In orthogonal frequency division multiplexing (OFDM) system, a guard interval (GI) is used to remove the inter-symbol interference (ISI) due to a multipath channel. It is difficult to set an optimal GI length in the environment whose multipath varies. In this paper, we propose a variable guard interval based on the estimated maximum delay of a multipath channel. The maximum delay is estimated from a channel impulse response (CIR), which is estimated by a preamble symbol. However, since the estimated CIR includes the noise, it is difficult to decide the optimal GI. In order to solve the problem, we introduce the method which selects the path whose signal to noise ratio is high. Additionally, the information of the optimal GI length is required to be transmitted from a receiver to a transmitter. In this paper, we use an acknowledgment (ACK) frame for the feedback of the GI information.

Motivated by different error characteristics of each path, we propose a study-based error recovery scheme for Networks-on-Chip (NoC). In this scheme, two study processes are executed respectively to obtain the characteristics of the errors in every link first; and then, according to the study results and the selection rule inferred by us, this scheme selects a better error recovery scheme for every path. Simulation results show that compared with traditional simple retransmission scheme and hybrid single-error-correction, multi-error-retransmission scheme, this scheme greatly improves the throughput and cuts down the energy consumption with little area increase.

Hybrid automatic repeat request (HARQ) is employed for the Evolved Universal Terrestrial Radio Access (E-UTRA) downlink. The ACK/NACK signals from each user equipment (UE) are multiplexed by code division multiple access (CDMA) and transmitted via a physical uplink control channel (PUCCH). The ACK/NACK signals are code spread by the cyclic shift (CS) sequences made from zero auto-correlation (ZAC) sequences; however, the orthogonality of these sequences is not guaranteed depending on the propagation channels; moreover, the amount of inter-code interference (ICI) depends on the delay spread of the channel and the transmitting timing control error of each UE. In the conventional PUCCH structure, ICI between two ACK signals does not degrade their detection performance, whereas ICI between an ACK signal and a NACK signal degrades the detection performance. This causes a serious gap between the detection performances of ACK and NACK signals, because generally in a PUCCH, there are more ACK signals than NACK signals. In this paper, we propose a novel phase rotation scheme on the constellations of ACK/NACK signals that can resolve this issue, and the simulation evaluation results confirm the benefits of the proposed phase rotation scheme.

This paper considers the problem of target location estimation in heterogeneous wireless sensor networks and proposes a novel algorithm using a factor graph to fuse the heterogeneous measured data. In the proposed algorithm, we map the problem of target location estimation to a factor graph framework and then use the sum-product algorithm to fuse the heterogeneous measured data so that heterogeneous sensors can collaborate to improve the accuracy of target location estimation. Simulation results indicate that the proposed algorithm provides high location estimation accuracy.

Instruction pre-execution is an effective way to prefetch data. We previously proposed an instruction pre-execution scheme, which we call two-step physical register deallocation (TSD). The TSD realizes pre-execution by exploiting the difference between the amount of instruction-level parallelism available with an unlimited number of physical registers and that available with an actual number of physical registers. Although previous TSD study has successfully improved performance, it still has an inefficient energy consumption. This is because attempts are made for instructions to be pre-executed as much as possible, independently of whether or not they can significantly contribute to load latency reduction, allowing for maximal performance improvement. This paper presents a scheme that improves the energy efficiency of the TSD by pre-executing only those instructions that have great benefit. Our evaluation results using the SPECfp2000 benchmark show that our scheme reduces the dynamic pre-executed instruction count by 76%, compared with the original scheme. This reduction saves 7% energy consumption of the execution core with 2% overhead. Performance degrades by 2%, compared with that of the original scheme, but is still 15% higher than that of the normal processor without the TSD.

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.

We develop an optimum code allocation scheme by investigating the peak to average power ratio (PAPR) characteristic of a down-link multi-carrier (MC)-CDMA system using Walsh-Hadamard code. It is shown that PAPR of a MC-CDMA system is highly dependent upon the selection of code combination. Based on this fact, we develop the allocation method which minimizes PAPR according to the number of active users. In addition, an efficient suboptimum code combination search scheme is also proposed for near minimum PAPR.

This paper proposes a framework for modular verification of evolving component-based software. This framework includes two stages: modular conformance testing for updating inaccurate models of the evolved components and modular verification for evolving component-based software. When a component is evolved after adapting some refinements, the proposed framework focuses on this component and its model in order to update the model and recheck the whole evolved system. The framework also reuses the previous verification results and the previous models of the evolved components to reduce the number of steps required in the model update and modular verification processes. An implementation and some experimental results are presented.

Delay Tolerant Networks (DTNs) are able to provide communication services in challenged networks where the end-to-end path between the source and destination does not exist. In order to increase the probability of message delivery, DTN routing mechanisms require nodes in the network to store and carry messages in their local buffer and to replicate many copies. When the limited buffer is consumed, choosing appropriate messages to discard is critical to maximizing the system performance. Current approaches for this are sub-optimal or assumed unrealistic conditions. In this paper, we propose an optimal buffer management scheme for the realistic situations where the bandwidth is limited and messages vary in size. In our scheme, we design a message discard policy that maximizes the message delivery rate. Simulation results demonstrate the efficiency of our proposal.

Workflow nets (WF-nets) are Petri nets which represent workflows. Soundness is a criterion of logical correctness defined for WF-nets. It is known that soundness verification is intractable. In this paper, we propose a method to verify soundness using a Linear Temporal Logic (LTL) model checking tool, SPIN. We give an LTL necessary and sufficient condition to verify soundness for WF-nets without livelock. Acyclic WF-nets have no livelock, but cyclic WF-nets may have livelock. We also give a necessary and sufficient condition to verify livelock. Meanwhile, we show that any LTL model checking tool cannot verify soundness for WF-nets with livelock. We give necessary conditions to verify soundness for them. Those conditions enable us to use SPIN even if a given WF-net has livelock. We also develop a tool to verify soundness based on our method. We show effectiveness of our method by comparing our tool with existing soundness verification tools on verification time for 200 cyclic ACWF-nets.

