Signal and noise on WLAN : Signal and noise on WLAN Presented By : Arul jaga raja
yogesun
vazumuni
vijalakshmi
Submitted to: MR.RAVI SHANKER
Guided By : Dr Jerry Gao
WLAN : WLAN A wireless local area network (LAN) is a flexible data communications system implemented as an extension to, or as an alternative for, a wired LAN.
(RF) technology, wireless LANs transmit and receive data over the air.
Wireless LAN Architecture (continued) : Network+ Guide to Networks, 4e 3 Wireless LAN Architecture (continued) Figure 3-41: An infrastructure WLAN
Wireless LAN Architecture : Network+ Guide to Networks, 4e 4 Wireless LAN Architecture Figure 3-42: Wireless LAN interconnection
Wireless LAN Configuration : Ch2:5
WirelessNet
Tseng Wireless LAN Configuration
LAN/WLAN World : LAN/WLAN World LANs provide connectivity for interconnecting computing resources at the local levels of an organization
Wired LANs
Limitations because of physical, hard-wired infrastructure
Wireless LANs provide
Flexibility
Portability
Mobility
Ease of Installation
WLAN technology : WLAN technology Manufacturers of wireless LANs have a range of technologies to choose from when designing a wireless LAN solution.
Narrow band.
All band (spread spectrum).
Infrared.
Signal range covers.
Narrow Band : Ch2:8
WirelessNet
Tseng Narrow Band A narrowband radio system transmits and receives user information on a specific radio frequency.
Narrowband radio keeps the radio signal frequency as narrow as possible just to pass the information.
Efficient use of radio spectrum; save bandwidth.
ex: television, AM, FM.
Licensed: FCC
Narrowband, Broadband, and Spread Spectrum Signals : Network+ Guide to Networks, 4e 9 Narrowband, Broadband, and Spread Spectrum Signals Broadband: uses relatively wide band of wireless spectrum
Offers higher throughputs
Spread spectrum: use of multiple frequencies to transmit a signal
Frequency hopping spread spectrum (FHSS)
Direct sequence spread spectrum (DSSS)
Spectra Comparison : 10 Spectra Comparison
Forms of Radio-based Wireless LAN : Ch2:11
WirelessNet
Tseng Forms of Radio-based Wireless LAN Wireless Local Bridge
Infrastructure
Ad Hoc
Radio-Based Wireless LANs : Ch2:12
WirelessNet
Tseng Radio-Based Wireless LANs Most widely used method
Adv: penetrating walls and other obstacles with little attenuation.
Disadv: security, interference, etc.
3 approaches:
ISM band
Narrow band
Spread spectrum
IEEE 802.11a and IEEE 802.11b : IEEE 802.11a and IEEE 802.11b IEEE 802.11a
Makes use of 5-GHz band
Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps
Uses orthogonal frequency division multiplexing (OFDM)
IEEE 802.11b
802.11b operates in 2.4 GHz band
Provides data rates of 5.5 and 11 Mbps
Complementary code keying (CCK) modulation scheme
For more information: http://home.no.net/coverage/rapport/80211.htm
SPREAD SPECTRUM : SPREAD SPECTRUM
Spread Spectrum Modulation : Ch2:15
WirelessNet
Tseng Spread Spectrum Modulation Definition: “spread” a signal’s power over a wider band of frequency.
Spread Spectrum : Ch2:16
WirelessNet
Tseng Spread Spectrum Disadv: This contradicts with the goal of conserving bandwidth.
Adv: less susceptible to electrical noise (especially from narrow band sources)
In World War II, US Army uses spread spectrum to avoid hostile jamming. (invented by Hedy Lamarr, an actress)
To spread a signal, there are two ways:
direct sequence (DSSS)
frequency hopping (FHSS)
Direct Sequence Spread Spectrum (DSSS) : Ch2:17
WirelessNet
Tseng Direct Sequence Spread Spectrum (DSSS) Use bit sequence to represent “zero” and “one” (Fig. 2-5)
Also referred to as “chipping code”.
Longer chipping codes are more resilient to noise.
