Research has been a long, challenging, yet exciting journey for me. Our research efforts have been mainly focusing on wireless personal-area (WPAN) and wireless local-area (WLAN) networking technologies. We classify our contributions into three major categories: Bluetooth-related issues, resource planning and routing protocols for IEEE 802.11-based wireless mesh networks, and characterizing the impact of underlying link-/physical-layer parameters on overall system performance. Below we summarize the three research tasks and their respective results.
Research Thrust I:
Bluetooth-related Problems Analysis and Protocols Design
Firstly, to address the master polling problem in Bluetooth, we have proposed an efficient Pattern Matching Polling (PMP) policy for ACL connections in a Bluetooth piconet. For each master-slave pair, by estimating both sides' packet arrival rates, the master judiciously selects a polling pattern that can best utilize the network bandwidth. Based on the selected pattern, the master then polls the slave with proper packet types at proper time slots. In return, the slave also replies with proper packet types. The ultimate goal is to reduce the number of NULL packets and unfilled payloads so as to increase bandwidth efficiency. The PMP policy has properly addressed the asymmetry of up- and down-link traffics and the various packet types of Bluetooth are fully exploited. Another merit of PMP is its simplicity - a pattern length of K=3 or 4 can already perform very well. Simulation experiments have demonstrated that the proposed PMP policy improved bandwidth efficiency and network throughput at the expense of moderate packet delays, compared to other polling approaches. In our current discussion, only DH1/3/5 are considered. To include DM1/3/5, we propose to estimate the packet error probability. Whenever the probability is below a threshold, we will adopt DH1/3/5; otherwise, we will switch to DM1/3/5, and the derivation of polling patterns is similar.
Secondly, operating in the unlicensed 2.4-GHz ISM band, a Bluetooth piconet will inevitably encounter the interference problem from other piconets. With a special channel model and packet formats, one research issue is how to predict the packet collision effect in a multipiconet environment. In several earlier works, this problem is studied, but the results are still very limited in that packets are usually assumed to be uniform in lengths and in that time slots of each piconet are assumed to be fully occupied by packets. These assumptions have been successfully removed in our analytic model. In addition, we further extend the model to take into account the frequency-hopping guard time effect in Bluetooth baseband. Our obtained results would offer a better way to estimate the network performance in a multipiconet environment.
Thirdly, as one of the killer applications, instant messaging has become a simple yet efficient tool for peer-to-peer communications in data networks. In telephone networks, short message services are gaining more popularity as well. However, this kind of services typically operates in their own respective networks and is triggered by fairly simple events (such as pushing a “send” button or pre-scheduling the transmission at later time). A promising direction is to trigger instant messages by environmental information from the physical world. In light of this, this work proposes to establish an event-driven messaging service over a cellular- and sensor-integrated network. We have prototyped a system which adopts Global System for Mobile Communication (GSM) as the cellular network, and Bluetooth technology as the sensor network. The latter is to realize a Bluetooth surveillance network with location-sensing capabilities to be deployed within an office building area. While using other technologies is possible, GSM and Bluetooth are two dominating technologies in telephone and data networks. So the proposed technology is immediately feasible, given the fact that many handsets are already Bluetooth-enabled. Through this combination, we demonstrated a visitor system (VS) that offers several attractive features/services for visitors arriving at an office. Messaging services in VS are driven by pre-configured events which can be collected from the Bluetooth surveillance network. Simple events might be a person entering/leaving a space, while complicated events might be a compound logic statement involving multiple users and multiple locations in VS. We believe that the proposed system justifies the potential of cross-network applications and services. Moreover, the proposed architecture takes a modular approach by dividing the system into several subsystems according to their functionality. Logically dispatching jobs is the key to future extensions and further value-added services. The system architecture and implementation details have been reported. Performance analyses were presented to model the detection latency of a Bluetooth sensor network.
