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title page
Abstract
Contents
1. Introduction 12
1.1. Research Motivation 12
1.2. Problem Description and Proposed System 14
1.3. Thesis Organization 15
2. Related Work 16
2.1. Maximizing Sleep Times of WLAN interfaces 16
2.2. Using the Lowest Possible Power Level for Communication 18
2.3. Summary 19
3. CoNet System 21
3.1. CoNet Group 23
3.2. Seamless Connection Handoff 24
3.2.1. Previous Approaches to Seamless Handoff 24
3.2.2. Seamless Handoff-Supported Group Initiation 25
3.2.3. Seamless Handoff-Supported Role Switching 31
3.3. Role Scheduling Algorithm 34
4. CoNet System Implementation 36
4.1. System Components 36
4.2. Network Management for Seamless Handoff 37
5. Performance Evaluation 40
5.1. Experimental Setup 40
5.2. Handoff time 42
5.3. Energy overhead of Role Switching 43
5.4. Energy-Saving Effect 44
5.4.1. Round-Robin Policy 44
5.4.2. Maximizing the Group-Lifetime 48
6. Conclusion 56
요약문 57
Appendix 58
A. An Intuitive User Interface for UFC, iThrow 58
A.1. Introduction 58
A.2. iThrow System 58
A.2.1. Motivation 59
A.3. System Components 59
A.4. iThrow 60
A.5. Target Selection 61
A.5.1. Target Searching with Graphical Feedback and Its Problems 61
A.5.2. Adaptive angle assignment 64
A.6. Experiment 64
A.6.1. Experiment Setup 64
A.6.2. Experiment Results 65
A.7. Conclusion 67
References 68
감사의 글 72
Table 1.1: ZigBee, Bluetooth and WLAN specifications 14
Table 5.1: Specification of computing devices used in our experiments. 41
Table 5.2: The handoff time (msec) in four role switching cases. 43
Table 5.3: Constant parameters used by the resource monitor for estimating the total energy consumption of the system. 50
Table 5.4: Experiment cases for evaluating the performance of the maximum-group-lifetime policy 52
Table A.1: UFC Operation Sets 62
Figure 1.1: U-TOPIA : Campus-wide ubiquitous computing environment 13
Figure 1.2: A user is wearing UFC. 13
Figure 1.3: Power consumption of UFC in the idle state. 15
Figure 2.1: On-demand paging scheme. 17
Figure 2.2: CoolSpots allow mobile devices to connect connect the backbone network using Bluetooth interfaces. 19
Figure 2.3: Problems in the related works. 20
Figure 3.1: Basic idea of the proposed system. 22
Figure 3.2: Estimated energy-saving effect of cooperative networking system. As the number of devices in the CoNet group increases, the power consumption of each device decreases 22
Figure 3.3: Network Access Point Profile stack. The Baseband, LMP and L2CAP are the part of the Bluetooth protocols. SDP is the Bluetooth Service Discovery Protocol. 24
Figure 3.4: Concept of the CoNet. 25
Figure 3.5: Grouping procedure 26
Figure 3.6: Before grouping. Devices use WLAN interfaces to communicate with the server. 27
Figure 3.7: C1 plays the role of master. C2 and C3 turn off WLAN to save energy. 28
Figure 3.8: After grouping. C1 creates two virtual interfaces with the IP addresses of C1 and C2. C1 also sends unsolicited ARP requests to update the AP's ARP cache. 29
Figure 3.9: Before grouping. The server and client directly exchange IP packets. 29
Figure 3.10: After grouping. Client1 (mater) forwards IP packets of Client2 (slave). 30
Figure 3.11: Handoff process. The handoff managers exchange messages each other to realize seamless handoff. 31
Figure 3.12: Before switching. Client1 is the mater. 32
Figure 3.13: After grouping. Client1 sends 'PREPARE' message to the next master, Client2. 33
Figure 3.14: After switching. NATs take place. 33
Figure 3.15: Role switching procedure 35
Figure 4.1: Software structure of UFC in CoNet. 37
Figure 4.2: Shell script-based network management, managing NAT configurations. 38
Figure 4.3: Shell script-based network management, managing virtual interface. 39
Figure 5.1: UFC hardware platform detached from the cloth for experiment. 40
Figure 5.2: Energy measurement setup consists of an Agilent E3648A dual output power supply connected to Windows XP desktop computer. 41
Figure 5.3: Block diagram of the energy measurement setup. 42
Figure 5.4: Power consumption of the UFC1 when it changes its role from slave to master. 45
Figure 5.5: Power consumption of the UFC1 when it changes its role from master to slave. 45
Figure 5.6: Power consumption of the wireless communication subsystem. 2 UFCs are cooperating with the round-robin role switching policy. 46
