An Investigation of the Impact of Signal Strength on Wi-Fi Link ...

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Figure 2.9: IEEE 802.11 MAC architecture [13]. DCF is a default medium access control mechanism <strong>of</strong> <strong>the</strong> IEEE 802.11, as known as CSMA/CA. DCF is implemented within wireless stations and APs. Thus, DCF supports both Ad-hoc mode and infrastructure mode. Fur<strong>the</strong>rmore, in order to reduce collision, a random back-<strong>of</strong>f time is used to resolve conflict during media contention. On <strong>the</strong> o<strong>the</strong>r hand, PCF is an optional feature which incorporates with DCF to provide a contention-free service. PCF requires point coordinators to ensure that <strong>the</strong> medium can provide a contention-free service. Point coordinators only exist in <strong>the</strong> AP, so PCF is available in <strong>the</strong> infrastructure mode. When PCF is enabled, time on medium is separated into two periods: contention-free period (CFP) and contention period. CFP is controlled by PCF and contention period is handled by DCF. <strong>An</strong> AP delivers a “beacon frame” at <strong>the</strong> beginning <strong>of</strong> CFP. In order to prevent DCF-based service to access medium, “beacon frame” is to lock out wireless medium by setting <strong>the</strong> maximum duration <strong>of</strong> CFP in all wireless stations. - 14 -
DCF is designed to provide “best-effort” service. Although PCF is designed to support real-time service, hidden nodes problem would lead to collisions during a contention-free period [22]. PCF is not an ideal protocol to support quality <strong>of</strong> service (QoS) and real-time application. The IEEE 802.11 committee proposed a new standard, called 802.11e, to support QoS and fair service in <strong>the</strong> IEEE 802.11 MAC layer. The IEEE 802.11e is a dominant protocol than PCF in QoS and fair service. Carrier-Sense Mechanism The IEEE 802.11 defines two types <strong>of</strong> carrier-sense mechanism: physical carrier-sense and virtual carrier-sense [13]. Physical carrier-sense is provided by PHY. Virtual carrier-sense mechanism is handled by MAC. Ei<strong>the</strong>r one <strong>of</strong> carrier-sense indicates that <strong>the</strong> medium is busy. The medium should be busy, o<strong>the</strong>rwise, it can be considered as idle. The virtual carrier-sense uses network allocation vector (NAV) to reserve <strong>the</strong> medium for a fixed time period. The function <strong>of</strong> <strong>the</strong> NAV is a timer to indicate <strong>the</strong> amount <strong>of</strong> time that <strong>the</strong> medium will be reserved. The carrier-sense mechanism uses NAV state, transmitter status and physical carrier-sense to determine <strong>the</strong> status <strong>of</strong> <strong>the</strong> medium. Figure 2.10: Network allocation vector [14]. The function <strong>of</strong> <strong>the</strong> NAV is shown in figure 2.10. A sender and a receiver reserve <strong>the</strong> medium by using NAV. The sender and receiver set up <strong>the</strong> NAV. O<strong>the</strong>r stations count - 15 -
Page 1 and 2: An Investi
Page 3 and 4: 2.3.5 Signal <stro
Page 5 and 6: Attestation of Aut
Page 7 and 8: Abstract Wireless local area networ
Page 9 and 10: List of Abbreviati
Page 11 and 12: List of Figures Fi
Page 13 and 14: List of Tables Tab
Page 15 and 16: Chapter 1 Introduction There has be
Page 17 and 18: WLAN performance evaluation and ana
Page 19 and 20: Chapter 2 Background and Related Wo
Page 21 and 22: The IEEE 802.11 networks have two o
Page 23 and 24: The coverage of a
Page 25 and 26: 2.2.1 Physical Layer Figure 2.8 sho
Page 27: throughput significantly at higher
Page 31 and 32: Figure 2.11: Backof</strong
Page 33 and 34: modulation in [37]. According to si
Page 35 and 36: Figure 2.12: Net throughput <strong
Page 37 and 38: As highlighted in [46, 47], distanc
Page 39 and 40: 2.3.2 Base Station Placement <stron
Page 41 and 42: gained an insight that this would m
Page 43 and 44: proposed to improve WLAN performanc
Page 45 and 46: specifications of
Page 47 and 48: dynamic and complicated. As argued
Page 49 and 50: In addition, we surveyed and review
Page 51 and 52: 4.1 Performance Metrics A stopwatch
Page 53 and 54: Model: DWL-G132 Specification: Sta
Page 55 and 56: Figure 4.1: WY building layout. - 4
Page 57 and 58: Figure 4.2 shows wireless configura
Page 59 and 60: 4.4.2 Wireless Adapter Configuratio
Page 61 and 62: 4.4.3 AP Operation Mode Two APs (D-
Page 63 and 64: meeting room with different distanc
Page 65 and 66: Scenario 4 In figure 4.12, two APs
Page 67 and 68: “(H-3.5m)F-H” is the</s
Page 69 and 70: Figure 4.16: Phase 2 measurement: A
Page 71 and 72: performed the prop
Page 73 and 74: The receiver sensitivity is an impo
Page 75 and 76: In table 5.1, the
Page 77 and 78: Ethernet connectio
Page 79 and 80:
sufficient signal coverage and thro
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throughput decreases along with low
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In table 5.1, when RSS is larger th
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(for example, measurement point “
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AP at Position “R” Figure 5.13
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The measurement results indicated t
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5.2.2 Throughput An</strong
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impact on RSS and throughput. Resul
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The throughput of
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The RSS of “WDS
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The average throughput of</
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The average data size of</s
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5.6.1 SOHO Environment Due to <stro
Page 105 and 106:
The following notes are needed to b
Page 107 and 108:
when APs were placed at positions
Page 109 and 110:
Real and accurate results for AP pl
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Chapter 7 Summary and Conclusions W
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planning. Propagation measurement (
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deployment. Many WLANs are deployed
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placement in indoor wireless system
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Communications, vol. 2, no. 5, pp.
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[56] J. K. L. Wong, M. J. Neve, and
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eceived signal strength of<
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Appendix A Preliminary Experimental
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2. AP Mode Measurement in t
Page 129 and 130:
7. The Ad-Hoc Mode Measurement on <
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Appendix B Phase 1 Experimental Res
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(P-1.5m)O-P 32.78 -86 193.6 0.453 N
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3. Access Point at Position “E-3M
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(C-5m)C-D 21.63 -83 46.8 1.875 NLOS
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J 9.00 -44 8.2 10.703 LOS (J-1.5m)J
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7. Access Point at Position “H”
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Figure B.2: Throughput map for AP a
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60 40 20 0 -20 -40 -60 -80 -100 Acc
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(N-3m)N-O 15.00 -72 15.6 5.626 NLOS
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(C-3m)C-D 14.32 -74 13.6 6.453 NLOS
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Figure B.8: Throughput map for AP a
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60 40 20 0 -20 -40 -60 -80 -100 Acc
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AP at A RX Position Left-Hand Area
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AP at L RX Position Left-Hand Area
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Appendix D Phase 3 Experimental Res
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TX at 2M from E-3M Data File: 153.6
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IEEE 802.11 b/g Access Point DWL-21
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Standards • IEEE 802.11g • IEEE
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1 Maximum wireless signal rate deri
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Wireless 108G Standards • 802.11b
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Wireless 108G Add 802.11g Wireless
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2.4GHz Omni-Directional 7dBi Indoor
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An Investigation of the Impact of Signal Strength on Wi-Fi Link ...

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