Research Thrust II:
Resource Planning and Routing Protocols for IEEE 802.11-based Wireless Mesh Networks
In light of the inherent coverage limitation and high deployment cost (incurred from the requirement of the available wired backbone behind each access point) of single-hop WLAN scenarios, during the past decade, the wireless cooperative multi-hop ad hoc networking has been noticed and considered as a promising operational architecture. By definition, a wireless ad hoc network is viewed as a collection of wireless hosts, which cooperatively establish communications, using no fixed infrastructure or centralized administration. The emerging wireless mesh network (WMN) is a variant of wireless ad hoc network proposed for last-mile wireless Internet access solutions. Interests in WMNs have indeed opened up new research venues and led to a fair amount of research activities in protocol design, implementation, and deployment. However, a number of performance related problems have still been left open. Excessive packet losses, unpredictable channel behaviors, inability to find stable and high-throughput paths, and throughput degradation due to intra-flow and inter-flow interference are among those most cited while not yet fully explored.
We observed that the joint resource planning and routing problem in a Multi-radio Multi-mode Multi-channel Multi-rate (M4) wireless mesh network has been largely ignored. Our approach is based on the linear programming methodology. Utilizing the well-known IEEE 802.11 channel contention model, we compute the near-optimal number of radio modules that should be equipped in each node and the channel that should be bound with each interface. We have designed two resource management and channel assignment algorithms: Decremental Interface Management (DIM) and Incremental Interface Management (IIM).
Our ultimate goal is to maximize the traffic volume in/out of Internet gateways of the mesh network, under the restrictions of network topology (connectivity status), available resources, and user's traffic needs. We summarize our contributions as follows.
Instead of considering only a single factor, our approach addresses all practical characteristics of wireless communications, including the available non-overlapping radio channels and the interference factors among neighboring mesh nodes.
Resources are allocated to mesh nodes based on user's traffic requirements, available hardware/radio modules, and gateway capacities. We allow nodes to have different numbers of radio interfaces. Not only addressing the related multi-channel issues, we also provide a guideline to wisely distribute the deployment costs considering an optimized network system. To the best of our knowledge, this may be the first work addressing resource planning in wireless mesh networks.
In order to enable simultaneous traffic incoming/outgoing through different radio modules of the same mesh host, we propose to perform multi-path packet forwarding (data flow splitting) to further exploit the benefits of having multiple radio transceivers.
Our mesh network architecture, linear programming model for network optimization, two resource management and channel assignment algorithms, and the multi-path packet forwarding strategy are completely new in this relevant research area. Detailed numerical verifications have been performed, and extensive simulative experiments in various network settings were conducted for performance corroboration.
Research Thrust III:
Characterizing the Impact of Underlying Link-/Physical-layer Parameters on Overall System Performance
We took a bottom-up link-layer approach, and tackled issues that work toward a better definition/characterization of wireless links and its implication for higher layer protocol design and optimization. We would like to (i) understand how, and to what extent, wireless links are affected by PHY/MAC attributes and other environmental factors, (ii) characterize the behavior of wireless links in such a way that they become amenable to rigorous analysis and reasoning, and (iii) identify control knobs in the MAC/PHY layers with which the network capacity can be optimized.
In CSMA/CA-based, multi-hop, multi-rate wireless networks, spatial reuse can be increased by tuning the carrier-sensing threshold Tcs to reduce the carrier sense range dcs. While reducing dcs enables more concurrent transmissions, the transmission quality suffers from the increased accumulative interference contributed by concurrent transmissions outside dcs. As a result, the data rate at which the transmission can sustain may decrease. How to balance the interplay of spatial reuse and transmission quality (and hence the sustainable data rate) so as to achieve high network capacity is thus an important issue. We investigated this issue by extending Cali's model and devising an analytical model that characterizes the transmission activities as governed by IEEE 802.11 DCF in a single-channel, multi-rate, multi-hop wireless network. The system throughput is derived as a function of Tcs, SINR, β, and other PHY/MAC system parameters. We incorporate the effect of varying the degree of spatial reuse by tuning the Tcs. Based on the physical radio propagation model, we theoretically estimate the potential accumulated interference contributed by concurrent transmissions and the corresponding SINR. For a given SINR value, we then determine an appropriate data rate at which a transmission can sustain. To the best of our knowledge, this is perhaps the first effort that considers tuning of PHY characteristics (transmit power and data rates) and MAC parameters (contention backoff timer) jointly in an unified framework in order to optimize the overall network throughput. Analytical results indicate that the systems throughput is not a monotonically increasing/decreasing function of Tcs, but instead exhibits transitional points where several possible choices of Tcs can be made. In addition, the network capacity can be further improved by choosing the backoff timer values appropriately.
