Wireless LAN IEEE802.11 Jun Murai/Larry Landweber For KEIO Univ., Univ. Wisconsin Madison, and...
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Transcript of Wireless LAN IEEE802.11 Jun Murai/Larry Landweber For KEIO Univ., Univ. Wisconsin Madison, and...
Overview
• Wireless Technologies– Air channels controls– Access methods
• CSMA/CA
• IEEE802.11 Standards
• Future
Characteristic of the wireless air channel
• Ad-hoc and Base station model• Fading, interference and noise• Efficient use of the available spectrum• Contention to take an air channel• Contention detection, multiple access and the ‘hidden
node problem’• Multiple International regulatory requirements• Mobility• Battery usage and power management • Security
Basics on Highs Speed Wireless
• Transmit and Receive– Difference of power– Make it difficult to do them together
• Diversity technologies– Select from multiple path signals– Integrated multiple path signals
• Modulation technologies– Non-Linear
• MSK(minimum shift keying), GMSK(Gaussian Filtered)
– Linear• BPSK(Binary Phase) QPSK(Quadrature Phase)
• Spread Spectrum– Direct sequence Modulation(DS)– Frequency Hopping Modulation(FH)– Chirp Modulation
Access Technologies
• Multiple Access technology– Multiple terminals to share the air channel
• Multiplex technology– A transmitting station to merge data
• Duplex technology– Sharing between uplink and downlink
• Access Algorithm– Control method for access
Multiple Access
• For multiple terminals to share the air channels• Three dimensions to consider
– Coding, Frequency, and Time
• TDMA– Time Division Multiple Access
• FDMA– Frequency Division Multiple Access
• CDMA– Code Division Multiple Access
Multiplex Technology
• For a station to merge signals• TDM
– Time Division Multiplex
• FDM– Frequency Division Multiplex
• CDM– Code Division Multiplex
• A frame to send, a slot to receive
Duplex Technology
• For uplink and downlink to share a space
• FDD– Frequency Division Duplex
• Static allocation
• TDD– Time Division Duplex
• Flexible allocation
• Portable phones
Access Algorithm
• Who take a control and how?
• Pre-assign– Static assignment
• Demand assign– Dynamic assignment– Slot allocation on TDMA
• Random assign
Summary of Access Method• Complex combination of four methods
– Multiple Access, Multiplex, Duplex, and Access algorithm
• Example of standard cell phone:– Uplink: TDMA (or CDMA+TDMA)– Downlink: TDM (or FDM)– Duplex: TDD (or FDD)– Access: Demand assign
• Example of LAN– Multiple access: CDMA (or TDMA)
• CSMA/CA (a complex combination of above)
– Duplex: none– Access algorithm: complex Random access
CSMA/CD
• CSMA/CD– Carrier Sense, Multiple Access/Collision Detect
ion
• For wire communication• No control BEFORE transmission
– Generates collisions
• Collision Detection– How?
CSMA/CA
• CSMA/CA– Carrier Sense, Multiple Access/Collision
Avoidance
• For wireless communication
• Collision avoidance BEFORE transmission– Pre-avoidance of collision
• Why avoidance on wireless?
Collision detection on wireless
• Difference on energy/power for transmit and receive– At maximum, transmission power is a million
times larger than receiving– Very hard to detect because of this difference
• Energy often matter on wireless environment– Portable devices/terminals with batteries
Backoff
• Decrease the possibility of contention/collision
• Backoff window– Time to wait ot avoid collision
• Random backoff– Use random length of time to wait
IFS – Inter Frame Spacing
• Defined length of time for control
• To assure the control of multiple access– DIFS – Distributed Inter Frame Spacing– PIFS – Point Inter Frame Spacing– SIFS – Short Inter Frame Spacing
• DIFS (MAX) > PIFS > SIFS (MIN)
Transmitter
Receiver
