In this unit we will see how WiFi networks work

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1 In this unit we will see how WiFi networks work

Wifi is a commercial term that is now used as a synonymous for wireless connectivity. A Wifi link connects a user to a wireless local area network using a radio frequency channel.

2 Wifi is a commercial term that is now used as a synonymous for wireless connectivity. A Wifi link connects a user to a wireless local area network using a radio frequency channel. All devices connected to the same access point are in the same local network and can share resources. Wireless local area access points can be connected to a wired network to cover a bigger physical area. In a lot of cases this wired connection also connects users to the Internet.

3 Nowadays, multiple devices incorporate this technology to connect to a network and share information: computers, smartphones, tablets, cameras, video-game consoles, and more

The standard that regulates these connections is the IEEE 802.11. It covers the media access and physical layers.

4 The standard that regulates these connections is the IEEE It covers the media access and physical layers. There are several versions of the standard, as new versions have been developed to add more features and bigger bandwidths.

5 Each of the Wifi standards define a set of radio communication channels one or several bands of the radio spectrum. The bands used by Wifi are free use bands, in which every application must tolerate the interference of other applications, so Wifi is prepared to work with interferences from other applications. For example, the 2,4 Ghz band used widespread for Wifi, is known as Industrial, Scientific and Medical radio band and is also used by microwave ovens, cordless phones, bluetooth devices or medical devices that use radio-frequency.

6 Odds are that the biggest interference you will find when using Wifi will come from other Wifi users. There are a few channels defined for Wifi in each band and, in the most used band, the 2,4 Ghz, the 13 channels defined are overlapping, so only 3 of them can be used in the same area without interference, as was depicted in the former slide. As almost every home user in the western world has their own Internet connection with a wireless router, you can find yourself in a situation as the one depicted in the slide, captured with a Wifi analyser program in a United States home. In this situation your laptop will indicate you that you have a very good signal but the connection speed will be poor, as you will be suffering a lot of interference. It is very likely that the new Wifi standards, that offer higher bandwidth using 2 or 3 channels, will make things worse in the future.

7 In corporate networks the same cellular structure as in cellular telephone networks is used to cover large areas. In the 2,4 GHz band this requires a careful planning of frequency reusing in non adjacent cells, as there are only 3 non overlapping channels.

8 The a was defined in 1999 and it allows speeds between 1.5 and 54 megabits per second using the 5 GHz band divided in 12 or 13 non overlapping channels. It has been more used in North America as at first this band was reserved for other uses in Europe. This band has the advantage of being less crowded that the 2,4 GHz band and having more non-overlapping channels and the disadvantage of having less range and penetration of obstacles because of its higher frequency.

9 The b family was defined in 2000 and transmits data at 11 megabits per second. It uses a different frequency band, which means that it is incompatible with a It defines 14 channels (of which only 11 can be used in the US) that overlap. Only 3 of them can be used at the same time. This band has been used intensively around the world and suffers from saturation. Channel 14 is only allowed in Japan.

10 802.11g is an update of b using the same band. It is backward compatible with b and incompatible with a.

11 The n family was defined in The main improvements over previous standards are that it can handle more than one antenna in the same device using a technology called MIMO (for Multiple Input Multiple Output), and that it reaches up to six hundred megabits per second. For that it uses several channels, which can be a problem in the saturated 2,4 GHz band. This standard is widely used in all the world, and is backward compatible with all previous standards.

12 The most recent specification refers to the ac family. It uses a different band at 5 GHz, faster but more sensitive to obstacles. It reaches 1 gigabit per second ac devices are still a bit expensive.

13 An unavoidable issue in wireless communication is that the radio signals are sent using the open space. So we should use systems to ensure that only authorised people can use an Access point and that nobody can eavesdrop the connections Because of that there are different protocols to ensure Authentication, Authorisation and Accounting of Users. The most updated ones are 802.1X for Authentication and WPA2 for Authorisation

14 The common way to connect to a Wifi network is using a Wifi hotspot, also called a Wifi Access Point. The existence of points that provides wireless access in public places, such as hotels, airports, libraries, or even in open areas on the street, is becoming more and more frequent. Some of these hotspots offer free Internet access and others charge for the connection time.

EIE324 Communication & Telecommunication Lab. Date of the experiment Topics: Objectives : Introduction Equipment Operating Frequencies

1 EIE324 Communication & Telecommunication Lab. Date of the experiment Topics: WiFi survey 2/61 Chanin wongngamkam Objectives : To study the methods of wireless services measurement To establish the guidelines