAN in order to achieve a high-quality video transmission of MPEG-4 stream: a device tells the piconet controller the maximum sizes of its frames along with the channel time requests, and then the controller allocates a channel time for the device according to the predefined MPEG frame sequence. Simulation results show that our scheme achieves significantly lower JFRs, lower delay variances, and higher throughputs than the standard scheduling scheme.

Adaptive MAC Protocol for Throughput Enhancement in Cognitive Radio Networks

Cognitive radio technology has been proposed to share the scarce spectrum resources without disturbing the legacy devices of wireless network. The cognitive radio device is allowed to use the spectrum only when it does not cause any interferences or collisions to the incumbent users. We suggest an adaptive MAC protocol for the purpose of a throughput enhancement in cognitive radio networks. Assuming the channel status is dynamically known to the devices, they change their transmission mode between frame recovery mode and dual transmit mode according to the channel status. When the cognitive channel is hard to use due to frame errors, the channel is used for the frame errors recovery. Otherwise, in addition to its own legacy channel, the cognitive channel can be used to increase the throughput. In this paper, we study the effect of using additional channel in the cognitive networks, and prove an adaptive method of MAC protocol in the interest of throughput enhancement in cognitive radio network, and prove the performance of our proposed mechanism by simulations.

Optimal flow control and capacity allocation in multi-service networks

The optimal flow control of noncooperative users in multiservice networks is investigated in a game-theoretic way. We adopt a model that differs from previously considered ones in that a users strategy (viz., flow or average rate) is constrained between two numbers: those are specified by the users quality of service requirements or by the users technology. Each user tries to maximize its own performance measure, defined by a utility function in a more or less standard fashion. We prove existence and uniqueness of the Nash equilibrium. There is a simple algorithm that determines this Nash equilibrium point (NEP). We also comment on the convergence properties of distributed algorithms towards this NEP. Finally, we give a suggestion on how noncooperative users may distribute their flows among several links, by imposing an appropriate pricing scheme that encourages load balancing.

A decentralized model for virtual path capacity allocation

We investigate the problem of virtual path (VP) capacity allocation in a decentralized way. Users (VP controllers), sharing common network resources, are assumed to control their VP capacities according to their performance measures. We formulate a model that differs from previous ones in two points: first, each user has its own performance objective that is simply assumed to be concave and smooth; second, a users strategy (VP bandwidth reservation) is constrained between two numbers. Adopting a standard game-theoretic formulation, we prove that there exists a unique network operating point-Nash equilibrium. We show several interesting properties of the equilibrium and also look at the convergence of some distributed algorithms. After studying the combined problem of routing and flow control in parallel link networks, we investigate the problem of VP capacity allocation in general topology networks, where fixed routing is assumed. Finally, examples of the model are presented.

An energy efficient power control mechanism for base stations in mobile communication systems

The development of ICT (Information and Communication Technology) industry has emerged as one of the major sources of world energy consumption Especially, energy consumption on base station is a large portion of total energy consumption In this paper we study with energy efficient power control mechanism for base station in mobile communication systems. We proposed a efficient sector power control based on distance between base station and mobile node. Also we proposed a sleep mode energy control mechanism In sleep mode energy saving protocol, each sector monitors the number of user in sector cell. If number of mobile node falls down a given threshold in sector cell, base station shuts down power. Simulation demonstrate the Tx energy of proposed algorithms and the tradeoff between energy saving and cell coverage

Distributed Multiple Access Control for the Wireless Mesh Personal Area Networks

Mesh networking technologies for both high-rate and low-rate wireless personal area networks (WPANs) are under development by several standardization bodies. They are considering to adopt distributed TDMA MAC protocols to provide seamless user mobility as well as a good peer-to-peer QoS in WPAN mesh. It has been, however, pointed out that the absence of a central controller in the wireless TDMA MAC may cause a severe performance degradation: e.g., fair allocation, service differentiation, and admission control may be hard to achieve or can not be provided. In this paper, we suggest a new framework of resource allocation for the distributed MAC protocols in WPANs. Simulation results show that our algorithm achieves both a fair resource allocation and flexible service differentiations in a fully distributed way for mesh WPANs where the devices have high mobility and various requirements. We also provide an analytical modeling to discuss about its unique equilibrium and to compute the lengths of reserved time slots at the stable point.

IP Mobility Performance Enhancement Using Link-Layer Prediction

In this paper, a prediction-based L2 Trigger approach is proposed for enhancing the performance of IP mobility in an integrated mobile Internet (e.g., Mobile WiMAX) and fast mobile IPv6 (FMIPv6) environment. The time series model of auto-regressive integrated moving average (ARIMA) is used to make short-term forecasting of mobile user’s signal strength. Through the forecast of the signal strength, layer-3 handover activities occur prior to the start of layer-2 handover process, and therefore, total handover latency as well as service disruption time can be reduced.

Use of vestigial power management bit within Wi-Fi frame structure of access point for coexistence of Wi-Fi and WiMAX systems in shared bands

Coexistence of more than one wireless communication systems in a shared band such as 2.4GHz ISM band has been one of hot research topics. As an example, there are many research results related to the coexistence of Wi-Fi and Bluetooth systems in the ISM band. Recently, many schemes for coexistence of Wi-Fi and WiMAX systems in shared bands such as 2.4GHz ISM band have been proposed. In this paper, proposed scheme for the coexistence of Wi-Fi and WiMAX systems is TDO (Time Division Operation) using of vestigial power management bit within Wi-Fi frame structure.

Enhancement of the IEEE 802.11 power saving mode by prioritized reservations

The increasing demand for real-time applications in WSN has raised the requirement of protocols considering both energy efficiency and end-to-end delay. A PSM is proposed in the IEEE 802.11 protocol to reduce the power consumptions of wireless nodes. Wireless nodes can stay in doze mode and periodically wake up to retrieve the frames buffered in the APs. However, the 802.11 PSM is not such energy efficiency for WSN. First, in the process of the nodes transmitting polling frames to AP, channel contentions may cause sensor nodes to deplete power quickly. Second, the mechanism of retrieving buffered frames can be inefficient since a polling frame is able to pick up only one data frame. Third, a prioritized service for urgent needs is not supported. In this paper, we propose a prioritized reservation scheme to enhance the IEEE 802.11 PSM. The concept of PSCW is suggested, during which PSM sensor nodes can retrieve the buffered frames using the reserved SPs, where the priorities of the PSM nodes are considered in scheduling the SPs. Through analytic models and discrete simulations, we show that our proposed mechanism outperforms the existing PSM schemes in terms of energy efficiency and prioritized services.

Energy Efficient Coexistence of WiFi and WiMAX Systems Sharing Frequency Band

Various wireless communication systems in a shared frequency band such as 2.4GHz ISM band are operating. This causes the mutual interference among the wireless communication systems, and makes worse the performance of each of them. They should use more energy to achieve the desired quality of service. Many studies have been carried out to solve the mutual interference problem, called the coexistence problem. In this paper, we quantitatively analyze the effect of the mutual interference between Wi-Fi and WiMAX systems, and propose a method to solve the problem and evaluate its performance by simulation.