Kyunghwi Kim

MBAL: A Mobile Beacon-Assisted Localization Scheme for Wireless Sensor Networks

Localization is one of the critical issues on wireless sensor networks. Localization schemes are classified into range-based and range-free according to the method of whether to use range information. In this paper, we propose a novel range-based localization scheme which involves a movement strategy of mobile beacon, called mobile beacon-assisted localization (MBAL). Contrary to many research activities which have been carried out to design localization schemes using mobile beacons only based on random movement method, we consider totally a new scheme providing movement path selection with a low computational complexity. A new range check technique is also adopted into the MBAL as a useful solution to the position-ambiguity problem of bilateration in order to improve the performance of the proposed localization scheme. Simulation results verify that the MBAL impressively achieves energy efficiency because of its mobile beacon based approach using the proposed movement strategy and range check technique.

Unusual renal cell carcinomas: a pictorial essay

Renal cell carcinoma (RCC) is the most common solid renal neoplasm. Clear cell (conventional) carcinoma is the most common pathologic subtype of RCC. Usually RCC is a hypervascular, solid, solitary mass with contour bulging. However, RCC can manifest different features according to the pathologic tumor subtypes. Preoperative diagnosis of cyst-associated RCC is very difficult, especially in cases of RCC originating in a cyst. Multiple or bilateral presentation of RCC occurs in fewer than 5% of cases. In addition, RCCs may demonstrate unusual findings such as infiltrative growth mimicking transitional cell carcinoma, fatty component mimicking angiomyolipoma, severe perinephric infiltration, and extensive calcifications mimicking inflammation or other tumor. RCCs can be associated with hereditary diseases such as von Hippel-Lindau disease. Familiarity with these radiologic features of unusual RCCs can help ensure correct diagnosis and proper management.

Joint flow and virtual machine placement in hybrid cloud data centers

With the advance of virtualization technology, the current generation of cloud data centers contains diverse applications which generate massive inter-rack traffic in a distributed and unpredicted manner. However, since existing network architectures are not suitable to supply enough network capacity, there have been several research trials to improve the network capacity with augmented wireless links. Especially, architectural design and link scheduling of wireless-cum-wired hybrid data center networks are of their main interests. However, the existing approaches for hybrid data center networks with direct wireless links have limited performance improvements, since virtual machines are typically placed with less consideration of traffic locality.To this end, in this paper, we conduct a novel approach to flow and virtual machine placement problems in hybrid data center networks. We first design a threshold-based, wireless link-aware flow placement algorithm with low complexity. To enhance traffic locality, we also suggest a set of virtual machine placement algorithms under the flow placement algorithm. To fully exploit the extra capacity of the wireless links, we propose a new clustering metric for the algorithms. Extensive simulation results in hybrid data center networks with 60 gigahertz wireless links shows that combination of the proposed algorithms achieves better performance compared to baseline algorithms in flow completion time, aggregate throughput, and computational complexity.

A MAC Protocol Using Road Traffic Estimation for Infrastructure-to-Vehicle Communications on Highways

The development of vehicular communication technology can make more intelligent transportation systems (ITSs) by enabling a large number of potential applications. In particular, infrastructure-to-vehicle (I2V) communication will support ITS applications and provide inexpensive high-rate Internet access as well. Thus, a study on I2V communications may improve the quality of experience of end users in vehicles, such as drivers and passengers. To this end, we propose a medium access control (MAC) protocol for I2V communications to improve the fairness of node throughput while maximizing the expected system throughput. We derive the way of estimating road traffic to precisely control the transmission probability of vehicles for maximizing system throughput. The estimation is performed by utilizing the spacing distribution model in transportation systems. Furthermore, we present a threshold to limit the number of transmitted packets for the fairness of the vehicles. The threshold is set based on the achievable node throughput and the estimated sojourn time. Through extensive simulations based on the empirical vehicular trajectory data, we demonstrate the improved performance of the proposed MAC protocol. The test results show that the expected system throughput is increased by more than 21.3% and that Jains fairness index with regard to the number of transmitted packets among the nodes is close to 1.

