Mobile Communications Chapter 7: Wireless LANs

Transcription

1 Mobile Communicaion Technology according o IEEE Local wireless neworks WLAN WiFi a h i/e/ /w b g Mobile Communicaions Chaper 7: Wireless LANs Characerisics IEEE PHY MAC Roaming.11a, b, g, h, i Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Personal wireless nw WPAN Wireless disribuion neworks WMAN (Broadband Wireless Access) + Mobiliy ZigBee Blueooh a/b WiMAX (Mobile Broadband Wireless Access) Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS a/b Characerisics of wireless LANs Advanages very flexible wihin he recepion area Ad-hoc neworks wihou previous planning possible (almos) no wiring difficulies (e.g. hisoric buildings, firewalls) more robus agains disasers like, e.g., earhquakes, fire - or users pulling a plug... Disadvanages ypically very low bandwidh compared o wired neworks (1-10 Mbi/s) due o shared medium many proprieary soluions, especially for higher bi-raes, sandards ake heir ime (e.g. IEEE ) producs have o follow many naional resricions if working wireless, i akes a vary long ime o esablish global soluions like, e.g., IMT-2000 Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Design goals for wireless LANs global, seamless operaion low power for baery use no special permissions or licenses needed o use he LAN robus ransmission echnology simplified sponaneous cooperaion a meeings easy o use for everyone, simple managemen proecion of invesmen in wired neworks securiy (no one should be able o read my daa), privacy (no one should be able o collec user profiles), safey (low radiaion) ransparency concerning applicaions and higher layer proocols, bu also locaion awareness if necessary Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS05 7.4

2 Comparison: infrared vs. radio ransmission Comparison: infrasrucure vs. ad-hoc neworks Infrared uses IR diodes, diffuse ligh, muliple reflecions (walls, furniure ec.) Advanages simple, cheap, available in many mobile devices no licenses needed simple shielding possible Disadvanages inerference by sunligh, hea sources ec. many hings shield or absorb IR ligh low bandwidh Example IrDA (Infrared Daa Associaion) inerface available everywhere ypically using he license free ISM band a 2.4 GHz Advanages experience from wireless WAN and mobile phones can be used coverage of larger areas possible (radio can penerae walls, furniure ec.) Disadvanages very limied license free frequency bands shielding more difficul, inerference wih oher elecrical devices Example Many differen producs infrasrucure nework AP ad-hoc nework AP wired nework AP: Access Poin AP Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Archiecure of an infrasrucure nework Archiecure of an ad-hoc nework STA 1 ESS LAN BSS 1 Access Poin BSS 2 Poral Disribuion Sysem Access Poin 802.x LAN Saion (STA) erminal wih access mechanisms o he wireless medium and radio conac o he access poin Basic Service Se (BSS) group of saions using he same radio frequency Access Poin saion inegraed ino he wireless LAN and he disribuion sysem Poral bridge o oher (wired) neworks Disribuion Sysem STA LAN IBSS 1 STA 2 IBSS 2 STA 3 Direc communicaion wihin a limied range Saion (STA): erminal wih access mechanisms o he wireless medium Independen Basic Service Se (IBSS): group of saions using he same radio frequency STA LAN STA 3 inerconnecion nework o form one logical nework (EES: Exended Service Se) based on several BSS STA LAN STA 5 Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS05 7.8

3 IEEE sandard Access Rouer wih Wireless Access Poin and Wireless NICs mobile erminal fixed erminal applicaion TCP IP LLC MAC PHY MAC PHY access poin LLC MAC PHY infrasrucure nework applicaion TCP MAC PHY Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS IP LLC Access Rouer wih Access Poin USB WNIC PC Card WNIC for a Noebook Compuer Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Inernal WNIC For Deskop PC 10 Anennas used in WLANs Layers and funcions Omni direcional anennas Transmi in all direcions simulaneously Used on mos WLANs Dipole anenna (rubber duck) Transmis in all direcion (verical, horizonal, up, down) Direcional anennas Projec signal only in one direcion Focused area; sronger signal; farher ranges Mos ofen used on inside of an exerior wall To reduce he securiy issue A poenial problem wih WLANs MAC access mechanisms, fragmenaion, encrypion MAC Managemen synchronizaion, roaming, MIB, power managemen PHY DLC LLC MAC PLCP PMD MAC Managemen PHY Managemen PLCP Physical Layer Convergence Proocol clear channel assessmen signal (carrier sense) PMD Physical Medium Dependen modulaion, coding PHY Managemen channel selecion, MIB Saion Managemen coordinaion of all managemen funcions Saion Managemen Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

