In Low Earth Orbit (LEO) satellite networks, the user distributions are unbalanced due to the geography and the population dispersion. As a result, some satellites have few traffic loads, while others have heavy traffic loads which often lead to congestion events. In this paper, we propose a novel load balancing method based on congestion prediction. In the proposed method, each satellite detects areas where congestion often occurs and conveys their positions to its adjacent satellites. In those areas, the concerned satellites perform load balancing algorithms to prevent congestion. The performance of the proposed method is evaluated through a number of simulations. The simulation results demonstrate that the proposed scheme improves packet drop rate, end-to-end delay, and throughput.

The R&D in satellite communications in Korea has been driven mainly by KCC (Korea Communications Commission) but in a small scale compared to Korea space development program organized by MEST (Ministry of Education, Science and Technology). Public and civilian satcom sector R&D has been led mainly by ETRI with small/medium companies contrary to rare investment in private sector while military sector R&D has been orchestrated by ADD with defense industry. By the COMS (Communication, Ocean and Meteorological Satellite) experimental Ka-band payload, Korea pursues a space qualification of own technology for national infrastructure evolution as well as industrialization of space R&D results. Once COMS launched and space qualified in 2009, subsequent application experiments and new technology R&D like UHDTV will entail service and industry promotion. The payload technology is expected for the next Korean commercial satellites or for new OBP satellites. The COMS ground control system and GNSS ground station technologies are under development for COMS operation and enhanced GNSS services along with advent of Galileo respectively. Satellite broadband mobile VSAT based on DVB-S2/RCS (+M) and low profile tracking antennas have been developed for trains, ships, and planes. While APSI is developing GMR-1 based Thuraya handset functions, ETRI is designing IMT-Advanced satellite radio interface for satellite and terrestrial dual-mode handheld communication system like Japanese STICS, with universities' satellite OFDM researches. A 21 GHz Ka-band higher-availability scalable HD broadcasting technology and SkyLife's hybrid satellite IPTV technology are being developed. In near term Korea will extend R&D programs to upgrade the space communication infrastructure for universal access to digital opportunity and safer daily life from disaster, and to promote space green IT industrialization, national security, and space resources sovereign. Japanese stakeholders are invited to establish a collaborative R&D with Korea for mutual benefit of the future.

Although a distributed index on a distributed hash table (DHT) enables efficient document query processing in Peer-to-Peer information retrieval (P2P IR), the index costs a lot to construct and it tends to be an unfair management because of the unbalanced term frequency distribution. We devised a new distributed index, named Huffman-DHT, for P2P IR. The new index uses an algorithm similar to Huffman coding with a modification to the DHT structure based on the term distribution. In a Huffman-DHT, a frequent term is assigned to a short ID and allocated a large space in the node ID space in DHT. Throuth ID management, the Huffman-DHT balances the index registration accesses among peers and reduces load concentrations. Huffman-DHT is the first approach to adapt concepts of coding theory and term frequency distribution to load balancing. We evaluated this approach in experiments using a document collection and assessed its load balancing capabilities in P2P IR. The experimental results indicated that it is most effective when the P2P system consists of about 30,000 nodes and contains many documents. Moreover, we proved that we can construct a Huffman-DHT easily by estimating the probability distribution of the term occurrence from a small number of sample documents.

It is well known that the performance of CDMA systems may degrade in the presence of spreading code mismatch. The diagonal loading multiple constrained minimum variance (DL-MCMV) approaches have been proposed to deal with the mismatch problem. However, they still cannot improve the robust capability efficiently due to the spreading code mismatch. In this letter, a detector based on the variable DL technique is presented that offers more robust capabilities than the MCMV and DL-MCMV detectors. Computer simulation results are provided that illustrate the effectiveness of the proposed detector.

This letter presents beam tilting characteristics of a slot antenna element with reactance loading. It is found that the beam tilt is obtained by controlling aperture electric field distributions with a loaded reactance on the slot. A large beam tilt angle is obtained when an inductive reactance element is loaded.

This Letter deals with the problem of non-line-of-sight (NLOS) in cellular systems devoted to location purposes. In conjugation with a variable loading technique, we present an efficient technique to make covariance shaping least squares estimator has robust capabilities against the NLOS effects. Compared with other methods, the proposed improved estimator has high accuracy under white Gaussian measurement noises and NLOS effects.

Basic features of fretting and factors affecting its deleterious effects on the performance of electrical/electronic connection were reviewed. It was shown that although the fretting cannot be eliminated completely, its deleterious effects can be substantially reduced by lubrication and also connection design.

