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Wireless/Cellular Technologies Prabhaker Mateti Mobile Communication Technology according to IEEE (examples) WiFi Personal wireless nw WPAN 802.15 ZigBee 802.11a 802.11h 802.11b 802.11g 802.15.4 802.15.5, .6 (WBAN) 802.15.4a/b/c/d/e/f/g 802.15.3b/c 802.15.1 802.15.2 802.15.3 Bluetooth Wireless distribution networks WMAN 802.16 (Broadband WirelessWiMAX Access) CEG436: Mobile Computing (PM) + Mobility [802.20 (Mobile Broadband Wireless Access)] 802.16e (addition to .16 for mobile devices) 2 Mobile Communications Schiller Chapter 3 : Media Access • Motivation • SDMA, FDMA, TDMA • Aloha, reservation schemes • Collision avoidance, MACA • Polling • CDMA, SAMA • Comparison Motivation • Can we apply media access methods from fixed/wired networks? • Example CSMA/CD – Carrier Sense Multiple Access with Collision Detection – send as soon as the medium is free, listen into the medium if a collision occurs (legacy method in IEEE 802.3) • Problems in wireless networks – signal strength decreases proportional to the square of the distance – the sender would apply CS and CD, but the collisions happen at the receiver – it might be the case that a sender cannot “hear” the collision, i.e., CD does not work – furthermore, CS might not work if, e.g., a terminal is “hidden” CEG436: Mobile Computing (PM) 4 Motivation - hidden and exposed terminals • Hidden terminals – – – – A sends to B, C cannot receive A C wants to send to B, C senses a “free” medium (CS fails) collision at B, A cannot receive the collision (CD fails) A is “hidden” for C A B C • Exposed terminals – – – – B sends to A, C wants to send to another terminal (not A or B) C has to wait, CS signals a medium in use but A is outside the radio range of C, therefore waiting is not necessary C is “exposed” to B CEG436: Mobile Computing (PM) 5 Motivation - near and far terminals • Terminals A and B send, C receives – signal strength decreases proportional to the square of the distance – the signal of terminal B therefore drowns out A’s signal – C cannot receive A A B C • If C for example was an arbiter for sending rights, terminal B would drown out terminal A already on the physical layer • Also severe problem for CDMA-networks - precise power control needed! CEG436: Mobile Computing (PM) 6 Access methods SDMA/FDMA/TDMA • SDMA (Space Division Multiple Access) – segment space into sectors, use directed antennas – cell structure • FDMA (Frequency Division Multiple Access) – assign a certain frequency to a transmission channel between a sender and a receiver – permanent (e.g., radio broadcast), slow hopping (e.g., GSM), fast hopping (FHSS, Frequency Hopping Spread Spectrum) • TDMA (Time Division Multiple Access) – assign the fixed sending frequency to a transmission channel between a sender and a receiver for a certain amount of time • The multiplexing schemes presented in chapter 2 are now used to control medium access. CEG436: Mobile Computing (PM) 7 MACA variant: DFWMAC in IEEE802.11 sender receiver idle idle packet ready to send; RTS RxBusy ACK time-out NAK; RTS wait for the right to send time-out; RTS data; ACK CTS; data wait for data wait for ACK ACK: positive acknowledgement NAK: negative acknowledgement CEG436: Mobile Computing (PM) RTS; CTS time-out data; NAK RxBusy: receiver busy RTS; RxBusy 8 Polling mechanisms • If one terminal can be heard by all others, this “central” terminal (a.k.a. base station) can poll all other terminals according to a certain scheme – now all schemes known from fixed networks can be used (typical mainframe - terminal scenario) • Example: Randomly Addressed Polling – base station signals readiness to all mobile terminals – terminals ready to send can now transmit a random number without collision with the help of CDMA or FDMA (the random number can be seen as dynamic address) – the base station now chooses one address for polling from the list of all random numbers (collision if two terminals choose the same address) – the base station acknowledges correct packets and continues polling the next terminal – this cycle starts again after polling all terminals of the list CEG436: Mobile Computing (PM) 9 Access method CDMA • CDMA (Code Division Multiple Access) – all terminals send on the same frequency probably at the same time and can use the whole bandwidth of the transmission channel – each sender has a unique random number, the sender XORs the signal with this random number – the receiver can “tune” into this signal if it knows the pseudo random number, tuning is done via a correlation function • Disadvantages: – higher complexity of a receiver (receiver cannot just listen into the medium and start receiving if there is a signal) – all signals should have the same strength at a receiver • Advantages: – – – – all terminals can use the same frequency, no planning needed huge code space (e.g. 232) compared to frequency space interferences (e.g. white noise) is not coded forward error correction and encryption can be easily integrated CEG436: Mobile Computing (PM) 10 SDMA/TDMA/FDMA/CDMA Approach Idea SDMA segment space into cells/sectors Terminals only one terminal can be active in one cell/one sector Signal separation cell structure, directed antennas TDMA segment sending time into disjoint time-slots, demand driven or fixed patterns all terminals are active for short periods of time on the same frequency synchronization in the time domain FDMA segment the frequency band into disjoint sub-bands CDMA spread the spectrum using orthogonal codes every terminal has its all terminals can be active own frequency, at the same place at the uninterrupted same moment, uninterrupted filtering in the code plus special frequency domain receivers Advantages very simple, increases established, fully simple, established, robust inflexible, antennas Disadvantages typically fixed inflexible, frequencies are a scarce resource flexible, less frequency planning needed, soft handover complex receivers, needs more complicated power control for senders typically combined with TDMA (frequency hopping patterns) and SDMA (frequency reuse) still faces some problems, higher complexity, lowered expectations; will be integrated with TDMA/FDMA capacity per km² Comment only in combination with TDMA, FDMA or CDMA useful digital, flexible guard space needed (multipath propagation), synchronization difficult standard in fixed networks, together with FDMA/SDMA used in many mobile networks GSM, DECT, TETRA, UMTS, LTE Schiller Chapter 4: Wireless Telecommunication Systems How does it work? • How can the system locate a user? • Why don’t all phones ring at the same time? • What happens if two users talk simultaneously? • Why don’t I get the bill from my neighbor? • Why can an Australian use her phone in Berlin? • Why can’t I simply overhear the neighbor’s communication? • How secure is the mobile phone system? • What are the key components of the mobile phone network? CEG436: Mobile Computing (PM) 13 GSM: Overview • GSM – Global System for Mobile Communication • formerly: Groupe Spéciale Mobile (founded 1982) – Pan-European standard (ETSI, European Telecommunications Standardization Institute) • GSM all over the world – 219 countries in Asia, Africa, Europe, Australia, America • USA: T-mobile, AT&T, Cinci Bell, … – > 4.2 billion subscribers in >700 networks – > 75% of all digital mobile phones – www.gsmworld.com/newsroom/market-data/index.htm CEG436: Mobile Computing (PM) 14 Performance characteristics of GSM • Communication – mobile, wireless communication; support for voice and data services • Total mobility – international access, chip-card enables use of access