A 4+12+16 amplitude phase shift keying (APSK) modulation outperforms other 32-APSK modulations such as rectangular or cross 32-quadrature amplitude modulations (QAMs) which have a high peak to average power ratio that causes non-negligible AM/AM and AM/PM distortions when the signal is amplified by a high-power amplifier (HPA). This modulation scheme has therefore been recommended as a standard in the digital video broadcasting-satellite2 (DVB-S2) system. In this letter, we present a new bits-to-symbol mapping with a better bit error rate (BER) for a 4+12+16 APSK signal in a nonlinear satellite channel.

The characteristics of a left-handed traveling-wave transistor, which is formulated as two composite right- and left-handed (CRLH) transmission lines with both passive and active couplings, are discussed for generating unattenuated waves having left-handedness. The design criteria for convective instability are described, together with results of numerical calculations that solve the transmission equation for the device.

A replacement of an expensive MgO protective layer with relatively inexpensive Lanthanum Hexa Boride (LaB6) has already been proposed. Since LaB6 is not transparent, unlike MgO, the LaB6 panel employs a long sustain gap structure. Since the sustain gap is 2.6 times larger than the distance between sustain and address electrodes, different driving methods from those of the conventional PDPs have to be adopted. For the driving technique of the sustain period, an application of delayed auxiliary pulses on A electrode and the overlap sustain pulse drive are proposed. Luminance degradation with higher sustain frequency driving can be compensated by use of a 2step sustain pulse driving. Low reset luminance and low address voltage are achieved with a square-ramp technique for the reset period. TV operation is successfully realized on AC PDP which incorporated the LaB6 cathodes.

Based on the theoretical analysis of literature, saturation in measured signal of active noise control (ANC) systems will degrade the convergence speed. However, the experiments show that the saturated input signal can speed up the convergence of the narrow-band ANC systems. This paper intends to remodel the saturation effects for feedforward and feedback ANC systems. Combining the action of analog-to-digital converters (ADC), the mathematical expression and block diagrams are proposed to model the saturation effects in the practical ANC systems. The derivation and simulation results show that since the saturation is able to amplify the principle component of signal, the convergence would be speeded up.

We investigate and propose the utilization of regenerative and non-regenerative relaying terminals in downlink cooperative MIMO communications, such as in base-station/router-relay-user transmission under different schemes. The source is equipped with multiple antennas, while the relays and destination are single-antenna terminals. From the source to the relays, symbols are transmitted using MIMO spatial-multiplexing technique. Depending on the type of relaying scheme, the relays either fully decode or amplify the received signal before retransmitting it to the destination using simple TDM transmission or Alamouti's space-time coding. We show that the proposed system realizes MIMO performance in single-antenna system environment, and performance-wise it is superior to existing transmission schemes, especially in low-SNR conditions. Furthermore, the proposed system is shown to give a diversity order of N-M+1, similar to that of MIMO V-BLAST system.

We consider a problem of global asymptotic stabilization of a class of feedforward nonlinear systems that have the unknown linear growth rate and unknown input delay. The proposed output feedback controller employs a dynamic gain which is tuned adaptively by monitoring the output value. As a result, a priori knowledge on the linear growth rate and delay size are not required in controller design, which is a clear benefit over the existing results.

We present an attractive approach for OFDM transmission using an adaptive pre-FFT equalizer, which can select ICI reduction mode according to channel condition, and a degenerated-inverse-matrix-based channel estimator (DIME), which uses a cyclic sinc-function matrix uniquely determined by transmitted subcarriers. In addition to simulation results, the proposed system with an adaptive pre-FFT equalizer and DIME has been laboratory tested by using a software defined radio (SDR)-based test bed. The simulation and experimental results demonstrated that the system at a rate of more than 100 Mbps can provide a bit error rate of less than 10-3 for a fast multi-path fading channel that has a moving velocity of more than 200 km/h with a delay spread of 1.9 µs (a maximum delay path of 7.3 µs) in the 5-GHz band.

On the use of a surveillance camera, there is a case where privacy protection should be considered. This paper proposes a new privacy protection method by automatically degrading the face region in surveillance images. The proposed method consists of ROI coding of JPEG2000 and a face detection method based on template matching. The experimental result shows that the face region can be detected and hidden correctly.

The algebra of communicating shared resources (ACSR) is a timed process algebra which extends classical process algebras with the notion of a resource. In analyzing ACSR models, the existing techniques such as bisimulation checking and Hennessy-Milner Logic (HML) model checking are very important in theory of ACSR, but they are difficult to use for large complex system models in practice. In this paper, we suggest a framework to verify ACSR models against their requirements described in an expressive timed temporal logic. We demonstrate the usefulness of our approach with a real world case study.

This paper proposes an architecture of an interference canceller for satellite communications with super-posed transmission, which is applicable not only to QPSK but also to 16QAM transmission to get higher satellite capacity. We implement it as an FPGA-based prototype and verify its performance. We propose here to use a new method to measure the satellite round-trip delay using an extended matched filter (EMF), which can work in low C/N conditions such as 0 dB and under. Given this performance, our canceller can work in a network in which forward and reverse links have the same power level. The results of the laboratory tests for QPSK show that interference can be suppressed by about 30 dB and that the BER degradation due to the canceller was small enough for operation.