Mobile Communications OverviewLecturer:Michael O'GradyCourse:MSc Ubiquitous & Multimedia SystemsUnit:Context Sensitive Service DeliveryLecture:

OutlineIntroduce some basic wireless conceptsDescribe the evolution of cellular telecommunications networksReflect on the services supportd by cellular networksConsider the issue of standardization in wireless communications

Recall: PSTNPublic Switched Telephone Network

Concatenation of the interconnected Networks operated by the various telephone companies (telcos) and public utility companies (PTTs) throughout the world

Originally - human operated (plugboards), analogue signalLater -Electromechanical switches

Today -Automated, digital

But the so-called last mile problem

Recall: PLMNPublic Land Mobile Network (PLMN)

Operated by either government agency or government appointed company. Objective is to deliver services to those members of the public who are mobile. May be considered an extension or an integral part of the PSTN. Uses Wireless technologies.

Advantages of WirelessConstant connectionAccess to up-to-date informationMinimum installation issuesFreedom to roamScalabilityNo cablesExtensibility e.g remote areas with satellite

Disadvantages of WirelessCareful planning of network essentialEnvironment generally hostileSecuritySafetyspectrum licensespoor data ratescost (domain dependant)

Some Historical DevelopmentsOrigins debatable but .1887 - Hertz demonstrates EM waves1896 - Marconi demonstrates wireless telegraph apparatus1901 - First radio signal across the Atlantic (Cornwall to Newfoundland)1914 - First wireless voice transmission1946 - PSTN augmented with wireless1947 - Cellular Network proposed

Why Cellular?Originally proposed by D. H. Ring in an unpublished paper.Why?Potential for existing systems to expand was severely limited.How?Reuse frequencies so as to maximize the use of the available radio spectrum thus improving scalability. Note: This issue will be revisited when the GSM architecture is discussed.

StandardizationAdvantages includeaccelerates the availability of new equipment and services lowers costs through increased competition ensures reliability of supply ensures interoperabilityDe Jure defined by industry groups or government agenciesDe Factoestablished as the result of a product dominating the market

1G - CharacteristicsAnalogue transmission technologyPioneered semiconductor and microprocessor technologyFocus on voiceData services almost non-existentIncompatible standards Different frequencies and signaling International roaming impossibleInefficient use of the radio spectrum

1G - NTTNippon Telephone & Telegraph (NTT)Now NTT DoCoMo1979TokyoWorlds first operational cellular system

1G - NMT-450Nordic Mobile Telephone 4501982SwedenFirst wireless communications standard deployed in EuropePioneered the use of light portable handsetsSupported international roaming

1G - AMPSAdvanced Mobile Phone System (AMPS)1982USAMandated (FCC) as the standard to which all operators in the USA had to adhere to.

1G - TACSTotal Access Coverage (TACS)1985UKAdaptation of AMPSComplies with frequency allocation in Europe

1G - Network Access TechniqueFrequency Division Multiple Access (FDMA)Subdivides the available spectrum into a number of frequency slotsEach user is assigned a separate frequency.

1G - ServicesStandard voiceNo data servicesNo supplementary services Call barring

The 1G LandscapeA series of incompatible networksLimited capacity for expansionLimited support for roamingSusceptible to interferencePoor securityNo support for wireless data No third party applications

Solution: 2GDigital techniques rather than analogueIncreased flexibility error control compressionMore efficient use of available bandwidthIncreased compatibility with the fixed component of the PSTNIncreased quality of servicePossibility of wireless data services

2G - GSMGlobal System for Mobile Communication (GSM)Conceived in 1982Deployed in 1992 in EuropeEuropean Telecommunications Standards Institute (ETSI)Most successful 2G system 863 million users in 197 countries

2G - D-AMPSDigital Advanced Mobile Phone Service (DAMPS) Also called IS-54 (Interim Standard 54)1991Dual mode terminals ensuring backward compatibilityIS-136 introduced in 1996Telecommunications Industry Association (TIA) TR-45 Committee

2G - IS-95Interim Standard 95 (IS-95)Also called cdmaOne1993USAQualcomm Inc.Pioneered the use of the network access technique CDMA

2G - PDCPersonal Digital Cellular (PDC)1991JapanTwo modes Full-rate Half-rate12% of global digital subscriptions in 1999.