points of different providers • Worldwide connectivity – one number, the network handles localization • High capacity – better frequency efficiency, smaller cells, more customers per cell • High transmission quality – high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains) • Security functions – access control, authentication via chip-card and PIN CEG436: Mobile Computing (PM) 15 Disadvantages of GSM • • • • no end-to-end encryption of user data roaming profiles accessible high complexity of the system several incompatibilities within the GSM standards CEG436: Mobile Computing (PM) 16 GSM: Mobile Services • Bearer Services • Telematic Services • Supplementary Services bearer services MS TE MT R, S GSM-PLMN Um transit network (PSTN, ISDN) source/ destination network TE (U, S, R) tele services CEG436: Mobile Computing (PM) 17 Bearer Services • Telecommunication services to transfer data between access points • Specification of services up to the terminal interface (OSI layers 1-3) • Different data rates for voice and data (original standard) – data service (circuit switched) • synchronous: 2.4, 4.8 or 9.6 kbit/s • asynchronous: 300 - 1200 bit/s – data service (packet switched) • synchronous: 2.4, 4.8 or 9.6 kbit/s • asynchronous: 300 - 9600 bit/s • Today: data rates of approx. 50 kbit/s possible – even more with new modulation CEG436: Mobile Computing (PM) 18 Telecommunication Services I • mobile telephony offering the traditional bandwidth of 3.1 kHz • Emergency number common number throughout Europe (112); mandatory for all service providers; free of charge; connection with the highest priority (preemption of other connections possible) • Multinumbering several ISDN phone numbers per user possible CEG436: Mobile Computing (PM) 19 Tele Services II: Non-Voice-Teleservices • group 3 fax • voice mailbox (implemented in the fixed network supporting the mobile terminals) • electronic mail (MHS, Message Handling System, implemented in the fixed network) • ... • Short Message Service (SMS) alphanumeric data transmission to/from the mobile terminal (160 characters) using the signaling channel, thus allowing simultaneous use of basic services and SMS (almost ignored in the beginning now the most successful add-on!) CEG436: Mobile Computing (PM) 20 Supplementary services • Services in addition to the basic services, cannot be offered stand-alone • Similar to ISDN services besides lower bandwidth due to the radio link • May differ between different service providers, countries and protocol versions • Important services – – – – – – identification: forwarding of caller number suppression of number forwarding automatic call-back conferencing with up to 7 participants locking of the mobile terminal (incoming or outgoing calls) ... CEG436: Mobile Computing (PM) 21 Architecture of the GSM system • GSM is a PLMN (Public Land Mobile Network) – several providers setup mobile networks following the GSM standard within each country – components • • • • MS (mobile station) BS (base station) MSC (mobile switching center) LR (location register) – subsystems • RSS (radio subsystem): covers all radio aspects • NSS (network and switching subsystem): call forwarding, handover, switching • OSS (operation subsystem): management of the network CEG436: Mobile Computing (PM) 22 GSM: overview OMC, EIR, AUC HLR NSS with OSS VLR MSC GMSC VLR fixed network MSC BSC BSC RSS CEG436: Mobile Computing (PM) 23 segmentation of the area into cells • use of several carrier frequencies • not the same frequency in adjoining cells • cell sizes vary from some 100 m up to 35 km depending on user density, geography, transceiver power etc. • hexagonal shape of cells is idealized (cells overlap, shapes depend on geography) • if a mobile user changes cells handover of the connection to the neighbor cell possible radio coverage of the cell cell idealized shape of the cell GSM: system architecture radio subsystem MS network and switching subsystem fixed partner networks MS ISDN PSTN MSC Um BTS Abis BSC EIR SS7 BTS VLR BTS BTS BSS HLR BSC A MSC IWF ISDN PSTN PSPDN CSPDN CEG436: Mobile Computing (PM) 25 Radio subsystem radio subsystem MS network and switching subsystem – MS (Mobile Station) – BSS (Base Station Subsystem): consisting of MS Um BTS Abis BTS • Components BSC MSC • BTS (Base Transceiver Station): sender and receiver • BSC (Base Station Controller): controlling several transceivers • Interfaces A BTS BTS BSC MSC – Um : radio interface – Abis : standardized, open interface with 16 kbit/s user channels – A: standardized, open interface with 64 kbit/s user channels BSS CEG436: Mobile Computing (PM) 26 • Network and switching subsystem network subsystem fixed partner networks •Components ISDN PSTN MSC SS7 EIR HLR ISDN PSTN PSPDN CSPDN CEG436: Mobile Computing (PM) MSC (Mobile Services Switching Center): IWF (Interworking Functions) ISDN (Integrated Services Digital Network) PSTN (Public Switched Telephone Network) PSPDN (Packet Switched Public Data Net.) CSPDN (Circuit Switched Public Data Net.) •Databases VLR MSC IWF • • • • • • • HLR (Home Location Register) • VLR (Visitor Location Register) • EIR (Equipment Identity Register) 27 GSM frequency bands (examples) Type Channels Uplink [MHz] Downlink [MHz] GSM 850 128-251 824-849 869-894 GSM 900 0-124, 9551023 876-915 921-960 890-915 880-915 935-960 925-960 classical extended 124 channels +49 channels GSM 1800 512-885 1710-1785 1805-1880 GSM 1900 512-810 1850-1910 1930-1990 GSM-R 955-1024, 0124 876-915 921-960 876-880 921-925 exclusive 69 channels CEG436: Mobile Computing (PM) 28 Mobile station • Terminal for the use of GSM services • A mobile station (MS) comprises several functional groups – MT (Mobile Terminal): • offers common functions used by all services the MS offers • corresponds to the network termination (NT) of an ISDN access • end-point of the radio interface (Um) – TA (Terminal Adapter): • terminal adaptation, hides radio specific characteristics – TE (Terminal Equipment): • peripheral device of the MS, offers services to a user • does not contain GSM specific functions – SIM (Subscriber Identity Module): • personalization of the mobile terminal, stores user parameters TE TA R CEG436: Mobile Computing (PM) MT S Um 29 Network and switching subsystem • NSS is the main component of the public mobile network GSM – switching, mobility management, interconnection to other networks, system control • Components – Mobile Services Switching Center (MSC) controls all connections via a separated network to/from a mobile terminal within the domain of the MSC - several BSC can belong to a MSC – Databases (important: scalability, high capacity, low delay) • Home Location Register (HLR) central master database containing user data, permanent and semipermanent data of all subscribers assigned to the HLR (one provider can have several HLRs) • Visitor Location Register (VLR) local database for a subset of user data, including data about all user currently in the domain of the VLR CEG436: Mobile Computing (PM) 30 Mobile Services Switching Center • The MSC (mobile services switching center) plays a central role in GSM – – – – – switching functions additional functions for mobility support management of network resources interworking functions via Gateway MSC (GMSC) integration of several databases • Functions of a MSC – – – – – – – specific functions for paging and call forwarding termination of SS7 (signaling system no. 7) mobility specific signaling location registration and forwarding of location information provision of new services (fax, data calls) support of short message service (SMS) generation and forwarding of accounting and billing