4 Physical layer (classical) FHSS PHY packe forma 3 versions: 2 radio (yp. 2.4 GHz), 1 IR daa raes 1 or 2 Mbi/s FHSS (Frequency Hopping Spread Specrum) spreading, despreading, signal srengh, yp. 1 Mbi/s min. 2.5 frequency hops/s (USA), wo-level GFSK modulaion DSSS (Direc Sequence Spread Specrum) DBPSK modulaion for 1 Mbi/s (Differenial Binary Phase Shif Keying), DQPSK for 2 Mbi/s (Differenial Quadraure PSK) preamble and header of a frame is always ransmied wih 1 Mbi/s, res of ransmission 1 or 2 Mbi/s chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code) max. radiaed power 1 W (USA), 100 mw (EU), min. 1mW Infrared nm, diffuse ligh, yp. 10 m range carrier deecion, energy deecion, synchronizaion Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Synchronizaion synch wih paern SFD (Sar Frame Delimier) sar paern PLW (PLCP_PDU Lengh Word) lengh of payload incl. 32 bi CRC of payload, PLW < 4096 PSF (PLCP Signaling Field) daa of payload (1 or 2 Mbi/s) HEC (Header Error Check) CRC wih x 16 +x 12 +x variable bis synchronizaion SFD PLW PSF HEC payload PLCP preamble PLCP header Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Synchronizaion DSSS PHY packe forma synch., gain seing, energy deecion, frequency offse compensaion SFD (Sar Frame Delimier) Signal Service daa rae of he payload (0A: 1 Mbi/s DBPSK; 14: 2 Mbi/s DQPSK) fuure use, 00: complian HEC (Header Error Check) variable bis synchronizaion SFD signal service lengh HEC payload PLCP preamble PLCP header Lengh proecion of signal, service and lengh, x 16 +x 12 +x 5 +1 lengh of he payload Traffic services MAC layer I - DFWMAC Asynchronous Daa Service (mandaory) exchange of daa packes based on bes-effor suppor of broadcas and mulicas Time-Bounded Service (opional) implemened using PCF (Poin Coordinaion Funcion) Access mehods DFWMAC-DCF CSMA/CA (mandaory) collision avoidance via randomized back-off mechanism minimum disance beween consecuive packes ACK packe for acknowledgemens (no for broadcass) DFWMAC-DCF w/ RTS/CTS (opional) Disribued Foundaion Wireless MAC avoids hidden erminal problem DFWMAC- PCF (opional) access poin polls erminals according o a lis Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

5 CSMA/CA How WiFi Works The Problem Ack Packe 1/3 access 1/10 access o channel Packe 1. Collisions are common and cosly 2. AP doesn ge more access o channel 3. More devices mean more collisions 4. Only AP is wired wai Reransmission random backoff Figure 6.6 Schemaics of Carrier Sense Muliple Access wih Collision Avoidance (CSMA/CA) Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS WLAN Media Access Conrol Disribued Coordinaion Funcion Uses CSMA/CA CA collision avoidance A saion wais unil anoher saion is finished ransmiing plus an addiional random period of ime before sending anyhing May use wo MAC echniques simulaneously Disribued Coordinaion Funcion (DCF) Also called Physical Carrier Sense Mehod Poin Coordinaion Funcion (PCF) Also called Virual Carrier Sense Mehod Opional: (can be se as always, never, or jus for cerain frame sizes Relies on he abiliy of compuers o physically lisen before hey ransmi When a node wans o send a message: Firs lisens o make sure ha he ransmiing node has finished, hen Wais a period of ime longer Each frame is sen using sop-and-wai ARQ By waiing, he lisening node can deec ha he sending node has finished and Can hen begin sending is ransmission ACK/NAK sen a shor ime afer a frame is received, Message frames are sen a somewha longer ime afer (ensuring ha no collision will occur) Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

