김훈 교수

This letter extends the proportional fair (PF) scheduling proposed in the high data rate (HDR) system to multicarrier transmission systems. It is known that the PF allocation (F. P. Kelly et al. (1998)) results in the maximization of the sum of logarithmic average user rates. We propose a PF scheduling that assigns users to each carrier while maximizing the sum of logarithmic average user rates.

It is known that amplitude fluctuations caused by amplified spontaneous emission noise can be converted into phase noise by Kerr nonlinearity, and this nonlinear phase noise can limit the performance of phase-shift-keying transmission systems. In this letter, we experimentally observe and study the performance degradation of differential phase-shift-keying transmission systems due to nonlinear phase noise. In order to clearly observe the effect, we intentionally add ASE noise to the DPSK signal

In this paper, we proposed a proportional fair (PF) scheduling algorithm for systems with multiple carriers such as orthogonal frequency division multiple access systems. The scheduler assigns users to carriers to maximize the sum of logarithmic transmission rate, which is compatible with the definition by RE Kelly (Journal Operational Research Soc., vol.49, p.237-252, 1998). It is shown that the PF scheduling in the high data rate (HDR) system proposed by Qualcomm is a special case of our propo

We assess, both by measurement and simulation, the receiver performance degradation caused by frequency offsets between the optical source and the delay interferometer for nonreturn-to-zero (NRZ) and return-to-zero (RZ) differential-phase-shift-keying (DPSK) and differential-quadrature-phase-shift-keying (DQPSK) systems. We find that NRZ- and RZ-DQPSK systems are about six times more sensitive to frequency offsets than NRZ- and RZ-DPSK systems operating at the same bit rate. We explain the reaso

In this letter, we present theoretical and experimental studies on the chirp of the dual-drive Mach-Zehnder (MZ) modulator with a finite DC extinction ratio. The chirp of the modulator was measured using the fiber response peak method and compared with the theoretically calculated values. The results show that the residual chirp of the MZ modulator could be substantially reduced by driving the modulator in a push-pull mode with unequal amplitude signals.

We report on the use of a delay interferometer (DI) to transmit 10-Gb/s optical signals from a 1.5-GHz-bandwidth reflective semiconductor optical amplifier (RSOA). The DI acts as a two-tap optical equalizer, compensating for the severe bandwidth limitation imposed by the RSOA. We demonstrate the successful transmission of 10.7-Gb/s nonreturn-to-zero signals over 50-km standard single-mode fiber with a 0.3-dB penalty.

The media access control (MAC) protocol in wireless sensor networks provides a periodic listen/sleep state for protection from overhearing and idle listening. However, many scenarios and applications exist in which sensor nodes must send data quickly to destination nodes. This paper proposes the priority-based quality-of-service MAC (PQMAC) protocol for wireless sensor networks. We use data priority levels to differentiate among data transmissions, and propose a MAC protocol based on these level

In this paper, we study two adaptive beam control techniques, where the beam divergence angle is adjusted at the transmitter to (i) maximize link availability or (ii) minimize transmitter power while maintaining target link availability. For this purpose, we provide closed-form expressions about the link availability and optimum beam divergence angle under the effect of generalized two-dimensional Gaussian distribution of the alignment error between the transmitter and receiver. These simple and

In direct-detection differential-phase-shift-keying (DPSK) systems, the signal-spontaneous emission beat noise introduces phase noise due to Kerr nonlinearity. In wavelength-division-multiplexed (WDM) systems, this nonlinear phase noise comes not only from the channel itself through self-phase modulation (SPM) but also from the other channels through cross-phase modulation (XPM). In this paper, we theoretically and experimentally investigate XPM-induced nonlinear phase noise. We calculate the pe

Sensor deployment to achieve better system performance is one of the critical issues in wireless sensor networks. An effective sensor deployment scheme is proposed for large-area sensor networks, where the event occurrence rate varies over the sensor-deployed region. By utilizing the local event occurrence rate and applying the analytical sensor detection capability expression for the problem formulation, the proposed scheme determines the optimal number of sensors for a typical surveillance sen

We propose and demonstrate a simple method to improve both the receiver sensitivity and spectral efficiency of the optical duobinary transmission system. Compared to the conventional duobinary signal generated by using an electrical low-pass filter, more than 1-dB improvement of receiver sensitivity and /spl sim/20% reduction in the spectral width are achieved simply by filtering the 10-Gb/s duobinary signals with a narrow-bandwidth (7 GHz) optical filter.

We present a novel optical single sideband (SSB) transmitter comprised of an electroabsorption modulated laser. The transmitter exploits the hybrid or compatible SSB structure wherein the directly modulated laser diode and the electroabsorption modulator function as phase and amplitude modulators, respectively. The theoretical analysis and experimental demonstration confirm the feasibility of optical SSB transmitter for radio-over-fiber applications by using this small semiconductor device.

Developing a computer vision-based algorithm for identifying dangerous vehicles requires a large amount of labeled accident data, which is difficult to collect in the real world. To tackle this challenge, we first develop a synthetic data generator built on top of a driving simulator. We then observe that the synthetic labels that are generated based on simulation results are very noisy, resulting in poor classification performance. In order to improve the quality of synthetic labels, we propose

We report the transmission of eight-channel 20-Gb/s differential quadrature phase-shift-keying signals over 310-km conventional single-mode fiber. The high spectral efficiency (0.8 b/s/Hz) and successful transmission are achieved without using polarization multiplexing, Raman amplification, and forward error correction.

In this paper, subcarrier allocation schemes for cellular orthogonal frequency division multiple access (OFDMA) systems with adaptive modulation and coding (AMC) is considered. An LP formulation with the constraints of quality-of-service (QoS) and limited bandwidth was made to achieve optimal system throughput. We propose an optimal subcarrier allocation scheme which allows cell coordination to assign subcarrier reuse factor and modulation scheme for each subcarrier. Also, to reduce computationa