information CEG436: Mobile Computing (PM) 31 Operation subsystem • The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems • Components – Authentication Center (AUC) • generates user specific authentication parameters on request of a VLR • authentication parameters used for authentication of mobile terminals and encryption of user data on the air interface within the GSM system – Equipment Identity Register (EIR) • registers GSM mobile stations and user rights • stolen or malfunctioning mobile stations can be locked and sometimes even localized – Operation and Maintenance Center (OMC) • different control capabilities for the radio subsystem and the network subsystem CEG436: Mobile Computing (PM) 32 GSM - TDMA/FDMA 935-960 MHz 124 channels (200 kHz) downlink 890-915 MHz 124 channels (200 kHz) uplink higher GSM frame structures time GSM TDMA frame 1 2 3 4 5 6 7 8 4.615 ms GSM time-slot (normal burst) guard space tail 3 bits user data S Training S user data 57 bits 1 26 bits 1 57 bits CEG436: Mobile Computing (PM) guard tail space 3 546.5 µs 577 µs 33 GSM hierarchy of frames hyperframe 0 1 2 2045 2046 2047 3 h 28 min 53.76 s ... superframe 0 1 0 2 1 ... 48 ... 49 50 24 6.12 s 25 multiframe 0 1 ... 0 24 1 2 120 ms 25 ... 48 49 50 235.4 ms frame 0 1 ... 6 7 4.615 ms slot burst CEG436: Mobile Computing (PM) 577 µs 34 GSM protocol layers for signaling Um Abis MS A BTS BSC MSC CM CM MM MM RR RR’ BTSM RR’ BTSM LAPDm LAPDm LAPD LAPD radio radio PCM PCM 16/64 kbit/s CEG436: Mobile Computing (PM) BSSAP BSSAP SS7 SS7 PCM PCM 64 kbit/s / 2.048 Mbit/s 35 Mobile Terminated Call 1: calling a GSM subscriber 2: forwarding call to GMSC 3: signal call setup to HLR 4, 5: request MSRN from VLR 6: forward responsible calling MSC to GMSC station 1 7: forward call to current MSC 8, 9: get current status of MS 10, 11: paging of MS 12, 13: MS answers 14, 15: security checks 16, 17: set up connection CEG436: Mobile Computing (PM) HLR 4 5 3 6 PSTN 2 GMSC 10 7 VLR 8 9 14 15 MSC 10 13 16 10 BSS BSS BSS 11 11 11 11 12 17 MS 36 Mobile Originated Call 1, 2: connection request 3, 4: security check 5-8: check resources (free circuit) 9-10: set up call VLR 3 4 6 PSTN 5 GMSC 7 MSC 8 2 9 MS 1 10 BSS Mobile Terminated/Originated Call MS MTC BTS MS MOC BTS paging request channel request channel request immediate assignment immediate assignment paging response service request authentication request authentication request authentication response authentication response ciphering command ciphering command ciphering complete ciphering complete setup setup call confirmed call confirmed assignment command assignment command assignment complete assignment complete alerting alerting connect connect connect acknowledge connect acknowledge data/speech exchange data/speech exchange CEG436: Mobile Computing (PM) 38 4 types of handover 1 2 3 4 MS MS MS MS BTS BTS BTS BTS BSC BSC BSC MSC MSC CEG436: Mobile Computing (PM) 39 Handover decision receive level BTSold receive level BTSold HO_MARGIN MS MS BTSold CEG436: Mobile Computing (PM) BTSnew 40 Handover procedure MS BTSold BSCold measurement measurement report result MSC HO decision HO required BSCnew BTSnew HO request resource allocation ch. activation HO command HO command HO command HO request ack ch. activation ack HO access Link establishment clear command clear command clear complete CEG436: Mobile Computing (PM) HO complete HO complete clear complete 41 DECT • DECT (Digital European Cordless Telephone) standardized by ETSI (ETS 300.175-x) for cordless telephones • standard describes air interface between base-station and mobile phone • DECT has been renamed for international marketing reasons into „Digital Enhanced Cordless Telecommunication“ • Characteristics – – – – frequency: 1880-1990 MHz channels: 120 full duplex duplex mechanism: TDD (Time Division Duplex) with 10 ms frame length multplexing scheme: FDMA with 10 carrier frequencies, TDMA with 2x 12 slots – modulation: digital, Gaußian Minimum Shift Key (GMSK) – power: 10 mW average (max. 250 mW) – range: approx. 50 m in buildings, 300 m open space CEG436: Mobile Computing (PM) 42 DECT system architecture reference model D4 D3 VDB D2 PA PA PT FT local network PT HDB D1 global network FT local network CEG436: Mobile Computing (PM) 43 DECT reference model C-Plane U-Plane network layer data link control application processes management signaling, interworking OSI layer 3 data link control OSI layer 2 medium access control physical layer CEG436: Mobile Computing (PM) • close to the OSI reference model • management plane over all layers • several services in C(ontrol)- and U(ser)-plane OSI layer 1 44 DECT layers I • Physical layer – modulation/demodulation – generation of the physical channel structure with a guaranteed throughput – controlling of radio transmission • • • • channel assignment on request of the MAC layer detection of incoming signals sender/receiver synchronization collecting status information for the management plane • MAC layer – maintaining basic services, activating/deactivating physical channels – multiplexing of logical channels • e.g., C: signaling, I: user data, P: paging, Q: broadcast – segmentation/reassembly – error control/error correction CEG436: Mobile Computing (PM) 45 DECT layers II • Data link control layer – creation and keeping up reliable connections between the mobile terminal and basestation – two DLC protocols for the control plane (C-Plane) • connectionless broadcast service: paging functionality • Lc+LAPC protocol: in-call signaling (similar to LAPD within ISDN), adapted to the underlying MAC service – several services specified for the user plane (U-Plane) • • • • null-service: offers unmodified MAC services frame relay: simple packet transmission frame switching: time-bounded packet transmission error correcting transmission: uses FEC, for delay critical, timebounded services • bandwidth adaptive transmission • “Escape” service: for further enhancements of the standard CEG436: Mobile Computing (PM) 46 DECT layers III • Network layer – similar to ISDN (Q.931) and GSM (04.08) – offers services to request, check, reserve, control, and release resources at the basestation and mobile terminal – resources • necessary for a wireless connection • necessary for the connection of the DECT system to the fixed network – main tasks • call control: setup, release, negotiation, control • call independent services: call forwarding, accounting, call redirecting • mobility management: identity management, authentication, management of the location register CEG436: Mobile Computing (PM) 47 Enhancements of the standard • Several „DECT Application Profiles“ in addition to the DECT specification – GAP (Generic Access Profile) standardized by ETSI in 1997 • assures interoperability between DECT equipment of different manufacturers (minimal requirements for voice communication) • enhanced management capabilities through the fixed network: Cordless Terminal Mobility (CTM) DECT DECT DECT basestation Common Portable Part Air Interface fixed network GAP – – – – DECT/GSM Interworking Profile (GIP): connection to GSM ISDN Interworking Profiles (IAP, IIP): connection to ISDN Radio Local Loop Access Profile (RAP): public telephone service CTM Access Profile (CAP): support for user mobility CEG436: Mobile Computing (PM) 48 UMTS and IMT-2000 • Proposals for IMT-2000 (International Mobile Telecommunications) – UWC-136, cdma2000, WP-CDMA – UMTS (Universal Mobile Telecommunications System) from ETSI • UMTS – UTRA (was: UMTS, now: Universal Terrestrial Radio Access) – enhancements of GSM • EDGE (Enhanced Data rates for GSM Evolution): GSM up to 384 kbit/s • CAMEL (Customized