6 Poin Coordinaion Funcion Solves Hidden Node problem Two compuers can no deec each oher s signals A compuer is near he ransmission limis of he AP a one end and anoher compuer is near he ransmission limis a he oher end of he AP s range Physical carrier sense mehod will no work Soluion Firs send a Reques To Send (RTS) signal o he AP Reques o reserve he circui and duraion AP responds wih a Clear To Send (CTS) signal, Also indicaes duraion ha he channel is reserved Compuer wishing o send begins ransmiing Prioriies MAC layer II defined hrough differen iner frame spaces no guaraneed, hard prioriies (Shor Iner Frame Spacing) highes prioriy, for ACK, CTS, polling response PIFS (PCF IFS) medium prioriy, for ime-bounded service using PCF (DCF, Disribued Coordinaion Funcion IFS) lowes prioriy, for asynchronous daa service medium busy PIFS conenion nex frame direc access if medium is free Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS CSMA/CA access mehod I compeing saions - simple version conenion window (randomized back-off mechanism) saion 1 bo e bo r bo e bo r bo e busy medium busy nex frame saion 2 bo e busy direc access if medium is free slo ime saion 3 busy saion ready o send sars sensing he medium (Carrier Sense based on CCA, Clear Channel Assessmen) saion 4 bo e busy bo e bo r if he medium is free for he duraion of an Iner-Frame Space (IFS), he saion can sar sending (IFS depends on service ype) if he medium is busy, he saion has o wai for a free IFS, hen he saion mus addiionally wai a random back-off ime (collision avoidance, muliple of slo-ime) if anoher saion occupies he medium during he back-off ime of he saion, he back-off imer sops (fairness) saion 5 busy bo e bo r bo e busy bo e bo r medium no idle (frame, ack ec.) bo e elapsed backoff ime packe arrival a MAC bo r residual backoff ime Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

7 CSMA/CA access mehod II DFWMAC Sending unicas packes sender receiver oher saions saion has o wai for before sending daa receivers acknowledge a once (afer waiing for ) if he packe was received correcly (CRC) auomaic reransmission of daa packes in case of ransmission errors daa waiing ime ACK conenion daa Sending unicas packes sender receiver oher saions saion can send RTS wih reservaion parameer afer waiing for (reservaion deermines amoun of ime he daa packe needs he medium) acknowledgemen via CTS afer by receiver (if ready o receive) sender can now send daa a once, acknowledgemen via ACK oher saions sore medium reservaions disribued via RTS and CTS RTS CTS daa NAV (RTS) NAV (CTS) defer access ACK conenion daa Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Fragmenaion DFWMAC-PCF I sender receiver oher saions RTS CTS frag 1 NAV (RTS) NAV (CTS) ACK 1 frag 2 ACK 2 NAV (frag 1 ) NAV (ACK 1 ) conenion daa poin coordinaor wireless saions saions NAV 0 medium busy 1 PIFS D 1 SuperFrame D 2 U 1 NAV U 2 Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

8 DFWMAC-PCF II Frame forma poin coordinaor wireless saions saions NAV D 3 PIFS D 4 NAV conenion free period U 4 CF end conenion period Types conrol frames, managemen frames, daa frames Sequence numbers imporan agains duplicaed frames due o los ACKs Addresses receiver, ransmier (physical), BSS idenifier, sender (logical) Miscellaneous byes sending ime, checksum, frame conrol, daa Duraion/ Address Address Address Sequence ID Conrol Frame Conrol Proocol version To Type Subype DS More Frag Power More Rery Mgm Daa Address Daa 4 bis From DS WEP Order CRC Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS MAC address forma Special Frames: ACK, RTS, CTS scenario o DS from address 1 address 2 address 3 address 4 DS ad-hoc nework 0 0 DA SA BSSID - infrasrucure 0 1 DA BSSID SA - nework, from AP infrasrucure 1 0 BSSID SA DA - nework, o AP infrasrucure nework, wihin DS 1 1 RA TA DA SA Acknowledgemen Reques To Send ACK RTS byes Frame Duraion Receiver CRC Conrol Address byes Frame Duraion Receiver Transmier CRC Conrol Address Address DS: Disribuion Sysem AP: Access Poin DA: Desinaion Address SA: Source Address BSSID: Basic Service Se Idenifier RA: Receiver Address TA: Transmier Address Clear To Send CTS byes Frame Duraion Receiver CRC Conrol Address Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

