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

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communications. Taipei is a busy city with many office buildings. It is a “concrete jungle”, especially in the metropolitan area. This kind of area is very unfavorable to signal transmission and it will cause serious multipath fading. Thus, the end users may scan the signal, but cannot establish a connection, or even have no signal at all. The other problem is AP. It includes numbers of user and locations. Most of APs are located outdoor, such as wire poles and street lights. Because APs are exposed outside and Taiwan is hot and humid, the failure rate will be high. Moreover these kinds of AP locations also have big security issues. There are 4600 APs in Taipei, management and maintenance is a big challenge. And since the AP installation is focus on population coverage, most suburb residents do not have WiFly signal. The Q-ware does not limit the numbers of user on an AP. Therefore it may cause congestion and channel overlapping problems. For channel allocation and reallocation, Linda Yeh, the Account Manager in Sales & Customer Service Dep. of Q-ware Systems & Services Corp. [148], said the company has a control platform to manage each AP’s operation channel. In a high density area, if there is congestion or channel overlapping the network engineers can use this platform to switch the operation channel for each AP to release the situation. However, the platform cannot solve the problem completely. In most high usage areas of WiFly, after switching channels, the problem still exists. She said this is because there are only three channels that can be used in one area. It is Wi-Fi’s inherent limitation. [148] The maximum data rate for each user was 512 kbps for both Uplink and Downlink. In January 2007, Q-ware upgraded to 1Mbps for Downlink and 512 kbps for Uplink. This speed is not a shearing speed, which means it will not be changed even if the users increased. [148] To avoid heavy traffic, Linda indicated that they have a flow control scheme to monitor the traffic flow for APs. The detail of flow control scheme is trade secret, thus she cannot provide more information for it. Channel overlapping and congestion are two major problems of signal transmission. There are several methods to solve the congestion issue, such as, hop-by-hop congestion control and multihop congestion control. [149][150] The main idea of these methods is to send a congestion feedback packet to slow down the source speed to release the congestion. The congestion control has been studied for years. Here is some related researche. [151] – [153] For improving signal stability, end users can install bridge or high power wireless network cards. These two methods can solve most signal instability. Q-ware also has to install more APs or use high power APs in high usage areas. Since WiMax licenses have been issued in Taiwan. It can also be a solution for signal stability and extending geographical coverage. About security vulnerability, Q-ware said that the wireless connection must be authorized before established and the user account needs two identifications to apply. However there is no one hundred percent security scheme. Users still have to protect their account information and PC from spy-programs. The responsibility is upon both WISP and the users. The Nortel Wireless Mesh Network solution is a suitable model for WiFly. However, no matter how perfect the model is, Taipei still has its intrinsic limitations, such as high office 84
uilding density, high population density, humid and hot weather, and unfavorable wired network infrastructure. Because the Nortel Wireless Mesh Network solution adopts mesh structure (APs and Ethernet communicate through Gateways), it decreases the difficulty while installing APs. Nevertheless, the APs’ power supply is still a big issue. And even through APs are not necessary to connect to Ethernet, the Gateways have to. One Gateway can support 120 APs, so 4600 APs need at least 39 Gateways. Considering the connection status, usage and AP locations, it is impossible to use just 39 Gateways to handle the whole network and it will cause serious congestion problem. Therefore, where to install the Gateways and how to wire the Gateways are other important issues. According to Linda Yeh, so far the company does not have an efficient way to solve channel overlapping and congestion problems completely. To install a booster to increase the signal power can be a good solution for these problems, but the National Communications Commission (NCC) has strict rules for signal power. Therefore, Q-ware does not have plans to install it. These problems are still pending. [148] The marketing problem is another big issue waiting to be solved. When WiFly first came out, it guarantees to provide ubiquitous connection to every citizen. However it was plagued with serious mechanical problems and that is not the only reason for low numbers of users. The WiFly did not meet the needs of end users. Before WiFly, Wi-Fi had been available in stores for years, such as McDonald’s and some coffee shops. This company was called Yaw Jenq Technology and the service was called “Easy- Up”. At that time the project was cooperated with Intel. It was the first WISP in Taiwan, but ended up in.bankruptcy in May 2005. Easy-Up brought new Internet access to people. This project officially began in May 2003. At that time the wireless interface is NB with built-in centrino platform. With Easy-Up, access internet in McDonald’s or other chain stores was slowly becoming a trend. Currently, sitting in a Starbucks, having a cup of coffee and browsing the Internet has become a very common activity. With regards to the service policy, Linda Yeh said that the indoor APs are used for mobile devices users and the outdoor APs are mainly for fixed users. The indoor APs are most installed in coffee shops, chain restaurants and other public areas, such as airports. In these places, the signal is more stable and the connection quality is better than outdoor. The outdoor APs are used to provide service to fixed users such as home and industries. These users can use bridges or antennas to receive WiFly signal. However because of many external factors, such as RF interference, weather and transmission path, the signal quality is not as good as the indoor APs. [148] In WiFly’s official website, there is a search engine for WiFly hotspot, but they do not provide AP location search. If a customer wants to know if are there any APs nearby, they need call Q-ware directly. [148] Wireless Internet access is definitely a business point. WiFly also has the ability to occupy a high market share. But the wrong market positioning and unfriendly pricing rate makes the usage much lower than the prediction. WiFly can never replace the ADSL at home. Therefore it is an 85
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THE FLORIDA STATE UNIVERSITY COLLEG
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TABLE OF CONTENTS List of Tables…
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5. Case study…………………
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LIST OF FIGURES Figure 2-1 The Evol
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LIST OF ABBREVIATIONS Abbreviation
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PSS Portable Subscriber Station 89
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CHAPTER ONE 1. Introduction The cel
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Table 1-1 Cont. 802.3an 2006 10GBAS
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2.1. Introduction CHAPTER TWO 2. 3G
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2.3. Development 3G has been in dev
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2.5. Conclusion WAP (Wireless Appli
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IEEE 802.11n is the newest standard
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Table 3-3 Cont. 10 2.457 X Y Y Y Y
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3.3.1.2. PLCP and PMD The physical
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Noise Codes). The most powerful con
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Figure 3-5 CCK Modulation HR-DSSS P
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other problem is inter-carrier inte
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Tab ble 3-5 OFDDM Modulaation and D
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and contains DSSS, CCK, PBCC (Packe
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3.3.2. MAC Layer 3.3.2.1. Introduct
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Virtual channel sensing he other me
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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: Operating environment specification
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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