Browsing by Author "Lin, Kate Ching-Ju"

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A Hint-based Random Access Protocol for mMTC in 5G Mobile Network
(2018-01-01)
Xu, Yining
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Ren, Yi
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Lin, Kate Ching-Ju
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Tseng, Yu-Chee
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資訊工程學系
With the increasing popularity of machine-type communication (MTC) devices, several new challenges are encountered by the legacy long term evolution (LTE) system. One critical issue is that a massive number of MTC devices trying to conduct random access procedures may cause significant collisions and long delays. In this work, we present a new random access mechanism by splitting the contention-based preambles in LTE into two logically disjoint parts, one for the user equipment (UE) being paged and the other for the UEs not being paged. Since the IDs of paged UEs are known by the base station, a novel hash-based random access, which we call hint, is possible. The main idea is to pre-allocate preambles to paged UEs in a contention-free manner and confines non-paged UEs to contend in a separate region. We further build a mathematical model to find the optimal ratio of pre-allocated preambles. Extensive simulations are conducted to validate our results.
acPad: Enhancing Channel Utilization for 802.11ac Using Packet Padding
(2017-01-01)
Lin, Chi-Han
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Chen, Yi-Ting
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Lin, Kate Ching-Ju
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Chen, Wen-Tsuen
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資訊工程學系
Multi-User Multiple Input Multiple Output (MU-MIMO) enables a multi-antenna access point (AP) to serve multiple users simultaneously, and has been adopted as the IEEE 802.11ac standard. While several PHY-MAC designs have recently been proposed to improve the throughput performance of a MU-MIMO WLAN, they, however, usually assume that all the concurrent streams are of roughly equal length. In reality, users usually have frames with heterogeneous lengths even after aggregation, leading to different lengths of transmission time. Hence, the concurrent transmission opportunities might not always be fully utilized when some streams finish earlier than the others in a transmission opportunity (TXOP). To resolve this inefficiency, this paper presents acPad, a PHY-MAC design that adds additional frames to fill up the idle channel time and better utilize the spatial multiplexing gain. Our acPad identifies proper users as the padding so as to improve the padding gain, while preventing this padding from harming all the ongoing streams. Our evaluation via large-scale trace-driven simulations demonstrates that acPad improves the throughput by up to 2.83x, or by 1.36x on average, as compared to the conventional 802.11ac.
Augmenting Indoor Inertial Tracking with Polarized Light
(2018-01-01)
Tian, Zhao
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Wei, Yu-Lin
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Chang, Wei-Nin
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Xiong, Xi
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Zheng, Changxi
Inertial measurement unit (IMU) has long suffered from the problem of integration drift, where sensor noises accumulate quickly and cause fast-growing tracking errors. Existing methods for calibrating IMU tracking either require human in the loop, or need energy-consuming cameras, or suffer from coarse tracking granularity. We propose to augment indoor inertial tracking by reusing existing indoor luminaries to project a static light polarization pattern in the space. This pattern is imperceptible to human eyes and yet through a polarizer, it becomes detectable by a color sensor, and thus can serve as fine-grained optical landmarks that constrain and correct IMU's integration drift and boost tracking accuracy. Exploiting the birefringence optical property of transparent tapes - a low-cost and easily-accessible material - we realize the polarization pattern by simply adding to existing light cover a thin polarizer film with transparent tape stripes glued atop. When fusing with IMU sensor signals, the light pattern enables robust, accurate and low-power motion tracking. Meanwhile, our approach entails low deployment overhead by reusing existing lighting infrastructure without needing an active modulation unit. We build a prototype of our light cover and the sensing unit using off-the-shelf components. Experiments show 4.3 cm median error for 2D tracking and 10 cm for 3D tracking, as well as its robustness in diverse settings.
