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

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down from <strong>the</strong> NAV to 0. If <strong>the</strong> NAV is not 0, it indicates <strong>the</strong> medium is busy. On <strong>the</strong> o<strong>the</strong>r hand, when <strong>the</strong> NAV is 0, <strong>the</strong> medium is available. The advantage <strong>of</strong> <strong>the</strong> NAV is to prevent interruption from o<strong>the</strong>r wireless stations during a sequence <strong>of</strong> frame transmission [14]. Random Back<strong>of</strong>f Time Before data transmission starts, a wireless station uses carrier-sense mechanism to determine if <strong>the</strong> medium is busy or idle. If <strong>the</strong> medium is busy, <strong>the</strong> wireless station will put back a DCF interframe space (DIFS) or an extended interframe space (EIFS). After DIFS and EIFS, <strong>the</strong> station will generate a random back<strong>of</strong>f time for ano<strong>the</strong>r deferral before transmission. The main purpose <strong>of</strong> <strong>the</strong> random back<strong>of</strong>f time is to reduce probability <strong>of</strong> collision during <strong>the</strong> period <strong>of</strong> contention between wireless stations. The formula which is used to generate random back<strong>of</strong>f time is given below, Back<strong>of</strong>f Time = Random () * a SlotTime [13] Random () is a pseudorandom integer which is determined by <strong>the</strong> contention window parameters. The value <strong>of</strong> aSlotTime is determined by characteristics <strong>of</strong> physical layer. Figure 2.11 shows <strong>the</strong> back<strong>of</strong>f procedure. As mentioned in [13], in <strong>the</strong> beginning <strong>of</strong> back<strong>of</strong>f procedure, <strong>the</strong> wireless station set back<strong>of</strong>f timer by using <strong>the</strong> back<strong>of</strong>f time formula. If <strong>the</strong> medium is free, <strong>the</strong> back<strong>of</strong>f procedure will deduct <strong>the</strong> aSlotTime time from back<strong>of</strong>f timer. If <strong>the</strong> medium is busy during a back<strong>of</strong>f time slot, <strong>the</strong> back<strong>of</strong>f procedure will be suspended. Then <strong>the</strong> medium will be determined busy or idle during DIFS or EIFS period before back<strong>of</strong>f procedure resumes. However, when <strong>the</strong> back<strong>of</strong>f timer reaches 0, transmission will start immediately. - 16 -
Figure 2.11: Back<strong>of</strong>f procedure [13]. 2.2.3 Radio Propagation Characteristics Although radio wave propagation is a complicated topic, it is necessary to understand <strong>the</strong> characteristics <strong>of</strong> radio propagation in WLAN design. In fact, radio wave propagation is influenced by many factors for instance, distance, radio frequency, geographical features, transmission power and reflections [18]. Therefore, it is very difficult to accurately estimate signal strength and quality <strong>of</strong> signal by analytical modeling and simulation in a particular propagation environment. Both <strong>the</strong> signal strength and radio propagation are affected by several factors, such as interference, multiple-path propagation, path loss and attenuation. Interference Man-made noise is a serious issue at 2.4 GHz ISM band. Many industrial, medical equipment and household appliances, for example, microwave ovens, Bluetooth devices, are operating at 2.4 GHz ISM band. When too many ISM devices operate in a small area, it results in interference as well as decline in performance. Especially, interference not only causes higher frame error rate, but also higher re-transmission rate. - 17 -
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: DCF is designed to provide “best-
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
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
Page 97 and 98:
The RSS of “WDS
Page 99 and 100:
The average throughput of</
Page 101 and 102:
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
Page 117 and 118:
placement in indoor wireless system
Page 119 and 120:
Communications, vol. 2, no. 5, pp.
Page 121 and 122:
[56] J. K. L. Wong, M. J. Neve, and
Page 123 and 124:
eceived signal strength of<
Page 125 and 126:
Appendix A Preliminary Experimental
Page 127 and 128:
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
Page 133 and 134:
(P-1.5m)O-P 32.78 -86 193.6 0.453 N
Page 135 and 136:
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
Page 151 and 152:
Figure B.8: Throughput map for AP a
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60 40 20 0 -20 -40 -60 -80 -100 Acc
Page 155 and 156:
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
Page 161 and 162:
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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