Browsing by Author "Chao, Hsi-Lu"

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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 Cross-layer Approach of Link Adaptation in IEEE 802.16 Broadband Wireless Access Systems
(2007)
Yu, Yu-Ting
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Chao, Hsi-Lu
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資訊工程學系
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Department of Computer Science
IEEE 802.16 Broadband Wireless Access system (BWA) is a promising emerging technology. In the IEEE 802.16 standard, multiple data transmission rates are defined by employing different modulation and channel coding schemes. How to select a proper mode affects the system performance significantly. In this paper, an efficient link adaptation scheme with QoS support is proposed The proposed scheme takes both QoS demand and channel condition into consideration to determine a proper transmission mode. The QoS demand of a connection is represented as an expected packet error rate (PER). Based on this expected PER, the BS calculates the required signal-to-noise ratio (SNR) threshold of each mode. By comparing the measured SNR and all modes' SNR thresholds, the BS then suggests the SS a proper transmission mode. We evaluate the proposed scheme by simulations. The simulation results show that the link adaptation scheme improves the average system throughput and guarantees each connection's QoS demand
A Local IP Access Mechanism for VoIP Service in LTE Home eNodeB Systems
(2013)
Chang, Chia-Hsuan
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Chao, Hsi-Lu
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Liu, Chia-Lung
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Huang, Kuei-Li
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Lin, Yi-Bing
The need for multimedia communication through wireless media brings development of 4G cellular wireless networks. Long Term Evolution (LTE) is one of 4G standards and specified in 3GPP. In an LTE system, home base station (HeNB) is designed for indoor usage. Since packets are always routed back to the core network before to destination, if two user equipments (UEs) stay in the same HeNB, the routing path is detour and results in longer packet delivery delay, jitters and thus lower data throughput. As a result, the idea of local IP Access (LIPA) was drawn and two solutions have been proposed. However, the two solutions would suffer from poor voice quality in a VoIP application. We propose a novel solution which establishes an additional data radio bearer (DRB) between UE and HeNB to detect local packets. Once local packets are detected, the data radio bearer is then responsible for local packet delivery. Simulation results show that our method outperforms the other two solutions in terms of packet delivery delay and mean opinion score (MOS).
A Novel Channel-Aware Frequency-Domain Scheduling in LTE Uplink
(2013)
Chao, Hsi-Lu
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Chang, Chia-Kai
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Liu, Chia-Lung
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資訊工程學系
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Department of Computer Science
Due to the power consumption issue of user equipment (UE), Single-Carrier FDMA (SC-FDMA) has been selected as the uplink multiple access scheme of 3GPP Long Term Evolution (LTE). Similar to OFDMA downlink, SC-FDMA enables multiple UEs to be served simultaneously in uplink as well. However, the single carrier characteristic requires that all the allocated subcarriers to a UE must be contiguous in frequency with each time slot. Moreover, a UE should adopt the same modulation and coding scheme at all allocated subcarriers. These two constraints do limit the scheduling flexibility. In this paper, we formulate the UL scheduling problem with taking two constraints into consideration. Since this optimization had been proven to be an NP-hard problem, we further develop a heuristic algorithm with low complexity. We demonstrate that competitive performance can be achieved in terms of system throughput, which is evaluated by using 3GPP LTE system model simulations.
Adaptive Downlink and Uplink Channel Split Ratio Determination for TCP-Based Best Effort Traffic in TDD-Based WiMAX Networks
(2009-02-01)
Chiang, Chih-He
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Liao, Wanjiun
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Liu, Tehuang
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Chan, Iam Kin
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Chao, Hsi-Lu
In this paper, we study the determination of downlink (DL) and uplink (UL) channel split ratio for Time Division Duplex (TDD)-based IEEE 802.16 (WiMAX) wireless networks. In a TDD system, uplink and downlink transmissions share the same frequency at different time intervals. The TDD framing in WiMAX is adaptive in the sense that the downlink to uplink bandwidth ratio may vary with time. In this work, we focus on TCP based traffic and explore the impact of improper bandwidth allocation to DL and UL channels on the performance of TCP. We then propose an Adaptive Split Ratio (ASR) scheme which adjusts the bandwidth ratio of DL to UL adaptively according to the current traffic profile, wireless interference, and transport layer parameters, so as to maximize the aggregate throughput of TCP based traffic. Our scheme can also cooperate with the Base Station (BS) scheduler to throttle the TCP source when acknowledgements (ACKs) are transmitted infrequently. The performance of the proposed ASR scheme is validated via ns-2 simulations. The results show that our scheme outperforms static allocation (such as the default value specified in the WiMAX standard and other possible settings in existing access networks) in terms of higher aggregate throughput and better adaptivity to network dynamics.
