Browsing by Author "Liu, Wei-Cheng"

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Analysis of Diversity-Multiplexing Tradeoff in a Cooperative Network Coding System
(2011-09-01)
Wang, Li-Chun
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Liu, Wei-Cheng
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Wu, Sau-Hsuan
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電機工程學系
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Department of Electrical and Computer Engineering
This paper addresses the analysis of diversity-multiplexing tradeoff (DMT) for a decode-and-forward (DF)-based cooperative network coding (CNC) system. The exact outage probability is also provided. Our results show that network coding can assist the relay node to improve multiplexing and diversity gain.
BER analysis in a generalized UWB frequency selective fading channel with randomly arriving clusters and rays
(2007)
Liu, Wei-Cheng
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Wang, Li-Chun
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電信工程研究所
;
Institute of Communications Engineering
In this paper, we present an analytical method to evaluate the bit error rate (BER) of the ultra-wideband (UWB) system in the IEEE 802.15.4a standardized channel model. The IEEE 802.15.4a UWB channel model is more general and based on more measurements than the earlier IEEE 802.15.3a model. It also poses new challenge in analyzing UWB performance in such a channel. First, the power delay profile become a function of randomly arriving cluster and ray arrival time. Second, the signal amplitude in the IEEE 802.15.4a channel is modeled by a Nakagami random variable of which the Nakagami fading parameter is log-normally distributed. Thus, the signal amplitude is a nonlinear function of a log-normally distributed random variable. By means of counting integral of Lebesgue measure theory, the analytical expression for the BER performance in the IEEE 802.15.4a UWB channel is presented. We apply this analytical model to investigate the impacts of various UWB channel parameters on the system performance and provide some useful insights into the design of UWB transceiver.
BER Analysis of the IEEE 802.15.4a Channel Model with RAKE Receiver
(2006)
Liu, Wei-Cheng
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Wang, Li-Chun
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電信工程研究所
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Institute of Communications Engineering
This paper provides the bit error rate (BER) analysis of the antipodal and orthogonal binary signals under the ultra-wideband (UWB) channel. We offer an analytical expression and its evaluation formula for the BER. The channel model we consider is the IEEE 802.15.4a UWB channel. We take into account of the impact or all the key parameters, including intercluster arrival rate, cluster decay constant, the inter-ray arrival rate, ray decay, constant, parameters of the power delay profile (PDP). and the distribution of a Nakagami fading signal. For the IEEE 802.15.4a UWB channel, the effects of clustering are characterized by a Poisson process, and the inter-ray arrival time is modeled as the hyperexponential random variable. We propose a systematic analytical method to evaluate the BER performance of the UWB signal associated with such Joint continuous Nakagami and discrete Poisson random variable. Thus, the developed analytical model is useful in evaluating the performance or an UWB signal in the IEEE 802.15.4a channel without time consuming simulations.
BER-minimized space-time-frequency codes for MIMO highly frequency-selective block-fading channels
(2008)
Liu, Wei-Cheng
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Wang, Li-Chun
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電信工程研究所
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Institute of Communications Engineering
In this paper, we present bit error rate (BER) minimized space time frequency (STF) block codes for multi input multi output (MIMO) highly frequency selective block fading channels. We consider the IEEE 802.15.3a ultra wide band (UWB) channel models (CM) 1-4. Based on a new STF block codes design criterion with the objective of minimizing BER, we develop an efficient searching algorithm for the design of the optimal STF block codes which maximize the coding gain. For 128 subcarriers with two subcarriers jointly encoding with 2-4 transmitting antennas, we find that the optimal STF block codes for all the IEEE 802.15.3a UWB channel models CM 1-4 can he found. Furthermore, the designed STF block codes outperform the recently published high rate full diversity STF codes [1] by I dB. Last, the proposed STF codes can be decoded by maximum likelihood decoding approach, which is simpler than the sphere decoding principle used in [1].
Bit Error Rate Analysis in IEEE 802.15.3a UWB Channels
(2010-05-01)
Wang, Li-Chun
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Liu, Wei-Cheng
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電信工程研究所
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Institute of Communications Engineering
In this paper, we present a computable bit error rate (BER) expression for the binary signals in the IEEE 802.15.3a ultra-wideband (UWB) channel. In the literature, the impacts of the RAKE receiver's finger numbers and lognormal shadowing on the BER performance have not been reported yet. We propose a characteristic function (CF) based BER formula to overcome the convergence problem of the existing moment generating function (MGF) approach when the BER calculation takes account of the shadowing effect. Simulation results demonstrate that the proposed CF-based computable BER formula can accurately estimate the complete effects of the cluster and ray arrival processes, the lognormal fading as well as shadowing, and the finger numbers at RAKE receivers.
Difference of Frame Inter-arrival Time Based Target Selection Scheme for Reducing Handoffs in Wireless Multi-hop Relay Networks
(2009)
Liu, Wei-Cheng
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Chen, Cheng-Min
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Wang, Li-Chun
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交大名義發表
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National Chiao Tung University
In this paper, we propose a novel target selection algorithm to reduce handoff frequency in wireless multi-hop relay networks. In a metropolitan environment, signals are reflected and shadowed by buildings. Thus the signal changes rapidly. To mend this problem, IEEE 802.16j Cranes a new network component relay station (RS) to improve coverage. Since an RS looks like a base station (BS) for MS, handoff frequency increases proportionally to the number of deployed RSs. Signaling overhead and interruption in upper layer application service become serious problems. The proposed target selection algorithm combining signal strength and time-of-arrival information of frame can reduce handoff frequency significantly.
