2Outline Some definitions Current situation Near Future 4G: what we really wantWhat are the obstaclesHigher Layer IssuesConclusions
3Definitions Definition of mobility: Definition of wireless: user mobility: users communicate anytime, anywhere, with anyonedevice portability: devices can be connected anytime, anywhere to the networkDefinition of wireless:Un-tethered, no physical wire attachmentThe need for mobility creates the need for integration of wireless networks into existing fixed network environments:local area networks: standardization of IEEEInternet: Mobile IP extension of the internet protocol IPwide area networks: e.g., internetworking of 3G and IP
4Current Situation Technological trends Issues in Wireless Systems Wireless vs FixedWireless LANSWireless PANsCellular
5Technological Trends Advances in Technology more computing power in smaller devicesflat, lightweight displays with low power consumptionuser interfaces suitable for small dimensionshigher bandwidthsmultiple wireless interfaces: wireless LANs, wireless WANs, home RF, wireless PANsNew Electronic Computing Devicessmall, cheap, portable, replaceable and most important of all USABLE!
6Sample Future Application: Vehicles transmission of news, road conditions, weatherpersonal communication using cellularposition identification via GPSinter vehicle communications for accident preventionvehicle and road inter communications for traffic control, signaling, data gatheringambulances, police, etc.: early transmission of patient data to the hospital, situation reportingentertainment: music, video
7An Integrated View ad hoc GSM, 3G, WLAN, Bluetooth, ... PDA, laptop, cellular phones,GPS, sensors
8Constraints of Portable Devices Power consumptionbattery capacity -> limited computing power, low quality/smaller displays, smaller disks, fewer options (I/O, CD/DVD)Device vulnerabilitymore rugged design required to withstand bumps, weather conditions, etc.theftLimited CapabilitiesSmall display size due to size and powercompromise between comfort/usability and portability (e.g., keyboard size)integration of character/voice recognition, abstract symbolsmemory limited by size and power
9Wireless vs Fixed Higher loss-rates due to interference other EM signals, objects in path (multi-path, scattering)Limited availability of useful spectrumfrequencies have to be coordinatedlower transmission rateslocal area: 2 – 11 Mbit/s, -> Mbit/swide area: 9.6 – 19.2 kbit/s -> Kbit/sHigher delays, higher jitterconnection setup time for cellular in the second range, several hundred milliseconds for wireless LAN systemsLower security, simpler active attackingradio interface accessible for everyonebase station can be simulated, thus attracting calls from mobile phonesAlways shared mediumsecure access mechanisms important
10Wireless LANs: Design Goals global, seamless operationlow power for battery useno special permissions or licenses needed to use the LANrobust transmission technologysimplified spontaneous cooperation at meetingseasy to use for everyone, simple managementprotection of investment in wired networkssecurity (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
11Wireless LANs: Standards (2M) -> b (11M) -> a (50-70M)Wider spectrum -> Higher bitratesGenerally used with access pointsAdhoc component not used, has flawsPoor support for real-time communicationsHiperLANEuropean standard for high bit rate (~25M) local transmission in 5GHz range over m
12Infrastructure vs Adhoc infrastructure networkAP: Access PointAPAPwired networkAPad-hoc network
13IEEE 802.11 MAC Traffic services Asynchronous Data Service (mandatory)Time-Bounded Service (optional)Access methods: Distributed Foundation Wireless MAC (DFWMAC)DFWMAC-DCF CSMA/CA (mandatory)collision avoidance via randomized „back-off“ mechanismminimum distance between consecutive packetsACK packet for acknowledgements (not for broadcasts)DFWMAC-DCF w/ RTS/CTS (optional)avoids hidden terminal problemDFWMAC- PCF (optional)access point polls terminals according to a list
14MAC Operation Priorities defined through different inter frame spaces no guaranteed, hard prioritiesSIFS (Short Inter Frame Spacing)highest priority, for ACK, CTS, polling responsePIFS (PCF, Point Coordination Function IFS)medium priority, for time-bounded service using PCFDIFS (DCF, Distributed Coordination Function IFS)lowest priority, for asynchronous data service
15Interframe Spacings DIFS DIFS PIFS SIFS medium busy contention next framet
17Bluetooth Low bitrate (1M), short distances (1-10m) in 2.4GHz ISM band Adhoc networking, cable and IrDA replacementNo mobilityNext generation higher bit rate (10M), longer distances (100m)Scatternets: multihop environment
20Cellular Systems: The essential elements of a cellular system are: Low power transmitter and small coverage areas called cellsSpectrum (frequency) re-useHandoff
21Cells (1/2)Space Division Multiplexing (SDM): base station covers a certain transmission area (cell)Mobile stations communicate only via the base stationAdvantages of cell structures:higher capacity due to frequency re-use -> higher number of usersless transmission power neededmore robust, decentralizedbase station deals with interference, transmission power, etc., locally
22Cells (2/2)Problems:fixed network needed for the base stationshandoffs (changing from one cell to another) necessaryinterference with other cellsCell sizes range from 100 m in dense urban areas to, e.g., 35 km in rural areasCells sizes drop for higher frequencies as propagation loss increases
23Multiplexing Techniques Multiplexing techniques are used to allow many users to share a common transmission resource.In the cellular case the users are mobile and the transmission resource is the radio spectrum.Sharing a common resource requires an access mechanism that will control the associated multiplexing mechanism.