Application for Mobile Enhanced Logic) • VHE (virtual Home Environment) – fits into GMM (Global Multimedia Mobility) initiative from ETSI – requirements • min. 144 kbit/s rural (goal: 384 kbit/s) • min. 384 kbit/s suburban (goal: 512 kbit/s) • up to 2 Mbit/s urban CEG436: Mobile Computing (PM) 49 IMT-2000 family Interface for Internetworking IMT-2000 Core Network ITU-T GSM (MAP) Initial UMTS (R99 w/ FDD) IMT-2000 Radio Access ITU-R ANSI-41 (IS-634) IP-Network Flexible assignment of Core Network and Radio Access IMT-DS IMT-TC IMT-MC IMT-SC IMT-FT (Direct Spread) (Time Code) (Multi Carrier) (Single Carrier) (Freq. Time) UTRA FDD (W-CDMA) 3GPP UTRA TDD (TD-CDMA); TD-SCDMA 3GPP cdma2000 UWC-136 (EDGE) UWCC/3GPP DECT CEG436: Mobile Computing (PM) 3GPP2 ETSI 50 UMTS protocol stacks (user plane) UE Uu UTRAN IuCS 3G MSC apps. & protocols Circuit RLC switched MAC RLC MAC AAL2 AAL2 radio radio ATM ATM UE Uu apps. & protocols IP, PPP, … PDCP Packet switched RLC SAR UTRAN IuPS SAR 3G SGSN Gn IP tunnel 3G GGSN IP, PPP, … GTP RLC GTP UDP/IP GTP UDP/IP UDP/IP MAC MAC AAL5 AAL5 L2 L2 radio radio ATM ATM L1 L1 CEG436: Mobile Computing (PM) PDCP GTP UDP/IP 51 Support of mobility: macro diversity • Multicasting of data via several physical channels – Enables soft handover – FDD mode only UE Node B • Uplink Node B RNC CN – simultaneous reception of UE data at several Node Bs – Reconstruction of data at Node B, SRNC or DRNC • Downlink – Simultaneous transmission of data via different cells – Different spreading codes in different cells CEG436: Mobile Computing (PM) 52 Support of mobility: handover • From and to other systems (e.g., UMTS to GSM) – This is a must as UMTS coverage will be poor in the beginning • RNS controlling the connection is called SRNS (Serving RNS) • RNS offering additional resources (e.g., for soft handover) is called Drift RNS (DRNS) • End-to-end connections between UE and CN only via Iu at the SRNS – Change of SRNS requires change of Iu – Initiated by the SRNS – Controlled by the RNC and CN Node B Iub UE CN SRNC Node B Iur Iu DRNC Iub CEG436: Mobile Computing (PM) 53 Example handover types in UMTS/GSM UE1 Node B1 UE2 UE3 UE4 RNC1 Iu Node B2 Iur Iub Node B3 RNC2 3G MSC2 BTS BSC 2G MSC3 Abis CEG436: Mobile Computing (PM) 3G MSC1 A 54 Breathing Cells • GSM – Mobile device gets exclusive signal from the base station – Number of devices in a cell does not influence cell size • UMTS – Cell size is closely correlated to the cell capacity – Signal-to-nose ratio determines cell capacity – Noise is generated by interference from • other cells • other users of the same cell – Interference increases noise level – Devices at the edge of a cell cannot further increase their output power (max. power limit) and thus drop out of the cell no more communication possible – Limitation of the max. number of users within a cell required – Cell breathing complicates network planning CEG436: Mobile Computing (PM) 55 Breathing Cells: Example CEG436: Mobile Computing (PM) 56 Long Term Evolution (LTE) • Initiated in 2004 by NTT DoCoMo, focus on enhancing the Universal Terrestrial Radio Access (UTRA) and optimizing 3GPP’s radio access architecture • Targets: Downlink 100 Mbit/s, uplink 50 Mbit/s, RTT<10ms • 2007: E UTRA progressed from the feasibility study stage to the first issue of approved Technical Specifications • 2008: stable for commercial implementation • 2009: first public LTE service available (Stockholm and Oslo) • 2010: LTE starts in Germany • LTE is not 4G – sometimes called 3.9G – Does not fulfill all requirements for IMT advanced CEG436: Mobile Computing (PM) 57 Key LTE features • Simplified network architecture compared to GSM/UMTS – Flat IP-based network replacing the GPRS core, optimized for the IPMultimedia Subsystem (IMS), no more circuit switching • Network should be in parts self-organizing • Scheme for soft frequency reuse between cells – Inner part uses all subbands with less power – Outer part uses pre-served subbands with higher power • • • • Much higher data throughput supported by multiple antennas Much higher flexibility in terms of spectrum, bandwidth, data rates Much lower RTT – good for interactive traffic and gaming Smooth transition from W-CDMA/HSPA, TD-SCDMA and cdma2000 1x EVDO – but completely different radio! • Large step towards 4G – IMT advanced • See www.3gpp.org for all specs, tables, figures etc.! CEG436: Mobile Computing (PM) 58 High flexibility • E-UTRA Operating Band E-UTRA (Evolved Universal Terrestrial Radio Access) – Operating bands 700-2700MHz – Channel bandwidth 1.4, 3, 5, 10, 15, or 20 MHz – TDD and FDD • Modulation – QPSK, 16QAM, 64QAM • Multiple Access – OFDMA (DL), SC-FDMA (UL) • Peak data rates – 300 Mbit/s DL – 75 Mbit/s UL – Depends on UE category • Uplink (UL) operating band BS receive UE transmit FUL_low – FUL_high 1920 MHz – 1980 MHz 1850 MHz – 1910 MHz 1710 MHz – 1785 MHz 1710 MHz – 1755 MHz 824 MHz – 849 MHz 830 MHz – 840 MHz 2500 MHz – 2570 MHz 880 MHz – 915 MHz 1749.9 MHz – 1784.9 MHz 1710 MHz – 1770 MHz 1427.9 MHz – 1447.9 MHz 699 MHz – 716 MHz 777 MHz – 787 MHz 788 MHz – 798 MHz Reserved Reserved 704 MHz – 716 MHz 815 MHz – 830 MHz 830 MHz – 845 MHz 832 MHz – 862 MHz 1447.9 MHz – 1462.9 MHz Cell radius – From <1km to 100km CEG436: Mobile Computing (PM) 1 2 3 4 5 1 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 ... 33 1900 MHz – 34 2010 MHz – 35 1850 MHz – 36 1930 MHz – 37 1910 MHz – 38 2570 MHz – 39 1880 MHz – 40 2300 MHz – Note 1: Band 6 is not applicable 1920 MHz 2025 MHz 1910 MHz 1990 MHz 1930 MHz 2620 MHz 1920 MHz 2400 MHz Downlink (DL) operating band BS transmit UE receive FDL_low – FDL_high 2110 MHz – 2170 MHz 1930 MHz – 1990 MHz 1805 MHz – 1880 MHz 2110 MHz – 2155 MHz 869 MHz – 894MHz 875 MHz – 885 MHz 2620 MHz – 2690 MHz 925 MHz – 960 MHz 1844.9 MHz – 1879.9 MHz 2110 MHz – 2170 MHz 1475.9 MHz – 1495.9 MHz 729 MHz – 746 MHz 746 MHz – 756 MHz 758 MHz – 768 MHz Reserved Reserved 734 MHz – 746 MHz 860 MHz – 875 MHz 875 MHz – 890 MHz 791 MHz – 821 MHz 1495.9 MHz – 1510.9 MHz 1900 MHz 2010 MHz 1850 MHz 1930 MHz 1910 MHz 2570 MHz 1880 MHz 2300 MHz – – – – – – – – Duplex Mode FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD 1920 MHz 2025 MHz 1910 MHz 1990 MHz 1930 MHz 2620 MHz 1920 MHz 2400 MHz TDD TDD TDD TDD TDD TDD TDD TDD 59 LTE frame structure Radio frame (10 ms) UL 0 1 2 FDD ... 7 8 9 7 8 9 Subframe (1 ms) DL 0 1 2 ... Synchronization is part of subframe 0 and 5 0 TDD 1 2 ... 7 8 9 ... UL/DL Downlink Pilot Time Slot (data plus pilot signal) Uplink Pilot Time Slot (random access plus pilot signal) Guard Period CEG436: Mobile Computing (PM) 60 LTE architecture Mobility Management Entity Serving Gateway Packet-data network Gateway Home Subscriber Server Policy and Charging Rules Function Uu UE2 MME eNode B eNode B X2-U/-C X2-U/-C UE1 Uu GPRS S10 S3 MME S1-MME HSS S6 S1-MME S11 eNode B X2-U/-C S4 PCRF S1-U eNode B X2-U/-C S1-U eNode B E-UTRAN CEG436: Mobile Computing (PM) S7 S-GW S5 S8 (roaming) P-GW Rx+ Internet, Operators… SGi EPC (Evolved Packet Core) 61 LTE advanced • GSM – UMTS - LTE – LTE advanced as candidate for IMT-advanced • • • • Worldwide functionality & roaming Compatibility of services Interworking with other radio access systems Enhanced peak data rates to support advanced services and applications (100 Mbit/s for high and 1 Gbit/s for low mobility) • 3GPP will be contributing to the ITU-R towards the development of IMT-Advanced via its proposal for LTE-Advanced. • Relay Nodes to increase coverage • 100 MHz bandwidth (5x LTE with 20 MHz) CEG436: Mobile Computing (PM) 62 Wireless IEEE 802.11 Schiller Chapter 7: Wireless LANs Characteristics of wireless LANs • Advantages – – – – very flexible within the reception area Ad-hoc networks without previous planning possible (almost) no wiring difficulties (e.g. historic buildings, firewalls) more robust against disasters like, e.g., earthquakes, fire - or users pulling a plug... • Disadvantages – typically very low bandwidth 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 802.11n) – products have to follow many national restrictions if working wireless, it takes a vary long time to establish global solutions like, e.g., IMT-2000 CEG436: Mobile Computing (PM) 64 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 • … CEG436: Mobile Computing (PM) 65 Comparison: infrared vs. radio transmission • Infrared – uses IR diodes, diffuse light, multiple reflections (walls, furniture etc.) • Advantages – simple, cheap, available in many mobile devices – no licenses needed – simple shielding possible • Disadvantages – interference by sunlight, heat sources etc. – many things shield or absorb IR light – low bandwidth • Example – IrDA (Infrared Data Association) interface available everywhere CEG436: Mobile Computing (PM) • Radio – typically using the license free ISM band at 2.4 GHz • Advantages – experience from wireless WAN and mobile phones can be used – coverage of larger areas possible (radio can penetrate walls, furniture etc.) • Disadvantages – very limited license free frequency bands – shielding more difficult, interference with other electrical devices • Example – Many different products 66 Comparison: infrastructure vs. ad-hoc networks infrastructure network AP AP wired network AP: Access Point AP ad-hoc network CEG436: Mobile Computing (PM) 67 802.11 - Architecture of an infrastructure network • 802.11 LAN STA1 – terminal with access mechanisms to the wireless medium and radio contact to the access point 802.x LAN • Portal • ESS • Portal – bridge to other (wired) networks • Distribution System – interconnection network to form one logical network (EES: Extended Service Set) based on several BSS BSS2 STA2 Access Point – station integrated into the wireless LAN and the distribution system Distribution System Access Point Basic Service Set (BSS) – group of stations using the same radio frequency BSS1 Access Point Station (STA) 802.11 LAN STA3 802.11 - Architecture of an ad-hoc network • Direct communication within a limited range 802.11 LAN – Station (STA): terminal with access mechanisms to the wireless medium – Independent Basic Service Set (IBSS): group of stations using the same radio frequency STA1 STA3 IBSS1 STA2 IBSS2 STA5 STA4 802.11 LAN IEEE standard 802.11 fixed terminal mobile terminal infrastructure network access point application application TCP TCP IP IP LLC LLC LLC 802.11 MAC 802.11 MAC 802.3 MAC 802.3 MAC 802.11 PHY 802.11 PHY 802.3 PHY CEG436: Mobile Computing (PM) 802.3 PHY 70 • 802.11 Layers and functions • PLCP MAC Physical Layer Convergence Protocol – access mechanisms, fragmentation, encryption • MAC Management – synchronization, roaming, MIB, power management – clear channel assessment signal (carrier sense) • PMD Physical Medium Dependent – modulation, coding • PHY Management – channel selection, MIB • Station Management LLC MAC MAC Management PLCP PHY Management PMD CEG436: Mobile Computing (PM) Station Management PHY DLC – coordination of all management functions 71 802.11 - Physical layer (legacy) • 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 – 850-950 nm, diffuse light, typ. 10 m range – carrier detection, energy detection, synchronization CEG436: Mobile Computing (PM) 72 FHSS PHY packet format (legacy) • Synchronization – synch with 010101... pattern • SFD (Start Frame Delimiter) – 0000110010111101 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) 80 16 12 • HEC (Header Error Check) synchronization SFD PLW 16 – CRC with x +x12+x5+1 PLCP preamble CEG436: Mobile Computing (PM) 4 16 PSF HEC variable bits payload PLCP header 73 802.11 - MAC layer I - 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 PCF (Point Coordination Function) • Access methods – DFWMAC-DCF CSMA/CA (mandatory) • 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) • Distributed Foundation Wireless MAC • avoids hidden terminal problem – DFWMAC- PCF (optional) • access point polls terminals according to a list CEG436: Mobile Computing (PM) 74 • Priorities 802.11 - MAC layer II – 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 direct access if medium is free DIFS CEG436: Mobile Computing (PM) contention next frame t 75 802.11 - CSMA/CA access method I • 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 (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) • if another station occupies the medium during the back-off contention window timeDIFS of the station, the back-off DIFS timer stops (fairness) (randomized back-off mechanism) medium busy direct access if medium is free DIFS CEG436: Mobile Computing (PM) next frame t slot time (20µs) 76 Special Frames: ACK, RTS, CTS bytes ACK • Acknowledgement 2 Frame Control bytes RTS • Request To Send 2 Frame Control bytes CTS 2 Frame Control 2 6 4 Receiver Duration CRC Address 2 6 6 4 Receiver Transmitter Duration CRC Address Address 2 6 4 Receiver Duration CRC Address • Clear To Send CEG436: Mobile Computing (PM) 77 802.11 - MAC management • 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 – integration into a LAN – roaming, i.e. change networks by changing access points – scanning, i.e. active search for a network • MIB - Management Information Base – managing, read, write CEG436: Mobile Computing (PM) 78 Synchronization using a Beacon (infrastructure) beacon interval (20ms – 1s) access point medium B B busy busy B busy B busy t value of the timestamp CEG436: Mobile Computing (PM) B beacon frame 79 Synchronization using a Beacon (adhoc) beacon interval station1 B1 B1 B2 station2 medium busy busy B2 busy busy t value of the timestamp CEG436: Mobile Computing (PM) B beacon frame random delay 80 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?) • APSD (Automatic Power Save Delivery) – new method in 802.11e replacing above schemes CEG436: Mobile Computing (PM) 81 Power saving with wake-up patterns (infrastructure) TIM interval access point DTIM interval D B T busy medium busy T d D B busy busy p station d t T TIM D DTIM B broadcast/multicast CEG436: Mobile Computing (PM) awake p PS poll d data transmission to/from the station 82 Power saving with wake-up patterns (ad-hoc) ATIM window station1 beacon interval B1 station2 A B2 B2 D a B1 d t B beacon frame awake CEG436: Mobile Computing (PM) random delay a acknowledge ATIM A transmit ATIM D transmit data d acknowledge data 83 802.11 - 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 • Fast roaming – 802.11r – e.g. for vehicle-to-roadside networks CEG436: Mobile Computing (PM) 84 • Data rate WLAN: IEEE• 802.11b Connection set-up time – 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 – DSSS, 2.4 GHz ISM-band • Security – Limited, WEP insecure, SSID • Availability – 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 – Many products, many vendors CEG436: Mobile Computing (PM) 85 IEEE 802.11b – PHY frame formats Long PLCP PPDU format 128 16 synchronization SFD 8 8 16 16 signal service length HEC PLCP preamble bits variable payload PLCP header 192 µs at 1 Mbit/s DBPSK 1, 2, 5.5 or 11 Mbit/s Short PLCP PPDU format (optional) 56 short synch. 