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 Efficient Measurement Report Mechanism for Long Term Evolution Networks
(2011)
Chou, Shih-Fan
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Chao, Hsi-Lu
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Liu, Chia-Lung
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資訊工程學系
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Department of Computer Science
LONG-TERM EVOLUTION (LTE) is expected to ensure 3GPP's competitive edge over other cellular technologies. The advantages of LTE include improving end-user throughputs, and reducing latency. LTE systems utilize a network-controlled and the user equipment (UE) assisted handover procedure for mobility in connected mode. In this paper, we first introduce the measurement report mechanism defined in the specification of LTE systems. We further explore possible problems and the impact on handover decision. Followed, we propose rules for timer adjustment, including timeToTrigger and reportInterval. Our mechanism aims at reducing incorrect handover decisions and maximizing the throughput performance. By conducting simulation, we evaluate the designed mechanism. The simulation results show that our proposed mechanism does achieve our design goals.
An implementation of QoS framework for heterogeneous networks
(2007)
Ho, Chang-Yang
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Chao, Hsi-Lu
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資訊工程學系
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Department of Computer Science
Due to the popularity of the IEEE 802.11-based LANs and fast development of the IEEE 802.16e MANs, we can expect a heterogeneous network consisting of 802.11-based and 802.16e networks in the near future. In such an environment, heterogeneous handoff is possible. How to keep guaranteeing the handoff connection its QoS demand, and in the meantime, avoid impacting on other connections is a challenge to support real-time applications in a heterogeneous network. In this paper, we develop a heterogeneous network in NS-2 simulator. In addition, we implement application mapping function, call admission control, and scheduling in this heterogeneous network to observe the QoS performance of a handoff connection. The simulation results show that our implemented modules support handoff connections' QoS demands in respect of throughput, and delay. In addition, the implemented call admission control algorithm reduces the blocking rate efficiently.
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.
CTAP-Minimized Scheduling Algorithm for Millimeter-Wave-Based Wireless Personal Area Networks
(2011-10-01)
Chao, Hsi-Lu
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Hsu, Ming-Pei
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資訊工程學系
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Department of Computer Science
Beamforming is used in IEEE 802.15.3c networks to avoid high propagation attenuation and path loss and improve the overall system throughput by exploiting spatial channel reuse. In this paper, we introduce design challenges of scheduling in beamforming-enabled IEEE 802.15.3c networks. These challenges include positioning, axis alignment, and interference relation verification. We then propose a joint design of axis alignment, positioning, and scheduling. The objectives of the proposed joint design are to reduce the consumed channel time, increase the degree of spatial channel reuse, and improve the channel utilization. For positioning, we define and prove a sufficient condition for anchor selection to improve positioning accuracy. The designed channel time allocation period (CTAP)-minimized scheduling algorithm is depicted as a two-layer flow graph, and it consists of the following three phases: 1) layer-1 edge construction; 2) layer-2 edge construction; and 3) scheduling. Through the observation of transmission and reception beams, we define a rule to verify the interference relation of two flows. In addition, given correct topology information, we prove that CTAP-minimized uses the least time to serve all data flows. We evaluate and compare our algorithm with existing approaches through simulations. The observed performance metrics include utilized channel time, system throughput, scheduling efficiency, and spatial channel reuse degree. The results show that CTAP-minimized performs well and achieves its objectives.
Effective Service Architecture and Antenna Allocation Mechanism for CoMP Transmissions in Ultra Dense Networks
(2019-09-01)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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Chao, Hsi-Lu
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Quek, Tony Q. S.
