Won-Hyuk Yang

A Node-Grade Based AODV Routing Protocol for Wireless Sensor Network

This paper proposes an improved Ad-hoc On-Demand Distance Vector (AODV) routing protocol based on node-grade to reduce the energy consumption of nodes in wireless sensor networks. The improved AODV called Grade-AODV (G-AODV) assigns a grade to each node according to the hop distance of the node to the sink node. The lower grade a node has, the closer it is to the sink. Each node is restricted to receive the route request (RREQ) packet from the nodes which have larger grade than itself. Therefore, the proposed G-AODV can reduce the energy consumption of nodes from two aspects: 1) the useless broadcast of RREQ can be avoided; 2) each packet uses less network resources because the route paths with less hop distance are set up. The performance of G-AODV is evaluated by simulation through OPNET modeler. The simulation results show that the G-AODV has better performance than AODV in view of the utilization and lifetime of network.

A bandwidth allocation algorithm for improving QoS in EPON with sleep mode

Recently, Ethernet Passive Optical Network (EPON) with sleep mode has been actively investigated to improve energy conservation in the broadband access network. EPON with cyclic sleep mode transmits up/downstream traffic at the same time and put into the sleep mode at idle time in Optical Network Unit (ONU). However, QoS requirement can be violated by the cyclic sleep mode. In this paper, we propose novel bandwidth allocation algorithm to maximize energy efficiency while satisfying QoS requirement. The main idea is to consider up/downstream traffic in order to determine suitable scheduling transmission period on Optical Line Terminal (OLT). To do this, it allocates bandwidth according to request from ONU, usually. However, when downstream traffic in OLT buffer exceeds predefined threshold, the proposed algorithm compares threshold to bandwidth request from ONU for reducing OLT traffic queuing delay. So, our proposed algorithm can satisfy both energy saving and QoS requirement. In order to evaluate the proposed algorithm, we perform simulation in terms of total and average sleep time of ONU, queuing delay of downstream traffic in OLT buffer.

Design of AWG-based WDM-PON architecture with multicast capability

Recently, the triple play service (TPS) has been considered to be a promising business model or application. Thus, the capability for multicast transmission has become a very important requirement for access networks. However, unlike existing passive optical networks (PONs), the arrayed-waveguide grating (AWG) based wavelength-division multiplexing (WDM)-PON does not have multicast capability because it is a P2P network for the downstream direction, from optical line terminal (OLT) to optical network units (ONUs). In this paper, AWG- based WDM-PON architecture with multicast capability is proposed. It provides high scalability and single copy broadcast (SCB) capability by employing multi-stage AWGs at a remote node (RN) and a multi-wavelength converter (MWC) at OLT. The performance of the proposed architecture is evaluated in terms of cost, scalability, link capacity and bandwidth per user, in both upstream and downstream directions, by comparison with other multicasting architectures.

Simulation study of communication network for wind power farm

Wind farm industry as a green energy is growing very fast. One of the most important demands in wind farm is to design a reliable communication network for wind power farm (WPF) monitoring. In this paper, a WPF network simulator is developed to evaluate the performance of a Wind Turbine (WT) which consists of logical nodes according to IEC 61400–25 standard. Each logical node can transmit analogue/status information collected from sensors and receive control information from the main controller. The amount of sensing data depends on the sampling frequency of monitoring devices. The functions of logical nodes are modeled by OPNET modeler in order to implement the simulator. Using the developed simulator, the performance of a wind turbine, which consists of nine logical nodes and Ethernet link, is evaluated according to various link speeds.

Bandwidth Allocation Algorithm for Improving QoS in EPON with Sleep Mode

Recently, as the interest in Green IT is exponentially increased, EPON with sleep mode has been studied to reduce energy consumption in access network. In oder to guarantee cyclic sleep for ONU(Optical Network Units), EPON with sleep mode transmits upstream and downstream data at the same time. However, since conventional algorithms for sleep mode in EPON allocate bandwidth to each ONU according to upstream bandwidth request, the QoS of downstream data is not guaranteed when the offered load of OLT is larger than that of ONU. In this paper, we propose a bandwidth allocation algorithm for improving QoS in EPON with sleep mode. The proposed algorithm compares its size with an upstream request of ONU when a downstream buffer in the OLT exceeds a QoS threshold. And then it allocates selectively a bandwidth that satisfies the required QoS between the bandwidth request of ONU and OLT. Therefore, the proposed algorithm can save energy through cyclic sleep of ONUs while guaranteeing the QoS of up/downstream data. In order to evaluate the proposed algorithm, we perform simulation in terms of total sleep time of ONUs, queueing delay between OLT and ONU, and the utilization of allocated bandwidth at OLT through OPNET.