IEEE 802.11 wireless network supports multiple link rates at the physical layer. Each link rate is associated with a certain required Signal-to-Interference-and-Noise Ratio (SINR) threshold for successfully decoding received packets. Suppose constant noise and no power adjustment strategy exists, apparently SINR is solely affected by the accumulated interference power level I. The method of selecting an appropriate link rate for transmitting/retransmitting packets is generally known as the link adaptation mechanism. Traditional link adaptation approaches try to reduce the transmit rate (hence lower SINR threshold is required) on transmission failures (potentially due to the increased denominator I of SINR), whereas upgrade the transmit rate (hence higher SINR threshold is required) on successful transmissions (potentially due to the decreased denominator I of SINR). The accumulated interference power level I in some sense indicates the medium congestion status. In 802.11, on transmission failures, the DCF performs a binary exponential backoff mechanism to discourage channel access attempts, hoping to reduce congestion. When traditional link adaptation is applied, both rate reduction and binary backoff represent double penalties for this wireless link, which may cause overly conservative transmission attempts. On the other hand, once transmission succeeds, 802.11 DCF resets the backoff contention window to the minimum value to encourage channel access attempts. At the same time, traditional link adaptation may also decide to increase the data rate, which leads to overly aggressive transmission attempts. We observe this improper interaction of link rate and backoff mechanism that harms the 802.11 system performance, due to separate consideration of those two parameters. In this work, rather than independently dealing with the two parameters, we proposed to perform link adaptations by firstly considering if a proper backoff window has been reached. Specifically, if the medium congestion level I can be reduced by imposing a larger backoff window on transmissions, then there may be no need to decrease the link rate, given SINR can be sustained. Conversely, if there is extra interference that may be tolerated in I, a smaller backoff window can be used to encourage more transmission activities while keeping the required SINR. In particular, a joint Adaptation of link Rate and backoff Contention window, abbreviated as ARC, is devised. Our ARC protocol first estimates the optimal contention window (optCW) based on Cal’i’s approximation methods. On transmission successes (failures), the current contention window size cwp should be compared with optCW. If cwp > optCW (cwp < optCW), then cwp is decreased (increased) to perform more aggressive (conservative) transmission attempts while leaving the link rate R unchanged. Otherwise, R is upgraded (reduced) to the next higher (lower) rate. One nice property of ARC is the ability to intelligently maintain link stability, avoiding unnecessary rate fluctuations. Simulation results showed that the proposed ARC protocol outperforms several traditional link adaptation mechanisms. We also proposed an analytic Markov chain model on ARC operations for performance validation.