Beam Configuration and Client Association for Access Points with Switched Beam Antennas
(2016-09-01)
Lin, Kate Ching-Ju
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Kuo, Tung-Wei
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Yan, Pei-Jiun
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Cheng, Wan-Jie
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Jeng, Shyh-Kang
Unlike conventional omnidirectional antennas, switched beam antennas exploit antenna arrays and signal processing techniques to focus energy in a specific beam-width and orientation. Recent research has shown that access points of a WLAN can exploit such switched beam antennas to increase the overall network capacity. The achievable sum rate of a WLAN with switch beam antennas is however mainly determined by how each AP selects its beam, including the orientation and width, and how each client associates with a proper AP. The goal of this paper is to solve the Joint Beam configuration and Client association (JBC) problem such that the sum rate of all clients in the network can be maximized. We formulate the JBC problem as a mixed integer linear programming model, and propose a 2-approximation algorithm to solve it. Our proposed algorithm has two distinctive properties: 1) it can be realized as a distributed protocol that allows the APs to configure their beams without the help of a central coordinator, and 2) it can be generally applied both in specific scenarios, where exact client locations are known, and in uncertain scenarios, where only geographic client distribution is given. Finally, we adjust the sum-rate maximization algorithm to the throughput maximization algorithm, which further takes medium sharing among clients into account. The simulation results show that the proposed algorithm outperforms both WLANs using omnidirectional antennas and other heuristics using switched beam antennas.
CELLI - Indoor Positioning using Polarized Sweeping Light Beams
(2017-01-01)
Wei, Yu-Lin
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Huang, Chang-Jung
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Tsai, Hsin-Mu
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Lin, Kate Ching-Ju
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資訊工程學系
CELLI: Indoor Positioning Using Polarized Sweeping Light Beams
(2017-01-01)
Wei, Yu-Lin
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Huang, Chang-Jung
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Tsai, Hsin-Mu
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Lin, Kate Ching-Ju
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資訊工程學系
Existing visible light positioning (VLP) systems leverage the high image resolution of a receiving camera to support high positioning accuracy. However, power-hungry cameras might not always be applicable for many scenarios, such as smart factories, in which small objects require to be accurately localized and tracked. In this paper, we introduce CELLI, an indoor VLP system that only uses a single luminary as the transmitter and requires only a simple light sensor to achieve an extremely high accuracy with centimeter-level error. The key idea is to provide the spatial resolution capability from the transmitter instead of the receiver, so that the complexity of the receiver can be minimized. In particular, a small LCD is installed at the transmitter to project a large number of narrow and interference-free polarized light beams to different spatial cells. A receiving light sensor identifies its located cell by detecting the unique polarization-modulated signals projected to that cell. CELLI further incorporates a number of novel designs to overcome the technical challenges such as reducing the positioning latency, which is typically limited by the long optical response time of an LCD, and transforming a cell coordinate to the global 3D position using only a single light. We have prototyped our design using off-the-shelf optical and electrical components, and experimentally shown that CELLI achieves a median 3D positioning error less than 11.8 cm and a median 2D positioning error to less than 2.7 cm.
Concurrent Packet Recovery for Distributed Uplink Multiuser MIMO Networks
(2016-12-01)
Shen, Wei-Liang
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Lin, Kate Ching-Ju
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Cheng, Wan-Jie
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Qiu, Lili
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Chen, Ming-Syan
While recent works on multiuser MIMO (MU-MIMO) mainly focus on boosting the throughput by enabling concurrent transmissions, less attention is paid to recovering concurrent erroneous streams. We however notice that uplink MU-MIMO is especially vulnerable to errors because error in any stream corrupts most of the other concurrent streams. Even worse, carrier sense and rate adaptation become more challenging in MU-MIMO, which further decreases reliability. Existing systems however recover errors by retransmitting all the streams in a corrupted packet, thereby taking away the significant performance benefit of MU-MIMO. To effectively harness the ideal gain of MU-MIMO, we develop Concurrent Packet Recovery (CPR), a recovery protocol customized for MU-MIMO. It has two distinctive features: (i) It judiciously selects the minimum number of streams to be retransmitted to support successful decoding; (ii) during retransmission, it utilizes the full degrees of freedom by allowing new streams to be sent in parallel. Our evaluation via testbed experiments and trace-driven simulations shows that CPR can efficiently recover both normal losses and collisions. For three-antenna AP scenarios, the throughput gain is up to 31.1 percent when no hidden terminal exists, and is 3.16x when 20 percent pairs of contending clients are hidden terminals.
