Browsing by Author "Cheng, Shau-Yu"

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Channel Estimator and Aliasing Canceller for Equalizing and Decoding Non-Cyclic Prefixed Single-Carrier Block Transmission via MIMO-OFDM Modem
(2011-01-01)
Cheng, Shau-Yu
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Tsai, Chueh-An
;
Hsu, Terng-Yin
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資訊工程學系
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Department of Computer Science
Without a cyclic prefix (CP), most single-carrier (SC) transmissions can not adopt frequency-domain equalizer (FDE) directly. This work utilizes frequency-domain channel estimator (FD-CE) and decision-feedback aliasing canceller (DF-AC) to produce single-FFT SC-FDE. In this way, non-CP single-carrier block transmission (SCBT) can be decoded using sphere decoder of MIMO-OFDM modems to support multimode and backward compatibility under an acceptable complexity in IEEE 802.11 very high throughput (VHT). An N-point FFT is sufficient to measure channel frequency responses (CFR) from L-sample preambles (L <= N/2). And then, M-bit block codes (M <= L) are decodable over frequency domains with DF-AC's help. Simulations and measurements imply that this work can ensure adequate performance, even if there is no CP existed against the distortions of multipath propagation.
DESIGN ISSUES AND EXPERIMENTAL STUDIES OF WIRELESS LAN MESH
(2010-04-01)
Lin, Ying-Dar
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Tsao, Shiao-Li
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Chang, Shun-Lee
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Cheng, Shau-Yu
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Ku, Chia-Yu
Wireless mesh networking, as a low-cost and reliable technology for rapid network deployment, has attracted considerable attention from academia and standardization in the industry. The IEEE 802.11s standard defines a wireless LAN mesh using the IEEE 802.11 medium access control and physical layers, and is one of the most active standards with increasing commercial opportunities. This study presents the design and development of a WLAN mesh system conforming to the latest IEEE 802.11s draft amendment. Without costly hardware modifications, the proposed solution is a pure software extension for commercial off-the-shelf WLAN chipsets. This study constructs an experimental testbed, and evaluates issues such as the transmission reliability of mesh broadcast-type control messages and multichannel transmissions. Experimental results demonstrate that the delivery of mesh broadcast-type control messages, such as routing construction frames, using the multiple acknowledged unicast scheme improves mesh stability from an 86 to a 98 percent success ratio in a 16-node grid. Transmitting packets using a single radio interface switching between multiple channels reduces inter-flow interference and doubles the throughput in our testbed.
Indoor deployment of IEEE 802.11s mesh networks: Lessons and guidelines
(2011-11-01)
Lin, Ying-Dar
;
Chang, Shun-Lee
;
Yeh, Jui-Hung
;
Cheng, Shau-Yu
;
資訊工程學系
Emerging wireless mesh networks (WMNs) are known for their fast and low cost deployment. Conventional mesh deployment focuses on the outdoor environment, which regards the wMNs as backbone networks. This study deploys and measures indoor IEEE 802.11s mesh networks to extend WLAN capabilities with extensive experiment configurations. The testbed is constructed in a laboratory and a field crossing three floors of a building. Disagreeing with previous research, the results of this study indicate that RTS/CTS can improve throughput by up to 87.5%. Moreover, compared with the IEEE 802.11b/g, 802.11n achieves better fairness for multi-stream or multi-hop communications. Experimental results also suggest that a longer beacon interval, e.g. 500 ms, can improve channel efficiency for a denser deployment. On the other hand, sparser deployments should use a shorter beacon interval, e.g. 100 ms, to enhance link stability. (C) 2011 Elsevier B.V. All rights reserved.