wlan © 2005 h. h’mimylecture 11, slide 1smu ee 8315 advanced topics in wireless communications -...

WLAN

© 2005 H. H’mimy Lecture 11, Slide 1SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05

Southern Methodist University

EETS 8315 / TC752-N

Advanced Topics in Wireless Communications

Spring2005

http://engr.smu.edu/eets/8315

Lecture 10: WLAN

Instructor: Dr. Hossam H’mimy, Ericsson [email protected]

(972) 583-0155

WLAN


Wireless Local Area Network WLAN • What is WLAN?

– extension to wired LAN– Popular in vertical markets (health care, retail, warehouses and

university campus– IEEE802.11, OpenAir2.4– Physical and MAC layer– rates 1- 11MHz , optimized for short range limited mobility– IEEE802.x LAN, x=3 Ethernet, x=5 Token ring

WLAN


• Issues– throughput degradation:Multipath, Interference– Interoperability: with wired LAN, with Wireless Nets– Battery– scalability

WLAN


WLAN Network Topology

• Extended Service Set (ESS) “Infrastructure”– support access to wired Net resource and wireless clients– transition of data between wired and wireless is via Access Points – Basic service set consist of AP and clients– coverage determined by AP

• Independent Basic Service Set (IBSS) “AdHoc”– Mutual communication between wireless clients– does not support access to wired Net– the adhoc network is created Spontaneously– single room, sales floor,..

BSS2

BSS1

WiredBackboneAP

AP

BSS1

WLAN


SGSN GGSNBSS

Office

ISP

Home

GPRS/UMTS

Ethernet

Internet

Wireless LAN Scenarios

WLAN


WLAN • MAC

– Media Access – CSMA/CA uses Distributed coordination function (DCF)

– WLAN radios are half duplex, 802.11 cannot detect collisions .– CA require the radio to listen before talking, then ACKed

– Priority based Access: uses Point coordination function (PCF) (optional) Used for Video and audio, with higher OH

– DCF and PCF can operate concurrently in same BSS

– Association : establish the wireless link between clients and AP (call set up with AP)

– Re-association: when the client moves from a basic service set (BSS) “cell” i.e. HO and roaming

WLAN


WLAN • MAC

– Authentication: provide a client with an ID – open system I.e any client can associate with any AP– Shared Key I.e. the clients having the key of specific AP can

associate to them only. (Wired Equivalent privacy WEP)– Privacy: WEP option encrypt the data before sent on air using

40bit encryption algorithm– Power Management 2 modes

– Active client powered up to transmit/receive– Power save no TX or RX

WLAN


Frames types

Management FramesAuthentication: A client asks an AP to be autt (open system or shared key)Deauthentication: A client or AP sends notice that it wishes to eauthenticate and end

communication. Association Request: A client asks an AP to be associated.Association Response: After an association request is received, the AP will respond with

an approval or denial of the request.Reassociation Request: When a client roams from one AP to another, it will send a

reassociation request to the new AP. This tells the new AP that it may need to communicate with the old AP to pick up any buffered packets, etc.

Reassociation Response: Same as an association response frame, except that it is in response to a reassociation request.

Disassociation: A client or AP sends notice that it wishes to disassociate and end communication. Disassociation cannot be refused.

Beacon: for synchronization purposes, announces the existence of the AP.Probe Request: client’s request for info in order to synchronize with an AP.Probe Response: AP responce with synchronization details

WLAN


Frames types ..

Control Frames

Request to Send (RTS)— A client asks an AP for permission to send data. This is a traffic management feature designed to help reduce collisions.

Clear to Send (CTS)— After an RTS is received, the AP will respond with a CTS frame indicating it is ready to receive data.

Acknowledgement (ACK): After a client or AP receives an error-free frame, it sends an ACK frame to the sender

Data Frames

Data frames contain the actual data traffic. Data can be WEP encrypted or plain text.

WLAN


WLAN • Physical

– PLCP: Phys. Layer Convergence Procedure– Maps the MAC data into frames suitable for PMD– PLCP for DSSS, FH, IR

– PMD: Phys. Medium Dependent– provides Mod, dmod– PMD for DSSS, FH, IR

– Operation ( carrier sense, Transmit, Receive)

MAC

PLCP

PMD

WLAN


WLAN • Physical layer (1,2Mbps)

– Diffused (refracted) IR (Baseband), 1-2m, limited to rooms– 2W, 4,16PPM, 1,2Mbps,

– DS-SS DQPSK 1,2 Mbps– FH-SS 2-4GFSK, 1Mbps

– 2.4GHz– 6dBi antennas– 1W max. US AP

IP

AdHoc Infrastructure

WLAN


WLAN

FHSS

Lowest

Lowest

low

highest

short

yes

Cost

power consumption

data rate per channel

aggregate capacity

range

RF regulations

DSSS

highest

highest

highest

low

longest

yes

IR

Lowest

Lowest

lowest

lowest

very short

no

WLAN


WLAN • IEEE802.11

– IEEE802.11 (FHSS) at 2.4GHZ– 79 Hops– channel is 1MHz

– IEEE802.11b ( WiFi) (DSSS) at 2.4GHz– 11 channels US, 4 Spain, 1 Japan, 14 Europe, 4 France– channel is 10MHz (1,2,5.5, 11 MHz)– select channels with 30MHz separation

– IEEE802.11a (WiFi) (OFDM) at 5GHz

WLAN


Family of WiFi

Technology

BandRangechannelsCh. BWData rate

Spreading

Modulation

802.11b

2.4 GHz<300 feet11 ( 3 no overlap) 22MHz11Mbps

DSSS

DBPSK (1Mbps)DQPSK (2Mbps)CCK (5.5 & 11Mbps)

802.11a

5 GHz~ 60 feet12 ( 4 out doors)USA20MHz54 Mbps

OFDM

BPSK (6 & 9 Mbps)QPSK (12 & 18 Mbps)16-QAM (24 & 36 Mbps)64-QAM (48 & 54 Mbps)

802.11g

2.4 GHz~ <300 feet11 ( 3 no overlap)22MHz54 Mbps

OFDM

DBPSK (1 Mbps)DQPSK (2 Mbps)CCK (5.5 & 11 Mbps)OFDM (6,12,18,36,48,54 Mbps)

CCK: complementary Code Keying

WLAN


• ISM 2.4G Band is 83.5MHz spectrum starting at 2.4GHz• In FH 79 channels @ 1MHz each• In DS 11 channels @ 22MHz each.