16 SFD 8 16 16 signal service length HEC PLCP preamble (1 Mbit/s, DBPSK) variable bits payload PLCP header (2 Mbit/s, DQPSK) 96 µs CEG436: Mobile Computing (PM) 8 2, 5.5 or 11 Mbit/s 86 Channel selection (non-overlapping) Europe (ETSI) channel 1 2400 2412 channel 7 channel 13 2442 2472 22 MHz 2483.5 [MHz] US (FCC)/Canada (IC) channel 1 2400 2412 channel 6 channel 11 2437 2462 22 MHz CEG436: Mobile Computing (PM) 2483.5 [MHz] 87 • Data rate WLAN: IEEE• 802.11a Connection set-up time – 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) – 6, 12, 24 Mbit/s mandatory • Transmission range – Connectionless/always on • – Typ. best effort, no guarantees (same as all 802.11 products) • • Frequency – Free 5.15-5.25, 5.25-5.35, 5.725-5.825 GHz ISM-band • Security – Limited, WEP insecure, SSID • Manageability – Limited (no automated key distribution, sym. Encryption) – 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 Quality of Service • 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 Availability – Some products, some vendors CEG436: Mobile Computing (PM) 88 IEEE 802.11a – PHY frame format 4 rate 1 12 1 6 reserved length parity tail 16 variable service payload 6 tail variable bits pad PLCP header PLCP preamble signal 12 data 1 6 Mbit/s CEG436: Mobile Computing (PM) variable symbols 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s 89 Operating channels of 802.11a in Europe 36 5150 40 44 48 52 56 60 64 channel 5180 5200 5220 5240 5260 5280 5300 5320 5350 [MHz] 16.6 MHz 100 5470 104 140 channel 5500 5520 5540 5560 5580 5600 5620 5640 5660 5680 5700 5725 [MHz] 16.6 MHz CEG436: Mobile Computing (PM) 108 112 116 120 124 128 132 136 center frequency = 5000 + 5*channel number [MHz] 90 Operating channels for 802.11a / US U-NII 36 5150 40 44 48 52 56 60 64 5180 5200 5220 5240 5260 5280 5300 5320 channel 5350 [MHz] 16.6 MHz 149 153 157 161 channel center frequency = 5000 + 5*channel number [MHz] 5725 5745 5765 5785 5805 5825 [MHz] 16.6 MHz CEG436: Mobile Computing (PM) 91 WLAN: IEEE 802.11 – current developments (06/2009) • • • 802.11c: Bridge Support – 802.11d: Regulatory Domain Update – • • • Support of additional regulations related to channel selection, hopping sequences 802.11e: MAC Enhancements – QoS – – • Definition of MAC procedures to support bridges as extension to 802.1D – – Enhance the current 802.11 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… supported by HCCA (HCF (Hybrid Coordinator Function) Controlled Channel Access, optional) Additional energy saving mechanisms and more efficient retransmission EDCA (Enhanced Distributed Channel Access): high priority traffic waits less for channel access 802.11F: Inter-Access Point Protocol (withdrawn) – Establish an Inter-Access Point Protocol for data exchange via the distribution system 802.11g: Data Rates > 20 Mbit/s at 2.4 GHz; 54 Mbit/s, OFDM – Successful successor of 802.11b, performance loss during mixed operation with .11b 802.11h: Spectrum Managed 802.11a – Extension for operation of 802.11a in Europe by mechanisms like channel measurement for dynamic channel selection (DFS, Dynamic Frequency Selection) and power control (TPC, Transmit Power Control) 802.11i: Enhanced Security Mechanisms – – – Enhance the current 802.11 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 CEG436: Mobile Computing (PM) 92 WLAN: IEEE 802.11– current developments (06/2009) • • • • • • • 802.11j: Extensions for operations in Japan – Changes of 802.11a for operation at 5GHz in Japan using only half the channel width at larger range 802.11-2007: Current “complete” standard – Comprises amendments a, b, d, e, g, h, i, j 802.11k: 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 802.11m: Updates of the 802.11-2007 standard 802.11n: 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 802.11p: 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 5.850-5.925GHz band in North America 802.11r: Faster Handover between BSS – – – Secure, fast handover of a station from one AP to another within an ESS Current mechanisms (even newer standards like 802.11i) 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 CEG436: Mobile Computing (PM) 93 WLAN: IEEE 802.11– current developments (06/2009) • 802.11s: Mesh Networking • 802.11T: Performance evaluation of 802.11 networks • • 802.11u: Interworking with additional external networks 802.11v: Network management • 802.11w: Securing of network control • • • • • 802.11y: Extensions for the 3650-3700 MHz band in the USA 802.11z: Extension to direct link setup 802.11aa: Robust audio/video stream transport 802.11ac: Very High Throughput <6Ghz 802.11ad: Very High Throughput in 60 GHz • Note: Not all “standards” will end in products, many ideas get stuck at working group level Info: www.ieee802.org/11/, 802wirelessworld.com, standards.ieee.org/getieee802/ • – Design of a self-configuring Wireless Distribution System (WDS) based on 802.11 – Support of point-to-point and broadcast communication across several hops – Standardization of performance measurement schemes – Extensions of current management functions, channel measurements – Definition of a unified interface – Classical standards like 802.11, but also 802.11i protect only data frames, not the control frames. Thus, this standard should extend 802.11i in a way that, e.g., no control frames can be forged. CEG436: Mobile Computing (PM) 94 Bluetooth • Basic 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 (already < 1€) – Short range (10 m), low power consumption, licensefree 2.45 GHz ISM – Voice and data transmission, approx. 1 Mbit/s gross data rate One of the first modules (Ericsson). CEG436: Mobile Computing (PM) 95 Bluetooth (was: ) • 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, www.bluetooth.org – 1999: erection of a rune stone at Ercisson/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 > 10000 members Common specification and certification of products CEG436: Mobile Computing (PM) 96 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. CEG436: Mobile Computing (PM) 97 …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…) CEG436: Mobile Computing (PM) This could be the “original” colors of the stone. Inscription: “auk tani karthi kristna” (and made the Danes Christians) 98 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, 1-100 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, point-to-point, circuit switched • Data link – ACL (Asynchronous ConnectionLess) – Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched • Topology – Overlapping piconets (stars) forming a scatternet CEG436: Mobile Computing (PM) 99 • • 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 P S S M • Master determines hopping pattern, slaves have to synchronize • 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 slaves (> 200 could be parked) CEG436: Mobile Computing (PM) P SB S P M=Master S=Slave SB P=Parked SB=Standby 100 Forming a piconet • All devices in a piconet hop together – Master gives slaves its clock and device ID • Hopping pattern: determined by device ID (48 bit, unique worldwide) P • Phase in hopping pattern determined by clock S SB SB • Addressing S M P SB – ActiveMember Address (AMA, 3 bit) SB SB SB S – Parked Member Address (PMA, 8 bit) SB SB P SB SB SB CEG436: Mobile Computing (PM) 101 Scatternet • Linking of multiple co-located piconets through the sharing of common master or slave devices Piconets (each with a P slave in one piconet and master – Devices can be of S capacity of S 720 kbit/s) another S P • Communication M between piconets P M SB jumping back – Devices S and forth between the M=Masterpiconets P SB SB S=Slave P=Parked SB=Standby CEG436: Mobile Computing (PM) S 102 Bluetooth protocol stack audio apps. NW apps. TCP/UDP vCal/vCard telephony apps. OBEX AT modem commands IP mgmnt. apps. TCS BIN SDP BNEP PPP Control RFCOMM (serial line interface) Audio Logical Link Control and Adaptation Protocol (L2CAP) Link Manager Host Controller Interface Baseband