Mobile Communications Chapter 5: Wireless local area networks

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1 Mobile Communications Chapter 5: Wireless local area networks Holger Karl Computer Networks Group Universität Paderborn

2 Goals of this chapter Look at two most prominent examples of local, non-cellular networks: Wireless LAN and wireless personal area networks System perspective: consider all relevant layers and their interactions Details of specific standards, as opposed to generic principles covered in earlier chapters Provide general context and new standard developments System concepts like radio frequency identifiers (RF-ID) Metro-area networks like IEEE /WiMax WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 2

3 Overview WLAN overview IEEE family WPAN: Bluetooth RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 3

4 Mobile Communication according to IEEE Local wireless networks WLAN WiFi a h i/e/n/ /w b g Personal wireless nw WPAN ZigBee Bluetooth a/b a/b Wireless distribution networks WMAN (Broadband Wireless Access) + Mobility WiMAX (Mobile Broadband Wireless Access) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 4

5 Some remarks on IEEE standards for mobile communication IEEE : Broadband Wireless Access / WirelessMAN / WiMax Wireless distribution system, e.g., for the last mile, alternative to DSL 75 Mbit/s up to 50 km LOS, up to 10 km NLOS; 2-66 GHz band Initial standards without roaming or mobility support e adds mobility support, allows for roaming at 150 km/h Unclear relation to , started as fixed system IEEE : Mobile Broadband Wireless Access (MBWA) Licensed bands < 3.5 GHz, optimized for IP traffic Peak rate > 1 Mbit/s per user Different mobility classes up to 250 km/h and ranges up to 15 km IEEE : Media Independent Handover Interoperability Standardize handover between different 802.x and/or non 802 networks IEEE : Wireless Regional Area Networks (WRAN) Radio-based PHY/MAC for use by license-exempt devices on a noninterfering basis in spectrum that is allocated to the TV Broadcast Service WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 5

6 Characteristics of wireless LANs Advantages Very flexible within the reception area (Almost) no wiring difficulties (e.g. historic buildings, firewalls) Ad hoc networks without previous planning possible More robust against disasters like, e.g., earthquakes, fire - or users pulling a plug... Disadvantages Typically very low data rate compared to wired networks (1-10 Mbit/s) due to shared medium Many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE n) Deployment is more difficult than it first appears Products have to follow many national restrictions if working wireless global solutions (e.g., IMT-2000) take a long time Security/privacy harder to achieve in broadcast media WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 6

7 Design goals for wireless LANs Global, seamless operation Low power for battery use No special permissions or licenses needed to use the LAN Robust transmission technology Simplified spontaneous cooperation at meetings Easy to use for everyone, simple management Protection of investment in wired networks Security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation) Transparency concerning applications and higher layer protocols, but also location awareness if necessary WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 7

8 Comparison: infrastructure vs. ad-hoc networks Infrastructure network AP AP Wired network AP: Access Point AP Ad hoc network WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 8

9 Overview WLAN overview IEEE family Architecture overview Physical layers Medium access control mechanisms MAC management Summary and overview of substandards WPAN: IEEE , Bluetooth & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 9

10 Architecture of an infrastructure network STA 1 ESS LAN BSS 1 Access Point BSS 2 Distribution System Access Point 802.x LAN Portal STA LAN STA 3 Station (STA) Terminal with access mechanisms to the wireless medium and radio contact to the access point Basic Service Set (BSS) Group of stations using the same radio frequency band Access Point Portal Station integrated into the wireless LAN and the distribution system Bridge to other (wired) networks Distribution System Interconnection network to form one logical network (ESS: Extended Service Set) based on several BSS Seamless mobility within one ESS WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 10

11 Architecture of an ad hoc network LAN Direct communication within a limited range STA 1 IBSS 1 STA 2 STA 3 Station (STA): terminal with access mechanisms to the wireless medium Independent Basic Service Set (IBSS): group of stations using the same radio frequency band IBSS 2 STA 5 STA LAN WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 11

12 IEEE standard Mobile terminal fixed terminal application TCP IP LLC access point LLC infrastructure network application TCP IP LLC MAC MAC MAC MAC PHY PHY PHY PHY WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 12

13 Layers and functions Physical Medium Dependent (PMD) Modulation, coding Physical Layer Convergence Protocol (PLCP) Clear channel assessment signal (carrier sense) PHY Management Channel selection, MIB MAC Access mechanisms, fragmentation, encryption MAC Management Synchronization, roaming, MIB, power management Station Management Coordination of all management functions PHY DLC LLC MAC PLCP PMD MAC Management PHY Management Station Management WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 13

14 Overview WLAN overview IEEE family Architecture overview Physical layers Medium access control mechanisms MAC management Summary and overview of substandards WPAN: IEEE , Bluetooth & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 14

15 Physical layer (classical) 3 versions: 2 radio (typ. 2.4 GHz), 1 IR Data rates 1 or 2 Mbit/s (FHSS (Frequency Hopping Spread Spectrum) Spreading, despreading, signal strength, typ. 1 Mbit/s Min. 2.5 frequency hops/s (USA), two-level GFSK modulation) DSSS (Direct Sequence Spread Spectrum) DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying), DQPSK for 2 Mbit/s (Differential Quadrature PSK) Preamble and header of a frame is always transmitted with 1 Mbit/s, rest of transmission 1 or 2 Mbit/s Chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code) Max. radiated power 1 W (USA), 100 mw (EU), min. 1mW (Infrared nm, diffuse light, typ. 10 m range Carrier detection, energy detection, synchronization) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 15