25CDMA: Overview Each channel has a unique code (not necessarily orthogonal)All channels use the same spectrum at the same timeAdvantages:bandwidth efficientno coordination and synchronization necessarygood protection against interference and tappingDisadvantages:lower user data rates due to high gains required to reduce interferencemore complex signal regeneration
27CDMA C/Cs (1/2)A CDMA system can be either code limited or interference limited.For an interference limited system, every user has a code, but only uses it when active, this is referred to as a soft capacity system. The more users active in the system, the more codes that are used. However as more codes are used the signal to interference (S/I) ratio will drop and the bit error rate (BER) will go up for all users.CDMA requires tight power control as it suffers from far- near effect. In other words, a user close to the base station transmitting with the same power as a user farther away will drown the latter’s signal. All signals must have more or less equal power at the receiver.
28CDMA C/Cs (2/2)Rake receivers can be used to improve signal reception. Time delayed versions (a chip or more delayed) of the signal (multipath signals) can be collected and used to make bit level decisions.Soft handoffs can be used. Mobiles can switch base stations without switching carriers. Two base stations receive the mobile signal and the mobile is receiving from two base stations (one of the rake receivers is used to listen to other signals).Burst transmission - reduces interference
29Spread Spectrum: Basis of CDMA Problem of radio transmission: frequency dependent fading can wipe out narrow band signals for duration of the interferenceSolution: spread the narrow band signal into a broad band signal using a special codeSide effects:coexistence of several signals without dynamic coordinationtap-proofTechniques: Direct Sequence, Frequency Hopping
30Operation of SS P f i) ii) sender P f iii) iv) user signal broadband interferencenarrowband interferencedetection atreceiverinterferencespread signalsignalspreadfpower
31SS and Fading narrowband channels spread spectrum channels channel quality2156narrowband channels34frequencynarrow band signalguard spacechannel quality222spread spectrum channels221frequencyspread spectrum
32Cellular: 2G Digital wireless Low bitrate voice and data services Circuit switchedMultiple standards: GSM, IS 136, IS 95Global roaming within similar systems onlyMessaging services: SMSWeb access: imode, wireless portals
33Cellular: 3GThe next generation cellular, 3G, is envisioned to enable communication at any time, in any place, with any form, as such, it will:allow global roamingprovide for wider bandwidths to accommodate different types of applicationssupport packet switching conceptsThe ITU named this vision: IMT-2000 (International Mobile Telecommunications 2000) with the hope of having it operational by the year 2000 in the 2000MHz range.
