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

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The interference from microwave oven is a quite common problem to degrade <strong>the</strong> performance <strong>of</strong> WLAN. Many previous studies have already addressed that microwave ovens have strong influence on <strong>the</strong> performance <strong>of</strong> WLANs [23-26]. Similar to WLAN devices, Bluetooth equipment shares 2.4 GHz ISM band as well. Bluetooth technology is widely used for data transmission between personal devices, for example laptop, PDA, mobile phone, and print. However, while Bluetooth devices and WLAN are operating concurrently and very closely, it could cause coexistence interference and degrade <strong>the</strong> performance <strong>of</strong> both devices [27-31]. Fur<strong>the</strong>rmore, as mentioned in [32], if <strong>the</strong> distance between Bluetooth devices and WLAN devices is less than 2 meters, <strong>the</strong> throughput will degrade significantly. Due to <strong>the</strong> interference from Bluetooth devices, throughput <strong>of</strong> <strong>the</strong> IEEE 802.11b stations degraded from 25% to 66% [33]. Fur<strong>the</strong>rmore, when Bluetooth interference leads to packet loss <strong>of</strong> WLAN, it cannot be solved by increasing transmission power <strong>of</strong> WLANs. However, decreasing transmission power <strong>of</strong> WLANs can mitigate <strong>the</strong> effects <strong>of</strong> interference to Bluetooth devices [31]. Even though <strong>the</strong> IEEE 802.11 standard defined 14 channels, only 3 non-overlapping channels (channel 1, 6 and 11) are available [34]. While two <strong>of</strong> APs are using same channel or adjacent channels, it could cause co-channel interference. The throughput would degrade 2 Mbps in <strong>the</strong> IEEE 802.11b WLANs due to adjacent channel interference[35]. Thus, co-channel interference results in reducing <strong>the</strong> capacity <strong>of</strong> WLAN, inefficiency <strong>of</strong> using radio spectrum and increasing deployment cost [18, 36]. In order to mitigate effects <strong>of</strong> co-channel interference, different orthogonal code sets CCK (DOC-CCK) modulation was developed instead <strong>of</strong> <strong>the</strong> IEEE 802.11b CCK - 18 -
modulation in [37]. According to simulation results, <strong>the</strong> DOC-CCK almost eliminates co-channel interference when two BSSs are located in <strong>the</strong> same area. In conclusion, interference <strong>of</strong> radio frequency is a usual problem and has significant impacts on data throughput in wireless communication. The studies give us an insight into understanding <strong>the</strong> impact <strong>of</strong> interference on WLAN performance and mitigating <strong>the</strong> effects <strong>of</strong> interference. The studies also have pr<strong>of</strong>ound implications for propagation measurement. Multiple-Path Propagation Reflection or diffraction leads to multiple-path propagation. Multiple-path propagation is a common event in <strong>the</strong> indoor environment. The radio signal would reflect from objects during transmission (e.g. wall, ceiling and <strong>of</strong>fice partition). The effect <strong>of</strong> multiple-path propagation causes <strong>the</strong> fading <strong>of</strong> radio signal, so that receiver would not get sufficient signal power [36]. Moreover, <strong>the</strong> reflected signals will arrive later than direct signal. The period used to identify duplicate signals is referred to “delay spread”. In general, <strong>the</strong> large delay spread number has better performance, because stations and APs have enough time to identify radio signals [38]. Attenuation When data transmission occurs between two wireless nodes, <strong>the</strong> signal power is dropping and getting weak. It is called attenuation [36]. Many factors could result in attenuation, for example, distance, obstruction, and multiple-path effect. Due to attenuation, received devices would not have sufficient signal strength. The performance would degrade significantly. Fur<strong>the</strong>rmore, metal door and structural - 19 -
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 and 28: throughput significantly at higher
Page 29 and 30: DCF is designed to provide “best-
Page 31: Figure 2.11: Backof</strong
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
Page 81 and 82: throughput decreases along with low
Page 83 and 84:
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
Page 99 and 100:
The average throughput of</
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The average data size of</s
Page 103 and 104:
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
Page 111 and 112:
Chapter 7 Summary and Conclusions W
Page 113 and 114:
planning. Propagation measurement (
Page 115 and 116:
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
Page 123 and 124:
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
Page 147 and 148:
(N-3m)N-O 15.00 -72 15.6 5.626 NLOS
Page 149 and 150:
(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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