Figure 5.7: Experimental setup for measuring the energy consumed by the wireless communication subsystem of the test CoNet terminal 46
Figure 5.8: Energy consumption ratio with data rate. All traffic is generated by the test CoNet terminal. 47
Figure 5.9: Energy consumption ratio with an aggregated data rate of all CoNet terminals except the test terminal. 47
Figure 5.10: Experimental setup with two UFCs and a test server for testing the maximum-group-lifetime policy. 51
Figure 5.11: Time varying behavior of power consumption with maximum-group-lifetime policy. B has the initial battery energy 1.5 times more than A (case 1 in Table 5.4). 52
Figure 5.12: Time varying behavior of power consumption with maximum-group-lifetime policy. B has the initial battery energy 2 times more energy than A (case 2 in Table 5.4). 53
Figure 5.13: Time varying behavior of power consumption with maximum-group-lifetime policy. A and B have the equal amount of energy. (case 3 in Table 5.4) 53
Figure 5.14: Time varying behavior of power consumption with maximum-group-lifetime policy. A and B have the equal amount of energy. (case 4 in Table 5.4) 54
Figure 5.15: Time varying behavior of power consumption with maximum-group-lifetime policy. A and B have the equal amount of energy. (case 5 in Table 5.4) 54
Figure 5.16: Time varying behavior of power consumption with maximum-group-lifetime policy. A and B have the equal amount of energy. (case 6 in Table 5.4) 55
Figure 5.17: Time varying behavior of power consumption with maximum-group-lifetime policy. A and B have the equal amount of energy. (case 7 in Table 5.4) 55
Figure A.1: Gesture sets of iThrow. 61
Figure A.2: Ray-based minimum angle selection. 63
Figure A.3: Graphical feedback helps the user to select the target device correctly. 63
Figure A.4: Adaptive angle assignment. 65
Figure A.5: Virtual space of the experiment environment. 65
Figure A.6: Angle table for the situation shown in Figure A.5. 66
Figure A.7: After the angle reassignment. 66
Figure A.8: Effect of adaptive angle assignment on selection time. 67
초록보기 더보기
In 2005, our research team launched a project aimed at realizing a campus-wide ubiquitous computing environment, named U-TOPIA. In U-TOPIA, there are many WLAN access points distributed in a wide mesh manner, allowing users to continuously access network services everywhere. Our team have also developed a wearable computing platform, named Ubiquitous Fashionable Computer, as a main user computing device in U-TOPIA. It possesses three wireless communication interfaces: WLAN, Bluetooth, and ZigBee. Thus, UFC users in U-TOPIA can use variety of wireless networking services from e-mail services to remote conference applications.
Sometimes, several UFC users get together and work for a common goal. For example, some friends on a bench connect to the same server and play on-line games together. In this case, individual battery lifetimes are critical factors that decide the lifetime of the group of friends. If one should quit because his battery runs out, then remaining others also can not continue playing game. Therefore, it is a challenging issue that how to extend the lifetime of a group when several UFC users work together.
In this thesis, we present an energy-saving system, named CoNet, which maximizes the lifetime of a UFC group by cooperative networking. In CoNet, UFCs with multiple wireless interfaces form a group and cooperate with each other to minimize the power consumption of the wireless interfaces so that they can work together for a longer period. Among the interfaces, WLAN consumes about 50% of the total power consumption. Thus, it is important to reduce the WLAN power-on time to increase the lifetime of UFC. In CoNet, one of the grouped UFCs becomes a Bluetooth access point for the group, allowing others can use low-power Bluetooth rather than high-power WLAN for wireless networking. Thus, others can significantly reduce the power total consumption, while the WLAN provider can not. In CoNet, under the role switching algorithm proposed in this thesis, UFCs periodically switch the role of providing WLAN to maximize the group-lifetime.
We have designed and implemented the concept of CoNet, and embedded it into UFCs for evaluating the energy-saving performance. Our result shows that CoNet extends the lifetime of a group up to 83%.
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