Deploying Chains of Virtual Network Functions: On the Relation Between Link and Server Usage
(2018-08-01)
Kuo, Tung-Wei
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Liou, Bang-Heng
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Lin, Kate Ching-Ju
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Tsai, Ming-Jer
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資訊工程學系
Recently, network function virtualization has been proposed to transform from network hardware appliances to software middleboxes. Normally, a demand needs to invoke several virtual network functions (VNFs) following the order determined by the service chain along a routing path. In this paper, we study the joint problem of the VNF placement and path selection to better utilize the network. We discover that the relation between the link and server usage plays a crucial role in the problem. Inspired by stress testing, we first propose a systematic way to elastically tune the link and server usage of each demand based on the network status and properties of demands. In particular, we compute a proper routing path length, and decide, for each VNF in the service chain, whether to use additional server resources or to reuse resources provided by existing servers. We then propose a chain deployment algorithm that follows the guidance of this link and server usage. Via simulations, we show that our design effectively adapts resource allocation to network dynamics and, hence, serves more demands than other heuristics.
Empowering Device-to-Device Networks with Cross-Link Interference Management
(2017-04)
Chiu, Shang-Lun
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Lin, Kate Ching-Ju
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Lin, Guang-Xun
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Wei, Hung-Yu
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資訊工程學系
Device-to-device (D2D) communications is an emerging service model that is currently under standardization by 3GPP. While D2D offloading has a great potential to relieve increasingly congested cellular networks, its benefits, however, come at a cost, namely interference. Most of the prevailing D2D designs conservatively avoid interference via either spectrum resource allocation or power control. These designs, however, do not exploit spatial degrees of freedom (DoF), which are inherently supported by multiantenna devices. In this work, we present MD2D, a multiuser D2D system that embraces concurrent D2D transmissions, while leveraging MIMO techniques to actively eliminate interference across D2D pairs. MD2D has a systematic methodology that checks whether the antenna combination in a D2D network is capable of eliminating cross-pair interference and, thereby, ensuring interference-free concurrent transmissions. If the interference can be eliminated, then MD2D applies a bucket-based DoF assignment algorithm to determine an effective antenna usage configuration that handles the interference. We evaluate our design via testbed experiments and large-scale simulations. The results show that, as compared to the traditional interference avoidance scheme, MD2D improves the throughput by 87.39 and 218.84 percent in a three-pair testbed and in large-scale simulations, respectively.
Enabling Identity-Aware Tracking via Fusion of Visual and Inertial Features
(2019-01-01)
Tsai, Richard Yi-Chia
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Ke, Hans Ting-Yuan
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Lin, Kate Ching-Ju
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Tseng, Yu-Chee
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資訊工程學系
Person identification and tracking (PIT) is an essential issue in computer vision and robotic applications. It has long been studied and achieved by technologies such as RFID or face/fingerprint/iris recognition. These approaches, however, have their limitations due to environmental constraints (such as lighting and obstacles) or require close contact to specific devices. Therefore, their recognition accuracy highly depends on use scenarios. In this work, we propose RCU (Robot Catch yoU), an accompanyist robot system that provides follow-me or guide-me services. Such robots are capable of distinguishing users' profiles in front of them and keep tracking a specific target person. We study a more challenging scenario where the target person may be under occlusion from time to time. To enable robust PIT, we develop a data fusion technique that integrates two types of sensors, an RGB-D camera and wearable inertial sensors. Since the data generated by these sensors share common features, we are able to fuse them to achieve identity-aware tracking. Practical issues, such as time synchronization and coordinate calibration, are also addressed. We implement our design on a robotic platform and show that it can track a target person even when no biological feature is captured by the RGB-D camera. Our experimental evaluation shows a recognition rate of 95% and a following rate of 88%.