Electrical life is an important parameter to estimate the reliability of a relay, and it is greatly affected by load current. In order to shorten the time of life test, load current stress accelerated life tests were carried out by using a life test system designed for relay in this paper. During the life test, many parameters such as the contact resistance, the closing time and the over-travel time of relay were measured for each operation to identify the failure modes. After the life test, the failure mechanisms under each current stress, which cause the same failure mode, were analyzed by investigating the variations of parameters and observing the morphology of contact surface. In addition, for the purpose of further studying the consistency of failure mechanisms between different current stress, a Weibull statistical analysis was adopted to estimate the shape parameter of Weibull distribution because the same shape parameter means the same failure mechanism. Finally, a statistical model for estimating the lifetime under load current stress was built. The research methods and conclusions mentioned in this paper are meaningful to perform the accelerated life tests for other types of relays.

Electrical contacts are the most important parts of electrical circuits, and many reliability problems of the circuits are related to contact failure. The contact resistance is one of the important factors for assessing connector reliability, and thus the prediction of contact resistance is essential to designing electrical terminals. In this study, embossments, each 1 mm to 3 mm in radius, were brought into contact with flat planes to simulate the point of contact on a terminal, and the contact resistance was measured using a four-probe method under a load up to 40 N. Copper alloy samples, each plated with tin or silver and having an embossment of 1 mm to 3 mm in radius, were used and the visually clear indentations resulting from the embossment to plane contact were measured to determine their areas. Since the contact resistance is dependent on the contact area, an FEM analysis must be carried out to determine the contact areas correctly. In this paper, an elasto-plastic FEM analysis was performed taking the plating layers into account, and a method was established to make precise determination of the contact areas for different shapes of contacts and loads. The resultant contact areas were used to calculate the contact resistance, which showed a good agreement with experimental results. It was established that the load-resistance curves can be predicted on the basis of the shapes of the contacts as well as plating.

Searching mechanisms employed in unstructured overlay networks typically hit multiple peers for the desired content. We propose the use of a simple method that raises the hit rates of unpopular contents and balances the loads by choosing the peer holding the least contents as the provider when multiple candidates exist.

Mutual interference among users can abruptly increase othercell interference and cause overload situation in coexisting WCDMA and HSDPA systems. Traffic overloading can degrade the performance of the systems. This letter proposes a new dynamic downlink load control (DDLC) algorithm to reduce performance degradation due to overload in the coexistence of WCDMA and HSDPA systems. With the proposed algorithm, the downlink load is controlled according to load states classified by two load-control thresholds, and traffic overloading is alleviated by dynamically adjusting the CQI values reported by users, based on the downlink load as well as channel variations. The proposed algorithm is simulated and results show that the DDLC scheme improves the performance of both WCDMA and HSDPA systems in terms of outage probability, total system throughput, and radio resource utilization.

This paper proposes the use of inter-cell transmission power control (TPC) with overload indicator (OLI) signaling to user equipment (UE) in addition to intra-cell TPC for the Evolved UTRA uplink. In the proposed inter-cell OLI transmission method, a cell site (Node B) selects UEs offering high-level interferences to the cell site based on the measured path loss difference, and then, the cell site transmits the OLI signal to the selected UEs. The simulation results show that the inter-cell TPC improves both the average user throughput and cell-edge user throughput at 5% in the cumulative distribution function (CDF) curve, assuming the same sector throughput. For instance, when the sector throughput is 1 Mbps using 1.08 MHz bandwidth, the inter-cell TPC with the proposed UE-common OLI scheme increases the average user throughput and the 5%-cell edge user throughput by approximately 41% and 53%, respectively, compared to the case with intra-cell TPC only. Furthermore, when the inter-cell TPC with the proposed UE-individual OLI is employed, the corresponding average user throughput and the 5% user throughput are increased by approximately 87% and 94%, respectively.

In LTE, AC barring check is performed before RRC connection. In some cells with a low access probability, the UEs keep retrying access which results in higher connection failure and longer access delay. We therefore propose balancing the UEs by adjusting the cell reselection criteria based on the access probability, so that the UEs shall be more encouraged to reselect a cell with a higher access probability.

