11-04-2010, 04:40 PM
[attachment=3159]
Wi-Fi the wireless wings
Abstract--In the recent decade Wi-Fi have got immense importance in many fields .Wi-Fi - short for "wireless fidelity" - is the commercial name for the 802.11 products that have flooded the corporate wireless local area network (WLAN) market and are becoming rapidly ingrained in our daily lives via public hotspots and digital home networks. In the following presentation we will be discussing about, what is Wi-Fi.?, Working of Wi-Fi, the Wi-Fi hotspots and its advantages. Wireless networks are easy to set up and inexpensive. They are also unobtrusive unless you are on the lookout for a place to use your laptop, you may not even notice when you are in a hotspot. In this article, we will look at the technology that allows information to travel over the air and also review what it takes to create a wireless network in your home. So by considering all these aspects in the field of Wi-Fi, the technology is found to be very encouraging.
Presented By:
Srinath Rajaram
K Tarun Kumar
Mallareddy Institute of Tech. & Science,
ECE III Year, Maisammaguda, Dhullapally, Secunderabad, India-500044.
Keywords:- Wi-Fi, OFDM, IEEE, Hotspot.
I. Introduction
It is strategically believed that wireless communication is playing a predominant role in life style of the mankind. Wireless Fidelity (Wi-Fi) is a queued up emerged technology to have a sustained growth in wireless communication.
Wi-Fi, short for "wireless fidelity", is the commercial name for the 802.11 products that have flooded the corporate wireless local area network (WLAN) market and are becoming rapidly ingrained in our daily lives via public hotspots and digital home networks. Authentication and confidentiality are crucial issues for corporate Wi-Fi use, but privacy and availability tend to dominate pervasive usage. However, because a technology's dependability requirements are proportional to its pervasiveness, newer applications mandate a deeper understanding of how much we can rely on Wi-Fi and its security promises. In this article, we present an overview of Wi-Fi vulnerabilities and investigate their proximate and ultimate origins.
II. IEEE Standards for Wi-Fi
The IEEE (Institute of Electrical and Electronics Engineers) has produced a set of standards and specifications for wireless networks under the title IEEE 802.11 that defines the format and structure of radio signals sent out by Wi-Fi networking routers and antennas.
A. IEEE 802.11b
802.11b is the slowest and least expensive standard. For a while, its cost made it popular, but now it's becoming less common as faster standards become less expensive. 802.11b transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to 11 megabits of data per second, and it uses complementary code keying (CCK) modulation to improve speeds.
B. IEEE 802.11a
802.11a transmits at 5 GHz and can move up to 54 megabits of data per second. It also uses orthogonal frequency-division multiplexing (OFDM), a more efficient coding technique that splits that radio signal into several sub-signals before they reach a receiver. This greatly reduces interference.
C. IEEE 802.11g
802.11g transmits at 2.4 GHz like 802.11b, but it's a lot faster -- it can handle up to 54 megabits of data per second. 802.11g is faster because it uses the same OFDM coding as 802.11a.
D. IEEE 802.11n
802.11n is the newest standard that is widely available. This standard is significantly improves speed and range. For instance, although 802.11g theoretically moves 54 Megabytes of data per second because of network congestion. 802.11n, however, reportedly can achieve speeds as high as 140MBps. The standard is currently in draft form. The Institute of Electrical and Electronic Engineers (IEEE) plans to formally ratify 802.11n by the end of 2009.
III. Working of Wi-Fi
A wireless network uses radio waves, just like cell phones, televisions and radios do. In fact, communication across a wireless network is a lot like two-way radio communication. Here's what happens:
1. A computer's wireless adapter translates data into a radio signal and transmits it using an antenna.
2. A wireless router receives the signal and decodes it. The router sends the information to the Internet using a physical, wired Ethernet connection.
The process also works in reverse, with the router receiving information from the Internet, translating it into a radio signal and sending it to the computer's wireless adapter.
The radios used for Wi-Fi communication are very similar to the radios used for walkie-talkies, cell phones and other devices. They can transmit and receive radio waves, and they can convert 1s and 0s into radio waves and convert the radio waves back into 1s and 0s. But Wi-Fi radios have a few notable differences from other radios: They transmit at frequencies of 2.4 GHz or 5 GHz. This frequency is considerably higher than the frequencies used for cell phones, walkie-talkies and televisions. The higher frequency allows the signal to carry more data.
A. OFDM
Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique to provide multiplexing in high-speed wireless applications (e.g. broadband wireless, 4G systems, LANs) in a hostile multipath environment with frequency-selective fading. OFDMA (Orthogonal Frequency Division Multiple Access is the multiuser OFDM) achieves high efficiency in multiuser environment by dividing the total available bandwidth to orthogonal narrow sub-bands to be shared by users in an efficient manner.
