Mobile Communications II From Cellular to Mobile Services

Transcription

1 Mobile Communications II From Cellular to Mobile Services Prof. Dr.-Ing. Rolf Kraemer chair owner telefon: fax: kraemer [ at ] ihp-microelectronics.com web:

2 General Information Lecture dates: Mostly Bi-weekly: 7 lectures; 11:30-13: :45-15: , , 22.11, , , , Exercise will be conducted by MSc. Nicole Todtenberg (todtenberg@ihpmicroelectronics.com) and MSc. Stephan Kornemann (kornemann@ihpmicroelectronics.com) Normally shifted one week from lecture 5 Exercices;11:30-13: , , , , Exams Oral Credits 6 Slides lecture and exercises one week before on www-server Lectures and exercises Material: Page 2

3 Mobile Communications II Chapter 2: GSM Global System for Mobile Communications Architectures and Overview Data services in GSM

4 GSM: Overview GSM formerly: Groupe Spéciale Mobile (founded 1982) now: Global System for Mobile Communication Pan-European standard (ETSI, European Telecommunications Standardisation Institute) In the context of UMTS 3GPP took over the completion of GSM and UMTS simultaneous introduction of essential services in three phases (1991, 1994, 1996) by the European telecommunication administrations (Germany: D1 and D2 and E) seamless roaming within Europe possible today many providers all over the world use GSM almost 7 billion (cellular) subscribers (of 2013) more than 80% of all digital mobile phones use GSM over 5 billion SMS per month in Germany (numbers of 2013) Chapter 2 Page 64

5 Frequencies used For GSM always a dual band allocation is necessary because of FDD! GSM 900: MHz; MHz GSM 1800: MHz; MHz GSM 1900 (PCS-1900): MHz; MHz (for US) GSM400: (for rural applications) 450,4-457,6 MHz; 460,4-467,7 MHz or 478,8-486 MHz; 488,8-496 MHz GSM-Rail Separate frequencies Additional services for rail application, monitoring control Advanced Speech Call Items (ASCI) Call Priorities Control of Trains, Signals for Trains up to 160Km/h Chapter 2 Page 65

6 Performance characteristics of GSM (wrt. analog sys.) Communication (mainly telephony) mobile, wireless communication; support for voice and data services Total mobility international access, chip-card enables use of access points of different providers (today the SIM is a part of the 3G and 4G standards) Worldwide connectivity one number, the network handles localization High capacity better bandwidth efficiency, smaller cells, more customers per cell (as compared with LTE, GSM cells are quite big and the efficiency is rather poor) 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 Chapter 2 Page 66

7 Disadvantages of GSM Performance: no full ISDN bandwidth of 64 kb/s to the user, no transparent D-channel (ISDN S 0 interface provides 2 B channels of 64 kb/s each and one D- channel of 16 kb/s for signaling purposes) Security/Privacy: no end-to-end encryption of user data abuse of private data possible roaming profiles (potentially) accessible Complexity/Cost high complexity of the system as opposed to the solutions like c-net as an island of communication (that was indeed one road-block at the introduction phase. Today GSM is rather simple as opposed to other wireless standards like e.g. LTE, n etc.) several incompatibilities within the GSM standards (but it was a huge amount of standard documents compared to any other standard so far) Chapter 2 Page 67

8 GSM: Mobile Services GSM offers several types of connections voice connections, data connections, short message service multi-service options (combination of basic services) Three service domains Bearer Services (only up to network layer) Telematic Services (end to end definition of services) MS TE Supplementary Services bearer services MT GSM-PLMN transit network source/ destination R, S (PSTN, ISDN) network (U, S, R) U m TE Transparent data access tele services MT: Mobile Termination PLMN: Public Land Mobile Network Chapter 2 Page 68 TE: Terminal Equipment

