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

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3.3.1.5. IEEE 802.11a and OFDM 3.3.1.5.1. Background Because there are lots of non-802.11 signals that also existed in the 2.4 GHz band, this band is often very crowded. For achieving higher speed and capacity, 802.11 Task group A (TGa) came out with a new standard. It used a 5 GHz un-licensed band and a different transmission method (OFDM). Although this standard was published in 1999, the practical hardware was not available until the end of 2001. At first, 802.11a used the UNII band and was specified for the U.S. only. Later, two similar standards were published. 802.11h is for Europe and 802.11j is for Japan. [08][30][31][43][44] OFDM (Orthogonal Frequency Division Multiplexing) was developed in the late 1960s. It is not a new theory however, because of the wireless technology it revived again. OFDM has several features. First, it uses multiple subcarriers to do a single transmission. Second, for simplifying equalization at receiver, it transforms scattered channels into parallel narrowband subchannels. Third it is based on simple mathematics. OFDM is related with FDM (Frequency Division Multiplexing), that both divide bandwidth into divisions which is called carriers or subcarriers and use them for transmitting information. [08][17][29][33][36] 3.3.1.5.2. Principles When transmitting data, OFDM chooses channels which overlap in frequency domain, but will not disturb with each other. Figure 3-7[17] These overlapping subcarriers are defined by mathematical calculation, therefore, they can travel individually, and this relationship is called orthogonal. With this feature, OFDM can increase capacity in the fixed bandwidth. Thus the overall performance is improved. [08][17][29] Figure 3-7 FDM and OFDM Although OFDM has better performance, there is still a cost. Inter-symbol interference (ISI) is a common problem when transmitting data. It mainly occurs when the delay that happens in different paths is too large and causes a later copy to shift onto a previously arrived copy. The 20
other problem is inter-carrier interference (ICI). When several subcarriers transmit in a channel and one of them shifts slightly then the interference between subcarriers would be occurred. To avoid these problems, scientists came out with several methods. The first method was to add a “guard time” between each subcarrier. A guard time is a silent period between two subcarriers, however this method wastes bandwidth and once the delay is too large then the orthogonality would be destroyed. The other way to avoid interference is using “cyclic prefix (CP)” and “cyclic postfix (PP)”. Figure 3-8[51] CP is a guard interval between the signal N and the signal N-1. PP is an interval in signal N+1 and N. The idea of CP is to extend the time range of signal N longer, so that even if interference happened it will not affect FFT block which is the information section of a signal carried. However, sometimes the problem not only comes from the previous signal, therefore, the guard interval will have two parts “cyclic prefix” and “cyclic postfix”. Here are some other studies about OFDM and interference: [30] – [40] Figure 3-8 CP and PP OFDM modem is based on block-by-block structure. The transmitter first converts the signal into N subcarriers and then uses IFFT (inverse Fast Fourier Transform) to modulate them into orthogonal waveforms. The receiver reverses the process by using FFT (Fast Fourier Transform). It will remove CP first and find the FFT block. Then it starts using FFT to demodulate the signal that has received. Finally, the information is recovered. Figure 3-9[51] OFDM has higher capacity and is more reliable than some of other methods. The mathematics of OFDM is FFT and IFFT; and they are not complicated. With FFT, the operation number in each signal is on the order of NlogN. This can be done easily by a program. That is the reason that OFDM is broadly used in wireless technology. [34][36] - [39] 21
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: Figure 3-5 CCK Modulation HR-DSSS P
Page 35 and 36: Tab ble 3-5 OFDDM Modulaation and D
Page 37 and 38: and contains DSSS, CCK, PBCC (Packe
Page 39 and 40: 3.3.2. MAC Layer 3.3.2.1. Introduct
Page 41 and 42: Virtual channel sensing he other me
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
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Table 5-5 Parameters of WLAN and Me
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Table 5-6 Features of Nortel Wirele
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• -101 dBm typical @ 1 Mbps Recei
Page 95 and 96:
Operating environment specification
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uilding density, high population de
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epeater r is developping and it wil
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Figure 5-17 WiBro Features The data
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Figure 5-19 U-RAS Premium Figure 5-
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In KT’s recent report, 60% of sub
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Figure 5-21 An Example Application
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Name Parameters Standard Table 5-10
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WiFly used Wi-Fi to cover 60% of th
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BIBLIOGRAPHY [01]. IEEE 802.11 offi
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[37]. Sun, Y.; "Bandwidth-efficient
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[88]. Mineno T.; Babji T.,"Issues a
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[117]. Yun Z.; Yuguang F., "Securit
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Network Operations and Management S
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