16 FHSS PHY packet format Synchronization Synch with pattern SFD (Start Frame Delimiter) start pattern PLW (PLCP_PDU Length Word) Length of payload incl. 32 bit CRC of payload, PLW < 4096 PSF (PLCP Signaling Field) Data of payload (1 or 2 Mbit/s) HEC (Header Error Check) CRC with x 16 +x 12 +x variable bits synchronization SFD PLW PSF HEC payload PLCP preamble PLCP header WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 16

17 DSSS PHY packet format Synchronization Synch., gain setting, energy detection, frequency offset compensation SFD (Start Frame Delimiter) Signal Data rate of the payload (0A: 1 Mbit/s DBPSK; 14: 2 Mbit/s DQPSK) Service future use, 00: compliant Length length of the payload HEC (Header Error Check) Protection of signal, service and length, x 16 +x 12 +x variable bits synchronization SFD signal service length HEC payload WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 17 PLCP preamble PLCP header

18 IEEE b PHY frame formats Long PLCP PPDU format variable bits synchronization SFD signal service length HEC payload PLCP preamble PLCP header 192 µs at 1 Mbit/s DBPSK 1, 2, 5.5 or 11 Mbit/s Short PLCP PPDU format (optional) variable bits short synch. SFD signal service length HEC payload PLCP preamble (1 Mbit/s, DBPSK) PLCP header (2 Mbit/s, DQPSK) 96 µs 2, 5.5 or 11 Mbit/s WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 18

19 IEEE b Channel selection (non-overlapping) Europe (ETSI) channel 1 channel 7 channel MHz [MHz] US (FCC)/Canada (IC) channel 1 channel 6 channel MHz [MHz] Because of limited spectrum and need for guard space, in practice only three channels concurrently useable in the same area WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 19

20 IEEE a PHY frame format variable 6 variable bits rate reserved length parity tail service payload tail pad PLCP header PLCP preamble signal data 12 1 variable symbols 6 Mbit/s 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 20

21 Operating channels for a / US U-NII channel [MHz] 16.6 MHz channel center frequency = *channel number [MHz] [MHz] 16.6 MHz WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 21

22 OFDM in IEEE a OFDM with 52 used subcarriers (64 in total) 48 data + 4 pilot (plus 12 unused subcarriers, serve as guard space) khz spacing pilot khz channel center frequency subcarrier number WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 22

23 IEEE h Update to a: Extend by Dynamic frequency selection Transmission power control Regulation allows h networks also outdoors Concerns about plain a about interference with radar systems prevented that Large power allowed 200 mw indoor EIRP 1000 mw outdoor EIRP WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 23

24 IEEE n: MIMO Put MIMO techniques into system Standard ratified October 2009 Some key figures (caution, marketing!) Operates at 2.4 GHz or 5 GHz bands 40 MHz bandwidth (per antenna) instead of usual 22 MHz Up to 150 MBit/s per content stream Up to 600 MBit/s total bandwidth (available: about 70 MBit/s) OFDM basis, plus BPSK/QPSK/QAM modulation About 70 meters indoor, 250 meters outdoor targeted WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 24

25 Overview WLAN overview IEEE family Architecture overview Physical layers Medium access control mechanisms MAC management Summary and overview of substandards WPAN: IEEE , Bluetooth & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 25

26 MAC layer DFWMAC Traffic services Asynchronous Data Service (mandatory) Exchange of data packets based on best-effort Support of broadcast and multicast Time-Bounded Service (optional) Implemented using Point Coordination Function (PCF) Access methods DFWMAC-DCF CSMA/CA (mandatory) DCF: Distributed Coordination Function Collision avoidance via randomized back-off mechanism Minimum distance between consecutive packets ACK packet for acknowledgements (not for broadcasts) DFWMAC-DCF w/ RTS/CTS (optional, practically always available) Distributed Foundation Wireless MAC Avoids hidden terminal problem DFWMAC-PCF (optional, not always available) Access point polls terminals according to a list WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 26

27 CSMA/CA access method and ACKs Sending unicast packets Station has to wait for DIFS before sending data Receivers acknowledge at once (after waiting for SIFS) if the packet was received correctly (CRC) Automatic retransmission of data packets in case of transmission errors sender DIFS data receiver SIFS ACK other stations waiting time DIFS contention data t WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 27

28 MAC layer priorities by different intervals Priorities Defined through different inter frame spaces No guaranteed, hard priorities SIFS (Short Inter Frame Spacing) Highest priority, for ACK, CTS, polling response PIFS (PCF IFS) Medium priority, for time-bounded service using PCF DIFS (DCF, Distributed Coordination Function IFS) Lowest priority, for asynchronous data service DIFS DIFS medium busy PIFS SIFS contention next frame direct access if medium is free DIFS t WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 28

29 Different Inter-Frame Spaces IEEE 802.xx 11a 11b 11g Slot time Δ 9 µ s 20 µ s 9 µ s 20 µ s (if no 11b devices are present) (if 11b devices present) SIFS 16 µ s 10 µ s 10 µ s DIFS 34 µ s 50 µ s 28 µ s DIFS = 2 Δ + SIFS WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 29

30 CSMA/CA and contention DIFS Station B checks medium medium busy DIFS contention window (randomized back-off mechanism) next frame Station A checks medium Station A: direct access if medium is free DIFS slot time t Station ready to send starts sensing the medium (Carrier Sense based on CCA, Clear Channel Assessment) If the medium is free for the duration of an Inter-Frame Space (IFS), the station can start sending (which IFS depends on service type) If the medium is busy, the station has to wait for a free IFS, then the station must additionally wait a random back-off time (collision avoidance, multiple of slot time) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 30

