Hae-Wook Choi

Simple full-range carrier frequency offset estimation for high speed CO-OFDM

We propose a simple, full-range carrier frequency offset (CFO) algorithm for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. By applying the Chinese remainder theorem (CRT) to training symbol of single frequency, the proposed CFO algorithm has wide range with shorter training symbol. We numerically and experimentally demonstrate the performance of CRT-based algorithms in a 16-ary quadrature amplitude modulation (QAM) CO-OFDM system. The results show that the estimation range of the CRT-based algorithm is full-range corresponding to the sampling frequency. Also, the bit error ratio (BER) degradation of the proposed algorithm with one training symbol is negligible. These results indicate that the proposed algorithm can be used as a wide range CFO estimator with an increased data rate in high speed CO-OFDM systems.

Spatial Modulation for High-Rate Transmission Systems

This paper proposes a high rate spatial modulation transmission scheme based on the concept of Spatial Constellation (SC) and SC codewords introduced in [1]. In the proposed scheme, transmitted signal vectors are generated by multiplying spatial SC codewords with constellation symbols drawn from a conventional QAM or PSK constellation. The entries of SC codewords will determine how the constellation symbols are weighted and which transmit antennas among a total of nT transmit antennas are activated to transmit the signals. Different SC codewords allow us to have different ways to transmit the constellation symbols. Thus, information bits are born not only by constellation symbols but also by SC codewords. The additional spectral efficiency offered by SC codewords is proportional to the number of SC codewords which can be designed for each antenna configuration. A new low-complexity maximum-likelihood (ML) decoder is also devised for signal recovery. In addition, a theoretical union bound on the bit error probability is derived. Simulation results, supported by the theoretical upper bound, are given to compare bit error rate (BER) performance of the proposed scheme with those of existing MIMO transmission counterparts in the literature for various antenna configurations.

Unified Performance Authoring Tool for Heterogeneous Devices and Protocols

A contents authoring software with device management for interactive shows and performances is proposed. The proposed system allows user to register and to manage various stage-related devices such as lighting system, fog generator, robots or multimedia players. In this paper, we describe software architecture, XML specification for unified protocol description, and user interface of the proposed system. The system can control multiple devices of heterogeneous protocols in timely manner. Once devices are registered, user can browse commands of each device and can organize commands to step-based list according to the performance scenario. Unlike current commercialized products, the system allows to manipulate authored list of commands during the show instantly. The proposed system also supports to control playback of authored commands by sensor inputs so that a player can trigger devices to execute according to events. The contributions of this paper can be summarized to three points; (1) define unified protocol description with XML structures for simplicity (2) give sensor triggering capability to control devices, and (3) implement fast and instant manipulation user interface during the show.

Simple Wide Range Carrier Frequency Offset Estimator for Coherent Optical OFDM

Coherent optical orthogonal frequency division multiplexing systems have a wide carrier frequency offset (CFO) range due to the frequency inaccuracy of lasers. In this letter, a simple wide range CFO estimator is proposed. In the proposed algorithm, wide estimation range and high accuracy are achieved by using a combination of the Chinese remainder theorem (CRT) for the integer part of CFO and fine estimation for the fractional part of CFO. For the proposed estimator, a training symbol structure consisting of two identical symbols is also suggested. The sizes of subsymbols of the training symbols are relatively prime to apply CRT. Simulations verify the validity of the proposed algorithm. The results indicate that the range of estimator is as large as the sampling frequency.

Real-Time Digital Signal Processing for High-Speed Coherent Optical OFDM Synchronization

In high-speed coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems, wide range estimation of carrier frequency offset (CFO) and hardware-efficient symbol timing synchronization are essential. The CFO estimation using the Chinese remainder theorem (CRT) was recently proposed to provide wide range estimation. In this paper, the feasibility of the proposed CRT-based CFO estimation method is demonstrated in a real-time CO-OFDM system. We also propose two-step symbol timing synchronization with simplified timing metric for CO-OFDM systems. The real-time experimental results show that the CRT-based CFO algorithm can estimate over a wide range corresponding to the sampling frequency and hardware efficient accurate symbol timing synchronization is achieved by the proposed synchronization method.