34IMT-2000 Vision Common spectrum worldwide (2.8 – 2.2 GHz band) Multiple environments, not only confined to cellular, encompasses: cellular, cordless, satellite, LANs, wireless local loop (WLL)Wide range of telecommunications services (data, voice, multimedia, etc.)Flexible radio bearers for increased spectrum efficiencyData rates of: 9.6Kbps or higher for global (mega cell), 144Kbps or higher for vehicular (macro cell), 384Kbps or higher for pedestrian (micro cell) and up to 2Mbps for indoor environments (pico cell)Global seamless roamingEnhanced security and performanceFull integration of wireless and wireline
353G TechnologiesW-CDMA backward compatible with GSM (called UMTS by the ETSI)The IS-95 standard (CDMAOne) is evolving its own vision of 3G: CDMA2000The IS-136 standard is evolving its own migration to 3G, Universal Wireless Communications, UWC-136 or IS-136 HS
363G TimeframeThe Japanese are leading the pack with their W-CDMA implementation. It is planned to be rolled out in the year 2001 (pushed back from spring to late fall).The Koreans plan to have CDMA2000 up an running before the world cup in 2002.The Europeans are pushing hard to UMTS up soon but the current push is for 2.5G, a middle of the road to protect current infrastructure investments.In the US no major push yet, some service providers are following in the footsteps of the Europeans by pushing a 2.5G solution.
37IMT 2000 Services (1/2) All of 2G plus ---> Higher Bit rates: 144Kbps or higher for vehicular (macro cell),384Kbps or higher for pedestrian (micro cell) andup to 2Mbps for indoor environments (pico cell)Billing/charging/user profilesSharing of usage/rate information between service providersStandardized call detail recordingStandardized user profiles
38IMT 2000 Services (2/2)Support of geographic position finding servicesSupport of multimedia servicesQoSAsymmetric linksFixed and variable rateBit rates of up to 2MpbsSupport of packet servicesInternet Access (wireless cellular IP - 3GPP)
39IMT 2000 Family ConceptThe IMT 2000 family concept defines some basic interoperability capabilities between different IMT 2000 technologies to enable global roaming!Different Radio Access Networks (RANs):CDMA2000W-CDMAUWC-136Different Core Network standardsIS 41GSMISDN
40Challenge of the Family Concept With IMT 2000 Standard Interfaces and Capabilities:Any Family RAN could interface with any Family Core Network for some minimum set of features.More advanced features are possible in limited regions where the Family RAN and the Family Core Network are optimally matchedThe Core Network functionality should be kept independent of the Radio technology.By maintaining independence, each can evolve separately based on needsUser Identity Modules (UIM) Plug-In modules could be used in locally rented handsets for Global Roaming with at least the minimum feature set. (similar to GSM SIMs)
41UIM Roaming UIM cards should allow a subscriber to obtain: Any IMT 2000 service/capability basic feature set onAny IMT 2000 Network family member (W-CDMA, CDMA2000 and UWC-136)UIM Card: will be a superset of the current GSM SIMContains all necessary information about the user’s service subscriptionsSupports user identity separate from handset identity:Allows a user to use different handsets, with all usage billed to the single userAllows a user to rent a handset in a foreign country/network and obtain instant service
42To realize the IMT 2000 Vision Physical interfaces are being standardized:UIM to handset interfaceRadio/Air interfacesRAN to Core NetworkNetwork to Network Interfaces (NNI) between Core NetworksRadio independent functions are being standardized:UIM to handsetHandset to Core NetworkNNI
43The next vision: 4G Higher bit rates (what else???): 2Mbps outdoor, high speed20Mbps indoor, low speedFull integration with IPv6, IP QoS and MoIPHigh capacity: 5 to 10 increaseMultimode terminals: seamless switching between different systemsCheaper infrastructure cost
44How to realize 4GHigher spectrum is required to accommodate higher bit rates (e.g., 2-4Mbps requires ~ 20MHz)Problems with propagation loss, attenuationHigher RF circuit lossesBoth of these require higher output power, e.g., 2Mbps at 5GHz requires 2400 times more power than 8Kbps at 2GHzAdaptive phased arrays are needed to achieve higher gains to counteract the losses listed aboveWith better antennas we get higher capacity systems as co-channel interference is reducedThese antennas are expensive but generally constitute the cheapest component of the system
45Issues to be considered Few studies exist that characterize the behaviour of the channel at these higher frequenciesThe increased gains claimed by phased antennas are based on theoretical studies and remain to be verified in live scenariosNew space time channel codes need to be defined that work optimally in this higher frequency rangeEqualization and decoding algorithms need to studied for space time coded systemsTo achieve better performance 3G uses specialized circuits, 4G should use instead general purpose DSP, and implement soft radios
46Higher Layer IssuesNetwork LayerTransport LayerMobility Support
47Network Layer What do cellular networks and wireless LANs provide? Wireless connectivityMobility at the data link layerWhat is Dynamic Host Configuration Protocol (DHCP)?It provides local IP addresses for mobile hostsIs not secureDoes not maintain network connectivity when moving aroundWhat the above do not provide:Transparent connectivity at the network layerMobility with local access, i.e, mobility at the data link layerThe difference between mobility and nomadicity!
