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