Eye On You: Fusing Gesture Data from Depth Camera and Inertial Sensors for Person Identification
(2018-01-01)
Chang, Wei-Chun
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Wu, Cheng-Wei
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Tsai, Richard Yi-Chia
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Lin, Kate Ching-Ju
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Tseng, Yu-Chee
Person identification (PID) is a key issue in many IoT applications. It has long been studied and achieved by technologies such as RFID and face/fingerprint/iris recognition. These approaches, however, have their limitations due to environmental constraints (such as lighting and obstacles) or require close contact to specific devices. Therefore, their recognition rates highly depend on use scenarios. To enable reliable and remote PID, in this work, we present EOY (Eye On You) 1, a data fusion approach that combines two kinds of sensors, a 3D depth camera and wearable sensors embedded with inertial measurement unit (IMU). Since these two kinds of data share common features, we are able to fuse them to conduct PID. Further, the result can be transferred to a mobile platform (such as robot) since we have less constraints on devices. To realize EOY, we develop fusion algorithms to address practical challenges, such as asynchronous timing and coordinate calibration. The experimental evaluation shows that EOY can achieve the recognition rate of 95% and is very robust even in crowded areas.
FDoF: Enhancing Channel Utilization for 802.11ac
(2018-02-01)
Lin, Chi-Han
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Chen, Yi-Ting
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Lin, Kate Ching-Ju
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Chen, Wen-Tsuen
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資訊工程學系
Multi-user multiple input multiple output (MU-MIMO) enables a multi-antenna access point to serve multiple users simultaneously, and has been adopted as the IEEE 802.11ac standard. While several PHY-MAC designs have recently been proposed to improve the throughput performance of a MU-MIMO WLAN, they, however, usually assume that all the concurrent streams are of roughly equal length. In reality, users usually have frames with heterogeneous lengths even after aggregation, leading to different lengths of a transmission time. Hence, the concurrent transmission opportunities might not always be fully utilized when some streams finish earlier than the others in a transmission opportunity. To resolve this inefficiency, this paper presents full degree-of-freedom (FDoF), a PHY-MAC design that exploits a novel power allocation scheme to reduce the idle channel time and further leverages frame padding to better utilize the spatial multiplexing gain. Unlike traditional MIMO power allocation, which aims at maximizing the theoretical sum-rate, FDoF's power allocation explicitly considers heterogeneous frame lengths and minimizes the channel time required to finish concurrent frames, as a result improving the effective throughput. FDoF's padding protocol then identifies proper users to reuse the remaining idle channel time, while preventing this padding from harming all the ongoing streams. Our evaluation via large-scale trace-driven simulations demonstrates that FDoF's improves the throughput by up to 2.83x, or by 1.36x on average, as compared to the conventional 802.11ac. By combining FDoF's power allocation with frame padding, the average throughput gain can be further increased to 1.75x.
Flow Classification for Software-Defined Data Centers Using Stream Mining
(2019-01-01)
Chao, Shou-Chieh
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Lin, Kate Ching-Ju
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Chen, Ming-Syan
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資訊工程學系
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Department of Computer Science
Traffic management is known to be important to effectively utilize the high bandwidth provided by datacenters. Recent works have focused on identifying elephant flows and rerouting them to improve network utilization. These approaches however require either a significant monitoring overhead or hardware/end-host modifications. In this paper, we propose FlowSeer, a fast, low-overhead elephant flow detection and scheduling system using data stream mining. Our key idea is that the features from flows' first few packets allow us to train the streaming classification models that can accurately and quickly predict the rate and duration of any initiated flow. With these predicted information, FlowSeercan adapt routing polices of elephant flows to their demands and dynamic network conditions. Another nice property of FlowSeeris its capability of enabling the controller and switches to perform cooperative prediction. Most of decisions can be made by switches locally, thereby reducing both detection latency and signaling overhead. FlowSeerrequires less than 100 flow table entries at each switch to enable cooperative prediction, and hence can be implemented on off-the-shelf switches. The evaluation via both experiments in realistic virtual networks and trace-driven simulations shows that FlowSeerimproves the throughput by multiple times over Hedera, which pulls flow statistics, and performs comparably to Mahout, which needs end-host modification.