31 Competing during backoff simple version DIFS DIFS bo e bo r DIFS bo e bo r DIFS bo e busy station 1 bo e busy station 2 busy station 3 station 4 bo e bo r bo e bo e busy busy bo e bo e bo r bo r Choose new backoff time after collision! station 5 busy medium not idle (frame, ack etc.) bo e elapsed backoff time t packet arrival at MAC bo r residual backoff time If another station occupies the medium during the back-off time of the station, the back-off timer stops (fairness) Station can start next back-off with this discounted timer, does not need to start afresh WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 31

32 Exponential backoff As usually done in CSMA-based backoff schemes, IEEE uses an exponential backoff After a failed transmission attempt, backoff window CW is doubled After a successful transmission attempt, CW is reset to initial value Dynamic CW necessary to adapt to different traffic patterns/ number of active terminals Few active terminals: Small CW allows low delay Many active terminals: Large CW reduces collision probability Typical values: Initially CW=7, maximum CW = 255 Values used: 7, 15, 31, 63, 127, 255 WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 32

33 Summary: Core state machine for backoff Packet to send; Channel is busy consecp := FALSE Wait for idle channel Wait for packet from higher layer Channel becomes busy Channel becomes idle Channel becomes busy Wait for DIFS 2 Packet to send; Channel is idle consecp := FALSE Wait for DIFS 1 DIFS expired; BO >= 0 - DIFS expired; BO == -1 BO := rand (0, w-1) Channel becomes busy; BO := BO - waiting time DIFS expired; consecp == TRUE BO := rand (0, w-1) Wait for backoff ACK arrived; Packet in send queue consecp := TRUE, w := CWmin, BO := -1 DIFS expired; consecp == FALSE BO := -1 Backoff done; BO := -1 Sending done Send packet ACK arrived; Send queue empty consecp := FALSE, w := CWmin, BO := -1 Variables and initial values: w = CWmin // current contention window BO = -1 // current number of backoff time slots consecp = FALSE // is this a consecutive packet? No ACK; w := min (2*w, CWmax) Wait for ACK Legend for transitions: EVENT ; GUARD CONDITION ACTION WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 33

34 DFWMAC RTS/CTS NAV Sending unicast packets Station can send RTS with reservation parameter after waiting for DIFS (reservation determines amount of time the data packet needs the medium) sender receiver Acknowledgement via CTS after SIFS by receiver (if ready to receive) Sender can now send data at once, acknowledgement via ACK Other stations store medium reservations distributed via RTS and CTS DIFS RTS SIFS CTS SIFS data SIFS ACK NAV (RTS) DIFS other NAV (CTS) data stations t WS 10/11, v. 1.3 Mobile defer Communications access - Ch. 5 - WLANs 34 contention

35 DFWMAC-PCF I t 0 t 1 SuperFrame medium busy point coordinator PIFS D 1 SIFS SIFS D 2 SIFS SIFS wireless stations U 1 U 2 stations NAV NAV WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 35

36 DFWMAC-PCF II t 2 t 3 t 4 PIFS SIFS CFend point coordinator D 3 D 4 SIFS wireless stations U 4 stations NAV NAV contention free period contention period t WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 36

37 MAC layer data frame format Types Control frames, management frames, data frames Sequence numbers Important against duplicated frames due to lost ACKs Addresses Receiver, transmitter (physical), BSS identifier, sender (logical) Miscellaneous Sending time, checksum, frame control, data bytes Duration/ Address Address Address Sequence ID Control Frame Control Address Data 4 bits CRC Protocol Type Subtype To From More Retry Power More version DS Frag Mgmt Data WEP Order DS WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 37

38 MAC address format Scenario to DS from DS address 1 address 2 address 3 address 4 Ad hoc network 0 0 DA SA BSSID - infrastructure 0 1 DA BSSID SA - network, from AP infrastructure 1 0 BSSID SA DA - network, to AP infrastructure network, within DS 1 1 RA TA DA SA LAN 802.x LAN DS: Distribution System AP: Access Point DA: Destination Address SA: Source Address BSSID: Basic Service Set Identifier RA: Receiver Address TA: Transmitter Address STA 1 ESS BSS 1 Access Point BSS 2 Portal Distribution System Access Point STA LAN STA 3 WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 38

39 Special Frames: ACK, RTS, CTS Acknowledgement ACK bytes Frame Duration Receiver CRC Control Address Request To Send RTS bytes Frame Duration Receiver Transmitter CRC Control Address Address Clear To Send CTS bytes Frame Duration Receiver CRC Control Address WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 39

40 Overview WLAN overview IEEE family Architecture overview Physical layers Medium access control mechanisms MAC management Summary and overview of substandards WPAN: IEEE , Bluetooth & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 40

41 MAC management Authentication Worthless, due to severe security flaws in original protocol (both open system and shared key authentication!) Security WEP is broken Synchronization Try to find a LAN, try to stay within a LAN Timer etc. Power management Sleep-mode without missing a message Periodic sleep, frame buffering, traffic measurements Association/Reassociation (after authentication) Integration into a LAN association request/response Upon association, AP signals new station to distribution system Roaming, i.e. change access points Scanning, i.e. active search for a network MIB Management Information Base Managing, read, write WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 41

42 Security: WEP Original Wired Equivalent Privacy (WEP) is a broken, completely insecure protocol No key management present! keys are practically not changed 40 bit long keys are vulnerable to brute force attacks Encryption keys can be reconstructed by observing data stream Irrespective of key length; problem: key streams are reused, reuse of initialization vectors And others WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 42

43 Security: 802.1x, i, WPA Remedy: 802.1x / EAP Dynamically generate session keys (using a RADIUS server, e.g.) Use session key to distribute encryption keys dynamically changed Usually only practical in larger installations Remedy: i / WiFi Protected Access (WPA) New encryption algorithms Standardized handshaking between mobile station and access points Simplified scheme to negotiate master secret (without need for RADIUS server, then uses pre-shared keys) Negotiation of encryption scheme between mobile and AP; per-mobile client exclusive session key Temporary key exchange (TKIP) still has some weaknesses Remedy: WPA2 Considered completely secure WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 43

