Wonjong Rhee

This paper investigates the problem of dynamic multiuser subchannel allocation in the downlink of OFDM systems. The assumptions are that the channel model is quasi-static and that the base station has perfect channel information. In traditional TDMA or FDMA systems, resource allocation for each user is non-adaptively fixed, and the water-filling power spectrum is known to be optimal. Since the subchannel allocations among the users are not optimized, a group of users is likely to suffer from poo

The advantages of multiuser communication, where many users are allowed to simultaneously transmit or receive in a common bandwidth, are considered for multiple-antenna systems in a high signal-to-noise ratio (SNR) regime. Assuming channel state information at receiver (CSIR) to be available, the ergodic capacity is characterized for both unbiased and biased channels, and the quantitative capacity gain of a multiple-antenna multiuser system is analyzed for multiple-access channels. For highly bi

Although promising results of high-performance AI algorithms have been reported in recent predictive maintenance researches, most of the existing studies merely deal with AI-only solutions and do not consider the interaction between humans and AI. In this study, we explicitly focus on the benefits of interactions where a human inspector is assisted by AI solutions. A case study is conducted for predictive maintenance of wind farms, where endoscopic images were used for bearing fault detection. T

Internet-connected devices, especially mobile devices such as smartphones, have become widely accessible in the past decade. Interaction with such devices has evolved into frequent and short-duration usage, and this phenomenon has resulted in a pervasive popularity of casual games in the game sector. On the other hand, development of casual games has become easier than ever as a result of the advancement of development tools. With the resulting fierce competition, now both acquisition and retent

This paper considers the optimal uplink transmission strategy that achieves the sum-capacity in a multiuser multi-antenna wireless system. Assuming an independent identically distributed block-fading model with transmitter channel side information, beamforming for each remote user is shown to be necessary for achieving sum-capacity when there is a large number of users in the system. This result stands even in the case where each user is equipped with a large number of transmit antennas, and it

Energy disaggregation, or nonintrusive load monitoring (NILM), is a technology for separating a household’s aggregate electricity consumption information. Although this technology was developed in 1992, its practical usage and mass deployment have been rather limited, possibly because the commonly used datasets are not adequate for NILM research. In this study, we report the findings from a newly collected dataset that contains 10 Hz sampling data for 58 houses. The dataset not only contains the

In this paper, the ergodic capacity region of multi-antenna multiple-access channels is derived, and the quantitative capacity gains of multiuser communication systems are investigated. In many multi-antenna communication scenarios, the ergodic capacity of multiuser systems, where many users are allowed to simultaneously transmit or receive in a common bandwidth, is shown to be significantly larger than that of single user systems.

Multiple-input multiple-output (MIMO) flat-fading channels with channel state information available at the receiver and channel state distribution available at the transmitter are considered. The ergodic capacity-achieving covariance matrix (ECACM) under an average input power constraint is shown to be not unique in general, and three sufficient conditions for the uniqueness are derived. Then, the structure of ECACM is characterized for certain classes of MIMO channels including the following cl

We present a performance comparison of two multicarrier modulation schemes (Bingham 1990), orthogonal frequency division multiplexing (OFDM) (Cimini Jr., 1985) and multitone with polyphase filter bank (MPFB), in the presence of frequency offset and delay spread. The bit error rate (BER) for the two systems in an additive white Gaussian noise (AWGN) channel and a two-ray Rayleigh fading channel is evaluated by computer simulation. It is shown that the sensitivity to frequency offset can be reduce

Multiple-input multiple-output (MIMO) flat fading channels with channel state information available at the receiver and channel state distribution available at the transmitter are considered. The ergodic capacity-achieving covariance matrix (ECACM) under an average input power constraint is shown to be not unique in general, and three sufficient conditions for the uniqueness are derived. Then, the ECACM structure is characterized for certain classes of MIMO channels including the following class

In this paper, we provide findings from an energy saving experiment in a university building, where an IoT platform with 1 Hz sampling sensors was deployed to collect electric power consumption data. The experiment was a reward setup with daily feedback delivered by an energy delegate for one week, and energy saving of 25.4% was achieved during the experiment. Post-experiment sustainability, defined as 10% or more of energy saving, was also accomplished for 44 days without any further interventi