9 R-Schnittstelle Vom CCITT definierte Referenz-Schnittsteile für den Anschluss von nicht ISDNkompatiblen Endgeräte an das ISDN-Netz. Die R-Schnittstelle befindet sich beim Teilnehmer. Physikalisch gesehen ist sie am Terminaladapter angebracht. U-Schnittstelle Beim ISDN-Basisanschluss wird der übertragungstechnische Abschluss der Netzseite als U-Schnittstelle bezeichnet. Die zweidrahtige Schnittstelle verfügt über 2 B-Kanäle mit jeweils 64 kbit/s und 1 D-Kanal mit 16 kbit/s. Die Entfernungsüberbrückung beträgt ca. 8 km. S-Schnittstelle, S-Bus 4-drahtige Schnittstelle am Basisanschluss, die als Anwenderschnittstelle dem Benutzer zur Verfügung gestellt wird. An der S-Schnittstelle, die vom ITU-T (CCITT) definiert worden ist, werden 2 B-Kanäle mit jeweils 64 kbit/s und 1 D- Kanal mit 16 kbit/s angeboten. An dieser Schnittstelle ist der Anschluss von 8 Endgeräten möglich, wobei 2 gleichzeitig betrieben werden können. Physikalisch wird eine Busleitung verlegt (S-Bus). Chapter 2 Page 69

10 Bearer Services Telecommunication services to transfer data between access points (R/S- Interface) Specification of services up to the terminal interface (OSI layers 1-3) Main differentiation between Transparent data service (only layer 1; no recovery, constant delay, BER~ 10-4 ) Non transparent data service (layer 1-3; FEC and ARQ implicit, undefined delay jitter, BER~10-7 ) Different data rates for voice and data in full duplex (original standard) data service (circuit switched) synchronous: 2.4, 4.8 or 9.6 kbit/s asynchronous: bit/s data service (packet switched) synchronous: 2.4, 4.8 or 9.6 kbit/s asynchronous: bit/s Today: data rates of approx. 50 kbit/s 150 Kbit/s possible (will be covered later in chapter on data services) Chapter 2 Page 70

11 Tele Services I Telecommunication services that enable voice communication via mobile phones All these basic services have to obey cellular functions, security measurements etc. Offered services mobile telephony primary goal of GSM was to enable mobile telephony offering the traditional bandwidth of 3.1 khz Codecs are use to transmit voice/data with good quality (today this is considered as not sufficient quality) 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 Chapter 2 Page 71

12 Tele Services II Additional services 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 using the signaling channel (max. length 160 B), thus allowing simultaneous use of basic services and SMS Currently more than 350 billion SMS mails are send/month worldwide SMS is used (normally as EMS or MMS) for several new messaging applications SMS is the only push service supported Chapter 2 Page 72

13 Supplementary services Services in addition to the basic services, cannot be offered stand-alone Similar to ISDN services besides lower rate 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) Closed group numbering. Chapter 2 Page 73

14 Architecture of the GSM system GSM is a PLMN (Public Land Mobile Network) several providers (worldwide) setup mobile networks following the GSM standard within each country components MS (mobile station) BS (base station) MSC (mobile switching center) LRs (location registers) subsystems RSS (radio subsystem): covers all radio aspects NSS (network and switching subsystem): call forwarding, handover, switching OSS (operation subsystem): management of the network Chapter 2 Page 74

15 GSM: overview NSS with OSS OMC, EIR, AUC HLR GMSC fixed network VLR MSC VLR MSC BSC BSC RSS Chapter 2 Page 75

16 GSM: elements and interfaces PCM-30 RSS NSS Several Sectors per BSS can be supported A bis A BSC VLR U m MS MSC radio cell HLR BTS O MS 100m-35km BSC VLR BTS MSC GMSC BSS radio cell MS IWF signaling ISDN, PSTN PDN RSS: Radio Subsystem NSS: Network & Switching Subsystem OSS: Operation Subsystem MS: Mobile Station BSS: Base-station Subsystem BSC: Base-station Control Centre BTS: Base-Transceiver Station MSC: Mobile Switching Centre VLR: Visitor Location Register HLR: Home Location Register GMSC: Gateway MSC IWF: Inter-working Function OMC: Operation Maintenance Centre EIR: Equipment Identity Register AUC: Authentication Centre OSS EIR AUC OMC X25-based SS7 Chapter 2 Page 76

17 Radio subsystem The Radio Subsystem (RSS) comprises the cellular mobile network up to the switching centers Components Base Station Subsystem (BSS): Base Transceiver Station (BTS): radio components including sender, receiver, antenna - if directed antennas are used one BTS can cover several cell-areas Base Station Controller (BSC): switching between BTSs, controlling BTSs, managing of network resources, mapping of radio channels (U m ) onto terrestrial channels (A interface) BSS = BSC + sum(bts) + interconnection Mobile Stations (MS) Chapter 2 Page 81

