Browsing by Author "Chang, Wei-Ju"

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A Novel Three-Dimensional Hybrid Spatial Model for Wideband MIMO Channel in Indoor Environments
(2010)
Tarng, Jenn-Hwan
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Chang, Wei-Ju
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Wu, Sung-Jung
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電機工程學系
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Department of Electrical and Computer Engineering
Studies of the effects of three-dimensional (3D) propagations on MIMO channel correlation and capacity have been presented in some literatures based on given 3D stochastic models of angle spectrum. However, it is only for narrowband MIMO channels and can not properly include specular reflections due to walls and/or the ground. In this letter, a hybrid spatial channel model, which combines a 3D ray-tracing based model for deterministic rays with a new 3D model for single-bounce randomly scattering rays, is proposed to investigate wideband spatial/polarized MIMO channel correlation. Based on the proposed model, the per-tap correlation among MIMO sub-channels is formulated and is validated by indoor measurements. From the comparison between measured and computed sub-channel correlations, it is found that our 3D model is more accurate than the 2D model, which only considers the propagation path in the horizontal plane, for both the co-polarized and the cross-polarized antenna cases. It is noted that the concept of effective scattering region is introduced in our model, which can increase computation efficiency without sacrifice the prediction accuracy.
Effects of bandwidth on observable multipath clustering in outdoor/indoor environments for broadband and ultrawideband wireless systems
(2007-07-01)
Chang, Wei-Ju
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Tarng, Jenn-Hwan
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電信工程研究所
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Institute of Communications Engineering
A multipath-clustering phenomenon, which is caused by the fact that scatterers tend to group together in realistic environments, has a significant impact on the channel capacity. For a band-limited system, due to the limitation of the signal time resolution, observable multipath-clustering is affected not only by propagation environments but also by the signal bandwidth. Since a larger bandwidth gives better time resolution, it is possible to observe more multipath components and, therefore, stronger clustering effects. In this paper, a new method based on the Delta-K model for multipath times of arrival (TOAs) is proposed to investigate and quantify the effect of signal bandwidth on observable multipath clustering. Furthermore, to completely characterize the time dispersion characteristics of the channel, a statistical model using a power ratio, a decay constant, and the Rician factor to describe multipath averaged power decay and amplitude fading is proposed. Newly derived formulas are given to relate the model parameters of a wideband signal, including those of the multipath TOA, averaged power decay, and amplitude fading, to those of a narrowband signal. The channel parameter estimation methods have been extensively validated by comparing the computed channel parameters with the ones extracted from the measured channel responses of 1.95 and 2.44 GHz broadband radios in metropolitan and suburban areas, and of 3-5 GHz ultrawideband signals in indoors.
Frequency-Space-Polarization on UWB MIMO Performance for Body Area Network Applications
(2008)
Chang, Wei-Ju
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Tarng, Jenn-Hwan
;
Peng, Szu-Yun
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電信工程研究所
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Institute of Communications Engineering
This letter experimentally investigates the performance of ultrawideband (UWB) radio technologies with multiple-input-multiple-output (MIMO) antennas for body area network (BAN) applications. Effects of array spacing, antenna polarization, bandwidth and propagation on UWB-MIMO channel capacity are analyzed. The key finding here is to that in BAN the MIMO channel capacity is mainly determined by the power imbalance between subchannels compared to the sub channel correlation for both spatial array and polar array. For spatial array, the measured results show that the MIMO channel capacity is decreased when the array spacing is increased, despite the spatial correlation coefficient is decreased. This phenomenon is different from that in wide area networks (WAN) and wireless local area networks (WLAN). It is because that power difference among elements of the spatial array is significant in BAN short-range communications compared to that in WAN and WLAN. For polar array, the achievable channel capacity is lower than that of the spatial array in line-of-sight (LOS) conditions due to high cross-polarization discrimination. Furthermore, the MIMO capacity is slightly dependent on the environments due to dominance of human body effect. It is also found that the MIMO channel capacity decreased with frequency or bandwidth.