“Wi-Fi Technology” Abstract In the past decade, wireless has grown from an obscure and expensive curiosity into a practical and affordable networking technology. Today’s most common wireless standard is 802.11b Ethernet, also called Wi-Fi (Wireless Fidelity). The 802.11b standard is fast enough to be practical and affordable enough for home networks. You can buy the components to set up a wireless network in nearly any store that sells computers. The convenience of wireless is appealing— you don’t have to deal with running cable, and you can move computers anywhere you want and still be connected to the network. Wireless is especially suited for use with laptop or notebook computers, offering users great freedom of movement. But enthusiasm for this new technology sometimes leads to the installation of a wireless network where a wired network would be more effective, economical, and secure. Wireless has shortcomings that make it ill suited for many networks. Yet its popularity and ongoing efforts to improve the technology make it a promising option in the future. The common usage of Wi-fi technology is for laptop users to gain Internet access in locations such as coffee shops, airports and so on. Types of Wireless LANs: A WI-FI network can operate in two modes: Ad-hoc mode Infrastructure mode In ad-hoc mode, your computers talk directly to each other and do not need an access point. In infrastructure mode, network traffic passes through a wireless access point. The Concept: Wi-Fi is short for Wireless Fidelity and is meant to be used generically when referring to any type of 802.11 network, whether 802.11b, 802.11a, 802.11g, dual-band, etc. Wi-fi is a wireless technology that uses radio frequency to transmit data through the air. An Access Point is a separate wireless unit, which has the ability to extend from the router to maximize wireless reception. Up to 16 users can connect to one access point .It allows several wireless clients to connect to a single device. Wi-fi hot spot is defined as any location in which wireless technology both exists and is available for use to consumers. Wi-fi was intended to be used for wireless devices and LANS, but is now often used for internet access. WI-FI Specification: Wi-Fi is a wireless technology that uses radio frequency to transmit data through the air. Quick/easy temp network access Staff access to corporate network Patron internet access (hotspot) Interconnecting two networks Mobility Flexibility Savings Expandability Advantages: Setup Cost – Reduced cabling required Flexibility – Quick and easy to setup in temporary or permanent space. Scaleable – Can be expanded with growth Freedom – You can work from any location that you can get a signal Lower total cost of ownership – Because of affordability and low install cost additionally Mobile Users – Can access the Corporate network from any public hotspot using VPN Range and Performance: Performance decreases as distance increases. 802.11a (Wireless Ethernet) Indoor 40-300 feet Outdoor 100 - 1000 feet 802.11b (Wireless Ethernet Refined) Indoor 100-300 feet Outdoor 400 – 1500 feet Interference - doors, walls, furniture, ceiling 253 maximum number of client per AP, but 15-20 recommended. Differences in wireless standards Wireless Wi-Fi Standards (802.11) Maximum 54 Mbps Speed WiMax (802.16) Coverage 300 feet 50 Miles Licences Mobile Option No Both Several Miles Yes No Yes Yes Pros Speed, Price Cons Short Range 10 to 100 Mbps Speed, Range, Versatile Interface Issues Mobile-Fi (802.20) 16 Mbps Speed, Mobility Coexistence: “wireless systems can be collocated without significantly impacting the performance of either” Bluetooth High Price Applications: 1. Wi-Fi with Bluetooth Technology In this section, we will be discussing how our Wi-Fi Technology works together with Bluetooth. Two prominent wireless technologies: 1. WPAN: Wireless Personal Area Networking Supports a short range (10m), implemented in Bluetooth Applications such as wireless headsets, PDAs, keyboards, mice, etc. 2. WLAN: Wireless Local Area Networking Supports wider range (100m), designed in Wi-Fi (802.11b) Applications such as wireless routers, wireless cards, wireless printers, etc. WPAN & WLAN are complementary Collocation of Wi-Fi and Bluetooth become increasingly significant. A cable replacement radio frequency technology: low cost, modest transfer rate, and