Research Projects:
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Universal Core Platform and Vision Enhancement based on AVIoT, Ting-Yu Lin, Co-Principal Investigator, August 2021 to July 2024, National Science and Technology Council (NSTC)
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In-depth Industrial Foundation Technology Project - Core Technology and Application Development based on M2M Networking (3/3), Ting-Yu Lin, Co-Principal Investigator, October 2019 to September 2020, Ministry of Science and Technology (MOST)
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Path Scheduling Mechanism Design and System Implementation for Multi-Robot Sensor Network Deployment, Ting-Yu Lin, Principal Investigator, August 2019 to July 2020, Ministry of Science and Technology (MOST)
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In-depth Industrial Foundation Technology Project - Core Technology and Application Development based on M2M Networking (2/3), Ting-Yu Lin, Co-Principal Investigator, October 2018 to September 2019, Ministry of Science and Technology (MOST)
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Path Scheduling Mechanism Design and System Implementation for Multi-Robot Sensor Network Deployment, Ting-Yu Lin, Principal Investigator, August 2018 to July 2019, Ministry of Science and Technology (MOST)
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Wearable Device and Platform for Community Interaction Applications, Ting-Yu Lin, Principal Investigator, January 2018 to July 2018, Ministry of Science and Technology (MOST)
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In-depth Industrial Foundation Technology Project - Core Technology and Application Development based on M2M Networking (1/3), Ting-Yu Lin, Co-Principal Investigator, October 2017 to November 2018, Ministry of Science and Technology (MOST)
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NCTU/Delta Cloud System Program Planning and Research Project (Phase Three), Ting-Yu Lin, Subproject Principal Investigator, September 2016 to August 2017, Delta Electronics
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Gradient Transmission Power Control and Routing Protocol for Carrier Sensing Wireless Networks: Parameter Analysis, Algorithm Design, and System Implementation (Continuation Project), Lin Ting-Yu, Principal Investigator, August 2016 to July 2017, Ministry of Science and Technology (MOST)
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Gradient Transmission Power Control and Routing Protocol for Carrier Sensing Wireless Networks: Parameter Analysis, Algorithm Design, and System Implementation, Ting-Yu Lin, Principal Investigator, August 2015 to July 2016, Ministry of Science and Technology (MOST)
- Joint Research Program between NCTU and Delta Cloud System (Second Phase), Ting-Yu Lin, April 2015 to March 2016, Delta Electronics
- Application of Genetic Algorithms to Optimize Multi-Interface Wireless Mesh Networks, Ting-Yu Lin, August 2014 to July 2015, Ministry of Science and Technology (MOST)
- Joint Research Program between NCTU and Delta Cloud System (First Phase), Ting-Yu Lin, January 2014 to December 2014, Delta Electronics
- Application of Genetic Algorithms to Optimize Multi-Interface Wireless Mesh Networks, Ting-Yu Lin, August 2013 to July 2014, National Science and Technology Council (NSTC)
- Design and Implementation of Coverage-Aware Sensor Automation Network Deployment Protocol for Smart Homes, Ting-Yu Lin, January 2013 to July 2013, National Science and Technology Council (NSTC)
- Design and Implementation of Coverage-Aware Sensor Automation Network Deployment Protocol for Smart Homes, Ting-Yu Lin, April 2012 to August 2012, National Science and Technology Council (NSTC)
- D-Link NCTU Joint Research Center Smart and Secure Home - Home Network and Smart Devices, Ting-Yu Lin, August 2011 to July 2012, D-Link Corporation
- MoE Program Aiming for the Top University and Elite Research Center Development Plan (ATU Plan) - Broadband Wireless Network Architecture, Ting-Yu Lin, January 2009 to December 2009, Ministry of Education (MOE)
- Two-Year Extension Project: Establishing an Efficient Wireless Mesh Network Using the Link Layer Model - Parameter Analysis, Algorithm Design, and Prototype System Implementation, Ting-Yu Lin, August 2008 to July 2010, National Science and Technology Council (NSTC)
- MoE Program Aiming for the Top University and Elite Research Center Development Plan (ATU Plan) - Broadband Wireless Network Architecture, Ting-Yu Lin, January 2008 to December 2008, Ministry of Education (MOE)
- Establishing an Efficient Wireless Mesh Network Using the Link Layer Model: Parameter Analysis, Algorithm Design, and Prototype System Implementation, Ting-Yu Lin, August 2007 to July 2008, National Science and Technology Council (NSTC)
- Resource Allocation and Routing Optimization Design on Wireless Multi-Hop Ad Hoc Networks, Ting-Yu Lin, April 2007 to October 2007, National Science and Technology Council (NSTC)
Biography