44 Synchronization using a Beacon (infrastructure) Beacons are sent by AP at fixed periods If medium is busy when a beacon is due, sent it ASAP once the medium is free But do not delay following beacons Use up-to-date timestamp in such a delayed beacon beacon interval access point medium B B B B busy busy busy busy value of the timestamp B beacon frame t WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 44

45 Synchronization using a Beacon (ad hoc) In ad hoc network, no AP available to send beacon Share burden among all stations, have them send out beacon periodically Each station tries to send beacon, applies standard backoff procedure before sending to reduce beacon collisions In case medium is busy at intended time, proceed as in AP case beacon interval station 1 B 1 B 1 station 2 medium B 2 B 2 busy busy busy busy t value of the timestamp B beacon frame random delay WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 45

46 Power management Idea: switch the transceiver off if not needed States of a station: sleep and awake Timing Synchronization Function (TSF) Stations wake up at the same time Infrastructure Traffic Indication Map (TIM) List of unicast receivers transmitted by AP Delivery Traffic Indication Map (DTIM) List of broadcast/multicast receivers transmitted by AP Ad hoc Ad hoc Traffic Indication Map (ATIM) Announcement of receivers by stations buffering frames More complicated no central AP Collision of ATIMs possible (scalability?) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 46

47 Power saving with wake-up patterns (infrastructure) TIM interval DTIM interval access point medium D B busy T T d D busy busy busy B station T TIM D DTIM p awake d t B broadcast/multicast p PS poll d data transmission to/from the station WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 47

48 Power saving with wake-up patterns (ad hoc) ATIM window beacon interval station 1 B 1 A D B 1 station 2 B 2 B 2 a d B beacon frame random delay A transmit ATIM t D transmit data awake a acknowledge ATIM d acknowledge data WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 48

49 Roaming No or bad connection? Then perform: Scanning Scan the environment, i.e., listen into the medium for beacon signals or send probes into the medium and wait for an answer Reassociation Request Station sends a request to one or several AP(s) Reassociation Response Success: AP has answered, station can now participate Failure: continue scanning AP accepts Reassociation Request Signal the new station to the distribution system The distribution system updates its data base (i.e., location information) Typically, the distribution system now informs the old AP so it can release resources Note: As long as the two APs (between which roaming occurs) are in the same ESS, no need to change IP address WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 49

50 Overview WLAN overview IEEE family Architecture overview Physical layers Medium access control mechanisms MAC management Summary and overview of substandards WPAN: IEEE , Bluetooth & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 50

51 WLAN: IEEE b Data rate 1, 2, 5.5, 11 Mbit/s, depending on SNR User data rate max. approx. 6 Mbit/s Transmission range 300m outdoor, 30m indoor Max. data rate ~10m indoor Frequency Free 2.4 GHz ISM-band Security Limited, WEP insecure, SSID Availability Many products, many vendors Connection set-up time Connectionless/always on Quality of Service Typ. Best effort, no guarantees (unless polling is used, limited support in products) Manageability Limited (no automated key distribution, sym. Encryption) Special Advantages/Disadvantages Advantage: many installed systems, lot of experience, available worldwide, free ISM-band, many vendors, integrated in laptops, simple system Disadvantage: heavy interference on ISM-band, no service guarantees, slow relative speed only WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 51

52 WLAN: IEEE a Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNR User throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54) MBit/s 6, 12, 24 Mbit/s mandatory Transmission range (typical antennas, system, ) 100m outdoor, 10m indoor E.g., 54 Mbit/s up to 5 m, 48 up to 12 m, 36 up to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60 m Frequency Free , , GHz ISM-band Security Limited, WEP insecure, SSID Availability Some products, some vendors Connection set-up time Connectionless/always on Quality of Service Typ. best effort, no guarantees (same as all products) Manageability Limited (no automated key distribution, sym. Encryption) Special Advantages/Disadvantages Advantage: fits into 802.x standards, free ISM-band, available, simple system, uses less crowded 5 GHz band Disadvantage: stronger shading due to higher frequency, no QoS WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 52

53 IEEE e Support for multimedia Goal: support delay-sensitive multimedia, streaming applications Problem of PCF Beacons delays unpredictable (medium might be busy after PIFS); simulations show mean 250 µ s delay After being polled, stations are allowed to send packets of variable lengths, at variable rate! no guarantees for other stations Extend DCF and PCF by Hybrid Coordination Function (HCF) Two methods of channel access Enhanced Distributed Channel Access (EDCA) HCF Controlled Channel Access (HCCA) Scenario assumption: BSS with at least a hybrid coordinator (typically, access point) and extended stations, implementing e WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 53

54 IEEE e EDCA Traffic classes to represent different requirements Each traffic class has specific parameters (e.g., backoff) E.g., backoff Arbitration Interframe Space, minimum size of the Contention Window Multiple flows of a terminal mapped to traffic class, each operating under its own parameters Each traffic class behaves as a virtual terminal for channel access Slightly modified rules for backoff countdown and increase In effect: only traffic differentiation, no real reservations/guarantees doi= &rep=rep1&type=pdf WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 54