Performance Analysis of Energy Savings according to Traffic Patterns in Ethernet with Rate Adaptation

Recently, Green IT has attracted much attention to solve economical and environmental problems. To save energy in communication systems, Energy Efficient Ethernet (EEE) has recently begun to explore rate adaptation for energy savings. We study the performance impact of traffic patterns on energy consumption via simulation. To evaluate the energy saving performance according to the traffic patterns, a simulator is designed to generate diverse traffic patterns in Ethernet with rate adaptation by using an OPNET modeler. The designed simulator consists of a Poisson process-based traffic generator, Pareto distribution based ON-OFF generator and Ethernet switch with rate adaptation. Using this simulator, the energy consumption is analyzed in terms of the usage time of links and the energy saving ratio.

Performance evaluation of energy saving in core router architecture with Low Power Idle for OBS networks

Recently, to overcome energy problems in networks, Low Power Idle(LPI) scheme was standardized by IEEE 802.3az Task Force Group in Sep. 30, 2010. However, most researches related LPI were focused on LAN such as Ethernet. In this paper, we evaluate performances of core router with LPI to analyze energy saving effect on OBS network. To do this, core router architecture with LPI which reduces energy consumption is proposed. The proposed architecture is comprised of control part of line card, a switch controller, BCP switch in Switching Control Unit(SCU), data transmission part of line card and burst switch fabric in switch block. In order to perform the LPI in core router, Sleep/wake controller controls line card from active to sleep state or vice versa depending on sleep/awake decision in traffic processer. The power consumption comparison and simulation results show that proposed architecture consume more energy about 1.3 times than conventional packet router. However, OBS core router with LPI can reduce energy consumption up to maximum 60% at low offered load.

Wake Transition Decision algorithm for energy saving in OBS network with LPI

The Low Power Idle (LPI) has been proposed by IEEE 802.3az Task Force to reduce energy consumption of network devices. Recently, many researches about the LPI have been progressing to maximize the sleep time and improve the performance of energy saving. However, most researches have not considered the effect of transition which causes additional energy consumption. The transition is a serious factor, which affect the performance of energy saving and QoS. Therefore, in this paper, we propose novel algorithms, called Wake Transition Decision(WTD) algorithms to reduce unnecessary transition in an OBS edge router with LPI. The Fixed Time based WTD algorithm(FT-WTD) reduces transition by waiting certain time before sleep transition. The Burst Length based WTD algorithm(BL-WTD) controls the unnecessary transition by keeping the active state of Tx module in an OBS edge router when burst length exceeds certain threshold. Simulation results show that not only approximately 30% of energy consumption can be decreased compared with exist LPI approach but also packet delay is kept within acceptable level by proposed algorithm.

Performance Evaluation of EPON-Based Communication Network Architectures for Large-Scale Offshore Wind Power Farms

In order to meet the growing demand of large-scale wind power farms (WPF), integration of high reliability, high speed, cost effectiveness and secure communication networks are needed. This paper proposes the Ethernet passive optical network (EPON) as one of promising candidates for next generation WPF. Critical communication network characteristics such as reliability, mean downtime, optical power budget, path loss and network cost are evaluated and compared with conventional switched-based architectures. The results show that our proposed EPON-based network architectures are superior to conventional switched-based architectures.

A simulation study of neighborhood discovery algorithm in Free Space Optical Sensor Networks

Free Space Optical Sensor Network (FSOSN) has attracted increasing attention for wireless multimedia applications due to the advantages of lower energy consumption, lower cost, and larger capacity. As the performance of FSOSN is restricted by its unidirectional link among nodes, the FSOSN needs efficient routing protocols and optimal virtual topology configuration. The scanning angle of transmitter plays an important role to establish routing path and construct virtual topology in FSOSN. In this paper, we simulate the neighborhood discovery algorithm to evaluate the performance affected by the scanning angle. Through the simulation, we evaluate the performance of neighborhood discovery algorithm affected by scanning angle and also find the optimal scanning angles for the FSOSN. Finally, we provide the insight into the design of FSOSN by investing the effect of scanning angle.