Efficient Chromatic Dispersion Precompensation for Coherent Optical OFDM

To reduce the guard interval, short-cyclic-prefix coherent optical orthogonal frequency division multiplexing (CO-OFDM) divides a band into two subbands and precompensates for chromatic dispersion (CD) with timing offset. Implementation using full band inverse discrete Fourier transformations (IDFTs), however, can excessively increase hardware complexity. We propose an efficient hardware implementation of IDFT with timing offsets for short-cyclic-prefix CO-OFDM. In addition, the residual intersubband CD induced by quantized timing offset is compensated using subcarrier-based phase rotation. By increasing the number of subbands efficiently and compensating for the residual intersubband CD, the transmission performance can be improved. Simulation results show 112-Gb/s single-channel transmission over a 2250-km standard single-mode-fiber with polarization division multiplexing 16 quadrature amplitude modulation (PDM-16 QAM) using 128 DFT with a 16 guard interval.

Modeling Student’s Handwritten Examination Data and Its Application Using a Tablet Computer

In this work, we propose a model of students’ examination data which can contain timestamp and handwriting information using a tablet computer. Stored data is consumed by students’ achievement recording software so that both teachers and students can trace their records at any time. The handwriting data in this work can be expressed as XML description so that other applications can use the data easily. The scope of this work is limited to store students’ examination information so that it is recommended to be combined with students’ profile or other valuable data. Inside the data, this work treats the examination information, question information, students’ response time of each question, and moreover, students’ behavioral factors including page navigation, removal and writing activities. With the students’ behavioral data, a visualization software can give user to suppose the student’s activity easily and vividly. In this work, we describes an example of visualization software which allows user to review recorded secondary students’ mathematics examination. Not only score-based assessment, our work may contribute to improve student’s assessment and feedback with various educational insights.

Efficient Pipelined Multistream AES CCMP Architecture for Wireless LAN

Widespread WLAN has used Advance Encryption Standard in Counter with Cipher Block Chaining Message Authentication Code Protocol (AES CCMP) as security services. As the next-generation WLAN adopts multiuser MIMO technology, multiple AES blocks are needed because this technology supports multiple packet transmission in parallel. To minimize the cost increase due to multiple AES blocks, we propose a pipelined AES architecture which processes multiple packets in parallel. By using a pipelined AES architecture instead of multiple AES blocks, efficiency is improved greatly since this pipelined architecture enables to sharing of the AES core. To find the optimum number of stages, we implemented pipelined architectures with various numbers of stages. The results show that a 3-stage pipeline is most efficient, and we achieve 4.34 Gpbs throughput with 2.39 Mbps/slice implementation cost of 1,817 slices and 0 BRAM using Xilinx Virtex 5. This efficiency results from the pipelined architectures high operating frequency and resource sharing.

Color Coding for Massive Bicycle Trajectories

As the smartphone market grows, tracking a person’s own positions become easier and popular. Especially for the bicycling, file based GPS data make it easier to manage and access personal trajectories. In this paper, we propose an effective color coding method for massive bicycle trajectories visualization. The motivation of the method is based on characteristics of the bicycle trajectories which have different spatial aspects compare to the automobiles. The proposed method modifies the color of the line segments based on the direction and flow, and provides visually enhanced trajectories. GPS data collected from Han riverside bicycle tracks were applied to the proposed visualization methods, and shown the potential possibilities for trajectory analysis.

Energy self-sufficient electrolysis apparatus for sterilization of portable toilet in small vessels

Marine caused pollution occurs mostly near coastal area and its main cause was known to be human feces issued from small vessels. To sterilize liquid pollutants from portable toilets of small vessels, an electrolysis treatment is judged to be the most economic and stable method considering an environment of its use. In this paper, we presents an electrolysis apparatus which is the most appropriate for sterilizing pollutants from portable toilets of small vessels and derives the minimum operating time of the apparatus for sterilizing norovirus which is a main target of marine caused pollution sources. In order to utilize renewable energy, we designed an apparatus which generates a renewable energy from solar cells. As a result, we could confirm the applicability of the proposed system with the results from experiments in three cases of different weather conditions.