Jihoon Choi

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— Transmit beamforming and receive combining are simple methods for exploiting spatial diversity in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. Optimal beamforming requires channel state information in the form of the beamforming vectors for each OFDM subcarrier. This paper proposes to a limited feedback(More)
—A frequency offset compensation method for OFDM-FDMA, that can correct offsets after the DFT via circular convo-lution, is proposed as an alternative to the direct method that corrects frequency offsets by multiplying the complex exponents of the offset estimates before the DFT. In contrast to the direct method whose complexity increases proportional to(More)
—This letter presents an efficient tag collision arbitration protocol, viz., the Fast Tree Traversal Protocol (FTTP). It estimates the number of tags using maximum likelihood estimation and adjusts the splitting factor to reduce the identification delay. We show that our protocol effectively reduces the identification delay via the performance analysis and(More)
— Spatial multiplexing with linear precoding is a simple technique to take advantage of the high spectral efficiency provided by multiple-input multiple-output (MIMO) systems, and it can be simply implemented over frequency selective channels by using orthogonal frequency division multiplexing (OFDM). This requires channel state information (CSI) at the(More)
A limited feedback-based transmit beamforming technique for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) is investigated in time-varying channels. The performance of the system is significantly degraded by outdated feedback information even when the channel varies slowly. To compensate for the impairment in(More)
With the expansion of the Internet and World Wide Web (or the Web), research environments have changed dramatically. As a result, the need to be able to efficiently and securely access information and resources from remote computer systems is becoming even more critical. This paper describes the development of an extendable integrated Web-accessible(More)
How can we discover interesting patterns from time-evolving high speed data streams? How to analyze the data streams quickly and accurately, with little space overhead? High speed data stream has been receiving increasing attentions due to its wide applications such as sensors, network traffic, social networks, etc. One of the most fundamental tasks in the(More)