Mobile Communications PDF Lecture Notes - York University

EECS 4215 Mobile Communications W2025, Section Z Cellular Networks  Review Physical layer Modulation (A-/F-/PSK, QAM, DS-/FHSS) Media Access Fixed/dynamic Wireless LANs and PANs/Bluetooth York University EECS 4215 Z (W2025) Wi...

EECS 4215 Mobile Communications W2025, Section Z Cellular Networks  Review Physical layer Modulation (A-/F-/PSK, QAM, DS-/FHSS) Media Access Fixed/dynamic Wireless LANs and PANs/Bluetooth York University EECS 4215 Z (W2025) Wireless LANs 2 Cellular networks 3 Penetration crtc.gc.ca York University EECS 4215 Z (W2025) Cellular Networks 4  Development of mobile telecommunication systems Graphic by Jochen H. Schiller York University EECS 4215 Z (W2025)  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 a Mexican use her phone in Canada? 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? York University EECS 4215 Z (W2025) 6  GSM: Overview GSM formerly: Groupe Spéciale Mobile (founded 1982) now: Global System for Mobile Communication Pan-European standard (ETSI, European Telecommunications Standardisation Institute) simultaneous introduction of essential services in three phases (1991, 1994, 1996) by the European telecommunication administrations Adopted at some point by many providers all over the world Seamless roaming possible across countries York University EECS 4215 Z (W2025) 7  Digital vs. Analog Systems 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 York University EECS 4215 Z (W2025) 8  Disadvantages of GSM There is no perfect system!! no end-to-end encryption of user data Reduced concentration while driving Electromagnetic radiation Abuse of private data possible Roaming profiles accessible High complexity of the system Several incompatibilities within the GSM standards E.g., frequencies used York University EECS 4215 Z (W2025) 9  GSM: Services GSM offers voice connections, data connections, short message service multi-service options (combination of basic services) Three service domains Bearer Services Telematic Services Supplementary Services York University EECS 4215 Z (W2025) Cellular Networks 10  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 York University EECS 4215 Z (W2025)  Tele Services Services have to obey cellular functions, security measures etc. Offered services mobile telephony primary goal of GSM was to enable voice mobile telephony offering the traditional bandwidth of 3.1 kHz emergency number (911, 112, 110…) mandatory for all service providers connection with the highest priority (preemption of other connections possible) multi-numbering several phone numbers per user possible non-Voice-Teleservices fax, voicemail, email, SMS York University EECS 4215 Z (W2025)  Supplementary services Services in addition to the basic services, cannot be offered stand-alone May differ between different service providers, countries and protocol versions Important services identification: forwarding of caller number suppression of number forwarding conferencing with up to 7 participants locking of the mobile terminal (incoming or outgoing calls)... York University EECS 4215 Z (W2025) Architecture of the GSM system GSM is a PLMN (Public Land Mobile Network) ◦ several providers set up mobile networks following the GSM standard within each country ◦ components ◦ MS (mobile station) ◦ BS (base station) ◦ MSC (mobile services 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 14 Ingredients 1: Mobile Phones, “PDAs”... Handy-Foto 1380 Handy-Foto 1255 The visible but smallest part of the network! 15 Ingredients 2: Antennas Still visible – cause many discussions… 16 Ingredients 3: Infrastructure 1 Base Stations Cabling Microwave links 17  Ingredients 3: Infrastructure 2 Not “visible”, but major part of the network (also from cost point of view) Management Databases Switching units Monitoring 18  GSM: overview OMC, EIR, AUC HLR GMSC NSS fixed network with OSS VLR MSC MSC VLR BSC BSC RSS 19  GSM: system architecture radio network and switching fixed subsystem subsystem partner networks MS MS ISDN PSTN Um MSC BTS Abis BSC EIR BTS SS7 HLR BTS VLR BSC ISDN BTS MSC PSTN A BSS IWF PSPDN CSPDN York University EECS 4215 Z (W2025) System architecture: radio subsystem radio network and switching subsystem subsystem MS (Mobile Station) MS MS BSS (Base Station Subsystem): consisting of Um BTS (Base Transceiver Station): sender and receiver BTS Abis BSC (Base Station Controller): controlling several transceivers BSC MSC BTS Interfaces Um: radio interface Abis: standardized, open A interface with 16 kbit/s user BTS BSC MSC channels BTS A: standardized, open interface BSS with 64 kbit/s user channels System architecture: network and switching subsystem network fixed partner Components subsystem networks MSC (Mobile Services Switching Center): IWF (Interworking Functions) ISDN ISDN (Integrated Services Digital Network) PSTN MSC PSTN (Public Switched Telephone Network) PSPDN (Packet Switched Public Data Net.) CSPDN (Circuit Switched Public Data Net.) EIR Databases HLR (Home Location Register) SS7 HLR VLR (Visitor Location Register) EIR (Equipment Identity Register) VLR ISDN MSC PSTN IWF PSPDN CSPDN GSM: cellular network segmentation of the area into cells possible radio coverage of the cell idealized shape of the cell cell multiple 