55 WLAN: IEEE future developments (03/2005) c: Bridge Support Definition of MAC procedures to support bridges as extension to 802.1D d: Regulatory Domain Update Support of additional regulations related to channel selection, hopping sequences e: MAC Enhancements QoS Enhance the current MAC to expand support for applications with Quality of Service requirements, and in the capabilities and efficiency of the protocol Definition of a data flow ( connection ) with parameters like rate, burst, period Additional energy saving mechanisms and more efficient retransmission f: Inter-Access Point Protocol Establish an Inter-Access Point Protocol for data exchange via the distribution system Currently unclear to which extend manufacturers will follow this suggestion g: Data Rates > 20 Mbit/s at 2.4 GHz; 54 Mbit/s, OFDM Successful successor of b, performance loss during mixed operation with 11b h: Spectrum Managed a Extension for operation of a in Europe by mechanisms like channel measurement for dynamic channel selection (DFS, Dynamic Frequency Selection) and power control (TPC, Transmit Power Control) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 55

56 WLAN: IEEE future developments (03/2005) i: Enhanced Security Mechanisms Enhance the current MAC to provide improvements in security. TKIP enhances the insecure WEP, but remains compatible to older WEP systems AES provides a secure encryption method and is based on new hardware j: Extensions for operations in Japan Changes of a for operation at 5GHz in Japan using only half the channel width at larger range k: Methods for channel measurements Devices and access points should be able to estimate channel quality in order to be able to choose a better access point of channel m: Updates of the standards n: Higher data rates above 100Mbit/s Changes of PHY and MAC with the goal of 100Mbit/s at MAC SAP MIMO antennas (Multiple Input Multiple Output), up to 600Mbit/s are currently feasible However, still a large overhead due to protocol headers and inefficient mechanisms p: Inter car communications Communication between cars/road side and cars/cars Planned for relative speeds of min. 200km/h and ranges over 1000m Usage of GHz band in North America WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 56

57 WLAN: IEEE future developments (03/2005) r: Faster Handover between BSS Secure, fast handover of a station from one AP to another within an ESS Current mechanisms (even newer standards like i) plus incompatible devices from different vendors are massive problems for the use of, e.g., VoIP in WLANs Handover should be feasible within 50ms in order to support multimedia applications efficiently s: Mesh Networking Design of a self-configuring Wireless Distribution System (WDS) based on Support of point-to-point and broadcast communication across several hops t: Performance evaluation of networks Standardization of performance measurement schemes u: Interworking with additional external networks v: Network management Extensions of current management functions, channel measurements Definition of a unified interface w: Securing of network control Classical standards like , but also i protect only data frames, not the control frames. Thus, this standard should extend i in a way that, e.g., no control frames can be forged. Note: Not all standards will end in products, many ideas get stuck at working group level Info: 802wirelessworld.com, standards.ieee.org/getieee802/ WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 57

58 WLAN physical layers overview 11 Frequency Hopping Spread Spectrum (FHSS) Direct Sequence Spread Spectrum (DSSS) Infraread 11a Orthogonal Frequency Division Multiplexing (OFDM) 11b High-rate DSSS using Complementary Code Keying (CCK) 11g OFDM ( extended-rate PHY ) 11n Multiple antennas, Multiple-Input Multiple-Output (MIMO) Channel bonding, jumbo frames WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 58

59 Overview WLAN overview IEEE family WPAN: Bluetooth, Bluetooth & friends Overview & history Piconets & scatternets Transmission in Bluetooth Power saving Further developments: IEEE & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 59

60 Bluetooth Idea Universal radio interface for ad-hoc wireless connectivity Interconnecting computer and peripherals, handheld devices, PDAs, cell phones replacement of IrDA Embedded in other devices, goal: 5 /device (Jan 2006: starting from 15 /USB bluetooth) Short range (10 m), low power consumption, license-free 2.45 GHz ISM Voice and data transmission, approx. 1 Mbit/s gross data rate One of the first modules (Ericsson). WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 60

61 Bluetooth History 1994: Ericsson (Mattison/Haartsen), MC-link project Renaming of the project: Bluetooth according to Harald Blåtand Gormsen [son of Gorm], King of Denmark in the 10th century 1998: foundation of Bluetooth SIG, : erection of a rune stone at Ericsson/Lund ;-) 2001: first consumer products for mass market, spec. version 1.1 released 2005: 5 million chips/week Special Interest Group Original founding members: Ericsson, Intel, IBM, Nokia, Toshiba Added promoters: 3Com, Agere (was: Lucent), Microsoft, Motorola > 2500 members Common specification and certification of products WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 61

62 History and hi-tech 1999: Ericsson mobile communications AB reste denna sten till minne av Harald Blåtand, som fick ge sitt namn åt en ny teknologi för trådlös, mobil kommunikation. WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 62

63 and the real rune stone Located in Jelling, Denmark, erected by King Harald Blåtand in memory of his parents. The stone has three sides one side showing a picture of Christ. Inscription: "Harald king executes these sepulchral monuments after Gorm, his father and Thyra, his mother. The Harald who won the whole of Denmark and Norway and turned the Danes to Christianity." Btw: Blåtand means of dark complexion (not having a blue tooth ) This could be the original colors of the stone. Inscription: auk tani karthi kristna (and made the Danes Christians) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 63

64 Characteristics 2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacing Channel 0: 2402 MHz channel 78: 2480 MHz G-FSK modulation, mw transmit power FHSS and TDD Frequency hopping with 1600 hops/s Hopping sequence in a pseudo-random fashion, determined by a master Time division duplex for send/receive separation Voice link SCO (Synchronous Connection Oriented) FEC (forward error correction), no retransmission, 64 kbit/s duplex, pointto-point, circuit switched Data link ACL (Asynchronous ConnectionLess) Asynchronous, fast acknowledge, point-to-multipoint, up to kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched Topology Overlapping piconets (stars) forming a scatternet WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 64

65 Bluetooth protocol stack audio apps. NW apps. vcal/vcard telephony apps. mgmnt. apps. TCP/UDP OBEX IP BNEP PPP AT modem commands TCS BIN SDP Control Audio RFCOMM (serial line interface) Logical Link Control and Adaptation Protocol (L2CAP) Link Manager Baseband Radio Host Controller Interface AT: attention sequence OBEX: object exchange TCS BIN: telephony control protocol specification binary BNEP: Bluetooth network encapsulation protocol SDP: service discovery protocol RFCOMM: radio frequency comm. WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 65