18 Cell structure Implements space division multiplex: base station covers a certain transmission area (cell) Mobile stations communicate only via the base station Advantages of cell structures: higher capacity, higher number of users less transmission power needed (important mainly for the mobile part) more robust, decentralized (less single points of failure) base station deals with interference, transmission area etc. locally Problems: fixed network needed for the base stations handover (changing from one cell to another) necessary interference with other cells Cell radius from some 100 m in cities to, e.g., 35 km on the country side (GSM900) 35 km is due to restriction to 6 bit Time advance signal (explained later) Chapter 2 Page 82

19 Frequency planning I Frequency reuse only with a certain distance between the base stations Standard model using 7 frequencies: f 3 f 5 f 2 f 4 f 6 f 5 f 1 f 4 f 3 f 7 f 1 Fixed frequency assignment: certain frequencies are assigned to a certain cell problem: different traffic load in different cells Dynamic frequency assignment: base station chooses frequencies depending on the frequencies already used in neighbor cells more capacity in cells with more traffic assignment can also be based on interference measurements f 2 Chapter 2 Page 83

20 GSM: cellular network possible radio coverage of the cell cell idealized shape of the cell use of several carrier frequencies not the same frequency in adjoining cells 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 What is the optimal cell to change to? What parameters can play a role? Chapter 2 Page 84

21 Frequency planning II f 3 f 1 f 2 f 3 f 2 f 3 f 1 f 3 f 1 f 2 f 3 f 2 f 3 f 1 f 3 f 1 f 2 f 3 3 cell cluster f 2 f 4 f 3 f 6 f 5 f 1 f 2 f 3 f 6 f 7 f 5 f 2 f 4 f 3 f 7 f 5 f 1 f 2 7 cell cluster f 2 f 3 f 1 f 2 f 3 f 1 f 1 h h 2 1 h 3 h 1 h 2 h 3 g 1 g 2 g 3 g 1 g 2 g 3 f 2 f 3 g 1 g 2 g 3 3 cell cluster with 3 sector antennas Chapter 2 Page 85

22 Example coverage of GSM networks ( T-Mobile (GSM-900/1800) Berlin Vodafone (GSM-900/1800) e-plus (GSM-1800) O 2 (GSM-1800) Chapter 2 Page 86

23 Base Transceiver Station and Base Station Controller Tasks of a BSS are distributed over BSC and BTS BTS comprises radio specific functions BSC is the switching center for radio channels Functions BTS BSC Management of radio channels X Frequency hopping (FH) X X Management of terrestrial channels X Mapping of terrestrial onto radio channels X Channel coding and decoding X Rate adaptation X Encryption and decryption X X Paging X X Uplink signal measurements X Traffic measurement X Authentication X Location registry, location update X Handover management X Chapter 2 Page 87

24 Mobile station 1 Terminal for the use of GSM services A mobile station (MS) comprises several functional groups MT (Mobile Termination): 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 (U m ) 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 MT R S U m Chapter 2 Page 88

25 Mobile Station 2 Each MS contains an International Mobile Equipment Identity (IMEI) The SIM personalizes a MS Contains Information for: authentication Key Accounting data Personal numbers Contract and service details PIN PUK International Mobile Subscriber Identity (IMSI) after being connected: Key for data encryption Temporary Mobile Subscriber Identity (TMSI) Location Area Identity (LAI) Transmit power for GSM 900 2W for GSM1800 1W 5W is permitted for GSM if no head contact is guaranteed Chapter 2 Page 89

26 SS7 System architecture: network and switching subsystem MSC network subsystem EIR fixed partner networks ISDN PST N Components 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.) MSC IWF HLR VLR ISDN PSTN PSPDN CSPDN Databases Chapter 2 Page 90 HLR (Home Location Register) VLR (Visitor Location Register) EIR (Equipment Identity Register)