Fig.1. Frequency domain view of principle of orthogonality.
By using OFDM desired bit rate can be achieved, bandwidth is used efficiently. OFDM is robust to fading. But guard intervals are necessary to avoid ISI (Inter Symbol Interference) and ICI (Inter Channel Interference). This OFDM has become a promising technology in the next generation of wireless communication.
Fig.2. Spectral Efficiency of OFDMA.
With the advent of OFDM there will no more be dedicated single user channels, thus improving the data rates, increasing flexibility.
B. CCKM
CCK is a variation on M-ary Orthogonal Keying modulation, which uses I/Q modulation architecture with complex symbol structures. CCK allows the 802.11b for multi-channel operation in the 2.4 GHz band using the existing 802.11 DSSS channel structure scheme. The spreading employs the same chipping rate and spectrum shape as the 802.11 Barkerâ„¢s code word. Spreading functions, allows three non-interfering channels in the 2.4 to 2.483 GHz band.
Fig.3. Multipath channel model
CCK Modulation performs well in single-path channel. CCK Modulation does not achieve acceptable error probability in a multi-path channel with this detector
IV. Hot Spots
Wi-Fi hotspots were first proposed by Brett Stewart at the NetWorld+Interop conference in The Moscone Center in San Francisco in August 1993. Stewart did not use the term 'hotspot' but referred to publicly accessible wireless LANs. Stewart went on to found the companies PLANCOM in 1994 (for Public LAN Communications, which became Mobile Star and then the Hotspot unit of T-Mobile USA) and Wayport in 1996.The term 'Hotspot' may have first been advanced by Nokia about five years after Stewart first proposed the concept.
During the dot-com boom and subsequent burst in 2000, dozens of companies had the notion that Wi-Fi could become the payphone for broadband. The original notion was that users would pay for broadband access at hotspots. Although some companies like T-mobile, and Boingo have had some success with charging for access, over 90% of the over 300,000 hotspots offer free service to entice customers to their venue.[citation needed]
Both paid and free hotspots continue to grow. Wireless networks that cover entire cities, such as municipal broadband have mushroomed. MuniWireless reports that over 300 metropolitan projects have been started. WiFi hotspots can be found in remote RV / Campground Parks across the US [1].
Many business models have emerged for hotspots. The final structure of the hotspot marketplace will ultimately have to consider the intellectual property rights of the early movers; portfolios of more than 1,000 allowed and pending patent claims are held by some of these parties.
The public can use a laptop, Wi-Fi phone, or other suitable portable device to access the wireless connection (usually Wi-Fi) provided. Of the estimated 150 million laptops, 14 million PDAs, and other emerging Wi-Fi devices sold per year for the last few years, most include the Wi-Fi feature.
For venues that have broadband Internet access, offering wireless access is as simple as purchasing one AP, in conjunction with a router and Connecting the AP to the Internet connection. A single wireless router combining these functions may suffice. Hotspots are often found at restaurants, train stations, airports, military bases, libraries, hotels, hospitals, coffee shops, bookstores, fuel stations, department stores, supermarkets, RV parks and campgrounds and other public places. Many universities and schools have wireless networks in their campus.
Fig.4.Wi-Fi Hotspots
A. Wi-Fi Cards
In order for computers to receive these radio signals, a network adapter must be installed on the computer. The network adapter in this case is called the Wi-Fi Card and it can take several physical forms. For laptops, this card will be a PCMCIA card in which you insert to the PCMCIA slot on the laptop. The other way is to buy a external adapter and plug it into a USB port. For personal computers, you can install plug-in PCI cards or a small external adapter for the USB port just like the one used for laptops. A network adaptor should be capable to use in any operating system such as WINDOWS, MAC OS, LINUX and UNIX as long as the driver for the adapter is accessible to download or install. As you already know, there are three forms of standards used for wireless networking: 802.11b, 802.11a, and 802.11g. Therefore, there are three different kinds of Wi-Fi cards that are available to purchase. The recommended Wi-Fi card to buy is the 802.11g because it has the advantage of higher speeds than the 802.11b (see the chart in the radio signals section). Although it is bit more expensive than the 802.11b, it is still worth the cost. A hotspot which contains 802.11 standards can hold up to as much as 100 802.11 cards within the vicinity. Below are pictures of how Wi-Fi cards appear and how it fits in the MCMCIA slot on the laptop.
