Browsing by Author "Wu, Sau-Hsuan"

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A BAN System for Realtime ECG Monitoring: from Wired to Wireless Measurements
(2011)
Chiu, Rong-Dong
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Wu, Sau-Hsuan
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電信工程研究所
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Institute of Communications Engineering
A body area network is developed for a 3-Lead wireless electrocardiography (ECG) monitoring system. To measure the 3-Lead ECG signals without using wires for electrodes to connect to a common ground, we study a new ECG sensing method that directly and synchronously measures the voltage differences across the nearby electrodes of distributed ECG leads. To verify the effectiveness of the proposed method, the qualities of the ECG signals acquired from various placements and distances between the electrodes are compared with the ones obtained with the standard wired ECG measurement method. The highest correlation coefficient between the wired and wireless ones is shown by experiments to be as high as 0.946. And the separation between the two electrodes of an ECG lead can be drastically reduced to around 10cm which is about the size of a medium adhesive tape. This shows that a 3-Lead wireless ECG monitoring system is in fact feasible. More advanced approaches may be developed based on the results obtained herein to further construct a 12-Lead wireless ECG system.
A CLOUD MODEL AND CONCEPT PROTOTYPE FOR COGNITIVE RADIO NETWORKS
(2012-08-01)
Wu, Sau-Hsuan
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Chao, Hsi-Lu
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Ko, Chun-Hsien
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Mo, Shang-Ru
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Jiang, Chung-Ting
The FCC's approval for the first commercial operation in TV white space gives new momentum to the development of cognitive radio in TVWS. On the other hand, the rapid growth of Cloud computing makes it possible and more economical to build a CR metropolitan area network with commodity hardware. In view of the opportunity and challenges brought about by these two technologies, we propose a CR cloud networking model that is able to support CR access in TVWS. Making use of the flexible and vast computing capacity of the cloud, a database and a cooperative spectrum sensing algorithm that estimates the radio power map of licensed users are realized on a CR cloud implemented with Microsoft's Windows Azure Cloud platform. The CRC can support CSS, dynamic spectrum access and mobility management. A medium access control protocol is also developed for this CRCN model to collect sensing reports and provide access to the TVWS and CRC services. Through this CRCN prototype, important network parameters such as the mean squared errors in CSS, the CR channel vacating delay, and the cloud-based handover time are measured for the design and deployment of the CRCN concept.
A Conceptual Model and Prototype of Cognitive Radio Cloud Networks in TV White Spaces
(2012)
Wu, Sau-Hsuan
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Chao, Hsi-Lu
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Jiang, Chung-Ting
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Mo, Shang-Ru
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Ko, Chun-Hsin
A Cognitive Radio Cloud Network (CRCN) model is proposed for wireless communications in TV White Spaces (TVWS). Making use of the flexible and vast computing capacity of the Cloud, a database and a sparse Bayesian learning (SBL) algorithm are developed for cooperative spectrum sensing (CSS) and implemented on Mocrosoft's Windows Azure Cloud platform. A medium access control (MAC) scheme is also prototyped for this CRCN model to collect sensing reports and access channels with Rice University's wireless access research platform (WARP). Through this CRCN prototype, important network parameters such as the mean squared errors in CSS, the time to detect the presence and/or the absence of primary users, and the channel vacating delay are measured and analysed for the design and deployment of the future CRCN.
A Proactive Indoor Positioning System in Randomly Deployed Dense WiFi Networks
(2016-01-01)
Ko, Chun-Hsien
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Wu, Sau-Hsuan
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電信工程研究所
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Institute of Communications Engineering
A new approach for indoor positioning is presented, aimed at designing a WiFi positioning system that is feasible and convenient for both service providers and end users. In the proposed approach, only access points (APs) need to collect the received signal strengthes (RSS) of mobile devices, and use these RSS samples to jointly estimate the devices' locations. To enhance the accuracy of positioning, the relationship between the RSS samples and their geometrical locations is explored, leading to a sparse Bayesian model for the radio power map of the RSS observations of each AP. With more than 20 training anchors, the accuracy of the proposed model-based positioning method can be lower than 3.4 meters in an indoor space with only 4 randomly deployed APs, which outperforms the fingerprinting method by 0.4 meter. Extensive experimental results also verify that the proposed positioning service can offer considerable accuracy with only limited efforts in training, suggesting that the prototype is realistic for randomly deployed dense WiFi networks.