PND: a p-persistent neighbor discovery protocol in wireless networks

In wireless communications research, a number of literature assume that every node knows all of its neighbor nodes. To this end, neighbor discovery research has been conducted, but it still has room for improvement in terms of discovery delay. Furthermore, prior work has overlooked energy efficiency, which is considered as the critical factor in wireless devices or appliances. For better performance with respect to the discovery delay and energy efficiency, we proposed a novel p-persistent-based neighbor discovery protocol and devised a simple and light algorithm estimating the number of neighbor nodes to support the proposed protocol. Our protocol requires a lower delay and a smaller number of messages for the discovery process than the existing protocols. For extensive performance evaluation, we adopted extra comparison targets from other research areas within the same context. Copyright

On the Calculation of the Maximal MOT Throughput in T-DMB

Digital multimedia broadcasting (DMB) is one of burgeoning communication technologies, which can provide audio, video, and data services to mobile terminals using broadcasting infrastructures. Data services in terrestrial- digital multimedia broadcasting (T-DMB) inherently have the disadvantage of retransmitting a lot of data unnecessarily for reliability. This paper proposes a novel optimized transmission policy using segment size and repetition number variability, which maximizes the object- level throughput as well as improves reliability. The theoretical modeling and simulation results demonstrate that our policy provides a throughput gain over the conventional protocol.

Flow and Virtual Machine Placement in Wireless Cloud Data Centers

Virtualization for cloud computing has been driving data centers to contain massive and diverse applications in a distributed manner. However, since existing network architectures do not supply enough network capacity for virtual machine (VM) interconnections, enhancing the network capacity with augmented wireless links has recently attracted a lot of research interests. Especially, architectural design and link scheduling of wireless data center networks (WDCNs) are of their main interests. However, the potential of WDCNs is under-estimated, since existing research efforts do not reflect flexibility of VM placement. To this end, in this paper, we explore another feasibility of WDCNs to combine dynamic VM placement algorithms. We design a low-complexity flow placement algorithm considering augmented wireless links with interference constraints, and discuss a set of VM placement algorithms under the flow placement algorithm. Our extensive evaluation of the algorithms in WDCNs with 60 GHz wireless links shows that combination of the flow and VM placement algorithms achieves better performance.

Minimizing the joining delay for cooperation in mobile robot networks

In this paper, we propose two joining delay minimization schemes (JDMS) and their hybrid version to minimize the delay that is caused by joining more robots to a cooperative working group of mobile-networked robots. The first scheme can operate without any feedback from the coordinator of the group, and therefore it utilizes a shorter time slot than does the second scheme. However, the second scheme can provide a stable slope of the joining delay, while the delay of the first scheme is rapidly increased when the number of the required robots approaches the number of the neighboring robots. We extensively analyze and evaluate these two schemes in terms of their joining delays, and then we derive the criteria for combining them for exploiting their opposite characteristics.

DSML: Dual Signal Metrics for Localization in Wireless Sensor Networks

In wireless sensor networks and wireless ad-hoc networks, localization systems have used diverse signal metrics such as Received Signal Strength Indicator (RSSI) and Time Difference of Arrival (TDoA) for accurate assignment of a node position. We propose a novel scheme that applies two signal metrics, which are TDoA and RSSI exclusively, into time- based positioning scheme (TPS). For energy-efficient coverage extension, the proposed scheme uses range check technique that reduces the communication energy consumption of nodes. With two location information of neighbor nodes, the node can calculate two candidate positions through bilateration. Without an additional beacon message reception, range check is applied to find the unique position between two candidate positions. Range check also can be carried out collaboratively in general environment with the information of two-hop neighbor nodes. At the performance evaluation, we analyze and test the reduced communication cost of nodes in the extended area. Also, it is shown that the ratio of unique position assignment is increased in the general environment by range check technique.

Delay minimization of tree-based neighbor discovery in mobile robot networks

In this paper, delay minimization schemes for tree-based neighbor discovery in mobile robot networks are proposed and analyzed. Depending on the tree construction scheme, the expected value of neighbor discovery delay is changed. In our study, we focus on M-ary and M-Binary tree-based neighbor discovery. Regarding the number of neighboring robots, M-ary tree-based neighbor discovery has low but steady performance whilst M-Binary tree-based neighbor discovery shows better performance for optimal M. The simulation results provide performance comparisons of these schemes.