Insoo Sohn

A Low Complexity PAPR Reduction Scheme for OFDM Systems via Neural Networks

Peak-to-average power ratio (PAPR) reduction is one of the key components in orthogonal frequency division multiplexing (OFDM) systems. Among various PAPR reduction techniques, artificial neural network (NN) has been one of the powerful techniques in reducing the PAPR due to its good generalization properties with flexible modeling and learning capabilities. In this letter, we propose a new method that uses NNs trained on the active constellation extension (ACE) signals to reduce the PAPR of OFDM signals. Unlike other NN based techniques, the proposed method employs a receiver NN unit, at the OFDM receiver side, achieving significant bit error rate (BER) improvement with low computational complexity.

Neural Network Based Simplified Clipping and Filtering Technique for PAPR Reduction of OFDM Signals

Many iterative clipping and filtering (ICF) based techniques have been proposed that achieve similar peak-to-average power ratio (PAPR) reduction of orthogonal frequency division multiplexing (OFDM) signals as the original ICF, but with lower complexity, such as the simplified clipping and filtering (SCF) technique. However, these low complexity methods require numerous complex fast Fourier transform (FFT) operations and parameter calculations. In this letter, we introduce a novel ICF method that uses an optimized mapper based on artificial neural network and SCF techniques. Compared to the conventional ICF based methods, the proposed scheme offers desirable cubic metric (CM) and bit error rate (BER) simulation results with significantly reduced computational complexity.

Simulation of Energy Conversion Efficiency of a Solar Cell with Gratings

In this work, a numerical analysis of a CIGS (CuIn1-xGaxSex) solar cell with a rectangular grating on the electrode is presented. The effects of the grating on the energy conversion efficiency are calculated using the RCWA (rigorous coupled wave analysis) method. In conventional CIGS solar cells, the thickness of the light absorption layer (CIGS) is 2 µm, at which the incident light is almost absorbed. By adopting a grating on the electrode and using a less than 1 µm CIGS layer, we obtained a higher efficiency compared to the conventional solar cells.

Access Point Selection Game with Mobile Users Using Correlated Equilibrium

One of the most important issues in wireless local area network (WLAN) systems with multiple access points (APs) is the AP selection problem. Game theory is a mathematical tool used to analyze the interactions in multiplayer systems and has been applied to various problems in wireless networks. Correlated equilibrium (CE) is one of the powerful game theory solution concepts, which is more general than the Nash equilibrium for analyzing the interactions in multiplayer mixed strategy games. A game-theoretic formulation of the AP selection problem with mobile users is presented using a novel scheme based on a regret-based learning procedure. Through convergence analysis, we show that the joint actions based on the proposed algorithm achieve CE. Simulation results illustrate that the proposed algorithm is effective in a realistic WLAN environment with user mobility and achieves maximum system throughput based on the game-theoretic formulation.

Localization performance analysis of KNN in IEEE 802.11 TGn channel

With growing demand for location based services, research on high resolution location estimation methods in indoor wireless environments have grown over the years. Currently the most popular localization method based on RSS is the fingerprinting KNN method proposed by Bahl and Padmanabhan due to its simplicity. In this paper we present the experimental results on the multiple antenna KNN method in IEEE 802.11 TGn MIMO channel models for high resolution location estimation.

Modeling and implementing small world network

For the past few years, there has been a growing interest in using the small world concept for optimizing wireless network topology. Even though, there are numerous review articles on the small world based on complex network theory, one might find it too theoretical for application to wireless network optimization research. In this paper we present basic concepts needed to model the small world network and provide implementation issues for designing the network.

Optimizing Cellular Networks Enabled with Renewal Energy via Strategic Learning

An important issue in the cellular industry is the rising energy cost and carbon footprint due to the rapid expansion of the cellular infrastructure. Greening cellular networks has thus attracted attention. Among the promising green cellular network techniques, the renewable energy-powered cellular network has drawn increasing attention as a critical element towards reducing carbon emissions due to massive energy consumption in the base stations deployed in cellular networks. Game theory is a branch of mathematics that is used to evaluate and optimize systems with multiple players with conflicting objectives and has been successfully used to solve various problems in cellular networks. In this paper, we model the green energy utilization and power consumption optimization problem of a green cellular network as a pilot power selection strategic game and propose a novel distributed algorithm based on a strategic learning method. The simulation results indicate that the proposed algorithm achieves correlated equilibrium of the pilot power selection game, resulting in optimum green energy utilization and power consumption reduction.

Mobile base station system based on UMTS-HSDPA high altitude platform station

Research on the integration of high altitude platform station (HAPS) with conventional 3G and future 4G mobile broadband communication networks has been increasing in the past few years due to various advantages the integrated system can offer. In this paper, we investigate a novel HAPS based mobile base station system using low altitude airship for high speed mobile broadband wireless services. Through capacity analysis and numerical results we show that the proposed system is a promising solution toward the future mobile base station system.