Fig.5. Wi-Fi Cards
Fig.6. Wi-Fi External adapter
B. Access points
Access points are often combined with other network functions. It is very likely that you will discover a separate access point that just plugs into a wired Local Area Network (LAN). If you already have more than one computer hooked together on the same network and want to have a good hotspot, you can buy a wireless access point and plug it in to the network. As mentioned earlier, radio signals can be received and transmitted by an antenna and a router. The router is an example of an access point of how multiple computers can be connected together in the same network both including the use of wires and wireless technology. So once you turn on your access point on, you will have a hotspot in your home and will have radio signal within a 100 feet radius. As for antennas, they have a higher signal transmission at a 300-500 feet radius. That is why hotels, campuses, libraries, etc, anything that is larger than your home is required to use antennas rather than routers.
Below are two different kinds of routers used to connect multiple computers on the same connection. The physical designs of access points various from one brand to the other. Here you can see one of Net Gearâ„¢s router and on the right, Linksysâ„¢s wireless router have different physical forms. Some look like devices that were intended to be placed in a standing position jut like the router on the right. Others have those normal flat looking routers like the one on the left. Some have internal antennas (which are not shown here) and others have short vertical antennas permanently affixed to the router just like the ones shown here. Regardless of its size and shape, all access points consist of a radio that transmits and receive signals and data between network stations and an Ethernet port that connects to a wired network (normal connection).
V. Advantages and Disadvantages of Wi-Fi
A. Advantages
1. Wi-Fi allows LANs to be deployed without cabling, typically reducing the cost of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.
2. Wi-Fi silicon pricing continues to come down, making Wi-Fi a very economical networking option and driving inclusion of Wi-Fi in an ever-winding array of devices.
3. Wi-Fi products are widely available in market. Different brands of access points and client network interfaces are interoperable at a basic level of service. Products designated as Wi-Fi certified by the Wi-Fi Alliance are interoperable and include WPA2 security.
4. Wi-Fi networks support roaming, in which a mobile client station such as a laptop computer can move from one access point to another as the user moves around a building or area.
5. Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world.
6. Security: Some Hotspots require WEP key to connect that is the connection is considered to be private or secure. As for open connections, anyone with a Wi-Fi card can gain access to that hotspot. WEP stands for Wired Equivalence Privacy. It is considered to be a complex encryption system that is made up of two differences. The first is the 64-bit encryption and the other is the 128-bit encryption. The 64-bit encryption was the original standard until it was easily bypassed
With the 64-bit encryption out of the way, the new and improved 128-bit encryption was made. It is much secure and is what most people use to enable WEP. So in order for a user to gain access to the internet under WEP, the user must input the WEP key code.
B. Disadvantages
1. Spectrum assignments and operational limitations are not consistent worldwide; most of Europe allows for an additional 2 channels beyond those permitted in the US; Japan has one more on top of that-and some countries like Spain, prohibit use of lower-numbered channels. Further more some countries such as Italy, used to require a Ëœgeneral authorizationâ„¢ for any Wi-Fi used outside an operators own premises, or require something akin to an operator registration.
2. EIRP in the EU is limited to 20 dbm consumption is fairly high compared to some other standards, making battery life and heat a concern.
3. The most common wireless encryption standard wired equivalent privacy or WEP, has been shown to be breakable even when correctly configured.
4. Wi-Fi Access points typically default to an open (encryption free) mode. Novice users benefit from a zero configuration device that works out of the box but might not intend to provide open wireless access to their LAN.
VI. Comparison of Wi-Fi with other parallel technologies
A comparison chart of Wi-Fi with other parallel technologies is shown in the table given at the bottom.
VII. Conclusions
Hence we infer from the above information that Wi-Fi is a very promising technology and it has a great advantage over the parallel technologies. Wi-Fi, the wireless LAN can be used to interconnect the different places in a same area or different areas. This can reduce the time consumption and can make life simpler. Hotspots are promisingly increasing their reliability in providing the service to make Wi-Fi a huge success. Although Wi-Fi is a bit power consuming, recent standards of IEEE (IEEE 802.11n) are making it more reliable. IEEE 802.11n which is to be released by the end of the year 2009 provides a speed of 140MBps, saving a lot of time. Thus after comparing Wi-Fi with other technologies we can say that itâ„¢s definitely one of the best technologies and with a better performance over others.
VIII. References
[1] Somsak Kittipiyakul and Tara Javidi, Resource Allocation in OFDMA Wireless Networks with Time-Varying Arrivals, IEEE.
[2] Andrea Goldsmith, Wireless Communications, Cambridge University Press, Cambridge, 2005.
[3] G. S. V. Radha Krishna Rao, G. Radhamani, ,WiMAX: A Wireless Technology Revolution, Auerbach Publications,NewYork,2008.
Table 1. Comparison of Wi-Fi With other parallel technologies.