9 MAC managemen Synchronizaion using a Beacon (infrasrucure) Synchronizaion beacon inerval ry o find a LAN, ry o say wihin a LAN imer ec. Power managemen sleep-mode wihou missing a message periodic sleep, frame buffering, raffic measuremens access poin B B B B Associaion/Reassociaion inegraion ino a LAN roaming, i.e. change neworks by changing access poins scanning, i.e. acive search for a nework MIB - Managemen Informaion Base managing, read, wrie medium busy busy busy busy value of he imesamp B beacon frame Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Synchronizaion using a Beacon (ad-hoc) Roaming saion 1 beacon inerval B 1 B 1 saion 2 B 2 B 2 medium busy busy busy busy value of he imesamp B beacon frame random delay No or bad connecion? Then perform: Scanning scan he environmen, i.e., lisen ino he medium for beacon signals or send probes ino he medium and wai for an answer Reassociaion Reques saion sends a reques o one or several AP(s) Reassociaion Response success: AP has answered, saion can now paricipae failure: coninue scanning AP acceps Reassociaion Reques signal he new saion o he disribuion sysem he disribuion sysem updaes is daa base (i.e., locaion informaion) ypically, he disribuion sysem now informs he old AP so i can release resources Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

10 WLAN: IEEE b Daa rae 1, 2, 5.5, 11 Mbi/s, depending on SNR User daa rae max. approx. 6 Mbi/s Transmission range 300m oudoor, 30m indoor Max. daa rae ~10m indoor Frequency Free 2.4 GHz ISM-band Securiy Limied, WEP insecure, SSID Availabiliy Many producs, many vendors Connecion se-up ime Connecionless/always on Qualiy of Service Typ. Bes effor, no guaranees (unless polling is used, limied suppor in producs) Manageabiliy Limied (no auomaed key disribuion, sym. Encrypion) Special Advanages/Disadvanages Advanage: many insalled sysems, lo of experience, available worldwide, free ISM-band, many vendors, inegraed in lapops, simple sysem Disadvanage: heavy inerference on ISM-band, no service guaranees, slow relaive speed only IEEE b PHY frame formas Long PLCP PPDU forma variable bis synchronizaion SFD signal service lengh HEC payload PLCP preamble Shor PLCP PPDU forma (opional) PLCP header 192 µs a 1 Mbi/s DBPSK 1, 2, 5.5 or 11 Mbi/s variable bis shor synch. SFD signal service lengh HEC payload PLCP preamble (1 Mbi/s, DBPSK) PLCP header (2 Mbi/s, DQPSK) 96 µs 2, 5.5 or 11 Mbi/s Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS b b (Con d) 5 MHz 2 Mbps Channel Cener Frequency (GHz) The b sandard defines a oal of 14 frequency channels. FCC allows channels 1 hrough 11 wihin he U.S. Mos of Europe can use channels 1 hrough 13. In Japan, only 1 choice: channel 14. Access Poin Mbps 11 Mbps Channel represens a cener frequency. Only 5 MHz separaion beween cener frequencies of channels. 3 Neighboring AP s use differen channels o reduce inerference. Reuse cluser size is equal o 3. Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

11 Channel selecion (non-overlapping) Wi-Fi basics Europe (ETSI) channel 1 channel 7 channel There are 3 channels (Ch 1, 6, 11) MHz [MHz] US (FCC)/Canada (IC) channel 1 channel 6 channel Mbps 1 1Mbps MHz [MHz] Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS IEEE b IEEE a Sandard approved Max Daa Rae Modulaion Frequency Mbps DSSS + CCK 2.4 GHz b grealy improved speed while mainaining compaibiliy wih b producs received mainsream recogniion as he firs wireless producs wih accepable speeds, affordable prices, and universal compaibiliy. More han 95% of odays WLAN infrasrucure includes b producs. Sandard approved Max Daa Rae Modulaion Frequency Mbps OFDM 5.2 GHz a grealy increased speed, bu decreased range. Even hough he a sandard was adoped in 1999, he firs a producs were no available unil lae a had a limied marke response because of is incompaibiliy wih b, shorer range, and higher coss. Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