Minimum length = 10 (by FCC)
IEEE 802.11 uses 11 chips per data bit.
FHSS : Ch2:18
WirelessNet
Tseng FHSS Hopping Code: to determine the order of hopping frequencies
The receiver must “listen” to incoming signals at the right time at the right frequency.
FCC regulation: at least 75 frequencies, with max. dwell time 400ms.
Adv.: very resilient to noise.
Orthogonal hopping codes: a set of hopping codes that never use the same frequencies at the same time (can be on-line adjusted by software).
Allow multiple wireless LANs to co-exist.
ALL bands : ALL bands
Broadband : Broadband (BW) is an emerging wireless technology that allows simultaneous wireless delivery of voice, data, and video.
BW is considered a competing technology with Digital Subscriber Line (DSL).
BW comes in two : (LMDS) &(MMDS).
Both operate in FCC-licensed frequency bands.
Bluetooth: : Bluetooth: It’s range wireless links between mobile PCs, mobile phones, and other portable handheld devices, and connectivity to the Internet.
If Bluetooth becomes an adopted technology, current WLANs will already be migrating to the 5 GHz band.
Slide 22 :
ISM Bands : Ch2:23
WirelessNet
Tseng ISM Bands In 1985, FCC modified part 15 to stimulate the use of wireless networks.
ISM=Industrial, Scientific, and Medical
Unlicensed, you can freely install and move.
ISM Spectrum Availability : Ch2:24
WirelessNet
Tseng ISM Spectrum Availability Only 2.4 GHz is the world-accepted ISM band.
902 MHz is easier in manufacturing.
Ultra Wide Band : 25 Ultra Wide Band Very low power: 200uW
Very wide bandwidth: 3.1-10.6 GHz
First designs: strings of pulses
First standard: 802.15.3-2002
New proposals in 802.15.3a:
Xtreme Spectrum DS-CDMA
MultiBand OFDM
New Motorola DS-UWB
Slide 26 : Infrared Technology
A third technology, little used in commercial wireless LANs, is infrared.
Infrared (IR) systems use very high frequencies.
IR cannot penetrate opaque objects. is either directed (line-of-sight) or diffuse technology.
High performance directed IR is impractical for mobile.
Characteristics of infrared-based connections : Characteristics of infrared-based connections Infrared radiation can't penetrate walls. This makes it easier to build a cell based network.(office building).
Objects in an office environment have Good reflection properties(40%-90%).
No multipath fading.
weak: Multipath dispersion, security.
Infrared Transmission : Network+ Guide to Networks, 4e 28 Infrared Transmission Transmitted by frequencies in the 300-GHz to 300,000-GHz range
Most often used for communications between devices in same room
Relies on the devices being close to each other
May require line-of-sight path
Throughput rivals fiber-optics
Antennas : Network+ Guide to Networks, 4e 29 Antennas Radiation pattern describes relative strength over three-dimensional area of all electromagnetic energy the antenna sends or receives
Directional antenna issues wireless signals along a single direction
Omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions
Range: geographical area an antenna or wireless system can reach
Signal Degradation : Network+ Guide to Networks, 4e 30 Signal Degradation Fading: change in signal strength resulting from electromagnetic energy being scattered, reflected, or diffracted after being issued by transmitter
Wireless signals experience attenuation
May be amplified and repeated
Interference is significant problem for wireless communications
Atmosphere saturated with electromagnetic waves
Signal Propagation : Network+ Guide to Networks, 4e 31 Signal Propagation Figure 3-39: Multipath signal propagation
Ranges of Technologies : 32 Ranges of Technologies
References : 33 References Articles:
“A Long-Term View of Short Range Wireless”, IEEE Computer, June 2001
“Wireless Data Blaster”, Scientific American, May 2002
Primary Standards:
IEEE 802.11 series, Wi-Fi
IEEE 802.15.1-2002, Bluetooth
IEEE 802.15.2-2003, Co-existence
IEEE 802.15.3-2002, High Rate PAN
IEEE 802.15.4-2003, Low Rate PAN
IEEE 802.16-2001, Fixed Wireless Broadband
Slide 34 : Thank u all