A Space-Time Precoded Hybrid Beamforming Architecture for Broadband Transmissions in 60GHz Radio
(2011)
Yin, Yu-Shiung
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Chiu, Lin-Kai
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Wu, Sau-Hsuan
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傳播研究所
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Institute of Communication Studies
A cost-effective architecture is studied for a joint radio frequency (RF) and baseband hybrid beamforming (HBF) method that uses planar antenna arrays (PAA) in 60GHz radio transmission. Under the hybrid architecture, a space-time precoded HBF scheme is presented to exploit the spatial diversity for non line-of-sight transmission in 60GHz radio. Furthermore, an efficient one-bit feedback (OBF) beamforming (BF) scheme is proposed to search for the pointing directions of each RF beamformer (BFer) of the HBF architecture. Simulation results show that the proposed HBF architecture can provide a 5 similar to 10dB gain in the signal to noise ratio compared to an architecture that uses the RF BF only. In addition, the OBF BF scheme converges close to the LOS transmission in 15 iterations, which is much more efficient than exhaustively searching for the BF directions.
AF Detection by Exploiting the Spectral and Temporal Characteristics of ECG Signals With the LSTM Model
(2018-01-01)
Chang, Yen-Chun
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Wu, Sau-Hsuan
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Tseng, Li-Ming
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Chao, Hsi-Lu
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Ko, Chun-Hsien
This research reinvestigates the detection of atrial fibrillation (AF) from a recurrent neural network (RNN) viewpoint. In particular, a long short-term memory (LSTM) model of RNN is designed to exploit the high-order spectral and temporal features of the multi-lead electrocardiogram (ECG) signals of patients with AF. To verify thethe proposed method, the LSTM model is tested with ECG data available from the PhysioNet and some normal ECG data collected in our labs. The results show that not only the deviation of the so-called RR intervals of ECG signals but also its temporal variations are critical to AF detection. The accuracy of AF detection can reach up to 98.3 %, with an LSTM model of using 30 hidden units. Considering more realistic applications, we further tested the model with subjects different from that of the training data. The accuracy is about 87% with high sensitivity. The experimental results show that the proposed model is able to effectively extract both the long-term and short-term characteristics of the spectral content of the AF ECG signals, making it a good candidate model for AF detection.
An Effective Antenna Allocation for CoMP Transmission in Dense Small Cell Networks
(2016-01-01)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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Chao, Hsi-Lu
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Liu, Chia-Lung
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Gan, Chai-Hien
Despite that network capacity can increase with cell densification, interferences from adjacent cells may deteriorate the throughput of users close to cell edges. To alleviate this problem and to offer a service quality with no significant cell edge degradation, we propose a feasible coordinated multi-point (CoMP) transmission architecture from a new look on antenna allocation in dense small cell networks (DSN). The CoMP idea is based on a two-step mechanism; the first step partitions the entire service region into multiple areas, and the second step adjusts the number of active users for each area. We then develop an antenna allocation algorithm to enhance the cell-edge user throughput, making use of the spatial multiplexing (SM) gain, array gain and cooperative diversity gain. Simulation results show that applying SM to DSN plays a crucial role to enhance the user throughput. And one of our proposed cooperative schemes is shown to have a great potential to improve the throughput for a large portion of users or the cell service area.
An Effective Approach to Evaluate the Training and Modeling Efficacy in MIMO Time-Varying Fading Channels
(2015-01-01)
Chiu, Lin-Kai
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Wu, Sau-Hsuan
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電信工程研究所
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Institute of Communications Engineering
The efficacy of channel modeling and training for multiple-input multiple-output (MIMO) time-varying flat faded Rayleigh channels is studied herein from the information-theoretical perspective. To characterize the channel dynamics in wide-sense stationary uncorrelated scattering wireless environments, proper autoregressive (AR) channel models for different fading speeds are discussed from the viewpoints of the mean squared error (MSE) and Bayesian Cramer-Rao lower bound (BCRB) of channel estimation. Furthermore, the training efficacy is examined with the achievable capacity when the MSE of channel estimation attains the BCRB. Our numerical simulations show that neither is the first-order AR model enough, nor is a large-order AR model needed for modeling time-varying fading channels. The analysis on BCRB also shows that the influence of the multiple access interference among transmit antennas is not negligible for channel estimation in time-varying fading channels even if using orthogonal sequences for training. As channel tracking can utilize the current and all past training symbols, the optimal training lengths for each data packet may be less than the number of transmit antennas. These results help re-examine the efficacy of model complexity and training overhead, and characterize the achievable rate for MIMO systems that use more practical methods in estimating Rayleigh fading channels.