48Mobile IP Mobile IP provides network layer mobility Provides seamless roaming‘‘Extends’’ the home network over the entire Internet
49Motivation for MoIP IP Routing Specific routes to end-systems? based on IP destination address, network prefix (e.g ) determines physical subnetchange of physical subnet implies change of IP address to have a topologically correct address (standard IP) or needs special entries in the routing tablesSpecific routes to end-systems?requires changing all routing table entries to forward packets to the right destinationdoes not scale with the number of mobile hosts and frequent changes in the location, security problemsChanging the IP-address?adjust the host IP address depending on the current locationalmost impossible to find a mobile system, DNS updates slowTCP connections break, security problems
50Scope of MoIP Mobile IP solves the following problems: if a node moves without changing its IP address it will be unable to receive its packets,if a node changes its IP address it will have to terminate and restart its ongoing connections everytime it moves to a new network area (new network prefix).Mobile IP is a routing protocol with a very specific purpose.Mobile IP is a network layer solution to node mobility in the Internet.Mobile IP is not a complete solution to mobility, changes to the transport protocols need to be made for a better solution (i.e., the transport layers are unaware of the mobile node’s point of attachment and it might be useful if, e.g., TCP knew that a wireless link was being used!).
51Requirements of MoIP Transparency Compatibility Security mobile end-systems keep their IP addresscontinuation of communication after interruption of link possiblepoint of connection to the fixed network can be changedCompatibilitysupport of the same layer 2 protocols as IPno changes to current end-systems and routers requiredmobile end-systems can communicate with fixed systemsSecurityauthentication of all registration messagesEfficiency and scalabilityonly little additional messages to the mobile system required (connection typically via a low bandwidth radio link)world-wide support of a large number of mobile systems
52Problems with MoIP Security Firewalls QoS authentication with FA problematic, for the FA typically belongs to another organizationno protocol for key management and key distribution has been standardized in the Internetpatent and export restrictionsFirewallstypically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling)QoSmany new reservations in case of RSVPtunneling makes it hard to give a flow of packets a special treatment needed for the QoSSecurity, firewalls, QoS etc. are topics of current research and discussions!
53Transport Layer Transport protocols typically designed for Fixed end-systemsFixed, wired networksTCP congestion controlpacket loss in fixed networks typically due to (temporary) overload situationsrouters have to discard packets as soon as the buffers are fullTCP recognizes congestion only indirectly via missing (I.e., timed out) acknowledgementsImmediate retransmissions unwise, they would only contribute to the congestion and make it even worseslow-start algorithm is used as a reactive action to reduce the network load
54Influences of Mobility and Wireless TCP assumes congestion if packets are droppedtypically wrong in wireless networks, here we often have packet loss due to transmission errorsfurthermore, mobility itself can cause packet loss, if e.g. a mobile node roams from one access point (e.g. foreign agent in Mobile IP) to another while there are still packets in transit to the old access point and forwarding from old to new access point is not possible for some reasonThe performance of unmodified (i.e., as is) TCP degrades severelynote that TCP cannot be changed fundamentally due to the large base of installation in the fixed network, TCP for mobility has to remain compatiblethe basic TCP mechanisms keep the whole Internet together
58File Systems Goal Problems Solutions efficient and transparent access to shared files within a mobile environment while maintaining data consistencyProblemslimited resources of mobile computers (memory, CPU, ...)low bandwidth, variable bandwidth, temporary disconnectionhigh heterogeneity of hardware and software components (no standard PC architecture)wireless network resources and mobile computer are not very reliablestandard file systems (e.g., NFS, network file system) are very inefficient, almost unusableSolutionsreplication of data (copying, cloning, caching)data collection in advance (hoarding, pre-fetching)
59Databases Request processing Replication management power conserving, location dependent, cost efficientexample: find the fastest way to a hospitalReplication managementsimilar to file systemsLocation managementtracking of mobile users to provide replicated or location dependent data in time at the right place (minimize access delays)example: with the help of the HLR (Home Location Register) in GSM a mobile user can find a local towing serviceTransaction processing“mobile” transactions cannot necessarily rely on the same models as transactions over fixed networks (ACID: atomicity, consistency, isolation, durability)
60WWW 1/3Protocol (HTTP, Hypertext Transfer Protocol) and language (HTML, Hypertext Markup Language) of the Web have not been designed for mobile applications and mobile devices, thus creating many problems!Typical transfer sizesHTTP request: byteResponses avg. <10 Kbyte, header 160 byte, GIF 4.1Kbyte, JPEG 12.8 Kbyte, HTML 5.6 kbyteAnd many large filesThe Web is no file systemWeb pages are not simple files to downloadstatic and dynamic content, interaction with servers via forms, content transformation, push technologies etc.many hyperlinks, automatic loading and reloading, redirectinga single click might have big consequences!