2G - Network Access TechniqueTime Division Multiple Access (TDMA)Users share a frequency band by multiplexing their transmissions in timeIn practice ..Available spectrum is divided into frequency channels (recall FDMA!)Each frequency channel is further subdivided into cyclic timeslots (1,2,3,1,2,3,1,2,3 )A call is assigned a time slot

2G - ServicesDepends on Network standard Operator policiesImproved standard telephony (speech)Basic wireless dataAdditional services Call barring

Example: GSM ServicesTeleservices Speech Emergency calls Short Message Service (SMS)Bearer Services Telefax Basic data (9.6kb/s)Supplementary Services Call forwarding Call barring

2G - 3G Transition Driver?

Higher data bandwidth requirementanticipated subscriber demand foraudio/Video streamingother multimedia servicescollaborative serviceslocation servicesPossibility of third party applications being developed

Recall: Circuit v Packet SwitchingCircuit Switched ..A dedicated channel is established for the duration of a callPacket Switched A message is subdivided into packets which are sent individually and may follow different routes to their destination. The packets are then used to reassemble the original message.

3G - Migration StrategiesMigrate straight to 3GThis approach is being take by some operators in Japan (PDC) and the USA (IS-95)

Migrate incrementally to 3GOperators progressively and incrementally incorporate a number of technologies into their networksThis approach is taken by operators in both Europe and the USA This strategy is sometimes referred to as 2.5G

2.5G - HSCSD (GSM)High Speed Circuit Switched Data (HSCSD)Uses existing GSM infrastructure and interfaceData rates of up to 57.6 kb/s (4 channels @ 14.4 kb/s)Inefficient for certain types of application

2.5G - GPRS (GSM)General Packet Radio Service (GPRS)Introduces packet switching to GSMAlways-onUses multiple timeslots (channels)14.4 kb/s per channelMaximum of 115.2 kb/s Dynamic resource allocationSupports IPBilling per KB, NOT per sec.

2.5G - EDGE (GSM)Enhanced Data rates for GSM Evolution (EDGE)Maximum 384 kb/s8 Phase Shift Keying (8PSK)Send more bits down the line3 fold increase over GSMTwo classes of handset:Class A (EDGE only on downlink)Class B ( EDGE on uplink and downlink)

2.5G - D-AMPS (IS-136+)Two phase migration path IS-136+Integrate GPRSNote: packet switching already supported by Cellular Digital Packet Data (CDPD)! IS-136 High Speed OutdoorIntegrate EDGE

Subscribers can roam between IS-136HS and GSM networks supporting EDGE

2.5G - IS-95B (IS-95)Enhanced version of IS-95 Already supports packet switching (CDPD)Maximum of 115.2 (8 channels @ 14.4kb/s)Realistically 28.8 kb/s to 57.6 kb/s on downlink 14.4 kb/s on uplink

2.5G - ServicesStandard services that can use packet switching: WWW browsing email file downloading e.g. mp3Multimedia Messaging Service (MMS)

3G - The IMT2000 InitiativeConceived in 1986Sought to define a single world-wide standard for accessing the global telecommunications infrastructure from both terrestrial and satellite mobile systemsProblem: backward compatibilitySo five standards approved for the air interface!

3G - Air Interface Standards IIMT-DS (Direct Spread), also known as Wideband CDMA Frequency Division Duplex (W-CDMA-FDD).IMT-TC (Time Code) or W-CDMA Time Division Duplex (W-CDMA-TDD). IMT-MC (Multi-Carrier) or CDMA2000.IMT-SC (Single Carrier), also known as EDGE or UWC-136.IMT-FT (Frequency Time), for cordless sytems e.g. DECT

3G - Interface Standards II

3G - Principal Requirements - ISupport for voice quality comparable with fixed line networks;Support for both circuit-switched and packet-switched data services;Support for roaming between different IMT-2000 operators;Support for greater capacity and improved spectrum efficiency;

3G - Principal Requirements - IIA data rate of 144 kb/s for users moving quickly e.g. moving vehicles;A data rate of 384 kb/s for pedestrians;A data rate of 2 Mb/s in a low mobility or office environment.