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.
Cooperative ARQ for Distributed Space-Time Coding: the Diversity-Multiplexing-Delay Tradeoff
(2008)
Chiu, Hsin-Li
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Wu, Sau-Hsuan
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電信工程研究所
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Institute of Communications Engineering
The throughput and the tradeoff between the diversity, multiplexing and the delay constraint of cooperative automatic retransmission request (ARQ) are investigated for distributed space-time coding (DSTC). According to the analysis, the maximum operational throughput turns out to be a piecewise linear curve with respect to the signal to noise ratio in decibel. In addition. the multiplexing gain divided by the average transmission times, referred to as the effective multiplexing gain, appears to be a better performance measure for delay-limited cooperative ARQ schemes. The tradeoff between the diversity and effective multiplexing gains is characterized for cooperative ARQ using DSTC in slow and fast fading channels, respectively.
Cooperative ARQs with Opportunistic Distributed Space-Time Coding: Effective Protocols and Performance Analysis
(2010)
Chiu, Hsin-Li
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Wu, Sau-Hsuan
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Li, Jin-Hao
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傳播研究所
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Institute of Communication Studies
The paper studies effective protocols and corresponding performance of automatic retransmission request (ARQ) via decode-and-forward (DF) opportunistic distributed space-time coding (ODSTC). Analysis shows that the diversity via ARQ can be drastically increased by allowing non-active relays to overhear the DSTC signal sent by the active relays. Nevertheless, simple schemes without overhearing may also achieve the same diversity when the link quality between the source-relay or the relay-destination is good, hence greatly alleviating the need for a complex protocol with overhearing. Moreover, using more relays opportunistically does provide a higher coding gain if the source-relay channel quality is extremely good, otherwise using two or three relays gives almost the same performance as if using all of them.
Cooperative Radio Source Positioning and Power Map Reconstruction: A Sparse Bayesian Learning Approach
(2015-06-01)
Huang, Din-Hwa
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Wu, Sau-Hsuan
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Wu, Wen-Rong
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Wang, Peng-Hua
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電機資訊學士班
It is known that in addition to spectrum sparsity, spatial sparsity can also be used to further enhance spectral utilization in cognitive radio systems. To achieve that, secondary users (SUs) must know the locations and signal strength distributions (SSDs) of primary users\' base stations (PUBSs). Recently, a group sparse total least squares method was developed to cooperatively sense the PUBSs\' signal strength and estimate their locations. It approximates PUBSs\' power decay with a path loss model (PLM), assumes PUBSs\' locations on some grid points, and then accomplishes the estimation tasks. However, the parameters of the PLM have to be known in advance, and the accuracy of the location estimation is bounded by the resolution of the grid points, which limit its practical applications. In this paper, we propose a sparse Bayesian learning method to solve the problems. We use a Laplacian function to model the power decay of a PUBS and then derive learning rules to estimate corresponding parameters. The distinct features of the proposed method are that most parameters are adaptively estimated, and little prior information is needed. To further enhance the performance, we incorporate source number detection methods in the proposed algorithm such that the number of the PUBSs can be precisely detected, facilitating the estimation of PUBSs\' locations and SSDs. Moreover, the proposed algorithm is modified into a recursive mode to adapt to SUs\' mobility and time-variant observations. Simulations show that the proposed algorithm has good performance, even when the spatial measurement rate is low.