Full-Duplex Constructive Relay for Wireless Multicast
(2018-01-01)
Chang, Che-Wei
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Lin, Kate Ching-Ju
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資訊工程學系
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Department of Computer Science
Full-duplex relaying has attracted a lot of attention recently due to its capability of receiving and forwarding simultaneously in the same frequency band. However, most of the existing designs focus on unicast communication and customize the relaying algorithm so as to maximize the receiving signal strength of a particular user. In this work, we aim at developing a full-duplex constructive forwarding system for wireless multicast. As different multicast members typically have heterogeneous channel state information, it is especially challenging to find a forwarding processing strategy that works fine for all the multicast members. To overcome this issue, we propose two models, one for maximizing the worst SNR of the multicast members while the other optimizing the overall reception quality, which is especially suitable for video multicast. We evaluate our designs via trace-driven simulations. The results demonstrate that we can consistently improve the worst SNR by 2-3 dB and the gain is especially significant for a large coverage network area.
Hey! I Have Something for You: Paging Cycle Based Random Access for LTE-A
(2018-01-01)
Hsu, Chia-An
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Ren, Yi
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Lin, Kate Ching-Ju
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Tseng, Yu-Chee
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資訊工程學系
The surge of M2M devices imposes new challenges for the current cellular network architecture, especially in radio access networks. One of the key issues is that the M2M traffic, characterized by small data and massive connection requests, makes significant collisions and congestion during network access via the random access (RA) procedure. To resolve this problem, in this paper, we propose a paging cycle-based protocol to facilitate the random access procedure in LTE-A. The high-level idea of our design is to leverage a UE's paging cycle as a hint to preassign RA preambles so that UEs can avoid preamble collisions at the first place. Our rpHint has two modes: (1) collision-free paging, which completely prevents cross-collision between paged user equipments (UEs) and random access UEs, and (2) collision-avoidance paging, which alleviates cross-collision. Moreover, we formulate a mathematical model to derive the optimal paging ratio that maximizes the expected number of successful UEs. This analysis also allows us to adapt dynamically to the better one between the two modes. We show via extensive simulations that our design increases the number of successful UEs in an RA procedure by more than 3x as compared to the legacy RA scheme of the LTE.
Inter-Client Interference Cancellation for Full-Duplex Networks
(2017-01-01)
Hsu, Kai-Cheng
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Lin, Kate Ching-Ju
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Wei, Hung-Yu
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資訊工程學系
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Department of Computer Science
Recent studies have experimentally shown the gains of full-duplex radios. However, due to its relatively higher cost and complexity, we can envision a more practical step in the network evolution is to have a full-duplex access point (AP) but keep the clients half-duplex. Unfortunately, the full-duplex gains can hardly be extracted in practice as the uplink transmission from a half-duplex client introduces inter-client interference to another downlink client. To address this issue, we present the design and implementation of IC2 (Inter-Client Interference Cancellation), the first physical layer solution that exploits the AP's full-duplex capability to actively cancel the interference at the downlink client. Such active cancellation not only improves the achievable capacity, but also better tolerates imperfect user pairing, simplifying the MAC design as a result. We build a prototype of IC2 on USRP-N200 and evaluate its performance via both testbed experiments and large-scale trace-driven simulations. The results show that, without IC2, about 60% of client pairs produce no gain from full-duplex transmissions, while, with IC2 the median throughput gain over conventional half-duplex networks can be 1.65x even when clients are simply paired randomly.