27 Network and switching subsystem NSS is the main component of the public mobile network GSM main services are: switching, mobility management, interconnection to other networks, system control; inter BSS Handover; inter MSC Handover, international location of terminals; roaming between network-operators 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 Has mainly same task as ISDN switch Databases (important: scalability, high capacity, low latency) Home Location Register (HLR) central master database containing all user data, permanent and semipermanent data of all subscribers assigned to the HLR (one provider can have several physical HLRs, but consider virtually as a distributed system) Visitor Location Register (VLR) local database for a subset of user data, including data about all user currently in the domain of the VLR Chapter 2 Page 91

28 Mobile Services Switching Center The MSC (mobile 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) access to 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 Chapter 2 Page 92

29 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 using TMN (Telecommunication Management Network) Chapter 2 Page 93

30 Air Interface Facts and Figures: Uses many of the introduced Multiplexing technologies SDMA for Cell structure and multi-segment BTS FDMA for user channels TDMA for more users per radio channel FDD for separation between up and down channel GSM carrier frequencies for up and 124 frequencies for down channel, 200 khz/channel; channel 1 and 124 not used (guard space); 32 channels used for OAM purposes GSM1800 2*374 carrier frequencies for up/down with 200kHz each Frame structure duration 4,615 ms 8 time slots of 577ms each TDMA shift each logical channel will be shifted be 3 time-slots in up and down direction Data Burst 546 ms+ 30,5 ms guard time for different path delays; theoretical throughput 33,8 kb/s Chapter 2 Page 94

31 GSM - TDMA/FDMA MHz 124 channels (200 khz) downlink GSM TDMA frame MHz 124 channels (200 khz) uplink higher GSM frame structures time ms guard space GSM time-slot (normal burst) tail user data S Training S user data tail 3 bits 57 bits 1 26 bits 1 57 bits 3 Chapter 2 Page 95 guard space µs 577 µs

32 Burst Structure Each data-burst contains: Training sequence of 26 bit 2 data fields of 57 bits + 1control bit each 2 tail sequences of 3 bit each set to 0 for modulation control Other burst types: Access Burst: for connection establishment Synchronization Burst Frequency Correction Burst Dummy Burst Chapter 2 Page 96

33 Logical Channels 1 Two different logical channel types: Traffic channel (TCH) to carry all information between users Control channel (CCH) to control system behaviour and guarantee proper systems functioning Traffic Channel Types: Full-Rate (TCH/F) 22,8 kb/s (TCH/FS) 13kb/s for speech coding Rest for FEC Half-Rate 11,4 kb/s (TCH/HS) 5,6 kb/s for speech coding Rest for FEC For data transmission TCH/4.8; TCH/9.6; TCH/14.4 Using different coder and FEC mechanisms Chapter 2 Page 97

34 Logical Channels 2 Control Channel Types Used for Media Access und User Mobility 3 types of control channel (with several sub-types): Broadcast Control Channel (BCCH) Data to all MS in a cell Contains Cell-ID; Frequency Hopping type; available frequencies in this cell, adjacent cell frequencies Subtypes: Frequency Correction Channel (FCCH) (special burst type); Synchronization Channel (SCH) (special burst type) Common Control Channel (CCCH) BTS/MS connection establishment data Paging channel (PCH) for BTS to MS call Random Access Channel (RACH) (special burst type) for MS connection request Access Grant Channel (AGCH) for BTS to MS channel association Chapter 2 Page 98

35 Logical Channels 3 Dedicated Control Channel (DCCH) Bidirectional Channels Stand Alone DCH (SDCCH) for signalling between MS and BTS Slow Associated Control Channel (SACCH) for each TCH and SDCCH Fast Associated Control Channel (FACCH) uses time slots of regular TCHs Chapter 2 Page 99

36 Frame Structure Not all combinations of frames are permitted: Each TCH/F is associated with a SACCH TTTTTTTTTTTTSTTTTTTTTTTTTXTTTTTTTTTTTTS 12* TCH 12* TCH 12* TCH 26 Slots Data Rate of TCH/F = 24/26*24,7kb/s= 22,8 kb/s Data Rate of SACCH= 1/26*24,7kb/s= 950b/s Chapter 2 Page 100

37 GSM hierarchy of frames hyperframe h 28 min s superframe s multiframe frame slot burst 120 ms Traffic multiframe ms Control multiframe ms 577 µs Chapter 2 Page 101