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Gan, Chai-Hien
A practical and effective service deployment method is proposed for coordinated multi-point (CoMP) transmissions in ultra-dense networks (UDN). Despite the potential of UDN for throughput enhancement, the throughput of edge users is still considerably deteriorated by interferences from adjacent cells. Applying the CoMP transmissions among cells appears to be a feasible solution to resolve this issue. However, the nature of the almost randomly deployed locations of small cell base stations (BSs) and their limited numbers of antennas make it difficult to design an effective resource coordination mechanism for the CoMP services in UDN. Reconsidering this problem from an antenna allocation viewpoint, we present a simple yet effective approach to improve the cell-edge throughput under a centralized radio access network architecture. The first step is to partition the entire service area into multiple subareas, and the second step is to allocate the antenna degrees of freedom to each subarea. To improve the scalability of this service method, a two-tier service deployment method is further introduced based on the BS clustering and service area partitioning of the entire network. The simulation results show that the proposed service architecture can provide a significant improvement on the cell-edge throughput while still maintaining a good average throughput in the UDN.
Energy-Saving Scheduling in IEEE 802.16e Networks
(2008)
Lin, Chia-Yen
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Chao, Hsi-Lu
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資訊工程學系
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Department of Computer Science
The advancement of mobile computing is mainly limited by battery lifetime of a end device, and thus power management is always a critical design issue in various wireless networks. To conserve power consumption of mobile subscribe stations (MSSs), three types of power saving classes are defined in the IEEE 802.16e standard. However, the defined power saving mechanism is per-connection basis, and thus when an MSS has multiple connections, the power saving efficiency degrades significantly. In this paper, a Least-Awake-Frames Scheduling (LAFS) algorithm is proposed to achieve both energy saving and Quatity-of-Service (QoS) fulfillment. The proposed LAFS consists of three phases to take all service classes into consideration. The goals of the first two phases are determining awake-frame candidate, sets for unsolicited grant service (UGS) connections and sleep/swake intervals for connections of the remaining service classes; the third phase is to determine sleep and awake frames of an MSS. The simulation results show that our proposed LAFS algorithm outperforms the power saving protocol defined in the IEEE 802.16e, and other existing power saving algorithms.
Evaluating and Improving the TCP/UDP Performances of IEEE 802.11(p)/1609 Networks
(2008)
Wang, Shie-Yuan
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Chao, Hsi-Lu
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Liu, Kuang-Che
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He, Ting-Wei
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Lin, Chih-Che
The IEEE 802.11(p)/1609 standard is an emerging technology for vehicular communication networks. It amends the IEEE 802.11-2007 standard and defines a new WAVE operational mode for vehicular environments. The WAVE mode utilizes a combined FDMA/TDMA scheme to manage network bandwidth. In this mode, a node must periodically switch its frequency channel between two different channels over time. Such a design may result in bandwidth wastage due to the residual time caused by channel switching. In this paper, we propose two easy-to-implement schemes to mitigate this problem and compare their TCP/UDP performances with those of the original scheme. Our simulation results provide many insights into the operations of these schemes on IEEE 802.11(p)/1609 networks and show that the proposed schemes always outperform the original scheme.
F(2)-MAC: an efficient channel sensing and access mechanism for cognitive radio networks
(2011-07-01)
Chao, Hsi-Lu
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Lou, TakChon
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Jiang, Shuhua
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資訊工程學系
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Department of Computer Science
One of the most challenging issues in cognitive radio (CR) systems is channel sensing and accessing. In this paper, a CR channel access mechanism is proposed. The mechanism consists of two phases: fast channel accessing and proactive channel vacating. In fast channel accessing, a pair of CR users time-efficiently searches an available channel to deliver data. In proactive channel vacating, a pair of CR users periodically makes channel access opportunities to primary users (PUs) and vacates the occupied channel as quick as possible. We utilize the concept of channel hopping to reduce the average channel searching time. Furthermore, our vacating mechanism allows CR users to create opportunities for PUs to claim the spectrum and thus minimize the caused interference to PUs. We evaluate the performance of our approach through a two-dimensional Markov chain model as well as simulations. The performance study indicates that the proposed protocol achieves low channel searching time, high throughput, and fairness.