– Max 3 non-overlapped DS 22 MHz channels

WLAN


WLAN• IEEE802.11 supports the mobility types

– No Transition

– BSS Transition: Terminal moves between BSSs of same ESS

– ESS Transition: Terminal moves between BSSs of different ESSs

• TCP/IP over WLAN– High overhead

– Inability to adjust under marginal conditions “ Fading, RF ..”(TCP Time out)

– Difficult to deal with Mobile node addresses

– for network with small number of terminals use MIDDLEWARE

WLAN


• Wi-Fi is addressing the low-latency requirements necessary for voice and video with proposed standard 802.11e, but current efforts are headed only toward improving latency with prioritization, not toward a guaranteed QoS.

WLAN


• 5GHz spectrum– 4 channels in 5.15-5.25GHz @ 40mW IEEE( 50mw FCC)– 4 channels in 5.25-5.35GHz @ 200mW IEEE( 250mw FCC)– 4 channels in 5.725-5.825GHz @ 800mW IEEE( 1w FCC)

( outdoor)

WLAN


What is HiperLAN/2

• The next and 3rd generation of Wireless LAN technology

• High Performance Radio Local Area Network Type 2

• Standard is being developed ERSI-BRAN

• HiperLAN/2 is the next generation of Wireless LAN

• Operates in the 5 GHz ISM band with dedicated spectrum

• Broadband communication, up to 54 Mbps at Radio I/F

• Connection-oriented protocol with QoS support• HiperLAN/2 Global forum (H2GF)

– Marketing– interoperability– regularity ( harmonize Spectrum 300MHz 5.15-5.35GHz, 5.725-5.825GHz)

WLAN


Complementing Wireless Solutions

Mbps1 10 1000.1

Out

door

Fixed

Walk

Vehicle

Indo

or

Fixed/Desktop

Walk

Mobility

Wideband Cellular

3G/UMTS WLAN

WPANBluetooth

GS

M, I

S-9

5, I

S-1

36

LAN

Wide Area Network (WAN)- Coverage

HiperLAN/2HiperLAN/2

WLAN


Spectrum Allocation on 5 GHz

US

Japan

Europe

Hiperlan

U-NII U-NII

5200 5400 5600 58005100 5300 5500 5700

High Speed Wireless Access

5.15 - 5.35

5.15 - 5.35 5.725 -5.825

5.470 - 5.725Hiperlan

5.15 - 5.25

Unlicensed

300 MHz

Licensed exempt

455 MHz

100 MHz

WLAN


Radio Network Functions

• HiperLAN/2 support number of radio network functions.

– Dynamic Frequency Selection: this allows several operators to

share available frequency spectrum

– Link Adaptation: optimize throughput WRT (C/I)

– Antennas: multi beam antennas are supported

– Handover: scheme is initiated by the MT

– Power Control: Transmitter power control is supported in both MT

and AP.

WLAN


HiPerLAN/2 Reference Model• MAC

– Dynamic TDMA/TDD with Centralized scheduling– AP or CC allocate resources

• RRC– radio resource control

• RLC• ACF Associated control function • DDC DLC connection control

PHY

LLC

MAC

Convergence layer CL

RRC, ACF, DCC, RLC

TCP/IP

WLAN


HiPerLAN/2 Physical layer• 20MHz channels• Link adaptation • OFDM

– robust against multipath– 52 subcarriers including 4 pilot

ModulationBPSKBPSKQPSKQPSK

16QAM16QAM64QAM*

Coding1/23/41/23/4

9/163/43/4

Bit Rate6Mbps9Mbps

12Mbps18Mbps27Mbps36Mbps54Mbps

S/P +

Time Frequency

* optional

WLAN


PHY

MAC

RRC ACF DCC

RLC

Convergence Layer

LLCLLC

Link adaptation based on the link quality

Logical Link Control• Link Adaptation

- dynamically selects phy mode for optimal transmission

• ARQ– Selective repeat– Discarding capability

– efficient for real time applications

• Short MAC frame allows re-transmission even for voice (2 ms)

C/I

Mb/

s

WLAN


BCCH FCCH Down-link data Up-link data RACH

MAC frame 2 ms

PHY

LLCRRC ACF DCC

RLC

Convergence Layer

MACMAC

Medium Access Control

• TDD/TDMA

• Dynamic allocation of uplink and downlink resources - no fixed slot structure

• Centralized scheduling– Considers QoS and link adaptation modes

• Peer-to-peer and multicast

WLAN


Cell based Packet based

ATM

Segmentation and re-assembly to / from 48 bytes packets Priority mapping from IEEE 802.1pAddress mapping from IEEE 802Multicast & broadcast handlingFlexible amount of QoS classes

PPP Ethernet

Convergence Layer

• 2 types of CL: Cell and Packet

• Multiple convergence layers

• One single convergence layer active at a time

• Mapping between higher layer connections/priorities and DLC connections/priorities

UMTS

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