Browsing by Author "Chang, Yu-Hao"

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Codeword Design for Ultra-Wideband (UWB) Precoding
(2010-01-01)
Chang, Yu-Hao
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Tsai, Shang-Ho
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Yu, Xiaoli
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Kuo, C. -C. Jay
;
電機工程學系
A precoding technique applied to symbols transmitted in an ultra-wideband (UWB) system can concentrate the signal power at the receiver for a higher data detection rate. The codeword design problem for optimal UWB precoding is investigated in this work. After the problem formulation, we examine its solution in the full-rank and the reduced-rank subspaces to obtain different tradeoffs between the detection performance and the amount of feedback messages. Furthermore, we propose two subspace selection schemes, each of which corresponds to a code design method. The resultant optimal codewords improve the performance of previous work significantly at the expense of a slightly increased amount of feedback messages. Finally, the performance of a precoded UWB system with various codewords is compared via computer simulation.
On robustness of ultra-wideband (UWB) precoding against timing jitter
(2007)
Chang, Yu-Hao
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Tsai, Shang-Ho
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Yu, Xiaoli
;
Kuo, C. -C. Jay
;
電機學院
The channel phase precoding (CPP) technique was recently proposed For the ultra-wideband (UWB) communication system in I I I to save the feedback overhead and the computational complexity as compared with the time-reversal prefilter (TRP) technique [2]. Two ideal assumptions have been made in both systems;, namely, the availability of accurate channel information and perfect synchronization of transmitted pulses. In this work, we examine the impact of timing jitter on the performance of TRP and CPP and show that the CPP-UWB system is more robust against the timing jitter than the TRP-UWB system.
Performance Enhancement of Channel-Phase Precoded Ultra-Wideband (CPP-UWB) Systems by Rake Receivers
(2008)
Chang, Yu-Hao
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Tsai, Shang-Ho
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Yu, Xiaoli
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Kuo, C. -C. Jay
;
電控工程研究所
We propose to use the Rake receiver to improve the system performance by collecting more signal power in an ultra-wideband (UWB) system precoded by the channel phase information, called the CPP-UWB system [1], in this work. The performance of the proposed system is determined by the selected channel taps and the corresponding combining schemes for those Rake fingers. Three combing schemes, i.e., the maximum ratio combining (MRC), the minimized mean square error (MMSE) and the zero-forcing (ZF), are proposed. When the MRC scheme is applied to the Rake receiver with M fingers, M channel taps can be easily found to maximize the averaged signal power at the receiver output by exploiting the property of the channel-phase-precoded channel. It is shown by simulation results that the proposed scheme significantly outperforms the precoding system using one matched filter as proposed in [1].
Slow surface passivation and crystal relaxation with additives to improve device performance and durability for tin-based perovskite solar cells
(2018-09-01)
Jokar, Efat
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Chien, Cheng-Hsun
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Fathi, Amir
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Rameez, Mohammad
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Chang, Yu-Hao
We investigated the doping effect of bulky organic cations with ethylenediammonium diiodide (EDAI(2)) and butylammonium iodide (BAI) as additives to passivate surface defects, to control the film morphology and to improve the crystallinity for inverted planar FASnI(3) perovskite solar cells. The addition of BAI altered significantly the orientation of crystal growth and improved the connectivity of the crystal grains, but the existence of pinholes in the surface of the pristine FASnI(3) films was unavoidable; this effect impeded further improvement of the device performance (PCE 5.5%), which is nevertheless superior to that of a pristine FASnI(3) film (PCE 4.0%). The addition of EDAI(2) had the effect of curing the pinhole problem, passivating the surface defect states, preventing Sn2+/Sn4+ oxidation and inducing slow relaxation of the crystal structure. In the presence of the EDAI(2) additive (1%), the FASnI(3) device attained the best initial efficiency, 7.4%, and the device performance continuously increased as a function of duration of storage; the maximum PCE, 8.9%, was obtained for a device stored in a glove box for over 1400 h with only slight degradation for storage beyond 2000 h. The observed slow passivation of surface defects and relaxation of crystal strain were verified with X-ray diffraction, X-ray photoelectron spectroscopy and photoluminescence decay techniques.
Ultrawideband transceiver design using channel phase precoding
(2007-07-01)
Chang, Yu-Hao
;
Tsai, Shang-Ho
;
Yu, Xiaoli
;
Kuo, C.-C. Jay
;
電控工程研究所
A novel transceiver design for ultrawideband (UWB) communication systems using the channel phase precoding (CPP) technique is proposed in this work. With the CPP-UWB transceiver, we encode data symbols using the reversed order of the channel phase. A simple phase estimation algorithm is presented for the CPP-UWB implementation. Owing to its ability to coherently combine the channel magnitude of every multipath, the CPP-UWB transceiver can achieve a higher data rate by shortening its symbol duration with a tolerable interference. The performance of the CPP-UWB can be further improved using an optimal code length and/or the MMSE receiver to suppress intersymbol interference.