12 IEEE g Wha is CCK? Sandard approved Max Daa Rae Modulaion Frequency Mbps (108 Mbps*) OFDM + CCK 5.2 GHz Complemenary Code Checking Was incorporaed ino DSSS beginning wih b o increase efficiency. CCK is a single carrier sysem, meaning ha all daa is ransmied by modulaing a single radio frequency or carrier g increased speed and range while mainaining compaibiliy wih b. Even hough g was no officially approved by IEEE unil June 2003, producs conforming o he draf were made available in lae Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS OFDM in IEEE a (and 11g) Range Comparison OFDM wih 52 used subcarriers (64 in oal) Daa is spli up among several closely spaced subcarriers or frequencies, increasing reliabiliy and speed (plus 12 virual subcarriers) khz spacingpilo khz channel cener frequency subcarrier number Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

13 Exising WLAN Sandards Wha Is Being Proposed for n? Sandard Approved Available Bandwidh Frequency Band of Operaion # Non-Overlapping Channels (US) Daa Rae per Channel b Sep MHz 2.4 GHz Mbps a Sep MHz 5 GHz Mbps g June MHz 2.4 GHz Mbps n? 83.5/580 MHz 2.4/5 GHz 3/ Mbps Main Feaures PHY MIMO-OFDM Beamforming Spaial Muliplexing Exended bandwidh (40MHz) Advanced coding MAC Aggregaion Block ACK Coexisence Power saving Modulaion Type DSSS, CCK OFDM DSSS, CCK, OFDM DSSS, CCK, OFDM, MIMO Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Wireless Fundamenals I Wireless Fundamenals II In order o successfully decode daa, signal srengh needs o be greaer han noise + inerference by a cerain amoun Higher daa raes require higher SINR (Signal o Noise and Inerference Raio) Signal srengh decreases wih increased range in a wireless environmen Throughpu 60 Daa Rae 1 50 Daa Rae Range Ways o increase daa rae: Convenional single x and rx radio sysems Increase ransmi power Subjec o power amplifier and regulaory limis Increases inerference o oher devices Reduces baery life Use high gain direcional anennas Fixed direcion(s) limi coverage o given secor(s) Use more frequency specrum Subjec o FCC / regulaory domain consrains Advanced MIMO: Use muliple x and / or rx radios! Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

14 Convenional (SISO) Wireless Sysems MIMO Wireless Sysems TX channel Convenional Single Inpu Single Oupu (SISO) sysems were favored for simpliciy and low-cos bu have some shorcomings: Ouage occurs if anennas fall ino null Swiching beween differen anennas can help Energy is wased by sending in all direcions Can cause addiional inerference o ohers Sensiive o inerference from all direcions Oupu power limied by single power amplifier RX TX D S P channel Muliple Inpu Muliple Oupu (MIMO) sysems wih muliple parallel radios improve he following: Ouages reduced by using informaion from muliple anennas Transmi power can be increased via muliple power amplifiers Higher hroughpus possible Transmi and receive inerference limied by some echniques D S P RX Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS MIMO Alernaives There are wo basic ypes of MIMO echnology: Beamforming MIMO Sandards-compaible echniques o improve he range of exising daa raes using ransmi and receive beamforming Also reduces ransmi inerference and improves receive inerference olerance Spaial-muliplexing MIMO Allows even higher daa raes by ransmiing parallel daa sreams in he same frequency specrum Fundamenally changes he on-air forma of signals Requires new sandard (11n) for sandards-based operaion Proprieary modes possible bu canno help legacy devices Beamforming MIMO Overview Consiss of wo pars o make sandard signals beer Uses muliple ransmi and/or receive radios o form coheren a/b/g compaible signals Receive beamforming / combining booss recepion of sandard signals Phased array ransmi beamforming o focus energy o each receiver TX TX D S P D S P RX RX Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