66 Overview WLAN overview IEEE family WPAN: Bluetooth, Bluetooth & friends Overview & history Piconets & scatternets Transmission in Bluetooth Power saving Further developments: IEEE & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 66

67 Piconet Collection of devices connected in an ad hoc fashion One unit acts as master and the others as slaves for the lifetime of the piconet Master determines hopping pattern, slaves have to synchronize S SB P M S S P Each piconet has a unique hopping pattern Participation in a piconet = synchronization to hopping sequence Each piconet has one master and up to 7 simultaneous, active slaves (> 200 could be parked ) M=Master S=Slave P SB P=Parked SB=Standby WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 67

68 Forming a piconet All devices in a piconet hop together (in frequency) Master gives slaves its clock and device ID Addressing ½ Hopping pattern: determined by device ID (48 bit, unique worldwide) Phase in hopping pattern determined by clock Active Member Address (AMA, 3 bit) Parked Member Address (PMA, 8 bit) SB SB ¹ SB SB» SB Á SB SB ¾ SB SB» S SB»» P P» M Á» SB S»» S P WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 68

69 Scatternet Linking of multiple co-located piconets through the sharing of common master or slave devices Devices can be slave in one piconet and master of another Communication between piconets Devices jumping back and forth between the piconets P S S Piconets (each with a capacity of 720 kbit/s) M=Master S=Slave P=Parked SB=Standby S SB P M SB S P M SB P S WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 69

70 Overview WLAN overview IEEE family WPAN: Bluetooth, Bluetooth & friends Overview & history Piconets & scatternets Transmission in Bluetooth Power saving Further developments: IEEE & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 70

71 Frequency selection during data transmission 625 µs f k f k+1 f k+2 f k+3 f k+4 f k+5 f k+6 M S M S M S M t f k f k+3 f k+4 f k+5 f k+6 M S M S M t f k f k+1 f k+6 M S M t WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 71

72 Baseband link types Polling-based TDD packet transmission 625µs slots, master polls slaves SCO (Synchronous Connection Oriented) Voice Periodic single slot packet assignment, 64 kbit/s full-duplex, point-to-point ACL (Asynchronous ConnectionLess) Data Variable packet size (1,3,5 slots), asymmetric bandwidth, point-to-multipoint MASTER SCO ACL SCO ACL SCO ACL SCO ACL f 0 f 6 f 8 f 12 f 4 f 20 f 14 f 18 SLAVE 1 f 1 f 7 f 9 f 13 f 19 SLAVE 2 f 5 f 21 f 17 WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 72

73 Robustness Slow frequency hopping with hopping patterns determined by a master Protection from interference on certain frequencies Separation from other piconets (FH-CDMA) Retransmission ACL only, very fast Forward Error Correction SCO and ACL Error in payload (not header!) NAK ACK MASTER A C C F H SLAVE 1 B D E SLAVE 2 G G WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 73

74 vs.(?) /Bluetooth Bluetooth may act like a rogue member of the network Does not know anything about gaps, inter frame spacing etc. f [MHz] b 2402 DIFS DIFS 500 byte DIFS 100 byte SIFS ACK SIFS ACK DIFS IEEE discusses these problems DIFS 100 byte 1000 byte SIFS ACK 500 byte Proposal: Adaptive Frequency Hopping A non-collaborative Coexistence Mechanism Real effects? Many different opinions, publications, tests, formulae, SIFS ACK SIFS ACK Results from complete breakdown to almost no effect DIFS 100 byte SIFS ACK Bluetooth (FHSS) seems more robust than b (DSSS) DIFS DIFS 100 byte DIFS SIFS ACK 500 byte DIFS 100 byte SIFS ACK t 3 channels (separated by installation) channels (separated by hopping pattern) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 74

75 Overview WLAN overview IEEE family WPAN: Bluetooth, Bluetooth & friends Overview & history Piconets & scatternets Transmission in Bluetooth Power saving Further developments: IEEE & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 75

76 Baseband states of a Bluetooth device standby unconnected detach inquiry page connecting transmit AMA connected AMA active park PMA hold AMA sniff AMA low power Standby: do nothing Inquire: search for other devices Page: connect to a specific device Connected: participate in a piconet Park: release AMA, get PMA Sniff: listen periodically, not each slot Hold: stop ACL, SCO still possible, possibly participate in another piconet WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 76

77 Example: Power consumption/csr BlueCore2 Typical Average Current Consumption (1) VDD=1.8V Temperature = 20 C Mode SCO connection HV3 (1s interval Sniff Mode) (Slave) 26.0 ma SCO connection HV3 (1s interval Sniff Mode) (Master) 26.0 ma SCO connection HV1 (Slave) 53.0 ma SCO connection HV1 (Master) 53.0 ma ACL data transfer 115.2kbps UART (Master) 15.5 ma ACL data transfer 720kbps USB (Slave) 53.0 ma ACL data transfer 720kbps USB (Master) 53.0 ma ACL connection, Sniff Mode 40ms interval, 38.4kbps UART 4.0 ma ACL connection, Sniff Mode 1.28s interval, 38.4kbps UART 0.5 ma Parked Slave, 1.28s beacon interval, 38.4kbps UART 0.6 ma Standby Mode (Connected to host, no RF activity) 47.0 µa Deep Sleep Mode(2) 20.0 µa Notes: (1) Current consumption is the sum of both BC212015A and the flash. (2) Current consumption is for the BC212015A device only. (More: ) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 77