We propose a learning and control model of the arm for a loading task in which an object is loaded onto one hand with the other hand, in the sagittal plane. Postural control during object interactions provides important points to motor control theories in terms of how humans handle dynamics changes and use the information of prediction and sensory feedback. For the learning and control model, we coupled a feedback-error-learning scheme with an Actor-Critic method used as a feedback controller. To overcome sensory delays, a feedforward dynamics model (FDM) was used in the sensory feedback path. We tested the proposed model in simulation using a two-joint arm with six muscles, each with time delays in muscle force generation. By applying the proposed model to the loading task, we showed that motor commands started increasing, before an object was loaded on, to stabilize arm posture. We also found that the FDM contributes to the stabilization by predicting how the hand changes based on contexts of the object and efferent signals. For comparison with other computational models, we present the simulation results of a minimum-variance model.

This paper addresses the interference and load imbalance problems in multi-radio infrastructure mesh networks where each mesh node is equipped with multiple radio interfaces and a subset of nodes serve as Internet gateways. To provide backbone support, it is necessary to reduce interference and balance load in Wireless Mesh Networks (WMNs). In this paper, we propose a new Load-Aware Routing Metric, called LARM, which captures the differences in transmission rates, packet loss ratio, intra/inter-flow interference and traffic load in multi-radio mesh networks. This metric is incorporated into the proposed load-balancing routing, called LBM, to provide load balancing for multi-radio mesh network. Simulation results show that LARM provides better performance compared to WCETT and hop-count routing metrics in LBM routing protocol.

We present a recovery scheme based on Self-protected Spanning Tree (SST), which recovers from failure all by itself. In the recovery scheme, the links are assigned birthdays to denote the order in which they are to be considered for adding to the SST. The recovery mechanism, named Birthday-based Link Replacing Mechanism (BLRM), is able to transform a SST into a new spanning tree by replacing some tree links with some non-tree links of the same birthday, which ensures the network connectivity after any single link or node failure. First, we theoretically prove that the SST-based recovery scheme can be applied to arbitrary two-edge connected or two connected networks. Then, the recovery time of BLRM is analyzed and evaluated using Ethernet, and the simulation results demonstrate the effectiveness of BLRM in achieving fast recovery. Also, we point out that BLRM provides a novel load balancing mechanism by fast changing the topology of the SST.

Cluster systems are prevalent infrastructures for offering e-services because of their cost-effectiveness. The objective of our research is to enhance their cost-effectiveness by reducing the minimum number of nodes to meet a given target performance. To achieve the objective, we propose a load balancing algorithm, the Nearest Underloaded algorithm (N algorithm). The N algorithm aims at quick solution of load imbalance caused by request departures while also preventing herd effect. The performance index in our evaluation is the xth percentile capacity which we define based on throughputs and the xth percentile response times. We measured the capacity of 8- to 16-node cluster systems under the N algorithm and existing Least-Loaded (LL) algorithms, which dispatch or transfer requests to the least-loaded node. We found that the N algorithm could achieve larger capacity or could achieve the target capacity with fewer nodes than LL algorithms could.

IEEE 802.11 MAC is the most commonly used protocol in multi-hop ad-hoc networks which need no infrastructure. In multi-hop ad-hoc networks based on IEEE 802.11, since nodes try transmitting their packets at every possible slot, there is a high packet loss probability. This degrades network performance attributes such as throughput and fairness. In this paper, we focus on achieving the maximum throughput of the given network topology by adding extra backoff time to random backoff time based on IEEE 802.11. Specifically, the optimal load rate is obtained with constraints of Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA) mechanism.

Due to the dynamic nature and uncertainty of grid computing, system reliability can become very unpredictable. Thus, a well-defined scheduling mechanism that provides high system availability for grid applications is required. In this letter, we propose a SLA-constrained policy-based scheduling mechanism to enhance system performance in grid. Also, we implement the proposed model and show that our policy-based scheduling mechanism can guarantee high system availability as well as support load balancing on an experimental basis.

In recent years, heterogeneous devices have been employed frequently in mobile storage systems because a combination of such devices can supply a synergistically useful storage solution by taking advantage of each device. One important design constraint in heterogeneous storage systems is to mitigate I/O performance degradation stemming from the difference between access times of different devices. To this end, there has not been much work to devise proper buffer cache management algorithms. This paper presents a novel buffer cache management algorithm which considers both I/O cost per device and workload patterns in mobile computing systems with a heterogeneous storage pair of a hard disk and a NAND flash memory. In order to minimize the total I/O cost under varying workload patterns, the proposed algorithm employs a dynamic cache partitioning technique over different devices and manages each partition according to request patterns and I/O types along with the temporal locality. Trace-based simulations show that the proposed algorithm reduces the total I/O cost and flash write count significantly over the existing buffer cache algorithms on typical mobile traces.