short range. Supports Pico nets of up to eight active devices with three synchronous connection-oriented links asynchronous connectionless. Pico net: an ad-hoc computer network It uses Frequency-Hop-Ping Spread Spectrum (FHSS) at 1600hops/s Data transfer rate 11Mb/s or higher Overview of Wi-Fi and Bluetooth Characteristics Wi-Fi (802.11b) Supports multipoint networking Data types as broadcast, multicast, unicast MAC address built-in, allowing unlimited number of devices to be active It uses direct-sequence spread spectrum Both Wi-Fi and Bluetooth share the same frequency band, 2.4Ghz Issues of Coexistence Both Wi-Fi & Bluetooth operate at the same time within the same frequency band, they will interfere with each other, creating in-band colored noise. The inference is called noise Noise: in-band noise & out-of-band noise In-band noise: the transmitter uses the undesired energy in frequencies to transmit the desired signal. Out-band noise: the transmitter does not use. White noise: interference from multiple sources without their coordination. Colored noise: interference transmitted by two intentional radiators, behave in time & frequency Occurrence of the interference: An 802.11b receiver senses both Bluetooth and 802.11b signals at the same time. The effect happens when Bluetooth signal is within the 22MHz wide pass band of the receiver. A Bluetooth receiver senses both 802.11b and Bluetooth signals at the same time. The inference occurs when the 802.11b signal is within the Bluetooth receiver. The interference reduces the performance of data transfer rate and packet lost. 2. WMM Power Save (Wi-Fi Multimedia Power Save) Extends battery life for Wi-Fi devices by increasing efficiency and flexibility of data transmission - Data indicates improvements ranging from 15 – 40% Uses mechanisms included in IEEE 802.11e standard Important milestone and enabler in the growth of Wi-Fi beyond the PC market into – Wi-Fi Cellular Convergence products – Voice over Wi-Fi applications – Consumer Electronics Features and Benefits of WMM Power Save Feature Individual applications (instead of the device driver) decide when the client communicates with the access point and how long it can doze Uses fewer packets to exchange data Coexists with legacy power save devices and networks – Legacy APs can support WMM Power Save clients (in legacy mode) & vice versa – Both AP and client must have WMM Power Save to take advantage of advanced features Benefit More finely tuned power save mechanism that is customized to individual applications More efficient data transfer than legacy power save = lower power consumption Devices work in all Wi-Fi networks, including legacy power save Easily upgradeable CONCLUSION: References: In this paper, we have presented a new technology called Wi-Fi, its standards, specifications, ranges and even its performance. Along with these we presented how this Wi-Fi works together with other technologies like Bluetooth and Multimedia. To our knowledge, Our main conclusion is that long-distance links can be planned well for predictable performance using Wi-fi. How-ever, any interference within the network can cause drastic reductions in performance. Interference can occur between adjacent links even in the so-called non-interfering channels. This means that it is important to develop the knowledge-base for deployment planning. [1] Akshaya: A Kerala state initiative for Creating powerful social and economic e-networks.http://www.akshaya.net/. Wi-Fi-based community networks have received a lot of attention in the recent past. The same is necessary for long-distance Wi-Fi deployments too, especially given its potential to provide truly pervasive networking. We believe that our measurement study is a significant step in this re-guard, and hope that the results will be useful in future de-ployments and protocol studies. [5] Sanjit Biswas and Robert Morris. Opportunistic Routing in Multi-Hop Wireless Networks. Acknowledgment We thank everyone who helped us at various levels [2] IEEE P802.11, The Working Group for Wireless LANs. http://grouper.ieee.org/groups/802/11/. [3] Radio laboratory handbook. http://wireless.ictp.trieste.it /handbook/index.html, [4] Pravin Bhagwat, Bhaskaran Raman, and Dheeraj Sanghi. Turning 802.11 Inside-Out. In HotNets-II, Nov 2003. [6] Mobile Computing / Netwoking by Ashoke .K Talukder & Roopa .R Yavagal