Note how a network using GPRS and EDGE meets most of these criteria!

3G - Network Access TechniqueCode Division Multiple Access (CDMA)Signal is modulated with high bandwidth spreading waveforms called signature waveforms or codes. Subscribers may submit at the same frequency and time but signal separation is facilitated via the signature waveform In contrast with TDMAMore robustLess susceptible to fading & interference

3G Networks

2G Network

3G Successor

GSM

UMTS

PDC

CDMA2000

IS-95

CDMA2000

DAMPS

IS-136HS or UMTS

Example: 3G Services (UMTS)Universal Mobile Telephone System (UMTS)Four QoS classes of servicesConversational ClassVoice, video telephony,video gamingStreaming Classmultimedia, video on demand, webcastInteractive ClassWWW browsing, database access, online gamingBackground Classemail, SMS, file downloading

Quality of Service (QoS)the collective effect of service performances which determine the degree of satisfaction of a user of a service ITU G1000 specification

Telecommunications WorldQoS encapsulates all aspects of a service that determine the degree of satisfaction with that service.

IP WorldQoS implies guaranteed bandwidth

Pronunciation check: QoS == kwoz

QoS: Network v CustomerNetwork performancePacket loss, transmission delay, bit error rates, call set-up times, etcBut customer interpretation?Thus Q.800 suggests:Focus on effects as perceived by customerNo assumptions about network designAll aspects of the service considered (from customer perspective)Network independent terms usedCan be assured to a user by a service provider

3.5GUMTSHigh Speed Downlink Packet Access (HSDPA)14 Mbps (but 1 Mbps per subscriber!)Incremental upgradeMore functionality in Node BBackward compatible with W-CDMAHigh Speed Uplink Packet Access (HSUPA)Other TechnologiesOFDN, WiMAX, etc, etc

4G- Some SpeculationsGlobal MobilityIncreased data rates..100Mbps?All IP networkWhen?

Standardisation - ITUFounded in 1865 in Paris by 20 European countriesinterconnection issuesequipment standardizationuniform instructions for operating equipmentaccounting procedures and rulesToday, affiliated with the UN500 new or revised recommendations every year!

Structure of the ITUTelecommunications Standardization (ITU-T)specifications for systems networks and servicesRadiocommunications (ITU-R)specifies technical characteristics of terrestrial and space based wireless services and systemsTelecommunications Development (ITU-D)reports, guidelines and recommendations for developing countries

Wireless StandardizationRecall IMT2000 visionTwo global partnerships comprising a number of traditional standardization bodies Third Generation Partnership Project (3GPP) Concerned with EDGE & UMTS advancement Third Generation Partnership Project 2 (3GPP2) Concerned with CDMA advancementNote that membership not mutually exclusive!

3GPP - Organizational Partners

3GPP2 - Organizational Partners

SummaryIntroduced wireless communicationsDescribed the evolution of the various generations of cellular networks Described the services supported by the various networks and the issues effecting their deploymentBriefly introduced the issue of standardization

Review QuestionsCompare and contrast the three generations of mobile networks.Trace the evolution of services from 1G to 3G.Identify the advantages and disadvantages of circuit switched and packet switched data services from both an operator and subscriber perspective.What benefits do standardization bring to network operators? Subscribers?