15 Benefis of Beamforming Mulipah Miigaion Benefis Power gain (applicable only o ransmi beamforming) Power from muliple PA s simulaneously (up o regulaory limis) Relaxes PA requiremens, increases oal oupu power delivered Array gain: dynamic high-gain anenna Inerference reducion Reduce co-channel iner-cell inerference Diversiy gain: combas fading effecs Mulipah miigaion Per- subcarrier beamforming o reduce specral nulls Muliple ransmi and receive radios allow compensaion of noches on one channel by nonnoches in he oher Same performance gains wih eiher muliple x or rx radios and greaer gains wih boh muliple x and rx radios Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Spaial Muliplexing MIMO Concep Spaial Muliplexing MIMO Difficulies TX Bi Spli Bi Merge RX TX Bi Spli Bi Merge RX Garbage Spaial muliplexing concep: Form muliple independen links (on same channel) beween ransmier and receiver o communicae a higher oal daa raes Spaial muliplexing concep: Form muliple independen links (on same channel) beween ransmier and receiver o communicae a higher oal daa raes However, here are cross-pahs beween anennas The correlaion mus be decoupled by digial signal processing algorihms Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS

16 WLAN: IEEE fuure developmens (03/2005) c: Bridge Suppor Definiion of MAC procedures o suppor bridges as exension o 802.1D d: Regulaory Domain Updae Suppor of addiional regulaions relaed o channel selecion, hopping sequences e: MAC Enhancemens QoS Enhance he curren MAC o expand suppor for applicaions wih Qualiy of Service requiremens, and in he capabiliies and efficiency of he proocol Definiion of a daa flow ( connecion ) wih parameers like rae, burs, period Addiional energy saving mechanisms and more efficien reransmission f: Iner-Access Poin Proocol Esablish an Iner-Access Poin Proocol for daa exchange via he disribuion sysem Currenly unclear o which exend manufacurers will follow his suggesion g: Daa Raes > 20 Mbi/s a 2.4 GHz; 54 Mbi/s, OFDM Successful successor of b, performance loss during mixed operaion wih 11b h: Specrum Managed a Exension for operaion of a in Europe by mechanisms like channel measuremen for dynamic channel selecion (DFS, Dynamic Frequency Selecion) and power conrol (TPC, Transmi Power Conrol) WLAN: IEEE fuure developmens (03/2005) i: Enhanced Securiy Mechanisms Enhance he curren MAC o provide improvemens in securiy. TKIP enhances he insecure WEP, bu remains compaible o older WEP sysems AES provides a secure encrypion mehod and is based on new hardware j: Exensions for operaions in Japan Changes of a for operaion a 5GHz in Japan using only half he channel widh a larger range k: Mehods for channel measuremens Devices and access poins should be able o esimae channel qualiy in order o be able o choose a beer access poin of channel m: Updaes of he sandards n: Higher daa raes above 100Mbi/s Changes of PHY and MAC wih he goal of 100Mbi/s a MAC SAP MIMO anennas (Muliple Inpu Muliple Oupu), up o 600Mbi/s are currenly feasible However, sill a large overhead due o proocol headers and inefficien mechanisms p: Iner car communicaions Communicaion beween cars/road side and cars/cars Planned for relaive speeds of min. 200km/h and ranges over 1000m Usage of GHz band in Norh America Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS WLAN: IEEE fuure developmens (03/2005) r: Faser Handover beween BSS Secure, fas handover of a saion from one AP o anoher wihin an ESS Curren mechanisms (even newer sandards like i) plus incompaible devices from differen vendors are massive problems for he use of, e.g., VoIP in WLANs Handover should be feasible wihin 50ms in order o suppor mulimedia applicaions efficienly s: Mesh Neworking Design of a self-configuring Wireless Disribuion Sysem (WDS) based on Suppor of poin-o-poin and broadcas communicaion across several hops : Performance evaluaion of neworks Sandardizaion of performance measuremen schemes u: Inerworking wih addiional exernal neworks v: Nework managemen Exensions of curren managemen funcions, channel measuremens Definiion of a unified inerface w: Securing of nework conrol Classical sandards like , bu also i proec only daa frames, no he conrol frames. Thus, his sandard should exend i in a way ha, e.g., no conrol frames can be forged. Noe: No all sandards will end in producs, many ideas ge suck a working group level Info: 802wirelessworld.com, sandards.ieee.org/geieee802/ Prof. Dr.-Ing. Jochen Schiller, hp:// MC SS