Seungwook Min

Merged SLM scheme for PAPR reduction of OFDM system with low complexity

Merged selected mapping (SLM) scheme is presented for reducing peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM). The concept of the proposed SLM scheme is based on a combination of advantages of the conventional low complexity SLM schemes by dividing inverse fast Fourier transform (IFFT) into k stage and remaining n-k stage and, then generating additional OFDM signal sequences without performing IFFT to the conventional SLM scheme. This scheme dramatically reduces computational complexity comparing with the conventional SLM schemes under the similar PAPR reduction performance.

On Approximate Euler Differential Equations

We solve the inhomogeneous Euler differential equations of the form and apply this result to the approximation of analytic functions of a special type by the solutions of Euler differential equations.

Stability of the Wave Equation with a Source

We prove the generalized Hyers-Ulam stability of the wave equation with a source, , for a class of real-valued functions with continuous second partial derivatives in and .

A Fixed Point Approach to the Stability of the Functional Equation

By applying the fixed point method, we will prove the Hyers-Ulam-Rassias stability of the functional equation under some additional assumptions on the function and spaces involved.

Radio frequency energy harvesting for wireless sensor networks

The need for the battery-free devices is increasing dramatically in many applications including medical and environmental monitoring, electric car charging, and wireless sensor networks. For wireless sensor networks, energy harvesting (EH) techniques based on various types of energy resources such as solar energy, thermal energy, radio frequency (RF) energy, and piezoelectric energy have been developed. Of these techniques, we particularly focus on the ambient RF EH. The systems harvesting ambient RF energy exploit energy sources already present in the surrounding environments, namely, TV, radio, cellular, satellite, and Wi-Fi systems. Ambient wireless EH technologies are generally used for low-power standalone electronics. EH from the surrounding RF environments can be an option to recharge wireless sensor networks. The amount of energy harvested from ambience primarily depends on the type of the harvesting device and the type of energy source. The harvested energy from ambience and the density of incident power according to the type of energy source are summarized in Georgiou et al. In the case of wireless LAN, for instance, the peak power density ranges from 30 pW/cm to 13.36 mW/cm with typical transmit power, channel status, and the distance between transmitter and receiver. If ambient energy sources are not available, wireless power transfer (WPT) can be a powerful technique to recharge devices for their sustainable operation. The WPT can be classified into near-field (NF) WPT, and far-field (FF) WPT, depending on the distance between the transmitter and the receiver. Most of NF-WPT techniques are induction-based: magnetic induction (or inductive power transfer (IPT)) and electrostatic induction (or capacitive power transfer (CPT)). The IPT is able to recharge the sensor devices with charging power ranging from low level (\1 W) to high level (.1 kW). Particularly, the high-power IPT has recently emerged as an attractive means of electric car charging. The CPT is suitable for low-power biomedical devices and mobile devices. The FF-WPT is based on magnetic resonance with RF. In RF-based WPT, a dedicated power beacon can be used for recharging while data are transmitted simultaneously. Wireless systems in support of simultaneous power and data transfer at different frequency bands are known as out-band system, whereas those working in the same frequency band are known as in-band systems. In the paper ‘‘Wireless-powered cooperative energy aware anycast routing in wireless sensor networks,’’ authors present a wireless-powered cooperative energy aware anycast routing protocol. Selection of relays with optional capability of EH and routing to destination are investigated with wireless sensor networks. They found from their study that maximization of lifetime and reduction in energy consumption of cooperative wireless sensor networks can be obtained by relays capable of EH. In another paper ‘‘Performance analysis of the clustering-based multi-hop wireless EH sensor networks over symmetric and asymmetric fading channels,’’ authors investigated clustering-based multi-hop relaying sensor network. They also considered relays capable of EH and proposed a relay selection scheme. It is found from their work that gain obtained from path loss reduction and relay diversity can mitigate potential performance degradation incurred by poor RF-to-DC conversion efficiency. They also showed comparative performance of their scheme with conventional multi-hop relaying scheme without clustering.

Stability of the Diffusion Equation with a Source

We will prove the generalized Hyers-Ulam stability of the (inhomogeneous) diffusion equation with a source, , for a class of scalar functions with continuous second partial derivatives.

Strategies for data stream mining method applied in anomaly detection

AbstractAnomaly detection, which is a method of intrusion detection, detects anomaly behaviors and protects network security. Data mining technology has been integrated to improve the performance of anomaly detection and some algorithms have been improved for anomaly detection field. We think that most data mining algorithms are analyzed on static data sets and ignore the influence of dynamic data streams. Data stream is the potentially unbounded, ordered sequence of data objects which arrive over time. The entire data objects cannot be stored and they need to be handled in one-time scanning. The data distribution of data stream may change over time and this phenomenon is called concept drift. The properties of data stream make analysis method different from the method based on data set and the analysis model is required to be updated immediately when concept drift occurs. In this paper, we summarize the characteristics of data stream, compare the difference between data stream and data set, discuss the problems of data stream mining and propose some corresponding strategies.

A flow admission control in Next Generation Networks with flow aggregate information exchange

Next Generation Networks (NGN) is defined as a set of multi-access, multi-transport, multi-service packet-based networks. There exists a variety of Quality of Service (QoS) architectures within NGN, therefore it is common to aggregate and de-aggregate flows at the boundaries of networks. A key question arises regarding the network performance is therefore whether we can guarantee end-to-end performance in this circumstance. In this work an efficient method for calculating end-to-end delay bounds of flows is given, which experience repetitive flow aggregations and de-aggregations. The calculation procedure requires network parameters exchanged among networks in the path as well as the traffic parameters of a flow. It is assumed that such parameters are exchanged according to a standard process recently approved in ITU-T. It is then suggested a simple admission control scheme for flows with strict delay bound requirements. In this scheme aggregation edge nodes store information only per flow aggregate; therefore the scalability is ensured. The delay bound and the admission control scheme are evaluated with simulations in a few realistic scenarios.

Carrier frequency synchronization based on pulse-pair method for 8-VSB DTV systems

Vestigial sideband (VSB) digital TV (DTV) systems do not show good performance in indoor environment or in motion, because they have difficulties in carrier recovery. In this paper, a pulse-pair method is proposed as a new carrier frequency recovery scheme for 8-VSB DTV systems. For estimating the desired frequency offset, the pulse-pair method uses the stochastic characteristics of the autocorrelation of the received 8-VSB pilot signal extracted by pilot extraction filters. Simulation results of the proposed scheme demonstrate that its acquisition range is ±250 kHz and the acquisition time averaged 3.8 ms in fading channels.