Diversity-Multiplexing Tradeoff Analysis of A Cooperative Network Coding System
(2009)
Wang, Li-Chun
;
Liu, Wei-Cheng
;
Wu, Sau-Hsuan
;
電信工程研究所
;
Institute of Communications Engineering
This paper addresses the analysis of diversity-multiplexing tradeoff (DMT) for a cooperative system using network coding, called the cooperative network coding (CNC) system, which combines a decode-and-forward (DF) relay with the information mixing and broadcast techniques. The outage probability in the high signal-to-noise ratio (SNR) regime is also provided in the closed-form. Our scheme has two users' nodes and one relay node. All nodes are half duplex, i.e., they cannot transmit and receive data at the same time. The two users can communicate to each other directly as well as via the relay node indirectly. Our results show that network coding can help the relay nodes provide cooperative multiplexing gain as well as diversity gain. Compared with the pure DF protocol of which maximal diversity and multiplexing gain are 1 and 1/2, respectively, the maximal diversity and multiplexing gain of the CNC protocol are 2 and 2/3, respectively. The CNC protocol has even better DMT performance than an improved version of DF, selection decode-and-forward (SDF), of which maximal diversity and multiplexing gain are 2 and 1/2, respectively. The impact of wireless lossy channel on performance gains of the network coding is analyzed and can be quantitatively evaluated in the presented DMT curve, which gives us more insight than the capacity analysis does. This is because the capacity analysis only tells us about the maximal error-free transmission rate, while the DMT curve gives us the optimal tradeoff between the error rate and data rate.
Joint Rate and Power Adaptation for Wireless Local Area Networks in Generalized Nakagami Fading Channels
(2009-03-01)
Wang, Li-Chun
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Liu, Wei-Cheng
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Chen, Anderson
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Yen, Kuang-Nan
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電信工程研究所
In this paper, a channel-driven rate and power adaptation (CDRPA) algorithm is proposed for wireless local area networks (WLANs) in generalized Nakagami fading channels. Through the channel information of the first packet, the CDRPA algorithm can lower the complexity of comparing various rates and power levels. In the case of the IEEE 802.11 WLAN, the computation complexity of the CDRPA algorithms is reduced by more than 94% compared with the complete-search link adaptation. A physical and/or medium access control (MAC) cross-layer analytical model is also developed to evaluate the goodput and energy efficiency of the carrier sense multiple access with a collision avoidance MAC protocol in Nakagami fading channels. Our numerical results show that the CDRPA algorithm is not only more energy efficient in the Nakagami fading channel but can also achieve comparable and even higher throughput compared with the complete-search link adaptation approach.
Less postoperative pain in patients receiving trans-oral vestibular endoscopic thyroidectomy: a plausible finding?
(2017-08-01)
Lan, Kuo-Mao
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Chen, Chia-Ming
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Chuang, Chia-Chun
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Lee, Chien-Ching
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Wang, Li-Kai
Performance Analysis of Pulse Based Ultra-Wideband Systems in the Highly Frequency Selective Fading Channel with Cluster Property
(2006)
Liu, Wei-Cheng
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Wang, Li-Chun
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電信工程研究所
;
Institute of Communications Engineering
This paper presents an analytical expression for the bit error rate (BER) of the antipodal and orthogonal binary signals in the ultra-wideband (UWB) channel, of which the unique characteristics include the cluster property and highly dense multipath effect. Specifically, we consider the IEEE 802.15.3a UWB channel and take into account of the impact of all the key parameters, consisting of the cluster arrival rate, cluster decay factor, the number of rays per cluster, and the distribution of a non-Rayleigh fading signal. For the IEEE 802.15.3a UWB channel, the effects of clustering are characterized by a Poisson discrete random variable, and the magnitude of the signal is modelled by lognormal random variable. In this paper, we develop an analytical model to compute the signal with such joint continuous lognormal and discrete Poisson random variable. Hence, the developed analytical model can be useful in evaluating the performance of an UWB signal in the IEEE 802.15.3a channel without time consuming simulations.
Statistical Analysis of a Mobile-to-Mobile Rician Fading Channel Model
(2009-01-01)
Wang, Li-Chun
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Liu, Wei-Cheng
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Cheng, Yun-Huai
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電信工程研究所
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Institute of Communications Engineering
Mobile-to-mobile communication is an important application. for intelligent transport systems and mobile ad hoc networks. In these systems, both the transmitter and receiver are in motion, subjecting the signals to Rician fading and different scattering effects. In this paper, we present a double-ring with a line-of-sight (LOS) component scattering model and a sum-of-sinusoids simulation method to characterize the mobile-to-mobile Rician fading channel. The developed model can facilitate the physical-layer simulation for mobile ad hoc communication systems. We also derive the autocorrelation function, level crossing rate (LCR), and average fade duration (AFD) of the mobile-to-mobile Rician fading channel and verify the accuracy by simulations.
Universal space-time-frequency block codes design for the multiband MIMO-OFDM systems
(2007)
Liu, Wei-Cheng
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Wang, Li-Chun
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電信工程研究所
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Institute of Communications Engineering