The End

POTS - Plain Old telephony ServiceCopper in on the ground - local loopFirst Solution ISDNAdslWireless Local Loop

The "last mile" problem, also referred to as local-loop bottleneck problem, occurs where "last mile" local area networks, which link devices within a building or a campus, join towide area networks, which crisscross countries and hold the Internet together. Advances in fiber technology have extended the capacity of wide area networks to trillions of bits per second. Meanwhile, the connections between these two domains have not kept pace, the vast majority of copper-wire circuits being limited to about the 1.5 Mbps rate of a so-called T1 line.The typical home user faces a more extreme case of the same affliction, with data crawling between computer and Internet about 30 times slower, through a modem and phone line operating at a mere 56 kilo bits per second (Kbps). The disconnect between backbone networks and the local loops of incumbent local exchange carriers, is a gap between 21st century communications demand and 1950s local loop infrastructure capability.

Smoke signalsExperiments on electromagnetic induction bt faraday1844 Morse code1866 - second atlandic cable1876 - bell files patent on telephone

1880 - first pay stations attend by people. No coins.

1920 - wireless deployed in police cars in Detriot.

Other advantages ???

Any disadvantages ??

About CDMA?qualcommPatent royalties?

Why traditionally important in telecomms?Susceptible to interference72% of world digital market70% world wireless marketHalf rate reduces voice quality and data transmission rates thus allowing more subscribers sgare the same bandwidthPacket Switching

Refers to protocols in which messages are divided into packets before they are sent. Each packet is then transmitted individually and can even follow different routes to its destination. Once all the packets forming a message arrive at the destination, they are recompiled into the original message. Most modern Wide Area Network (WAN) protocols, including TCP/IP, X.25, and Frame Relay, are based on packet-switching technologies. In contrast, normal telephone service is based on a circuit-switching technology, in which a dedicated line is allocated for transmission between two parties. Circuit-switching is ideal when data must be transmitted quickly and must arrive in the same order in which it's sent. This is the case with most real-time data, such as live audio and video. Packet switching is more efficient and robust for data that can withstand some delays in transmission, such as e-mail messages and Web pages. A new technology, ATM, attempts to combine the best of both worlds -- the guaranteed delivery of circuit-switched networks and the robustness and efficiency of packet-switching networks.

Circuit SwitchedA type of communications in which a dedicated channel (or circuit) is established for the duration of a transmission. The most ubiquitous circuit-switching network is the telephone system, which links together wire segments to create a single unbroken line for each telephone call. The other common communications method is packet switching, which divides messages into packets and sends each packet individually. The Internet is based on a packet-switching protocol, TCP/IP.

Circuit-switching systems are ideal for communications that require data to be transmitted in real-time. Packet-switching networks are more efficient if some amount of delay is acceptable.

Circuit-switching networks are sometimes called connection-oriented networks. Note, however, that although packet switching is essentially connectionless, a packet switching network can be made connection-oriented by using a higher-level protocol. TCP, for example, makes IP networks connection-oriented.

HSCSD [ETSI TS 101 625] is the first extension to GSM aimed at addressing the need for higher data rates. It uses the existing GSM infrastructure and air interface so its integration is straightforward. Data rates of up to 57.6 kb/s (4 channels @ 14.4 kb/s) are supported. As a physical channel must be maintained for the duration of the call, HSCSD is inefficient for certain types of application e.g. WWW browsing when data would come in bursts and there would be long periods of inactivity.

GPRS [GL00] [ETSI TS 101 344] introduces packet-switching technology to GSM. In comparison with HSCSD, GPRS is a very significant upgrade. Packet switching has been utilised by many fixed line networks including X.25, Frame Relay, ATM and the Internet, and is particularly suitable to bursty traffic such as that generated by browsing the WWW. Subscribers can simply use standard IP addresses for accessing other data networks. Resource allocation in a GPRS network is dynamic and dependent on both availability and demand thereby gaining maximum benefit from the infrastructure and available spectrum. In comparison with GSM, connection set-up is far quicker at typically less than a second and data rates are significantly higher. Like HSCSD, GPRS increases the data rate by using multiple timeslots. In standard GSM, a single caller occupies one out of the eight available timeslots. By using multiple timeslots per user, the data rate can be increased according to the number of timeslots used. Assuming a standard rate of 14.4 kb/s per channel (timeslot), data rates of 28.8 kb/s (using two channels), 43.2 kb/s (3 channels) or a maximum of 115.2 kb/s can be achieved using all eight channels. In theory, higher data rates can be achieved if no error checking is performed. In practice, network and terminal constraints are likely to limit the data rates offered to customers. However, depending on application requirements and network capacity, the data rate itself can be dynamically changed during the actual duration of a call.