Cooperative Sensing of Wideband Cognitive Radio: A Multiple-Hypothesis-Testing Approach
(2010-05-01)
Wu, Sau-Hsuan
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Yang, Chao-Yuan
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Huang, D. -H. Tina
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電信工程研究所
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Institute of Communications Engineering
A low-complexity decision fusion method is proposed for cooperative spectrum sensing (SS) of wideband cognitive radio (CR) using multiple-hypothesis testing. To maintain the quality of SS in multiple channels, performance indices of false-sensing rate and false-ignorance rate are defined for the Benjamini-Hochberg (BH) procedure to control the false-alarm ratio (FAR) and missing ratio (MR) of SS, respectively. Extended from these results, a double BH procedure is further studied in an attempt to simultaneously attain a low FAR and MR. In addition to identifying the availability of channels, a signal strength-estimation scheme that features multiple-hypothesis testing is also proposed to classify the level of the SNR for cooperative SS. Simulation results show that the double BH procedure can suppress both the FAR and the MR at a high SNR while maintaining a considerable FAR in the low-SNR regime. As such, the system can enjoy throughput enhancement by allowing more active cognitive access at a high SNR and still prevent introducing excessive multiple-access interference to the primary users when their SNRs are weak. On the other hand, for SNR classification, simulations also show that the SNR can be classified within one level, plus or minus the true strength with more than a 96% chance. This allows the system to employ more generic protocols such as concurrent transmissions for cognitive access.
Cooperative Spectrum Sensing and Locationing: A Sparse Bayesian Learning Approach
(2010)
Huang, D-H Tina
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Wu, Sau-Hsuan
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Wang, Peng-Hua
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傳播研究所
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Institute of Communication Studies
Based on the concept of sparse Bayesian learning, an expectation and maximization algorithm is proposed for cooperative spectrum sensing and locationing of the primary transmitters in cognitive radio systems. Different from typical approaches, not only the signal strength, but also the number and the radio power profiles of the primary transmitters are estimated, which greatly facilitates resource management in cognitive radio. Furthermore, the proposed algorithm can still roughly reconstruct the power propagation map of the primary transmitters even when the measurement rate is below the lower bound for which compressive sensing (CS) can reconstruct signals with the l(1)-norm optimization method. Compared with the typical CS and Bayesian CS algorithms, simulation results show that average mean squared errors (MSE) of the estimated power propagation map are lower with the proposed algorithm. Besides, the computational complexity is also lower owing to bases pruning. The MSE of the location estimation are also shown to demonstrate the capability of the proposed algorithm.
Cooperative Spectrum Sharing and Scheduling in Self-Organizing Femtocell Networks
(2014-01-01)
Chao, Hsi-Lu
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Wu, Sau-Hsuan
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Huang, Yu-Han
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Li, Shang-Chen
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資訊工程學系
A cooperative spectrum sharing, power allocation and user scheduling method is studied in this work under the framework of LTE self-organizing femtocell networks. Making use of dynamic channel and power allocation, and interference control, all femto access points (APs) in a self-organizing network (SON) can share the channels available to the SON with guaranteed quality of service. Simulation results show that the effective channel usage ratio can reach 75% in average even with no explicit cellular planning inside the service area of an SON. This result supports the feasibility of randomly deploying large numbers of femto APs in metropolitan areas based on the concept of SON.
Cross-Layer Performance Analysis of Cooperative ARQ With Opportunistic Multi-Point Relaying in Mobile Networks
(2018-06-01)
Chiu, Hsin-Li
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Wu, Sau-Hsuan
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電信工程研究所
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Institute of Communications Engineering
A cross-layer analysis framework is developed for the design and performance evaluations of cooperative automatic repeat request (ARQ) with opportunistic multi-point relaying (OMPR) in mobile networks. In particular, three exemplar OMPR functions and their combinations are studied for opportunistic distributed space-time coded (ODSTC) retransmissions in time-division duplex long-term evolution advanced systems. According to the complexities and coordination delays of the OMPR functions, the influences of channel fading on the spatial and temporal diversities offered by ODSTC-based ARQ and their impacts on the system throughput, transmission energy consumption, and relays' queuing delays can be evaluated effectively under this framework. Based on the analytical results, a rate adaptation strategy is also proposed to maximize the system throughput subject to constraints on queuing delays at relay stations (RSs) and packet error rates at mobile stations (MSs). Analysis and simulation results show that in typical vehicular speeds, using maximally two active RSs for ODSTC is a very robust and effective choice to provide near best system throughput with less energy consumptions and lower protocol complexities. The throughput gains over a system without using RS retransmissions range from 16 similar to 80% for cell-edge MSs, with only 25 similar to 45% of the transmission energy consumption.