Radio AT: attention sequence OBEX: object exchange TCS BIN: telephony control protocol specification – binary BNEP: Bluetooth network encapsulation protocol CEG436: Mobile Computing (PM) SDP: service discovery protocol RFCOMM: radio frequency comm. 103 625 µs Frequency selection during data transmission fk M fk+1 S fk+2 M fk+3 S fk+4 M fk+5 S fk+6 M t fk M fk+3 S fk+4 M fk+5 S fk+6 M t fk M fk+1 S fk+6 M t CEG436: Mobile Computing (PM) 104 Baseband • Piconet/channel definition • Low-level packet definition – Access code • Channel, device access, e.g., derived from master 68(72) – Packet header 54 0-2745 bits access code packet header payload • 1/3-FEC, active member address (broadcast + 7 slaves), link type, alternating bit ARQ/SEQ, checksum 4 64 preamble sync. (4) 3 (trailer) AM address CEG436: Mobile Computing (PM) 4 1 type flow 1 ARQN 1 SEQN 8 bits HEC 105 SCO payload types payload (30) HV1 audio (10) HV2 audio (20) HV3 audio (30) DV audio (10) FEC (20) FEC (10) header (1) payload (0-9) 2/3 FEC CRC (2) (bytes) CEG436: Mobile Computing (PM) 106 ACL Payload types payload (0-343) header (1/2) payload (0-339) DM1 header (1) payload (0-17) DH1 header (1) payload (0-27) DM3 header (2) payload (0-121) DH3 header (2) payload (0-183) DM5 header (2) payload (0-224) DH5 payload (0-339) header (2) CRC (2) 2/3 FEC CRC (2) (bytes) CRC (2) 2/3 FEC CRC (2) CRC (2) 2/3 FEC CRC (2) CRC (2) AUX1 header (1) payload (0-29) CEG436: Mobile Computing (PM) 107 Baseband data rates ACL 1 slot 3 slot 5 slot SCO Type Payload User Header Payload [byte] [byte] FEC CRC Symmetric Asymmetric max. Rate max. Rate [kbit/s] [kbit/s] Forward Reverse DM1 1 0-17 2/3 yes 108.8 108.8 108.8 DH1 1 0-27 no yes 172.8 172.8 172.8 DM3 2 0-121 2/3 yes 258.1 387.2 54.4 DH3 2 0-183 no yes 390.4 585.6 86.4 DM5 2 0-224 2/3 yes 286.7 477.8 36.3 DH5 2 0-339 no yes 433.9 723.2 57.6 AUX1 1 0-29 no no 185.6 185.6 185.6 HV1 na 10 1/3 no 64.0 HV2 na 20 2/3 no 64.0 HV3 na 30 no no 64.0 DV 1D 10+(0-9) D 2/3 D yes D 64.0+57.6 D Data Medium/High rate, High-quality Voice, Data and Voice CEG436: Mobile Computing (PM) 108 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 SLAVE 1 SLAVE 2 SCO f0 ACL f4 SCO f6 f1 ACL f8 f7 f5 SCO f12 f9 ACL f14 SCO f18 f13 ACL f20 f19 f17 f21 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 Error in payload (not header!) • Forward Error Correction – SCO and ACL MASTER SLAVE 1 SLAVE 2 NAK A C B C D F ACK H E G G Baseband states of a Bluetooth device unconnected standby detach inquiry transmit AMA park PMA hold AMA Standby: do nothing Inquire: search for other devices Page: connect to a specific device Connected: participate in a piconet CEG436: Mobile Computing (PM) page connecting connected AMA active sniff AMA low power Park: release AMA, get PMA Sniff: listen periodically, not each slot Hold: stop ACL, SCO still possible, possibly participate in another piconet 111 Example: Power consumption/CSR BlueCore2 • Typical Average Current Consumption1 – VDD=1.8V Temperature = 20°C – Mode • • • • • • • • • • • • SCO connection HV3 (1s interval Sniff Mode) (Slave) SCO connection HV3 (1s interval Sniff Mode) (Master) SCO connection HV1 (Slave) SCO connection HV1 (Master) ACL data transfer 115.2kbps UART (Master) ACL data transfer 720kbps USB (Slave) ACL data transfer 720kbps USB (Master) ACL connection, Sniff Mode 40ms interval, 38.4kbps UART ACL connection, Sniff Mode 1.28s interval, 38.4kbps UART Parked Slave, 1.28s beacon interval, 38.4kbps UART Standby Mode (Connected to host, no RF activity) Deep Sleep Mode2 • Notes: – – 1 2 26.0 mA 26.0 mA 53.0 mA 53.0 mA 15.5 mA 53.0 mA 53.0 mA 4.0 mA 0.5 mA 0.6 mA 47.0 µA 20.0 µA Current consumption is the sum of both BC212015A and the flash. Current consumption is for the BC212015A device only. CEG436: Mobile Computing (PM) 112 Example: Bluetooth/USB adapter (2002: 50€, today: some cents if integrated) CEG436: Mobile Computing (PM) 113 L2CAP - Logical Link Control and Adaptation Protocol • Simple data link protocol on top of baseband • Connection oriented, connectionless, and signaling channels • Protocol multiplexing – RFCOMM, SDP, telephony control • Segmentation & reassembly – Up to 64kbyte user data, 16 bit CRC used from baseband • QoS flow specification per channel – Follows RFC 1363, specifies delay, jitter, bursts, bandwidth • Group abstraction – Create/close group, add/remove member CEG436: Mobile Computing (PM) 114 L2CAP logical channels Master Slave L2CAP L2CAP 2 d L2CAP 1 1 d d d d 1 baseband signalling CEG436: Mobile Computing (PM) Slave baseband ACL connectionless 1 d d 2 baseband connection-oriented 115 L2CAP packet formats Connectionless PDU 2 length 2 2 CID=2 0-65533 PSM bytes payload Connection-oriented PDU 2 length 2 CID 0-65535 bytes payload Signalling command PDU 2 length 2 CID=1 bytes One or more commands 1 code CEG436: Mobile Computing (PM) 1 ID 2 length 0 data 116 Security User input (initialization) PIN (1-16 byte) E2 link key (128 bit) E3 encryption key (128 bit) Pairing Authentication key generation (possibly permanent storage) Authentication Encryption key generation (temporary storage) Encryption E2 link key (128 bit) E3 encryption key (128 bit) Keystream generator Keystream generator payload key PIN (1-16 byte) Ciphering payload key Cipher data Data CEG436: Mobile Computing (PM) Data 117 SDP – Service Discovery Protocol • Inquiry/response protocol for discovering services – – – – – – Searching for and browsing services in radio proximity Adapted to the highly dynamic environment Can be complemented by others like SLP, Jini, Salutation, … Defines discovery only, not the usage of services Caching of discovered services Gradual discovery • Service record format – Information about services provided by attributes – Attributes are composed of an 16 bit ID (name) and a value – values may be derived from 128 bit Universally Unique Identifiers (UUID) CEG436: Mobile Computing (PM) 118 Additional protocols to support legacy protocols/apps. • RFCOMM – Emulation of a serial port (supports a large base of legacy applications) – Allows multiple ports over a single physical channel • Telephony Control Protocol Specification (TCS) – Call control (setup, release) – Group management • OBEX – Exchange of objects, IrDA replacement • WAP – Interacting with applications on cellular phones CEG436: Mobile Computing (PM) 119 Profiles Represent default solutions for a certain usage model • • • • • • • • • • • • • Generic Access Profile Service Discovery Application Profile Cordless Telephony Profile Intercom Profile Serial Port Profile Headset Profile Dial-up Networking Profile Fax Profile LAN Access Profile Generic Object Exchange Profile Object Push Profile File Transfer Profile Synchronization Profile – Vertical slice through the protocol stack – Basis for interoperability CEG436: Mobile Computing (PM) Protocols • Applications Profiles Additional Profiles Advanced Audio Distribution PAN Audio Video Remote Control Basic Printing Basic Imaging Extended Service Discovery Generic Audio Video Distributio 120 Hands Free Bluetooth versions • Bluetooth 1.1 – also IEEE Standard 802.15.1-2002 – initial stable commercial standard • Bluetooth 1.2 – also IEEE Standard 802.15.1-2005 – eSCO (extended SCO): higher, variable bitrates, retransmission for SCO – AFH (adaptive frequency hopping) to avoid interference • Bluetooth 2.0 + EDR (2004, no more IEEE) – EDR (enhanced date rate) of 3.0 Mbit/s for ACL and eSCO – lower power consumption due to shorter duty cycle • Bluetooth 2.1 + EDR (2007) – better pairing support, e.g. using NFC – improved security • Bluetooth 3.0 + HS (2009) – Bluetooth 2.1 + EDR + IEEE 802.11a/g = 54 Mbit/s CEG436: