Signals
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Signal and noise on WLAN
Presented By : Arul jaga raja yogesun vazumuni vijalakshmi Submitted to: MR.RAVI SHANKER
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)
Figure 3-41: An infrastructure WLAN 3
Network+ Guide to Networks, 4e
Wireless LAN Architecture
Figure 3-42: Wireless LAN interconnection 4
Network+ Guide to Networks, 4e
Wireless LAN Configuration Ch2:5 WirelessNet Tseng
LAN/WLAN World
LANs provide connectivity for interconnecting computing resources at the local levels of an organization Wired LANs
Limitations because of physical, hardwired infrastructure
Wireless LANs provide Flexibility Portability Mobility Ease of Installation
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
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
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)
9
Network+ Guide to Networks, 4e
Spectra Comparison 10
Ch2:11 WirelessNet Tseng
Forms of Radio-based Wireless LAN Wireless
Local Bridge Infrastructure Ad Hoc
Radio-Based Wireless LANs Ch2:12 WirelessNet Tseng
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 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:
SPREAD SPECTRUM
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
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)
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.
Ch2:17 WirelessNet Tseng
FHSS Ch2:18 WirelessNet Tseng
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-
ALL BANDS
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:
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.
ISM Bands Ch2:23 WirelessNet Tseng
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
Only 2.4 GHz is the world-accepted ISM band. 902 MHz is easier in manufacturing.
Ultra Wide Band 25
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
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 infraredbased 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
Transmitted by frequencies in the 300GHz 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
28
Network+ Guide to Networks, 4e
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 anNetwork+ antenna or Guide to Networks, 29 wireless system can reach 4e
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 30
Network+ Guide to Networks, 4e
Signal Propagation
Figure 3-39: Multipath signal propagation 31
Network+ Guide to Networks, 4e
Ranges of Technologies 32
References 33
Articles: “A
Long-Term View of Short Range Wireless”, IEEE Computer, June 2001 “Wireless Data Blaster”, Scientific American, May 2002
Primary Standards: IEEE IEEE IEEE IEEE IEEE IEEE
802.11 series, Wi-Fi 802.15.1-2002, Bluetooth 802.15.2-2003, Co-existence 802.15.3-2002, High Rate PAN 802.15.4-2003, Low Rate PAN 802.16-2001, Fixed Wireless Broadband
Presented By : Arul jaga raja yogesun vazumuni vijalakshmi Submitted to: MR.RAVI SHANKER
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)
Figure 3-41: An infrastructure WLAN 3
Network+ Guide to Networks, 4e
Wireless LAN Architecture
Figure 3-42: Wireless LAN interconnection 4
Network+ Guide to Networks, 4e
Wireless LAN Configuration Ch2:5 WirelessNet Tseng
LAN/WLAN World
LANs provide connectivity for interconnecting computing resources at the local levels of an organization Wired LANs
Limitations because of physical, hardwired infrastructure
Wireless LANs provide Flexibility Portability Mobility Ease of Installation
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
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
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)
9
Network+ Guide to Networks, 4e
Spectra Comparison 10
Ch2:11 WirelessNet Tseng
Forms of Radio-based Wireless LAN Wireless
Local Bridge Infrastructure Ad Hoc
Radio-Based Wireless LANs Ch2:12 WirelessNet Tseng
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 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:
SPREAD SPECTRUM
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
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)
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.
Ch2:17 WirelessNet Tseng
FHSS Ch2:18 WirelessNet Tseng
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-
ALL BANDS
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:
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.
ISM Bands Ch2:23 WirelessNet Tseng
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
Only 2.4 GHz is the world-accepted ISM band. 902 MHz is easier in manufacturing.
Ultra Wide Band 25
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
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 infraredbased 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
Transmitted by frequencies in the 300GHz 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
28
Network+ Guide to Networks, 4e
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 anNetwork+ antenna or Guide to Networks, 29 wireless system can reach 4e
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 30
Network+ Guide to Networks, 4e
Signal Propagation
Figure 3-39: Multipath signal propagation 31
Network+ Guide to Networks, 4e
Ranges of Technologies 32
References 33
Articles: “A
Long-Term View of Short Range Wireless”, IEEE Computer, June 2001 “Wireless Data Blaster”, Scientific American, May 2002
Primary Standards: IEEE IEEE IEEE IEEE IEEE IEEE
802.11 series, Wi-Fi 802.15.1-2002, Bluetooth 802.15.2-2003, Co-existence 802.15.3-2002, High Rate PAN 802.15.4-2003, Low Rate PAN 802.16-2001, Fixed Wireless Broadband
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