78 Example: Bluetooth/USB adapter (2002: 50 ) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 78

79 WPAN: IEEE Bluetooth Data rate Synchronous, connection-oriented: 64 kbit/s Asynchronous, connectionless kbit/s symmetric / 57.6 kbit/s asymmetric Transmission range POS (Personal Operating Space) up to 10 m with special transceivers up to 100 m Frequency Free 2.4 GHz ISM-band Security Challenge/response (SAFER+), hopping sequence Availability Integrated into many products, several vendors Connection set-up time Depends on power-mode Max. 2.56s, avg. 0.64s Quality of Service Guarantees, ARQ/FEC Manageability Public/private keys needed, key management not specified, simple system integration Special Advantages/Disadvantages Advantage: already integrated into several products, available worldwide, free ISM-band, several vendors, simple system, simple adhoc networking, peer to peer, scatternets Disadvantage: interference on ISMband, limited range, max. 8 devices/network&master, high setup latency WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 79

80 Overview WLAN overview IEEE family WPAN: Bluetooth, Bluetooth & friends Overview & history Piconets & scatternets Transmission in Bluetooth Power saving Further developments: IEEE & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 80

81 WPAN: IEEE Future developments : Coexistance Coexistence of Wireless Personal Area Networks (802.15) and Wireless Local Area Networks (802.11), quantify the mutual interference : High-Rate Standard for high-rate (20Mbit/s or greater) WPANs, while still lowpower/low-cost Data Rates: 11, 22, 33, 44, 55 Mbit/s Quality of Service isochronous protocol Ad hoc peer-to-peer networking Security Low power consumption Low cost Designed to meet the demanding requirements of portable consumer imaging and multimedia applications (meaning what?) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 81

82 WPAN: IEEE Future developments 2 Several working groups extend the standard a: Alternative PHY with higher data rate as extension to Applications: multimedia, picture transmission b: Enhanced interoperability of MAC Correction of errors and ambiguities in the standard c: Alternative PHY at GHz Goal: data rates above 2 Gbit/s Not all these working groups really create a standard, not all standards will be found in products later WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 82

83 WPAN: IEEE Future developments : Low-Rate, Very Low-Power Low data rate solution with multi-month to multi-year battery life and very low complexity Potential applications are sensors, interactive toys, smart badges, remote controls, and home automation Data rates of kbit/s, latency down to 15 ms Master-Slave or Peer-to-Peer operation Up to 254 devices or simpler nodes Support for critical latency devices, such as joysticks CSMA/CA channel access (data centric), slotted (beacon) or unslotted Automatic network establishment by the PAN coordinator Dynamic device addressing, flexible addressing format Fully handshaked protocol for transfer reliability Power management to ensure low power consumption 16 channels in the 2.4 GHz ISM band, 10 channels in the 915 MHz US ISM band and one channel in the European 868 MHz band Basis of the ZigBee technology WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 83

84 ZigBee Relation to similar to Bluetooth / Pushed by Chipcon, ember, freescale (Motorola), Honeywell, Mitsubishi, Motorola, Philips, Samsung More than 150 members Promoter (40000$/Jahr), Participant (9500$/Jahr), Adopter (3500$/Jahr) No free access to the specifications (only promoters and participants) ZigBee platforms comprise IEEE for layers 1 and 2 ZigBee protocol stack up to the applications WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 84

85 WPAN: IEEE Future developments 4 Several working groups extend the standard a: Alternative PHY with lower data rate as extension to Properties: precise localization (< 1m precision), extremely low power consumption, longer range Two PHY alternatives UWB (Ultra Wideband): ultra short pulses, communication and localization CSS (Chirp Spread Spectrum): communication only b: Extensions, corrections, and clarifications regarding Usage of new bands, more flexible security mechanisms : Mesh Networking Partial meshes, full meshes Range extension, more robustness, longer battery live Not all these working groups really create a standard, not all standards will be found in products later WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 85

86 RF Controllers ISM bands Data rate Typ. up to 115 kbit/s (serial interface) Transmission range m, depending on power (typ mw) Frequency Typ. 27 (EU, US), 315 (US), 418 (EU), 426 (Japan), 433 (EU), 868 (EU), 915 (US) MHz (depending on regulations) Security Some products with added processors Cost Cheap: Availability Many products, many vendors Connection set-up time N/A Quality of Service none Manageability Very simple, same as serial interface Special Advantages/ Disadvantages Advantage: very low cost, large experience, high volume available Disadvantage: no QoS, crowded ISM bands (particularly 27 and 433 MHz), typ. no Medium Access Control, 418 MHz experiences interference with TETRA WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 86

87 Overview WLAN overview IEEE family WPAN: Bluetooth, Bluetooth & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 87

88 RFID Radio Frequency Identification (1) Data rate Transmission of ID only (e.g., 48 bit, 64kbit, 1 Mbit) kbit/s Transmission range Passive: up to 3 m Active: up to m Simultaneous detection of up to, e.g., 256 tags, scanning of, e.g., 40 tags/s Frequency 125 khz, MHz, 433 MHz, 2.4 GHz, 5.8 GHz and many others Security Application dependent, typ. no crypt. on RFID device Cost Very cheap tags, down to 1 (passive) Availability Many products, many vendors Connection set-up time Depends on product/medium access scheme (typ. 2 ms per device) Quality of Service none Manageability Very simple, same as serial interface Special Advantages/Disadvantages Advantage: extremely low cost, large experience, high volume available, no power for passive RFIDs needed, large variety of products, relative speeds up to 300 km/h, broad temp. range Disadvantage: no QoS, simple denial of service, crowded ISM bands, typ. one-way (activation/ transmission of ID) WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 88

