Yu-Suk Sung

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.

Be Cautious When Analyzing the Sampling Clock Offset in OFDM Systems

Many studies have analyzed the effects of sampling clock offset (SCO) on orthogonal frequency-division multiplexing (OFDM) systems. The results of these studies are based on one of two discrete representations of continuous time-domain OFDM signals: (1) a subcarrier set consisting of both negative and positive frequencies, or (2) a subcarrier set comprising only positive frequencies. This paper discusses whether there is any difference between the two representations in the presence of SCO. When SCO is not considered, both representations are equivalent because of aliasing. In the presence of SCO, we derive a closed form of signal-to-interference-plus-noise ratio (SINR) expressions for both cases and compare their performances in terms of SINR by numerical analysis. The latter representation shows worse SINR performance compared to the former representation because the effect of SCO is more relevant for high frequencies and the latter representation has complex exponentials with high frequencies. Therefore, for fair comparisons of performance, caution is needed when analyzing SCO in OFDM systems.