Jinwon Choi

Frequency-Dependent UWB Channel Characteristics in Office Environments

This paper reports frequency-dependent ultrawideband (UWB) channel characteristics. Measurements were performed in 103 receiver locations of six different office environments. From the measured data, the effect of frequency on the path-loss properties of a UWB signal is analyzed. After analyzing the path-loss behavior to propagation environments, the path-loss exponent variation models are developed in various environments as a function of frequency. Based on these models, path-loss prediction is performed, and the accuracy of the prediction is compared with those of existing path-loss models. In addition, the frequency-dependent UWB channel correlation characteristics are investigated. For the frequency correlation statistics of the UWB channel, double-slope models representing correlation coefficients are established with and without line-of-sight (LOS) paths. Using these correlation models, a channel gain estimation algorithm is proposed. The performance of the proposed estimation algorithm is evaluated with estimation parameters, and it is confirmed that the proposed estimation algorithm has better performance than the conventional algorithm using a linear interpolation algorithm.

Empirical Ultra Wide Band Path Loss Model in Office Environments

This paper reports the empirical path loss model of ultra wide band (UWB) communications in office environments. The channel transfer functions of 46 transmitter-receiver location pairs are acquired using channel measurement system based on frequency sweep method. From the measured data, parameters of log-distance path loss formula are extracted considering propagation environments and existence of a line of sight path. The effect of frequency to the path loss properties of ultra wideband signal is presented also. Finally, statistical properties of received signal power with respect to the receiver conditions are analyzed

Empirical Ultra Wide Band Channel Model for Short Range Outdoor Environments

This paper reports the empirical ultra wide band (UWB) channel model for short range outdoor environments. The measurements were performed based on the frequency sweep method in frequency domain at two different parking lot environments. From the measured channel transfer functions, parameters of log-distance path loss law and the effect of frequency to the path loss exponent are extracted. The distribution of received signal is analyzed to the existence of line-of-sight (LOS) path also. For the characterization of frequency dependent UWB channel parameters, standard deviation and correlation properties of channel gain in frequency domain are analyzed. The standard deviation increases with transmitter-receiver separation in LOS condition and the correlation is regressed to the double-slope model.

An improved throughput estimation method and dynamic user association in multi-cell networks

In this paper, we propose an effective user association rule for resolving the unbalanced loading problem in multi-cell cellular networks. We first derive an improved user throughput estimation formula for the proportional fair (PF) scheduling algorithm under the Rayleigh fading environment. Our simple and accurate throughput estimation can be regarded as an extended version of the conventional scheme which is only valid when the data rate function is linear. Based on this result, we also develop a centralized user association framework, where a central node periodically determines the overall association of the system. The simulation results show that our load balancing algorithm achieves almost 90% of the upper limit of the system.

Effect of Metal Door on Indoor Radio Channel

This paper reports the variation of indoor radio channel caused by metal door. The simulation results using the finite difference time domain (FDTD) method and measurement results using the vector network analyzer in frequency domain are used for the characterization of received signal strength variation by metal door. Target frequency bands are three - sensor band, 802.11b ISM band, and 802.11a UNII band. From the simulation and measurement results, the effect of door angle to the received signal strength in three frequency bands and effect of radio frequency to variation are investigated. And FDTD simulation parameters for different environments are suggested.