89 RFID Radio Frequency Identification (2) Function Standard: In response to a radio interrogation signal from a reader (base station) the RFID tags transmit their ID Enhanced: additionally data can be sent to the tags, different media access schemes (collision avoidance) Features No line-of sight required (compared to, e.g., laser scanners) RFID tags withstand difficult environmental conditions (sunlight, cold, frost, dirt etc.) Products available with read/write memory, smart-card capabilities Categories Passive RFID: operating power comes from the reader over the air which is feasible up to distances of 3 m, low price (1 ) Active RFID: battery powered, distances up to 100 m WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 89

90 RFID Radio Frequency Identification (3) Applications Total asset visibility: tracking of goods during manufacturing, localization of pallets, goods etc. Loyalty cards: customers use RFID tags for payment at, e.g., gas stations, collection of buying patterns Automated toll collection: RFIDs mounted in windshields allow commuters to drive through toll plazas without stopping Others: access control, animal identification, tracking of hazardous material, inventory control, warehouse management,... Local Positioning Systems GPS useless indoors or underground, problematic in cities with high buildings RFID tags transmit signals, receivers estimate the tag location by measuring the signal s propagation time WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 90

91 RFID Radio Frequency Identification (4) Security Denial-of-Service attacks are always possible Interference of the wireless transmission, shielding of transceivers IDs via manufacturing or one time programming Key exchange via, e.g., RSA possible, encryption via, e.g., AES Future Trends RTLS: Real-Time Locating System big efforts to make total asset visibility come true Integration of RFID technology into the manufacturing, distribution and logistics chain Creation of electronic manifests at item or package level (embedded inexpensive passive RFID tags) 3D tracking of children, patients WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 91

92 RFID Radio Frequency Identification (5) Devices and Companies AXCESS Inc., Checkpoint Systems Group, GEMPLUS, Intermec/Intellitag, I-Ray Technologies, RF Code, Texas Instruments, WhereNet, Wireless Mountain, XCI, Only a very small selection WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 92

93 RFID Radio Frequency Identification (6) Example Product: Intermec RFID UHF OEM Reader Read range up to 7m Anticollision algorithm allows for scanning of 40 tags per second regardless of the number of tags within the reading zone US: unlicensed 915 MHz, Frequency Hopping Read: 8 byte < 32 ms Write: 1 byte < 100ms Example Product: Wireless Mountain Spider Proprietary sparse code anti-collision algorithm Detection range 15 m indoor, 100 m line-of-sight > 1 billion distinct codes Read rate > 75 tags/s Operates at 308 MHz WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 93

94 RFID Radio Frequency Identification (7) Relevant Standards American National Standards Institute ANSI, Automatic Identification and Data Capture Techniques JTC 1/SC 31, rfidstds/sc31.htm European Radiocommunications Office ERO, European Telecommunications Standards Institute ETSI, Identification Cards and related devices JTC 1/SC 17, Identification and communication ISO TC 104 / SC 4, rfidstds/tc104.htm Road Transport and Traffic Telematics CEN TC 278, Transport Information and Control Systems ISO/TC204, rfidstds/isotc204.htm WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 94

95 RFID Radio Frequency Identification (8) ISO Standards ISO MH Data Identifiers EAN.UCC Application Identifiers ISO Syntax for High Capacity ADC Media ISO Transfer Syntax ISO Part 2, khz Part 3, MHz Part 4, 2.45 GHz Part 5, 5.8 GHz Part 6, UHF ( MHz, 433 MHz) ISO RFID Device Conformance Test Methods ISO RF Tag and Interrogator Performance Test Methods WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 95

96 Overview WLAN overview IEEE family WPAN: Bluetooth, Bluetooth & friends RF-ID WiMAX/IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 96

97 WiMAX / IEEE Goal: mid-range wireless distribution at high data rates, no/low mobility wimaxforum.org/ Material from WiMAX forum whitepapers; Ghosh, Wolter, Andrews, & Chen, Broadband Wireless Access with WiMAX/801.16:Current Performance WS 10/11, v. 1.3 Benchmarks Mobile and Communications future Potential, IEEE - Ch. Comm. 5 - WLANs Mag, Feb

98 WiMAX marketing WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 98

99 IEEE standard Overview Huge number of options to ensure quick worldwide adoption Combined into profiles for interoperability WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 99

100 IEEE PHY Frequencies: 2-11 GHz licensed and GHz unlicensed Need for non-line-of-sight operation Various PHY sub-standards WirelessMAN-SCa: Single carrier WirelessMAN-OFDM: 256 sub-carrier OFDM, TDMA multiple access 192 used for data, 8 pilots, 56 guard bands Flexible cyclic prefixes to adapt to diverse delay spread situations WirelessMAN-OFDMA: 2048 sub-carrier OFDM, multiple access by assigning subcarrier subsets to stations + TDMA component Implementation more difficult than pure OFDM scheme Bandwidth allocation: Any integer multiple of 1.25, 1.5, or 1.75 MHz, up to 20 MHz Restricted by profiles Both TDD and FDD possible, supports full-duplex subscriber stations WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 100

101 IEEE PHY Advanced features Adaptive modulation/coding (16a/d) Seven modulation/code rate combinations For trading off reliability $ performance, similar to Adaptation of parameters per station, per frame possible Space-time block codes 2x1 or 2x2 Alamouti codes diversity gain Two-antenna transmit diversity WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 101

102 IEEE MAC layer Goal: Efficient MAC for point-to-multipoint (PMP) operation At high data rates, various QoS requirements Many terminals per channel, IP data, VoIP, legacy voice Support both FDD and TDD Operation is heavily controlled by the basestation Somewhat complicated frame structure WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 102

103 Future enhancements to IEEE WS 10/11, v. 1.3 Mobile Communications - Ch. 5 - WLANs 103

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