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 and can be quite irregular) if a mobile user changes cells, hand over of the connection to the neighbor cell 23  https://en.wikipedia.org/wiki/GSM_frequency_bands GSM frequency bands (examples) Type Channels Uplink [MHz] Downlink [MHz] GSM 850 128-251 824-849 869-894 GSM 900 0-124, 955-1023 876-915 921-960 classical 124 channels 890-915 935-960 extended +49 channels 880-915 925-960 GSM 1800 512-885 1710-1785 1805-1880 GSM 1900 512-810 1850-1910 1930-1990 GSM-R 955-1024, 0-124 876-915 921-960 exclusive 69 channels 876-880 921-925 (GSM-Railway) - Additionally: GSM 400 (also named GSM 450 or GSM 480 at 450-458/460-468 or 479-486/489-496 MHz) - Please note: frequency ranges vary depending on the country - Channels at the lower/upper edge of a frequency band are typically not used 24  Base Transceiver Station and Base Station Controller Tasks of a BSS are distributed over BSC Functions Management of radio channels BTS BSC X Frequency hopping (FH) X X and BTS Management of terrestrial channels Mapping of terrestrial onto radio channels X X Channel coding and decoding X BTS comprises radio Rate adaptation Encryption and decryption X X X specific functions Paging Uplink signal measurements X X X Traffic measurement X BSC is the switching Authentication Location registry, location update X X Handover management X center for radio channels York University EECS 4215 Z (W2025)  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 – now more and more replaced with eSIM TE TA MT Um R S York University EECS 4215 Z (W2025)  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 factors: scalability, high capacity, low delay) Home Location Register (HLR) central master database containing user data, permanent and semi-permanent 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 York University EECS 4215 Z (W2025)  Mobile Services Switching Center The MSC (mobile services switching center) plays a central role in GSM switching functions management of network resources interworking functions Functions of an 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 York University EECS 4215 Z (W2025) GSM - TDMA/FDMA 935-960 MHz (GSM-900, e.g., Europe) 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 guard space tail user data S Training S user data tail space 3 bits 57 bits 1 26 bits 1 57 bits 3 546.5 µs 577 µs 30 Mobile Terminated Call 1: calling a GSM subscriber 4 2: forwarding call to GMSC HLR VLR 5 3: signal call setup to HLR 8 9 3 6 14 15 4, 5: request MSRN from VLR calling 7 PSTN GMSC MSC 6: forward responsible station 1 2 MSC to GMSC 10 10 13 10 7: forward call to 16 BSS BSS BSS current MSC 11 11 11 8, 9: get current status of MS 10, 11: paging of MS 11 12 17 12, 13: MS answers MS 14, 15: security checks 16, 17: set up connection GMSC: Gateway Mobile Switching Center 33  Mobile Originated Call 1, 2: connection request 3, 4: security check VLR 5-8: check resources (free 3 4 circuit) PSTN 6 GMSC 5 MSC 7 8 9-10: set up call 2 9 1 MS BSS 10 34 Types of handover 1 2 3 4 MS MS MS MS BTS BTS BTS BTS BSC BSC BSC MSC MSC 36 Handover decision receive level receive level BTSold BTSnew HO_MARGIN MS MS BTSold BTSnew 37 Data services in GSM I Data transmission standardized with only 9.6 kbit/s ◦ advanced coding allows 14.4 kbit/s ◦ not enough for Internet and multimedia applications HSCSD (High-Speed Circuit Switched Data) ◦ mainly software update ◦ bundling of several time-slots to get higher AIUR (Air Interface User Rate, e.g., 57.6 kbit/s using 4 slots @ 14.4) ◦ advantage: ready to use, constant quality, simple ◦ disadvantage: channels blocked for voice transmission AIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F14.4 4.8 1 9.6 2 1 14.4 3 1 19.2 4 2 28.8 3 2 38.4 4 43.2 3 57.6 4 39 GPRS protocol architecture MS Um BSS Gb SGSN Gn GGSN Gi apps. IP/X.25 IP/X.25 SNDCP GTP SNDCP GTP LLC LLC UDP/TCP UDP/TCP RLC BSSGP IP IP RLC BSSGP MAC MAC FR FR L1/L2 L1/L2 radio radio 44  Some GSM enhancements GSM EMS/MMS EMS: 760 characters possible by chaining SMS, animated icons, ring tones, was soon replaced by MMS (or simply skipped) MMS: transmission of images, video clips, audio see WAP 2.0 / chapter 10 EDGE (Enhanced Data Rates for Global [was: GSM] Evolution) 8-PSK instead of GMSK, up to 384 kbit/s new modulation and coding schemes for GPRS ➔ EGPRS MCS-1 to MCS-4 uses GMSK at rates 8.8/11.2/14.8/17.6 kbit/s MCS-5 to MCS-9 uses 8-PSK at rates 22.4/29.6/44.8/54.4/59.2 kbit/s York University EECS 4215 Z (W2025) 48 UMTS, LTE Cellular Networks 49  3G and 4G Higher speed needed Better modulation Non-symmetric transfer rates Simplification of protocols Voice over IP York University EECS 4215 Z (W2025) Cellular Networks 50  3G FDMA and TDMA is replaced by CDMA Voice: similar to GSM, separate from data Examples CDMA2000, UMTS, HSPA+ York University EECS 4215 Z (W2025) Cellular Networks 51  4G OFDM(A) enables better spectrum efficiency Voice Originally sent using 3G or 2G protocols Later: using packets, like any data in LTE Data FDD and TDD possible, network aggregation Examples LTE, LTE advanced York University EECS 4215 Z (W2025) Cellular Networks 52  5G Possibility of coexistence with earlier technologies Adds new high-frequency bands (short- range) York University EECS 4215 Z (W2025) Cellular Networks 53