Ryan Heaton

Dick Al-Bayaty

Wi-FiHow Wireless Communication works

Overview

What is Wi-FiHistoryEthernetIEEE standards 802.11(amendments a,b,g,n)2.4GHz /5GHz differences

What is Wi-FiWi-Fi is a means which allows for electronic devices to

talk to one another or exchange data through radio waves.Common devices utilizing Wi-Fi:

Computers Smartphones Video game consoles Tablets

The History1985: FCC releases ISM band

1991: Wi-Fi creates by NCR Corporation/AT&T

1992 & 1996: CISRO obtains patents for methods that were used to “Unsmear” the Wi-Fi signal

1999: Wi-Fi name trademarked

The HistoryInitially meant for cashier systems, the first wireless

products were brought on the market under the name WaveLAN with speeds of 1Mbps/2Mbps

It is continually advancing under IEEE amendments 802.11a →802.11b → 802.11g → 802.11n

The History                     

802.11Release

Date

Freq. BandwidthData

rate per stream

AllowableModulation

Approximate indoor range

Approximate outdoor range

protocol (GHz) (MHz) (Mbit/s)[7]MIMO strea

ms(m) (ft) (m) (ft)

— Jun-97 2.4 20 1, 2 1DSSS, FHS

S20 66 100 330

a Sep-995

206, 9, 12,

18, 24, 36, 48, 54

1 OFDM35 115 120 390

3.7 — — 5,000 16,000

b Sep-99 2.4 201, 2, 5.5,

111 DSSS 35 115 140 460

g Jun-03 2.4 206, 9, 12,

18, 24, 36, 48, 54

1OFDM, DS

SS38 125 140 460

n Oct-09 2.4/5

20

7.2, 14.4, 21.7, 28.9, 43.3, 57.8,

65, 72.24

OFDM

70 230 250 820

40

15, 30, 45, 60, 90,

120, 135, 150

70 230 250 820

ac (DRAFT) Nov. 2011 5

20 up to 87.6

8

       40 up to 200        

80up to 433.3

      

           

ISM BandISM stands for industrial, scientific, and

medical.ISM bands are set aside for equipment that is

related to industrial or scientific processes or is used by medical equipment.

The ISM band is license-free, provided that devices are low-power.

The 802.11 standard is contained by the ISM band.

ISM Band

U-NII (Unlicensed National Information Infrastructure) Bands

802.11n can operate at the 5G U-NII bands:

U-NII Low (U-NII-1): 5.15-5.25 GHz(indoor use only)

U-NII Mid (U-NII-2): 5.25-5.35 GHz.

U-NII Worldwide: 5.47-5.725 GHz.

U-NII Upper (U-NII-3): 5.725 to 5.825 GHz.

2.4GHz vs. 5GHz2.4 GHz band is divided into 11 overlapping channels spaced

by 5 MHz.5GHz band is less likely to be congested. 2.4GHz is more prone to interference, commonly used.The 5GHz band offers much higher throughput with the same

channel width.

2.4GHz vs. 5GHz2.4GHz covers a substantially larger range than 5GHz.Higher frequency wireless signals of 5GHz networks do

not penetrate solid objects nearly as well as 2.4GHz.In general, the higher the frequency of a wireless signal,

the shorter its range.

2.4GHz vs. 5GHz5GHz and 2.4GHz are simply different frequencies, each with

its advantages and disadvantages. To get the best of both worlds, some recent routers have the capability for dual-band operation in both ranges simultaneously.

5GHz offers higher throughput at a shorter distance, while 2.4GHz offers increased coverage and higher solid object penetration.

Protocol Stack

Wireless LAN Networks

Wireless LAN NetworksAd-Hoc

Point-to-pointMesh

InfrastructureStar topology

WLAN Architecture—Ad Hoc Ad-Hoc mode: Peer-to-peer setup

where clients can connect to each other directly.

WLAN Architecture — Mesh Mesh: Every client in

the network also acts as an access or relay point, creating a “self-healing” and (in theory) infinitely extensible network. Not yet in

widespread use, unlikely to be implemented residentially.

Infrastructure network

Comparison of Two StructuresInfrastructure Ad

hocExpansion XFlexibility XControl XRouting XCoverage XReliability X

How does the RF propagate?

AntennasWLAN equipment usually comes with a built-

in omni-directional antenna, but some select products will let you attach secondary antennas that will significantly boost range.

AntennasAntennas come in

many shapes and styles:Omni-directional:

Vertical Whip Ceiling mount

Directional: Yagi “Pringles can” Wall mounted panel Parabolic dish

How Can Several Users Communicate Simultaneously?

There is a difference between a network designed for voice conversation and one for data exchange.For voice conversations, like telephone and cell

phone calls, each person has a dedicated channel during the entire conversation.

For data exchange, many users can share one channel. A user sends information when no one else is sending.

802.11e: QoS facilitates prioritization of data, voice, and video transmissions.

Share One Channel in Data Communication In data communication, data are grouped into

packets/frames. Each packet/frame contains a number of bits of information.

Devices (phones, computers, etc.) do not communicate simultaneously, similar to the concept of sharing a single connection (the air in this case); only one person can use it at one time.

Share One Channel in Data Communication

Send RTS packetReceive CTS packet

Send data packets Send EOB packet

Receive EOBC packetNo CTS packet

Generate random wait time Resend RTS

Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA)

Security802.11i provides security enhancements

WEP – Wired Equivalent PrivacyAdditional Security Measures

WPA – Wi-Fi Protected AccessWPA2

Questions/Comments