Inter-Client Interference Cancellation for Full-Duplex Networks With Half-Duplex Clients
(2019-10-01)
Lin, Kate Ching-Ju
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Hsu, Kai-Cheng
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Wei, Hung-Yu
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資訊工程學系
;
Department of Computer Science
Recent studies have experimentally shown the gains of full-duplex radios. However, due to its relatively higher cost and complexity, we can envision a more practical step in the network evolution is to have a full-duplex access point (AP) but keep the clients half-duplex. Unfortunately, the full-duplex gains can hardly be extracted in practice as the uplink transmission from a half-duplex client introduces inter-client interference to another downlink client. To address this issue, we present the design and implementation of IC2 (Inter-Client Interference Cancellation), the first physical layer solution that exploits the AP's full-duplex capability to actively cancel the interference at the downlink client. Such active cancellation not only improves the achievable capacity, but also better tolerates imperfect user pairing, simplifying the MAC design as a result. We build a prototype of IC2 on USRP-N200 and evaluate its performance via both testbed experiments and large-scale trace-driven simulations. The results show that, without IC2, about 60% of client pairs produce no gain from full-duplex transmissions, while, with IC2 the median gain of the achievable rate over conventional half-duplex networks can be 1.65x and 1.47x for 1- and 2-antenna scenarios, respectively, even when clients are simply paired randomly.
LiCompass: Extracting Orientation from Polarized Light
(2017-01-01)
Wei, Yu-Lin
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Wu, Hsin-I
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Wang, Han-Chung
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Tsai, Hsin-Mu
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Lin, Kate Ching-Ju
Accurate orientation information is the key in many applications, ranging from map reconstruction with crowdsourcing data, location data analytics, to accurate indoor localization. Many existing solutions rely on noisy magnetic and inertial sensor data, leading to limited accuracy, while others leverage multiple, dense anchor points to improve the accuracy, requiring significant deployment efforts. This paper presents LiCompass, the first system that enables a commodity camera to accurately estimate the object orientation using just a single optical anchor. Our key idea is to allow a camera to observe varying intensity level of polarized light when it is in different orientations and, hence, perform estimation directly from image pixel intensity. As the estimation relies only on pixel intensity, instead of the location of the anchor in an image, the system performs reliably at long distance, with low resolution images, and with large perspective distortion. LiCompass' core designs include an elaborate optical anchor design and a series of signal processing techniques based on trigonometric properties, which extend the range of orientation estimation to full 360 degrees. Our prototype evaluation shows that LiCompass produces very accurate estimates with median errors of merely 2.5 degrees at 5 meters and 7.4 degrees at 2.5 meters with an irradiance angle of 55 degrees.
Location-Independent WiFi Action Recognition via Vision-based Methods
(2016)
Chang, Jen-Yin
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Lee, Kuan-Ying
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Wei, Yu-Lin
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Lin, Kate Ching-Ju
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Hsu, Winston
Due to die characteristics of ubiquity, non occlusion,privacy preservation of Win, many researchers have devoted to human action recognition using WiFi signals. As demonstrated in [1], Channel State information (CSI), a fine-grained information capturing the properties of WiFi signal propagation, could be transformed into images for achieving a promising accuracy on action recognition via vision-based :methods. However, from the experimental results shown in [1], the CSI is usually location dependent, which affects the recognition performance if signals are recorded in different places. In this paper. We propose a location-dependency removal method based on Singular Value Decomposition (SVD) to eliminate the background CSI and effectively extract the channel information of signals reflected by human bodies. Experimental results show that our method considering the correlation of CST streams could achieve promising accuracy above 90% in identifying six actions even testing in live different rooms.
On Efficient Multipolling with Various Service Intervals for IEEE 802.11e WLANs
(2011)
Chou, Chin-Wen
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Lin, Kate Ching-Ju
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Lee, Tsern-Huei
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電信工程研究所
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Institute of Communications Engineering
Hybrid coordination function (HCF) is proposed in IEEE 802.11e standard to support quality of service (QoS). HCF defines two channel access mechanisms; one of them is HCF controlled channel access (HCCA) designed for contention free transmission. In HCCA, each QoS-enhanced station (QSTA) obtains polled transmission opportunity (TXOP) from the hybrid coordinator (HC), which is in charge of scheduling the channel access and responding the poll messages to each QSTA. However, forwarding polling messages causes a significant overhead and degrades the channel utilization of data transmission. The goal of this work is to develop an efficient multipolling scheme that can reduce the overhead of polling messages. The simulation results show that the proposed algorithm can reduce the control overhead and, thus, improve the channel utilization significantly.