Implementing GPRS requires a radical shift in billing policies.A major step in the evolution of GSM is the implementation of EDGE [ETSI TR 150 059] which will further exploit the advantages of GPRS by increasing the data rate to 385 kb/s. Since the data rate for GSM and HSCSD is limited by the physical number of timeslots, the only way to increase data rates is to send more bits down the line each time. EDGE achieves this by using a new modulation scheme - Eight Phase Shift keying (8PSK). This provides a 3-fold increase over standard GSM, which uses Gausian Minimum Shift Keying (GMSK). EDGE is sometimes regarded as a generic air interface technology as it can operate in two modes: packet-switched or enhanced GPRS (EGPRS) for GPRS traffic, and enhanced HSCSD (ECSD) for circuit-switched traffic. As pre-existing GSM or GPRS protocols are reused as much as possible, the introduction of EDGE requires few changes in the network hardware and software. However, with respect to the actual mobile terminal or handset, the EDGE standard defines two classes:

Class A defines an implementation where EDGE is only used on the downlink, i.e. between the base station and the mobile. Standard GMSK is used on the uplink i.e. mobile to base station. In this way the cost of the mobile is kept down while performance issues would rarely be affected as most applications require more data being transferred on the downlink than the uplink e.g. web browsing.

Class B requires a full EDGE implementation on the downlink and the uplink.

IS-136, also known as TIA/EIA-136, has a two-phase migration path towards 3G as defined in the UWC-136 3G submission to the ITU [UWC-136], referred to IS-136+ and IS-136HS respectively.IS-136+ is the first phase of the migration path in which significant enhancements will be made for improved voice and data communications. In contrast to standard GSM, IS-136 supports packet switching via the Cellular Digital Packet Data (CDPD) system. CDPD can also be used with AMPS and IS-95. Though it had been widely anticipated that an enhanced version of CDPD would be used as part of the 3G evolution process [FHK+99], a strategic decision was made by the Universal Wireless Consortium (UWC) in January 1998 to use GPRS and EDGE [ZAB99]. The integration of GRPS into IS-136 is a fundamental objective for IS-136. IS-136 High Speed Outdoor (IS-136HS Outdoor) is the second phase of the migration path and is primarily concerned with the introduction of EDGE. Like GSM, data rates of up to 384 kb/s will be achievable. Once this data service, technically referred to as EGPRS-136, is operable, subscribers can roam between IS-136HS and any GSM networks that have deployed EDGE.

Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system. Each signal travels within its own unique frequency range (carrier), which is modulated by the data (text, voice, video, etc.).

Orthogonal FDM's (OFDM) spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the "orthogonality" in this technique which prevents the demodulators from seeing frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion. This is useful because in a typical terrestrial broadcasting scenario there are multipath-channels (i.e. the transmitted signal arrives at the receiver using various paths of different length). Since multiple versions of the signal interfere with each other (inter symbol interference (ISI)) it becomes very hard to extract the original information.

OFDM is sometimes called multi-carrier or discrete multi-tone modulation. It is the modulation technique used for digital TV in Europe, Japan and Australia.

1. Telecommunication Standardisation (ITU-T)This sector is concerned with the development of specifications for telecommunications systems, networks and services. Areas covered include operation, performance and maintenance. The critical areas of charging and accounting are also covered. 2. Radiocommunications (ITU-R)The ITU-R specifies the technical characteristics of both terrestrial and space-based wireless services and systems, as well as defining the relevant operational procedures.3. Telecommunications Development (ITU-D)Concerned with aiding decision-makers in developing countries, the ITU-D prepares recommendations, handbooks, guidelines and reports on best industry practices.