Other
DataRTS
ACKCTS
DIFS
DIFS
SIFS SIFS SIFS
NAV(RTS)NAV(CTS)
Defer Access Backoff process
Contention Window
DIFS: Distributed IFSRTS: Request To SendSIFS: Short IFSCTS: Clear To Send
ACK: AcknowledgementNAV: Network Allocation VectorDCF: Distributed Coordination Function
RTS-CTS-DATA-ACK
Transmitter
Receiver
Other
Data
DIFS
DIFS
SIFS
Defer Access Backoff process
Contention Window
DIFS: Distributed IFSSIFS: Short IFS
RTS: Request To SendCTS: Clear To SendACK: Acknowledgement
DATA-ACK
ACK
Transmitter
Receiver
Other
NAV: Network Allocation VectorRTS: Request To SendCTS: Clear To SendACK: Acknowledgement
DIFS: Distributed IFSPIFS: Point IFSSIFS: Short IFS
Fragmentation
RTS
SIFS
CTS
SIFS
SIFS
ACK0
SIFS
SIFS
ACK1
SIFS
SIFS
ACK2
SIFS
NAV(CTS)NAV(RTS) NAV(Fragment0)NAV(Fragment1)
NAV(ACK0) NAV(ACK1)
Fragment0 Fragment1 Fragment2
SIFS
PIFS
DIFSBack off Window
NAV: Network Allocation VectorPCF: Point Coordination FunctionDCF: Distributed Coordination FunctionB: Beacon Frame
DCF and PCF
NAV NAV
B PCF B PCFBusyDCF DCF
Distribution System
• Used to interconnect wireless cells– multiple BSS, Basic Service Set, connected
together from an ESS, Extended Service Set– Allow mobile stations to access fixed resources
• Not part of 802.11 standard– could be bridged IEEE LANs, wireless, other
networks…– Distribution System Services are defined
802.11 wireless LAN StandardIEEE 802.11 Wireless LAN Standard
Frequency 2.4GHz 2.4GHz Infra-red(850mm~950mm)
Spread Spectrum DSSS FHSS
Baseband Modulation DBPSK DQPSK 2GFSK 1GFSK 16-PPM 4-PPM
Max bandwidth 1Mbps 2Mbps 1Mbps 2Mbps 1Mbps 2Mbps
Access Control CSMA/CA, RTS/CTS
Area(open air/office) 100~300m/20~100m 20~30m/about 5m
IEEE 802.11 Technical Term
• DBPSK: Differential Binary Phase Shift Keying• DQPSK: Differential Quadrature Phase Shift Keying• 2GFSK: 2Level Gaussian-filltered Frequency Shift Keying• 4GFSK: 4Level Gaussian-filltered Frequency Shift Keying• 16-PPM: 16 Pulse Position Modulation• 4-PPM: 4 Pulse Position Modulation• RTS/CTS: Request To Send / Clear To Send
FHSS - hopping frequency
Country/Area LowestFrequency
Highest Frequency
Regulated Frequency range
North America 2,402 2,480 2,400~2,4835
Europe 2,402 2,480 2,400~4,2835
Japan 2,473 2,495 2,471~2,497
Spain 2,417 2,473 2,445~2,475
France 2,448 2,482 2,4465~2,4835
FHSS - # of Channel
Country/Area # of ChannelsHopping Frequency
Minimum number of Channels
North America 79 75
Europe 79 20
Japan 23 --
Spain 27 20
France 35 20
EHF(m
illi-wave)SHF
(micro-wave)
VHFUHF
UHFW
ired LAN
Middle Speed 2.4GHz Range LAN
High Speed5GHz Range LAN
Very High Speed60 GHz Range LAN
4Mbps/16MbpsToken RingIEEE 802.5
10MbpsEthernet
IEEE 802.3
25/52/100MbpsATM-LAN
(ATM Forum)
100MbpsFast EthernetIEEE 802.3u
156/622 MbpsATM-LAN
(ATM Forum)
1000MbpsGigabit Ethernet
IEEE 802.3z, 802.3ab
Bandwidth
Frequency
IEEE802.111Mbps/2Mbps
IEEE802.11b5.5Mbps/11Mbps
(1)IEEE 802.11a 6/12/24Mbps
(2)HIPERLAN (ETSI BRAN)Type ½: 23.5/25Mbps
(3)WATM (ATM Forum) 25Mbps
19GHz range LAN10Mbps (ARIB)
(1) 156MbpsMMAC(Japan)
(2) 156MbpsMEDIAN (German)
300GHz
30GHz
3GHz
300MHz
1GHz
EHF: Extremely High FrequencySHF: Super High FrequencyUHF: Ultra High FrequencyVHF: Very High FrequencyWLAN : Wireless LANIEEE: Institute of Electrical EngineeringARIB: Association of Radio Industries and BusinessCCK: Complementary Code KeyingOFDM: Orthogonal Frequency Division MultiplexingHIPERLAN: High Performance Radio LANETSI: Europe Telecommunications Standards InstituteBRAN: Broadband Radio Access NetworkWATM: Wireless ATMMMAC: Multimedia Mobile Access Communication SystemsMEDIAN: Wireless Broadband CPN (Computer Premises Network)/ LAN for
Professional and Residential Multimedia ApplicationsFWA: Fixed Wireless Access
WirelessTechnical Term