61WWW 2/3 Characteristics Problems stateless, client/server, request/responseneeds a connection oriented protocol (TCP), one connection per request (some enhancements in HTTP 1.1)primitive caching and securityProblemsdesigned for large bandwidth (compared to wireless access) and low delaylarge and redundant protocol headers (readable for humans, stateless, therefore large headers in ASCII)uncompressed content transferusing TCPDNS lookup by client causes additional traffic and delays
62WWW 3/3 Caching POSTing (i.e., sending to a server) quite often disabled by information providers to be able to create user profiles, usage statistics etc.dynamic objects cannot be cachednumerous counters, time, date, personalization, ...mobility quite often inhibits cachessecurity problemscaches cannot work with authentication mechanisms that are contracts between client and server and not the cachetoday: many user customized pages, dynamically generated on request via CGI, ASP, ...POSTing (i.e., sending to a server)can typically not be buffered, very problematic if currently disconnectedMany unsolved problems!
63HTML and Mobility HTML Mobile devices Additional “features” designed for computers with “high” performance, color high-resolution display, mouse, hard disktypically, web pages optimized for design, not for communicationMobile devicesoften only small, low-resolution displays, very limited input interfaces (small touch-pads, soft-keyboards)Additional “features”animated GIF, Frames, ActiveX Controls, Shockwave, movie clips,many web pages assume true color, multimedia support, high-resolution and many plug-insWeb pages ignore the heterogeneity of end-systems!e.g., without additional mechanisms, large high-resolution pictures would be transferred to a mobile phone with a low-resolution display causing high costs
64WWW and Mobility Application gateways, enhanced servers Examples simple clients, pre-calculations in the fixed networkCompression, transcoding, filtering, content extractionautomatic adaptation to network characteristicsExamplespicture scaling, color reduction, transformation of document formatPresent only parts of the image: detail studies, clipping, zoomingheadline extraction, automatic abstract generationHDML (handheld device markup language): simple language similar to HTML requiring a special browserHDTP (handheld device transport protocol for HDMLProblemsproprietary approaches, require special enhancements for browsersheterogeneous devices make approaches more complicated
65What is happening 1/2 HTTP/1.1 client/server use the same connection for several request/response transactionsmultiple requests at beginning of session, several responses in same orderenhanced caching of responses (useful if equivalent responses!)semantic transparency not always achievable: disconnected, performance, availability -> most up-to-date version...several more tags and options for controlling caching (public/private, max-age, no-cache, etc.)encoding/compression mechanism, integrity check, security of proxies, authentication, authorization...
66What is Happening 2/2 Enhanced browsers Client Proxy Pre-fetching, caching, off-line usee.g. Internet ExplorerClient Proxye.g., Caubweb, TeleWeb, Weblicator, WebWhacker, WebExClient and network proxycombination of benefits plus simplified protocolse.g., MobiScape, WebExpressSpecial network subsystemadaptive content transformation for bad connections, pre-fetching, cachinge.g., Mowgli
67ConclusionsThe problems with 3G are mostly infrastructure cost relatedThe problems facing 4G are much more fundamentalIt is absolutely imperative that we start to think about what the future will be like so that we can direct our energies to solving these problemsWireless systems will become pervasive and will exist in a multitude of flavors (sensors, satellites, LANs, PANs, cellular, access, etc,).We need to be able to provide a seamless integration of all these systemsStill need work at higher layers for true nomadicity, not just wireless and mobility