WLAN © 2005 H. H’mimyLecture 11, Slide 1SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 Southern Methodist University EETS 8315 / TC752-N Advanced Topics in Wireless Communications Spring Lecture 10: WLAN Instructor: Dr. Hossam H’mimy, Ericsson Inc. (972)

WLAN © 2005 H. H’mimyLecture 11, Slide 2SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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 © 2005 H. H’mimyLecture 11, Slide 3SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 Issues –throughput degradation:Multipath, Interference –Interoperability: with wired LAN, with Wireless Nets –Battery –scalability

WLAN © 2005 H. H’mimyLecture 11, Slide 4SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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 Wired Backbone AP BSS1

WLAN © 2005 H. H’mimyLecture 11, Slide 5SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 SGSNGGSNBSS Office ISP Home GPRS/UMTS Ethernet Internet Wireless LAN Scenarios

WLAN © 2005 H. H’mimyLecture 11, Slide 6SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 WLAN MAC –Media Access –CSMA/CA uses Distributed coordination function (DCF) –WLAN radios are half duplex,  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 © 2005 H. H’mimyLecture 11, Slide 7SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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 © 2005 H. H’mimyLecture 11, Slide 8SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 Frames types Management Frames Authentication: 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 © 2005 H. H’mimyLecture 11, Slide 9SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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 © 2005 H. H’mimyLecture 11, Slide 10SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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 © 2005 H. H’mimyLecture 11, Slide 11SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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-SS2-4GFSK, 1Mbps –2.4GHz –6dBi antennas –1W max. US AP IP AdHoc Infrastructure

WLAN © 2005 H. H’mimyLecture 11, Slide 12SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 WLAN FHSS Lowest low highest short yes Cost power consumption data rate per channel aggregate capacity range RF regulations DSSS highest low longest yes IR Lowest lowest very short no

WLAN © 2005 H. H’mimyLecture 11, Slide 13SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 WLAN IEEE –IEEE (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 © 2005 H. H’mimyLecture 11, Slide 14SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 Family of WiFi Technology Band Range channels Ch. BW Data rate Spreading Modulation b 2.4 GHz <300 feet 11 ( 3 no overlap) 22MHz 11Mbps DSSS DBPSK (1Mbps) DQPSK (2Mbps) CCK (5.5 & 11Mbps) a 5 GHz ~ 60 feet 12 ( 4 out doors)USA 20MHz 54 Mbps OFDM BPSK (6 & 9 Mbps) QPSK (12 & 18 Mbps) 16-QAM (24 & 36 Mbps) 64-QAM (48 & 54 Mbps) g 2.4 GHz ~ <300 feet 11 ( 3 no overlap) 22MHz 54 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 © 2005 H. H’mimyLecture 11, Slide 15SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 ISM 2.4G Band is 83.5MHz spectrum starting at 2.4GHz In FH 79 1MHz each In DS 11 22MHz each. –Max 3 non-overlapped DS 22 MHz channels

WLAN © 2005 H. H’mimyLecture 11, Slide 16SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 WLAN IEEE 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 © 2005 H. H’mimyLecture 11, Slide 17SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 Wi-Fi is addressing the low-latency requirements necessary for voice and video with proposed standard e, but current efforts are headed only toward improving latency with prioritization, not toward a guaranteed QoS.

WLAN © 2005 H. H’mimyLecture 11, Slide 18SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 5GHz spectrum –4 channels in 40mW IEEE( 50mw FCC) –4 channels in 200mW IEEE( 250mw FCC) –4 channels in 800mW IEEE( 1w FCC) ( outdoor)

WLAN © 2005 H. H’mimyLecture 11, Slide 19SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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 GHz, GHz)

WLAN © 2005 H. H’mimyLecture 11, Slide 20SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 Complementing Wireless Solutions Mbps Outdoor Fixed Walk Vehicle Indoor Fixed/ Desktop Walk Mobility Wideband Cellular 3G/UMTS WLAN WPAN Bluetooth GSM, IS-95, IS-136 LAN Wide Area Network (WAN) - Coverage HiperLAN/2

WLAN © 2005 H. H’mimyLecture 11, Slide 21SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 Spectrum Allocation on 5 GHz US Japan Europe Hiperlan U-NII High Speed Wireless Access Hiperlan Unlicensed 300 MHz Licensed exempt 455 MHz 100 MHz

WLAN © 2005 H. H’mimyLecture 11, Slide 22SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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 © 2005 H. H’mimyLecture 11, Slide 23SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 DLUL time MAC frame 2 ms BCHFCHSCHLCHSCHLCHRCH BCCHFCCHDLCHIBCHDCCHSBCHUDCHRACH-PRACH-UP Broadcast Control Channel Conveys AP-specific info such as AP-id Frame Control Channel Describes the exact MAC frame structure DLC Control channel Bi-directional ARQ signalling. Resource requests in uplink. inbound Control channel MAC-id transfer. Random access response... Dedicated Control Channel Conveys most RCP signalling. Set-up at association per MT. Slow Broadcast Channel Conveys wake-up and AP frequency change messages. User Data Channel Conveys user data by means of ARQ-protocol. Logical Channels Transport channels Random Access Control Channel-Partitioned Used for resource requests from certain Mts. Random Access Control Channel-UnPartitioned Used for resource requests from any MT and at assoc. Logical and Transport Channels

WLAN © 2005 H. H’mimyLecture 11, Slide 24SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 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 © 2005 H. H’mimyLecture 11, Slide 25SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 HiPerLAN/2 Physical layer 20MHz channels Link adaptation OFDM –robust against multipath –52 subcarriers including 4 pilot Modulation BPSK QPSK 16QAM 64QAM* Coding 1/2 3/4 1/2 3/4 9/16 3/4 Bit Rate 6Mbps 9Mbps 12Mbps 18Mbps 27Mbps 36Mbps 54Mbps S/P + Time Frequency * optional

WLAN © 2005 H. H’mimyLecture 11, Slide 26SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 PHY MAC RRCACFDCC RLC Convergence Layer LLC 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 © 2005 H. H’mimyLecture 11, Slide 27SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 BCCHFCCHDown-link dataUp-link dataRACH MAC frame 2 ms PHY LLC RRCACFDCC RLC Convergence Layer MAC 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 © 2005 H. H’mimyLecture 11, Slide 28SMU EE 8315 Advanced Topics in Wireless Communications - Spring’05 Cell basedPacket based ATM Segmentation and re-assembly to / from 48 bytes packets Priority mapping from IEEE 802.1p Address mapping from IEEE 802 Multicast & broadcast handling Flexible 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