Mobile Computing (PM) 121 WPAN: IEEE 802.15.1 – Bluetooth • Data rate – Synchronous, connection-oriented: 64 kbit/s – Asynchronous, connectionless • 433.9 kbit/s symmetric • 723.2 / 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 CEG436: Mobile Computing (PM) • 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 active devices/network, high set-up latency 122 WPAN: IEEE 802.15 – future developments 1 • 802.15.2: Coexistance – Coexistence of Wireless Personal Area Networks (802.15) and Wireless Local Area Networks (802.11), quantify the mutual interference • 802.15.3: 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 CEG436: Mobile Computing (PM) 123 WPAN: IEEE 802.15 – future developments 2 • Several working groups extend the 802.15.3 standard • 802.15.3a: - withdrawn – Alternative PHY with higher data rate as extension to 802.15.3 – Applications: multimedia, picture transmission • 802.15.3b: – Enhanced interoperability of MAC – Correction of errors and ambiguities in the standard • 802.15.3c: – Alternative PHY at 57-64 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 … CEG436: Mobile Computing (PM) 124 WPAN: IEEE 802.15 – future developments 3 • 802.15.4: 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 20-250 kbit/s, latency down to 15 ms – Master-Slave or Peer-to-Peer operation – Up to 254 devices or 64516 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 – www.zigbee.org CEG436: Mobile Computing (PM) 125 ZigBee • Relation to 802.15.4 similar to Bluetooth / 802.15.1 • Pushed by Chipcon (now TI), ember, freescale (Motorola), Honeywell, Mitsubishi, Motorola, Philips, Samsung… • More than 260 members – about 15 promoters, 133 participants, 111 adopters – must be member to commercially use ZigBee spec • ZigBee platforms comprise – IEEE 802.15.4 for layers 1 and 2 – ZigBee protocol stack up to the applications CEG436: Mobile Computing (PM) 126 WPAN: IEEE 802.15 – future developments 4 • • • • 802.15.4a: – – – Alternative PHY with lower data rate as extension to 802.15.4 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 802.15.4b, c, d, e, f, g: – – – Extensions, corrections, and clarifications regarding 802.15.4 Usage of new bands, more flexible security mechanisms RFID, smart utility neighborhood (high scalability) 802.15.5: Mesh Networking – – Partial meshes, full meshes Range extension, more robustness, longer battery live 802.15.6: Body Area Networks – Low power networks e.g. for medical or entertainment use • 802.15.7: Visible Light Communication • Not all these working groups really create a standard, not all standards will be found in products later … CEG436: Mobile Computing (PM) 127 Some more IEEE standards for mobile communications • IEEE 802.16: 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 802.16e adds mobility support, allows for roaming at 150 km/h • IEEE 802.20: 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 Relation to 802.16e unclear • IEEE 802.21: Media Independent Handover Interoperability – Standardize handover between different 802.x and/or non 802 networks • IEEE 802.22: Wireless Regional Area Networks (WRAN) – Radio-based PHY/MAC for use by license-exempt devices on a non-interfering basis in spectrum that is allocated to the TV Broadcast Service CEG436: Mobile Computing (PM) 128 RF Controllers – ISM bands • Data rate • – Typ. up to 115 kbit/s (serial interface) • Transmission range – 5-100 m, depending on power (typ. 10-500 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: 10€-50€ • Availability 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 – Many products, many vendors CEG436: Mobile Computing (PM) 129 RFID – Radio Frequency Identification (1) • • Data rate – Transmission of ID only (e.g., 48 bit, 64kbit, 1 Mbit) – 9.6 – 115 kbit/s Transmission range – Passive: up to 3 m – Active: up to 30-100 m – Simultaneous detection of up to, e.g., 256 tags, scanning of, e.g., 40 tags/s • Frequency • Security • Cost • Availability – 125 kHz, 13.56 MHz, 433 MHz, 2.4 GHz, 5.8 GHz and many others – Application dependent, typ. no crypt. on RFID device – Very cheap tags, down to 1€ (passive) – Many products, many vendors CEG436: Mobile Computing (PM) • 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) 130 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 CEG436: Mobile Computing (PM) 131 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 time of flight CEG436: Mobile Computing (PM) 132 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 CEG436: Mobile Computing (PM) 133 RFID – Radio Frequency Identification (5) • Relevant Standards – American National Standards Institute • – Automatic Identification and Data Capture Techniques • – ISO TC 104 / SC 4, www.autoid.org/tc104_sc4_wg2.htm, www.aimglobal.org/standards/rfidstds/TC104.htm Road Transport and Traffic Telematics • – JTC 1/SC 17, www.sc17.com, www.aimglobal.org/standards/rfidstds/sc17.htm, Identification and communication • – ETSI, www.etsi.org, www.aimglobal.org/standards/rfidstds/ETSI.htm Identification Cards and related devices • – ERO, www.ero.dk, www.aimglobal.org/standards/rfidstds/ERO.htm European Telecommunications Standards Institute • – JTC 1/SC 31, www.uc-council.com/sc31/home.htm, www.aimglobal.org/standards/rfidstds/sc31.htm European Radiocommunications Office • – ANSI, www.ansi.org, www.aimglobal.org/standards/rfidstds/ANSIT6.html CEN TC 278, www.nni.nl, www.aimglobal.org/standards/rfidstds/CENTC278.htm Transport Information and Control Systems • ISO/TC204, www.sae.org/technicalcommittees/gits.htm, www.aimglobal.org/standards/rfidstds/ISOTC204.htm CEG436: Mobile Computing (PM) 134 RFID – Radio Frequency Identification (6) • ISO Standards – ISO 15418 • MH10.8.2 Data Identifiers • EAN.UCC Application Identifiers – ISO 15434 - Syntax for High Capacity ADC Media – ISO 15962 - Transfer Syntax – ISO 18000 • • • • • Part 2, 125-135 kHz Part 3, 13.56 MHz Part 4, 2.45 GHz Part 5, 5.8 GHz Part 6, UHF (860-930 MHz, 433 MHz) – ISO 18047 - RFID Device Conformance Test Methods – ISO 18046 - RF Tag and Interrogator Performance Test Methods CEG436: Mobile Computing (PM) 135 ISM band interference OLD • Many sources of interference – – – – – Microwave ovens, microwave lighting 802.11, 802.11b, 802.11g, 802.15, … Even analog TV transmission, surveillance Unlicensed metropolitan area networks … NEW • Levels of interference – Physical layer: interference acts like noise • Spread spectrum tries to minimize this • FEC/interleaving tries to correct © Fusion Lighting, Inc., now used by LG as Plasma Lighting System – MAC layer: algorithms not harmonized • E.g., Bluetooth might confuse 802.11 CEG436: Mobile Computing (PM) 136 802.11 vs.(?) 802.15/Bluetooth DIFS 802.15.1 79 channels SIFS ACK SIFS DIFS ACK 100 byte DIFS 100 byte (separated by installation) 500 byte SIFS ACK SIFS ACK DIFS 100 byte SIFS DIFS ACK DIFS SIFS DIFS ACK 100 byte 500 byte SIFS ACK 2402 SIFS ACK 500 byte DIFS DIFS DIFS f [MHz] • Bluetooth may act like a rogue member of the 802.11 network 802.11b 2480 – Does not know anything about gaps, inter frame spacing etc. 3 channels 1000 byte 100 byte (separated by hopping pattern) t • IEEE 802.15-2 discusses these problems – Proposal: Adaptive Frequency Hopping • a non-collaborative Coexistence Mechanism • Real effects? Many different opinions, publications, tests, formulae, … – Results from complete breakdown to almost no effect – Bluetooth (FHSS) seems more robust than 802.11b (DSSS) CEG436: Mobile Computing (PM) 137 Wireless IEEE 802.11 • Traditional • Bluetooth • Infrared CEG436: Mobile Computing (PM) 138 The WiMAX Possibility • Wireless & Mobile Broadband at 10-30 miles range CEG436: Mobile Computing (PM) 139