F-2-MAC: an efficient channel sensing and access mechanism for cognitive radio networks
(2011-07-01)
Chao, Hsi-Lu
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Lou, TakChon
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Jiang, Shuhua
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資訊工程學系
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Department of Computer Science
One of the most challenging issues in cognitive radio (CR) systems is channel sensing and accessing. In this paper, a CR channel access mechanism is proposed. The mechanism consists of two phases: fast channel accessing and proactive channel vacating. In fast channel accessing, a pair of CR users time-efficiently searches an available channel to deliver data. In proactive channel vacating, a pair of CR users periodically makes channel access opportunities to primary users (PUs) and vacates the occupied channel as quick as possible. We utilize the concept of channel hopping to reduce the average channel searching time. Furthermore, our vacating mechanism allows CR users to create opportunities for PUs to claim the spectrum and thus minimize the caused interference to PUs. We evaluate the performance of our approach through a two-dimensional Markov chain model as well as simulations. The performance study indicates that the proposed protocol achieves low channel searching time, high throughput, and fairness.
Joint Relay Selection and Scheduling Algorithm for Inter-Piconet Communications in Millimeter Wave Wireless Personal Area Networks
(2011)
Liu, Jen-Hsi
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Chao, Hsi-Lu
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資訊工程學系
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Department of Computer Science
Beamforming technique is used in IEEE 802.15.3c networks to avoid high propagation attenuation and path loss, and improve the overall system throughput by exploiting spatial channel reuse. In this paper, we introduce the necessity and design challenges of inter-piconet communications. Based on our observation, we propose a joint design of relay selection and scheduling. For relay selection, we define "interference-free", "concurrence-restricted extent", and "concurrence index" for properly selecting relays to improve the degree of spatial channel reuse. The designed scheduling consists of two phases: intra-piconet flow scheduling and inter-piconet flow scheduling. After performing phase 1 operations, intra-piconet flows are scheduled and the total required channel time is known. The phase 2 operations are to use the least channel time extension to schedule all inter-piconet flows. We evaluate our algorithm through simulations. The results show that the joint algorithm performs well and does achieve its objectives.
Joint Routing and Spectrum Allocation for Multi-Hop Cognitive Radio Networks with Route Robustness Consideration
(2011-09-01)
Shih, Chao-Fang
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Liao, Wanjiun
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Chao, Hsi-Lu
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資訊工程學系
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Department of Computer Science
In this paper, we introduce the concept of "route robustness" for path selection in multi-hop cognitive radio networks. We demonstrate that the aggregate throughput and the robustness of routes determined by the proposed route selection strategy are superior to existing rate-based selection strategies. The rationale behind our approach is to guarantee a basic level of robustness for a set of routes (referred to as skeletons in this paper). Then, we select some routes from this robust route set and determine the spectrum to be allocated on each link along these routes such that the system throughput is maximized. We also design a polynomial time algorithm for this problem, and evaluate our proposed mechanism via simulations. The results show that our proposed algorithm indeed achieves a near optimal solution of this problem for multi-hop overlay CR networks.
Joint Switched-Beam Training and Rate Adaptation Schemes for MIMO WLANs
(2017-01-01)
Wang, Ju-Chia
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Chiu, Hsin-Li
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Sun, Chia-Shan
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Chao, Hsi-Lu
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Wu, Sau-Hsuan
A joint beam training and rate adaptation mechanism for downlink transmissions is presented for multiple input multiple output systems with switched beam antennas. The proposed method only depends on the beam patterns and the acknowledgement (ACK) replied by the receiver, and is compatible with the legacy WiFi standards. This feature makes not only the complexity of the beam training scheme extremely low, but also the feasibility relatively high. Due to the practical limitations of antenna designs and manufacturing, beam patterns may not have distinctive directivity for certain directions. Therefore, beam pattern scaling is utilized to make the resultant beam patterns match well with the ideal user directions and channel conditions. Simulation results with real switched beam patterns show that the precision of the training scheme is very high.