Diversity and Directivity Tradeoff in Indoor 60 GHz MIMO Channels: A Case Study with Dual-Polarized Hybrid Planar Antenna Arrays
(2014)
Wu, Sau-Hsuan
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Chin, Lin-Kai
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電機工程學系
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Department of Electrical and Computer Engineering
The channel capacity of indoor 60 GHz radio is studied in this work from the diversity and the directivity viewpoints of multiple input multiple output (MIMO) wireless systems. To characterize the diversity and directivity (DnD) tradeoff of using planar antenna arrays (PAA) in indoor 60 GHz channels, a hybrid architecture for dual polarized PAA (DP-PAA) is employed to exploit the potential advantages between the two extremes of this DnD tradeoff. A DP-PAA under this hybrid architecture can either be configured to apply the spatial multiplexing (SM) gain of MIMO channel diversity, or to enhance the array gain with beamforming directivity. Furthermore, the polarization diversity of DP-PAA can provide the system with a minimum degree of SM gain and compensate the coverage hole of a single-polarized PAA. Through theoretical investigations and numerical simulations, we show that the indoor 60 GHz channel of using a hybrid DP-PAA pair at both the transmitter and the receiver can approximately be modeled as a Kronecker MIMO channel. In addition, using the directivity of DP-PAA can lead to a higher channel capacity than using its spatial diversity under FCC\'s 40 dBm equivalent isotropically radiated power limit for indoor unlicensed 60 GHz This prevents the use of expensive high-dimensional MIMO to improve the channel capacity of indoor 60 GHz radio.
Diversity-Multiplexing Tradeoff Analysis of A Cooperative Network Coding System
(2009)
Wang, Li-Chun
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Liu, Wei-Cheng
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Wu, Sau-Hsuan
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電信工程研究所
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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.
Effective Cooperative ARQ Protocols with the Opportunistic Selective AF Relaying: The Perspectives of Outage versus Packet Error Probabilities
(2011)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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傳播研究所
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Institute of Communication Studies
In contrast to the outage analysis, the packet error rates (PERs) of two types of cooperative automatic retransmission request (ARQ) protocols with opportunistic selective amplified-and-forward (OSAF) relaying are investigated from the perspective of the maximum likelihood sequence detection (MLSD). The results show that PERs with the threshold requirements derived from the outage analysis cannot benefit from the diversity via opportunistic retransmissions. Based on the PER analysis, effective threshold setting methods for the two types of ARQs are developed to avoid the diversity losses during ARQs, and verified via simulations using convolutional codes. In contrast to the ARQ protocols with the typical opportunistic AF relaying, the new threshold setting methods allow the OSAF ARQ protocols to provide for practical systems a spatial and temporal diversity comparable to what predicts with the outage analysis.
Effective Protocols and Channel Quality Control Mechanisms for Cooperative ARQ With Opportunistic AF Relaying
(2018-03-01)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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電信工程研究所
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Institute of Communications Engineering
Incorporating relaying techniques into automatic repeat reQuest (ARQ) in general will provide diversity and throughput enhancements. However, when opportunistic amplify-and-forward (AF) relaying is applied to cooperative ARQ, the system design becomes much more involved. First, our capacity outage analysis shows that the temporal diversities of ARQs with a single AF relay cannot be exploited unless the channel quality to the relay exceeds a threshold. This notion of selective AF relaying is extended to systems with multiple relays in an attempt to jointly explore the temporal and spatial diversities with ARQ. Two types of selective and opportunistic AF relaying schemes are then developed for such kinds of relay-assisted ARQ. And our analysis further shows that the temporal and spatial diversities cannot be fully exploited without the use of overhearing among relays and a proper link quality control mechanism to prescreen the overheard signals. This quality control mechanism is implemented with a set of thresholds designed for each hop of the relaying path. Feasible threshold setting methods are also developed for the proposed ARQ protocols to achieve their potential diversities. In contrast to our designs, the ARQ scheme with the typical opportunistic AF relaying method suffers from severe diversity losses. Simulations also show that the proposed ARQ schemes are more effective in throughput enhancement, and can provide cell-edge users almost three times the throughput gain in comparison with ARQ with no relay-assisted forwarding.