A comparison of wi-fi and wimax with case studies - Florida State ...

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3.3.2.3. Hidden node and CSMA/CA When a station is communicating with another station, there is an existing risk that the packets may collide. It is due to the hidden node problem. Each station has limited coverage, so stations may not be aware of the other nearby stations. Thus if there are more than two stations that try to transmit a signal to the same station at the same time, and then the collision will happen. In Figure 3-15, station A and C are hidden nodes to each other. If station A is sending a signal, station C cannot be aware of it. Since most stations are half-duplex (cannot transmit and listen at the same time), the collision is difficult to be detected. In Figure 2-17, it shows that only station B knows collisions happened. [17][55] Figure 3-15 The Hidden Node Problem To deal with this problem, 802.11 WG uses a different method from Ethernet. With wired transmission they use CSMA/CD (Carrier Sense Multiple Access/Collision Detection), but since the wireless transmission has very limited resource and is not as reliable as Ethernet, 802.11 WG turns to use collision avoidance (CSMA/CA). There are two technologies used in CSMA/CA, physical channel sensing and virtual channel sensing. [17][55] Physical channel sensing When a station wants to send signals, for example, it senses the channel first. If the channel is idle, it just sends. During the transmission, it will not sense the channel at the time, but keeps sending signals. However if the channel is busy, it will wait until the channel is idle and then start the transmission. Once a collision occurs, the stations will wait for certain time, by using the Ethernet binary exponential back off algorithm, and then try again later. [17][55] 28
Virtual channel sensing he other method, virtual channel sensing, is shown in figure 3-16 [55] and figure 3-17[55]. When station A wants to send signals to station B, it will send a RTS (Request to Send) frame to the station to occupy a channel first. If the channel is idle, station B will send CTS (Clear to Send) frame back. When station A receives CTS, it will start to transmit a signal. When the process is initiated, an important “timer” is including in RTS and CTS frame which called NAV (Network Allocation Vector). The information that is included in NAV is how long the channel will be occupied. One operation contains RTS, CTS, data frames and ACK (Acknowledgement). NAV will set how long it will take including the last ACK frame. Therefore, since station D is within the range of station A, it will receive RTS and then stop completely from occupying the channel until NAV counter becomes zero. It is the same with station D. Station C will receive CTS, so it will also wait until the operation is completed. However, before the ACK is received by station A, the NAV is expired. Then the operation has to run again. [17][55] Figure 3-16 CDMA/CA Figure 3-17 Virtual Channel Sensing 29
Page 1 and 2: THE FLORIDA STATE UNIVERSITY COLLEG
Page 3 and 4: TABLE OF CONTENTS List of Tables…
Page 5 and 6: 5. Case study…………………
Page 7 and 8: LIST OF FIGURES Figure 2-1 The Evol
Page 9 and 10: LIST OF ABBREVIATIONS Abbreviation
Page 11 and 12: PSS Portable Subscriber Station 89
Page 13 and 14: CHAPTER ONE 1. Introduction The cel
Page 15 and 16: Table 1-1 Cont. 802.3an 2006 10GBAS
Page 17 and 18: 2.1. Introduction CHAPTER TWO 2. 3G
Page 19 and 20: 2.3. Development 3G has been in dev
Page 21 and 22: 2.5. Conclusion WAP (Wireless Appli
Page 23 and 24: IEEE 802.11n is the newest standard
Page 25 and 26: Table 3-3 Cont. 10 2.457 X Y Y Y Y
Page 27 and 28: 3.3.1.2. PLCP and PMD The physical
Page 29 and 30: Noise Codes). The most powerful con
Page 31 and 32: Figure 3-5 CCK Modulation HR-DSSS P
Page 33 and 34: other problem is inter-carrier inte
Page 35 and 36: Tab ble 3-5 OFDDM Modulaation and D
Page 37 and 38: and contains DSSS, CCK, PBCC (Packe
Page 39: 3.3.2. MAC Layer 3.3.2.1. Introduct
Page 43 and 44: SIFS (Short InterFrame Spacing) Fig
Page 45 and 46: Figure 3-20 WEP Frame and Operation
Page 47 and 48: 3.4.2. MIMO (Multiple-Input/Multipl
Page 49 and 50: 4.1. The background of IEEE 802.16
Page 51 and 52: The working groups of WiMax Forum a
Page 53 and 54: Table 4-1 Thee Basic Datta of IEEE
Page 55 and 56: Figure 4-1 The Layer Structure of I
Page 57 and 58: codes ( (CTC) and low densityy pari
Page 59 and 60: 4.3.1.2.2. AAS (Advanced Antenna Sy
Page 61 and 62: Best-effort service (BE) This schem
Page 63 and 64: Encryption Figure 4-4 PKM Protocol
Page 65 and 66: 4.3.2. IEEE 802.16e-2005, the newes
Page 67 and 68: transmiission, the aadjacent cellls
Page 69 and 70: the uplink bandwidth periodically f
Page 71 and 72: Figure 4-7 Coverage and Capacity fo
Page 73 and 74: CHAPTER FIVE 5. Case study This cha
Page 75 and 76: increased bandwidth, fixed connecti
Page 77 and 78: Figure 5-3 Landis Green Figure 5-4
Page 79 and 80: Table 5-2 Xirrus XS-3700 AP Technol
Page 81 and 82: • Automatic Tx power selection
Page 83 and 84: Table 5-4 Cont. 71
Page 85 and 86: 5.1.3. Analysis The FSU wireless ne
Page 87 and 88: since the January 2006. The populat
Page 89 and 90: Table 5-5 Parameters of WLAN and Me
Page 91 and 92:
Table 5-6 Features of Nortel Wirele
Page 93 and 94:
• -101 dBm typical @ 1 Mbps Recei
Page 95 and 96:
Operating environment specification
Page 97 and 98:
uilding density, high population de
Page 99 and 100:
epeater r is developping and it wil
Page 101 and 102:
Figure 5-17 WiBro Features The data
Page 103 and 104:
Figure 5-19 U-RAS Premium Figure 5-
Page 105 and 106:
In KT’s recent report, 60% of sub
Page 107 and 108:
Figure 5-21 An Example Application
Page 109 and 110:
Name Parameters Standard Table 5-10
Page 111 and 112:
WiFly used Wi-Fi to cover 60% of th
Page 113 and 114:
BIBLIOGRAPHY [01]. IEEE 802.11 offi
Page 115 and 116:
[37]. Sun, Y.; "Bandwidth-efficient
Page 117 and 118:
[88]. Mineno T.; Babji T.,"Issues a
Page 119 and 120:
[117]. Yun Z.; Yuguang F., "Securit
Page 121 and 122:
Network Operations and Management S
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